Historic note
 Front Cover

Group Title: Circular - University of Florida Institute of Food and Agricultural Sciences ; 671
Title: Iron ochre and related sludge deposits in subsurface drain lines
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00067212/00001
 Material Information
Title: Iron ochre and related sludge deposits in subsurface drain lines
Series Title: Circular Florida Cooperative Extension Service
Physical Description: 11 p. : ; 23 cm.
Language: English
Creator: Ford, Harry W., 1922-
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1985?
Subject: Sewage sludge precipitants   ( lcsh )
Sewage -- Environmental aspects   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Bibliography: p. 12.
Statement of Responsibility: Harry W. Ford.
General Note: Cover title.
Funding: Circular (Florida Cooperative Extension Service) ;
 Record Information
Bibliographic ID: UF00067212
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 15174653

Table of Contents
    Historic note
        Historic note
    Front Cover
        Front cover
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
Full Text


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida

Circular 671




Harry W. Ford

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Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
John T. Woeste, Dean for Extension


Harry W. Ford

In subsurface drains, there are four known types of sludge deposits
that are associated with bacterial activity. These are ochre, manganese
deposits, sulfur slime, and iron sulfide. Iron deposits, collectively
named ochre, are the most serious and widespread. Ochre deposits and
associated slimes are usually red, yellow, or tan in color. Ochre is
filamentous (from bacterial filaments), amorphous (more than 90%
water), and has a high iron content (2 to 65% dry wt.). It is a sticky mass
combined with an organic matrix (2 to 50% dry wt.) that can clog drain
entry slots, drain envelopes, and the valleys of the corrugations be-
tween envelope and inlet slots. Elements like aluminum, magnesium,
sulfur, and silicon are often present. Ochre can usually be detected at
drain outlets or in manholes as a voluminous and gelatinous mass. Un-
fortunately, ochre may also be present in drain sublaterals, and not
necessarily at the outlets. Under those conditions, it can usually be
detected by excavation of poorly drained spots in a field. There are still
disagreements concerning the physical, chemical, and biological fac-
tors contributing to ochre formation. For example, the gelatinous mass
can trap fine soil particles so that ochre may contain more than 30 per-
cent sand. In addition, old ochre can become crystalized and hard.
In certain areas of the western United States, manganese, when pres-
ent under suitable conditions in ground water, can form a drain-
clogging, bacterially enhanced gelatinous black deposit. Manganese
has not been a serious problem in the eastern United States.
Sulfur slime is a yellow to white stringy deposit formed by the oxida-
tion of the hydrogen sulfide that may be present in ground water.
Soluble sulfides are oxidized to elemental sulfur, predominately by the
bacteria Thiothrix nivea and Beggiatoa sp., so that globules of elemen-
tal sulfur are deposited within the filaments of the bacteria. The fluffy
masses of slime are held together by intertwining of the long filaments
of the bacteria. Sulfur slime has not been a serious problem in most

Dr. Ford is Professor (Emeritus), Citrus Research and Education Center, IFAS,
University of Florida, Lake Alfred, Florida 33850.

agricultural drains. It can be found most frequently in muck soils. It
may be present in sites designed for subirrigation if the well water used
for irrigation contains hydrogen sulfide.
Iron sulfide is a gelatinous black precipitate formed from the reaction
between ferrous iron and hydrogen sulfide. It will usually not stick to
light sandy soil particles. It becomes a clogging agent when present in
amounts that can block soil pores. Iron sulfide can be found when drains
are buried in mixed soil profiles, gulleys, river flood plains, or when top-
soil or organic debris are used to blind the drains during installation.
In general, iron sulfide should not be a serious problem for most
installations that do not blind the drains with topsoil or debris of
organic matter.

