EPA-600/4-76-026
June 1976
Environmental Monitoring Series
MONITORING GROUNDWATER QUALITY:
MONITORING METHODOLOGY
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/4-76-026
June 1976
MONITORING GROUNDWATER QUALITY:
MONITORING METHODOLOGY
by
David K. Todd
Richard M. Tinlin
Kenneth D. Schmidt
Lome G. Everett
General Electric Company—TEMPO
Center for Advanced Studies
Santa Barbara, California 93101
Contract No. 68-01-0759
Project Officer
George B. Morgan
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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This report has been reviewed by the Environmental Monitoring and Support Labora-
tory-Las Vegas, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and policies of
the U.S. Environmental Protection Agency, nor does mention of trade names or commer-
cial products constitute endorsement or recommendation for use.
ii
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ABSTRACT
The first section of this report describes the needs, objectives, and con-
straints of monitoring groundwater quality with particular emphasis on the
problem as viewed by the United States Environmental Protection Agency,
given its legislative mandates in the Federal Water Pollution Control Act
Amendments of 1972 (PL 92-500), and the Safe Drinking Water Act of 1974
(PL 93-523). The second section develops a methodology for monitoring
groundwater quality degradation resulting from man's activities. The
methodology is presented in the form of a series of procedural steps ar-
ranged in chronological order. By so doing, a straightforward sequence of
actions is outlined which can lead to a groundwater pollution monitoring pro-
gram in a given area. The third and final section of the report provides
information on groundwater quality. A description is given of the geologic
framework governing the movement of groundwater, and natural underground
water quality. The occurrence of groundwater pollution, including its dis-
tribution, mechanisms, attenuation, evaluation, and trends is presented.
The constituents in polluted groundwater and the various sources and causes
of pollution are reviewed. The section ends with a discussion of water qual-
ity in relation to water use.
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ACKNOWLEDGMENTS
Dr. Richard M. Tinlin, Dr. Lome G. Everett, and the late Dr. Stephen
Enke of General Electric —TEMPO were responsible for management and
technical guidance of the project under which this report was prepared. In
addition to the principal authors the following consultants made contributions
to this report: Mr. Harvey O. Banks, Belmont, California; Mr. Harry
LeGrand, Raleigh, North Carolina; and Dr. Don L. Warner, Rolla, Missouri.
The following officials were responsible for administration and technical
guidance of the project for the U.S. Environmental Protection Agency:
Office of Research and Development (Program Area Management)
Mr. Albert C. Trakowski, Jr.
Mr. John D. Koutsandreas
Environmental Monitoring and Support Laboratory, Las Vegas
(Program Element Direction)
Mr. George B. Morgan
Mr. Edward A. Schuck
Mr. Leslie G. McMillion
Mr. Donald B. Gilmore
IV
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TABLE OF CONTENTS
Page
ABSTRACT iii
ACKNOWLEDGEMENTS iv
LIST OF FIGURES vlf
LIST OF TABLES x;
SECTION I - INTRODUCTION 1
BACKGROUND AND SCOPE 1
Monitoring Groundwater Quality: Methods and Costs 2
Monitoring Groundwater Quality: Data Management 2
Monitoring Groundwater Quality: Economic Framework
and Principles 2
Monitoring Groundwater Quality: Illustrative Examples 3
PURPOSE AND APPROACH 4
Ambient Trend Monitoring 4
Source Monitoring 4
Case Preparation Monitoring 5
Research Monitoring 5
NEEDS AND OBJECTIVES 5
Economic Needs and Objectives 5
EPA Needs and Objectives 8
Monitoring Objectives 11
CONSTRAINTS 13
SECTION II - MONITORING METHODOLOGY 15
CONCEPT OF A MONITORING METHODOLOGY 15
IMPLEMENTATION OF A MONITORING
METHODOLOGY 16
Step 1 — Select Area or Basin for Monitoring 16
Step 2 — Identify Pollution Sources/ Causes and Methods
of Waste Disposal 20
Step 3 — Identify Potential Pollutants 25
Step 4 — Define Groundwater Usage 32
Step 5 — Define Hydrogeologic Situation 34
Step 6 — Study Existing Groundwater Quality 39
Step 7 — Evaluate Infiltration Potential of Wastes at
the Land Surface 42
Step 8 — Evaluate Mobility of Pollutants from the
Land Surface to Water Table 46
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CONTENTS (continued)
Page
Step 9 — Evaluate Attenuation of Pollutants in
the Saturated Zone 51
Step 10 — Prioritize Sources and Causes 54
Step 11 — Evaluate Existing Monitoring Programs 57
Step 12 — Establish Alternative Monitoring Approaches 58
Step 13 — Select and Implement the Monitoring Program 64
Step 14 — Review and Interpret Monitoring Results 65
Step 15 — Summarize and Transmit Monitoring Information 65
SECTION III - GROUNDWATER QUALITY 84
HYDROGEOLOGIC FRAMEWORK 84
Geologic Formations as Aquifers 84
Groundwater Movement 86
Natural Chemical Quality 87
OCCURRENCE OF GROUNDWATER POLLUTION 91
Definition 91
Distribution of Pollutants 91
Mechanisms of Pollution 92
Attenuation of Pollution 104
Distribution of Pollution Underground 106
Evaluation of Pollution Potential 110
Trends in Groundwater Pollution 112
CONSTITUENTS IN POLLUTED GROUNDWATER 112
Quality Categories 112
Effects of Water Use 112
SOURCES AND CAUSES OF POLLUTION 120
Agricultural Sources and Causes . 120
Municipal and Industrial Sources and Causes 124
Groundwater Basin Management 133
Miscellaneous 136
QUALITY IN RELATION TO WATER USE 138
Water Quality Standards 138
Drinking Water 139
Industrial Water 139
Irrigation Water 139
Livestock Water 142
REFERENCES 143
APPENDIX - METRIC CONVERSION TABLE 154
VI
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LIST OF FIGURES
Figure No. Title Page
1 Boundaries of the Santa Clara-Calleguas groundwater basin,
Ventura County, California. 19
2 Relation of groundwater pollution plume size and orientation
for a pollution source near a river with different groundwater
flow directions. 36
3 Groundwater flow system under idealized homogeneous aquifer
conditions. 37
4 Idealized pollution plume configuration for various locations
of surface pollution sources. 38
5 Flow lines for steady-state conditions in an aquifer and
positions of a pollution front advancing from a percolation
pond. 39
6 Water table contours in the vicinity of Stockton, California,
Fall 1964. 40
7 Distribution of saline water in a confined aquifer resulting
from an oilfield brine disposal pit in southwestern Arkansas. 41
8 Vertical bar graph of chemical quality expressed in milli-
equivalents per liter. 68
9 Vertical bar graph of chemical quality expressed in milli-
equivalents per liter which also shows hardness as CaCOg
in milligrams per liter. 69
10 Vertical bar graph of chemical quality expressed in milli-
equivalents per liter which also shows silica in millimoles
per liter. 69
11 Radial vector diagram of chemical quality expressed in milli-
equivalents per liter. 70
12 Pattern diagram of chemical quality expressed in milliequivalents
per liter. 71
13 Circular diagram of chemical quality with subdivisions showing
percentages of total milliequivalents per liter. 72
v?f
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FIGURES (continued)
Figure No. Title Page
14 Trilinear diagram of chemical quality expressed in percentages
of cations and anions as milliequivalents per liter and repre-
sented by two points and a circle. 73
15 Comprehensive trilinear diagram of chemical quality in which
five points represent the proportions of cations and anions to-
gether with total dissolved solids in milligrams per liter and
hardness as CaCO3 in milligrams per liter. 74
16 Variation in chloride concentration with time for-groundwater
at Burlington, Massachusetts. 75
17 Seasonal variation in nitrate concentration for groundwater at
Fresno, California. 76
18 Variation in electrical conductivity of groundwater along the
length of the Santa Ana River Basin, California. 78
19 Variation of total dissolved solids with well depth in a portion
of the Santa Clara-Calleguas groundwater basin, Ventura County,
California. 79
20 Isosalinity map of groundwater in the Santa Clara-Calleguas
groundwater basin, Ventura County, California, as of 1966. 80
21 Vertical cross section showing groundwater pollution movement
from waste disposal ponds and control by cooling water recharge
ponds and purge wells. 81
22 Contours of chloride concentration in groundwater surrounding
a brine disposal pit in southwestern Arkansas. 82
23 Plume of groundwater pollution from a landfill near Munich,
West Germany, shown by lines of chloride concentration. 83
24 Unconfined and confined aquifers. 86
25 Cumulative curves showing the frequency distribution of various
constituents in potable water. 89
26 A hypothetical drainage basin in a humid region showing in plan
view the distribution of zones of polluted water in the upper part
of the zone of saturation. 93
27 Disposal of household wastes through a conventional septic tank
system. 94
28 Diagram showing percolation of pollutants from a disposal pit to
a water table aquifer. 95
VIII
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FIGURES (continued)
Figure No. Title Page
29 Diagram showing the horizontal movement of pollutants
beneath a disposal pit as a result of clay lenses in the vadose
zone above the water table. 96
30 Illustration of a line source of groundwater pollution caused
by a leaking sewer. 96
31 Diagram showing pollution of an aquifer by leaching of surface
solids. 97
32 Diagram showing how polluted water can be induced to flow
from a surface stream to a well. 97
33 Diagram showing floodwater entering a well through an im-
properly sealed gravel pack. 98
34 Diagram showing movement of pollutants from a recharge well
to a nearby pumping well. 99
35 Diagrams showing spread of pollutants injected through wells
into water table and artesian aquifers. 100
36 Diagrams showing reversal of aquifer leakage by pumping. 101
37 Diagrams showing aquifer leakage by vertical movement of
water through a nonpumping well. 102
38 Diagrams showing lines of flow of pollutants from a recharge
pond above a sloping water table. 103
39 Diagram showing migration of saline water caused by lowering
of water levels in a gaining stream. 105
40 Plan view of a water table aquifer showing the hypothetical
areal extent to which specific pollutants of mixed wastes at
a disposal site disperse and move to insignificant levels. 107
41 Types of pollution plumes in the upper part of the zone of
saturation (plan view). 107
42 Changes in plumes and factors causing the changes. 109
43 Rating chart for pollution potential in unconfined aquifers of
unconsolidated alluvial materials. Ill
44 Estimated trend of groundwater pollution in the United States
during the 20th century. 113
45 Water quality cycle—sources and uses of water and effects on
water quality. 116
46 Agricultural uses of water and their effects on water quality. 117
ix
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FIGURES (continued)
Figure No. Title Page
47 Industrial uses of water and their effects on water quality. 118
48 Commercial uses of water and their effects on water quality. 119
49 Domestic uses of water and their effects on water quality. 121
50 Schematic vertical cross section through a coastal aquifer
showing freshwater and seawater circulations with a transition
zone. 134
51 Schematic diagram of upconing of underlying saline water to
a pumping well. 135
52 Diagram illustrating the relation of water pollution to impair-
ment for a given water use. 138
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LIST OF TABLES
Table No. Title Page
1 Major sources and causes of groundwater pollution and
methods of waste disposal 21
2 Classification of major potential pollutants in groundwater 26
3 Major sources of groundwater pollution and types of pollutants 26
4 Inorganic chemical pollutants 27
5 Analyses of chemical quality of groundwater presented in
tabular form 67
6 Relative abundance of dissolved solids in potable water 88
7 Major natural constituents in groundwater — their sources
and effects upon usability 90
8 Classifications of water 92
9 Explanation of plumes shown in Figure 41 108
10 Parameters and constituents which may be included in
analyses of groundwater quality 114
11 Principal sources and causes of groundwater pollution 122
12 Normal range of mineral pickup in domestic sewage 127
13 Drinking water standards of the U.S. Public Health Service 140
14 Guide for evaluating the quality of water used for irrigation 141
15 Guide for evaluating the quality of water used by livestock 142
xj
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SECTION 1
INTRODUCTION
BACKGROUND AND SCOPE
Groundwater serves as a major source of water supply in the United
States. Public water supplies for one--third of the nation's 100 largest
cities are derived from groundwater. It is estimated that in rural areas 95
percent of the domestic water and over half of the water for livestock and
irrigation are obtained from underground resources. Furthermore, most
of the day-to-day base flow of the nation's rivers and streams originates
from groundwater discharge.
