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Evaluating Trace Metal Mobilization During Managed Aquifer Recharge

Permanent Link: http://ufdc.ufl.edu/UFE0043570/00001

Material Information

Title: Evaluating Trace Metal Mobilization During Managed Aquifer Recharge
Physical Description: 1 online resource (1 p.)
Language: english
Creator: Norton, Stuart Bryan
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: anoxic -- aquifer -- arsenic -- asr -- chloramines -- dechlorimination -- dechlorination -- degas -- degasification -- dissolved -- injection -- managed -- mar -- membrane -- oxidation -- oxygen -- pyrite -- pyritic -- recharge -- recovery -- storage -- wells
Environmental Engineering Sciences -- Dissertations, Academic -- UF
Genre: Environmental Engineering Sciences thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The implementation of Managed Aquifer Recharge (MAR) techniques, such as Aquifer Storage and Recovery (ASR) and Artificial Recharge (AR), is being constrained by the recent finding of trace-metal mobilization, with arsenic occurring above the 10 µg/L Maximum Contaminant Level (MCL) at ASR sites. This research program has demonstrated that the mobilization of arsenic can be controlled by the removal of the primary oxidizers (i.e., dissolved oxygen (DO) and chloramine) from ASR source water. The removal of 99.93% of DO, through membrane degasification, and 90% of chloramine, by sodium bisulfite, from the ASR source water resulted in an approximate 94% reduction in the total arsenic recovered at the Bradenton ASR site. The peak total arsenic concentration in recovered water at the Bradenton site was 75 µg/L during the high-DO test. In contrast to the high-DO test, the peak arsenic concentration during the low-DO test was 12 µg/L. Leaching profiles for arsenic, sulfate, molybdenum, antimony, vanadium and uranium from batch studies of purposefully unpreserved core varied significantly from that of preserved core in both the native groundwater and source water phases. Falling Head Permeameter (FHP) tests, which provided measurements of vertical permeability (Kv) ranging from 3E-5 to 6E-2 feet (ft) per day, and preliminary column tests were conducted using an intact-core column design. Results from these tests may be used to support the design of future column experiments that will aid the development of reactive transport models. The reactive transport code PHT3D was utilized to simulate arsenic transport at the Bradenton site. The model results provide further support that sorption to iron oxides (FeOH) is the primary mechanism controlling arsenic mobility during ASR. The calibrated model was used to evaluate operational approaches for controlling arsenic mobility over 10 years of ASR cycles, under different operational strategies. The model results indicate that a combination of the Target Storage Volume (TSV) approach with degasification of ASR injectate to DO concentrations of less than 1 ppm may be useful at Bradenton for meeting both the MCL for arsenic, in the aquifer, and the Secondary Maximum Contaminant Level (SMCL) for sulfate, in recovered water.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Stuart Bryan Norton.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Annable, Michael D.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043570:00001

Permanent Link: http://ufdc.ufl.edu/UFE0043570/00001

Material Information

Title: Evaluating Trace Metal Mobilization During Managed Aquifer Recharge
Physical Description: 1 online resource (1 p.)
Language: english
Creator: Norton, Stuart Bryan
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: anoxic -- aquifer -- arsenic -- asr -- chloramines -- dechlorimination -- dechlorination -- degas -- degasification -- dissolved -- injection -- managed -- mar -- membrane -- oxidation -- oxygen -- pyrite -- pyritic -- recharge -- recovery -- storage -- wells
Environmental Engineering Sciences -- Dissertations, Academic -- UF
Genre: Environmental Engineering Sciences thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The implementation of Managed Aquifer Recharge (MAR) techniques, such as Aquifer Storage and Recovery (ASR) and Artificial Recharge (AR), is being constrained by the recent finding of trace-metal mobilization, with arsenic occurring above the 10 µg/L Maximum Contaminant Level (MCL) at ASR sites. This research program has demonstrated that the mobilization of arsenic can be controlled by the removal of the primary oxidizers (i.e., dissolved oxygen (DO) and chloramine) from ASR source water. The removal of 99.93% of DO, through membrane degasification, and 90% of chloramine, by sodium bisulfite, from the ASR source water resulted in an approximate 94% reduction in the total arsenic recovered at the Bradenton ASR site. The peak total arsenic concentration in recovered water at the Bradenton site was 75 µg/L during the high-DO test. In contrast to the high-DO test, the peak arsenic concentration during the low-DO test was 12 µg/L. Leaching profiles for arsenic, sulfate, molybdenum, antimony, vanadium and uranium from batch studies of purposefully unpreserved core varied significantly from that of preserved core in both the native groundwater and source water phases. Falling Head Permeameter (FHP) tests, which provided measurements of vertical permeability (Kv) ranging from 3E-5 to 6E-2 feet (ft) per day, and preliminary column tests were conducted using an intact-core column design. Results from these tests may be used to support the design of future column experiments that will aid the development of reactive transport models. The reactive transport code PHT3D was utilized to simulate arsenic transport at the Bradenton site. The model results provide further support that sorption to iron oxides (FeOH) is the primary mechanism controlling arsenic mobility during ASR. The calibrated model was used to evaluate operational approaches for controlling arsenic mobility over 10 years of ASR cycles, under different operational strategies. The model results indicate that a combination of the Target Storage Volume (TSV) approach with degasification of ASR injectate to DO concentrations of less than 1 ppm may be useful at Bradenton for meeting both the MCL for arsenic, in the aquifer, and the Secondary Maximum Contaminant Level (SMCL) for sulfate, in recovered water.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Stuart Bryan Norton.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Annable, Michael D.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043570:00001


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1 EVALUATING TRACE METAL MOBILIZATION DURIN G MANAGED AQUIFER RECHARGE By STUART BRYAN NORTON A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2011

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2 2011 Stuart Bryan Norton

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3 To Glad ys and Elijah, with all my love

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4 ACKNOWLEDGMENTS I sincerely appreciate the financial support for this project provided by the South West Florida Water Management District. This project was also funded, in part, by the Florida Geological Survey. M atching funds, for student support, were provided by the University of Florida Water Resource Research Cente r through the USGS 104B gr ant program. T he delivery of this project was aided by in kind services provided by the University of Florida Department of Environmental Engineering Sciences and Department of Soil and Water Sciences. The Bradenton Degasification Pilot project was coope ratively funded by the Southwest Florida Water Management District, City of Bradenton, St. Johns River Water Management District, South Florida Water Management District and Peace River Manasota Regional Water Supply Authority. The contributions of these organizations are gratefu lly acknowledged. The guidance and support that I have received from my supervisory committee (Drs. Mike Annable, Kirk Hatfield, Jean Claude Bonzongo, Willie Harris and Mark Newman) is greatly appreciated. I thank the City of Bra denton, specifically Seth Kohn and Claude Tankersley, for allowing me to use the Bradenton ASR site as a case study. I thank my friends at the Florida Geological Survey for providing technical input and support, and for assisting with the bench scale exp eriments The Southwest Florida Water Management District, specifically Mr. Don Ellison is also acknowledged for their technical support, as well as core collection. My scholarly interests have long been nurtured by my mother. I thank her for many years of loving guidance, encouragement and support. This research would not have been possible without the commitment of these individuals.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ .......... 9 ABSTRACT ................................ ................................ ................................ ................... 12 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 14 Manage d Aquifer Recharge ................................ ................................ .................... 14 Mobilization of Metals During MAR ................................ ................................ ......... 16 Occurrence of Arsenic Bearing Minerals in the Suwannee Limestone ................... 17 Conceptual Model ................................ ................................ ................................ ... 18 2 BRADENTON ASR DEGASIFICATION PILOT TEST ................................ ............ 21 Objective ................................ ................................ ................................ ................. 21 Methods ................................ ................................ ................................ .................. 21 Bradenton Potable ASR Facility ................................ ................................ ....... 21 Degasification Pilot System ................................ ................................ .............. 22 Site Hydrogeology ................................ ................................ ............................ 23 Cycle Test Program ................................ ................................ .......................... 25 Sampling Protocols ................................ ................................ .......................... 27 Results an d Discussion ................................ ................................ ........................... 28 Comparison of High DO and Low DO Cycle Test Results ............................... 28 Analytical Methods ................................ ................................ ........................... 29 DO Consumption Rates and Redox Equilibration ................................ ............. 30 Arsenic Mobility ................................ ................................ ................................ 31 Repetitive High DO ASR Cycling ................................ ................................ ..... 32 3 INFLUENCE OF CORE PRESERVATION METHODS ON ASR BATCH STUDIES ................................ ................................ ................................ ................ 39 Objective ................................ ................................ ................................ ................. 39 Methods ................................ ................................ ................................ .................. 39 Core Collection and Preservation ................................ ................................ ..... 39 Core Crushing and Splitting ................................ ................................ .............. 42 Mineralogical Characterization ................................ ................................ ......... 44 Native Groundwater and ASR Source Water Collection ................................ ... 44 Bench scale Leaching Experiments ................................ ................................ 45 Results and Discussion ................................ ................................ ........................... 47

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6 Matrix Geochemistry ................................ ................................ ........................ 47 Mineralogical Composition ................................ ................................ ............... 47 Be nch scale Experiments ................................ ................................ ................. 48 4 DESIGN INTACT CORE COLUMN EXPERIMENTS ................................ .............. 70 Objective ................................ ................................ ................................ ................. 70 Methods ................................ ................................ ................................ .................. 70 Falling Head Permeam eters ................................ ................................ ............. 70 Core Column Design and Evaluation Testing ................................ ................... 72 Core Column Reactive Transport Model ................................ .......................... 75 Results and Discussion ................................ ................................ ........................... 76 Falling Head Permeameters ................................ ................................ ............. 76 Co re Column Design and Evaluation Testing ................................ ................... 76 Core Column Reactive Transport Model ................................ .......................... 77 5 REACTIVE TRANSPORT MODELING ................................ ................................ ... 86 Objective ................................ ................................ ................................ ................. 86 Methods ................................ ................................ ................................ .................. 86 Site Description ................................ ................................ ................................ 86 Mass Transport Modeling ................................ ................................ ................. 88 Reactive Transport Modeling ................................ ................................ ............ 88 Geochemical Modeling ................................ ................................ ..................... 89 Graphical User Inter face ................................ ................................ ................... 89 3 D Flow and Conservative Transport Model ................................ ................... 90 Initial flow and transport model setup ................................ ......................... 90 Expanded flow and transport model ................................ ........................... 92 Axisymmetric Flow and Reactive Transport Model ................................ ........... 93 Model setup ................................ ................................ ............................... 93 Temporal discretization ................................ ................................ .............. 94 Geochemical reaction framework ................................ ............................... 95 Conservative transport and reaction model calibration .............................. 96 Reactive transport model validation ................................ ........................... 97 Predictive simulations ................................ ................................ ................ 98 Results and Discussion ................................ ................................ ........................... 99 3 D Fl ow and Conservative Transport Modeling ................................ .............. 99 Axisymmetric Flow and Reactive Transport Model ................................ ......... 101 Predictive Modeling ................................ ................................ ........................ 105 6 CONCLUSIONS ................................ ................................ ................................ ... 138 Bradenton ASR Degasification Pilot Test ................................ .............................. 138 Influence of Core Preservation Methods on ASR Batch Studies .......................... 138 Design Intact Core Column Experiments ................................ .............................. 139 Reactive Transport Modeling ................................ ................................ ................ 140

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7 APPENDIX A ANALYTICAL LABORATORY TECHNIQUES ................................ ...................... 144 Sample Pulverization (from Activation Laboratories) ................................ ............ 144 Hydrogeochemistry Cation Analyses ................................ ................................ .... 144 Ion Chromatography ................................ ................................ ............................. 145 Lithogeochemical Analysis ................................ ................................ .................... 145 In stru mental N eutron Activation Analysis (INAA) ................................ ........... 145 Major Elements ................................ ................................ .............................. 146 Base Metals and Selected Trace Elements ................................ .................... 146 Carbon and Sulfur ................................ ................................ .......................... 147 Mercury ................................ ................................ ................................ .......... 147 B LITHOCHEMISTRY RESULTS ................................ ................................ ............. 148 C GEOPHYSICAL LOGS ................................ ................................ ......................... 150 LIST OF REFERENCES ................................ ................................ ............................. 152 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 156

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8 LIST OF TABLES Table page 2 1 Well construction details for the Bradenton HSPS ASR facility .......................... 35 2 2 Bradenton ASR water quality summary ................................ .............................. 35 2 3 Bradenton ASR cycle test program summary ................................ ..................... 36 3 1 First split of Core 1 and Core 2 ................................ ................................ ........... 58 3 2 Second split of Core 1 and Core 2 ................................ ................................ ...... 58 3 3 Final mass of crushed core samples ................................ ................................ .. 59 3 4 Whole rock geochemistry. ................................ ................................ .................. 61 3 5 Selected analytical results for NGW and SW ................................ ..................... 62 4 1 Physical measurements of cores used in this study. ................................ .......... 79 4 2 FHP test results ................................ ................................ ................................ .. 82

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9 LIST OF FIGURES Figure page 1 1 Pyrite oxidation process ................................ ................................ ..................... 19 1 2 Reductive dissolution process ................................ ................................ ............ 20 2 1 Site location map. ................................ ................................ ............................... 33 2 2 Bradenton ASR site plan ................................ ................................ .................... 34 2 3 Total arsenic concentrations at ASR 1 during the full scale high DO recovery event and the low DO recovery event. ................................ ............................. 36 2 4 TDS and total arsenic concentrations at SZMW 1 during Cycle Tests 5 6 and Cycle Test 8 recharge events ................................ ................................ ............. 37 2 5 TDS and total arsenic concentrations at SZMW 1 during Cycle Tests 5 6 and Cycle Test 8 recovery events. ................................ ................................ ............ 37 2 6 Field DO and ORP measurements during Cycle Tests 5 6 and Cycle Test 8 recovery events ................................ ................................ ................................ .. 38 2 7 Total arsenic concentrations measured during recover y of Cycle Tests 1 4 and Cycle Test 7 ................................ ................................ ................................ 38 3 1 Core placed onto 2 inch split PVC well screen. ................................ .................. 54 3 2 Core preservation vessels in storage rack. ................................ ......................... 55 3 3 Retsch BB100 jaw crusher. ................................ ................................ ................ 56 3 4 Crushed core in vacuum dessiccator. ................................ ................................ 57 3 5 Fritsch rotary cone divider. ................................ ................................ ................. 57 3 6 Vacuum carboys used in NGW sample collection. ................................ ............. 59 3 7 Sealed reaction vessels. ................................ ................................ ..................... 60 3 8 Sealed reaction vessels in fume hood at FGS lab. ................................ ............. 60 3 9 Dissolved oxygen concentrations in bat ch reactors over time. ........................... 63 3 10 Ox idation Reduction Potential measurements in batch reactors over time. ........ 63 3 11 Dissolved arsenic leachate concentrations in batch reactors over time. ............. 64

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10 3 12 Dissolved iron leachate concentrations in batch reactors over time. .................. 64 3 13 Dissolved manganese leachate concentrations in batch reactors over time. ..... 65 3 14 Dissolved sulfate concentrations in batch reactors over time. ............................ 65 3 15 Dissolved sulfate concentrations in batch reactors during native groundwater phase. ................................ ................................ ................................ ................. 66 3 16 Dissolved molybdenum leachate concentrations in batch reactors over time. .... 66 3 17 Dissolved antimony leachate concentrations in batch reactors over time. .......... 67 3 18 Dissolved vanadium leachate concentrations in batch reactors over time. ......... 67 3 19 Dissolved uranium leachate concentrations in batch reactors over time. ........... 68 3 20 Dissolved cesiu m leachate concentrations in batch reactors over time. ............. 68 3 21 Dissolved barium leachate concentrations in batch reactors over tim e. ............. 69 4 1 Photos of Falling Head Permeameters ................................ ............................... 79 4 2 Photos of core columns ................................ ................................ ...................... 80 4 3 Core column model domain and discretization. ................................ .................. 81 4 4 Preliminary arsenic leaching results from colu mn of unpreserved 465 ft core .... 82 4 5 Preliminary arsenic leaching results from column of preserved 463 ft core. ....... 83 4 6 Head distribution during 1 D core column model. ................................ ............... 84 4 7 Simulate d arsenic concentrations at core column outlet. ................................ .... 85 5 1 Initial 3D model domain and grid spaci ng. ................................ ........................ 108 5 2 Profile view of 3d model domain ................................ ................................ ....... 109 5 3 Expanded 3 D model domain ................................ ................................ ........... 110 5 4 Profile view of expanded 3D model. ................................ ................................ 111 5 5 Axisymmetric flow and reactive transport model domain. ................................ 112 5 6 3D flow model results under varying model domains ................................ ....... 114 5 7 3D transport mo del T DS results under varying model domains. ...................... 115 5 8 Profile view of init ial 3D model transport results ................................ ............... 116

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11 5 9 Expanded 3D transport model results ................................ .............................. 117 5 10 Profile view of expanded 3D model transport results ................................ ........ 118 5 11 Profile view of reduced 3D model transport results ................................ .......... 119 5 12 Head calibration results at SZMW 1 for 2 D reactive transport model. ............. 120 5 13 Sulfate calibration results for 2 D reactive transport model .............................. 121 5 14 Arsenic calibration results for 2 D reactive transport model ............................. 122 5 15 S imulated sulfide results for 2 D reactive transport model ............................... 123 5 16 Spatial distribution of sulfate in 2 D reactive transport model. .......................... 124 5 17 Spatial distribution of arsenic in 2 D reactive transport model. ....................... 124 5 18 Spatial distrib ution of FeOH in 2 D reactive transport model. ........................... 125 5 19 Sp atial d istribution of DO in 2 D reactive transport model. ............................... 1 26 5 20 Spatial distribution of arsenic in 2 D reactive transport model. ......................... 127 5 21 Spatia l distribution of sulfide in 2 D reactive transport model. ........................ 127 5 22 Sulfate calibration results for 2 D reactive transport model. ............................. 128 5 23 Arsenic calibration results f or 2 D reactive transport model ............................. 129 5 24 Simulated sulfide resul ts f or 2 D reactive transport model ............................... 130 5 25 Predicted sulfate concentrations at ASR 1 during TSV simulations. ................ 131 5 26 Predicted arsenic concentrations at ASR 1 during TSV simulations. ............... 132 5 27 Predicted arsenic concentrations at SZMW 1 during TSV simulations ............. 133 5 28 Predicted arsenic results at ASR 1 during full volume ASR recovery under varying recharge DO concentrations ................................ ................................ 134 5 29 Predicted arsenic results at SZMW 1 during full volume ASR recovery under varying recharge DO concentrations ................................ ................................ 135 5 30 Predicted arsenic results at ASR 1 during TSV simulations under varying recharge DO concentrations ................................ ................................ ............. 136 5 31 Predicted arsenic results at SZMW 1 during TSV simulations under varying recharge DO concentrations ................................ ................................ ............. 137

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12 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy EVALUATING TRACE METAL MOBILIZATION DURIN G MANAGED AQUIFER RECHARGE By Stuart Bryan Norton December 2011 Chair: Michael D. Annable Major: Environmental Engineering Sciences The implementation of Managed Aquifer Recharge (MAR) techniques, such as Aquifer Storage and Recovery (ASR) and Artificial Recharge (AR), is being constrained by the recen t finding of trace metal mobilization, with arsenic occurring above the 10 g/L Maximum Contaminant Level (MCL) at ASR sites. This research program has demonstrated that the mobilization of arsenic can be controlled by the removal of the primary oxidizers (i.e., dissolved oxygen (DO) and chloramine) from ASR source water. The removal of 99.93% of DO, through membrane degasification, and 90% of chloramine, by sodium bisulfite, from the ASR source water resulted in an approximate 94% reduction in the total ar senic recovered at the Bradenton ASR site. The peak total arsenic concentration in recovered water at the Bradenton site was 75 g/L during the high DO test. In contrast to the high DO test, the peak arsenic concentration during the low DO test was 12 g/L Leaching profiles for arsenic, sulfate, molybdenum, antimony, vanadium and uranium from batch studies of purposefully unpreserved core varied significantly from that of preserved core in both the native groundwater and source water phases. Falling

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13 Head P ermeameter (FHP) tests, which provided measurements of vertical permeability (Kv) ranging from 3E 5 to 6E 2 feet (ft) per day, and preliminary column tests were conducted using an intact core column design. Results from these tests may be used to support t he design of future column experiments that will aid the development of reactive transport models. The reactive transport code PHT3D was utilized to simulate arsenic transport at the Bradenton site. The model results provide further support that sorption to iron oxides (FeOH) is the primary mechanism controlling arsenic mobility during ASR. The calibrated model was used to evaluate operational approaches for controlling arsenic mobility over 10 years of ASR cycles, under different operational strategies. The model results indicate that a combination of the Target Storage Volume (TSV) approach with degasification of ASR injectate to DO concentrations of less than 1 ppm may be useful at Bradenton for meeting both the MCL for arsenic, in the aquifer, and the Secondary Maximum Contaminant Level (SMCL) for sulfate, in recovered water.

