United States Office of EPA
Environmental Protection Drinking Water 570/9-78-005
Agency
Water
svEPA Executive Summary
of the Report
"Surface Impoundments
and Their Effects on
Ground-Water Quality
in the United States
—A Preliminary Survey"
June 1978
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EPA 57C/9-78-005
EXECUTIVE SUMMARY OF THE REPORT
"SURFACE IMPOUNDMENTS AND THEIR EFFECTS ON GROUND-WATER
QUALITY IN THE UNITED STATES—A PRELIMINARY SURVEY"
PREPARED FOR THE
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF DRINKING WATER
STATE PROGRAMS DIVISION
GROUND WATER PROTECTION BRANCH
by
Geraghty & Miller, Inc.
TAMPA, FLORIDA
EPA Project Officer
Ted L. Swearingen
June 1978
U
0 Fr,,:^..nrv,<.-! ruction Agency
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CONTENTS
Page
INTRODUCTION 1
PHYSICAL AND OPERATIONAL FEATURES OF IMPOUNDMENTS 2
Types, Uses, and Construction 2
Selected Impoundment Practices 3
NUMBERS OF IMPOUNDMENT SITES AND FLOW DATA 6
Sources of Data 6
Preliminary Impoundment Count 7
CHEMICAL CONTENTS OF IMPOUNDED WASTES 9
Character of the Wastes 9
Relation to Ground-Water Quality 10
PATTERNS OF GROUND-WATER CONTAMINATION AND CASE HISTORIES ... 11
General Nature of the Contamination Threat 11
Patterns of Contamination 11
Evidence of Contamination from Case Histories 1^
TECHNOLOGICAL CONTROLS 15
Contamination-Prevention Techniques 15
STATE REGULATORY CONTROLS 23
Agency Organization and Operation 23
Technical Design Criteria 25
SUMMARY OF FINDINGS 28
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CONTENTS (Continued)
Figure 1 Block Diagram (A) Showing the Aquifer System
and Areal Extent of Plume of Plating Wastes
in South Farmingdale, Nassau County, N. Y.,
and Downgradient Section (B) Showing Vertical
Distribution of Hexavalent Chromium Content
In 1962 13
Table 1 Summary of the Numbers of Impoundment Sites,
by Major Categories and States 8
i i
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INTRODUCTION
During the period October 1976 to April 1978, EPA (U.S. Environmental
Protection Agency) completed an investigation of the potential impact on
underground drinking water sources of a variety of surface impoundments
that are used for the treatment, storage, or disposal of wastes. These
impoundments are commonly referred to as "ponds, pools, lagoons, and
pits." The investigation was made as part of EPA's responsibility for
controlling subsurface emplacement of wastes as mandated by the Safe
Drinking Water Act [P.L. 93-523, Section 1442(a)(8)(c)]. The principal
objective of the investigation was to compile preliminary background
information, on a State-by-State basis, on the number of surface impound-
ments, composition of the impounded wastes, mechanisms of ground-water
contamination, selected case histories, remedial actions and costs, and
existing State regulations. The information was obtained mainly through
literature review and through visits, correspondence, and telephone
contacts with Federal and State agencies; no field studies or field
counts of impoundments were made. Among the limitations in conducting
the study were the scantiness of readily available data from central
sources and a lack of uniformity among the States in compiling infor-
mation on impoundments.
The data contained herein have been summarized from the final report of
the investigation entitled "Surface Impoundments and Their Effects on
Ground-Water Quality in the United States—A Preliminary Survey." This
report was prepared for the EPA, Office of Drinking Water (formerly
Office of Water Supply), by Geraghty & Miller, Inc., Consulting Geologists
and Hydrologists, with assistance from Arthur D. Little, Inc., Consultants,
who supplied material on the chemical content of wastes and remedial
actions and costs. The above report can be obtained from EPA, Office of
Drinking Water, 401 M Street, S.W., Washington, D.C., 20460. In addition
to this study, EPA has recently completed or is presently sponsoring a
number of studies containing information on surface impoundments, including
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an evaluation of techniques for managing and monitoring hazardous-waste
facilities, regional studies of ground-water contamination, effects of
waste-disposal practices, and an assessment of the effects of surface
impoundments by the States themselves.
PHYSICAL AND OPERATIONAL FEATURES OF IMPOUNDMENTS
TYPES, USES, AND CONSTRUCTION
Waste impoundments may be natural or man-made depressions, may be lined
or unlined, and may range in area from a few tenths of an acre to hundreds
of acres. Generally, impoundments are excavated to relatively shallow
depths above the water table, and some may be built on the land surface
by construction of dikes or revetments. Most impoundments are rectan-
gular or square; some are circular or irregular. Impoundments may be
operated individually or may be interconnected, with flow taking place
from one impoundment to another in series or in parallel. Many impound-
ments discharge, either continuously or periodically, to streams,
lakes, bays, or the ocean; these are called "discharging" impoundments.
Others lose their fluid contents by evaporation or infiltration; these
are called "non-discharging" impoundments.
Some impoundments are designed specifically to permit seepage of fluids
into underlying earth materials and are commonly referred to as perco-
lation, infiltration, or seepage ponds or lagoons. Others, designed to
be watertight, are lined with clay, asphalt, metal, or synthetic membranes
or are sited on clayey soils having a very low permeability. Some
unlined impoundments are thought to be "self-sealing" as a result of
deposition or precipitation of fine-grained materials. Treatment ac-
complished in impoundments includes reduction in temperature of cooling
water, pH adjustment, chemical coagulation and precipitation, and
biological oxidation.
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The term "pit" is usually applied to a small impoundment that serves a
special purpose. For example, pits may be used on farms as storage and
curing facilities for animal wastes. In industry, they may be used to
discharge highly treated wastewater into the ground. Most pits used for
permanent storage of toxic wastes are lined. Many abandoned sand and
gravel pits or rock-quarry pits are used to dispose of septic-tank
wastes and municipal and industrial sludges.
Factors influencing the potential for ground-water contamination by
seepage from unlined surface impoundments include soil permeability,
depth to the water table, rates of precipitation and evaporation, nature
and volume of wastes, and geochemical characteristics of the soils. The
chemical composition of the wastes, especially those consisting of toxic
or hazardous substances, is also an important factor in evaluating the
potential for ground-water contamination.