Ferrous Iron in Ground Water
Although iron is present in just about every soil type, it may not be in
soluble ferrous form. Ferrous iron is a primary raw material for ochre
formation, and it must be in solution in the ground water rather than
just located on soil particles. Ferrous iron will be present in the ground
water of flooded soils only after the soil oxygen has been depleted. When
that happens, certain iron-reducing bacteria attack and reduce insolu-
ble ferric iron associated with mineral and organic soil particles. The
biological action of the bacteria is energy intensive, so that energy
sources that can be utilized by bacteria must be present. There is now
sufficient evidence to indicate that iron cannot be reduced in a flooded
soil without the action of specific bacteria. Reducing conditions are not
enough. The bacterial bodies must be present and in direct contact with
iron attached to soil particles.
There is often more ferrous iron in the ground water of sandy soils and
organic muck soils than in loamy and clay soils. Sandy soils usually
have the most ochre problems. Flooding sandy soils excludes air rapidly
and less energy is required for bacteria to reduce iron to the soluble fer-
rous form. Sandy soils may receive sufficient organic carbon from plant
roots or organic residues. Iron is often available from within
sandy clay pockets and organic pans (spodic horizons). Organic and
muck soils usually have sufficient iron and readily available organic
carbon. Consequently, muck soils often have severe problems from
ochre clogging. Clay soils, unless mixed with organic matter, have little
if any ferrous iron in the ground water, even when flooded for extended
periods. There are several reasons. First, the suitable organic carbon
level is often insufficient for strong iron reduction. Second, there seems
to be a strong electrochemical attraction between the ferrous iron ion
and the clay particle. Soil pH is also an interacting factor because the
amount of ferrous iron is usually higher in the ground water at pH
values below 7.0.

Soluble ferrous iron flowing in ground water enters a different
environment as it approaches the drain and passes through the drain
envelope. If a low level of oxygen is present, certain filamentous and
rod-shaped bacteria can precipitate some of the ferrous iron, forming
insoluble ferric iron and incorporating it into the complex called ochre.

Permanent and Temporary Ochre
Although soil pH, soil type, soil temperature, and reducing conditions
influence ochre deposition, the problem must be subdivided into two
main categories. One is a temporary problem called autochthone and
the other a permanent clogging difficulty, technically called
allochthone (meaning: of foreign origin). Temporary ochre as a clogging
factor may diminish or disappear over a period of 3 to 8 years, if drains
are maintained in a free-flowing condition. It usually occurs rapidly
and often can be detected at drain outlets within the first few months
after drain installation. If drains can be maintained in working order,
ferrous iron reaching them may diminish over a period of time. Perma-
nent ochre is the most serious problem because it continues to be a clog-
ging agent for the life of the drainage system, regardless of treatment.
Permanent ochre problems in the United States have occurred in pro-
files with extensive residual iron and natural energy and from soluble
reduced iron flowing into a drainage site from surrounding areas.
Valleys at the base of escarpments are typical of this condition. Exten-
sive amounts of reducible clays or boglike organic materials usually
underlie permanent ochre sites. There are known ochre locations
where iron originated 3 to 4 miles from a drainage site. Thus, it is
important to consider topographical terrain features when estimating
the potential for permanent ochre formation. In general, sites con-
sidered to have permanent ochre potential should not be tile-drained
without extensive modifications in design and provisions for con-
tinuous maintenance.

Processes of Ochre Deposition

Based on controlled studies, the minimum ferrous iron concentra-
tions that can stimulate ochre formation is between 0.15 and 0.22 mg/1
(parts per million). Iron-precipitating bacteria must be present for
extensive clogging to occur, even when other conditions are just right
for chemical precipitation of the iron. Iron alone does not have serious
sticking properties. The reaction in drain tubes is a combination of
bacterial precipitation and the incorporation of chemically precipitated
iron into the sticky slimes of the bacterial masses involved in the
ochre matrix.