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14 CHAPTER 1 INTRODUCTION Managed Aquifer Recharge Due to the growing demand on water resources within the State of Florida, alternative water supply and water storage technologies are becoming increasingly attractive to water resource managers. M AR techniques, such as AR and ASR, have the potential to provide much of the s easonal or long term storage needed for many municipalities within areas of increased water demand. However, as with any engineered water supply process, these facilities must meet stringent Federal and State regulations to insure the protection of human health and the health of the environment. MAR is a broad classification for various techniques that includes Rapid Infiltration Basins (RIBs), AR, ASR, and others techniques for the direct recharge of an aquifer. Currently, Florida's water management d istricts are in the planning phase of several large scale AR projects involving the direct injection of surface water and reclaimed water to offset pumping from municipal well fields. In addition, the Southwest Florida Water Management District (SWFWMD) h as recently contracted with an engineering firm to complete a feasibility study for increasing groundwater levels, via direct recharge of the Upper Floridan aquifer, within the Most Impacted Area (MIA) of the Southern Water Use Caution Area (SWFWMD 2008). ASR may be defined as the recharge of an aquifer during times of surplus water supply and recovery of the stored water during times of increased demand, often via a single well. In Florida, ASR is typically used for seasonal storage of potable water tha t is in excess during the rainy season (mid summer through mid fall), with recovery occurring during the dry season (spring). There are 10 operational ASR facilities in

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15 Florida (FDEP 2007), to date, and another 80+ ASR facilities in development. An addit ional 300+ ASR wells are in development in Florida as part of the Comprehensive Everglades Restoration Program (CERP), with numerous other ASR facilities operating or in development world wide. Recently, ASR facilities in southwest Florida utilizing the Su wannee Limestone of the Upper Floridan aquifer for seasonal water storage have reported arsenic (As) concentrations in recovered water at levels greater than 112 g/L (Arthur et al. 2002). On January 23, 2006 the Maximum Contaminant Level (MCL) for As was lowe red from 50 g/L to 10 g/L ( Chapter 62 550 F.A.C). The mobilization of As above the MCL has, therefore, become the primary issue restricting the implementation of these alternative water supply technologies. Research completed to date suggest s tha t the injection of treated potable water, containing high levels of oxidizers (e.g., DO, nitrate and chlorine) into a anoxic/reduced aquifer produces a physio chemical response thereby releasing As, and other trace metals, from the solid phase (Arthur et a l. 2002; Jones and Pichler 2007; Mirecki 2006; Norton 2007; Price and Pichler 2006; Prommer and Stuyfzand 2005). Since the mobilized As may present a hazard to human health and the environment, it is critical to understand the mechanisms controlling the fate and transport of As. MAR facilities in Florida that have experienced As above the MCL will be required to adopt corrective measures that are protective of both human health and the environment. These corrective measures may include pretreatment techniques designed to modify aqueous geochemistry (e.g., deoxygenation) of the source water operational approaches, such as the Target Stora ge Volume (TSV) approach (Pyne

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16 2006), for managing the mobility of As during ASR, and/or institutional controls on groundwater use. In order to determine the adequacy of these management strategies for protecting human health and the environment, a thorou gh understanding of the geochemical processes that control As mobilization during MAR must be established. Mobilization of Metals During MAR The mobilization (chemical leaching) of As during ASR in Florida was first reported by the Florida Geological Surve y (FGS) (Arthur et al 2000 ; 2001 ; 2002 ; 2005). While investigating the geochemical response that occurs during ASR, FGS reported that facilities in southwest Florida utilizing the Suwannee Limestone of the Upper Floridan aquifer for ASR were experiencing As concentrations in recovered water up to 130 g/L, more than 10 times the MCL. FGS reported that other trace metals including molybdenum (Mo), iron (Fe) and uranium (U), in addition to As, were also mobilized during ASR. Arthur (2002 ; 2005) suggest th at native minerals (i.e., pyrite) containing As are oxidized during ASR, by the recharge of waters with relatively high levels of dissolved oxygen and other oxidizers, releasing As and other trace metals into solution. Similar results were reported by Rui ter and Stuyfzand (1998) and Prommer and Stuyfzand (2005) at the Dizon site in the Netherlands indicating trace metal mobilization during ASR, and the study thereof, has global implications. More recently, by applying Istok push pull test assessment method s to the Bradenton ASR dataset, Norton (2007) found that DO is rapidly consumed during ASR with a decay rate (k) of 0.5 day 1 at 25C. Arsenic was reported during recovery at the Bradenton ASR site at a maximum concentration of 75 g/L in water recovered from the ASR well. However, the maximum As concentration detected at the nearby storage zone observation well (r = 224 ft) was 20 g/L during the tests, despite the injection

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17 volume (160 MG) being around four times larger than that required to intersect t he storage zone well (40 MG). This indicates the mobility of As is retarded within the matrix. Occurrence of Arsenic Bearing Minerals in the Suwannee Limestone To identify the source of arsenic in ASR, Price and Pichler (2006) completed a mineralogical an d geochemical analysis of more than 300 core samples collected from the Suwannee Limestone formation in southwest Florida. The results of this analysis without minor min eral phases) samples of the Suwannee Limestone at concentrations of around 1.7 mg/kg. Arsenic was reported at higher concentrations of 9.5 mg/kg in organic material). T association of arsenic with trace mineral phases, such as pyrite and organic material. Therefore, the resulting average arsenic concentration of 3.5 mg/kg reported by Price and Pichler (2006) fo r the bulk Suwannee Limestone may be skewed slightly as the average arsenic concentration of 3.5 mg/kg is near the 2.6 mg/kg global average concentration for limestone reported by Smedley and Kinniburgh ( 2001 ). Price and Pichler (2006) concluded that mineral grains of pyrite are generally associated with high porosity zones. Samples of pyrite were selected from the cores and were analyzed for arsenic concentration. T he results show that pyrite is generally rich in arsenic with an average arsenic concentration of 2300 mg/kg. This is within the arsenic concentration range for pyrite of 100 to 77000 mg/kg provided by Smedley and Kinniburgh ( 2001) Additionally, organic material and other trace minerals identified

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18 within core samples were analyzed and were not found to be a significant source of arsenic. The results of this study indicate that 1) the high arsenic concentrations present within the Suwannee Limestone are associated with pyrite minerals and 2) the bulk aquifer matrix contains relatively low levels of arsenic (Price and Pichler 2006). Conceptual Model The conceptual model for arsenic mobilization during ASR is based on the formalized by Mirecki 2006 and supported by Arthur and others 2001 2002 2005 Price and Pichle r 2006 and others. uring injection, under progressively oxidizing conditions, arsenic rich pyrite becomes unstable and releases arsenic, ferrous iron and other trace metals into solution (Figure 1 1) Ferrous iron released during pyrite oxidation is oxidized and precipitates as hydrous ferric oxides (HFO) some distance from the ASR well. The newly formed HFOs provide sorption si tes for the mobilized arsenic. During recovery, progressively more reducing ( i.e., sulfidic) native groundwater returns near the ASR bore hole causing reductive dissolution of the HFO surface sites, rere leasing arsenic into solution (Figure 1 2). An alte rnate, or complementary, mechanism for arsenic mobilization during recovery may be desorption from HFO surface sites. D uring recovery, when native groundwater (high TDS) returns near the ASR bore hole, competition between arsenic and other anions for the finite number of sorption sites on HFO rereleases arsenic into solution by desorption. Results presented by Norton (2007), Arthur and others (2007), and Prommer and Stuyfzand (2005) support this hypothesis. However, based on the results of geochemical m ixing models of three ASR sites located within southwest Florida, Jones and Pichler (2007) explain that HFOs are not stable within the full range of ASR waters.

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19 This suggests that As could not be removed from solution by the formation of, and complexation of As with, HFOs. The mechani sms controlling As mobilization therefore, must be defined. Figure 1 1. Pyrite oxidation process, leading to arsenic mobilization and formation of arsenic adsorption sites, during aquifer recharge

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20 Figure 1 2. Reductive d issolution process showing release of arsenic from HFOs during recovery

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21 CHAPTER 2 BRADENTON ASR DEGASI FICATION PILOT TEST Objective The conceptual model, presented above, for arsenic mobilization during ASR suggest that the injection of oxidizers, primar ily DO, into a reduced (i.e., sulfidic) aquifer releases arsenic by dissolution of arsenic rich pyrite. The objective of this research was to confirm if the removal of oxidizers, primarily DO through membrane degasification from ASR source water c an control the mobilization of arsenic during ASR. Methods Bradenton Potable ASR Facility The City of Bradenton High Service Pump Station (HSPS) Potable Water ASR Facility (ASR 1) was used as the case study for this research project. The site is located nea r downtown Bradenton in western Manatee County, Florida (Figure 2 1). Site selection was based on both the availability and comprehensiveness of data sets collected during eight test cycles conducted at the project site. Information presented in this stu dy was obtained from the October 2006, City of Bradenton, Potable ASR Cycle Test Summary Report (2 006 ) and the February 2004, City of Bradenton, ASR Program, Phase II Well Construction Report (2 004 ). Dr. Norton worked as project manager and technical spec ialist during the permitting, design, construction and operational testing of the Bradenton ASR facility and Degasification Pilot system. The City of Bradenton operates a conventional surface water treatment plant on Ward Lake. The lake was created in 1936 when the City constructed an 838 foot broad crested weir impounding the Braden River. As the sole source of water for the City, the reservoir was expanded in 1985 to meet the

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22 ation ( DelCharco and Lewelling 1997 ). Water and distribution to downtown Bradenton. In 2003 the City constructed an ASR facility (ASR 1) at the HSPS site as a way to sto emergency water supply shortfalls. Potable water is injected into ASR 1 either via high service pumps or by gravity flow from onsite above ground storage tanks. Water stored in ASR 1 is recovered via a single vertical turbine pump. During testing, recovered operational, the recovered water will be disinfected and piped either directly to water distribution system or to storage in existing above ground storage tanks. As shown in Figure 2 2, ASR facilities at the HSPS Site include an ASR well (ASR 1) with a single storage zone monitoring well (SZMW 1) located 224 ft North of ASR 1. An intermediate aquifer monitoring well (AFMW 1) and a water table monitoring well (WTMW 1) are located 20.4 and 11.2 ft east of ASR 1, respectively. Well construction details, including screen or open hole intervals, and casing size and elevations ar e provided in Table 2 1. Degasification Pilot System To test if the removal of DO from ASR source water could control the mobilization of arsenic during ASR, a full scale, 1 million gallon per day (MGD) pre treatment pilot study was implemented at the Bra denton ASR facility. This system included sixteen 14 inch by 28 inch Liqui Cel membrane contactors mounted on a manifold in a four by four configuration. The system was designed to function through application of approximately 28 inches of vacuum and ni trogen sweep gas, which are applied

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23 simultaneously to the vaporous side of the hydrophobic membranes to achieve greater than 3 log (99.93 %) DO removal. Substantial chloramine removal (90%) by addition of sodium bisulfite was performed prior to membrane de gasification to increase the life span of the membrane contactors, and to further reduce the potential for arsenic mobilization. A comparison of native groundwater, potable water and degasified water quality is presented in Table 2 2 Site Hydrogeology Peek ( 1958 ) described the geologic formations of Manatee County to include surficial soil, sands, a nd limestone of recent to Pl e i stocene age of approximately 0 to 60 feet thickness. The surficial soils are underlain by Miocene age sediments that make up t he Hawthorn Group. The Hawthorn Group is an interlayered sequence of sediments that includes phosphatic clays, marl, sands, silts and limetones with an approxima te thickness of 150 to 360 feet The Miocene age Tampa Member, of the Arcadia Formation, form s the base of the Hawthorn Group and is described by Peek ( 1958 ) as a white, gray, and/or tan, generally dense, hard, sandy, and partly phosphatic limestone with an approximate thickness of 125 to 235 feet. The Oligocene age Suwannee Limestone is separa ted from the Hawthorn Group by sandy clay to clayey sand confining unit ( Yobbi and Halford 2006 ). The Suwannee Limestone is described as a creamy white and tan, soft to hard, granular, porous, crystalline, and partly dolomitic limestone with a thickness o f approximately 150 to 300 feet. The Suwannee Limestone is underlain by a thick (approximately 1700 to 2000 feet) sequence of carbonate rocks that includes the Eocene age Ocala Limestone, Avon Park Formation, Lake City Limestone, and Oldsmar Limestone ( Pe ek 1958 ).

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24 The sedimentary deposits described by Peek ( 1958 ) form the multi layered aquifer system present in the study area. Three aquifers the surficial aquifer, intermediate aquifer system, and Floridan aquifer are present ( Yobbi and Halford 2006 ). All deposits overlying the Hawthorn Group make up the surficial aquifer. The surficial aquifer is separated from the Hawthorn Group by a confining unit consisting of sandy clay, clay, and marl. The Hawthorn Group sediments form the intermediate aquifer system that contains up to three water producing zones within the study area. The producing zones are separated by confining units and are composed primarily of carbonate rocks. The Suwannee Limestone and Avon Park Formation are the two major water prod ucing zones within the Upper Floridan aquifer and are separated by the less permeable Ocala Limestone ( Yobbi and Halford 2006 ). A review of boring logs, geophysical logs, and a video survey log completed during well construction indicates that the surficia l aquifer is approximately 35 feet thick at the Bradenton HSPS site ( City of Bradenton 2004 ). The surficial aquifer consists of silty sand, of medium to coarse grains, with some shell present in the lower portion. Limestones, clays, and siltstones of the Hawthorn Group are present at the site from approximately 35 to 295 feet bls. Gray to yellow, hard, fossiliferous limestone, likely the Tampa Member, is present from approximately 295 to 400 feet bls. Carbonates of the Upper Floridan aquifer underlay th e Tampa Member with the Suwannee Limestone contact at approximately 400 feet bls. The Suwannee Limestone was described as a brownish gray to yellowish gray, partly micritic or crystalline, hard, limestone. Borings completed at ASR 1 and SZMW 1 were termi nated at approximately 550 feet bls (City of Bradenton 2004) Therefore, the thickness of the Suwannee Limestone and depth to

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25 the Ocala Limestone contact were not determined. A generalized geologic profile is included below (Figure 2 2 ). Both ASR 1 and SZMW 1 were initially drilled to approximately 550 feet bls. However, ASR 1 was grouted back to 505 feet bls due to the presence of a horizontal cavity of approximately foot thick below this depth as noted in the ASR 1 video survey log. The geophysical logs and video survey completed at ASR 1 indicate that the primary productive interval of ASR 1 is between 460 and 485 feet bls with a few thin, approximately 2 inch thick, porous intervals or solution features present. No other significa nt high p orosity zones were identified (City of Bradenton 2004 ). Water quality samples collected prior to cycle testing (Table 2 2) indicate brackish native aquifer conditions with a measured TDS concentration of 1,200 mg/L at the Bradenton site The p rimary constituent of the native TDS value is sulfate, which was measured at 640 mg/L. Native groundwater chloride concentrations are low, reported at 38 mg/L. The Oxidation Reduction Potential ( ORP ) measured at 64 mV, DO concentration measured near th e resolution (i.e., 0.01 mg/L) of the field probe and total sulfide concentration, measured at 2.3 mg/L, indicate s trongly reducing (i.e., sulfate reducing) native aquifer conditions were present at the site Cycle Test Program Each ASR facility is held to a set of regulations administered by the Florida Department of E nvironmental Protection (FDEP) ( Ch. 62 528 F.A.C. ). These regulations require that for injection into an Underground Source of Drinking Water (USDW), the injectate must at a minimum meet t he PDWS, and cannot cause the exceedance of any PDWS constituent in the aquifer including the 10 g/L MCL for arsenic ( Richta r 2006 ).

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26 To demonstrate compliance with the regulations, Cycle Tests consisting of injection, storage and recovery are conducted at each facility before the facility is placed into operation. Cycle Tests are designed and permitted on a site specific basis and generally reflect the intended operational approach of the facility. Eight Cycle Tests (Cycles 1 through 8) were completed at the site. Testing began in September 2004 and was completed in February 2011. The first seven Cycle Tests were conducted with injectate containing a normal DO concentration of approximately 8.5 mg/L. Cycle Test 8 was the first test to implement the degasification and chloramine control process, and resulted in injectate DO concentrations of 6 g/L and chlora mine concentrations of approximately 0.5 mg/L. The first series of tests (Cycle Tests 1 4) were conducted to measure the near borehole geochemical response that occurs during ASR and were limited to a 10 MG recharge. Storage periods in Cycle Tests 1 3 were approximately 6 to 13 days followed by the complete recovery of the stored water. In Cycle Test 4 the storage duration was extended to 28 days to allow the injected water to further equilibrate with the aquifer. Cycle Tests 5 and 6 were designed t o test water quality changes as recharge water moved past SZMW 1 by increasing the cycle volume to reach the planned storage volume of 160 MG. Cycle Test 5 included a 50 MG recharge event, with only 10 MG recovered. This approach allowed for monitoring o f the advective front of recharge water as it moved past SZMW 1. Cycle Test 6 provided for the injection of an additional 120 MG. In that 40 MG remained from Cycle Test 5, this brought the total recharge volume to the planned operational volume of 160 MG After an initial 10 MG

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27 recovery event, the remaining 150 MG was left in storage for 60 days, and then 120 MG was recovered. The remaining 30 MG was recovered prior to Cycle Test 7. Cycle Test 7, the final high DO test, included a 40 MG recharge event. This test was followed by the first over recovery of recharge water to return the system to near native, low ORP conditions prior to implementation of the Degas test. Cycle Test 8, the Degas test, was permitted as a full scale (160 MG) low DO (DO < 10 g/L) recharge event which would be directly comparable to results from Cycle Test 6. While t he total volume recharged during Cycle Test 8 was the same as Cycle Test 6, the recovery (pumping) rates were 1.53 and 0.97 MGD, respectively (Table 2 3). T her e were no indications (e.g., turbidity and specific conductance measurements and limited filtered sampling) however, of altered colloidal transport processes due to the lower recovery rate Table 2 2 provides a comparison of recharge water quality with native groundwater conditions during the full scale high DO test (i.e., Cycle Tests 5 6) and the full scale low DO test (i.e., Cycle Test 8). Additional Cycle Test details are provided in Table 2 3 Sa mpling Protocols Water quality data from Bradenton ASR facility were collected in accordance with the FDEP construction permit. As required by the construction permit, all groundwater samples were collected in accordance with FDEP Standard Operating Proce dures (SOP s laboratory supplied containers. The samples were not filtered, per FDEP SOPs. Upon collection, the samples were immediately chilled (iced) to 4C and were shipped t o an offsite laboratory for analysis. All laboratory analyses were performed by National Environmental Laboratory Accreditation Conference (NELAC) certified labs using

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28 FDEP approved analytical methods. Field parameters (i.e., pH, DO, ORP, specific conduc tance ) were measured using a Yellow Springs Instrument (YSI), Inc. 556 MPS instrument or YSI 6600 EDS data logging sonde. The field instruments utilized at Bradenton include ORP probes which use platinum electrodes, Ag/AgCl reference electrodes and 3 mola r KCl ele ctrolyte solutions, which yield s an offset to the Standard Hydrogen Electrode ( SHE ) of +200 mV, per the manufacturer s specifications. All field instruments were calibrated and deployed in accordance with FDEP S OPs. Performance specifications for the field instruments can be found at YSI.com Results and Discussion Comparison of High DO and Low DO Cycle Test Results A comparison of the results from the full scale (160 MG) high DO test (Cycle Tests 5 6) and full scale low DO test (Cycle Test 8) demonstrated that the removal of the primary oxidizers (i.e., DO and Cl 2 ) from ASR source water by membrane degasification inhibited the mobilization of arsenic during ASR, thereby reducing concentrations in the recove red water to below the 10 g/L MCL (Figure 2 3 ). The results from the low DO test (Cycle Test 8) demonstrated a 50 fold reduction in the peak arsenic concentration over the previous high DO tests (Cycle Tests 5 6). The late peak arsenic concentration of 75 g/L encountered during the high DO tests (Cycle Tests 5 6) occurred with 71% of the stored water recovered. The late peak arsenic concentration of 1.48 g/L encountered during the low DO test (Cycle Test 8) occurred with 79% of the stored water recove red. Both tests, however, showed arsenic concentrations slightly above the 10 g/L MCL during the initial recovery (pumping) phase. The initial arsenic spikes occurred at 6% and 21% of the stored water recovered during the Cycle Tests 5 6 recovery event s.