The natural quality of groundwater tends to be degraded by activities of
man. Wastes which are not discharged into lakes, streams or the ocean are
deposited on land and from there may migrate downward to pollute ground-
water. The extent of this pollution has grown concomitantly in recent dec-
ades with increases in population, agriculture, and industry; however, in-
formation as to the magnitude of the problem is meager.
Currently, the U.S. Environmental Protection Agency (EPA) has an inves-
tigational program of groundwater pollution underway on a regional basis.
From the reports already issued (Fuhriman and Barton, 1971; Scalf et al. ,
1973; van der Leeden et al. , 1973, 1975; Miller et al. , 1974), it is appar-
ent that there are literally millions of point sources of pollution in existence.
Section I of this report introduces the subject and describes the needs,
objectives, and constraints of groundwater quality monitoring, particularly
from the viewpoint of the EPA and its given legislative mandates.
Section II presents the monitoring methodology in the form of a series
of procedural steps arranged in chronological order. By so doing a
straightforward sequence of actions is outlined which can lead to a ground-
water quality monitoring program in a given area. To suggest the scope of
the monitoring methodology, the 15 steps involved are listed below:
Step 1 — Select Area or Basin for Monitoring
Step 2 — Identify Pollution Sources, Causes, and Methods of Waste
Disposal
Step 3 — Identify Potential Pollutants
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Step 4 — Define Groundwater Usage
Step 5 — Define Hydrogeologic Situation
Step 6 — Study Existing Groundwater Quality
Step 7 — Evaluate Infiltration Potential for Wastes at the
Land Surface
Step 8 — Evaluate Mobility of Pollutants from the Land
Surface to the Water Table
Step 9 — Evaluate Attenuation of Pollutants in the
Saturated Zone
Step 10 — Prioritize Sources and Causes
Step 11 — Evaluate Existing Monitoring Programs
Step 12 — Establish Alternative Monitoring Approaches
Step 13 — Select and Implement the Monitoring Program
Step 14 — Review and Interpret Monitoring Results
Step 15 — Summarize and Transmit Monitoring Information
The report concludes with a list of references pertaining to groundwater
quality and pollution.
It should be noted that this report is one of a series of five reports pub-
lished by the U. S. Environmental Protection Agency. Although this report
is self-contained in the material presented, the other reports provide im-
portant supplemental data, information, and examples. The four related
reports are briefly described in the following paragraphs.
Monitoring Groundwater Quality: Methods and Costs
This report (Everett et al. , 1976) summarizes specific techniques
available for monitoring groundwater quality together with detailed esti-
mates, where available, of their costs.
Monitoring Groundwater Quality: Data Management
This report (Hampton, 1976) examines the requirements of a ground-
water quality data management information system, reviews existing sys-
tems, and identifies how existing capabilities can be utilized for a ground-
water quality monitoring program.
'Monitoring Groundwater Quality: Economic Framework
and Principles
This report (Crouch et al. , 1976) reviews the existing institutional and
2
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legal structure pertaining to groundwater pollution, presents a hydrogeologic
case study as a framework for discussion of economic issues of groundwater
monitoring, and analyzes economic principles pertaining to groundwater pol-
lution monitoring.
Monitoring Groundwater Quality: Illustrative Examples
This report (Tinlin, 1976) is designed to show by example selected source-
specific and pollutant-specific monitoring procedures. The report first de-
scribes five case histories of actual groundwater pollution. The monitoring
techniques which were employed in each case are given as well as a retro-
spective view of these techniques and their efficacy. The report concludes
with four illustrative examples for selecting a preferred groundwater pollu-
tion monitoring program. These examples are: agricultural return flow,
septic tanks, percolation ponds, and solid waste landfills.
In addition to the above reports, the following EPA reports were pre-
pared as a part of this same study and serve as corollary contributions to
the monitoring methodology:
EPA-600/4-73-001a
(NTIS #PB-232-ll6/46l)
EPA-600/4-73-001b
(NTIS #PB-232-117/WP)
EPA-680/4-74-001
(NTIS #PB-235-556/
8WP)
EPA-680/4-74-002
(NTIS #PB-241-078)
EPA-680/4-74-003
(NTIS #PB-241-402)
EPA-680/4-75-008
Groundwater Pollution Features of Federal
and State Statutes and Regulations, by
Fritz van der Leeden (Geraghty & Miller,
Inc. ), July 1973.
Polluted Groundwater! Some Causes.
Effects. Controls, and Monitoring, by
Harvey O. Banks, Geraghty & Miller,
Inc. (James J. Geraghty, David W. Miller,
Nathaniel M. Perlmutter, and George R.
Wilson), David C. Kleinecke, P. H.
McGauhey, Charles F. Meyer (Editor),
Richard M. Tinlin, David K. Todd,
Edward J. Tschupp, and Don L. Warner,
July 1973.
Polluted Groundwater; A Review of the
Significant Literature, by David K. Todd
and Daniel E. McNulty, March 1974.
Polluted Groundwater; Estimating the
Effects of Man's Activities, by John F.
Karubian, June 1974.
Rationale and Methodology for Monitoring
Groundwater Polluted by Mining Activities.
by Don L. Warner, June 1974.
Monitoring Disposal-Well Systems, by
Don L. Warner, July 1975.
3
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PURPOSE AND APPROACH
The monitoring methodology described in this report is intended to serve
as a set of guidelines for developing and implementing a groundwater quality
monitoring program. It should be apparent that factors such as climate, hy-
drology, population, pollution sources, and water use vary from place to
place; therefore, the design of an appropriate monitoring program will also
vary accordingly. No one set of guidelines can cover all situations; however,
with judgment the approach presented herein can be extended and interpreted
to meet most other situations which will be confronted in the field.
The physical, chemical, and biological mechanisms governing ground-
water pollution are reasonably •well understood. Yet, - applying this knowl-
edge to the many different situations which can result from superimposing a
given groundwater pollution source upon particular hydrogeologic environ-
ments is difficult. Nonetheless, this report is intended to be a handbook or
manual for the development and implementation of a methodology for moni-
toring groundwater quality. The methodology is expressed in a generalized
form so that it can be usefully employed by regional, State, and local water
pollution control agencies and is applicable to all types of groundwater aqui-
fers, areas, and basins. Alternatives in the decision-making process lead-
ing to the final monitoring program are considered throughout the method-
ology.
Monitoring may be defined as a scientifically designed surveillance sys-
tem of continuing measurements and observations, including evaluation pro-
cedures. The EPA is currently involved in establishing, in cooperation with
the States, a national groundwater quality monitoring system as part of its
legislatively directed program to prevent, reduce, and eliminate groundwater
pollution.
Four basic types of monitoring have been defined by the EPA. In terms
of groundwater quality, these may be interpreted as follows:
Ambient Trend Monitoring
This concerns measurements of groundwater quality and deviations in re-
lation to standards, and involves temporal and spatial trends within a
groundwater basin or area.
Source Monitoring
This involves the measurement of effluent quantity and quality for pollu-
tion sources which may affect groundwater.
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Case Preparation Monitoring
This serves to gather evidence for enforcement actions of past, existing
or anticipated groundwater pollution situations; implied are carefully docu-
mented measurements within a circumscribed area.
Research Monitoring
This contributes to research investigations on groundwater quality and
pollution occurrence and movement.
Of the four above types, the monitoring methodology is directed largely
toward source monitoring. Case preparation and research monitoring, while
providing valuable data, are clearly specialized needs which do not lend
themselves to a national program. Ambient trend monitoring provides back-
ground quality information on groundwater resources (such as the ongoing
programs of the U. S. Geological Survey). Thus, a national program to pro-
tect groundwater quality relative to those activities of man which pollute
groundwater will focus primarily on measurements relating to pollution
sources and methods of waste disposal which contribute to pollution. Fur-
thermore, because it is infeasible to monitor all sources and causes of pol-
lution, the methodology concentrates on identifying the most important
sources and methods of disposal. In essence then the methodology becomes
a resource allocation problem with the goal of developing a cost-effective
monitoring program which will contribute most to the protection of the na-
tion's groundwater s.
NEEDS AND OBJECTIVES
Growing evidence indicates that the nation's groundwater s (like its other
resources such as air and surface water) are becoming excessively polluted.
Groundwaters are not being efficiently allocated among their alternative uses.
Wastes are an unavoidable byproduct of all man's activities and, recognizing
that, these wastes must be disposed of somewhere. The substantive ques-
tions of optimum production of wastes and their optimum disposal must be
addressed. Clearly, the nation's aquifers, like every other sector of the
environment, must serve as a repository for the disposal of some of soci-
ety's wastes. The question, then, is not "can wastes be placed on and in the
ground? " but rather "where and how much? "
Economic Needs and Objectives
In order to maximize the value of groundwater resources from society's
point of view, it is necessary that they be used in optimal amounts for vari-
ous appropriate purposes such as irrigation, cooling, drinking, etc, as well
as for the disposal of wastes.
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The reason that groundwaters become excessively polluted is exactly the
same as the reason that our other environmental resources become exces-
sively polluted; namely, the fact that well-specified (and, therefore, easily
enforceable) property rights do not exist in the resource. As Corker's
(1971) authoritative legal analysis makes abundantly clear, property rights
in groundwater are very poorly specified. As a result, some parties use
other parties' groundwater resources without authorization as a receptor for
their wastes, thereby imposing uncompensated damages on the resource
owner. In the absence of any obligation to compensate parties whose ground-
water is serving as a waste disposal site, such waste disposal service ap-
pears to be free to the polluter (although it is obviously not free from soci-
ety's point of view). In such a situation, the polluter will utilize such a
service until the marginal private benefit he obtains by using that service is
driven down to zero, even though the marginal social cost may be positive
and large. Consequently, the aquifer's waste receptor capabilities are
abused, and groundwater becomes excessively polluted.
When well-specified property rights to a resource do not exist, the
market processes through which our resources are normally allocated break
down as an efficient resource allocation mechanism. Therefore, if re-
sources to which well-specified property rights do not exist are to be effi-
ciently allocated among their alternative uses, it is not possible to rely on
the normal allocation mechanism provided by market processes. The re-
source must, instead, be managed by some public agency.
As pointed out by the U. S. Council on Environmental Quality (1973, Chap-
ter 3), efficient management of our environmental resources requires that
consideration be given to four categories of costs. First, there are damage
costs. These are costs which are generated directly by a polluting activity.
With respect to groundwater resources, one example •would be increased
physiological damage caused by pollution of drinking water. Another exam-
ple would be crop losses resulting from salt buildup in an irrigation well.
Second, there are avoidance costs. These are costs which are incurred by
society in order to avoid, or reduce, damage costs. With respect to ground-
water resources, one example would be the importation of unpolluted water
to replace that previously obtained from a well that has become polluted.