There are several kinds of processes involved in ochre deposition. All
of them do not occur under the same conditions. All of the reactions do
require some oxygen to be present in the drain line.
1. Oxidation of the iron by certain bacteria predominantly on the out-
side of the organisms, as shown by electron micrograph pictures.
2. Auto-oxidation (chemical change) and precipitation with subse-
quent accumulation of the colloidal iron on the sticky surfaces of
bacterial slimes.
3. Bacterially precipitated iron from completed soluble organic-iron
compounds. The soluble complex before precipitation may be either
ferrous or ferric iron.
The most effective iron-precipitating bacteria in drain pipes have
been groups consisting of long filaments, such as Gallionella, Lep-
tothris, and Sphaerotilus. These bacteria are large enough to be seen
with the low power of a regular-light microscope. They can grow quite
rapidly and the intertwined masses are capable of bridging small open-
ings. The sticking and oxidizing properties can be demonstrated by
using glass slides mounted in the flowing water (2). The precipitated
iron and bacterial layer on the glass cannot be washed off in a stream of
water. The same reaction probably occurs in drain pipes.
There are certain rod bacteria, such as Pseudomonas and
Enterobacter, that can precipitate iron, but the volumes of ochre pro-
duced are not as large as with the filamentous types.
It has been noted that iron can be precipitated near the bodies of
bacteria when polysaccharides are present. The polysaccharides in
question are complex, rather sticky carbohydrate compounds that can
be formed by bacteria. It is not known with certainty if polysaccharides
formed by bacteria contain iron-oxidizing enzymes or whether only
previously oxidized iron may be trapped in the slime.
There is a type of ochre that forms only at low pH, when pyritic soils
are drained. Pyrites are formed from iron and hydrogen sulfide over a
long period of time in flooded marine deposits. When such soils are
drained, the pyrites first oxidize to ferrous iron and sulfates. The
sulfates change to sulfuric acid, which lowers the soil pH below 3.5. The
rod-shaped bacterium Thiobacillus ferrooxidans, which can function
only in an acid environment, then converts the soluble iron into ochre.
Pyritic soils, often called acid sulfate soils, are found most frequently in
coastal agricultural areas, like northwestern Europe and the Scandina-
vian countries. Except for reclaimed strip mines (coal contains a signifi-
cant amount of pyrites), acid sulfate ochre is not considered to be
widespread in the United States.
There are variations in the compositions of ochre from different areas
of the world. Those with the most organic carbon content seem to have
the strongest sticking properties and are the most difficult to remove
from drain pipes using acid treatments or water-jet cleaning.

Some compounds stimulate the formation of ochre by enhancing
growths of bacteria that are involved in iron precipitation. Low concen-
trations of tannic acid, hypochlorous acid (bleach), and acrolein (a toxic
aldehyde compound) below biocidal strength can actually stimulate
bacterial activity and subsequently increase ochre deposition.
Organo-iron completing is a complicating factor that makes it dif-
ficult to predict rates of precipitation. Iron will complex with a large
number of organic compounds, such as humic, tartaric, lactic, ascorbic,
and citric acids, as well as another group called aromatic hydroxyl com-
pounds. The complexes, which can enhance ochre deposition, are
usually stable and can remain in solution even in ponds and canals. In
contrast, certain of the same organo-iron complexes can inhibit ochre
formation. In controlled studies, tannins inhibited bacterial activity at
10 ppm (but they stimulated ochre production at 1 ppm).
In summary, while iron flowing into drains is a necessary condition
for ochre formation, it is difficult to predict with accuracy the quantity
of ochre that may form. The biotic factors at any given location can only
be assumed because they seem to be everywhere.

Where Is Ochre Deposited?
Ochre can be found in the drain filter envelope, the zone abutting the
envelope, the openings (slots or holes) in the drains, and within the
drain tube itself. Most clogging in 4-inch diameter corrugated
polyethylene tubing can be traced to sealing of the inlet openings and
accumulations within the valleys of the corrugations, particularly
when synthetic drain envelopes are used. Within the tubing itself, the
heaviest accumulation of ochre appears to be in the lower third of the
drain length, although the lower third is usually not the region of max-
imum ochre formation.