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29 An initial arsenic spike (12 g/L) was also reported in the first sample collected during the Cycle Test 8 recovery event, with less than 0.1% of the stored water recovered. Each of these spikes coincides with the initial startup of the ASR 1 well pum p following a storage event (Figure 2 3 and Table 2 3 ). Therefore, additional tests are ongoing to determine if this may be related to stressing the aquifer (e.g., pumping), well construction and development, formation and transport of colloids or other causes. More importantly, arsenic concentrations during the low DO test present a divergent trend from the previous high DO test results at both the ASR 1 well and SZMW 1 well. Arsenic did not exceed the MCL at SZMW 1 during the low DO test, as the peak arsenic concentration was 8.25 g/L (Figure 2 4 ), while arsenic was measured at 20 g/L at SZMW 1 during the high DO test (Figure 2 5 ). These results demonstrate that with degasification, the Bradenton Potable ASR facility meets regulatory compliance wit h the 10 g/L arsenic MCL. Analytical Methods Mass balance calculations were performed as a means of comparing the mass of DO recharged and arsenic released during the full scale high DO (Cycle Tests 5 6) and low DO (Cycle Test 8) test events. Using the average DO concentration of 8.51 mg/L measured during the 160 MG (6.1E+08 L) recharge event, the total mass of DO injected during Cycle Tests 5 6 was 5,200 kg (1.6E+05 mol). Following pyrite oxidation stoichiometry, it is assumed that 3.75 mol of DO (i.e. O 2 ) are consumed for each mol of pyrite (i.e., FeS 2 ) reacted ( Caldeira et al. 2003) To that end, the theoretical mass of pyrite reacted during the injection of 160 MG of high DO water was 5,200 kg (4.3E+04 mols). Using the reported average weight perc ent of arsenic in pyrite in the Suwannee Limestone of 0.23% ( Price and Pichler 200 6), and assuming congruent dissolution of

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30 pyrite, the theoretical mass of arsenic released during the full scale high DO test event was 12 kg. Integrating by employment of t he trapezoidal rule indicates that the total mass of arsenic recovered (Figure 2 3 ) during Cycle Tests 5 6 was 15.6 kg of arsenic, slightly greater but within the range of the predicted value of 12 kg. By applying the same assumptions, for comparison with the high DO test, the total mass of DO injected during the low DO test (Cycle Test 8) was 3.7 kg (110 mol), which was calculated using the average DO concentration of 6 g/L recorded during the 156 MG (5.9E+08 L) recharge event. The theoretical mass of py rite reacted and arsenic released during Cycle Test 8 were 3.7 kg (32 mol) and 8.4 g, respectively. By employing integration, the total mass of arsenic recovered (Figure 2 3 ) during Cycle Test 8 was calculated to be 0.96 kg, assuming that arsenic values re ported below the laboratory Method Detection Limit (MDL) were equal to of the MDL. While the theoretical mass of arsenic released (12 kg) during Cycle Tests 5 6 was slightly lower than to the actual mass of arsenic recovered (15.6 kg), the actual mass o f arsenic recovered (0.96 kg) during the low DO test (Cycle Test 8) exceeded the predicted arsenic value (8.4 g). It is hypothesized that this may be due to the recovery of residual arsenic released during previous high DO Cycle Tests. None the less, thi s approach illustrates that the removal of 99.93% of DO and 90% of chloramine from the ASR source water resulted in an approximate 94% reduction in the total arsenic recovered during Cycle Test 8, as compared to Cycle Tests 5 6. DO Consumption Rates and Re dox Equilibration A rapid near borehole geochemical response was measured during recharge of high DO source water. The rate of DO consumption was measured during the full scale (160 MG) high DO test (Cycle Tests 5 6), as shown in Figure 2 6 with the DO

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31 concentration approaching the limit of the probe after less than 10% of the stored water recovered. Norton ( 200 7) applied the Push Pull Test (PPT) analytical technique as a means of quantifying the temperature dependent DO consumption rate for the Bradent on ASR site. Using the PPT technique to evaluate data collected during Cycle Tests 1, 2, 5, and 6, a pseudo first order DO decay rate of 0.5 day 1 at 25C was derived. These results suggests that DO is rapidly consumed near the ASR borehole. Furthermore the DO consumption rate corresponds with a rapid decrease in field ORP measurements, from oxic recharge water values around +5 1 0 mV to sub oxic values around +1 40 mV with less than 10 % of the stored water recovered (Figure 2 6 ). In contrast to the results from the high DO tests, ORP measurements during the low DO (Cycle Test 8) event showed suboxic values of +70 mV at the beginning of recovery with values trending downward to approximately 30 mV indicating anoxic conditions near the end of the recovery event. DO was consistently measured near the resolution of the field probe during the Cycle Test 8 recovery event. Arsenic Mobility The mobility of arsenic appears to be retarded within the matrix, with the bulk of the arsenic remaining near the ASR 1 borehole. Given the lack of a clear contrast in the native groundwater and recharge water chloride concentrations (Table 2 2 ), TDS was u sed as a surrogate for a conservative tracer. The arrival of the advective front was shown by the breakthrough of TDS at SZMW 1 during Cycle Tests 5 6 and 8 at approximately 40 MG recharged (Figure 2 4 ). While the arrival of the advective front at SZMW 1 occurred early in the recharge event, arsenic was not reported at SZMW 1 in significant concentrations. However, arsenic concentrations appeared to spike at SZMW 1 during the Cycle Tests 5 6 recovery events (Figure 2 5 ) with the peak arsenic

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32 (20 g/L) con centration measured at SZMW 1 near the end of recovery. This is much lower than the peak arsenic (75 g/L) concentration measured at ASR 1 during Cycle Tests 5 6, which suggests that much of the arsenic is removed from solution by sorption to the aquifer matrix within 224 feet of the ASR borehole. Repetitive High DO ASR Cycling Results from the initial 10 MG high DO tests (Cycle Tests 1 4) showed consistent trends, with the peak arsenic concentrations of 15 to 23 g/L detected near the end of the recovery events (Figure 2 7 ). There was no significant change in the peak arsenic (20 g/L) concentration reported during Cycle Test 4 that included a storage interval of 28 days, which was approximately two to three weeks longer than the 6 13 days of storage dur ing Cycle Tests 1 3. The peak arsenic concentration reported during the 40 MG high DO test (Cycle Test 7) occurred at the end of recovery, with 101 % of the stored water recovered. Repetitive cycling with high DO source water during Cycle Tests 1 4 did not appear to significantly affect the peak arsenic concentration in the recovered water. However, the late arrival of arsenic during Cycle Test 7, which followed the full scale high DO tests (Cycle Tests 5 6), may suggest some degree of arsenic removal from the matrix, or pyrite passivation, by repetitive exposure of the aquifer matrix with high DO source water. Regardless, the Bradenton ASR system exceeded the 10 g/L arsenic MCL during each of the high DO source water recharge events (Cycle Tests 1 th rough 7). Therefore, application of a pretreatment technique for controlling arsenic mobility is required.

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33 Figure 2 1. Site location map. ROMP TR 9 1, ROMP TR 9 2 and Bradenton ASR 1 are wells included in this study.

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34 Figure 2 2. Bradenton ASR site plan, showing process flow diagram, and generalized geologic cross section (City of Bradenton 2004) for the Bradenton ASR facility. Not to scale. Thickness of Suwannee and Ocala Limestones undetermined.

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35 Table 2 1. Well construction details for the Bradenton HSPS ASR facility Well Name Casing Depth (feet bls a ) Nominal Casing Outside Diameter (inches) Casing Material Open Hole Interval (feet bls a ) Top of Well Casing Elevation b (msl c ) ASR 1 415 17.4 PVC 415 550 (plugged back with cement to 505) 20.54 SZMW 1 400 6.625 PVC 400 548 20.16 AFMW 1 200 8.625 PVC 200 230 19.58 WTMW 15 4 PVC screened from 5 15 20.26 a = feet below land surface (bls); b = as surveyed on October 8, 2003; c = feet above mean sea level (msl) ( City of Bradenton 2004 ) Table 2 2. Bradenton ASR water quality summary Sample Location SZMW 1 a ASR 1 b ASR 1 c Field Parameters DO (mg/L) 0.02 1 8.51 1.63 6E 3 4E 3 2 ORP (mV) 64 4 5 60 43 3 29 46 Chloramines (mg/L) N M 3.80 0.60 3 0.45 0.32 3 Laboratory Parameters Arsenic (g/L) <2.8 <1.32 0.5 0.2 Chloride (mg/L) 38 30 4 41 5 TDS (mg/L) 1,200 323 23 449 51 Sulfate (mg/L) 640 154 9 209 30 Sulfide (mg/L) 2.3 5 BDL BDL a = Background (i.e., native) water quality results as measured on 11/9/2003 b = Average recharge water quality concentrations measured during Cycle Test 5 and 6 (high DO) c = Average recharge water quality concentrations measured during Cycle Test 8 (low DO) 1 = measured value is at the resolution of the YSI 556 field probe 2 = measured by Orbisphere 410/1056 O2 analyzer 3 = measured by Hach Cl 17 analyzer 4 5 = Measured at end of Cycle Test 1 recovery event NM = not measured BDL = below method detection limit

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36 Table 2 3. Bradenton ASR cycle test program summary Cycle Test Start Date End Date Storage Duration (Days) Pumping Rates a (MGD) Recharge Volume (MG) Recovery Volume (MG) Net Volume b (MG) 1 9/9/2004 12/1/2004 9 1.69 / 1.87 10.3 10.4 0.1 2 12/1/2004 12/20/2004 6 1.67 / 1.87 10.0 10.6 0.1 3 12/24/2004 1/19/2005 13 1.67 / 1.87 10.0 10.0 0.7 4 1/20/2005 3/1/2005 28 1.65 / 1.78 9.4 9.4 0.7 5 8/9/2005 9/22/2005 0 1.38 / 1.43 50.2 8.9 40.6 6a 10/11/2005 1/20/2006 1 1.30 / 1.53 120.1 10.2 150.5 6b 3/21/2006 4/7/2006 60 1.53 119.9 30.6 6c 8/21/2007 9/14/2007 413 1.25 29.9 0.7 7 9/14/2007 1/29/2008 0 1.03 / 1.45 40.1 79.9 39.1 8 7/28/2009 2/15/2011 105 0.52 / 0.97 156.2 156.2 39.1 a = Average injection rate (+) and recovery rate ( ) b = Cumulative (residual) volume at end of cycle Figure 2 3 Total a rsenic (g/L) concentrations at ASR 1 during the full scale high DO (Cycle Tests 5 6) recovery event and the low DO (Cycle Test 8) recovery event. Values reported below the method detection limit (MDL) plotted at of the MDL.

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37 Figure 2 4 TDS (mg/L) and total arsenic (g/L) concentrations at SZMW 1 during Cycle Tests 5 6 and Cycle Test 8 recharge events. Native conditions shown at volume recharged = 0 MG. Values reported below the MDL plotted at of the MDL. Figure 2 5 TDS (mg/L) and total arsenic (g/L) concentrations at SZMW 1 during Cycle Tests 5 6 and Cycle Test 8 recovery events. Values reported below the MDL plotted at of the MDL.

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38 Figure 2 6 Field DO (mg/L) and ORP ( mV) measurements during Cycle Tests 5 6 and Cycle Test 8 recovery events. ORP values corrected to the SHE. Figure 2 7 Total a rsenic (g/L) concentrations measured during recovery of Cycle Tests 1 4 (10 MG tests) and Cycle Test 7 (40 MG test), all high DO tests. Values reported below the MDL plotted at of the MDL.

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39 CHAPTER 3 INFLUENCE OF CORE PR ESERVATION METHODS O N ASR BATCH STUDIES Objective Laboratory scale investigations of arsenic mobilization during ASR completed to date have relied upon core materials that have been in storage under atmospheric (i.e., warehouse) conditions (Arthur et al. 2007 ; Fischler et al. 2010 ; Arthur et al. 2007 ) The results of these studies may have been impacted by the alteration (e.g., pyrite oxidation) of the core samples by exposure to an oxygen rich environment. Therefore, the objective of this research is to evaluate the effect of cor e preservation techniques on ASR laboratory studies Tests were completed to compare ASR batch study leaching profiles using splits of preserved and purposefully unpreserved core material. Considering the costs and effort related to core collection and preservation, the results of these tests will be used to determine the need or justification for preserving core materials during future laboratory studies. Methods Core Collection and Preservation In August 2009, the Suwannee Limestone was cored at the SW FWMD Regional Observation and Monitoring Program (ROMP) TR 9 1 well site (Figure 2 1) located in west central Hillsborough County at latitude 27 N longitude 82 W Cores were collected using the SWFWMD's wire line coring rig (CME 85 d rill rig) and a 2 inch core barrel (Bit make: Boart Longyear; Bit Serial Number: 1NQ475/1; Bit Model Number: 20.25 CT; Bit Size: 2.980 inch OD and 1.875 inch ID core bit). These tools produce an approximate 1.8 inch OD core. The drill rig was set up appr oximately 56 feet e ast of the TR 9 1 well site.

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40 Surface casings were installed, prior to coring, to maintain bore hole competence within the upper unconsolidated sediments and to prevent cross connection of waters between productive intervals of the Hawt horn Group, including the Arcadia Formation and its Tampa Member, and the underlying Suwannee Limestone. A 6 inch steel casing was grouted in place across the unconsolidated surficial sediments and into the Arcadia formation from 0 to 70 feet (ft) below l and surface (bls). A 4 inch temporary steel casing was set near the bottom of the Arcadia Formation from 0 to 148 ft bls. Finally, a temporary 3 inch steel casing was installed just into the top of the Suwannee Limestone from 0 to 290 ft bls. T o minimize core exposure to atmospheric conditions (i.e., maintain nat ive conditions) during drilling, t he new borehole was allowed to flow under artesian pressure, after air lifting and after periods where the bore hole was shut in (e.g., overnight). M ake up water used to cool the bit was pumped from the nearby TR 9 1 well which is constructed with an open bore hole interval of 124 to 288 ft bls that crosses the Tampa Member, a low to moderate productive unit within the Hawthorn Group sediments. Samples collected at the TR 9 1 well showed the source of drilling makeup water to be reducing, with a strong sulfur odor. T he volume of water used during each core run was logged (range = 55 to 141 gallons) T he air lift technique was used to clear the bore hole of cutt ings approximately every 20 ft by inserting a PVC tremie pipe to approximately 100 ft bls which is 190 ft above the top of the core interval With the outer core barrel sitting near the bottom of the open hole, air was pushed into the upper casing. As the air rises and expands it creates a lift (suction) effect and pulls water into the borehole from the lower formation. The water rises with the air and is

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41 allowed to discharge at the surface. While care was taken to m aintain native conditions during coring, it's possible that air was entrained through the pipes, hoses, pumps, and tanks that make up the drilling system. However, allowing the well to flow under artesian conditions should have minimized exposure of the c ore to non native conditions. The entire thickness of the Suwannee Limestone, from 290 to 480 ft bls, was cored using this procedure. In general, core recovery rates were high, exceeding 90% recovered for 22 of the 38 core attempts. Core recovery was le ss than 10% in 7 of the 38 cores, with only 3 having no (0%) recovery. Low core recovery occurred from 305 to 325 ft bls, 360 to 365 ft bls, and 470 to 480 ft bls (at the Ocala Limestone contact). Core recovery appeared to be low in areas of high porosit y, fractures, and/or poorly indurated sediments. The lower segment of the bore hole, below 365 ft, appeared to be well indurated and yielded several (13) complete cores (5 ft in length). Upon retrieval of the core from the core barrel, the core was pla ced onto 5 ft sections of longitudinally split 2 inch Sch 40 PVC 0.10 inch slot well screen (Figure 3 1). Photographs of the core were taken and the core was covered with the top half of the well screen. The two halves were then taped together using viny l tape and the core was inserted into the core storage vessels. The core storage vessels were constructed of 3 inch Sch. 80 PVC pipe, capped on each end, with an inlet and outlet brass valves near each end of the pipe and a dual scale pressure/vacuum gaug e installed a t the outlet (top) valve (Figure 3 2 ). New natural sponges were used as packing material to fill the gap between the inner core sleeve and outer core storage vessel. Once the vessels were capped, at the upper valve, a vacuum ( 28 to 29 inch Hg) was applied for less than 1 minute. This was followed by the application of a positive nitrogen (N 2 )

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42 head of 11 to 12 psi, at the lower valve, while continuing to pull the vacuum at the top valve. The N 2 feed line was purged prior to connection at t he lower valve. The N 2 flow was then turned off by closing the lower valve and a vacuum of 28 to 29 inches Hg was again applied. This procedure, vacuum and N 2 flush was repeated three times prior to the final fill of N 2 of 11 to 15 psi. This procedur e was applied to each vessel and, to date ( December 2011) none of the vessels has lost more than around 1 2 psi of pressure. of core was deliberately left unpreserved and stored only in cold storage boxes. Core Crushing and Splitting In January 2010, two five feet sections of preserved core representing the 445 to 450 ft bls and 450 to 455 ft bls depth intervals at the ROMP TR 9 1 si te were transported to the FGS Hydrogeochemistr y L aboratory in Tallahassee for sample preparation. This depth interval represents the approximate middle section of the typical ASR storage interval. Around seven to eight ft of preserved core representing a continuous section from about 447.5 to 455 ft bls was crushed, homogenized and split into sixteen aliquots of approximately 300 g using the following procedures. Upon retrieval from the core storage vessels, the core was placed in vacuum desiccators for drying. Once dry, the core samples were crus hed using a Retsch BB100 jaw crusher set to 8 10 mm (Figure 3 3). The rock crusher was cleaned with a nylon brush then vacuumed and jetted with compressed air between rock samples The removable sample compartment was washed and rinsed with DDI then 2 pro panol and jetted with compressed air. The crushed core material was placed in clea n glass beakers and returned to the vacuum desiccators (Figure 3 4).

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43 Once the cores were dry, the samples we re weighed. The dry weight of C ore 1 (450 to 455 ft core) and C ore 2 (447.5 to 450 ft core) w ere 3640 g and 1742 g, respectively. Therefore, an even split of C ore 1 would yield eight samples of approximately 455 g each and C ore 2 would yield eight samples of approximately 218 g each. To homogenize the crushed core m aterial, Core s 1 and 2 were split int o eight samples each as detailed in Table 2 1 using a Fritsch Rotary Cone Divider (Fig ure 3 5 ). This unit is accurate to within 0.42 percent, which is significantly better than the The Fritsch Divider was cleaned with a nylon brush and soapy water rinsed with tap water and DDI, then 2 propanol and jetted with compressed air between samples Samples 1 1, 1 4, 1 5 and 1 8 of Core 1 (Table 3 1) were combined with samples 2 2, 2 4, and 2 5 of Core 2. Samples 1 2, 1 3, 1 6, and 1 7 of Core 1 were combined with samples 2 6, 2 7 and 2 8 of Core 2. The two sets of mixed core material were then each split a second time to provide 16 total aliquots of about 300 g each (Table 2 2). Aliq uot 9 (Table 3 2) was then split into eight subsamples of about 40 g each, and one of these subsamples was split into eight samples of about 5 g each. This core material was added to Aliquots 1, 5, 6, 10, 11, 12, 14 and 16 as needed to bring the total sam ple weight up to at least 300 g (Table 3 3). Once splitting was complete, nine samples (Aliquots 1, 3, 5, 6, 7, 10, 11, 12 and 13) were placed into vacuum d esiccators for preservation. Three samples (Aliquots 4, 8 and 14) were placed in glass beakers, which were left open to the atmosphere and placed on a shelf in the FGS laboratory to be stored at ambient conditions. These three purposely unpreserved samples were misted with DDI water every two to three weeks.

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44 Th re e sam ples (Aliquots 2, 13 and 15) were sent to Activation Laboratories Ltd. for lithogeochemical analysis. Pulverization was completed by Activation Laboratories Ltd. (Actlabs; analysis code RX4) as rock powder is required for this analysis. Appendix A provid es more detail on the pulverization procedure and lithogeochemical analysis Subsamples were also sent to UF Soil and Water Sciences department for mineralogical analysis Mineralogical Characterization Limestone samples from TR 9 1 core (445 to 455 ft bls ) were analyzed via x ray diffraction (XRD), scanning electron microscopy (SEM), electron microprobe analysis (EM), and energy dispersive x ray fluorescence elemental spectrometry (EDS) by Dr. Willie Harris, at the UF Soil and Water Science Department, as part of the SWFWMD arsenic study (Norton et al. 2011) The purpose of this effort was to confirm the similarity of the TR 9 1 core material to geochemical/ mineralogical results of Suwannee Limestone cores presented by Price and Pichler 2006 Arthur et al. 2007 Budd 2007 ; and others. Details of these procedures are provided in the SWFWMD report (Norton et al. 2011). Native Groundwater and ASR Source Water Collection On June 8, 2010, n ative groundwater (NGW) was collected from ROMP well TR 9 2 locate d approximately 5 miles northeast of TR 9 1 2 1). TR 9 2 was completed with a bore hole open to the Suwannee Limestone from 247 462 ft bls. Three sealed flow through containers were construc ted using 20 liter Nalgene Heavy Duty Vacuum Carboys ( Cole Parmer Catalog No. 2226 0050) for collection, storage and transport of the NGW (Figure 3 6) At the wellhead, the c arboys were connected in series using vinyl tubing and Nalgene

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45 Filling Venting Closures (Catalog No. 2162 0050). A vacuum ( 26 to 27 inch Hg) was pulled on the c arboys, and the c arboys filled with N 2 (approximately 3 to 4 psi). This procedure, vacuum and N 2 flush was repeated three times prior to collection of NGW at TR 9 2 to prevent exposing the NGW to atmospheric conditions The TR 9 2 well was purged three well volumes and field parameters measured for stability, prior to collection of NGW. Samples were collected for offsite laboratory analys e s for all major cations and anions, metals, alkalinity and physical parameters using accepted field and laboratory methods (Appendix A). Samples were collected and analyzed onsite for sulfide and reduced iron using a Hach DR 2800 spectrophotometer and physical parameter s (i.e., pH, temperature, specific conductance DO and ORP ) using a Hach HQ40d multi parameter meter. The ORP probe s include d a platinum electrode, a Ag/AgCl reference electrode and 3 molar KCl electrolyte solution, which yields an offset to the SHE of +2 10 mV, per H ach.com. Typical ASR source water (SW) is potable (tap) water This is municipally treated water with high, saturated to supersaturated, DO and chlorine or chloramines concentrations ranging from 3.5 to 4.5 mg/L. Therefore, for the second protocol, tap water from the Bradenton High Service Pump Station (ASR 1 site) was used in this study (Figure 2 1) On July 19, 2010, ASR source water was collected from a hose bib at the Bradenton ASR site using three 5 gallon plastic carboys. The hose b ib was flushed for 5 minutes and each c arboy was flushed with SW three times prior to filling. On July 20, 2010, the SW was transported to the FGS lab in Tallahassee Florida. Bench scale Leaching Experiments To evaluate the effect of core preservation on ASR batch studies, while simulating ASR conditions, two test phases were employed. The first phase was designed to

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46 simulate batch reactors under reducing (i.e., low ORP) native groundwater (NGW) conditions. The second phase was designed to simulate the recharge of oxidizing (i.e., high DO) source water (SW) conditions. As described above, the cores were split into preserved and purposefully unpreserved fractions in January 2010. Ba tch reactor tests were setup in June 2010, after 6 months of core stora ge (preserved vs. unpreserved storage) The initial test phase included placing the previously described core samples into sealed reaction vessels (Figures 3 7 and 3 8 ) with 1 L of NGW. The first phase (Phase 1) was initiated on June 9, 2010, within 24 t o 25 hours of collection of the NGW. During this phase, the rock samples were allowed to equilibrate with NGW for six weeks (41 days) under a N 2 headspace Samples were collected for onsite and offsite laboratory analys e s at a frequency of three sample e vents per week for the first three weeks and once a week sampling thereafter All trace metal samples were filtered onsite to 0.45 m prior to preservation with nitric acid. The second phase (Phase 2) required replacement of th e NGW with high DO SW. Pha se 2 was initiated on July 20, 2010. NGW was removed from the 1 L reaction vessels via a peristaltic pump and replaced with 1 L of SW, collected on July 19, 2010 at the Bradenton Potable ASR site. After replacement of the NGW with SW a N 2 head was applie d to the reaction vessels. The rock samples were allowed to equilibrate with the high DO source water for 5 weeks (38 days) during Phase 2. Samples were collected for onsite and offsite laboratory analys e s at a frequency of three sample events per week f or the first three weeks and once a we ek sampling thereafter.