Third, there are abatement costs. These are costs associated with the re-
duction of pollution. Such reduction of pollution can be achieved either by
controlling the source or by treating the polluted water. With respect to
groundwater resources, one example would be the deep injection into a safe
geologic zone of noxious effluents previously disposed of at the land surface,
into the atmosphere, surface waters, or landfill. Fourth, there are trans-
action costs. Transaction costs include the cost of resources allocated to
the establishment, and of enforcement of environment-preserving policies
and regulations. With respect to groundwater resources, the most impor-
tant example of a transaction cost, and of special relevance to this study,
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would be the cost of monitoring groundwater pollution either to generate in-
formation on quantity and quality or to detect violations of, and ensure com-
pliance with, groundwater quality standards.
The essential principle to note is that these four cost categories are, in
general, interdependent. Thus, any new groundwater quality policy will
probably affect all four categories. For example, if a policy is introduced
which is designed to reduce groundwater pollution, it will certainly reduce
damage costs but may very well increase abatement, avoidance, and moni-
toring costs. Usually, each feasible groundwater quality policy will affect
these four categories of cost differently. Obviously the only groundwater
quality policy alternative that should be seriously considered for implemen-
tation is that set of policies for which the reduction in damage costs exceeds
the net increase, if any, in avoidance, abatement, and monitoring costs. To
go even further than this, the most efficient, or optimal, groundwater quality
policy among the feasible set of alternatives is that policy which minimizes
the sum of the damage costs, avoidance costs, abatement costs, and moni-
toring costs for a given groundwater pollution situation. Implicitly, the
minimization of these costs is equivalent to the maximization of society's
income or gross national product.
To illustrate by example, sewer leakage is known to pollute groundwater
and may, therefore, impose certain damage costs and avoidance costs.
However, with present technology there is no way of controlling this source
of pollution that does not impose abatement costs that are far in excess of
the reduction in damage and avoidance costs which would be achieved. It
follows that the efficient policy is not to monitor and abate this pollution
source, but simply to accept the existing level of damage and avoidance
costs.
Of course, in many other groundwater pollution situations the reduction
in damage costs will exceed the increase in avoidance, abatement, and
monitoring costs that bring these reductions about. The objective then be-
comes that of selecting the avoidance, abatement, and monitoring strategy
which generates, at the margin, decreases in damage costs just equal to
the increases in the avoidance, abatement, and monitoring costs required
by the strategy.
The attainment of this objective will not simply involve the minimization
of monitoring costs by the responsible government agency. For example, in
any given groundwater pollution situation there may well be several different
abatement strategies, each with an associated monitoring requirement, that
would achieve the desired level of groundwater quality. If the public agency
responsible for selecting among the abatement and monitoring strategies
simply chooses that alternative which minimizes its own monitoring costs,
this could imply higher private abatement costs with the result that the com-
bined monitoring and abatement costs of that policy would be greater than
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the combined monitoring and abatement costs of some other strategy.
Clearly, this would not be efficient from society's point of view.
EPA Needs and Objectives
The needs and objectives of the EPA for those data pertaining to ground-
water quality which must be obtained through monitoring programs, are dic-
tated by the mandates and requirements of the Federal Water Pollution Con-
trol Act, as amended (Public Law 92-500; 33 USC 1151, et seq. ), and the
Safe Drinking Water Act (Public Law 93-523; 42 USC 300f, et seq. ).
FEDERAL WATER POLLUTION ACT, AS AMENDED. The objective of
the Act as amended as stated in Sec. 101 (a) is:
Sec. 101. (a) The objective of this Act is to restore and main-
tain the chemical, physical, and biological integrity of the Na-
tion1 s waters. . .
The definition of "pollution" given in the Act indicates clearly the wide
spectrum of groundwater quality problems and of the sources and causes of
those problems that may need to be considered in designing a groundwater
quality monitoring program:
Sec. 502. (19) The term 'pollution1 means the man-made or man-
induced alteration of the chemical, physical, biological, and ra-
diological integrity of water.
The Act directs that specific programs be developed to improve and main-
tain groundwater quality:
Sec. 102. (a) The Administrator (of EPA) shall, after careful
investigation, and in cooperation with other Federal agencies,
State water pollution control agencies, interstate agencies, and
the municipalities and industries involved, prepare or develop
comprehensive programs for preventing, reducing, or elimi-
nating the pollution of the navigable waters and ground waters
and improving the sanitary condition of surface and underground
waters. In the development of such comprehensive programs
due regard shall be given to the improvements which are neces-
sary to conserve such waters for the protection and propagation
of fish and aquatic life and wildlife, recreational purposes, and
the withdrawal of such waters for public water supply, agricul-
tural, industrial, and other purposes. For the purpose of this
section, the Administrator is authorized to make joint inves-
tigations with any such agencies of the condition of any waters
in any State or States, and of the discharges of any sewage,
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industrial wastes, or substances which may adversely affect
such waters. [Emphasis added]
Development of cost-effective programs to accomplish this purpose requires
an adequate data base that can only be obtained by carefully designed and im-
plemented monitoring programs.
Establishment and conduct of monitoring programs is mandated by the
Act:
Sec. 104. (a) The Administrator (of EPA) shall establish national
programs for the prevention, reduction, and elimination of pollu-
tion and as part of such programs shall: . . .
(5) in cooperation with the States, and their political subdivi-
sions, and other Federal agencies establish, equip, and main-
tain a water quality surveillance system for the purpose of
monitoring the quality of the navigable waters and ground
waters and the contiguous zone and the oceans. . .and shall
report on such quality. . . [Emphasis and insertion added]
Sec. 106. (e) Beginning in fiscal year 1974 the Administrator
shall not make any grant under this section (Sec. 106) to any
State which has not provided or is not carrying out as a part
of its program. . .
(1) the establishment and operation of appropriate devices,
methods, systems, and procedures necessary to monitor.
and to compile and analyze data on (including classification
according to eutrophic condition), the quality of navigable
waters and to the extent practicable, ground waters in-
cluding biological monitoring; and provision for annually
updating such data and including it in the report required
under section 305 of this Act; ... [Emphasis and insertion
added]
SAFE DRINKING WATER ACT. This Act, which became effective 16
December 1974, places additional responsbilities of major public health and
economic significance upon the Administrator of the EPA to protect the na-
tion's groundwater resources. The following excerpts from the Act indicate
the nature and extent of those responsibilities:
Sec. 1424. (e) If the Administrator (of EPA) determines, on
his own initiative or upon petition, that an area has an aquifer
which is the sole or principal drinking water source for the
area and which, if contaminated, would create a significant
hazard to public health, he shall publish notice of that determination
-------
in the Federal Register. After the publication of any such
notice, no commitment for Federal financial assistance (through
a grant, contract, loan guarantee, or otherwise) may be entered
into for any project which the Administrator determines may con-
taminate such aquifer through a recharge zone so as to create a
significant hazard to public health, but a commitment for Federal
financial assistance may, if authorized under another provision
of law, be entered into to plan or design the project to assure
that it will not, so contaminate the aquifer. [Emphasis and in-
sertion added]
Sec. 1442. (a)(l) The Administrator may conduct research,
studies, and demonstrations relating. . .to the provision of a
dependably safe supply of drinking water, including. . .
(E) improved methods of protecting underground water
sources of public water systems from contamination. . .
Sec. 1442. (a)(4) The Administrator shall conduct a survey
and study of. . .
(A) disposal of waste (including residential waste) which may
endanger underground water which supplies, or can reason-
ably be expected to supply, any public water systems, and
(B) means of control of such waste disposal. . .
Sec. 1442. (a)(5) The Administrator shall carry out a study
of methods of underground injection which do not result in
the degradation of underground drinking water sources.
(6) The Administrator shall carry out a study of methods
of preventing, detecting, and dealing with surface spills of
contaminants which may degrade underground water sources
for public water systems. . .
(8) The Administrator shall carry out a study of the natur e
and extent of the impact on underground water which sup-
plies or can reasonably be expected to supply public water
systems of (A) abandoned injection or extraction wells;
(B) intensive application of pesticides and fertilizers in
underground water recharge areas; and (C") ponds, pools,
lagoons, pits, or other surface disposal of contaminants in
underground water recharge areas. [Emphasis added]
To carry out these responsibilities effectively, detailed information for
many aquifers on groundwater quality, geology, hydrology and the sources
10
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and causes of groundwater quality impairment, will be necessary. Ground-
water quality monitoring programs must be designed to provide such data
where and when required.
INTERSTATE COMPACTS. A few interstate compacts — the Federal-
interstate compacts for the Delaware River Basin and the Susquehanna River
Basin are examples — provide authority for the compact commissions to
monitor groundwater quality and to develop and implement plans for quality
protection.
STATE STATUTES AND REGULATIONS. State laws and implementing
regulations vary widely from State to State as regards both groundwater
quality monitoring and the development and implementation of plans for
quality protection. In California, the State Water Resources Control Board
and the nine regional water quality control boards have broad authority and
responsibilities in this regard under Division 7 of the Water Code (Porter-
Cologne Water Quality Control Act, as amended). Likewise, the Water Code
provides with respect to the State Department of Water Resources:
2Z9. (Water Code) The Department of Water Resources, either
independently or in cooperation with any person or any county,
State, Federal, or other agency, to the extent that funds are
allocated therefore, shall investigate conditions of the quality of
all waters (including ground waters) within the State, including
saline waters, coastal and inland, as related to all sources of
pollution of whatever nature and shall report thereon to the
Legislature, to the board (State Water Resources Control Board),
and to the appropriate regional water quality control board an-
nually, and may recommend any steps which might be taken to
improve or protect the quality of such waters. The department
shall coordinate its investigations fully with the board. [Em-
phasis and insertions added]
The Water Code of the State of Texas provides similar authorities and
responsibilities to the Texas Water Quality Board, and, to some extent, to
the Texas Water Development Board.
Some States have not yet progressed as far in monitoring and planning for
the improvement and protection of groundwater quality.
Monitoring Objectives
Simply stated, the objective of a monitoring program should be to collect,
manage, and analyze the data on groundwater quality and the sources and
causes of groundwater pollution, and the other information — geologic, hy-
drologic, and economic — necessary to enable the EPA and the State(s)
11
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involved to fulfill their statutory responsibilities as regards protection of
groundwater quality, that is ".. .to restore and maintain the chemical, phys-
ical, and biological integrity of the nation's waters.. . "
To fulfill that objective, a specific monitoring program must be developed
and implemented for each groundwater basin; such a program will be the end
result of the application of the monitoring methodology described in this re-
port. The data to be obtained may be needed for one or more of the follow-
ing purposes, depending upon the types, extent, and seriousness of quality
problems, and the present and future importance of the groundwater system
as a source of water supply:
• Provision of background information and quality
• Detection of quality trends
• Identification and assessment of the sources and causes
of pollution
• Planning — including formulation, calibration, verification,
and use of planning models
• Establishment of water quality standards and effluent
limitations
• Formulation of other regulatory control and management
actions necesiary to protect quality
• Compliance
• Enforcement
• Reporting.
For a groundwater basin which is already extensively developed, or in proc-
ess of development, all these purposes must generally be served, although
the relative emphasis will vary.
A wide range of types of data may be needed, depending upon the partic-
ular groundwater system involved, its importance, uses, its present and
potential quality problems, and the information already available. In addi-
tion to water quality data this information should include:
• Geologic characteristics
• Hydrology
• Hydraulic characteristics
• Land use
• Water resource development and use
12
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• Demographic and economic conditions
• Waste generation and disposal.