SELECTED IMPOUNDMENT PRACTICES
Domestic Sewage Wastes
Domestic sewage wastes, generally defined as wastes of predominantly
human origin, are commonly collected, treated, and disposed of by com-
munity waste-handling systems owned by municipalities, towns, and
subdivisions; institutions such as schools, parks, hospitals, and jails;
and commercial establishments such as motels, restaurants, gas stations,
and mobile home parks. Treatment systems for domestic sewage range in
size from small units handling about 20,000 gpd (gallons per day) to
larger units handling about 200 mgd (million gallons per day) or more.
Lagoons or ponds are used as minor or major components of such systems.
For example, oxidation or waste-stablization ponds and lagoons are the
principal waste-treatment units in over 4,000 communities, 90 percent of
which have less than 5,000 residents.
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Sludge from community waste-treatment systems is treated and disposed of
by several methods, including drying in shallow rectangular impoundments
that have permeable sand bottoms and are constructed with or without
underdrains for Jeachate control. In some waste-treatment systems, the
partly dehydrated sludge is disposed of in unlined storage lagoons;
after being filled, these lagoons are covered and abandoned.
Industrial Wastes
Industry employs a wide variety of practices in treating and disposing
of waste fluids and sludge, including discharge into ponds for storage,
evaporation, recycling, or infiltration. Stabilization ponds are one of
the major waste-treatment systems used by industries because industrial
wastes are highly variable in composition and may require blending with
other fluids. Industrial sludge with or without pretreatment and di-
gestion may be stored in impoundments before disposal in landfills or
spreading on the land.
Large volumes of cooling water, mainly from power plants, may be stored
in very large cooling ponds and then ultimately discharged to streams or
recycled through the plants. Ail—scrubber wastes and cooling-tower
blowdown may be discharged to streams with or without treatment or may
be discharged to lagoons for treatment and retention. Settling ponds
are commonly used to handle ash residues from coal-burning utilities.
Filter backwash and sludge from municipal water-treatment plants are
commonly classified as industrial wastes and generally require treatment
before disposal to streams or ponds. The metal smelting and refining
industry uses predominantly unlined settling pits and basins for handling
waste and scrubber waters.
Oil and Gas Extraction Wastes
The oil and gas extraction industry is believed to be one of the largest,
if not the largest, user of surface impoundments in the United States.
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Oil and gas is produced commercially in 31 States; Texas, Oklahoma,
Louisiana, California, Wyoming, and Alaska are among the leading pro-
ducers. The number of impoundments differs from State to State, not
only in proportion to the production of oil and gas, but also in
relation to methods of extraction such as water flooding for secondary
recovery.
"Evaporation" ponds formerly were used extensively in Oklahoma, Texas,
and elsewhere for disposal of brine and salt water associated with oil
and gas extraction. Most of these impoundments were unlined; conse-
quently, large quantities of salty water were lost not only by evapo-
ration but also by seepage into underlying permeable shallow aquifers.
Numerous incidents of brine contamination of wells and streams resulted
from the use of these disposal methods in Texas and other States.
However, earthen ponds excavated in clay, or lined with clay or other
material of low permeability, are permitted by a number of States for
evaporation of brine and for emergency uses.
Animal Feedlot and Other Agricultural Wastes
The principal potential mechanism for contamination of ground water from
feedlot operations is seepage of contaminated water from lagoons that
compose parts of waste-disposal systems. Virtually every State has some
concentrated anima1-feeding facilities for cattle, sheep, hogs, or
poultry. Several hundred thousand animal-feeding operations of all
types and sizes generate on the order of several billion tons of wastes
per year.
Among the types of impoundments used in agricultural waste-disposal
systems are debris basins, disposal lagoons, aerated lagoons, holding
ponds, and storage lagoons. Debris basins are used to collect solids in
runoff from pens and lots; they commonly precede a holding pond. Holding
ponds are used to store the liquid part of runoff and animal wastes;
they are generally designed to be leakproof and to have sufficient
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capacity to prevent overflow except during severe storms or other
emergencies. Lagoons are designed and operated to encourage biological
decomposition of organic wastes; the effluent may be disposed of by
evaporation or by land spreading. Lagoons are also used to store manure
temporarily or permanently.
NUMBERS OF IMPOUNDMENT SITES AND FLOW DATA
SOURCES OF DATA
The principal regulatory agencies in all States were contacted either by
mail or telephone for readily available data on municipal, industrial,
agricultural, and oil and gas impoundments. Only 19 States provided
computer printouts of industrial or other impoundments that included in-
formation on the name of the facility, Standard Industrial Classification
(SIC) number, type of treatment, and flow. Some States provided copies
of river basin reports that contained data only for impoundment facilities
related to municipal and industrial point-source discharges to streams.
Visits were made to 16 States to consult with State personnel on case
histories of contamination and regulations, to identify impoundment
users from NPDES (National Pollution Discharge Elimination System)
permit lists, and to examine records of non-discharging impoundments.
Because of time and budget limitations, no attempt was made to visit all
States or to make a thorough review of the files of the States visited.
Impoundment inventory data from Federal sources consisted mainly of an
EPA printout of municipal waste facilities on a State-by-State basis,
showing type of treatment, flow data, and population served. EPA also
supplied lists of NPDES permitted facilities by State, SIC code number,
and permit number.
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Inquiries were made by telephone and mail to all EPA Regional Offices
for impoundment inventory and case-history data, and visits were made to
several EPA Regional Offices to review NPDES lists and files. Other
Federal sources of data on impoundments included the U.S. Bureau of
Census, U.S. Department of Agriculture, the U.S. Department of Army, and
the U.S. Geological Survey.
PRELIMINARY IMPOUNDMENT COUNT
Table 1 shows the total number of waste-impoundment sites of all types,
by States, for which data were available or could be reasonably estimated,
The minimum estimated total impoundment site count was 132,709*. of
which about 75 percent consisted of industrial waste sites, 15 percent
of agricultural waste sites, and 10 percent of municipal, institutional,
and private/commercial (domestic or sanitary waste) sites. New Mexico
led all other States in the number of waste impoundment sites, with a
total of about 16,200; Rhode Island had the smallest count—an estimated
total of 30.