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47 As described below, DO was rapidly consumed, or lost to the headspace, during Phase 2 and arsenic concentrations remained relatively low. Therefore, o n August 26, 2010, a third phase (Phase 3) was initiated. The caps were loosened on the reaction vessels in order to allow the head space to equilibrate with atmospheric (lab) condit ions, thereby introducing more oxygen into solution. The reaction vessels were allowed to equilibrate with atmosphere (lab) conditions for 4 weeks (31 days) during Phase 3. Samples were collected for onsite and offsite laboratory analysis at a frequency of on e sample per week. Results and Discussion Matrix Geochemistry A subset of the whole rock geochemical analytical results completed by Activation Labs Ltd. are presented in Table 3 4 for comparison with results from bench scale leaching experiments with the complete results provided in Appendix B. Arsenic was reported at 2 mg/kg in each of the three samples submitted for whole rock geochemical analysis. In addition to arsenic, and excluding organic carbon, the analytical results show little deviation from the mean values for three spl it samples for all compounds analyzed (Table 3 4). This indicates that the core crushing and splitting technique applied herein sufficiently homogenized the samples. Mineralogical Composition The results of the analysis completed by Dr. Willie Harris ind icate that the bulk rock of the TR 9 1 core is predominately calcite (CaCO 3 ) and includes a minor amount of quartz and very small amounts of aragonite (Norton et al. 2011) Dr. Harris reported that the composition of the TR 9 1 rock core is similar to th at of other Florida Suwannee Limestone specimens analyzed via XRD (Budd 2007 ) ; with the exception that aragonite

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48 was not identified by Budd. Analysis of the noncarbonated mineral fraction indicated the presence of pyrite in very low concentration. These results confirm that the mineralogical composition of the TR 9 1 core is similar to cores of the Suwannee Limestone used in previous batch studies completed by FGS and others. While no arsenic bearing minerals were detected, arsenic was identified in one iron sulfide particle and in one iron oxide particle. The presence of iron oxide in the samples suggest that oxidation of the core sample had occurred. Additionally, the association of arsenic with iron oxide in the sample indicates this as a sink and/or a source of arsenic. Bench scale Experiments NGW collected from the ROMP TR 9 2 well site was strongly reducing (i.e., anoxic and sulfidic) with field ORP values of less than 87 mV DO concentrations near the resolution (0.01 mg/L) of the Hach HQ4 0d DO probe, and total sulfide concentrations measured at the wellhead ranged from 2.7 to 3.3 mg/L (Table 3 5). In contrast to NGW, the SW collected at the Bradenton ASR site was strongly oxidizing with typical field ORP values of +500 to +600 mV, saturat ed DO concentrations of around 7 to 10 mg/L and chloramine levels of 3.5 to 4.5 mg/L (City of Bradenton 2006). Table 3 5 provides a subset of the NGW and SW field measurements and laboratory analytical results. DO concentrations generally remained low, near the resolution (0.01 mg/L) of the probe, during the NGW phase (Figure 3 9 ). However, there was a slight rise in the DO concentration measured in Vessel 4 (0.48 mg/L) near the end of the NGW phase. There was also a spike in DO measured in Vessel 6 of 1.35 mg/L at an elapsed time (ET) of 7 days. This spike coincides with a spike in ORP in Vessel 6 that was measured during the same sampling event (ET of 7 days (Figure 3 1 0 ) ). While a N 2 headspace

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49 was maintained during the NGW phase, this may indicate some degree of oxygen contamination as the reaction vessels were opened to allow access during sample collection and for the probes used to measure the physical parameters (e.g., temperature, pH, DO, etc.). The initial measurement of DO in the blank of 3 .76 mg/L during the SW phase was lower than expected (Figure 3 9) The measurement was taken less than 24 hours after collection of the SW from the Bradenton ASR site and suggests oxygen was consumed (e.g., biological oxygen demand) during transport from the field to the FGS laboratory. Also, the rapid decrease in DO in the blank upon application of the N 2 headspace indicates degassing of the SW. It was for these reasons that a 3 rd phase with an air headspace was initiated. DO concentrations increased to saturated levels, near 7.9 mg/L, during the 3 rd phase with equilibration with laboratory atmospheric conditions occurring within approximately 4 days. The initial ORP measurement in the blank of 6 6 mV, during the NGW phase, was about 140 to 190 mV lower than the ORP values measured in vessels with core materials (Figure 3 1 0 ). Since the core was collected from the same interval as the NGW, the separation in the initial ORP values suggests that the core samples had been oxidized or that some air was introduced during placement of the core into the reaction vessels. With respect to ORP values, the vessels containing core materials appear to reach equilibrium with the NGW after 5 da ys The narrow range of ORP values of 233 to 202 mV recorded at an ET of 5 days is within the measurement error of 50 mV reported for this probe. The overall increasing trend in ORP values during the NGW phase suggests some degree of oxygen contamina tion of the reaction vessels.

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50 Total dissolved sulfide (H 2 S/HS ) was measured in the field at the pump outlet from 2.7 to 3.3 mg/L and at the carboy outlet from 2.1 to 2.5 mg/L during NGW collection at the TR 9 2 site on June 8 th in Vessels 1 7 due to the large sample volume (10 mL) required for analysis. However, total sulfide was measured in the carboys (Carboy No. 3) at 2.30 mg/L at the start of the bench scale experiment. Sulfide was measured in Carboy No. 3 at 1.82 mg/L at a n ET of 1 day, decreasing to 0.88 mg/L after 16 days and was undetectable (<20 g/L) after 33 days The carboys were kept closed under a N 2 headspace during these tests. Sulfide was measured below the detection limit in Vessels 8 13 which were NGW blanks discussed in Chapter 3 of th e SWFWMD arsenic report, after an ET of 7 days (Norton et al. 2011). Therefore, in addition to DO and ORP measurements, the decreasing trend in sulfide measurements provides further indication of oxygen contamination of the r eaction vessels. Arsenic leaching occurred during the NGW phase (Figure 3 1 1 ). The peak arsenic concentration of 22.7 g/L measured is nearly 190 times the background NGW concentration of 0.12 g/L measured at TR 9 2. Arsenic leaching occurred to a lesser degree during the SW phase s with the peak arsenic concentration of 5.76 g/L measured at the end of Phase 3 (SW air headspace). The release of arsenic from the core material during NGW phase may be attributed to; 1) pyrite oxidation, 2) reductive dissolution of iron oxides formed during core collection, storage, or sample preparation (i.e., crushing and splitting), 3) desorption of arsenic from iron oxides (i.e., anion exchange) due to competition for sorption sites by other anions (e.g., HCO 3 H 2 PO 4 ) or, 4) the dissolution of other arsenic bearing minerals other than pyrite. More relevant to

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51 the current objective is the separation of arsenic values in batch reactors containing preserved and unpreserved cores. While the overall trends are very similar, arsenic concentrations in the preserved core vessels are less variable than those of the unpreserved core, especially during the NGW phase. For example, the peak arsenic concentrations for the vessels containing preserved core occurred at an ET of 14 days and fall within a narrow range of 20.4 to 21.2 g/L. At the same time, arsenic concentrations in the unpreserved cores ranged from 14.6 to 22.2 g/L. The core splitting technique utilized herein has been shown to produce well homogenized samples, as described above. The cores were handled (i.e., collected, crushed and split) in the same manner up to the point at which three sets of core were placed on the shelf (i.e., purposefully unpreserved) and the remaining cores were returned to the vacuum desiccators (i.e., preserved). Therefore, the differences in the behavior of these cores would be due to the exposure of the three unpreserved cores to atmospheric conditions during the 6 month storage period. Assuming pyrite oxidation occurred du ring core storage, as follows, the formation of iron oxides (HFOs) would be expected: FeS 2 + 15/4 O 2 + 7/2 H 2 O = Fe(OH) 3 + 2 SO 4 2 + 4 H + ( 3 1) If HFOs were formed during core storage, the release of iron by reductive dissolution of HFOs would be ex pected during the NGW (i.e., sulfidic) phase. However, iron concentrations remained low and not variable during all three phases of the study (Figure 3 1 2). The above observations could suggest that the release of arsenic observed under the reducing NGW phase is likely not due to the dissolution of Fe (oxy) hydroxide minerals. However, the presence of sulfide and the chalcophilic character of

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52 reduced iron can lead to a fast removal of iron from solution via precipitation as iron sulfide, hence limiting iron solubility. The spikes of iron may be attributed to contamination by the laboratory probes during sample collection. The intermediate cation manganese tends to mirror the redox sensitive behavior of iron in environmental systems, having an ionic radius similar to iron in the 2+ and 3+ oxidation states (Railsback 2003). The release of manganese into solution would be expected if reductive dissolution of manganese oxides, formed during core storage, occurred. Like iron, however, manganese concentrations remained low during the NGW phase (Figure 3 13). Manganese sorption onto solid surfaces appears to have occurred during the SW N 2 headspace phase, as the manganese concentration in the blank was approximately 14 times greater than the concentration in the other vessels containing SW plus rock. The declining manganese concentration in the blank during the SW air headspace phase indicates precipitation under high DO conditions. As shown in Equation 3 1, another indicator of pyrite oxidation during core storage is the production of sulfate (SO 4 2 ) by the oxidation of sulfide (S 2 ). As seen in Figure 3 14, sulfate concentrations were higher during the NGW phase in the vessels with unpreserved core than the vessels containing preserved core. Sulfate concentrations were also greater in the vessels with core than the NGW and SW blanks The resolution of the sulfate data is improved in Figure 3 15 by alt ering the scale for the NGW phase. The initial rise in sulfate concentrations in all vessels may, in part, be attributed to the oxidation of dissolved sulfide to sulfate. However, the sulfate concentrations in the vessels with preserved cores and unprese rved cores are approximately 20 mg/L and 30 mg/L greater than the blank, respectively. This suggests

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53 that both the preserved and unpreserved cores had undergone some level of oxidation, with the unpreserved core being more oxidized than the preserved core As a Group VI element, molybdenum tends to mimic the behavior of sulfur in environmental systems, with stable oxidation states of + 2, +4 and +6 (Railsback 2003) Like sulfate, there is a net separation in molybdenum concentrations between vessels with p reserved and unpreserved core materials (Figure 3 16). Molybdenum concentrations are greatest in the unpreserved core vessels during the NGW phase. This trend reverses during the Phase 3 (SW air headspace) with molybdenum concentrations greatest in the preserved core vessels. A further indication of oxidation of the cores during the 6 month core storage period is provided in Figures 3 17 through 3 19. The separation in the trends for preserved and unpreserved core vessels for antimony and vanadium, and to a lesser degree uranium, suggest oxidation of the purposefully unpreserved cores during core storage. Furthermore, the antimony, vanadium and uranium concentrations measured during NGW phase are much higher than the concentrations reported for NGW at the TR 9 2 site (Table 3 5). Desorption of antimony, vanadium, and uranium from solid surfaces, possibly iron and/or manganese oxide surfaces, is likely occurring. Like other Group I and Group II elements, cesium and barium are not sensitive to changes in the redox environment. With a relatively low ionic charge and large ionic radius, yielding an ionic potential of less than 2.5, these elements tend to exhibit a conservative (non reactive) behavior in environmental systems (Railsback 2003). The concentr ations of these elements, however, decline over time during the NGW and SW phases (Figures 3 20 and 3 21). The concentrations in the vessels containing core

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54 material are also lower than that of the vessel containing the blank This suggests that cesium a nd barium are sorbing to the surface sites created during crushing of the rock core. Figure 3 1. Core placed onto 2 inch split, 0.10 slot, Sch. 40 PVC well screen. (Photo courtesy Stuart Norton)

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55 Figure 3 2. Core preservation vessels in storage rack. (Photo courtesy Stuart Norton)

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56 Figure 3 3. Retsch BB100 jaw crusher (Photo courtesy Cindy Fischler)

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57 Figure 3 4. Crushed core in vacuum dessiccator. (Photo courtesy Cindy Fischler) Figure 3 5 Fritsch rotary cone divider. (Photos courtesy Cindy Fischler)

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58 Table 3 1. F irst split of Core 1 and Core 2 Core 1 (450 455 ft bls) Weight (g) Core 2 (447.5 450 ft bls) Weight (g) 1 1 473.45 2 1 216.63 1 2 466.20 2 2 225.56 1 3 449.58 2 3 212.56 1 4 436.07 2 4 215.15 1 5 459.33 2 5 208.57 1 6 437.94 2 6 236.12 1 7 461.95 2 7 201.89 1 8 448.38 2 8 211.11 sum (g) 3632.9 sum (g) 1727.6 loss (g) 6.8 loss (g) 14.1 Table 3 2. Second split of Core 1 and Core 2 Aliquot Weight (g) Aliquot Weight (g) 1 299.4 9 318.5 2 324.7 10 307.0 3 310.1 11 289.0 4 313.4 12 302.0 5 296.5 13 323.8 6 286.8 14 292.7 7 316.7 15 319.9 8 307.2 16 301.5 sum (g) 2454.8 sum (g) 2454.5

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59 Table 3 3. Final mass of crushed core samples Aliquot Sample Added (g) Final Weight (g) Vessel ID Comments 1 7.6 307.0 Vessel 1 Preserved 2 0.0 324.7 Activation Labs L ithogeochem sample 3 0.0 310.1 Vessel 2 Preserved 4 0.0 313.4 Vessel 4 Unpreserved 5 13.2 309.7 Vessel 3 Preserved 6 24.2 311.0 Vessel 8 Preserved 7 0.1 316.8 Vessel 9 Preserved 8 0.0 307.2 Vessel 5 Unpreserved 9 Split into subsamples 10 4.0 311.0 Vessel 10 Preserved 11 20.5 309.5 Vessel 11 Preserved 12 6.3 308.3 Vessel 12 Preserved 13 0.0 323.8 Activation Labs Lithogeochem sample 14 15.7 308.4 Vessel 6 Unpreserved 15 0.0 319.9 Activation Labs Lithogeochem sample 16 8.9 310.4 Vessel 13 Preserved Figure 3 6. Vacuum carboys used in NGW sample collection at ROMP well TR 9 2. (Photo courtesy Cindy Fischler)

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60 Figure 3 7 Sealed reaction vessels. (Photo courtesy Stuart Norton) Figure 3 8. Sealed reaction vessels in fume hood at FGS lab. (Photo courtesy Stuart Norton)

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61 Table 3 4. Whole rock geochemistry. Analyte SiO 2 Al 2 O 3 Fe 2 O 3 MnO MgO CaO Na 2 O K 2 O P 2 O 5 As MDL 0.01 0.01 0.01 0.001 0.01 0.01 0.01 0.01 0.01 1 Unit % % % % % % % % % ppm UF 1 4.11 0.24 0.12 0.004 0.7 51.97 0.04 0.05 0.07 2 UF 2 3.96 0.19 0.09 0.004 0.66 52.45 0.04 0.04 0.08 2 UF 3 3.81 0.18 0.08 0.004 0.65 52.25 0.04 0.04 0.07 2 mean 3.96 0.2 0 0.1 0 0.004 0.67 52.22 0.04 0.04 0.07 2 std dev 0.15 0.03 0.02 0 0.03 0.24 0 0.01 0.01 0 Analyte S(T) SO4 C(T) C(G) C (O) Mo Rb Sb U V MDL 0.01 0.3 0.01 0.05 0.05 2 1 0.1 0.01 5 Unit % % % % % ppm ppm ppm ppm ppm UF 1 0.15 0.3 11.7 < 0.05 0.65 4 1 0.2 7.03 27 UF 2 0.14 < 0.3 11.6 < 0.05 0.28 4 < 1 0.3 7.25 25 UF 3 0.13 < 0.3 11.6 < 0.05 0.24 4 < 1 0.2 6.76 22 mean 0.14 11.6 0.39 4 0.2 7.01 25 std dev 0.01 0.1 0.23 0 0.1 0.25 3 (T) = total, (G) = graphite, (O) = organic

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62 Table 3 5. Selected an alytical results for NGW and SW Sample ID NGW a SW a b Date 06/08/10 07/20/10 Time 7:00 AM 10:45 AM Analyte Unit Method MDL pH 7.24 7.72 S.U. Probe T 26.1 27.7 o C Probe COND. 15229 835 uS Probe DO 0.03 3.76 mg/L Probe ORP 79 mV Probe Ca 148000 61700 g/L ICP MS 700 Na 70600 71800 g/L ICP MS 5 K 2680 7320 g/L ICP MS 30 Mg 65800 17100 g/L ICP MS 1 Ba 70.6 33 g/L ICP MS 0.1 V < 0.1 0.3 g/L ICP MS 0.1 As 0.12 0.37 g/L ICP MS 0.03 Fe < 10 20 g/L ICP MS 10 Mn 0.4 6.3 g/L ICP MS 0.1 Mo 0.2 < 0.1 g/L ICP MS 0.1 Sb 0.01 0.06 g/L ICP MS 0.01 Cs 0.017 0.065 g/L ICP MS 0.001 U 0.026 0.315 g/L ICP MS 0.001 F 0.54 0.76 mg/L IC 0.01 Cl 226 49.1 mg/L IC 0.03 NO 2 (as N) < 0.04 < 0.02 mg/L IC 0.01 Br 0.92 0.19 mg/L IC 0.03 NO 3 (as N) < 0.04 1.22 mg/L IC 0.01 PO 4 3 (as P) < 0.08 0.26 mg/L IC 0.02 SO 4 2 380 241 mg/L IC 0.03 Alk. (as CaCO 3 ) 133 69 mg/L TITR 2 CO 3 2 < 1 < 1 mg/L TITR 1 HCO 3 133 69 mg/L TITR 1 a = metal sample s filtered to 0.45 m, b = sample collected from Vessel 7

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63 Figure 3 9 Dissolved oxygen (DO) concentration s (mg/L) in batch reactors over time. Figure 3 1 0 O xidation Reduction Potential ( ORP) measurements ( mV) in batch reactors over time ORP values corrected to the SHE.

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64 Figure 3 1 1 Dissolved a rsenic (As) leachate concentrations (g/L) in batch reactors over time. Figure 3 1 2. Dissolved i ron (Fe) leachate concentrations (g/L) in batch reactors over time.

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65 Figure 3 13 Dissolved m anganese (Mn) leachate concentrations (g/L) in batch reactors over time. Figure 3 14 Dissolved s ulfate (SO 4 2 ) concentrations (mg/L) in batch reactors over time

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66 Figure 3 15 Dissolved s ulfate (SO 4 2 ) concentrations (mg/L) in batch reactors during native groundwater (NGW) phase. Figure 3 16 Dissolved m olybdenum (Mo) leachate concentrations (g/L) in batch reactors over time.

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67 Figure 3 17 Dissolved a ntimo ny (Sb) leachate concentrations (g/L) in batch reactors over time Figure 3 18 Dissolved v anadium (V) leachate concentrations (g/L) in batch reactors over time.

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68 Figure 3 19 Dissolved u ranium (U) leachate concentrations (g/L) in batch reactors over time. Figure 3 2 0 Dissolved c esium (Cs) leachate concentrations (g/L) in batch reactors over time.

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69 Figure 3 2 1 Dissolved b arium (Ba) leachate concentrations (g/L) in batch reactors over time.