Soil Conditions That Contribute to Ochre Formation

Extensive surveys have been conducted throughout the United
States to determine if there are relationships between soil types and
ochre accumulation in drains. types of soils that appeared to show the
most potential for ochre formation were fine sands and silty sands,
organic soils and soils with organic pans (spodic horizons), and mineral
soil profiles with mixed organic matter. Gullies, flood plains of rivers,
and depressions containing organic residues frequently encounter
ochre problems. Sites being utilized for sprinkling of sewage effluent
and cannery plant wastes usually furnish sufficient energy for reduc-
tion reactions. Therefore, all sprinkled soil should be considered poten-
tially serious for ochre hazard if the profiles can undergo flooding for
extended periods.

The least likely candidates for ochre hazard were found to be silty
clays and clay loams. When flooded, they were usually deficient in
ferrous iron in the soil solution.
It is possible to survey individual soil types for ochre potential. The
method involves incubation of soil samples in the laboratory (4). In Flor-
ida, 50 soil types were considered suitable for citrus trees after drain-
age. Of these, 26 were rated serious for ochre-forming potential. Six
were rated serious for permanent ochre and 20 for temporary clogging.
Ochre sites are not uniformly distributed, although they have been
found in most states in the United States. For drainage installations as
a whole, probably less than 10% are subject to ochre hazard.

Measuring Iron in the Ground Water
It is possible to estimate the maximum potential for ochre before
installing drains, as well as to estimate whether specific soil types or
profiles can be considered susceptible.
The ferrous iron content of the ground water flowing into a drain has
been found to be a reliable indicator of the potential for ochre clogging.
The need for an easy, reliable method has been recognized and several
systems have been devised, and discarded. Analyzing the soils for total
iron is of no value because the values do not indicate easily reducible
soluble ferrous iron nor the complex interactions between soil pH and
soil type.
The details of a reliable and rapid testing procedure (4) that can be
used to measure the ochre clogging potential before installing drains
has been developed and tested extensively in numerous locations in the
United States. Ten ml of on-site ground water can be collected in
syringes and pressure filtered through 0.45 micron membranes into a
sulfamic acid-phenanthrolene reagent in completely closed systems.
The reagent turns red with ferrous iron. Soil samples, either air-dried
or moist, will yield results similar to ground water. The soil is placed in
test tubes containing water and incubated at 30C for 2 weeks. A sup-
plemental energy source can also be added to tubes as a basis for
establishing whether the soil is deficient in natural energy. After
incubation, the supernatant is filtered (the same as for ground water)
into sulfamic acid reagent. The ground water procedure and the soil in-
cubation method permit such variables as pH and soil type to be ignored
because the tests measure only the soluble iron in solution which would
be available for ochre formation. If certain terrain features are known,
the test results are helpful in estimating whether ferrous iron is
flowing in from surrounding areas or escarpments and whether the
potential ochre problems may be permanent or temporary. The most
information can be obtained when the ground water method and soil

method are used together. For example, ground water readings higher
than soil incubated "water only" readings usually indicate that the fer-
rous iron in the profile is coming from a different depth zone or the field
has been flooded for a long period.
One of the more promising possibilities for the soil incubation method
may be for rating soil types that have been collected by soil survey
teams. In Florida, soils stored for 3 to 5 years still contained iron reduc-
ing bacteria. The soils were suitable for estimating ochre potential for
individual soil types. There are limitations to such a broad-based
system, but the results could serve as an initial point of reference.
There are certain on-site observations that may give clues to poten-
tial ochre formation in advance of drainage. Surface water in canals
may contain an oil-like film that is usually iron and may contain Lep-
tothrix bacterial filaments. Gelatinous ochre may form on the ditch
banks or bottoms of canals. Ochre may also form layers in the soil pro-
file. In some locations, there may be iron concretions or so-called iron
rocks. The presence of spodic horizons (organic layers) suggest ochre
potential, and most organic soils, such as mucks, have some potential
for ochre problems.