The total number of municipal impoundment sites was about 6,300, and the
minimum total flow from these sites was about k.2 bgd (billion gallons
per day). About 27,800 general industrial sites had a minimum total
flow of about 27-3 bgd. The total industrial flow figure, which is
heavily weighted by a large amount of cooling-pond water for power
plants, is incomplete due to scanty data.
The number of impoundment sites at institutional facilities such as
jails, hospitals, schools, and public buildings totalled about 1,500
with the highest number, 150, in Florida. Impoundment sites at private/
The actual number of impoundments most likely is several times greater
than the total site count; the national average is estimated to be 2 to
3 impoundments per site.
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Table 1. SUMMARY OF THE NUMBERS OF IMPOUNDMENT SITES,
BY MAJOR CATEGORIES AND STATES
State
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
Muni-
cipal
156
6
52
180
245
137
11
4
118
195
5
76
413
183
257
256
29
81
3
53
5
142
235
283
332
130
223
23
8
9
38
33
147
250
88
260
104
51
2
255
192
58
379
38
12
90
91
48
223
64
6,273
Private-
Commercial
130
-
63
50
560
125
-
10
1,200
225
5
20
100
117
245
64
26
150
10
20
15
93
54
129
1,092
20
15
50
10
20
28
100
81
10
100
50
28
41
10
191
10
30
358
8*
9
51
16
83
50
15
5,887
Institu-
tional
50
-
55
10
118
10
-
3
150
79
5
10
50
62
54
14
6
50
5
18
5
3
14
49
50
8
8
10
2
5
2
50
25
5
50
15
10
90
5
58
5
34
142
4*
2*
77
11
6
11
5
1,510
tndus-
trial
583
100
44
66
782
103
48
33
217
205
29
24
445
357
210
164
944
552
44
321
40
279
52
266
213
64
1,180
110
41
230
63
308
282
76
1,460
354
88
12,300
12
81
34
215
1,042
68
244
1,409
255
1,631
103
73
27,844
Oil & Gas
Extraction
2
9
6
540
910
4,617
-
-
0
-
-
-
2,000
752
-
4,525
1,000
8,841
-
-
-
2,020
-
363
6
825
200
15
-
-
16,000
265
-
1,900
11,000
989
-
2,500
-
-
30
100*
6,000
317
0
100
-
1,000
-
5,000
71,832
Agricul-
tural
669
15
112
107
1,106
245
37
13
350
734
34
454
659
1,067
700
1,063
136
323
175
111
8
692
1,185
586
1,064
316
703
53
44
13
45
204
503
543
498
338
527
359
1
326
379
339
515
234
62
389
672
35
598
22
19,363
Total
1,590
130
332
953
3,721
5,237
96
63
2,035
1,438
78
584
3,667
2,538
1,466
6,086
2,141
9,997
237
523
73
3,229
1,540
1,676
2,757
1,363
2,329
261
105
277
16,176
960
1,038
2,784
13,196
2,006
757
15,341
30
911
650
776
8,436
669
329
2,116
1,045
2,803
985
5,179
132,709
Probably incomplete.
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commercial facilities, such as camps, hotels, motels, restaurants, gas
stations, and mobile home sites, totalled about 5,900, with the highest
number, 1,200, in Florida. Agricultural impoundment sites, mostly at
feedlots, totalled about 19,^00, with the highest number, 1,185, in
Minnesota.
The total number of oil and gas impoundments is about 71,800; the
highest estimated total by an individual State is 16,000 in New Mexico.
Oil and gas impoundments are used principally for emergency purposes,
such as temporary storage of salt water or petroleum. Other uses are
brine disposal and separation of water, oil, and gas. Burn pits and
cuttings or mud pits were not included in the count; if these had been
included, the total number of oil and gas impoundments most likely would
have been increased by some tens of thousands.
CHEMICAL CONTENTS OF IMPOUNDED WASTES
CHARACTER OF THE WASTES
Impounded wastes may be liquid, semi-solid, or solid and may range from
harmless to highly toxic, depending on the nature and concentration of
the const!tutents. The wastes may be classified according to source as
industrial and domestic (includes municipal, commercial, and institu-
tional). From a chemical viewpoint, the wastes entering impoundments
are composed of inorganic or organic substances or a combination of the
two.
Inorganic industrial waste streams are generally characterized in terms
of suspended solids, TDS (total dissolved solids), pH, acidity or alka-
linity, and specific cations and anions, including heavy metals that
form part of a chemical process or product. Treatment is generally
physicochemical in nature with separation of suspended solids by the use
of settling ponds, clarifiers and thickeners, filters, centrifuges, and
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coagulation tanks. Dissolved solids can be removed by precipitation,
ion exchange, and reverse osmosis or can be neutralized or oxidized.
The parameters that are commonly used to characterize organic industrial
waste streams are BOD (biochemical oxygen demand), COD (chemical oxygen
demand), TOC (total organic carbon), oil and grease, and suspended
solids. Other potential contaminants in industrial waste streams are
miscellaneous organic chemicals, including phenols, cyanide, and
chlorinated hydrocarbons.
Domestic sewage effluent has a high IDS content, various nitrogen com-
pounds, phosphate, sulfate, chloride, BOD, and coliform bacteria. Most
of these are natural constituents of human wastes. Locally, detergents,
phosphate, heavy metals, and other compounds derived from man's activ-
ities are also present in sewage. Some municipal sewage consists of a
mixture of domestic and industrial wastes. Sludge from sewage-treatment
plants commonly contains heavy metals as well as pathogenic organisms.
Leaching of organic substances, nitrate, and other constituents from
sewage sludge placed on unlined drying beds or in lagoons is a potential
cause of ground-water contamination.
RELATION TO GROUND-WATER QUALITY
Except for a few constituents derived from or adsorbed on aquifer
materials during movement of fluids into and through an aquifer, con-
taminated ground water beneath and near many impoundments, as shown by
case-history studies, commonly reflects the approximate character of the
source fluids in impoundments. Knowledge of the composition of the
impounded waste fluids, therefore, can provide a basis for predicting or
explaining the composition of ground water that may be contaminated by
seepage of waste fluids from impoundments,.