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70 CHAPTER 4 DESIGN INTACT CORE COLUMN E XPERIMENTS Objective Laboratory studies of Florida ASR sites completed to date have relied upon crushed core materials (Arthur et al 200 7; Fischler et al 2010 Arthur et al 2007 ). As described in Chapter 3 of this dissertation crushing the rock core increases t he exposed surface area, thereby increasing the potential for oxidation of the core which has been shown to affect leaching test results. For flow through column experiments, crushing the core also alters the porosity, and both flow paths and rates throug h the core material. Therefore, the objective of this research was to design and test columns experiments capable of supporting intact limestone core materials for use in future leaching studies. Methods Falling Head Permeameters As a first step in a rock core flow through column design, t wo Falling Head Permeameters (FHP s ) were constructed to determine the vertical permeability (Kv) of the cores and test sleeves for sealing the outside of the core within the core column. The upper stand pipe s of the two FHPs devices which act ed as the reservoir for applying the falling head, w ere constructed of 1.5 inch clear Sch. 40 PVC pipe and were 42 and 49 inches in length. The lower segment s of the FHPs which h e ld the rock core w ere constructed using 2 inch cle ar Sch. 40 PVC pipe, each segment was 12 inches long (Figure 4 1). To prevent short circuiting of flow between the core and the PVC pipe, a natural rubber sleeve was used to seal the outer wall of the core segment to the PVC. The

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71 rubber sleeve was inser ted into the 2 inch pipe and the ends of the rubber sleeve were then pulled back over the edge of the PVC pipe, from the inside of the pipe the natural rubber was pulled outward, and clamped to the pipe using metal ring clamps (Figure 4 1) Pulling a vacu um on the space between the inner wall of the pipe and the rubber sleeve caused the sleeve to expand as it was pulled against the inner wall of the pipe. This allowed a segment of rock core which was in contact with the upper stand pipe to be inserted into the sleeve. The vacuum was released holding the core and stand pipe in place. The vacuum was them replaced with light pressure using compressed air from 0 to 15 psi Silicon e tubing (medical/surgical) of various dia meters (0.75 to 1.5 inch) were also tested, as this was thought to offer a more inert alternative to natural rubber during leaching experiments. However, while one may exist, an appropriate size (ID and wall thickness) of s ilicon e tubing that would accomm odate 2 inch core wasn't found. Because the outside diameter ( OD ) of the 1.5 inch PVC is 1.9 inches which is near the OD of the core and the upper stand pipe rest s on the top of the core, there is little restriction of flow due to flexing of the rubber c ore sleeve into the small gap between the core and the stand pipe A second segment of 1.5 inch PVC was inserted into the bottom of the device to contact the bottom of the rock core and thus prevent restriction of flow. The FHPs discharge water through t ubing connected to a lower reservoir used to maintain a constant outlet head. During the falling head test, the in the upper stand pipe reducing measurement errors. Damp sponges were placed on the top of the upper stand pi pe to minimize evaporative losses during the test Physical measurements were taken on the cores prior to estimating Kv values (Table 4 1). Using the FHP approach, the Kv values of four

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72 unpreserved sections of core material from 292 ft, 294 ft, 350 ft an d 465 ft bls w ere measured. Core Column Design and Evaluation Testing A core column was setup and tested using the general design of the FHPs, discussed above (Figure 4 2). In addition to the s ilicon e tubing and natural rubber sleeves, a polytetrafluoroet hylene (PTFE), or more commonly Teflon, 2 inch heat shrink tubing was evaluated for use in intact core columns. Solid Sch. 80 PVC rods were machined to length, drilled through the center and tapped on one end for tube fitting. These sections were used in sealing the top and bottom of the core column during testing (Figure 4 2). These PVC segments replaced the upper reservoir and lower pipe of the FHPs. Stainless steel compression fittings, 1/8 inch Teflon tubing and various valves and gas tubing materials were used to connect the core column to the water reservoirs (carboys), vacuum pump, and the compressed air and N 2 gas supplies. The 1/8 inch Teflon tubing was extended through the solid PVC segments to near the face of the core such that the am ount of dead space between the PVC plug and th e core was minimized. Gas pressure (i.e., N 2 or compressed air) was applied to the carboys for use in driving water flow through the columns. The column was orientated in a vertical position, with the inlet o n bottom and outlet on top, to allow the column to be filled from the bottom to the top to minimize trapping of air in the column, which could affect flow through the core. After the initial test, a stainless steel 3 way valve was placed in line at the in let (i.e., bottom) of the core to allow switching between the carboys used as reservoirs. The inclusion of the 3 way valve allowed for switching between carboys of various source water chemistr ies without introducing laboratory air into the system.

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73 Two ro ck core column tests were completed as part of this research to evaluate and improve column design and determine the appropriate flow rates, and associated heads, for column experiments. Samples were collected and analyzed for total arsenic at the U.F. D epartment of Environmental Engineering laboratory via a Hydride Generation Atomic Fluorescence Spectrometry (HG AFS). The purpose of collecting these samples was to attempt to measure the magnitude and arrival time of the peak arsenic concentration, in su pport of determining sample volume, sample frequency, and the appropriate sample acidization/dilution factor for analysis via HG AFS. These preliminary tests did not, however, include an initial native groundwater phase and, therefore, do not truly repres ent ASR conditions.. The first column test utilized the unpreserved core material from TR 9 1 (465 ft bls) that had been previously used in the FHPs, described above. This core was chosen for the first test of the column because it was thought to be expen dable material, and the Kv was known. Tap water was sparged with N 2 for approximately 2 hours for use as a low DO source of water during the first phase of the test. A N 2 head of approximately 4.5 to 5 psi was applied to the carboy to drive flow during t he test. Six samples of approximately 11 to 24 mL each were collected over a 5 minute period during the first phase. The total sample volume collected over this period was 90 mL, thus the approximate flow rate through the column was 18 m L /min. After app roximately 2. 1 pore volumes, estimated based on a total porosity of 25 % (Table 4 1), the source water was switched to standard tap water contained in the second carboy. Compressed air was used to control the head and drive flow during the second phase of the test. Since the flow rate was higher than expected during the first phase, the inlet pressure

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74 was reduced to 1.5 to 2 psi. Eight samples, ranging from approximately 12 to 20 mL, were collected over a 1 hour period. The total sample volume collected over this period was approximately 106 mL, thus the approximate flow rate through the column was 2.5 mL/min. All samples were acidified with HCl upon collection. Samples were prepared for analysis via HG AFS using a 3:1 dilution with 10% HCl and 1% Thiou rea. The second test utilized preserved core material from TR 9 1 at 463 ft bls. This core had been in storage under a positive N 2 head (11.5 psi), since it's collection on September 1, 2009 (approximately 20 months). Prior to opening the core storage ve ssel, a carboy containing tap water was sparged with N 2 for approximately 2 hours and the column and tubing was flushed with N 2 The core was immediately placed into the column upon opening of the core storage vessel. The total time of exposure to the at mosphere was less than 1 minute. Approximately 1.5 to 2 psi of N 2 was applied at the carboy to drive water flow during this test. Fourteen samples were collected over a 3 hour period with an average flow rate of approximately 1 m L /min. After approximate ly 2.0 pore volumes based on an estimated total porosity of 25% (Table 4 1), the 3 way valve position was turned to the closed position and the column was left under a N 2 head overnight. A 1.5 to 2 psi head of compressed air was applied to the second car boy containing standard tap water to drive flow during the second phase of the test. Approximately 1. 3 pore volumes of standard tap water were flushed through the 463 ft core during the second phase of the test collecting ten samples (approximately 10 mL) over a 2 hour period. The 3 way valve was closed and the system was left under compressed air pressure for approximately 22 hours to simulate shut in under high DO cond itions. After the high DO shut in period, another 10 samples (approximately 10 mL

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75 each) were collected and 1 .1 pore volume s w ere flushed through the core. All samples were acidified with HCl upon collection. Samples were prepared for analysis via HG AFS using a 3:1 dilution with 20% HCl and 1% Thiourea. Core Column Reactive Transport Model A reactive transport model was setup and run to simulate arsenic leaching during an intact core column test. The model was based on the reactive transport model prese nted in Chapter 5 of this dissertation The model domain was similar to the dimensions of the 463 ft core described above (Table 4 1), with a y axis of 16 cm representing the length of the core. The x axis was 4.5 cm, which is the diameter of the 463 ft core, and the z axis was 3.5 cm. This resulted in a modeled cross section area of 15.8 cm 2 which is close to that of the 463 ft core. The 1 D model was discretized vertically, into 40 rows (Figure 4 3 ) A CHB of 1.34 m was applied at row 1 to represen t the head (2 psi) at the core inlet and CHB of 0.01 m was applied at row 40 to represent the head (0 psi) at the core outlet, during the preliminary column test, described above. The geochemical conditions were kept the same as those discussed in Chapter 5 with the initial whole rock chemistry provided below and the NGW and SW concentrations matching those of the Bradenton ASR site. A point source was applied at the upper (inlet) CHB to provide NGW inflow into the column over a 1 day period, followed by SW inflow over a 2 0 day period. Because the Kv of the 463 ft core was not measured, the Kv was set to 6E 2 ft/day (0.02 m/day), which is similar to that measured for the 465 ft core (Table 4 2 ). T he vertical dispersivity and effective porosity (n e ) valu es applied in the model were 0. 4 m and 0. 15 respectively as these were calibration parameters determined in Chapter 5 An observation point placed at the column outlet was used to monitor effluent water concentration over the 2 1 day simulation.

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76 Results and Discussion Falling Head Permeameters Results from the FHPs indicate a nearly three order of magnitude variance in the vertical permeabilities of the core segments tested (Table 4 2 ). The measured vertical permeability value was lowest for the cores f rom the upper portion (i.e., 292 and 294 ft bls) of the TR 9 1 borehole which contained more limestone mud than the cores from the lower portion of the borehole. The deeper cores with a relatively higher moldic porosity, therefore, represent the typical ASR storage interval of the Suwannee Limestone Given this, cores from the 465 ft interval were selected for the ASR batch studies discussed in Chapter 3 and in the evaluation (preliminary) testing of the core column design. Core Column Design and Evalu ation Testing The initial column test, using the unpreserved core from 465 ft bls at TR 9 1, showed a pe ak arsenic concentration at 5.5 g/L occurring after 2. 7 pore volumes of water flow through the column (Figure 4 4 ) The arrival of the peak just afte r the switch from N 2 sparged tap water to standard tap water suggest oxidative leaching of arsenic from the core. The data were analyzed twice (Run A and Run B) via HG AFS to attempt to address the erra t ic behavior (noise) of the data at concentrations below 2 g/L. Also, sampling may not have been frequent enough to capture the peak arsenic concentration as the pore volume of this core was relatively low, estimated at 43 mL assuming a total porosity of 25% (Table 4 1). This preliminary test demonstrated that arsenic was leached form the core used in the column study and a peak was observed following a change in injected water quality.

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77 The leaching test results from the second column experiment, using the preserved core from 463 ft bls at TR 9 1 (Figure 4 5 ), show a peak arsenic concentration of 27.8 g/L occurred at a pproximately 1.8 pore volumes of water flow. The initial arsenic concentrations in effluent was approximately 15 g//L. The peak arsenic concentratio n was measured during the initial (N 2 sparged tap water) phase which suggest s that the N 2 sparge didn't adequately suppress source water oxidation potential to within the pyrite stability field. It's likely that other oxidizers, in addition to oxygen, we re present in the tap water used in this experiment Also, later in the experiment, arsenic concentrations spiked after the 22 hour shut in period, suggesting that the reactions that yield arsenic may be kinetically limited. The second column test benefit ted from the increased sampling frequency, which yielded a smother curve of arsenic concentration in column effluent (Figure 4 5 ). This core segment was also longer than the previous core (16 cm), with an estimated pore volume of 64 mL assuming a total p orosity of 25% (Table 4 1). This is approximately 46% greater than the 465 ft bls core. Also, the use of 20% HCl and 1% Thiourea as the solvent, over the 10% HCl in the previous test, in sample preparation appears to have improved the resolution of the d ata. The second column test represents a refinement of the experimental method and again demonstrate s that the columns yield arsenic concentrations in the range observed in batch studies R esponses to chang es in injected water quality were evident. Core Column Reactive Transport Model The distribution of heads simulated by th e 1 D model, shown in Figure 4 6 is governed by the CHBs and Kv applied in the model The model predicted vertical flow velocity (Vy) of 103 cm/day yields a column discharge rate of 244 .1 cm 3 /day or 10.2

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78 cm 3 /hr, given a cross sectional area of 15.8 cm 2 and n e of 0. 15 This is substantially less than the discharge rate of approximately 50 cm 3 /hr measured during the preliminary column test of the 463 ft bls cor e. This suggests that either the model input parameters are incorrect or there was short circuiting of flow along the walls of the column during the preliminary column core, not measured, is significant ly different than the Kv value ( 465 ft core ) used in the model Model results show a spike in arsenic concentrations at approximately 1.2 days, or approximately 5 hours after the switch from NGW to SW (Figure 4 7) with a peak simulated arsenic concentration of 2.8 g/L occurring at 2.9 days. A t about 4 days ET, t he simulated arsenic concentration appears to stabilize at around 2.3 g/L. The arsenic concentration remains stable for the remainder of the simulatio n, suggesting that the modeled system had reached equilibrium.

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79 Figure 4 1. Photos of Falling Head Permeameters used in this study. (Photos courtesy Stuart Norton) Table 4 1. Physical measurements of cores used in this study. Core ID (ft bls) 292 294 350 463 465 Diam e ter (cm) 4.7 4.5 4.3 4.5 4.5 Length (cm) 5.0 10.8 4.3 16.0 10.9 Total Volume (cm 3 ) 86.8 171.8 62.5 254.6 173.4 Estimated Pore Volume (mL) A 22 43 16 64 43 A Pore volume estimate based on assumed total porosity of 25 %

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80 Figure 4 2. Photos of core columns used in this study. (Photos courtesy Stuart Norton)

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81 Figure 4 3 Core column model domain and discretization.

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82 Table 4 2 FHP test results Core Sample Depth FHP Results (Kv) 292 ft bls 6.7 E 4 ft/day 294 ft bls 2 .4 E 5 ft/day 350 ft bls 3 .6 E 2 ft/day 465 ft bls 5.9 E 2 ft/day Figure 4 4 Preliminary arsenic (g/L) leaching results from column of unpreserved 465 ft core. Samples analyzed twice (Run A and Run B) by HG AFS.

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83 Figure 4 5 Preliminary arsenic (g/L) leaching results from column of preserved 463 ft core.

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84 Figure 4 6 Head (m) d istribution during 1 D core column model.

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85 Figure 4 7 Simulated arsenic concentrations ( g/L ) at core column outlet.

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86 CHAPTER 5 REACTIVE TRANSPORT M ODELING Objective To adequately assess the impacts of ASR, a thorough understanding of the mechanisms controlling the transport of trace metals during ASR is required Reactive transport models (e.g., PHT3D) are useful tools for increa sing our understanding of geochemical processes under dynamic flow regimes by linking the geochemical modeling code PHREEQC 2 with the transport code MT3DMS, and the underlying flow model MODFLOW (Prommer and Post 2010 ). Unfortunately, the addition of the model subroutines increases the computational load resulting in long model run times. Model domains, therefore, must be carefully chosen to limit the scale to the area of interest, while providing defensible results. The first objective of this modeling effort was to c onstruct a fully three dimensional ( 3 D ) flow and transport model of the Bradenton ASR site for use in comparing the results of flow and transport models under varying model domains The second objective of this modeling effort was to comp lete the setup of a reactive transport model for 1) evaluating the conceptual model of arsenic mobility during ASR described above and 2) simulating operational approaches ( i.e. the T SV approach), and pretreatment techniques, for controlling arsenic mobilization. Methods Site Description The Bradenton potable ASR facility (Figure 2 1) presented in Chapter 2, was selected as the case study for this modeling exercise due to the relative completeness of the dataset, number of test cycles conducted, and similarity of construction and operation to other ASR sites in southwest Florida. The Bradenton ASR facility uses

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87 potable water from a conventional water treatment facility for recharge in ASR. A single ASR well (ASR 1), storage zone monitoring well (SZM W 1), intermediate aquifer monitoring well (AFWM 1) and water table monitoring well (WTMW 1) are located at the site. ASR 1 was constructed to a total depth of 505 feet (ft) below land surface (bls), with a 90 ft open bore hole within the Suwannee Limesto ne of the Upper Floridan aquifer. SZMW 1 is located approximately 224 ft north of ASR 1, with an open bore hole constructed across the ASR storage zone (City of Bradenton 2004). A generalized geologic profile is provi ded as Figure 2 2 Well construction details, including screen or open hole intervals, and casing size and elevations are provided in Table 2 1 Eight cycle tests have been completed at the site as described in Table 2 3 The first four cycles, Cycle Test 1 4, were small volume tests, appro ximately 10 MG each, to measure the near borehole geochemical response during ASR. Cycle Test 5 6 were designed to test the ASR facility at the planned operational volume of 160 MG (City of Bradenton 2006). Cycle Test 7, a 40 MG test, was the final test, prior to implementing Degasification of the ASR source water during Cycle Test 8. The Degasification system was constructed to test if the removal of oxidizers, primarily dissolved oxygen (DO), can control the mobilization of arsenic during ASR. Cycle T est 8 was operated at 160 MG, to mirror the full scale high DO test completed during Cycle Test 5 6. Cycle testing, under standard ASR conditions (i.e., high DO source water) began in September 2004 (Cycle Test 1) and was completed (Cycle Test 7) in Janua ry 2008, a period of 1176 days. Cycle Test 8 (i.e., the low DO source water test) began in July 2009 and was completed in February 2011. The total elapsed time for Cycle Test 1 8 includes a period of 2289 days (6.3 years), which demonstrates the complexi ty of running full scale

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88 operational tests. From a modeling perspective, the long duration of the field test increases model run times, thereby reducing the number of model simulations that can be completed for calibrating, validating, and refining the mo del. Mass Transport Modeling The M odular 3 D imensional M ulti S pecies T ransport (MT3DMS) model was selected for modeling ASR transport processes. MT3DMS is a program for simulating advection, dispersion, and chemical reactions (single species) within a gro undwater flow system (Zheng and Wang 1999) MT3DMS includes the third order Total Variation Diminishing (TVD) scheme for solving the advection term. This is important for modeling ASR as the TVD scheme is mass conservative and doesn't introduce artificia l oscillation or excessive numerical dispersion. MT3DMS also includes Finite Difference (FD) techniques for solving the advection term. While the TVD scheme may be best suited for three dimensional (3 D) modeling of ASR conservative transport processes, the TVD scheme highly variable layer thickness or grid spacing such as the two dimensional (2 D) reactive transport model discussed below. Both FD and TVD schemes were, therefore, applied herein. Reactive Transport Mod eling The reactive transport code PHT3D was used for mo deling the field scale ASR tests The acronym PHT3D refers to a reactive, via PHREEQC (PH), 3 dimenstional (3 D) transport (T) model. PHT3D couples the transport code MT3DMS with the geochemical model PHREEQC 2 (Prommer and Post 2010) Coupling is performed via subroutines, allowing the structure of the main models, MT3DMS and PHREEQC, to remain largely unchanged. PHT3D uses a split operator technique, whereas once a flow field is established in MODFLOW, the model calls MT3DMS to begin the transport

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89 simulation. For each transport step run in MT3DMS, the model calls PHREEQC 2 to complete the geochemical reaction step. Geochemical Modeling The USGS geochemical model PHREEQC (Parkhurst and Appelo 1999) underlies PHT3D, performing all aqueous geochemical calculations. The acronym PHREEQC stands for the most important parameters of the model; namely PH (pH), RE (redox), EQ (equilibrium) and C (programming language). PHREEQC is based on equilibrium chemistry and simulates chemical reactions and transport process in natural or polluted water. Of importance to this study, PHREEQC 2 (version 2) is capable of simulating the mixing of waters, addition of net irreversible reactions to solution, dissolvin g and precipitating phases to achieve equilibrium with the aqueous phase, effects of changing temperature, ion exchange equilibria, surface complexation equilibria, fixed pressure gas phase equilibria, advective transport, kinetically controlled reactions, solid solution equilibria, and variation of the number of exchange or surface sites in proportion to a mineral or kinetic reactant. Graphical User Interface All flow and transport modeling discussed herein was completed using the G raphical User Interface (G UI ) Visual MODFLOW Premium (Version 2010.1) Visual MODFLOW includes MT3DMS for transport modeling, the PHT3D (Version 2.0) reactive transport code and MODFLOW 2000. The structure of the groundwater flow model MODFLOW 2000, developed by the U.S. Geolog ical Survey, is presented by Harbaugh and others 2000.

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90 3 D Flow and Conservative Transport Model Initial flow and transport model setup A 3 D radial flow and conservative (i.e., nonreactive ) transport model was setup to simulate transport of the pseudo con servative tracer Total Dissolved Solids (TDS) at the Bradenton ASR site TDS was selected as the tracer due to the lack of a clear contrast between the native groundwater and recharge water chloride concentrations. The model was constructed to simulate f low and transport during the single full volume ( 160 MG) test (Cycle Tests 5 6a). Smaller volume (10 MG) test s were the first cycles (Cycles 1 4) completed at Bradenton. However, these volum es are not large enough for the complete breakthrough of the adv ective front at the storage zone monitoring well (SZMW 1). Valid ation of the flow and transport model was performed by simulating Cycles 1 4, Cycle 7 and 8 (Degas cycle) during reactive transport modeling, described below. The 3 D conservative transport m odel domain was 10,000 ft by 10,000 ft in the horizontal plan (xy axis), centered at ASR 1, and was +18 ft (land surface) to 1200 ft in the vertical plan (z axis). The model was discretized into 73 rows by 73 columns and 2 3 layers with non uniform grid spacing (Figure 5 1 ) The horizontal grid spacing range d from 6.8 ft by 6.8 ft at ASR 1 and 305 ft by 305 ft at the x/y intersect (model corner). The vertical grid spacing varies with the finest resolution ( 9 ft ) within the open bore hole of the ASR well and the largest interval (240 ft) representing the lowermost layer of the model (Figure 5 2 ). There were 10 layers included within the 90 ft ( 415 ft to 505 ft bls) ASR bore hole (storage zone interval) to acco unt for the vertically layered horizontal permeabilit y (Kh) reported in the drilling logs and geophysical logs taken during construction of ASR 1 and SZMW 1 (Appendix D) A single high permeability layer was

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91 included to represent the high flow zone locate d around 4 5 5 to 4 65 ft bls. This interval coincides with the high permeability zone indicated by the expansion of the caliper, increase in flow and decrease in conductance shown by the geoph ysical logs completed at SZMW 1 The colors in Figure 5 2 rep resent the vertical layering of hydraulic permeabilities including the surficial aquifer (Layer 1 is white: Kxy z = 25 ft/day), confining layers (Layers 2, 4, and 6 are blue: Kxy = 0.01 ft/day and Kz = 0.0001 ft/day), intermediate aquifer(s) (Layers 3 and 5 are green: Kxy = 0.5 ft/day and Kz = 0.05 ft/day), Suwannee Limestone (Layers 7 12 and 14 21 are grey: Kxy = 16 ft/day and Kz = 0.16 ft/day), high permeability layer of the Suwannee Limestone (Layer 13 is red: Kxy = 230 ft/day and Kz = 2.3 ft/day), Ocala Limestone (Layer 22 is yellow: Kxy = 2 ft/day and Kz = 0.02 ft/day) and Avon Park Formation (Layer 23 is red: Kxy = 230 ft/day and Kz = 2.3 ft/day). A vertical conduit was also included to allow for vertical flux between layers to represent the migration of fluids along the annulus of the well casing of ASR 1 (violet: Kxy z = 42 ft/day). Constant head boundaries (CHBs) were set at the eastern and western extents of the model domain. These boundaries are based on regional potentiometric surface maps provide d online by the Southwest Florida Water Management District. The general gradient is to the west with a head change of 1.95 ft per 10,000 ft, during the fall and winter months. During the spring months the gradient reverses, due to inland pumping, to an easterly direction with a head change of 0.25 ft/day per 10,000 ft. C HBs were added to the northern and southern extents of the model by linearly interpolating the CHBs between the eastern and western boundaries.