Measures to Minimize Drain Clogging
There is no known economical, long-term method for effectively con-
trolling ochre clogging in drains having serious ochre potential.
Although options are limited, the emphasis must be on "living with the
problem." It is necessary to follow certain practices to minimize the
1. Precipitating iron in the soil by promoting oxidation. All measures
that minimize the development of anaerobic flooded conditions are
acceptable. Closer spacings and shallower depths of drains may, for
certain sites, be beneficial. The fundamental point is that iron cannot
flow in the ground water until it is reduced. Soil aeration prevents
reduction. A number of methods have been tried and recommended for
soil aeration, but they have limitations. If soil type and soil moisture
permit, immature soils containing high levels of ferrous iron could
either be predrained with mole drains or by trench drains. The method
can be used only on sites that have temporary clogging hazard and clay
contents of about 30%. It is quite possible that iron precipitated in the
soil could, under reducing conditions, become soluble again. There are
recommendations in Germany for deep ground breaking with suitable
plows, use of a two-stage drain system with one drain on a different
level than the first drain, and preliminary drainage with open trenches
for 2 to 3 years.

2. Surface liming. This has been suggested to immobilize iron. In
addition to atmospheric oxygen, calcium also promotes oxidation. In
theory, this method should reduce ochre by precipitating iron in the
soil, but it has not worked well in practice. In one experimental site in
Florida, liming served only to increase the formation of ochre by raising
the drain depth soil pH from 4.2 to 6.0. The drain zone at pH 6.0 proved
to be a desirable range for bacterial activity. Tb obtain any reasonable
degree of success, the lime application must be considerably higher
than for normal agricultural use. The lime must change the pH in the
entire soil profile all the way down to drain depth, and liming must be
undertaken as a long-term project. There are data from Germany that
such high lime applications could reduce the water conductivity of the
soil profile an undesirable reaction.
3. Liming the drain trench. The purpose here is to precipitate iron
and prevent ochre formation in drains. It was found to be unsatisfactory
in Germany. Iron in combination with lime in the trench decreased
permeability, which defeated the purpose of a permeable backfill in a
drain trench.
In 1961, slag gravel from the production of elemental phosphorus was
used as an envelope for drains in Florida. The system eventually failed
because the slag disintegrated and formed a seal around the drain.
Lime rock will do the same thing. A similar reaction occurred in Ger-
many with the use of copper slag, but because of the bactericidal action
of copper, the blockage from slag took about 8 years.
4. Drain envelopes. A drain envelope or filter is necessary for sandy
soils. A graded gravel envelope is best, although it can become clogged
under conditions of severe ochre potential. Gravel has been used for
many years, but it is no longer cost effective in some regions. Thin syn-
thetic fabrics are now used extensively in humid areas of the United
States and in locations not subject to clogging from ochre and associated
slimes. The principal materials being installed at present are spun
bonded nylon, spun bonded polypropylene, and a knitted sock. The
materials have been evaluated for ochre clogging under laboratory con-
ditions and the knitted polyester material showed the least clogging in
all studies involving drain configurations in the bottoms of plexiglas
chambers. Surveys of selected drainage sites show that ochre clogging
with the synthetic materials seem to occur first in the slots and valleys
(the space between the envelope and slots) and can be present in
amounts sufficient to cause drain failure. The spun bonded fabrics also
clog from ochre deposits in which the iron precipitating bacteria grow
across the voids in the fabrics. The sock resisted the membrane clogging
action but not the clogging of the valleys and slots. This could be a
potential problem in sites rated severe for ochre.