An effective monitoring program must recognize the dynamic nature of
ground-water systems as affected by both natural phenomena and man-induced
changes. The program must, therefore, be continuing. Its scope and rela-
tive emphasis will change over time. The data obtained must be adequate to
enable prediction of potential quality problems and for formulation of plans
for prevention of groundwater pollution.
CONSTRAINTS
There are several constraints to be considered in the design of a cost-
effective monitoring program — institutional, budgetary, legal, social, and
personnel.
At the Federal level, there are several agencies in addition to the EPA
and USGS which collect groundwater quality data and which possess informa-
tion of value to a comprehensive groundwater quality monitoring program.
Their monitoring activities are accomplished in support of their statutorily
authorized programs which involve groundwater and its uses in some man-
ner. Other programs of particular significance are those of U.S. Bureau of
Reclamation, U.S. Army Corps of Engineers, and U.S. Soil Conservation
Service.
There are several State agencies which have statutorily defined authori-
ties and responsibilities with respect to groundwater, and which conduct
monitoring activities. Such State entities may include:
• Water resource planning and management agencies
• Water quality control agencies
• Water rights administration
• Department of public health
• Universities
• Soil conservation agencies.
The authorities, responsibilities, and activities of the several State agencies
may overlap to some extent.
At the regional and local levels of government, counties, municipalities,
and special political jurisdictions such as water supply, sanitary, flood con-
trol, and water conservation districts, have interests and responsibilities
with respect to groundwater, and many conduct extensive monitoring pro-
grams.
13
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The authorities, responsibilities, and programs of the several agencies at
each governmental level and the data already available from their monitoring
activities must be taken into account in designing a new monitoring system.
The number of geologists, hydrologists, and water quality specialists
competent to design and implement a groundwater quality monitoring program
and to make effective use of the data generated is limited.
Funds available for monitoring activities are generally scarce, particu-
larly at the State, regional, and local levels of government. Any increase
in budgets will take place gradually and then only on well-documented justifi-
cation. As a consequence, the implementation of expanded monitoring pro-
grams must, in general, take place gradually.
14
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SECTION II
MONITORING METHODOLOGY
CONCEPT OF A MONITORING METHODOLOGY
The basic purpose of a methodology for monitoring groundwater pollution
is to provide a framework for the planning and development of a monitoring
program. The methodology should serve two roles simultaneously. First,
it should assist a local designated monitoring agency (DMA) to design and to
implement a monitoring program. The second role should be to guide gov-
ernmental agencies at the State and national levels in establishing realistic
monitoring priorities, not only in terms of what should be monitored and
where, but also in terms of timing and funding.
The monitoring methodology described in the following sections is predi-
cated upon the technical effort being organized and conducted by or under the
direct supervision of personnel with professional training in water resources
engineering or groundwater geology. This requirement is essential in view
of the fact that it is infeasible to summarize the full background of hydroge-
ology, involving the occurrence, distribution, and movement of groundwater,
as well as its geochemistry, which would be needed to establish a successful
monitoring program. Section III of this report has been prepared specifical-
ly for hydrologists and geologists not familiar with groundwater quality prob-
lems. It is recommended that these individuals review Section III prior to
using this section.
Various personnel arrangements can be anticipated for implementing the
monitoring methodology. Indicative of the possibilities are the three follow-
ing situations:
• In an urbanized local area the DMA might possess a sufficiently
large technical staff so that the organization and conduct of the
monitoring program could be handled entirely by this in-house
group. Similarly, for a relatively undeveloped area where the
monitoring program would be small, a single technically com-
petent member of the DMA might personally supervise the pro-
gram.
• Where the staff of a DMA is inadequate, responsibility for the
monitoring program could be subcontracted to a firm of con-
sulting engineers or geologists specializing in groundwater.
15
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An arrangement of this sort could function either on a contin-
uing basis or until an adequate in-house staff became available.
• With the passage of time and the full development of a monitoring
program, surveillance of existing and potential sources of pol-
lution will assume a standardized routine. Thereafter, atten-
tion will tend to be focused primarily on the monitoring of new
developments, such as landfills, feedlots, industrial plants,
subdivisions, etc. Because plans for each new development
will need to be reviewed and approved by the DMA, it follows
that inclusion of an adequate monitoring system will become a
contingency for approval. Under these circumstances much of
the work required to extend the monitoring program for these
new developments will be completed by the engineering firms
responsible for their design.
Finally, it should be understood that the methodology presented herein
must of necessity be somewhat generalized. There is an infinite number of
combinations of pollution causes, hydrogeologic situations, and monitoring
methods, among other variables, that can govern the implementation of a
monitoring program. Therefore, persons involved in a monitoring program
will be required to exercise professional judgment in order to interpret and
to apply this methodology to the specific local situations which they encoun-
ter. Examples are given for illustrative purposes and case histories are
presented by Tinlin (1976).
IMPLEMENTATION OF A MONITORING METHODOLOGY
The following material describes procedures for implementing a ground-
water pollution monitoring program. These apply to a specified local area
under the jurisdiction of a DMA. The procedures are described as a series
of steps arranged in chronological order. In practice, however, activities
of different steps will overlap in order to make efficient use of personnel
and time.
The steps constitute a series of monitoring objectives for a DMA. Taken
together they constitute a monitoring methodology which can assist a DMA at
any location in the United States to initiate its groundwater pollution moni-
toring program.
Step 1 — Select Area or Basin for Monitoring
The selection of areas to be monitored will be made within a State by the
appropriate State water pollution control agency that, in cooperation with the
"EPA, carries out the mandates of PL 92-500 and PL 93-523. The basis for
selecting areas will be governed, in general, by a combination of adminis-
trative, physiographic, and priority considerations. Each of these factors
will be reviewed in the following paragraphs.
16
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ADMINISTRATIVE CONSIDERATIONS. The initiation of a monitoring
program requires that a local DMA be specified. In many situations the req-
uisite agency with the necessary technical staff may be a county, district, or
regional water organization. Thus, the area to be monitored can often be
made to correspond to the jurisdictional area of the DMA. The size of a
particular area may vary from a few square miles to thousands of square
miles. * Size alone is less important than the ready accessibility of all por-
tions of the area to the DMA as well as hydrogeologic knowledge of the area
possessed by the DMA.
It should be recognized that political boundaries frequently create prob-
lems in terms of water management. Such a boundary may cross a major
groundwater basin so that, for example, pollutants from an adjoining area
may be entering from sources not subject to monitoring by the DMA. Clear-
ly, such situations should be minimized as much as possible; alternatively,
cooperation among DMA's sharing common groundwater pollution problems
will be essential to the success of their respective monitoring programs.
PHYSIOGRAPHIC CONSIDERATIONS. The physiographic basis for se-
lecting monitoring areas recognizes that groundwater basins are distinct
hydrographic units containing one or more aquifers. Such basins usually,
but not always, coincide with surface water drainage basins. By establish-
ing a monitoring area related to a groundwater basin, total hydrologic in-
flows to and outflows from the basin are fully encompassed. This permits
all pollution sources and their consequent effects on groundwater quality to
be monitored by a single DMA. Where basins are extensive, monitoring
areas become too large to be practical. Boundaries should then be drawn
parallel to groundwater flows or where cross-flow components are insignif-
icant. Most groundwater basins in the United States have been mapped,
based on hydrogeologic investigations, and information is available from
State water agencies and/or the U.S. Geological Survey.
PRIORITY CONSIDERATIONS. It is recognized that establishment of a
national program to assess the impact of man's activities on groundwater
quality will develop gradually because of administrative, budgetary, and
personnel constraints. Since it is the stated intent of the EPA to rely on the
States to select the areas to be monitored and to conduct the appropriate
monitoring activities, any national program which evolves will as a conse-
quence be built upon the data and information generated by these State moni-
toring activities.
A first consideration of a State will be to select and prioritize those
groundwater aquifers subject to the greatest pollution threat. This first
level of prioritization is necessary to provide a starting point for application
of the groundwater monitoring methodology. Rarely will sufficient data and
*See Appendix for conversion to metric units.
17
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information be available from the start to make anything but a gross ap-
praisal of the threat to a State's groundwater resources.
In order for the application of the methodology to be most effective on a
spatial basis, areas which have the largest number of identified or potential
pollution sources and where there is a high utilization of groundwater should
be ranked and sectioned off as areas within which to apply the monitoring
methodology. By utilizing the above two criteria in combination with the ad-
ministrative and physiographic considerations previously set forth, the total
area of a State can be divided into areas which may require a monitoring
program.
Illustrative of this procedure is an expanded priority scheme for ground-
water monitoring developed by the State of California. Here groundwater
basins are ranked according to the following five criteria.
• Basin population
• Agricultural use of groundwater
• Estimated usable groundwater capacity
• Availability of an alternate water supply source
• Number of existing quality problems which threaten
the groundwater resource.
This list essentially restates the two criteria described above but attempts
to add further insight into water resource management rather than a ground-
water pollution monitoring program. This approach developed in California
is cited as an example only and is not necessarily recommended by the EPA.
In summary, the administrative, physiographic, and priority considera-
tions provide a rationale for selecting monitoring areas. To be applied
within a given State they must be interpreted as guidelines because various
special or local conditions will frequently have to be accommodated. Com-
promises will be inevitable, but careful initial selection of monitoring areas
can simplify and make more effective the subsequent monitoring program
undertaken by each DMA.
EXAMPLE — BASIN BOUNDARY AREA. Figure 1 shows the boundaries
selected for defining the groundwater basin in the Santa Clara-Calleguas
area in southwestern Ventura County, California. The northern and south-
ern boundaries were placed along mountain ridges where groundwater flow
would be either nonexistent or parallel to the boundary. The eastern bound-
ary was drawn at the county line, a political boundary, but here this also co-
incides closely with the drainage divide of the stream systems. The west-
ern boundary was the seacoast. The predominant groundwater flow is in a
southwesterly, or down-valley, direction toward the sea except locally
18
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*
.
*-%-4^
^
S«ra „£;.
**"
-•••' '** *«E*
"M s *"7
S-—J tMumuxjf^r ..^
-p.^-^ v«W«« i^4,
J}XNAJtO ^ ^
SLAIN \
!•*' .>'X
£ | ^-y
INTRA BASIN BOUNDARY
] WATER BEARING AREA
NON WATER BEARING AREAS
Figure 1. Boundaries of the Santa Clara-Calleguas groundwater basin, Ventura
County, California (California Department of Water Resources, December
1974).
-------
where major pumping centers cause deviations or reversals of the flow di-
rection.
It should be noted in Figure 1 that the water-bearing area occupies some
192, 000 acres and that this is only a fraction of the total area, hence moni-
toring would be restricted to only those portions of the area containing
groundwater. Six population centers lie within the area (Ventura, Oxnard,
Santa Paula, Fillmore, Piru, and Moorpark) with a total 1970 population of
330,000. The aquifers are all composed of alluvial materials with uncon-
fined, confined, and multiple types being present. The area of urban land
use totals 27,000 acres, while agricultural use covers 106,000 acres. Av-
erage annual precipitation is 15. 05 inches, which occurs chiefly in winter
from North Pacific storms.
Step 2 — Identify Pollution Sources/
Causes and Methods of Waste Disposal
The design of a monitoring program requires that the potential sources
and causes of groundwater pollution and methods of waste disposal within an
area be identified. Groundwater pollution sources can be conveniently
placed into six major groups. Municipal, agricultural, and industrial are
three major groups. For purposes of monitoring groundwater pollution, oil-
field wastes and mining wastes are considered of sufficient importance to
also be listed as major groups. The remaining sources are grouped under
miscellaneous. Of considerable importance to monitoring efforts is the
identification of the type of source, as to whether it is a point, line, or dif-
fuse, source. Several sources have more than one primary disposal method.