Most of the dissolved inorganic and organic constitutents in waste
fluids can move readily into ground water by direct seepage of the
fluids through the sides and bottoms of unlined impoundments. Similarly,
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solids in impoundments may be leached by precipitation or by inflow of
other fluids, and following dissolution, the leachate may seep into
ground water. Although such factors as pH, sorptive capacity, and the
low permeability of some soils may slow down or impede the movement of
selected ions, many waterborne contaminants, given an adequate source of
supply, sufficient time, and a hydraulic gradient, have the potential
for eventually reaching the water table and moving downgradient in an
aqui fer.
PATTERNS OF GROUND-WATER CONTAMINATION AND CASE HISTORIES
GENERAL NATURE OF THE CONTAMINATION THREAT
A large majority of the surface impoundments in the nation are unlined;
consequently, waste fluids that seep down from them constitute a poten-
tial threat to the natural chemical quality of underground drinking-
water sources, public supply and private water wells, and surface water.
Only a very small percentage of these impoundments are monitored routinely
or have been investigated in sufficient detail to show the full nature
and extent of the contamination threat, but enough case histories have
been compiled to indicate that the potential threat could be widespread.
Many impoundments are considered to be virtually watertight, either be-
cause of excavation in relatively impermeable natural materials such as
clay and silt or the use of liners. Some impoundments are thought to be
"self-sealing" and generally present no significant threat to water
quality unless the watertight seal is ruptured accidentally or the
impoundment overflows.
PATTERNS OF CONTAMINATION
Patterns of contamination of ground water resulting from seepage of
wastes from surface impoundments have some common features. Contaminated
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fluid first seeps out through the bottom or sides of the impoundment
under the influence of gravity or hydraulic head differences and then
moves slowly downward until it reaches the water table. In beds of
extremely low permeability, the fluid may move only a fraction of an
inch over a long period of time, but in more permeable materials, the
fluid may move at rates of up to several feet per day or more.
Although the concentrations of constituents in wastewater are altered by
various physical, chemical, and biological reactions during passage
through the unsaturated zone, most dissolved constituents have the po-
tential for entering the underlying saturated zone of the aquifer,
especially where the sorptive capacity of the soils is exhausted by con-
tinuous seepage of contaminated fluids. Upon reaching the water table,
the pattern of flow and the chemical character of the contaminated
fluids are influenced by various mechanisms, such as hydraulic head
differences, vertical and horizontal permeabilities, attentuation pro-
cesses, nature of the soils, precipitation, density differences, and
other hydrogeologic or geochemical factors.
Generally, the contaminated water seeping into an aquifer from an im-
poundment assumes the form of a discrete body or plume of contamination.
The plume is elongated in the direction of ground-water movement and is
usually at least several times longer than it is wide. The boundaries
of a plume, which are marked by a zone of dispersion or zone of mixed
waters, may be relatively smooth or irregular. Figure 1 shows a plan
view and a cross section of an actual plume of metal-plating wastes in
Long Island, New York, that contains hexavalent chromium and other heavy
metals. The plume, which is now about 1 mile long and 750 feet wide,
began developing beneath a cluster of unlined leaky disposal basins in
19^*1 and is moving very slowly downgradient in a shallow unconfined
aquifer. Chromium and cadmium determined in samples from a nearby
stream indicate that the contaminated ground water is seeping laterally
and upward into the stream.
12
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(A)
DISPOSAL
•*-
ASINS
SOUTH FARMINGDALE
INDUSTRIAL AREA
PLATIN8-WASTE
EFFLUENT
DIRECTION OF GROUND-WATER
FLOW
A A' LINE OF SECTION SHOWN
ON FIGURE IB
(B)
A
60'-
40'-
20-
SEA
20'-
WATER TABLE
UPPER GLACIAL AQUIFER
SEE LINE OF SECTION ON FIGURE IA
EXPLANATION
— 5— CHROMIUM CONTENT.IN MG/L
ZOO
500
400
8OO FT.
100 METRES
Figure 1. Block diagram (A) showing the aquifer system and areal extent of
plume of plating wastes in South Farmingdale, Nassau County, N. Y., and
downgradient section (B) showing vertical distribution of hexavalent chromium
content in 1962. (After Perlmutter, N. M., and Lieber, M., 1970, U.S.
Geological Survey Water Supply Paper 1879G)
13
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Plumes tend to become longer, wider, and thicker as contaminated fluids
continue to seep from source impoundments and move downgradient. In
places, the leading edge of a plume may be stabilized at a discharge
boundary such as a stream or a line of pumping wells.
Contaminants in ground water can be removed or reduced in concentration
by attenuation. Attenuation mechanisms include sorption, ion exchange,
dispersion, and radioactive decay. The rate of attenuation is a function
of the types of contaminants and of the characteristics of the local
hydrogeologic framework. Predicting the degree to which contaminants
may become attenuated is extremely difficult because of wide differences
in the chemical properties of contaminants, in soil properties, and in
the hydrologic environment from place to place. Despite the potential
for attenuation of wastes, case-history data show that plumes originating
by seepage from impoundments can extend downgradient thousands of feet
in highly permeable aquifers, especially those composed of sand, gravel,
and 1imestone.
EVIDENCE OF CONTAMINATION FROM CASE HISTORIES
About 85 case histories in 29 States, selected from an estimated several
hundred to potentially thousands of cases of ground-water and/or surface-
water contamination associated with leaky impoundments, are summarized in
the main report of this investigation. Most of the data were summarized
from reports published by EPA and from various scientific, technical,
and trade journals; data on a small number of cases were obtained
directly from some State agencies by mail or during visits. The cases
examined were selected at random and were not intended to indicate
either the actual or relative magnitude of the contamination problem in
any particular industry or State. A number of States such as California,
Texas, and Pennsylvania, which have large staffs and stringent controls,
have numerous case histories in their files; whereas other States, with
small investigatory and enforcement programs, reported few or no contami-
nation incidents from waste impoundments.