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92 Three head observation wells SZMW 1, ASR 1 and AFMW 1 were included as calibration targets. Observation wells were also placed near the CHBs at the eastern, western, northern and southern boundaries of the model. Wells AFMW 1 and SZMW 1 were used as concentration calibration targets during tra nsport modeling E xpanded flow and transport model To test the impact of the placement of C HBs on model results, the initial model domain was expanded (doubled) to 20,000 ft by 20,000 ft by resetting the model extents to 5,000 to 15,000 in the XY domain. The model was also re orientated along the XY axis so that predominate groundwater flow path was aligned with the direction of the X axis. The CHBs were moved to the new model boundari es. The model grid (XY) was redefined to include a uniform grid spacing of 766 ft by 766 ft near the model boundary. Cell size was reduced to 37 ft X 37 ft by inserting 20 rows and 20 columns into each existing row and column of the model area within app roximately 2,000 ft of the ASR well. T he cell size was decreased to 12 ft X 12 ft by inserting three rows and columns into each existing row and column of the model area within approximately 385 ft of the ASR well (Figure 5 3 ). To reduce model run times cells that lie outside the radius of influence on transport for the ASR well were set inactive to transport in MT3DMS All cells, however, remained active to flow in MODFLOW For layers 1 5 th e area set active were within horizontal extent of the redef ined grid (i.e., 385 ft from ASR 1) to allow transport along the vertical conduit at ASR 1 C onstant c oncentration boundaries were set at the edge of the refined grid. The area within approximately 2,000 ft of the ASR well was set active to transport fo r layers 6 21 (Figure 5 4 ) and constant concentration boundaries were set at the horizontal extent of this area. The permeability of the high Kh layer

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93 (layer 13) was increased to 280 ft/day, to achieve a match in heads at SZMW 1. All other properties wer e kept the same as initial model. As a final comparison, t he boundaries of the expanded flow and transport model domain w ere reduced to the original positions (X: 0 ft to 10,000 ft and Y: 0 to 10,000 ft) for comparison with results from the 20,000 by 20,00 0 ft model. In this version the CHBs were relocated to the original placement used in the initial flow and transport model (10,000 ft X 10,000 ft area model). Axisymmetric Flow and Reactive Transport Model Model s etup Typical model run times for simula ting the 330 day (Cycle Test 5 6) event, under fully 3 D flow and transport conditions, were approximately 10 to 12 hours. Therefore, t o reduce model run times during simulation of reactive transport, the 3 D model was translated to a 2 D axisymmetric model that represents the ASR storage interval. This was done be swapping the y and the z axes such that the y axis represent s the vertical depth of the 90 ft (27 m) ASR storage interval and the z axis represent s the horizontal thickness of the model. Th e x axis represents the horizontal distance from the ASR well. While the ASR well was placed at center of the 3 D model grid, in the 2 D model the ASR well represents the x = 0 m model boundary. T he 2 D model therefore, represents one quarter o f the rad ially symmetric domain (i.e., a one of the radial flow field) The thickness of the z axis (i.e., model thickness) was inc rease d with distance from the ASR well (Figure 5 5 part A ) This was done to account for the radially decreasing flo w velocities encountered during ASR test events as the aquifer volume

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94 increases radially with distance from the ASR well. The thickness of the z axis increases with distance from the ASR 1 well is determined as follows : (B x nce to the midpoint of cell X. (5 1) For example, the thickness of the cell that represents the perimeter of the circle at distance x = 523.5 m from the injection well which is the 2 D model boundary, is 806.6 m The 2 D model domain included 523.5 m in the horizontal plane (x axis), 27 m in the vertical plane (y axis) and was discretized into 6 8 columns (Figure 5 5 ). The horizontal grid spacing ranged from 1 m at ASR 1 a nd 20 m at the model boundary. Constant head and constant concentration bound ary conditions were applied to the model boundary (x = 523.5 m). To address the vertical layered permeability of the storage zone, described above, the 2 D model was divided into 5 layers. Layer thickness varied from 8.3 m, 4 m, 2.9 m, 3.8 m and 8 m for layers 1 through 5 respectively. Layer 3, with a thickness of 2.9 m, therefore, represents the high permeability layer at 455 to 465 ft bls identified in th e geophysical logs (Attachment D) and was assigned a permeability value of 3 5 m/day (Figure 5 5 part B ) Layer 1, representing the upper most segment of the Suwannee Limestone, was assigned a permeability value of 3.5 m/day. All other layers were assigned a permeability value of 1 2.5 m/day. Temporal d iscretization The flow and reactive transport model was run for a simulation period of 1176 days, representing Cycle Tests 1 7. To represent the different phases of the ASR testing time was discretized into 31 hydraulically differing stress periods that varied in

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95 leng th from 1 and 424 days. These stress periods were further subdivided into multiple time steps as presented in Table 5 1. Geochemical reaction framework Native groundwater at the Bradenton site is highly reducing (i.e., sulfidic and anoxic). The native gr oundwater calcium and bicarbonate concentrations indicate equilibrium with calcite at a pH of 7.2 to 7.3 S.U. In contrast to these conditions, the recharge water is highly oxic with DO concentrations ranging from near saturated to supper saturated and sl ightly alkaline with pH values ranging from 7.8 to 8.3 S.U. The reaction network utilized herein is largely based on the work done by Descourvieres and others (2010), Wallis a nd others (2010) and the modeling of the Bradenton ASR site by Wallis and others including this author (2011 ). The reaction network included equilibrium and kinetic mineral based reactions. The three equilibrium mineral phases included in the model are 1) Calcite (CaCO 3 ), to provided buffering capacity for the acid released during pyrite oxidation, 2) amorphous HFOs (Fe(OH 3 )), to provide a sink for arsenic released during pyrite oxidation, and 3) siderite (FeCO 3 ), to allow precipitation of iron released by desorption from HFOs or dissolution of HFOs during recovery events. Pyrite ( FeS 2 ) was included as a kinetic mineral, with pyrite oxidation by oxygen following Williamson and Rimstidt (1994). Arsenopyrite was included in the model as the source of arsenic and was kinetically linked to pyrite oxidation. Therefore, the behavior of arsenopyrite in the model was governed by pyrite. Arsenopyrite was sto i chiometrically linked to pyrite oxidation as described in Wallis and others (2010) and Descourvieres and others (2010), with the molar ratio of arsenic to FeS 2 based on data by Price a nd Pichler (2006). The inclusion of these minerals in the

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96 reaction model is supported by calculated saturation indices of native and recovered water and sediment analysis provide by Price and Pichler (2006). Surface complexation of arsenic to HFOs was proposed in the conceptual model as the key parameter controlling arsenic mobility during ASR. This process was included in the reaction network by coupling the moles of the surface complex sites to the mass of HFO in the aquifer ( Wallis et al. 2010 ). Th e properties of HFO were defined according to the values proposed by Dzombak and Morel (1990) The database of Dzombak and Morel ( 1990 ) was extended to included reactions for ferrous iron ( Fe 2+ ) and bicarbonate ( HCO 3 ) ( Appelo et al 2002 ) to allow for com petition of inorganic solute species for the sorption sites provided by HFO. In addition, one cation exchanger site was included to account for the exchange of cations and hydrogen on clay surfaces. The vertically layered distribution of pyrite within the ASR storage interval generally follows the input concentrations used by Wallis and others (2011). An initial pyrite concentration of 1E 4 mol/L bulk rock was applied to layers 1, 2 and 4 (Figure 5 5 part C ). Layer 3, representing the high permeability unit, was given an initial pyrite concentration of 1.17E 2 mol/L bulk rock. An initial pyrite concentration of 2.54E 3 mol/L bulk rock was applied to layer 5. Conservative transport and r eacti on model calibration Conservative transport and reaction mode l calibration were performed simultaneously by the calibration of the pseudo conservative tracer sulfate during reactive model runs. Since TDS was not included as a reactive phase in the 2 D model, and differences in chloride concentrations between the AS R source water and native groundwater were negligible, s ulfate was selected as the (pseudo ) conservative species for monitoring transport of the advective front. Recharge sulfate concentrations

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97 were generally less than 220 mg/L, representing only approxi mately 33 % of the native groundwater concentration (660 mg/L) Therefore, the impact of pyrite oxidation on modeled sulfate concentration s is assumed minimal due to the high native concentrations. The physical m odel transport properties (i.e., effective porosity (n e ) and dispersivity) were adjusted to fit simulated sulfate concentrations with those observed at ASR 1 and SZMW 1 during Cycle Test 1 through 7. The initial effective porosity and dispersivity values were 15% and 4 m, respect ively. Reaction model calibration was performed by fitting three adjustable parameters including 1) the stoichiometric ratio of As within pyrite, 2) the initial concentrations of pyrite in the aquifer matrix and 3) the HFOs sorption site density. The prim ary constraints for the estimation parameters include total dissolved arsenic, ferrous iron and DO concentrations as observed at ASR 1 and SZMW 1 during Cycle Test 1 through 7. The initial pyrite concentration and the stoichiometric ratio of arsenic in py rite were kept within the range of values provided by Price and Pichler (2006). While some sedimentological data of the Suwannee Limestone is available to support model calibration, the amount of sorption sites on HFO in the sediment and the cation exchang e capacity of the sediment for the Bradenton ASR site are not known. The total number of sites was, therefore, was used as a fitting parameter. One cation exchanger site was included in the model to account for the exchange of cations and hydrogen on clay surfaces. This, however, was not altered during modeling runs R eacti ve transport model validation Model validation was concurrent with model calibration given that multiple stress periods (i.e., Cycle Tests) were simulated over 1176 days In addition to Cycle Tests 1 7, the model was extended to 2289 days to include Cycle Test 8, the low DO (i.e.,

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98 average injectate DO = 6.2 ppb ) test cycle. Mo del validation was therefore, performed over seven standard ASR (i.e., high DO) source water test cycles and one low DO test cycle. Predictive simulations The calibrated model was employed to test three techniques for controlling arsenic mobilization. This included an operational (i.e., TSV) approach where a large volume of water (i.e., the buffer zone) is left unrecovered (i.e., in storage). Maintenance of the buffer zone is performed to reduce the mixing between sulfidic native ground water and high DO recharge water, thereby controlling the mobilization of arsenic (Pyne 2006). The second technique tested inc luded the ASR source water degasification technique discussed in Chapter 2, under varying injectate DO concentrations. Finally, the third technique tested included a combination of the TSV and ASR degasification techniques Each of the techniques w as si mulated over a 10 year time horizon (i.e., 10 ASR test cycles) Simulating the TSV technique was performed under two standa rd ASR source water (i.e., DO = 10 mg/L ) scenarios. The first scenario include d the recharge of an unrecovered 160 MG buffer zone, d uring year 1 Th e formation of the buffer zone was followed by nine cycles that included a 120 MG recharge event a 90 day storage period and a 90 MG recovery event. Therefore, in addition to the 160 MG buffer zone, a residual 30 MG was left in storage d uring each cycle resulting in 430 MG in storage at the end of year 10. The second TSV technique that was simulated included the build out of the buffer zone over a 10 year period. That is, each cycle included a 120 MG recharge event, a 90 day storage per iod and a 90 MG recovery event. By leaving a residual 30 MG in storage during each year, the total volume in storage at the end of the

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99 10 year period was 300 MG. For comparison with the TSV approach, the model was also run for 10 test cycles under full ( i.e., 100%) recovery of the stored water. These tests included a 120 MG recharge event, a 90 day storage period, and a 120 MG recovery event, leaving no residual (i.e., no buffer zone). The calibrated model was used to test ASR degasification technique s under varying DO concentrations of 10 ppm, 1 ppm, 100 ppb and 10 ppb. T he four DO injectate concentrations w ere tested over a 10 year period simulating 10 test cycles The test cycles included a 120 MG injection event, 90 day storage period and a 120 M G recover event (i.e., 100% recovery of the stored water) The calibrated model was also used to test a combination of the TSV approach under varying inlet D O concentrations. The tested DO concentrations were 10 ppm, 1 ppm, 10 0 ppb and 10 ppb. Ten test c ycles were run for each DO concentration with a recharge volume of 120 MG, 90 day storage period and a recovery volume of 90 MG. This approach resulted in a residual annual storage volume (i.e., buffer zone) of 30 MG, with 300 MG remaining in storage at th e end of the 10 year period. Results and Discussion 3 D Flow and Conservative Transport Modeling A reasonable fit of the observed versus calibrated heads was achieved with the initial flow model (xy domain = 10,000 X 10,000 ft). A plot of observed versus simulated heads over time is provided in Figure 5 6 The transport simulation also achieved a reasonable fit for TDS concentrations at the SZMW 1 and AFWM 1 wells. The early arrival of the tracer at SZMW 1 during recharge and recovery demonstrates the hi gh permeability layer's control on conservative transport process during ASR (blue line in Figure 5 7 ). Figure 5 8 provides a simulation profile view of TDS concentrations at full

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100 volume (160 MG recharged), showing that the spread of the low TDS recharge water into the storage zone, and vertically near the annulus of the well casing, is controlled by the horizontal and vertical high permeability layers, respectively. Refinement of the initial model improves the resolution of the flow and transport model re sults, as shown in Figure 5 9 The refined (i.e., expanded 3D) model results demonstrates the variability in the arrival time of the conservative tracer within the vertically layered storage zone. Recharge (low TDS) water is first to arrive at the SZMW 1 within the high permeability layer (blue line in Figure 5 9 ). This layer is also the first to see TDS climb to near native conditions during the recovery event. Mixing of water between layers is responsible for the spread of the data presented in Figur e 5 9 The layers cl osest (vertically) to the high permeability zone experience the greatest degree of mixing with this zone. Tracer arrival is much slower at the layers that are more distant (vertically) to the high permeability layer. This can also be seen in the profile view of the expanded 3D model at full volume (i.e., 160 MG recharge) in Figure 5 1 0 A reasonable fit of the observed versus modeled flow and transport results was achieved with the expanded 3D model domain (xy domain = 20,000 X 20,00 0 ft). As shown in Figures 5 6 and 5 7 these results are nearly identical to th e initial 3D model The simulated profile view of the expanded 3D model results, provided in Figure 5 10, is also very similar to the initial 3D model, provided in Figure 5 8 The reduced 3D model (xy domain = 10,000 ft by 10,000 ft) provides the best comparison of results with the expanded model domain (xy domain = 20,000 ft X 2 0,000 ft). As can be seen in Figure 5 6 reducing the model domain decreased the simulated heads at SZMW 1 by approximately 2.5 ft. This can be attributed to moving the eastern

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101 and western CHB s 5,000 ft closer to the ASR well. There wasn't, however, a noticeable change in arrival of the conse rvative tracer at the SZMW 1 well as this is controlled by pumped water (Figure s 5 7 and 5 1 1 ). This suggest that, while the model domain, and thereby position of CHBs, governs model flow processes, conservative transport behavior is cted by CHB position. Axisymmetric Flow and Reactive Transport Model R esults from the five layer 2 D flow model provide a reasonable fit with heads observed at SZMW 1 (Figure 5 1 2 ) during the 1176 day simulation representing Cycles Tests 1 7. As seen in F igure 5 1 2 t he observed heads measured immediately preceding and following a recharge or recovery event were used to determine the CHBs for that stress period. There was no effort made, however, to simulate the observed (i.e., seasonal) pattern of aquife r heads during the ASR storage periods or inter cycle storage events. Simulation of the pseudo conservative tracer sulfate shows a reasonable fit of the model results to the observed data at ASR 1, in both timing and magnitude, during Cycle Tests 1 through 7 (Figure 5 1 3 ). The timing of the breakthrough at SZMW 1 also provides a reasonable fit to the observed data during the recharge events given an effective porosity of 15% The early arrival of the pseudo conservative tracer at the observation well dur ing the small volume (i.e., 40 MG) test cycles suggest that advective transport at the Bradenton site is governed by the layered permeability of the ASR storage interval. Furthermore, the shape of the advective front during larger test cycles at SZMW 1, given the relatively low input dispersion value of 4 m, suggest that dispersion in the Bradenton ASR system is driven by mixing between layers of high and low permeability. This demonstrates the need or justifica tion for including the high

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102 permeability la yer in the reactive transport model, as descr ibed in the 3 D modeling above. These methods are appropriate for modeling the advection dominated system, generated by the relatively high, as compared to native, flow velocities created during ASR Simulated results at ASR 1 (Figure 5 14 ) show the correct timing (match) for the arsenic concentrations re released to solution during recovery of the small volume tests (i.e., Cycle Tests 1 4 and Cycle Test 7 ) However, during the large (i.e., 160 MG) cyc le test (Cycle 6a c ) recovery event the simulated recovered arsenic concentrations arrives approximately 2 0 days early, as compared to the observed data, at ASR 1. The simulated results for the large Cycle 6a c recovery event shows arsenic arrive at the A SR well in a single event. The observed data, however, indicates that there were two arsenic peaks during this recovery event, as recovery of the stored water was interrupted, with no pumping from ET of 590 days to 1014 days, due to FDEP permitting requir ements (Table 2 3). The m agnitude s of the simulated arsenic concentrations do not consistently match the observed data. The simulated results yield a peak arsenic concentration of 96 g/L during the Cycle 6 a recovery event. This is approximately 28 % percent higher than the peak arsenic concentration of 75 g/L observed during the Cycle 6 a recovery event. This suggests that further refinement of the initial input values for pyrite, arsenopyrite and FeOH surface site density are needed to provid e th e correct mass of arsenic and adequate number of surface sites for retarding the mobilization of arsenic near the ASR well.