Table 1 summarizes the sources and causes of pollution, and common meth-
ods of waste disposal, where applicable.
MUNICIPAL. Three urban groundwater pollution sources are associated
with sewage: sewer leakage, sewage effluent disposal, and sewage sludge
disposal. Urban runoff, solid wastes, and lawn fertilizers are other sources
of importance. Since septic tanks also occur in rural areas, they are dis-
cussed under a separate heading.
Sewer Leakage. One of the more recently recognized sources of ground-
water pollution is leakage from sewer lines. Most monitoring programs for
detection of sewer leakage are not designed for groundwater pollution evalu-
ations. In the case of leakage from deep sewers, all of the topsoil and a
significant part of the vadose zone may be bypassed. Information on the lo-
cation of sewered areas and major sewers can be obtained from local public
works departments, sanitation districts, and regulatory agencies. Perti-
nent information on the sizes of major sewers, type of pipe and joints, age,
pressurization, and leaks should be compiled.
20
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TABLE 1. MAJOR SOURCES AND CAUSES OF GROUNDWATER POLLUTION AND METHODS OF
WASTE DISPOSAL
N)
SOURCE
Municipal
Sewer Leakage
Sewage Effluent
Sewage Sludge
Urban Runoff
Solid Wastes
Lawn Fertilizers
Agricultural
Eva potronspi ration
and Leaching
(Return Flow)
Fertilizers
Soil Amendments
Pesticides and
Herbicides
Animal Wastes
(Feed lots and
Dairies)
Stockpiles
Industrial
Cooling Water
Process Waters
Storm Runoff
Boiler Slowdown
Stockpiles
Water Treatment
Plant Effluent
Hydrocarbons
Tanks and Pipeline
Leaks
Oilfield Wastes
Brines
Hydrocarbons
Mining Wastes
Miscellaneous
Polluted Precipitation
and Surface Water
Septic Tanks and
Cesspools
Highway Deicing
Seawater Intrusion
CATEGORY
Point
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Line
X
X
X
X
X
X
X
X
Diffuse
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
COMMON METHOD OF DISPOSAL
Percolation
Pond
X
X
X
X
X
X
X
NOT APPLICABLE —
X
X
NOT APPLICABLE -
X
X
X
NOT APPLICABLE —
NOT APPLICABLE —
NOT APPLICABLE -
Surface Spreading
and Irrigation
X
X
X
X
X
X
X
X
X
X
X
X
X
Seepage Pits
and Trenches
X
X
X
X
Dry Stream
Beds
X
X
X
X
X
Landfills
X
X
X
X
X
X
Disposal
Wells
X
X
X
X
X
X
X
X
X
X
Injection
Wells
X
X
X
X
X
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Sewage Effluent. Sewage effluent has commonly been disposed of to
groundwater by a number of methods. Crop and forest irrigation, percola-
tion basins, dry stream beds, and disposal wells have been commonly used
for disposal of sewage effluent. Information on the location of treatment and
disposal facilities, methods of treatment and disposal, and effluent volumes
can be obtained from local public works departments, sanitation districts,
and regulatory agencies. Percolation basins and dry stream beds used for
disposal can be commonly seen on aerial photographs and crop surveys may
indicate lands where sewage effluent is used for irrigation.
Sewage Sludge. Sewage sludge is often allowed to dry in open basins from
which percolation may occur. Also, the dried sludge is commonly applied to
agricultural lands as fertilizer. Information on the weight of sludge produc-
tion and method of disposal can be obtained from local public works depart-
ments and sanitation districts. Sludge drying beds may be located from
aerial photographs.
Urban Runoff. Precipitation falling on paved and other impermeable
areas can pick up significant pollutant loads. Much storm water runoff is
now being collected, treated, and disposed of separately from sewage.
Common methods of disposal include percolation ponds, dry stream chan-
nels, disposal wells, and irrigation. Information on treatment and disposal
methods and volumes of waste water can be obtained from local flood control
districts, public works departments, and regulatory agencies.
Solid Wastes. Locations of municipal solid waste disposal sites can be
obtained from public works departments, local sanitary districts, and regu-
latory agencies. Regional solid waste planning documents may also be avail-
able. The type of site (sanitary landfill or refuse dump), the type of wastes,
the annual volume or weight, and the provisions for control of leachate
should be determined.
Lawn Fertilizers. Applications of water and fertilizer in amounts
greater than that used by plants in urban areas can produce groundwater pol-
lution. Information on types of fertilizers and amounts is difficult to obtain,
because of the diversity of practice from one household to the next. Fertil-
izer consumption may be estimated from sales records by manufacturers or
retailers. Information on irrigation rates would be important but are usual-
ly not available.
AGRICULTURAL.
Evapo trans pi ration and Leaching. The process of irrigation of agricul-
tural lands generally results in some water percolating past the root zone.
This percolating water is usually degraded with respect to the applied water
due to concentration by evapotranspiration, dissolution of mineral matter in
the soil, and additives that are applied at the land surface. Fertilizers,
22
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soil amendments, and pesticides are considered separately in this section
due to their importance in groundwater pollution. Irrigated lands can be
identified from aerial photographs or crop surveys, available from the USDA
Agricultural Research Service, farm advisors, or irrigation districts. Data
on the quality of return flow is rarely available. However, estimates can be
made based on the water application rates and consumptive use. The volume
of return flow can be calculated from records of precipitation, applied water,
and evapotranspiration.
Records of applied water volumes may be obtained from irrigation dis-
tricts, farmers, power companies, and governmental agencies concerned
with water delivery. The calculation of return flow volumes is more fully
discussed in Step 7 of this report.
Fertilizers. Fertilizers in modern agriculture are applied to almost all
crops, whether irrigated or not. Fertilizer application rates usually vary
with crop type, soil conditions, and irrigation practice. Local farm advi-
sors can provide information on types and amounts of fertilizers applied.
Records of fertilizer sales from manufacturers or retailers can be used to
estimate application rates. Regulatory agencies may also have data on fer-
tilizer use.
Soil Amendments. Soil amendments are applied to irrigated lands to alter
the physical or chemical properties of the soil. Acid soils may be treated
with lime to raise the pH, thus creating more favorable growing conditions
for plants. Gypsum or sulfur is widely used to increase infiltration rates on
some soils. Irrigation waters in which sodium is the predominant cation
may produce dispersion of the soil structure and result in low infiltration
rates. The calcium in the applied gypsum replaces sodium in the soil and
counteracts this soil clogging. Substantial amounts of these soil amendments
may eventually be leached into the groundwater, thereby increasing its salin-
ity. Records of application rates may be obtained from farm advisors and
manufacturers.
Pesticides and Herbicides. Pesticides may be significant in agricultural
areas as a diffuse source of groundwater pollution. Pesticides, insecticides,
herbicides, fungicides, and other chemicals are used to control nuisance or-
ganisms. Although many pesticides can be retained in the soil or degraded,
some have been found to be readily leached into the groundwater. Farm ad-
visors may have information on the types of pesticides used and application
rates. Manufacturers, retailers, and regulatory agencies may have records
on amounts sold in certain areas.
Animal Wastes. Livestock wastes generally constitute a minor ground-
water pollution source, except where large numbers of animals are confined
within small areas. This situation is usually limited to feedlots and dairies.
Dairies present additional problems related to the disposal of wash water.
23
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Animal waste disposal by percolation ponds and crop irrigation is common.
Feedlots and dairies can be located from land-use maps, zoning maps, and
aerial photographs. Information on the number of animals, annual weight
of solid waste, and volume of liquid waste can be obtained from farm advi-
sors, dairy and feedlot operators, cattle and dairy associations, and regula-
tory agencies.
Stockpiles. Unprotected stockpiles in agricultural areas may result in
groundwater pollution, particularly where substantial leaching into the soil
occurs. These stockpiles include manure; solid chemicals, such as gypsum
or sulfur; and miscellaneous waste solids and liquids, such as pesticide con-
tainers. Field surveys are often necessary to detect such occurrences.
INDUSTRIAL. Industrial waste flows are usually related to the amount of
raw material processed, to the amount of finished product, or to the number
of people employed in the factory. Data on industrial waste flows can be ob-
tained from local industries and regulatory agencies. Stockpiles and perco-
lation ponds can be seen on aerial photographs. Data on injection wells have
been compiled by the U. S. Geological Survey.
OILFIELD WASTES. Brines are commonly withdrawn from the ground
during oil and natural gas production and must subsequently be discarded.
Disposal of brines in percolation ponds and injection wells has been wide-
spread. Brines may also be disposed of in dry stream beds, while some
brines of low salinity may be used for crop irrigation. Hydrocarbons may
be another source of groundwater pollution where wastes are confined in
ponds at the land surface. Improperly constructed producing or injection
wells can cause significant groundwater pollution. Information on quantity
and type of wastes is often available from State oil and gas commissions,
regulatory agencies, and local operators.
MINING WASTES. The mining and milling of coal and metallic ores,
whether from surface or underground mines, can cause groundwater pollu-
tion; therefore, these installations need to be clearly identified if they occur •
in a monitoring area. Information on mines, their types, their depth, their
areal extent, and the amounts and composition of wastes produced is usually
available from a State mining agency, the U. S. Bureau of Mines, mining
companies, and regulatory agencies.
MISCELLANEOUS.
Polluted Precipitation and Surface Water. Precipitation can be polluted
from municipal sources, such as industries and automobile exhaust, as well
as agricultural activities, such as the application of ammonia fertilizers. In
humid areas, where rainfall is readily leached into the groundwater, pollut-
ants from precipitation may reach the water table. In arid areas, the pollut-
ants in precipitation may accumulate on the land surface and subsequently be
24
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leached by irrigation water. Areas where infiltration and percolation to the
groundwater may occur from polluted surface water should be identified. In-
filtration and percolation rates may be available from hydrogeologic studies
by the U. S. Geological Survey, State geological or water agencies, or others.
Septic Tanks and Cesspools. In unsewered areas large numbers of septic
tanks and cesspools may be found. Although each is a point source with re-
spect to an individual lot, over large areas septic tanks are diffuse sources
of groundwater pollution. Methods of disposal commonly include seepage
pits, seepage trenches, and occasionally disposal wells. Location densities,
and estimated volume of effluent can be obtained from zoning maps, public
works departments, sanitation districts, and regulatory agencies.
Highway Deicing. Sodium chloride and calcium chloride salts are com-
monly applied to roads to inhibit or to remove ice. Information on the appli-
cation of salts for deicing of roadways in winter can be obtained from State
and local transportation offices. Data should be collected on which roadways
are regularly treated with salt and on the estimated application rate, such as
tons of salt per lane mile.
The above listing provides an orderly basis for identifying the principal
sources and causes of groundwater pollution within a monitoring area. An
important footnote is that the listing stresses present-day sources and
causes; however, historical sources and causes which are no longer present
or active, such as former refuse dumps, brine disposal ponds, and feedlots,
among others, may still be responsible for pollution today. This occurs be-
cause of the relatively long residence time of pollutants in most groundwater
systems, which may be on the order of decades or centuries. It follows,
therefore, that while identifying present sources and causes, an effort
should also be made to find previous ones that may no longer be visible on
the landscape but may be quite evident underground. Examination of old land
use or zoning maps and early aerial photographs should prove helpful for this
purpose. Furthermore, conversations with long-time residents who are
knowledgeable of local activities may reveal information about pollution
sources in previous times.