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The case-history data indicate a general prevalence of contamination
problems in the industrial eastern and north-central regions of the
United States and also in other scattered areas, particularly in some
western and southwestern States where mining and oil and gas extraction
are major industries. In addition to these industries, the case histories
cover a wide range of other industries, including: timber, pharmaceu-
ticals, steel mills, paper mills, metal plating, meat processing, and
one national research laboratory where impoundments are used to dispose
of chemical and radioactive wastes. Among the contaminants reported in
ground water and/or surface water near impoundments that seep are
chloride, sulfate, phosphate, nitrate, ammonia, arsenic, chromium,
cadmium, fluoride, zinc, nickel, selenium, molybdenum, pesticides,
herbicides, phenols, tannic acid, other miscellaneous inorganic and
organics, and radionuclides such as tritium, cobalt-60, and strontium-90.
TECHNOLOGICAL CONTROLS
CONTAMI NAT ION-PREVENTI ON TECHNIQUES
Direct Methods
A number of direct methods are available that will prevent contaminated
fluids in an impoundment from coming into contact with uncontaminated
ground water. Some of these methods are applicable only during the
construction of new impoundments, and others may be applied to new or
existing impoundments. Although many variations and combinations of
these techniques are potentially applicable, it is believed that the
techniques summarized below cover the range of currently available
technology for preventing or controlling ground-water contamination from
impoundments.
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Alternative 1 - Installation of Impermeable Membrane
One of the commonly used methods for preventing ground-water contamina-
tion from impoundments is the installation of an impermeable membrane on
the bottom and sides of the impoundment. The membranes most commonly
used are made from synthetic materials such as butyl rubber, polyvinyl
chloride, polyethylene, polypropylene, and nylon.
Usually, an impermeable membrane must be installed during the construction
of an impoundment. The only way to install an impermeable membrane in
an existing impoundment is to remove the impounded material, install the
membrane, and then replace the material on top of the membrane--a pro-
cedure that can be exceedingly difficult, costly, and environmentally
risky. If the principal function of an impoundment is the treatment of
wastewater, it may be possible to drain the impoundment and to install a
membrane. If the installation delays production or if it requires un-
scheduled plant shutdowns, the resulting costs could make the use of
this alternative economically prohibitive.
Alternative 2 - Installation of a Layer of Impermeable Material
Bentonite clay or local clay of suitable characteristics is used to form
an impermeable layer on the bottom and sides of an impoundment. It is
usually pumped in as a thick slurry and allowed to compact either by
subsidence or by mechanical means. Although clay Is not completely
impermeable, it does have a significant advantage over other membrane
liners in that it generally will not deteriorate with age. Also,
because it is plastic, it tends to be self-sealing if punctured.
As in the case of impermeable membranes, bentonite and other slurry-like
layers are usually installed during the initial construction of an im-
poundment; installation is not feasible in most operating waste impound-
ments because of high costs and physical difficulties.
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Alternative 3 ~ Collection of Contaminated Water Seeping from an
Impoundment
Where Alternatives 1 and 2 are not feasible, prevention or alleviation
of ground-water contamination can be accomplished by collecting the
contaminated water seeping from the impoundment and either returning it
to the impoundment or treating it to remove the objectionable contami-
nants prior to reuse or discharge to a stream or lake.
A number of collection systems can be used to intercept contaminated
ground water near the boundary of an impoundment. The three most commonly
used systems are infiltration galleries, wellpoint systems, and conven-
tional wel1s.
Infiltration Galleries. An infiltration gallery consists of a
gravel-packed trench containing a horizontal perforated pipe along the
trench bottom which connects to a vertical casing and pumping system.
Infiltration galleries may be useful in places where hydrogeologic
conditions make it difficult for standard wells to intercept all the
contaminated ground water.
Wei 1 point Systems. A standard wellpoint system is useful in
dewatering part of an aquifer where the depth to the water table is less
than the suction limit, about 25 feet below the land surface. The
system consists of a line of screened wellpoints connected to riser
pipes, a common header pipe, and a centrifugal pump. Under corrosive
conditions, such as pumping acid ground water or water containing high
concentrations of dissolved salts, polyvinyl chloride (PVC) wellpoints
and headers are used.
Conventional Wells. A series of individual conventional wells can
be used to dewater the ground-water reservoir to any depth, provided
submersible pumps are installed. Each well is drilled at spacings
dependent upon the soil conditions and the corresponding ground-water
17
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flow rates. A cone of depression is formed in the water table at each
pumped well; the series of pumped wells is designed to have overlapping
cones of depression in order to provide a uniform lowering of the water
table. In employing this technique, the water drained from the assembly
of collection points is combined into a single contaminated waste stream
that can be returned to the impoundment or treated prior to discharge.
Alternative 4 - Return of the Collected Water Back to the Impoundment
After collection of contaminated water seeping from an impoundment, as
described in Alternative 3 above, the treated water may be discharged to
a surface stream, recharged into the aquifer, or simply returned to the
impoundment. Although costly and difficult, returning collected water
to an impoundment is an attractive alternative because it may not
require extensive wastewater treatment; however, this technique is
feasible only where it does not cause the level of fluids to rise and
eventually overflow the impoundment.
Alternative 5 ~ Physicochemical Immobilization of Waste Material
A number of proprietary techniques are currently available that are
intended to convert waste slurries, sludges, and other semi liquid
materials into a solid and more chemically stable mass that is less
conducive to leaching. All of these techniques involve some method of
mixing the waste material with an immobilizing agent that can be
composed of either an inorganic cementitious or an organic polymeric
substance.
Inherent in the process is the problem of movement or transfer of material
If the immobilization is performed directly as the waste is generated,
the task is merely one of mixing the waste stream with the immobilizing
agent and depositing it in an appropriate impoundment. If, on the other
hand, the intent is to immobilize the entire body of waste already
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deposited in a large impoundment, the overall task is far more difficult
and costly.
Alternative 6 - Ground-Water Cutoff Wall
A ground-water cutoff wall can be a partial barrier, blocking off the
upstream portion of an impoundment that is built in a narrow channel
bounded by essentially impermeable materials, or it can encircle the
entire impoundment, essentially forming a complete impermeable barrier.