5. Size ofthe entry holes in drain tubes. There are data from Germany
to indicate that the larger the openings in the drains the longer the
period before drain outflow may be severely restricted. Observations in
the United States suggest ochre adheres to the frayed plastic edges
abutting the water inlet slots. Cleanly cut inlet slots are essential.
Small slots also limit the effectiveness of jet rinsing as a method for
cleaning drains installed with synthetic envelopes. Care must be taken
to insure that the size of the opening or slot is compatible with graded
gravel envelopes or base soil.
6. Copper placed in filter envelopes. This has been used with some
success in Germany; the results have not been very successful in
Florida. In one experiment, the copper sulfate reacted with hydrogen
sulfide, forming black insoluble copper sulfide.
7. Copper dumped directly into drains. At the upper end, this will
keep the drain free of visible ochre with 3 ppm soluble copper in the line
provided the pH of the water is less than 7.0. The amount and frequency
of treatment may cause a pollution problem.
8. Self-cleaning grades. These have not worked well in Florida
studies. Reports from other countries claim that the grade must be at
least 0.5% to have any effect. The only significant effect could be
washing out the growths inside the tubes.
9. Bactericides incorporated into the pipe during manufacture. In
theory, this would be an excellent method if thin coatings of ochre
would not prevent release of the biocide. The method would be of benefit
at sites that have temporary ochre potential, where 6 months of protec-
tion immediately after drain installation might be all that is necessary.

10. Submerged outlet. This is an old recommendation that has been
used with some success when the entire drain is permanently under
water. There are limitations. The line must be completely under water
over its entire length throughout the year. This could require that the
drains be on flat grade. The depth of ground water coverage must be at
least one foot, and there are unpublished data from California
indicating coverage had to be almost 4 feet. Ochre can form if the lines
should become aerated for even a short period of time.
11. Organic envelope materials. Pine and oak sawdust delayed ochre
development at drain inlet openings for extended periods in Florida;
however, pine sawdust eventually disintegrated at several sites sub-
jected to alternate wetting and drying. Early studies with cypress
sawdust indicated favorable action against ochre problems, and the
cypress wood did not disintegrate. Unfortunately, cypress and oak
sawdust may no longer be available in quantity. The sawdust created

an anaerobic environment and may have been somewhat toxic to the
ochre enhancing bacteria. The sawdust also contained aromatic
hydroxyl compounds that completed iron. The use for envelopes ofmost
types of peat and muck that are available in the United States should be
avoided. They can increase ochre problems and enhance clogging.
12. Iron complexes that have some bacterial inhibiting activity. Tan-
nins from Turkish oak and the Mimosa shrub will combine with iron to
form ink (iron tannate), which is a black colloidal material. The inklike
substance will flow from the drain as a black deposit. Iron bacteria are
inhibited when concentrations of tannins are above 10 ppm. It is
extremely difficult to control tannin concentrations, since the chips
containing tannins are spread through the factory-wrapped straw or
cocofiber filter. Tannins can affect fish populations and the black
discolorations of the ditch water have caused pollution problems by
exceeding the permissible limits for tannins in water. There are
no sources of the factory-wrapped material in the United States. The
use of a complex that has bacterial inhibition is an excellent approach,
but unfortunately no other materials have been found to take the place
of tannins.
13. Ochre removal from drains. The use of high and low pressure
water jetting has been successful in cleaning many drains clogged with
ochre. Most of the commercial cleaning has been on drains installed in
gravel envelopes. Pressures as high as 1300 psi at the pump have been
used. There are data from the Netherlands that the pressure at the noz-
zle should not exceed 400 psi in sandy soils, otherwise sand around the
drains may destabilize and flow into the drain. Only limited data are
available for jetting drains wrapped with synthetic envelopes and
installed in sandy soils. As previously indicated, the principal problem
with the synthetic envelope method is the growth of ochre in the valleys
and slots of the corrugated tubing. The jetting water must pass through
the slots and be deflected by the envelope in order to clean the valleys.
The larger the slots or openings the better the potential for cleaning the
valleys and envelope. Valleys were cleaned at 100 psi at the nozzle
when the drain openings were holes rather than slots. Short, narrow
slots (1/16" x 9/16") with a sock envelope restricted cleaning of the
valleys at 400 psi at the nozzle. Only about 30% of the ochre was re-
moved from the valleys of the corrugations, although the inside of the
drains were cleaned. The sock was not damaged at 400 psi, and sand did
not enter the drain. It was concluded that many older installations may
be unsatisfactory for jet rinsing because of small slot sizes. Jetting
nozzles should be designed for agricultural drains rather than
municipal sewer lines.