Step 3 — Identify Potential Pollutants
Having identified the pollution sources and the methods of disposal, the
next step is to identify potential pollutants for each source. Major determi-
nations in a water analysis are classified into physical, inorganic chemical,
organic chemical, bacteriological, and radiological (Table 2). Table 3 sum-
marizes the major sources of groundwater pollution and the types of pollut-
ant generally present. The trace element portion of the inorganic chemicals
has been separated into another category for discussion purposes.
25
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TABLE 2. CLASSIFICATION OF MAJOR POTENTIAL POLLUTANTS IN
GROUND WATER
Physicol
Temperature
Density
Odor
Turbidity
Inorganic Chemical
Major Constituents
Other Constituents
Trace Elements
Gases
Bacteriological
Coliform Group
Pathogenic Micro-
organisms
Enteric Viruses
Organic Chemical
Carbon
Chlorophylls
Extractable Organic Matter
Methylene Blue Active
Substances
Nitrogen
Chemical Oxygen Demand
Phenolic Material
Pesticides (Insecticides
and Herbicides)
Radiological
Gross Alpha Activity
Gross Beta Activity
Strontium
Radium
Tritium
TABLE 3. MAJOR SOURCES OF GROUNDWATER POLLUTION AND TYPES
OF POLLUTANTS
SOURCE
Municipal
Sewer Leakage
Sewage Effluent
Sewage Sludge
Urban Runoff
Solid Wastes
Lawn Fertilizers
Agricultural
Evapotranspiration and Leaching
Fertilizers
Soil Amendments
Pesticides
Animal Wastes (Feedlots and
Dairies)
Stockpiles
Industrial
Cooling Water
Process Waters
Storm Runoff
Boiler Slowdown
Stockpiles
Water Treatment Plant Effluent
Hydrocarbon)
Tank and Pipeline Leakage
Oilfield Wastes
Brines
Hydrocarbons
Mining Wastes
Miscellaneous
Polluted Precipitation and
Surface Water
Septic Tanks and Cesspools
Highway Deicing
Seawater Intrusion
TYPE OF POLLUTANT
Physical
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Primary
Variable
Minor
Primary
Minor
Minor
Secondary
Variable
Primary
Secondary
Minor
Variable
Minor
Minor
Primary
Inorganic
Chemical
Primary
Primary
Primary
Secondary
Primary
Primary
Primary
Primary
Primary
Minor
Primary
Primary
Minor
Primary
Secondary
Secondary
Primary
Primary
Secondary
Variable
Primary
Secondary
Primary
Variable
Primary
Primary
Primary
Trace
Elements
Secondary
Secondary
Primary
Variable
Primary
Minor
Minor
Secondary
Minor
Minor
Minor
Minor
Primary
Primary
Variable
Primary
Variable •
Secondary
Secondary
Variable
Primary
Secondaiy
Primary
Variable
Minor
Minor
Primary
Organic
Chemical
Primary
Primary
Primary
Primary
Primary
Minor
Minor
Secondary
Minor
Primary
Secondary
Variable
Minor
Variable
Primary
Minor
Variable
Minor
Primary
Variable
Minor
Primary
Variable
Variable
Secondary
Secondary
Minor
iacteriological
Primary
Primary
Primary
Minor
Secondary
Minor
Minor
Minor
Minor
Minor
Primary
Variable
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Variable
Primary
Minor
Minor
Radiological
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Minor
Variable
Minor
Minor
Variable
Minor
Minor
Variable
Minor
Minor
Variable
Variable
Minor
Minor
Minor
26
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Physical parameters, such as temperature and density, are of most con-
cern in industrial and oilfield wastes. Inorganic chemicals are generally of
primary concern in virtually all wastes. Trace elements are of concern in
most categories of sources other than agricultural. Organic chemicals ap-
pear to be of concern in wastes from many types of sources. Bacteriologi-
cal parameters are of primary concern in municipal sources, animal wastes,
and in septic tank effluent or cesspool wastes. Radiological parameters are
generally only of concern in some industrial and mining wastes. Major at-
tenuation mechanisms can operate on many physical, organic chemical, bac-
teriological, and radiological constituents in passage through the topsoil and
adequate thicknesses of the vadose zone. However, in the case of inorganic
chemicals, these attenuation mechanisms are less effective. The attenua-
tion mechanisms are described in more detail in the following steps; how-
ever, they have been considered in identifying potential groundwater pollut-
ants.
Table 4 represents the inorganic chemical pollutants and gases common
in groundwater or wastes. Pollutants are grouped on the basis of major
TABLE 4. INORGANIC CHEMICAL POLLUTANTS
Major
Calcium
Magnesium
Sodium
Potassium
Carbonate
Bicarbonate
Sulfate
Chloride
Nitrate
Total Dissolved Solids
PH
Electrical Conductivity
Oxidation Potential
Other Trace
Vanadium
Molybdenum
Bromide
Iodide
Nickel
Aluminum
Cobalt
Lithium
Sulfide
Beryllium
Others
Silica
Boron
Fluoride
Nitrogen Forms
Phosphorus Forms
Hardness
Gases
Methane
Hydrogen Sulfide
Carbon Dioxide
Dissolved Oxygen
Residual Chlorine
Drinking Water Trace
Iron
Manganese
Arsenic
Barium
Cadmium
Hexavalent Chromium
Copper
Cyanide
Lead
Selenium
Silver
Zinc
Mercury
27
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constituents commonly found in groundwater, additional constituents of inter-
est in water use, trace elements of interest for drinking water quality, and
additional trace elements common in some wastes.
The reports by Todd and McNulty (1974) and Meyer (1973) contain infor-
mation regarding case histories of groundwater pollution. Data on the com-
mon specific pollutants in the major pollution sources are discussed in the
following paragraphs.
MUNICIPAL. Five major municipal sources of pollutants can occur.
Sewage Effluent. For most secondary treated sewage effluent, the com-
mon specific pollutants are similar to those found in raw sewage. Thus,
this discussion pertains to leaking sewers also. The inorganic composition
of sewage effluent usually reflects the inorganic composition of the water
supply. Little or none of the inorganic chemicals is removed during sec-
ondary treatment. Many heavy metals such as zinc, copper, iron, manga-
nese, chromium, cadmium, lead, mercury, cobalt, and arsenic may enter
sewage as a discharge from industry. However, many of the trace metals
are removed with the sewage sludge. About 50 milligrams per liter (mg/1)
of organic matter is usually present in secondary sewage effluent. More
than one-half of the effluent organics is generally soluble. Hunter and
Kotalik (1973) and the American Chemical Society (1969) presented data on
constituents in sewage effluent. The effects of sewage effluent disposal on
groundwater were discussed by Ellis (1973), Hughes et al. (1974), Schmidt
(1973), Began (1961), and Bouwer et al. (1972).
Sewage Sludge. Peterson et al. (1973) discussed the constituents in sew-
age sludge. Most constituents considered under "sewage effluent" would be
applicable, except there is more emphasis on trace elements, as those
found in raw sewage are commonly concentrated in the sewage sludge.
There have been few reported groundwater quality investigations beneath
sludge drying beds; however, there is little doubt that this is a major point
source of groundwater pollution.
Storm Runoff. The pollutants in storm runoff have been more widely
recognized subsequent to the large-scale separation of this waste from sew-
age. Of concern to groundwater pollution is the presence of nitrogen and
phosphorus, trace elements, and organic chemicals. High contents of lead
and zinc have commonly been found in storm runoff. Gasoline, oil, grease,
and pesticides are also common. (Sartor and Boyd, 1972).
Solid Wastes. Leachate analyses are highly variable; however, the
major inorganic chemical constituents are usually present. Trace elements
include iron, manganese, barium, chromium, lead, selenium, zinc, and
possibly others. Organic chemicals are abundant in leachate. Hughes et al.
(1971), Schneider (1970), California Department of Water Resources (1969),
28
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Weaver (1964), and Salvato et al. (1971) discussed constituents in solid
wastes. There are a large number of evaluations concerning the effects of
leachates on groundwater quality. Zanoni (1971), Apgar and Langmuir
(1971), Kimmel and Braids (1974), Zenone et al. (1975), Weist and Pettijohn
(1975), Coe (1970), Seitz (1972), and Andersen (1972) have reported on these
evaluations.
Lawn Fertilizers. Primary concerns in lawn fertilizers are nitrogen,
phosphorus, and potassium. Fertilizers are discussed more extensively
under the section on Agricultural Sources.
AGRICULTURAL. Water percolating past the root zone in irrigated
areas commonly is degraded compared to the applied water. This degrada-
tion is due to evapotranspiration, leaching of salts from the soil, and addi-
tives applied in the irrigation water, such as fertilizers, soil amendments,
and pesticides.
Evapotranspiration and Leaching. Of major concern here are the major
inorganic chemical constituents. In general the most mobile or soluble con-
stituents will be concentrated the most by evapotranspiration. Of the major
chemical constituents, sodium, chloride, nitrate, and boron are the most
mobile in usual soil-groundwater systems. Law et al. (1970), Skogerboe
and Law (1971), Flack and Howe (1974), and Fuhriman and Barton (1971)
discussed return flow from agricultural lands. Mineral dissolution can oc-
cur in all areas. Salts in the topsoil and vadose zone in arid areas can also
be dissolved by waters percolating from irrigation. Of most concern are
sodium, calcium, chloride, bicarbonate, boron, and total dissolved solids.
Doneen (1967) and the University of California at Davis (1968) discussed
these phenomena for newly-developed lands in California.
Fertilizers. The primary fertilizers are nitrogen, phosphorus, and po-
tassium. Significant amounts of other major chemical constituents can be
added in compound form with the fertilizer, such as chloride in potassium
chloride. Secondary fertilizers are calcium, magnesium, sulfur, boron,
manganese, copper, zinc, molybdenum, chloride, cobalt, vanadium, and
sodium. The major concerns in most groundwater systems are nitrate and
the accompanying increase in salinity related to the application of nitrogen.
Ammonia also has the ability to replace many other cations on the exchange
complex of the soil thus allowing them to be leached into the groundwater.
The literature is voluminous, and often contradictory, on the effects of fer-
tilizers on groundwater quality. Mink (1962), Moore (1970), Willrich and
Smith (1970a), Tisdale and Nelson (1966), Fitzsimmons et al. (1972), and
Shaw (1968) have discussed fertilizers and groundwater pollution.
Soil Amendments. The most common soil amendments of importance to
groundwater pollution are gypsum, lime, and manure. Manure, in part,
29
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falls under the fertilizer category. Gypsum contains calcium and sulfide,
and lime commonly contains calcium or calcium and magnesium carbonate.
Sulfur may be applied to calcic solid in the elemental form. The pH and bi-
carbonate are important parameters, as lime is frequently applied to change
the soil pH. When gypsum is applied, it frequently results in the leaching of
sodium held in the soil, along with sulfate. Buckman and Brady (1969) dis-
cussed soil amendments and their use in agriculture.
Pesticides and Herbicides. Pesticides, herbicides, fungicides, and other
chemicals are used for nuisance organism control. Drinking water stand-
ards are proposed for the common chlorinated hydrocarbons and for total
organophosphorus and carbamate compounds. Thus, for monitoring ground-
water pollution, DDT, 2,4-D, lindane, and herbicides are major concerns.
Willrich and Smith (1970b), California Department of Water Resources
(1968), Johnston et al. (1967), Scalf et al. (1968), Dregne et al. (1969), and
Schneider et al. (1970), discussed pesticides and groundwater pollution.