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103 While the magnitude of the simulated peak arsenic concentration (i.e., 1 9 g/L) is close to that observed (24 g/L) at SZMW 1 during the Cycle 6a recovery event, the distribution of the s imulated arsenic concentrations do es not fit the observed data (Figure 5 1 4 ) The simulated peak arsenic concentration arrive d at SZMW 1 around 85 days earlier than the observed data, where the peak c oncentration was measured at ET = 616 days Model results suggest that, at this time, dissolved arsenic concentrations would be negligible at SZMW 1 Further refinement of m odel input parameters, including initial pyrite concentrations and Fe OH surface s ite density, may be needed to improve the simulation of the relatively low level arsenic concentrations observed at SZMW 1. The simulated sharp spikes in arsenic at ASR 1 and SZMW 1, during recovery events, is likely governed by the inclusion of FeOH as an equilibrium phase in the reaction network In reality, the dissolution of FeOH may be kinetically controlled as t he observed data shows a broader, m ore dispersed, arsenic curve at ASR 1 and SZMW 1 during recovery events (Figure 5 1 4 ). Th e model appears to generate artificially sharp spikes in arsenic concentrations during recovery as the return of reduced (i.e., native) groundwater toward the ASR well causes desorption of arsenic from the FeOH surface site s or the re release of sorbed arsenic upon the dissolution of the FeOH. This front of reduced groundwater, shown as the return of native sulfide (i.e., 2.3 mg/L) at around ET = 550 days (Figure 5 1 5 ), mov es along with the advective front and rapidly re releases nearly all the sorbed arsenic into solut ion at a rate greater than the field data would suggest occurs

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104 Model results indicated that the pseudo conservative tr acer sulfide extends less than 300 m from the ASR well during the Cycle 6 (160 MG) recharge event (Figure 5 16 ). The model domain is, therefore, large enough to contain the advective front, under the single layer ( 2 D ) modeling scenario, preventing the interception of recharge water at the constant head and concentration boundary located at 523.5 m. The peak dissolved arsenic concentrat ion at the end of the Cycle 6 (160 MG) recharge event is 8 E 8 mol/L, which is less than 6 g/L (Figure 5 1 7 ). The arsenic concentration front is also very broad, with low levels of dissolved arsenic extending out to 2 4 0 m from the ASR well. Iron oxides, formed by the oxidation of pyrite, are distributed up to 6 0 m from the ASR borehole (Figure 5 1 8 ) with the greatest concentration (6E 3 mol/L bulk rock ) o f FeOH located within the high permeability layer and low concen trations (less than 2E 4 mol/L bulk rock ) in the other layers. Th e DO concentration gradient is an inverse distribution of FeOH, as most of the DO is consumed (Figure 5 19 ) near the ASR borehole within the high permeability layer. Given the lower pyrite concentration in the low permeability layers (i.e., layers 1, 2, 4 and 5), DO travels further in the se layers DO is rapidly consumed in layer 3 which contains two orders of magnitude more pyrite than the low permeability layers DO is, however, consumed prior to arriving at SZMW 1 at the end of the 160 MG recharge event. The model results suggests that the solubility, and thereby mobility, of arsenic during recharge is effectively limited by sorption to FeOH surface sites. During recovery, the model s uggest that the arsenic front collapsed back toward the ASR well, with little arsenic remaining in solution (Figure 5 2 0 ), as sulfidic native groundwater water returns near the ASR well (Figure 2 1 ) The observed a rsenic

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105 concentrations however, remained e levated, above background levels, at the end of the Cycle 6c a 30 MG recovery event ( Table 2 3 and Figure 5 1 4 ). The model results show that all the FeOH was dissolved during the recovery event, as sulfidic conditions returned near the ASR well. Model results for sulfate arsenic and sulfide during Cycle Tests 1 8, including the low DO test cycle, are presented in Figures 5 22 through 5 24 respectively. As previously discussed, simulated sulfate concentrations are a good fit for observed sulfate conc entrations at ASR 1 and, to a lesser degree, SZMW 1 during each cycle. Simulated arsenic concentrations generally match the timing but not magnitude of observed arsenic concentrations during the early high DO test (i.e., Cycle Test 1 7) However, the mod el results suggest that arsenic concentrations would be negligible during the low DO (Cycle Test 8) test. The relatively low concentrations of arsenic (peak 12 g/L) measured at ASR 1 during the Cycle Test 8 recovery event may be due to the recovery of re sidual arsenic sorbed to FeOH during previous high DO test. Alternatively, other oxidizers, such as nitrate and chloramines, not included in the reaction network may be responsible for liberating arsenic during the low DO test. Predictive Modeling A comp arison of two TSV scenarios was performed to assess this approach for minimizing arsenic mobilization and improving ASR recovery efficiency. The first scenario included modeling the recharge of 160 MG during year 1, leaving this in place as a buffer zone, and then nine years of recharge of 120 MG, followed by a 90 day storage period, and the recovery of 90 MG. The total storage volume at the end of year 10 for the first scenario was 430 MG. The second scenario included 10 successive events that included the recharge of 120 MG, followed by 90 days of storage, and the

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106 recovery of 90 MG. The total storage volume at the end of year 10 for the second scenario was 300 MG. A third scenario was included, for comparison with the TSV approach, which utilized full (100%) recovery of the stored water. This included 10 test cycles with 120 MG recharge events, 90 day storage periods, and 120 MG recovery events. Recovered sulfate concentrations remain below the SMCL of 250 mg/L at ASR 1 during the TSV scenario that included the initial 160 MG buffe r zone (F igure 5 25). This would allow for recovery of 90 MG of stored water on an annual basis, following the development of the 160 MG buffer zone. Sulfate concentrations were below the SMCL of 250 mg/L at ASR 1 during the TSV modeling scenario that included the 30 MG buffer following the fourth recovery event. Sulfate remained above the SMCL during each recovery event under the full (100%) recovery scenario. Therefore, a minimum buffer volume of 120 MG (4 years at 30 MG added each year) is needed to meet the SMCL for sulfate during planned operations at the Bradenton ASR site. Recovered arsenic concentrations remain below the 10 g/L MCL at ASR 1 during each of the recovery events for the TSV simulation that included the 160 MG buffer zone, reaching a maximum concentration of about 4 g/L after year 3 (Figure 5 26 ) The peak recovered arsenic concentration was about 88 g/L at ASR 1 during the simulated TSV scenario that included the 30 MG buffer zone. This concentration declined to below the MCL during year 2, matching the arsenic data pattern seen during the first TSV scenario (i.e., 160 MG buffer) during year 3. Arsenic peaked a t a maximum concentration of approximately 100 g/L during year 2 of the full (100%) recovery modeling scenario, declining to below the MCL during year 4.

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107 A peak arsenic concentration of approximately 20 g/L was predicted at SZMW 1 under the TSV modelin g scenario that included the 160 MG buffer zone (Figure 5 27). Arsenic concentrations decreased, remaining below the MCL, after year 2 at the observation well The peak arsenic concentrat ion predicted at SZMW 1 during the TSV modeling scenario that inclu ded the 30 MG buffer zone was approximately 40 g/L, occurring during the third recovery event. Arsenic concentrations are predicted to decline to below the MCL at SZMW 1 after year 4 under the second TSV (i.e., 30 MG buffer zone) scenario Arsenic conce ntrations are predicted to remain elevated above the MCL at SZMW 1 during the full (100%) recovery scenario, reaching a peak concentration of approximately 42 g/L during year 6. The modeling of the pretreatment technique with residual DO concentrations o f 10 ppm, 1 pp m 1 00 ppb and 10 pp b suggest that DO removal to an injectate concentration of less than 1 ppm DO is required to reduce arsenic concentrations in recovered water to below the 10 g/L arsenic MCL (Figure 5 28 ). Degasifying the ASR source wate r to a DO residual of 100 ppb, or less, resulted in negligible recovered arsenic concentrations at ASR 1. Predicted arsenic concentrations remained below the MCL at SZMW 1 during each test cycle under degasified (i.e., 1 ppm residual DO, or less) injectat e water conditions (Figure 5 29). Modeling a combination of the TSV technique ( i.e., scenario 2 with a 30 MG buffer zone) and the degas pretreatment technique indicates that compliance with the arsenic MCL can be achieved after year 6, given a recharge DO concentration o f 1 ppm (Figure 5 3 0 ). Predicted arsenic concentrations were negligible for recharge DO concentrations of 100 ppb or less at both the ASR well and observation well (Figure 5 31).

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108 Figure 5 1 Initial 3D m odel domain ( xy domain = 10,000 ft by 10,000 ft) and grid spacing. Layer 1 shown in plan view.

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109 Figure 5 2 Profile view of 3d mo del domain (Z) depicting vertical layering. Colors indicate zones of hydraulic permeability (white = 25 ft/day, blue = 0.01 ft/day, green = 0.5 ft/day, grey = 16, yellow = 2 and red = 230 ft/day).

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110 Figure 5 3 Expanded 3 D model domain (xy domain = 20,000 ft by 20,000 ft) with refined grid spacing. Layer 1 shown in plan view.

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111 Figure 5 4. Profile view of expanded 3D model. Green area indicates model area inactive to transport (white area active to transport)

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112 Figure 5 5. Axisymmetric flow and reactive transport model domain. A) 2 D model x and z axes with thickness increasing with distance from x = 0 m. B) 2 D model x and y axes and discretization. Red z one represents high permeability unit where Kx = 35 m/day, white zones Kx = 12.5 m/day and green zone represents low permeability unit where Kx = 3.5 m/day. A) Initial pyrite distribution where white zone represents pyrite = 1E 4 mol/L bulk rock, red zone represents pyrite = 1.17E 2 mol/L bulk rock and green zone repre sents pyrite = 2.54E 3 mol/L bulk rock. A B C

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113 Table 5 1. Time discretization during reactive transport modeling. Stress Period Start (day) End (Day) Period Length Time Steps 1 0 6 6 48 2 6 16 10 5 3 16 22 6 24 4 22 28 6 24 5 28 35 7 5 6 35 41 6 24 7 41 45 4 5 8 45 53 8 32 9 53 65 12 5 10 65 71 6 24 11 71 72 1 5 12 72 78 6 24 13 78 107 29 5 14 107 112 5 20 15 112 273 161 20 16 273 310 37 148 17 310 317 7 28 18 317 336 19 5 19 336 429 93 372 20 429 430 1 5 21 430 437 7 28 22 437 497 60 5 23 497 514 17 68 24 514 525 11 5 25 525 591 66 264 26 591 1015 424 20 27 1015 1039 24 96 28 1039 1078 39 156 29 1078 1106 28 112 30 1106 1149 43 5 31 1149 1176 27 108

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114 Figure 5 6 3D flow m odel results under varying model domains. Initial and reduced model xy domains were 10,000 ft by 10,000 ft. Expanded model xy domain was 20,000 ft by 20,000 ft. Blue points are heads observed at SZMW 1 and r ed points heads observed at AFMW 1 during Cycles 5 6a. So lid lines are simulated results.

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115 Figure 5 7. 3D transport model Total Dissolved Solids (TDS) results under varying model domains. Initial and reduced model xy domains were 10,000 ft by 10,000 ft. Expanded model xy domain was 20,000 ft by 20,000 ft. Blue points are TDS concentrations (mg/L) observed at SZMW 1 and red points TDS concentrations (mg/L) observed at AFMW 1 during Cycles 5 6a. Solid lines are simulated results.

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116 Figure 5 8. Profile view of initial 3D model transport results (time = 156 days, volume = 160 MG recharged; xy domain = 10,000 X 10,000 ft). Red is background TDS at 1,200 mg/L. Blue is recharge TDS at 320 mg/L. Contour labels (white boxes) are mg/L TDS

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117 Figure 5 9. Expanded 3D transport model results (TDS in mg/L). Red and blue data points are observed data for AFMW 1 and SZMW 1, respectively. Solid lines are simulated results.

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118 Figure 5 10. Profile view of expanded 3D model transport results (time = 156 days, volume = 160 MG recharged; xy domain = 20,000 X 20,000 ft). Red is background TDS at 1,200 mg/L. Blue is recharge TDS at 320 mg/L. Contour labels (white boxes) are mg/L T DS. White area represents model cells inactive to transport.

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119 Figure 5 11. Profile view of reduced 3D model transport results (time = 156 days, volume = 160 MG recharged; xy domain = 10,000 X 10,000 ft). Red is background TDS at 1,200 mg/L Blue is recharge TDS at 320 mg/L. Contour labels (white boxes) are mg/L TDS. White area represents model cells inactive to transport.

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120 Figure 5 12. Head (m) calibration results at SZMW 1 for 2 D reactive transport model. Total elapsed time is 1176 days (simulated Cycles 1 7). Simulated results are show as solid line.

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121 Figure 5 13. Sulfate (mg/L) calibration results at ASR 1 (red) and SZMW 1 (blue) for 2 D reactive transport model. Total elapsed time (ET) is 1176 days (Cycles 1 7). Simulated resu lts are show as solid line.

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122 Figure 5 14. Arsenic (g/L) calibration results at ASR 1 (red) and SZMW 1 (blue) for 2 D reactive transport model. Total elapsed time (ET) is 1176 days (Cycles 1 7). Simulated results are show as solid line.

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123 Figure 5 15 Simulated sulfide (mg/L) results at ASR 1 and SZMW 1 for 2 D reactive transport model. Total elapsed time is 1176 days (Cycles 1 7). Total dissolved sulfide not consistently measured at the Bradenton ASR site.

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124 Figure 5 16. Spatial distribution of pseudo conservative tracer sulfate (mol/L) in 2 D reactive transport model. Dark blue area is recharge sulfate concentration (2E 3 mol/L) and red area represents background sulfate concentration (6E 3 mol/L). Total elapsed time is 429 days (end of Cycle 6, 160 MG recharged). Vertical and horizontal scales in meters. Figure 5 17. Spatial distribution of arsenic (mol/L) in 2 D reactive transport model. Red area represents arsenic contour interval of 8.0E 8 mol/L (6 g/L) and dark blue area represents background arsenic concentration (less than 1E 8 mol/L or less than 1 g/L). Total elapsed time is 429 days (end of Cycle 6, 160 MG recharged). Vertical and horizontal scales in meters.

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125 Figure 5 18. Spatial distribution of FeOH (mol/L bulk rock) in 2 D reactive transport model. Total elapsed time is 429 days (end of Cycle 6, 160 MG, recharge event). Vertical and horizontal scales in meters

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126 Figure 5 19 Spatial distribution of DO (mol/L) in 2 D reactive transport model. Red area represents recharge DO concentration of 2.5E 4 mol/L (8 mg/L) and dark blue area represent s background DO concentration (0 mol/L). Total elapsed time is 429 days (end of Cycle 6, 160 MG, recharge event). Vertical and horizontal scales in meters

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127 Figure 5 20 Spatial distribution of arsenic (mol/L) in 2 D reactive transport model. Total elapsed time is 1039 days (end of Cycle 6c, 30 MG recovery event, to return system storage volume to 0 MG). Vertical and horizontal scales in meters. Figure 5 2 1 Spatial distribution of sulf ide (mol/L) in 2 D reactive transport model. Total elapsed time is 1039 days (end of Cycle 6c, 30 MG recovery event, to return system storage volume to 0 MG). R ed area represents background sulf ide concentrat ion (7.2 E 5 mol/L or 2.3 mg/L ) Vertical and horizontal scales in meters.

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128 Figure 5 2 2 Sulfate (mg/L) calibration results at ASR 1 (red) and SZMW 1 (blue) for 2 D reactive transport model. Total elapsed time (ET) is 2289 days (Cycles 1 8). Simulate d results are show as solid line.

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129 Figure 5 23 Arsenic (g/L) calibration results at ASR 1 (red) and SZMW 1 (blue) for 2 D reactive transport model. Total elapsed time (ET) is 2289 days (Cycles 1 8). Simulated results are show as solid line.

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130 Figure 5 24 Simulated sulfide (mg/L) results at ASR 1 and SZMW 1 for 2 D reactive transport model. Total elapsed time (ET) is 2289 days (Cycles 1 8). Total dissolved sulfide not consistently measured at the Bradenton ASR site.

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131 Figure 5 25 Predicte d sulfate ( m g/L) concentrations at ASR 1 during TSV simulations. F ull (100%) recovery of stored water shown as black line TSV simulation with unrecovered 30 MG buffer zone shown as red line and TSV simulation with unrecovered 160 MG buffer zone shown as blue line. Total simulation time is 10 years.

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132 Figure 5 26 Predicted arsenic (g/L) concentrations at ASR 1 during TSV simulations. F ull (100%) recovery of stored water shown as black line TSV simulation with unrecovered 30 MG buffer zone shown as r ed line and TSV simulation with unrecovered 160 MG buffer zone shown as blue line. Total simulation time is 10 years.

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133 Figure 5 27 Predicted arsenic (g/L) concentrations at SZMW 1 during TSV simulations. F ull (100%) recovery of stored water shown as black line TSV simulation with unrecovered 30 MG buffer zone shown as red line and TSV simulation with unrecovered 160 MG buffer zone shown as blue line. Total simulation time is 10 years.

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134 Figure 5 28 Predicted arsenic (g/L) results at ASR 1 during full volume ASR recovery (120 MG recharge and 120 MG recovery events) under varying recharge DO concentrations of 10 ppm (red line), 1 ppm (blue line), 100 ppb (black line) and 10 ppb (green line). Total simulation time is 10 years.

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135 Figure 5 29 Predicted arsenic (g/L) results at SZMW 1 during full volume ASR recovery (120 MG recharge and 120 MG recovery evens) under varying recharge DO concentrations of 10 ppm (red line), 1 ppm (blue line), 100 ppb (black line) and 10 ppb (green line). Total si mulation time is 10 years.

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136 Figure 5 3 0 Predicted arsenic (g/L) results at ASR 1 during TSV simulations with unrecovered 30 MG buffer zone under varying recharge DO concentrations of 10 ppm (red line), 1 ppm (blue line), 100 ppb (black line) and 10 ppb (green line). Total simulation time is 10 years.

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137 Figure 5 3 1 Predicted arsenic (g/L) results at SZMW 1 during TSV simulations with unrecovered 30 MG buffer zone and under varying recharge DO concentrations of 10 ppm (red line), 1 ppm (blue line) 100 ppb (black line) and 10 ppb (green line). Total simulation time is 10 years.

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138 CHAPTER 6 CONCLUSIONS Bradenton ASR Degasification Pilot Test Results from the Bradenton ASR Degas Pilot Test confirmed that the mobilization of arsenic can b e controlled by the removal of the primary oxidizers (i.e., DO and chloramine) from ASR source water. The removal of 99.93% of DO and 90% of chloramine from the ASR source water resulted in an approximate 94% reduction in the total arsenic recovered at th e Bradenton site. Influence of Core Preservation Methods on ASR Batch Studies Leaching profiles for arsenic, sulfate, molybdenum, antimony, vanadium and, to a lesser degree, u ranium in the unpreserved core varied significantly f rom that of the preserved co re in both the NGW and SW phases. This suggests that the unpreserved core was significantly altered (i.e., oxidized) during the 6 month core storage period. Core preservation is necessary to prevent the alteration (i.e., oxidation) of core materials inte nded for use in trace metal leaching studies. Both the preserved core and unpreserved core showed some degree of oxidation. The core preparation method (i.e., crushing) used during the current batch experiments is necessary to homogenize the samples into even splits/replicates. However, the rock surface area created by crushing the core likely contributes to oxidation of the core material. Furthermore, the behavior of non redox sensitive elements (e.g., cesium and barium) indicates that sorption onto sol id surfaces affects batch study leaching profiles. DO, ORP and total sulfide measurements indicate oxygen contamination of the batch reactors, despite the application of a N2 headspace. Oxygen likely enters the reaction vessels when the vessels are opened during sample collection and placement

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139 entering the vessels through the sample ports (i.e., caps) on the reaction vessels. The mineralogical composition of the TR 9 1 core was found to be similar to that of the Suwannee Limestone cores evaluated by Price and Pichle r 2006; Arthur et al. 2007, and Budd 2007. While heterogeneities likely exist, the geochemical behavior of the TR 9 1 core material in ASR batch studies wo uld, therefore, be expected to be similar to Suwannee Limestone core used in previous batch studies. Design Intact Core Column Experiments The FHP tests conducted using the rock core column design provided measurements on Kv over three orders of magni tude ranging from 3E 5 to 6E 2 ft /day. The higher values correspond to zone used for ASR. The results indicate that the method used to seal the rock core in the column is preventing significant flow along the wall of the rock core. Column tracer tests are ne eded, however, to confirm these results and demonstrate the short circuiting of tracer transport is minimal. Additional test are needed to assess the composition of the materials used to seal in the rock core and the potential for impacting leaching test results (e.g., by addition of a carbon source). The two preliminary arsenic leaching column tests conducted demonstrate that the rock cores yield arsenic and show responses to changes in injected water quality. The column tests were capable of delivering water with different quality during smooth transitions. The sampling frequency was adequate to observe changes in arsenic concentrations during the limited water flow tests. The sampling frequency and flow rates of core column experiments should be caref ully considered to provide useful test results. A small head, of 1 to 2 psi, was adequate to drive flow through the cores during the preliminary tests.

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140 Additional laboratory test and modeling efforts are needed to finalize a calibrated model of core colum n experiments. The tracer tests, proposed above, are needed to improve the modeling of the physical transport processes. Reactive transport modeling of core column experiments would also benefit from improved column test. The column test should begin wi th an initial (equilibration) phase of NGW and then switch to high DO SW. As observed in the preliminary tests, core column experiments can easily be performed in the laboratory or potentially at the field site if maintaining native water quality is deemed critical. The use of preserved intact core materials in leaching experiments has several benefits over unpreserved and/or significantly altered (e.g., crushed) core materials. Additional column tests should be performed to improve our understanding of t race metal mobilization during ASR. These column studies should include a substantial equilibration phase to produce stable conditions under reduced (i.e., native groundwater) conditions. This could then be followed by a transition to oxygen rich water t o observe geochemical changes including arsenic release. Additional experiments could include a comparison between preserved and unpreserved rock core materials. Also, a comparison between crushed and intact cores from the same depth interval may improve our understanding of ASR batch studies. Finally, column tests would be ideal for evaluating the effect of carbon sources in the injected water on the mobilization of arsenic, as well as ASR pretreatment methods being currently investigated at the field s cale. Reactive Transport Modeling The 3 D flow and conservative transport model achieved a reasonable fit of the observed data at the observation well SZMW 1 with the inclusion of a horizontal high

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141 permeability layer within the ASR storage interval This demonstrates the effects on mass transport in ASR systems with storage zones having vertically layered permeabilities. The natural confinement of the site is adequate to preclude vertical mixing of recharge water with native groundwater in overlying intervals during ASR. The small amount of mixing that occurs between the storage interval and the intermediate aquifer is li kely due to the imperfect installation/construction of the ASR well. The inclusion of a vertical high permeability layer at the ASR well provided a, relatively small, conduit for mass exchange between the model layers allowing for an improved fit with the heads and TDS values at the AFMW 1 well. While arsenic has not been detected at elevated levels in the AFMW 1, and modeling of reactive transport processes across these layers is, therefore, not needed, the mass balance of recharge vs. recovered water ca n be slightly altered by this vertical flow path. This small loss of water is not likely significant from an ASR perspective, it is important, however, to account for this at the model scale. Heads within the storage zone are impacted by distance to CHBs. Model predicted heads decreased by 2.5 ft at SZMW 1 when reducing the model xy domain in 20,000 f t by 2 0,000 ft to 1 0,000 ft by 1 0,000 ft T racer arrival times are similar however, between models suggesting little impact on transport processes at radius = 224 ft from ASR well, due to a reduction in size the xy domain. This is important consideration as mo del transport times can be reduced by limiting number of cells active to transport

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142 The reactive transpo rt network provided by Wallis and others ( 2011) is appropriate for modeling arsenic mobilization during ASR. The model results provide further confirmation that sorption to FeOH is the primary mechanism controlling arsenic mobility during ASR. As previou sly stated, modeling can be an iterative process. The kinetics of FeOH formation during recharge and dissolution during recover should also be investigated. Future models should consider the input of dissolved organic carbon in ASR recharge water and res ulting biologically mediated response(s). Finally, the inclusion of arsenic in the model as a trace constituent of pyrite, rather than a separate phase (i.e., arsenopyrite), should be considered. Predictive modeling provides a comparison of operational (e .g., TSV versus pretreatment) strategies for meeting compliance with the MCL for arsenic, in the aquifer, and improving recovery efficiency by meeting the SMCL for sulfate, in recovered water. Modeling of the TSV approach, with a large (i.e., 160 MG) buff er zone, indicates compliance with the SMCL for sulfate can be meet of 10 years of repetitive operational cycling at Bradenton. However, results from predictive simulations show that compliance with the arsenic MCL will not occur at all points and all tim es within the aquifer A combination of the TSV approach with degasification of ASR injectate to DO concentrations of less than 1 ppm may be useful at Bradenton for meeting both the MCL for arsenic, in the aquifer, and the SMCL for sulfate, in recovered w ater. The Bradenton ASR geochemical data set is fairly comprehensive, in relation to other ASR datasets in Florida. However, the measurement of all major cations and anions, DOC and total sulfide wasn't consistently performed. These parameters should

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143 be included in future ASR sampling regimes to support the further development of reactive transport models.