The feasibility of employing a ground-water cutoff wall is largely
dependent on local hydrogeologic conditions, and it is unlikely that
this alternative can be used for many existing impoundments.
Two general types of cutoff walls are: (a) slurry trench cutoffs and
(b) grout cutoffs. Slurry trench cutoffs have been used in dam construc-
tion for about kO years and in construction of underground walls. Wall
depths of as much as 150 feet have been reported. The trench construction
usually involves excavation, filling with bentonite clay slurry, and
backfilling with soil. Grout cutoffs are less commonly used as imperme-
able barriers than slurry trench cutoffs because it is difficult to
insure that a continuous grout curtain is formed. Grouting involves
drilling holes at selected intervals and injecting the grout solution so
that it flows laterally to form a continuous wall.
Alternative 7 ~ Capping of the Impoundment Surface
Capping an impoundment is intended to prevent precipitation from percolating
down through the waste material and eventually reaching the water table.
Capping involves placing an impermeable barrier on top of the wastes.
Depending on the physical features of the impoundment, this type of
barrier can either be an impermeable membrane or a layer of impermeable
material such as bentonite clay. In some places it may be feasible to
immobilize the upper surface of the waste materials in an impoundment by
physicochemical methods.
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Capping is not applicable to impoundments containing fluids because
where a waste is already in a fluid form it is capable of seeping
through the bottom and sides of an impoundment regardless of whether or
not there is a cap over it. Capping is also ineffective in preventing
a rising water table from coming in contact with and dissolving impounded
waste material.
Alternative 8 - Treatment of Contaminated Water
Where it is not possible to prevent the generation of a contaminated
waste stream, and where the wastes cannot be returned to the source
impoundment, then normally the stream must be treated to remove objec-
tionable contaminants before it can be disposed of into the environment.
The type of treatment depends on the overall chemical composition of the
waste, the specific contaminants to be removed, and the required compo-
sition of the treated effluent.
Although literally hundreds of configurations could be generated from
the available types of standard wastewater-treatment and associated
sludge-handling equipment, six basic process modules have been defined
in this study. The modules, used in various combinations, represent by
function the most commonly used types of treatment systems; these are
described briefly as follows:
Equalization. Equalization is the use of a holding basin to damp
out variations in wastewater flow and composition. An equalization
basin is typically installed between the point of collection of the
wastewater and the treatment system proper. Many equalization basins
are mildly agitated to insure proper mixing of the incoming and stored
wastewater.
Biological Treatment. Biological treatment refers to a whole
family of treatment processes designed to remove organic material from
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wastewater by means of biochemical oxidation, using naturally occurring
microorganisms. In biological treatment, the organic content of the
wastes serves as the food source for the microorganisms, which covert
the waste into carbon dioxide, water, and cell mass; these end products
then are readily separated from the wastewater as a sludge.
Activated Carbon Adsorption. Adsorption is a complex surface
phenomenon in which chemical species in solution or colloidal form
preferentially migrate and become attached to the surface of the ad-
sorptive material. Granular activated carbon is the most commonly used
adsorbent in wastewater treatment, primarily due to its pore structure
which provides a very large adsorptive surface. Activated carbon
adsorption is generally used for the removal of organic matter that is
partly or totally refractory to biological treatment and to effect
further removal of organic matter.
Heavy-Meta1s Remova1. Heavy metals in wastewater can either be in
solution or in the form of solid particles. Because of the filtering
action of the soil, the heavy metals of principal concern in ground-water
contamination are those that are in the soluble phase.
A variety of processes are available for removing heavy metals from
wastewater. The most widely used processes are precipitation and
settling. Most heavy metals have very low solubility under alkaline
conditions, and the addition of lime, soda ash, or other alkaline sub-
stances to a wastewater containing heavy metals will cause a large
fraction of the metals to precipitate from solution as complex metal
hydroxides and carbonates.
Conventional solids recirculation clarifiers are generally used for the
settling of the metallic precipitates. The precipitated material is
removed from the clarifier as a wet sludge and usually is subjected to
dewatering prior to ultimate disposal. The disposal of metallic hydrox-
ide and metallic carbonate sludges requires careful consideration
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because a significant amount of these materials can be resolubi1ized
under mildly acidic conditions (pH k to 5) and may cause renewed con-
tamination problems.
Dissolved-Solids Removal. Wastewater contains a wide range in type
and concentration of IDS. Depending on the chemical composition of the
wastewater, some of the dissolved-solids constituents are man-made
contaminants, and others consist mainly of naturally occurring dissolved
inorganic salts. The previously described biological treatment, carbon
adsorption, and heavy-metals removal processes help reduce the overall
IDS content, but generally the objective is to eliminate specific
chemical constituents.
Removal of dissolved solids is usually directed toward wastewater
containing high concentrations (more than 5,000 milligrams per litre)
of inorganic dissolved solids and is exceedingly difficult and expensive
for highly soluble species. Technology similar to desalination techniques
must be employed, and the disposal of the salts eliminated from the
wastewater can be a significant problem.
Indi rect Methods
The following methods can be used in places where a ground-water supply
is already extensively contaminated. These techniques would not be
acceptable generally as a control strategy for the installation of a new
impoundment.
Alternative 9 - Development of a New Source of Water Supply in an
Uncontaminated Area
Even after the source of contamination is removed, it can take many
years for contaminated ground water to be flushed out of an aquifer
naturally. During that period, the users of the contaminated ground
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water may have no other choice than to obtain a supply of water else-
where. Generally, this requires construction of an entirely new water-
supply system consisting of a well field, a water-treatment plant (if
needed), a water-storage reservoir, and water transmission lines.
Alternative 10 - Treatment of Contaminated Ground Water Prior to its Use
In places where the level of ground-water contamination is not prohibi-
tively high, it may be possible to install additional treatment steps at
a water-treatment plant that can make use of the contaminated ground
water by reducing the concentrations of contaminants to acceptable
levels. The type of treatment will, of course, depend on the specific
contaminants that must be removed. It is usually not feasible to treat
highly contaminated water supplies, partly because of the high cost and
partly because of the inability of assuring a continuous supply of water
that meets drinking water standards.