Animal Wastes. Constituents of concern in animal wastes are somewhat
similar to those found in human sewage, including many of the major inor-
ganic chemical constituents, particularly nitrate, chloride, sulfate, and
total dissolved solids. Organic matter and bacteriological constituents are
also present. Willrich and Smith (1970c), Stewart et al. (1967, 1968), Loehr
(1967), Concannon and Genetelli (1971), Gillham and Webber (1969), and
Adriano et al. (1971) have discussed animal wastes and groundwater pollution.
INDUSTRIAL. Pollution from industry includes the following six types.
Cooling Water. Major degradation of cooling water results from temper-
ature increases and possibly from some trace elements introduced as addi-
tives, such as rust inhibitors. If large amounts of evaporation occur brines
may result, and concerns for overall salinity and the major inorganic chem-
ical constituents would be increased.
Process Water. Industrial process water is highly variable; however, in
general, trace elements will be of major concern. These could be intro-
duced from raw materials and chemicals used in the process, Temperature
and density could be important. The major inorganic chemical constituents
would usually be of concern, as well as overall salinity. Organic chemicals
would be common constituents, such as hydrocarbons, reagents added for
processing, etc. Radioactive components are important in the disposal of
nuclear plant wastes and certain other operations. Radium, strontium, and
alpha and beta activity are major criteria for drinking water.
Storm Runoff. The quality of storm runoff is highly influenced by house-
keeping procedures and drainage systems. If significant amounts of solids
and liquids are spilled, blown by the wind, and left to accumulate on the top-
soil or impermeable surfaces, they can be subsequently mobilized by storm
30
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runoff. The major concerns are organic chemicals, such as hydrocarbons,
and possibly trace elements. Major inorganic chemicals are also important.
Boiler Slowdown. Major concerns with boiler blowdown water are tem-
perature and several of the major inorganic chemicals, namely, silica,
calcium, magnesium, bicarbonate, and selected trace elements.
Stockpiles. Stockpiles for storage of raw materials, products, byprod-
ucts, and wastes at industrial sites would be highly variable, somewhat simi-
lar to process water. However, physical parameters would generally be of
less importance.
Water Treatment Plant Effluent. Some of the major inorganic chemicals
would be of concern, particularly sodium, chloride, calcium, sulfate, bi-
carbonate, and nitrate, and total dissolved solids. In some cases, selected
trace elements may be of concern.
Studies of industrial waste pollution of groundwater are numerous. Ex-
amples are Tucker (1971), Smith (1971), Williams and Wilder (1971), Matis
(1971), Sweet and Fetrow (1975), Walker (1961), Deutsch (1961), Walton
(1961), and Hanby et al. (1973).
OILFIELD WASTES. Brines and hydrocarbons are present in oilfield
wastes.
Brines. Density and possibly temperature could be important for oilfield
brines. The major inorganic chemical constituents are of concern, particu-
larly sodium, chloride, calcium, sulfate, bicarbonate, and total dissolved
solids. Boron, ammonium, fluoride, bromide, and iodide are also common
in brines. Many trace elements are commonly present such as lead, iron,
strontium, zinc, manganese, nickel, and aluminum.
Hydrocarbons. Materials such as oil can pollute groundwater, and thus
hydrocarbons are of major concern.
References by Mattox (1970) and White et al. (1963) detail the composition
of saline waters. Many references have documented groundwater pollution
from disposal of oilfield wastes, such as Fryberger (1975), Pettyjohn (1972),
Bain (1970), Krieger and Hendrickson (I960), Knowles (1965), and McMil-
lion (1965).
MINING WASTES. Waste production from mining activities has been dis-
cussed in detail by Williams (1975). In general the major inorganic chemi-
cal constituents will be important and often trace elements will be of pri-
mary concern. Nitrogen forms may be used in explosives and could appear
in the groundwater. Trace elements will depend on constituents of ore proc-
essed and reagents added. Organic chemicals may be added as reagents and
radiological constituents may be present in the ore.
31
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MISCELLANEOUS. Miscellaneous sources of pollution are the following.
Septic Tanks and Cesspools. The constituents of importance are general-
ly similar to those in sewage effluent, except trace elements will usually be
absent. Also the chances for nitrification in the topsoil or vadose zone are
generally better in the case of septic tanks. Polta (1969), Waltz (1971),
Schmidt (1972), Quan et al. (1974), and Pitt (1974) have discussed the
groundwater pollution due to individual sewage disposal systems.
Highway Deicing. Of primary concern in highway deicing are sodium,
chloride, and calcium. Some organic chemicals are periodically used.
Saline Water Intrusion. The same constituents are of interest as for
brines under Oilfield Wastes.
Step 4 — Define Groundwater Usage
To evaluate the impact of pollution or potential pollution of groundwater,
the usage of the resource becomes a key item. Thus, it is important to de-
fine both the quantities of groundwater being extracted or projected to be ex-
tracted, and the locations of major pumping centers within a monitoring
area. Pumpage data on a gross basis are usually available from the U.S.
Geological Survey, State water agencies, and some local water agencies.
Often it will be necessary to refine the data in order to make them useful in
developing an effective monitoring program.
Pumpage will usually vary on a weekly and on a monthly basis; however,
in many cases mean annual extractions will be sufficient to evaluate ground-
water flows and pollutant movement for monitoring purposes. These data
will serve as inputs to the hydrogeologic analysis in a subsequent step.
Determination of groundwater pumpage depends on the type of use. The
basic categories of use — municipal, industrial, agricultural, and rural —
are described below in terms of how their pumpage quantities can be defined.
MUNICIPAL USE. Groundwater pumpage for an urban area is often
available from records of water purveyors. Furthermore, locations and
yields of individual wells and well fields are usually known.
INDUSTRIAL USE. Many industries purchase water from municipal
sources; consequently, under these circumstances groundwater use is in-
corporated in the municipal category. On the other hand, some industries
use self-supplied water, and a portion of these draw upon groundwater
through wells. On a national basis the following types of industries are the
heaviest users of groundwater:
32
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Rank in Terms of
Total Groundwater Use Type of Industry
1 Oil Refining
2 Paper Manufacturing
3 Metal Working
4 Chemical Manufacturing
5 Building, Air Conditioning and
Refrigerating
6 Distilling
7 Ice Manufacturing and Cold Storage
8 Food Processing
9 Rubber Manufacturing
10 Meat Packing
11 Brewing
12 Railroad Yards
13 Gas and Electricity-
14 Dairying
15 Electric Equipment Manufacturing
If no local summary of industrial use of self-supplied ground-water is
available from appropriate public agencies, pertinent industries will have to
be identified. Industrial areas can be located from aerial photographs or
zoning maps; industries which do not receive municipal water can then be
contacted to obtain their annual groundwater pumpage data. Often these are
not directly available and must be estimated from the type of industry, num-
ber of workers, units of production, or other factors.
AGRICULTURAL USE. In the Western United States groundwater is used
mostly in irrigated agriculture; however, data on such usage are also gen-
erally difficult to obtain. Accurate records of pumpage are rarely kept by
farmers, and, in fact, most irrigation wells are not equipped with flow
meters. Pumpage estimates can be made by either of two methods. One is
to determine cropping patterns of areas irrigated by wells, using aerial
photographs and crop surveys. By knowing the consumptive use of the crops
and representative irrigation efficiencies (from local farm advisors) and
mean annual growing season rainfall (from U.S. National Weather Service
records), the total applied water for irrigation purposes can be computed.
In areas where both surface water and groundwater are used, the portion of
applied water supplied by groundwater can usually be determined from irri-
gation district records. A second approach is to obtain records of power
consumption for representative pumps and of pump discharges per unit of
power use from electric utility companies. These data enable the quantities
of water pumped to be calculated. Where such data are available for only a
fraction of the irrigated area, extrapolation to the gross area can be made;
however, results can be subject to error if significant differences in pump-
ing levels exist.
33
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RURAL USE. Data will rarely be available on pumpage from individual
domestic water supply wells in rural areas. Estimates of pumpage can be
made, however, by multiplying rural population figures by typical per capita
water use. In general, these pumpage rates are so scattered over agricul-
tural areas that they do not influence the groundwater flow. However, the
existence of the rural use should be recognized, particularly in the event of
a localized pollution problem.
In summary, the total of the four above groundwater uses provides the
usage data for a monitoring area. Locations of major pumping centers,
such as well fields of municipalities and large industries, should be identi-
fied. Average pumpage rates over uniform subareas, such as irrigated
lands, should be defined from irrigation well pumping rates and well densi-
ties. Great precision in determining groundwater pumpage is not as impor-
tant as a comprehensive coverage of all significant pumpage within an area.
Step 5 — Define Hydrogeologic Situation
To understand where and how groundwater pollution occurs and moves
within a monitoring area, the hydrogeologic framework must be understood.
This information will aid in the design of an effective as well as an efficient
groundwater quality monitoring system.
Because some subsurface data are available in most areas of groundwater
development, initial hydrogeologic work will consist of gathering, organiz-
ing, and analyzing existing information. On other occasions, geologic or
hydrologic investigations requiring field work will be necessary. Specific
materials needed for the monitoring program, as well as how they are ob-
tained, include:
• Aquifer locations, depths, and areal extents — from geologic data
• Transmissivities of aquifers — from well pumping tests and
geologic data
• Map of groundwater levels — from observations of well levels
• Map of depths to groundwater — from water level and topographic
data
• Areas and magnitudes of natural groundwater recharge — from
precipitation, evapotranspiration, soils, land use, and water level
data
• Areas and magnitudes of artificial groundwater recharge — from
irrigation and recharge data
• Areas and magnitudes of natural groundwater discharge — from
streamflow and water level data
34
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• Directions and velocities of groundwater flows — from water
level and transmissivity data.
Information sources for preparation of the above items should normally
include State geologic and water agencies, local water agencies, the U. S.
Geological Survey, and the U. S. National Weather Service.
In preparing the above materials it should be kept in mind that these serve
as tools for monitoring; consequently, the hydrogeologic effort should not be-
come an obstacle to the completion of the monitoring program. All hydro-
geologic data are incomplete in a relative sens. . What is needed is an over-
all picture of the hydrogeologic situation in the monitoring area. Initially,
refinement is less important than comprehensive coverage, no matter how
preliminary or approximate. Categories indicating ranges rather than spec-
ific values, such as for transmissivity or dissolved solids, are often suffi-
cient. Also, it should be recognized that with time and with increasing
amounts of groundwater data, knowledge of the hydrogeologic situation will
gradually improve.
EXAMPLE 1 - POLLUTION PLUME GEOMETRY. Figure 2 shows
examples of the configurations of pollution plumes resulting from a pollution
source, such as a landfill, located near a river. In Figure 2(A) the angle
between the groundwater flow direction and the river is relatively large.
This limits the extent of the plume; furthermore, where the source is located
close to the river, the plume is smaller. In Figure 2(B) the angle between
the groundwater flow direction and the river is relatively small; this creates
elongated plumes, particularly where the source is some distance from the
stream.
EXAMPLE 2 - GROUNDWATER FLOW SYSTEM. Figure 3 depicts
schematically a groundwater flow system under idealized homogeneous aqui-
fer conditions. Groundwater travels along flow paths which extend from
areas of groundwater recharge to areas of groundwater discharge. Horizon-
tal and vertical gradients are indicated by equipotential lines; potential, or
total head, is simply the elevation to which water will rise in a cased well
from a point source below the water table. Groundwater moves in the direc-
tion of decreasing total head. In recharge and discharge areas, movement
may have an appreciable vertical component; between these end areas, flow
is predominantly horizontal. Any pollution will travel along the flow line
where it occurs.