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144 APPENDIX A ANALYTICAL LABORATOR Y TECHNIQUES Sample P ulverization (from Activation Laboratories) As a routine pra ctice with rock and core, the entire sample is crushed to a nominal minus 10 mesh (1.7 mm), mechanically split (riffle) to obtain a representative sample and then pulverized to at least 95% minus 150 mesh (106 microns). A sand blank is run between each sa mple to avoid contamination. Quality of crushing and pulverization is routinely checked as part of our quality assurance program. The only contamination from crushing and milling is Fe which depends on sample hardness (0.01 to 0.2% Fe added). Hydrogeochemistry C ation A nalyses Samples must be acidified prior to analysis. Water samples are analyzed by Perkin Elmer Sciex ELAN 6000, 6100 or 9000 ICP/MS. A blank and two water standards are run at the beginning and end of each group of 32 samples. A reagent blank is run at the beginning of the group and every tenth sample is run in duplicate. If instrument suppression occurs, sample(s) affected are re run at appropriate dilutions until response is normal. Dilution factors will increase by the same factor that samples were diluted. For analysis of marine waters or brines, detection limits will be correspondingly elevated depending on the dilution necessary to run the water samples. Sample introduction, ionization, detection and data output are contro lled by the system computer. Values which exceed the upper limits should be analyzed by Code 6 inductively coupled plasma optical emission spectrometer (ICP/OES). The ICP technique relies on placing the sample material into solution using specific parti al leaches, single acids, mixed acids or fusion techniques using fluxes. The

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145 sample solution is then introduced into a radio frequency excited plasma (~8000K). Atoms within the samples are excited to the point that they emit wavelength specific photons or light which is characteristic of a particular element. The number of photons produced is directly related to the concentration of that element in the sample. Ion Chromatography Un acidified water samples are analyzed using the DIONEX DX 120 Ion Chromatogr aphy System to determine and quantify a group of seven anions. This analysis is applicable to concentrations less than 75 mg/L for Cl, NO2 and NO3 ; less than 50 mg/L for F; less than 125 mg/L for PO4 ; less than 250 mg/L for Br and less than 375 mg/L for SO4 Samples exceeding this range (with high total dissolved solids) must be diluted to avoid over saturation. Measurement uncertainty is evaluated and controlled by an appropriate quality assurance program, including the use of regular laboratory dupl icates of samples and verification of the precision/calibration of the instrument through regular runs of various primary dilution standard solutions. Lithogeochemical Analysis Instrumental N eutron A ctivation A nalysis (INAA) A 1 g aliquot is encapsulated i n a polyethylene vial and irradiated with flux wires and an internal standard (1 for 11 samples) at a thermal neutron flux of 7 E 12 n cm 2 s 1 After a seven day decay to allow Na 24 to decay the samples are counted on a high purity Ge detector with resolu tion of better than 1.7 KeV for the 1332 KeV Co 60 photopeak. Using the flux wires, the decay corrected activities are compared to a calibration developed from multiple certified international reference materials. The standard present is only a check on a ccuracy and is not used for calibration purposes. From 10 30% of the samples are rechecked by re measurement. For values exceeding

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146 the upper limits, assays are recommended. One standard is run for every 11 samples. One blank is analyzed per work order. Duplicates are analyzed when samples are provided. Major E lements A 0.2 g sample is mixed with a mixture of lithium metaborate/lithium tetraborate and fused in a graphite crucible. The molten mixture is poured into a 5% nitric acid solution and shaken unt il dissolved (~ 30 minutes). The samples are run for major oxides and selected traces on a combination simultaneous/sequential Thermo Jarrell Ash Enviro II ICP. Calibration is achieved using a variety of international reference materials. Independent contr ol standards are also analyzed. Results on the international standards run with the samples are appended at the end of the report. Base M etals and S elected T race E lements A 0.25 g sample is digested with four acids beginning with hydrofluoric, followed b y a mixture of nitric and perchloric acids, heated using precise programmer controlled heating in several ramping and holding cycles which takes the samples to dryness. After dryness is attained, samples are brought back into solution using hydrochloric a cid. With this digestion certain phases may be only partially solubilized. These phases include zircon, monazite, sphene, gahnite, chromite, cassiterite, rutile and barite. Ag greater than 100 ppm and Pb greater than 5,000 ppm should be assayed as high lev els ma y not be solubilized. Only sulf ide sulfur will be solubilized. An in lab standard (traceable to certified reference materials) or certified reference materials are used for quality control. Samples are analyzed using a Perkin Elmer Optima 3000 ICP.

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147 Carbon and S ulfur Total carbon and sulfur are determined on an ELTRA CS 2000 Carbon Sulfur Analyzer. A weighed sample is mixed with iron chips and a tungsten accelerator and is then combusted in an oxygen atmosphere at 1370C. The moisture and dust are removed and the CO2 gas and SO2 gas are measured by a solid state infrared detector.CO2 is determined by determined by digestion with 2N perchloric acid and the dissolved CO2 is titrated using a UIC coulometer. The separate sample is ignited at 600C in o rder to drive off the CO2 and the organic carbon. The remaining C is graphitic carbon which is analyzed as above. Organic carbon is determined by difference after subtracting the above species. Sulfide sulfur is determined by calculating remaining sulfur a fter sulfate sulfur is subtracted from total sulfur. Sulfate sulfur is determined by roasting at 850C to drive off the sulfide sulfur with analysis of the sulfur in the roast residue. This is converted to sulfate by calculation. Mercury A 0.5 g sample is digested with aqua regia at 90C. The Hg in the resulting solution is oxidized to the stable divalent form. Since the concentration of Hg is determined via the absorption of light at 253.7 nm by Hg vapor, Hg (II) is reduced to the volatile free atomic s tate using stannous chloride. Argon is bubbled through the mixture of sample and reductant solutions to liberate and to transport the Hg atoms into an absorption cell. The cell is placed in the light path of an Atomic Absorption Spectrophotometer. The maxi mum amount absorbed (peak height) is directly proportional to the concentration of mercury atoms in the light path. Measurement can be performed manually or automatically using a flow injection technique (FIMS). Hg analysis is performed on a Perkin Elmer FIMS 100 cold vapor Hg analyzer.

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148 APPENDIX B LITHOCHE MISTRY R ESULTS Activation Laboratories Report Date: 2/22/2010 Analyte Symbol Hg SiO2 Al2O3 Fe2O3(T) MnO MgO CaO Na2O K2O TiO2 P2O5 LOI Total Unit Symbol ppb % % % % % % % % % % % % Detection Limit 5 0.01 0.01 0.01 0.001 0.01 0.01 0.01 0.01 0.001 0.01 0.01 Analysis Method Hg FIMS FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP FUS ICP UF 1 < 5 4.11 0.24 0.12 0.004 0.7 51.97 0.04 0.05 0.042 0.07 41.68 99.04 UF 2 < 5 3.96 0.19 0.09 0.004 0.66 52.45 0.04 0.04 0.042 0.08 41.72 99.29 UF 3 < 5 3.81 0.18 0.08 0.004 0.65 52.25 0.04 0.04 0.036 0.07 41.84 99 Analyte Symbol Au Ag As Ba Be Bi Br Cd Co Cr Cs Cu Ga Unit Symbol ppb ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Detection Limit 1 0.5 1 1 1 0.1 0.5 0.5 0.1 0.5 0.1 1 1 Analysis Method INAA INAA / TD ICP INAA FUS ICP FUS ICP FUS MS INAA TD ICP INAA INAA FUS MS TD ICP FUS MS UF 1 < 1 < 0.5 2 13 < 1 < 0.1 1.8 < 0.5 1.2 21.1 < 0.1 4 < 1 UF 2 < 1 < 0.5 2 12 < 1 < 0.1 1.8 < 0.5 1.3 19.8 < 0.1 3 < 1 UF 3 < 1 < 0.5 2 11 < 1 < 0.1 1.8 < 0.5 1.2 21.4 < 0.1 3 < 1 Analyte Symbol Ge Hf Hg In Ir Mo Nb Ni Pb Rb S Sb Sc Unit Symbol ppm ppm ppm ppm ppb ppm ppm ppm ppm ppm % ppm ppm Detection Limit 0.5 0.1 1 0.1 1 2 0.2 1 5 1 0.001 0.1 0.01 Analysis Method FUS MS FUS MS INAA FUS MS INAA FUS MS FUS MS TD ICP TD ICP FUS MS TD ICP INAA INAA UF 1 < 0.5 0.9 < 1 < 0.1 < 1 4 1.1 2 < 5 1 0.112 0.2 0.41 UF 2 < 0.5 0.8 < 1 < 0.1 < 1 4 1.1 1 < 5 < 1 0.105 0.3 0.37 UF 3 < 0.5 0.6 < 1 < 0.1 < 1 4 1.5 2 < 5 < 1 0.098 0.2 0.42

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149 Analyte Symbol Se Sn Sr Ta Th U V W Y Zn Zr La Ce Unit Symbol ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Detection Limit 0.5 1 2 0.01 0.05 0.01 5 1 1 1 1 0.05 0.05 Analysis Method INAA FUS MS FUS ICP FUS MS FUS MS FUS MS FUS ICP INAA FUS ICP INAA / TD ICP FUS MS FUS MS FUS MS UF 1 5.8 < 1 640 0.03 0.57 7.03 27 < 1 4 2 49 2.27 3.12 UF 2 6.1 < 1 638 0.03 0.46 7.25 25 < 1 6 3 39 2.34 3 UF 3 4.9 < 1 621 0.04 0.39 6.76 22 < 1 3 2 32 2.01 2.55 Analyte Symbol Pr Nd Sm Eu Gd Tb Dy Ho Er Tl Tm Yb Lu Unit Symbol ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Detection Limit 0.01 0.05 0.01 0.005 0.01 0.01 0.01 0.01 0.01 0.05 0.005 0.01 0.002 Analysis Method FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS FUS MS UF 1 0.48 1.93 0.43 0.076 0.46 0.06 0.44 0.09 0.27 < 0.05 0.03 0.23 0.029 UF 2 0.48 2.03 0.39 0.074 0.48 0.06 0.47 0.1 0.31 < 0.05 0.04 0.27 0.032 UF 3 0.41 1.85 0.32 0.061 0.41 0.05 0.37 0.08 0.25 < 0.05 0.026 0.2 0.02 Analyte Symbol Mass C Total C Graph C Organ CO2 Total S SO4 Unit Symbol g % % % % % % Detection Limit 0.01 0.05 0.05 0.01 0.01 0.3 Analysis Method INAA IR IR IR COUL IR IR UF 1 1.604 11.7 < 0.05 0.65 40.4 0.15 0.3 UF 2 1.57 11.6 < 0.05 0.28 41.4 0.14 < 0.3 UF 3 1.5 11.6 < 0.05 0.24 41.6 0.13 < 0.3 < symbol = below method detection limit

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150 APPENDIX C GEOPHYSICAL LOGS Appendix C 1. Geophysical logs completed at SZMW 1. Arrow points to potential high permeability zone at approximately 465 ft bls as indicated by expansion of caliper and decrease in resistivity (RES).

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151 Appendix C 2. Geophysical logs completed at SZMW 1. Arrow points to potential high permeability zone at approximately 465 ft bls as indicated by expansion of caliper and incr ease in flow (flow in GPM).

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152 LIST OF REFERENCES Appelo, C. A. J., M.J.J. Van der Weiden, C. Tournassat and L. Charlet, L. 2002 Surface complexation of ferrous iron and carbonate on ferrihydrite and the mobilization of arsenic. Environmental Science & Technology 36, 3096 3103. Arthur, J.D., J. B. Cowart, and A. A. Dabous 2000. Arsenic and uranium mobilization during aquifer storage and recovery in the Floridan aquifer system. Florida Peninsula: Geological Society of America Abstracts with Programs 32. Arthur, J.D., J.B. Cowart, and A.A. Dabous 2001. Florida a quifer s torage and r ecovery g eochemical s tudy: y ear t hree p rogress report, In Florida Geological Survey Open File Report 83. Arthur, J.D., A.A. Dabous, and J.B. Cowart 2002. Mobilization of arsenic and other trace elements during aquifer storage and recovery, southwest Florida. In: U.S. Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2 4, 2002, U.S. Geological Survey Open File Report 02 89, 44 47 Art hur, J. D., A.A. Dabous and J.B. Cowart 2005 Water r ock g eochemical c onsiderations for a quifer s torage and r ecovery; Florida case s tudies In Underground Injection Science and Technology Developments in Water Science; Tsang, C.F., Apps, J.A., Eds.; El sevier: Amsterdam 52, 327 339. Arthur, J. D., A.A. Dabous and C. Fischler 2007 Bench scale geochemical assessment of water rock interactions: City of Sanford aquifer storage and recovery facility, Florida Geological Surv ey Final Repo rt, August 3, 2007. A r thur, J.D., C. Fischler, A.A. Dabous, D.A. Budd, and B.G. Katz 2007 Geochemical and mineralogical characterization in potential aquifer storage and recovery storage zones in the Florida Aquifer system Comprehensive Everglades Restoration Plan Report, Reference Agre ement OT040175. Budd, D.A. 2007 Mineralogical abundances as determined by x ray diffraction in select samples of the upper Floridan Aquifer. Appendix 15 In Geochemical and mineralogical characterization in potential aquifer storage and re covery storage zones in the Florida Aquifer system. Comprehensive Everglades Restoration Plan Report, Reference Agreement OT0 40175. Caldeira, C. L., V.S.T. Ciminelli A. Dias, K. and Osseo Asare 2003. Pyrite o xidation in a lkaline s olutions: n ature of t he p roduct l ayer, Internationa l Journal of Mineral Processing 72, 373 386. City of Bradenton 2004 ASR Program, Phase II Well Construction Report, February, 2004. City of Bradenton 2006 Bradenton ASR Cycle Test Summary Report, October, 2006.

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153 DelCharco M.J., and B.R. Lewelling 199 7 Hydrologic description of the Braden river watershed, west central Florida: In U.S. Geological Survey Open File Report 96 634. Descourvieres, C., H. Prommer C. Oldham, J. Greskowiak and N. Hartog 2010, Kinetic reaction m odeling f ramework for i dentifying and q uantifying r eductant reactivity in h eterogeneous a quifer s ediments. Environmental Science & Technology 44, 6698 6705. Dzombak, D. A. and F.M.M. Morel 1990 Surface complexation modeling Wiley and Sons: New York. F ischler, C., P. Hansard S.B. Norton and A.D. Arthur 2010 Geochemical testing program for the Cape Coral a quifer s torage and recovery system pilot, Florida Geological Survey, Final Report, April 15, 2010. Florida Department of Environmental Protection 2007. Map and Summary Table of Aquifer Storage and Recovery Facilities in Florida, Dated August, 2007, Accessed March 29, 2010, Available for download at: http://www.dep.state.fl.us/water/uic/ Florida Administrative Code. Drinking Water Standards, Monitoring, and Reporting. F.A.C. 62 550, 82 p. Accessed April 10, 2007, Available for download at: http://www.dep.state.fl.us/leg al/rules/drinkingwater/62 550.pdf Florida Administrative Code. Underground Injec tion Control, F.A.C. 62 528, Accessed April 10, 2007, Available for download at: http://www.dep .state.fl.us/legal/Rules/shared/62 528/62 528.pdf Harbaugh, A. W, E.R. Banta, C.M. Hill, and M.G. McDonald 2000 MODFLOW 2000, The U.S. Geological Survey modul ar ground water model user guide to modularization concepts and the ground water flow process, In U.S. Geological Survey, Open File Report 00 92. Jones, G. W. and T. Pichler. 2007. Relationship between pyrite stability and arsenic mobility during Aquifer Storage and Recovery in Southwest Central Florida: Environmental Science and Technology 41, 723 730. Mirecki, J.E., 2006. Geochemical models of water quality changes during aquifer storage and recovery (ASR) cycle tests, Phase I: Geochemical Models Using Existing Data In U.S. Army Corps of Engineers, Engineer Research and Development Center Report TR 06 8. Norton, S B., 2007. Quantifying the n ear b orehole g eochemical r esponse d uring a quifer s torage and r ecovery: a a nalytical t echniques to ASR c ycle t t hesis, University of Florida, Gainesville, FL

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154 Parkhurst D. L., and C.A.J. Appelo 1999 User's g uide to p hreeqc (Version 2), a c omputer p rogram for s peciation, batch r eaction, one d imensional t ransport and i nverse g eochemical c alc ulations. In U.S. Geological Survey, Water Resources Investigations Report 99 42 59. Peek, Harry M. 1958. Ground water r esources of Manatee County, Florida Report of Investigations No.18; Florida Geological Survey, Tallahassee, FL Price, R.E., and T. Pichler 2006. Abundance and mineralogical association of arsenic in the Suwannee Limestone (Florida): Implications for arsenic release during water rock interaction: Chemical Geology 228, 44 56 Prommer, H., and P.J. Stuyfzand 2 005. Identification of temperature depend ent water quality changes during a deep well injection experiment in a pyritic aquifer Environmental Science and Technology 39, 2200 2209. Prommer, H., and V.E.A. Post. 2010. A reactive multicomponent model for saturated porous media, In Version 2.0, User http://www.pht3d.org Pyne, D. 2006 The Target Storage Volume (TSV): A proven approach for achieving high recovery efficiency and for attenuating arsenic, In American Groundwater Trust Aquifer Storage Recover y VI Conference, Orlando, FL, October 2006. Railsback B.L. 2003 Earth's s cientist p eriodic t able of the e lements and t heir i ons. Geology, Geological Society of America acc essed on March 25, 2011, available for download at: http://www.gly.uga.edu/railsback/PT.html Richtar, J. 2006. Regulatory Update Permitting requirements for operating ASR investigations and projects Aquifer Storage Recovery VI Conference, Orlando, FL, hosted by American Groundwater Trust, October 2006. Ruiter, H. and P.J. Stuyfzand 1998 An experiment on well recharge of oxic water into an anoxic aquifer : in Peters, J.H., et al., eds., Artificial R echarge of Groundwater : Rotterdam, N etherlands, A.A. Balkema Smedley, P.L., and D.G. Kinniburgh 2001 Source and behavior of a rsenic in Natural Waters, In U.N. Synthesis Report on Arsenic in Drinking Water; Geneva, Wo rld Health Organization Southwest Florida Water Management District. 2008. A memorandum regarding: regional reclaimed water partnership, In SWFWMD Project Meeting Summary, July 15, 2008. Wallis, I., H. Prommer C.T. Simmons, V. Post and P.J. Stuyfzand 2010 Evaluation of c oncep tual and n umerical m odels for a rsenic m obilization and a ttenuation during m anaged aquifer r echarge. Environmental Science & Technology 44 5035 5041.

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155 Wallis, I., H. Prommer T. Pichler, V. Post, S.B. Norton, M.D. Annable and C.T. Simmons 2011 A process based reactive transport model to quantify arsenic mobility during aquifer storage and recovery, Environmental Science & Technology 45, 6924 6931 Williamson, M. A. and J.D. Rimstidt 1994 The kinetics and e lectrochemical r ate d etermining s tep of a queous p yrite o xidation. Geochimica Et Cosmochimica Acta, 58, 5443 5454. Yobbi, D.K., and K.J. Halford. 2006. Numerical simulation of aquifer tests, west central Florida; Scientific Investigations Report 2005 5201; U.S. Geological Survey. Zheng, C. and P. P. Wang 1999 MT3DMS A modular three dimensional multispecies transport model, University of Alabama, In U.S. Army Corps of Engineers Contract Report SERDP 99 June 1998, Revised November 1999.

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156 BIOGRAPHICAL SKETCH Stuart Bryan Norton was born in Clinton, North Carolina where he learned the value of hard work At the age of 16, Stuart and his family moved to Mandarin, a suburb of Jacksonville, Florida. While spending time with friends who owned a small environmental consulti ng firm, he developed a strong interest in environmental science and a deep respect for the environment. After graduating from Mandarin High School, he attended the University of Florida where he earned a Bachelor of Arts degree in geology in 1998. In 199 9 Stuart began his career with the consulting engineering firm Mactec, Inc. At Mactec, Stuart worked as a field geologist completing numerous rapid site assessments, implementing remedial actions, and performing post closure assessments at industrial, pet roleum, and dry cleaner sites in Florida. In 2001 Stuart began working with the Florida based consulting engineering firm Jones, Edmunds & Associates, Inc. During his tenure with Jones Edmunds & Associates, Inc. Stuart managed several ASR and groundwater supply projects in Florida, while working towards his Masters of Science degree in Environmental Engineering Sciences at the University of Florida. His current position as ASR Project Specialist with the City of Bradenton, Florida has allowed him to cont inue as the project technical lead for the Bradenton ASR Degasification Pilot Project, while completing his education. He received his Ph.D. from the University of Florida in the fall of 2 011 Stuart married Gladys Enid Santana in 2004, with whom Stuart spends much of his free time. Along with their three year old son Elijah, the couple regularly pursues leisure interests including traveling, beach combing, canoeing, tail gating at University of Florida Gator football games, and other activities.