STATE REGULATORY CONTROLS
AGENCY ORGANIZATION AND OPERATION
Regulation of surface impoundments by the States is generally in the
hands of one or more State agencies, depending on the types of impounded
wastes and methods of discharge. In many States, for example, the
Health Department has primary responsibility for the regulation of
municipal waste discharges, whereas some other agency administers
regulations to control industrial waste discharges. Interagency coordi-
nation is often through a policymaking commission or board, composed of
representatives of agencies such as Oil and Gas Boards, Mining Departments,
Water Resources Commissions, Parks Departments, and Agricultural Depart-
ments. Most State agencies responsible for the protection of ground-
water quality have promulgated their regulations largely on the basis of
liberal interpretations of the intent of State law rather than on
specific statutory directives.
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Waste impoundments may be permitted under Federal or State controls or
a combination of both. Twenty-eight States have been authorized by EPA
to administer NPDES permit programs for controlling waste discharges to
navigable waters and their tributaries. States with and without NPDES
authorization commonly operate a State Pollutant Discharge Elimination
System (SPDES) similar to the Federal system. In addition, some type of
permit or certificate of approval is required in many States for operating
various types of non-discharging impoundments such as evaporation or
seepage ponds.
Regulations differ somewhat from State to State with regard to reporting
by operators, agency inspection of facilities, procedures involving
violations of regulations, penalties, and public participation in such
matters as the issuance or denial of permits and the promulgation or
amendment of regulations. The legal procedures for dealing with
violations include: a letter of warning or request to "show cause,"
usually following informal contact with the alleged violator, and
invocation of regulatory requirements for remedial actions, usually in
staged fashion, with a deadline set for final compliance. Violations
may result in fines, or the courts may order imprisonment, a fine, or
both.
Permit requirements for impoundments by State agencies range from highly
detailed to very generalized. Although most States, for example, request
general data such as the location, type of construction, and use of
impoundments, only some States have very detailed requirements concerning
information on the local hydrogeologic environment, complete chemical
analyses and volumes of contaminated fluids entering and leaving impound-
ments, use of linings, monitoring systems including sampling wells,
periodic field inspections, and other specific elements relating to
ground-water quality protection.
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Even in States where the rules and regulations appear to provide some
measure of ground-water protection, the regulatory agencies may be
confronted with workloads far beyond the capacities of their present
staffs; therefore, many are unable to carry out the kinds of investi-
gations that would be needed to properly enforce the regulations or to
document suspected contamination incidents. Moreover, few State agencies
are able to assign staff personnel to work exclusively on surface
impoundments and thereby maintain adequate surveillance over these
faci1i ties.
TECHNICAL DESIGN CRITERIA
Municipal and Industrial Impoundments
Specific design guidelines or requirements for impoundments, by a few
selected States, are summarized below. in many States, however, design
requirements mainly emphasize construction and operational criteria that
have little or no effect in preventing ground-water contamination.
Mi sspuri. The "Guide for the Design of Municipal Waste Stabiliza-
tion Lagoons in Missouri" stipulates that:
"The ability to maintain a satisfactory water level in the
lagoons is one of the most important aspects of design.
Removal of coarse top soil and proper compaction of subsoil
improves the water-holding characteristics of the bottom.
Removal of porous areas, such as gravel or sand pockets, and
replacement with well compacted clay or other suitable
material may be indicated. Where excessive percolation is
anticipated, sealing of the bottom with a clay blanket,
bentonite, asphalt, or other similar mater .ould be given
consideration. A maximum percolation rate of 0.25 inches per
day for the finished lagoon floor is included in the specifi-
cations for construction."
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Tennessee. The "Outline of Engineering Requirements" of the
Department of Public Health calls for: (a) location of wastewater oxi-
dation ponds and lagoons 1,000 feet or more from homes, main roads, and
business establishments; (b) prohibition against the entry of surface
water into the impoundments; (c) a minimum top width of 8 feet for
embankments; (d) preference for circular or square design; (e) 2 feet
of freeboard for ponds of 3 acres or less, and at least 3 feet of free-
board for ponds over 3 acres; and (f) prefilling of the lagoon prior to
operation, and installation of a gage to measure, water levels daily for
several days.
Washington. "Design Guidelines for Water Treatment Plant Solids
Disposal" stipulates with regard to settling ponds that: (a) each
impoundment must provide 1 1/2 hours of detention time at maximum
backwash rate, plus storage space for solids; and (b) sludge entering
dewatering ponds should not consist of more than 8 to 10 percent solids.
Minnesota. Minnesota's "Criteria for Sewage Stabilization Ponds"
specifies that: (a) the permeability of the pond seal must be as low as
possible and in no case should seepage loss through the seal exceed 500
gallons per acre per day; (b) specifications for siting and construction
are based upon a testing program; (c) an approved system of ground-water
monitoring wells or lysimeters is required around the perimeter of a
pond site; and (d) monitoring is determined on a case-by-case basis
depending on proximity to water supplies and on maximum ground-water
levels.
Oil and Gas Impoundments
Regulation and surveillance of discharges to impoundments associated
with the extraction of oil and gas on private and State lands are usually
part of the responsibility of a State Oil and Gas Board. Generally, the
degree to which these boards are required to cooperate with State water-
pollution control agencies is dictated by the operational rules of the
26
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State Water Resources Commission or other water-pollution control policy-
making body. Commonly, the Oil and Gas Commission or Board is represented
in the membership of the policymaking unit, which provides a means of
coordination with other agencies in matters related to control of water
pollution. Typical coordinating agencies are the Geological Survey, the
Health Department, and the Department of Water Resources.
Nearly all oil- and gas-producing States allow earthen storage pits and
ponds for handling produced water; requirements range from temporary or
emergency use only to evaporation use only. Most States stipulate that
the impoundments must be constructed in a clayey, impervious soil or
have a lining of some type. Generally, however, the regulations are not
specific with regard to the type of lining required. A permit or approval
for the use of an impoundment is required in most States.
Feedlot Impoundments
State regulations governing animal feedlot operations may be more or
less stringent than the NPDES requirements for a point-source discharge.
State permits usually apply to both large and small operations and, in
some States, is based upon considerations of the ratio of animals to
land area. Retention impoundments are the principal form of waste
treatment. Most States can require additional treatment as a condition
of permit issuance or renewal.