Jet cleaning has also been unsatisfactory if delayed until the ochre
has aged and become crystalline. Pressure requirements will exceed
the 400 psi at the nozzle, which is suggested as the upper limit for sandy
soils and synthetic envelopes until further data are available.
A second method for cleaning drains involves an acid solution to
dissolve the iron. The method cannot be used with synthetic envelopes.
Sulfur dioxide mixed with water forms sulfurous acid. A 2% solution in
drain lines containing less than 5% organic matter will usually remove
the ochre. Up to 7% sulfur dioxide gas may be required if the organic
content is high, since the acid does not remove the organic matrix
easily. Sulfur dioxide is a pollutant and can kill fish unless neutralized.
The acid method was used extensively in southern California but has
been superseded by jet rinsing.
Hydrochloric, sulfuric, and sulfamic acids have been used, but the
outflow after treatment must be neutralized to prevent pollution. None
of the acids should be used on synthetic envelopes.
14. Installation procedures that may minimize ochre problems for
shallow type drains in humid areas.
Drains should not be installed below the water table. If possible,
the soil should be dry.
Drains should open into ditches rather than through collector
systems. A small area in a field may be ochreous, so that the
trouble could be confined to a single drain. Cleaning is also easier
for single drains.
Clogging in the zone abutting the envelope is more severe shortly
after drain installation. The best method would be to jet the drains
during the first year rather than wait until the drains are clogged.
Vents at the upper ends of lines have been used as ports to pour
large quantities of water into the drains for flushing action,
although this method would not help clean the valleys of the cor-
Shallow drains and closely spaced drains that flow infrequently
are not as troublesome, even though the site may be rated serious
for ochre potential.
Drains in marl soils usually have fewer problems, unless the
drains are installed deep in the soil profile.
Avoid blinding the drain with top soil or organic materials (except
sawdust). Oak and pine sawdust, either for "blinding" applica-
tions or full envelopes, may delay ochre formation in drain inlet
openings for extended periods.

* Herringbone or similar drain designs should have entry ports for
jet rinsing.
Use drain tubing with the largest slots or holes allowed within the
limits of national drain tubing standards. Slots or holes should be
cleanly cut and without fragments of plastic on which ochre can
adhere. It should be noted that both smooth bore and corrugated
pipes can accumulate ochre. Published reports from Germany sug-
gest that certain plastics may contribute to ochre formation by
completing iron on surfaces of the pipes, but no recent confirma-
tion tests have been conducted.

References/Further Reading
1. Ford, H. W. 1979. The complex nature of ochre. Kulturtechnik and
Flurbereinigung 20: 226-232.
2. Ford, H. W. 1979. Characteristics of slimes and ochre in drainage
and irrigation systems. TRANSACTIONS of the ASAE 22(5):
3. Ford, H. W. 1982. Biological clogging of drain envelopes. Proc. 2nd
Int. Drainage Workshop 1: 215-220.
4. Ford, H. W. 1982. Estimating the potential for ochre clogging before
installing drains. TRANSACTIONS of the ASAE 25(6): 1597-1600.
5. Kuntze, Herbert. 1982. Iron clogging in soils and pipes analysis
and treatment. Pitman Publishing Inc., 1020 Plain Street,
Marshfield, MA.

This publication was promulgated at a cost of $851.50, or 34 cents per
copy, to disseminate information on ochre and sludge deposits to growers,
extension agents and researchers in the fruit industry of Florida. 9-2.5M-85

Tefertller, director, In cooperation with the United States Department I
of Agriculture, publishes this information to further the purpose of the
May 8 and June 30, 1914 Acts of Congress; and Is authorized to pro-
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