Title: Presentation to determine the effects of the pumping of water from the St. Petersburg Section 21 well field
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 Material Information
Title: Presentation to determine the effects of the pumping of water from the St. Petersburg Section 21 well field
Alternate Title: Hudson, Herbert E., Jr. President Water and Air Research, Inc. Presentation to determine the effects of the pumping of water from the St. Petersburg Section 21 well field on the property owned by Casa Properties, Inc. call Lorenzo Lakes.
Physical Description: 12p.
Language: English
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Notes
General Note: Box 3, Folder 5B ( WATER SHORTAGE, VOL. I. B3F5 ), Item 92
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
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Bibliographic ID: UF00051661
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: Levin College of Law, University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Full Text










PRESENTATION BY

HERBERT E, HUDSON, JR., PRESIDENT

WATER AND AIR RESEARCH, INC.





Mr. Chairman, Members of the District Board,

my name is Herbert E. Hudson, Jr. I head Water and

Air Research, Inc., a consulting group in Gainesville,

which specializes in furnishing scientific and engineer-

ing expertise.

I have been engaged by Casa Properties, Inc.

to determine the effects of the pumping of water from the

St. Petersburg Section 21 well field on the property owned

by Casa Properties, Inc. called Lorenzo Lakes, at which

site it proposes to build a planned unit development

focused on five lakes on the site.

In order to determine what has transpired at

Lorenzo Lakes as a result of the pumping at the Section

21 well field by St. Petersburg, I have used several

hydrological approaches to evaluate groundwater behavior

in the vicinity of the well field.


Area Supplying Water to Section 21

The first method that I used began with determin-

ing the area that is tributary to the well field. This













first figure (Figure 1) shows the potentiometric contour

maps for September 1972 prepared for the District by

the U. S. Geological Survey. I have used the method of

stream-lines to establish the extent of the area tributary

to the Section 21 well field. The boundary of this area

is shown as the heavily dashed line which runs upslope

from the well field past Bird Lake and further to the

northeast. This area, drawn by means of a standard

engineering procedure, gives a tributary area for the

well field of about 17 square miles. The tributary area

is defined as that area within which the current water

is flowing toward the well field. In September 1972

the mean pumping rate at the Section 21 well field was

16.5mgd which was slightly more than the 10-year average

of 15.8 mgd withdrawn from the field. Both of these

figures are smaller than the maximum month's pumping rate

at this well field which has been as high as 23mgd. The

Pasco County well field several miles north of Section 21

had not yet gone into operation. Since that time the Pasco

County well field has been placed in service. It is now

taking water that was formerly flowing toward the Section

21 well field with the result that the tributary area for









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Section 21 has been reduced from a 17-mile area to about

10 square miles.

The safe yield of the tributary area has been

computed by using the District average of the available

recharge of 650,000 gallons per day per square mile. Using

this unit recharge value the 1972 safe yield was found

to be llmgd. Operation of the Pasco County well field

had reduced this capacity to 7mgd by June 1973.

Within the 17-mile area, St. Petersburg has

been taking more water than the area can supply. Even

if the Section 21 well field capacity were limited, as

recently proposed, to 10mgd, this would leave only lmgd

to allot to the other 16 square miles within the 1972

area tributary.

It appears that, with the adverse effects of

Pasco County well field, capacity at Section 21 will

deteriorate and a 10mgd capacity appears to be an ex-

cessive figure.

I do not know what the current uses within the

tributary area amount to but it is obvious that the total

taking by all users including St. Petersburg within the

area cannot safely be more than 7 to 10mgd.


Distance Drawdown Approach

The amount of water removed from storage in the






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area near the Section 21 well field has been estimated

by using a distance-drawdown curve prepared by J. W.

Stewart of the Geological Survey for the District in 1968.

Using this curve I calculate that during the past 10 years,

water has been removed from storage in the area at a rate

of approximately 8mgd. If we add this 8mgd figure to the

7 to llmgd safe yield of the tributary area we get a total

that agrees reasonably well with the 15.8mgd average pump-

ing for the past 10 years. Thus, it is computed that 1/3

of the water withdrawn from the Section 21 well field has

been taken out of storage in the area tributary to the

field.