Iowa's feedlot regulations exemplify those of States with detailed
regulatory provisions. This State, for example, makes a regulatory
differentiation between permit requirements for open feedlots and for
fully or partly enclosed confined operations and requires that an open
feedlot have a permit if beef cattle population exceeds 100 and lot area
per animal is less than 600 square feet. Confined feeding facilities
are classified by the number of different species whose wastes are
discharged to a lagoon or holding basin, and a permit is necessary for
27
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beef cattle populations exceeding 20. The Iowa regulations also provide
that, regardless of size, land-carrying capacity, or other specific
provisions, all feedlots are subject to inspection if it is determined
that a water-pollution problem exists. Permits are required for new
operations and expansions of existing facilities. A separate permit
must be granted prior to construction, installation, or modification of
a waste-storage and disposal system for a permitted facility.
SUMMARY OF FINDINGS
1. There is a minimum estimated total of about 132,700 sites in the
United States where municipal, industrial, or agricultural impound-
ments are used for the treatment, storage, or disposal of wastes.
A large percentage of the sites contain more than one impoundment,
and most likely, the total number of impoundments is several times
greater than the total number of sites.
2. Industrial impoundments constitute about 75 percent of the total
number of impoundments and are most numerous in the oil and gas
extraction and mining industries. The mining, paper and pulp, and
electrical utility industries operate some of the largest impound-
ments .
3. Municipal, commercial, and institutional impoundments comprise
about 10 percent of the total number of impoundments and are used
for processing and disposing of sanitary wastes. Agricultural
impoundments constitute about 15 percent of the total number of
impoundments and are used mainly in handling wastes from animal
feedlot operations.
^. Billions of gallons of wastes are placed daily in surface impound-
ments. These wastes contain a wide variety of organic and inorganic
substances, some of which are highly toxic.
28
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5. Most impoundments are unlined, and because a large percentage of
them are underlain by permeable soils, the potential for downward
seepage of contaminated fluids into the ground water is high.
However, only incomplete data are available on the comparative
volumes of contaminated fluids that are lost by seepage into the
ground water, by evaporation, and by discharge to surface-water
bod ies.
6. Some contaminants that seep from impoundments may be attenuated in
the soil by ion exchange, adsorption, or other geochemical reactions.
Others can move readily through soil and into shallow unconfined
aquifers, especially where the sorptive capacity of the soil is
exhausted by continuous seepage of contaminated fluids.
7. Incidents of ground-water contamination from impoundments have been
reported in nearly all States. Although only 85 case histories of
contamination involving industries are summarized in the main
report, hundreds more of all types are believed to be in the files
of State agencies.
8. Case-history studies generally show that the water in shallow
unconfined aquifers is the first to be contaminated by seepage of
wastes from impoundments. The contaminated ground water is
generally in the form of a discrete plume that may be localized or
that may extend as much as one mile or more downgradient from an
impoundment.
9. Actions that can be taken to prevent or alleviate contamination of
ground water from impoundments include: installing impermeable
liners; constructing various collection and recycling systems, such
as underdrains, infiltration galleries, and wells; pretreating
wastes; and retarding or preventing the movement of contaminated
ground water by means of hydraulic or physical barriers. Where
29
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none of the foregoing techniques is feasible, it may be necessary
to shut down the impoundment and to substitute other waste-disposal
methods. Applicability of specific remedial actions at individual
sites should be determined on a case-by-case basis. Some preventive
measures are feasible only during the construction of new impound-
ments.
10. Costs of preventive or remedial actions at individual impoundment
sites can range from tens of thousands of dollars to millions of
dollars.
11. State pollution control or environmental control agencies commonly
issue some form of approval for the use of many types of waste
impoundments; these range from simple letters of authorization to
very restrictive permits. Many States provide guidelines or have
specific requirements for siting, construction, operation, and
monitoring of impoundments. Many of these requirements, however,
relate to construction and operational features that are not
necessarily effective in preventing contamination of ground water.
12. There is a wide diversity in the degree of ground-water protection
afforded presently by State rules and regulations relating to
surface impoundments because of: (a) manpower and budget defi-
ciencies, (b) inadequate knowledge of the scope and nature of the
problem, and (c) the fact that many regulatory programs are not
stringent enough to deal with the contamination threat.
30
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TECHNICAL REPORT DATA
(Please read Instructions on tlic reverse before completing)
1. REPORT NO.
EPA-570/9-78-005
4. TITLE AND SUBTITLE
Executive Summary of the Report - Surface Impoundments
and Their'Effects on Ground-Water Quality in the United
Sfiafees - A Preliminary Survey
3 RECIPIENT'S ACCESSION NO.
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Ground Water Protection Branch
Office of Drinking Water
U.S. Environmental Protection Agency
10. PROGRAM ELEMENT NO.
11 CONTRACT/GRANT NO.
Contract 68-01-4342
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
401 M Street S.W.
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
14 SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The data contained herein have been summarized from the final report of the
investigation entitled "Surface Impoundments and Their Effects on Ground-Water
Quality in the United States - A Preliminary Survey." The investigation was designed
to provide broad background information on the use of municipal, industrial, and
agricultural surface impoundments in the United States, with particular reference
to the potential threats they may pose to the quality of underground drinking water
resources and to methods of controlling or abating such threats. The study
was made by EPA as part of that agency's responsibility for controlling subsurface
emplacement of wastes, as mandated by Section 1422(a)(8)(c) of the Safe Drinking
Water Act (P.L. 93-523). The principal subjects covered in the report ere: (1)
numbers, types and uses of impoundments, (2) chemical characteristics of the
impounded wastes, (3) mechanisms by which wastes that seep from impoundments may
contaminate ground water, (4) selected case-history data on ground-water
contamination, (5) technical controls and costs for preventing and alleviating
contamination, and (6) State regulatory controls over the use of impoundments.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Surface Impoundments, ground water
quality protection, pits, ponds and
lagoons, seepage
5/G
5/E
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASSJThisReport)
Unclassified
21. NO. OF PAGES
30
20. SECURITY CLASS fThis page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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£ US GOVERNMENT FHINTIKG OFFICE 197S -281-147/1
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