In other words, St. Petersburg has been withdraw-

ing water at a rate of approximately 50% greater than can

safely be taken from the tributary area. This does not

take into account the needs and uses of other land owners

in the area.


Computation of Inflow

The flow from the area tributary to the well field

can be computed by another method which is based on the use

of the coefficient of transmissibility, the length of a:

contour across the area, and the average slope of the









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potentiometric surface across that contour. This compu-

tation has been made using the June 1973 data for the flow

crossing an assumed 32.5 foot contour. The result of this

computation was a determination that the amount of water

crossing the 32.5 foot contour toward Section 21 was 20.4mgd

at a time when Section 21 was being pumped at a rate of

23mgd.

Thus, the water flow toward the well field was

being withdrawn at a rate of nearly Imgd per square mile

in excess of the mean safe yield or water crop. This

means that the water could only have come from storage

in the upper aquifer with, as a consequence, a lowered

water level in that aquifer. For those who are not familiar

with geological situations, perhaps I should explain that

in this area water can be obtained from two separate layers

in the earth.

One of these is the limestone which comprises the

Floridan Aquifer and the other, which overlies the Floridan

Aquifer, is an unconsolidated sandy aquifer that does not

yield much water to wells but which has substantial water

storage capacity. The upper aquifer yields water down-

ward to the Floridan aquifer. The result of excessive









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pumping has been a decline in water levels in the upper

aquifer which is shown by this next figure (Figure 2).


Cross Section Examples

The District in cooperation with the USGS, has

been measuring water levels in both aquifers in a large

number of observation wells in and near Section 21.

Using these data, we have prepared two cross sections

through the Lorenzo Lakes property. The locations of

these sections are shown in Figure 1. These sections

show the ground surface elevation, and they also show

the former water table. This defines the locations of

lakes that once existed on the site. Figure 3 also shows

the water levels in the Floridan Aquifer and in the

Surficial Aquifer. The levels in the Surficial Aquifer

are 8 to 13 feet lower than they were before the Section

21 well field was placed in service. The same kind of

information on a different section is shown on Figure 4.

This section is located to show the conditions from ob-

servation well 421 near Platt Lake, across the Lorenzo

Lakes property to Hillsborough #13 well. The current ob-

servations, compared with the former water table data,

again show substantial lowering in the water tabY. in the








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Lorenzo Lakes property.


Resulting Damage

Two of the 5 former water-table lakes on the

site have been completely drained; two contain only

puddles; one is relatively unaffected; and one is affected

to a lesser degree because of the presence of unusually

impermeable soils in its vicinity as determined by bor-

ings-at the site.

Another consequence of the withdrawal of water

from storage has been the development of a number of

new small sinkholes on the Lorenzo Lakes property. Their

youthfulness is easily established by examining the

breakage of roots of still-green grasses.

The re-establishment of the former lakes on

the site is an essential element of the proposed Lorenzo

Lakes planned unit development. The increased proclivity

of the area to form sinkholes, due to the overpumpage

at Section 21, is expected to materially add to the cost

and difficulty of re-establishing the lakes.

Prior to becoming aware of these new sinkholes

we had estimated the cost of restoring the lakes on the

Lorenzo Lakes property at about $300,000.00. This








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estimate was based on sealing the lake bottom with bentonite

and constructing a well to pump into the lakes. After

discovering new sinkholes on the land, it appears reason-

able to anticipate that more of them may form under the

lakes when they are filled, and the cost of sealing these

sinkholes will increase the total cost substantially.

If the water levels in the surficial aquifer remain low

as a result of pumping at the Section 21 well field, and

if the lakes are re-established, we can anticipate a

much greater trend toward formation of new sinkholes

under the new refilled lakes with substantial expenditures

needed for corrective action.

The only solution I can see to reduce the threat

to the lakes is to so reduce pumping rates at Section 21

that the levels within the Lorenzo Lakes surficial aquifer

will rise at least to the bottom of the lakes to provide

the necessary support for the lakes.

Gentlemen, I appreciate the opportunity to

present this information to you.
















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September 1972 Floridan














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FIGURE 1. AREA TRIBUTARY TO SECTION 21 WELLFIELD. September 1972.
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