EXAMPLE 3 — COMPLEX PLUME GEOMETRIES. Figure 4 presents
an idealized vertical aquifer cross-section, somewhat similar to Figure 3,
together with the pollution plumes for various locations of pollution sources.
Note that Sources A-l and A-2 create short plumes because they are close
to streams, while B and C are longer because they are more distant.
Source F, located in a discharge area, has no effect on groundwater quality.
35
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Figure 2. Relation of groundwater pollution plume size and orientation for a pollution
source near a river with different groundwater flow directions (Palmquist and
Sendlein, 1975).
36
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Figure 3. Groundwater flow system under idealized homogeneous aquifer conditions
(modified after Born and Stephenson, 1969).
Sources D and E-2 cause two plumes in different directions, while E-1 is
responsible for three distinct plumes. Clearly, recognition of the hydro-
geological conditions controlling the number, shape, and locations of pollu-
tion plumes is essential in selecting groundwater monitoring sites.
EXAMPLE 4 - POLLUTION FROM A PERCOLATION POND. Figure
5 illustrates how hydrogeologic conditions can influence the movement of pol-
lution from a percolation pond. Here the aquifer is recharged by a lake on
the north side, while on the southwest a river both recharges and receives
discharge from the aquifer. Near the center of the aquifer a well field
creates a radially converging flow pattern, and south of it is located a re-
charge pond which is maintained at a constant water level. Flow lines of
groundwater for steady-state conditions are shown on Figure 5. In addi-
tion, it is assumed that at a certain time, pollution is introduced into the
pond. By means of an electronic analog model, the advancing pollution
front can be calculated. Positions of the front for 40 and 80 days after the
beginning of pollution are shown in Figure 5. Note that between these two
time intervals pollution has reached both the well field and the river. The
dashed lines define the ultimate limits of pollution from the percolation pond.
EXAMPLE 5 EFFECT OF PUMPING ON GROUNDWATER FLOW.
Figure 6 provides dramatic evidence of how heavy pumping in an urban area
can influence groundwater flow directions. Solid lines are water table con-
tours; these show that the water table is more than 70 feet below sea level
37
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D RIVER
RIVER
! A-l
Figure 4. Idealized polluHon plume configuration for various locations of surface
pollution sources (modified after Palmquist and Sendlein, 1975).
in the center of Stockton, California. It can be seen that any pollutants in
the groundwater are transported toward the city from a large area. If such
a cone of depression results from pumping of water supply wells, the con-
centrating effect of the wells moves all pollution into them, which is clearly
undesirable.
EXAMPLE 6 - DENSITY EFFECT ON POLLUTION DISTRIBUTION.
Figure 7 shows the distribution of saline water below a brine disposal pit in
an oil field in southwestern Arkansas. Because the brine is denser than
native groundwater, it has traveled to the bottom of the sandy confined aqui-
fer and thereafter has spread laterally. The primary extension of pollution
is southward due to the natural groundwater gradient in this direction. If
the pollutant had possessed a density more nearly that of the native ground-
water, it would be expected to drift horizontally near the top of the aquifer.
Thus, the physical character of a pollutant can have a significant effect on
how it moves within an aquifer.
38
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IMPERMEABLE
BOUNDARY
WELL FIELDS
IMPERMEABLE
BOUNDARY
KEY
STREAM LINE
POSITION OF FRONT
AFTER 40 DAYS.
•- 40
Figure 5. Flow lines for steady-state conditions in an aquifer and positions of a
pollution front advancing from a percolation pond (Cole, 1975).
Step 6 — Study Existing Groundwater Quality
In order to define the groundwater quality problems within a monitoring
area, an assessment needs to be made of the background quality situation.
To do this, recent groundwater quality data need to be collected and re-
viewed. Attention should be focused first on the natural groundwater
39
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(SEA LEVEL DATUM)
. 5O APPROXIMATE ELEVATION OF
WATER IN WELLS (SEA LEVEL
DATUM)
Figure 6. Water table contours in the vicinity of Stockton, California, Fall 1964
(California Department of Water Resources, 1967).
40
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POTENTKDMETRIC SURFACE
^*£^^Qf£±^*ri&^ • \
180
1000
LEGEND:
000
o
500 1000 1500 2000
DISTANCE FROM DISPOSAL WELL (feet)
I
CHLORIDES IN mg/liter 11/69-4/70
SAMPLE TAKEN DURING DRILLING
PERMANENT SAMPLING POINT
Figure 7. Distribution of saline water in a confined aquifer resulting from an oilfield brine disposal pit
in southwestern Arkansas (modified after Fryberger, 1975).
-------
quality. A map of indicators of pollution in groundwater, taking into account
variations as a function of depth, should be prepared from available well
water analyses. This map will typically show a limited range of values with-
in an extensive aquifer. However, if considerable variability or isolated
anomalies are evident, these may be indicative of the presence of pollution.
To verify possibilities of pollution, regions or localities displaying unu-
sual quality data must then be examined in conjunction with the inventory of
pollution sources and methods of disposal (Step 2) and with hydrogeologic
data (Step 5). Where these jointly suggest the physical feasibility of pollu-
tion, it is reasonable to assume that pollution exists. Once pollution is ten-
tatively identified, the specific pollutants involved, the areal extent, and the
direction and rate of movement can be defined at least approximately.
It is often surprising how many quality data, after investigation, are ac-
tually available. A certain amount of ingenuity is required to locate frag-
mented data and to interpret them in terms of the subsurface situation.
Judgment, however, must frequently be exercised so as to select meaningful
data and to avoid those -which are erroneous.
In addition to collecting current data, past groundwater quality records
should be reviewed wherever possible. Historical quality records are help-
ful in establishing the quality of native groundwater, in evaluating quality
trends with time and in relating changes in groundwater quality to sources
and causes.
Information sources for groundwater quality data should normally include
State geologic and water agencies, the U.S. Geological Survey, local water
and regulatory agencies, and industries with self-supplied groundwater.
It should be recognized that significant portions of a monitoring area may
entirely lack groundwater quality data, so that no direct indications of pol-
lution can be obtained. However, sources and causes as well as hydrogeo-
logic evidence may suggest locations of potential pollution. Verification can
only come with the implementation of the monitoring program.
Step 7 — Evaluate Infiltration Potential
of Wastes at the Land Surface
Following the development of an understanding of the hydrogeologic
framework, a key step in the methodology will be to determine the volume
of polluted water which will pass through the vadose zone into the zone of
saturation. This volume will vary depending on the method of waste dispos-
al used and the infiltration characteristics of the soil. The monitoring
methods applicable to the above determination are discussed in detail in
Section III of a companion report (Everett et al. , 1976).
42
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Considering the common methods of waste disposal presented previously
in Step 2, Table 1, the total volume of polluted water associated with surface
spreading, irrigation, or disposal into dry stream beds, will move directly
into the topsoil or stream bed. The volume of polluted water associated
with percolation ponds, seepage pits, trenches, or landfills will bypass the
topsoil and enter the underlying portion of the vadose zone or saturated zone
depending on the depth to the water table.
Disposal -wells used to dispose of storm water and domestic sewage fre-
quently are terminated in the vadose zone. The volume of polluted water
reaching the zone of saturation will be equal to the volume discharged into
the well, minus that portion retained by the soil. A properly designed in-
jection well for disposal of industrial wastes or brines will completely by-
pass the vadose zone and all freshwater aquifers. Monitoring procedures
for injection wells are discussed at length by Warner (1975).
The water budget method can be used to calculate infiltration from sur-
face spreading or irrigation. In the water budget approach, waste water
discharge and precipitation are volumetric ally summed as the input, and in-
filtration is computed as the difference between this input and evapotrans-
piration. Applied water volumes can be determined from records of waste
water discharge /surface water deliveries, and groundwater pumpage. Pre-
cipitation volumes can usually be extrapolated from rainfall gaging stations
in nearby areas. Monthly rainfall determinations are often suitable; how-
ever, in areas with highly variable precipitation, such as in Southwestern
States, onsite measurements may be necessary.
Evapotranspiration from areas where surface spreading or irrigation is
used can be determined by a number of methods (Gruff and Thompson, 1967;
Blaney and Griddle, 1962; Lowry and Johnson, 1942; Penman, 1948; and
Thornthwaite, 1948). These methods are generally based on different group-
ings of climatological parameters. For example, the Blaney-Griddle method
depends primarily on temperature and percentage of daylight hours. In
general the Penman and Thornthwaite methods are more applicable to humid
areas, whereas the Blaney-Griddle method is more applicable to semiarid
areas.
Different values of evapotr an s pi ration and consumptive use are usually
obtained for different crops and soil conditions. Thus, the cropping pattern
must be known, and factors such as double-cropping considered. Sufficient
field tests have been conducted in many areas so that evapotranspiration and
consumptive use for major crops are well established. In some areas, data
may have to be extrapolated from similar areas. Evapotranspiration rates
will generally be needed on at least a monthly basis, and sometimes weekly.
In summing up the water budget components for surface spreading and
irrigation, the infiltrating component is divided into two components. A
43
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portion of this component is diverted into soil moisture retention. This soil
moisture component will be gradually depleted by transpiration during peri-
ods of zero recharge. When the field capacity requirements have been satis-
fied the remaining portion will percolate to the zone of saturation.
In many parts of the arid and semiarid West, significant volumes of
waste waters are disposed of into normally dry stream channels. Disposal
of mining wastes and sewage effluent in Arizona and oilfield wastes in Cali-
fornia by this method is common. That portion which does not leave the area
as runoff or evaporate infiltrates into the stream bed. Part of the percolate
will be held in storage and the remainder will flow on to the zone of satura-
tion. The portion held in storage will be quite small relative to that of a
normal soil profile because of the high permeability associated with stream
bed materials.
Stream flow records at different gaging stations along the particular reach
under investigation, combined with records of precipitation, evaporation,
estimates of soil moisture content, and stream flow diversions, can be used
to calculate percolation to the water table. In some areas the U. S. Geologi-
cal Survey, State geological or water agencies, or others may have already
made estimates of infiltration.
The water budget method can also be used to calculate seepage from per-
colation ponds. In this context, "percolation pond" is used to signify any
pond which permits significant movement of water into the underground.
Waste discharge and precipitation are volumetrically summed as the input,
and seepage is calculated as the difference between input and evaporation.
Storage changes in the pond must also be taken into account. Evaporation
from free-water surfaces can be determined from measurements using land
pans or floating pans (Harbeck et al. , 1958; Kohler et al. , 1955; Follans-
bee, 1933; and Rohwer, 1933). Monthly values will often suffice; however,
in some cases weekly or daily values are necessary.
Factors such as salinity of waste water can affect the evaporation rate.
In general, with increasing salinity the vapor pressure of water decreases,
resulting in a lower evaporation rate. In considering evaporation from free-
water surfaces from ponds of different sizes, consideration should be given
to edge effects. That is, evaporation rates depend on the characteristics of
the surrounding land, for example, whether it is cultivated or undeveloped.
In some ponds such as mine tailings ponds, water may occur in several
states — such as free water, moist tailings, and wet tailings. Where ponds
are periodically dried to improve infiltration rates, evaporation from moist
areas and wet areas must be considered separately from the free-water
evaporation. Methods for determining such evaporation are not well devel-
oped. Field measurements using lysimeters can be used as an independent
check on evaporation from soil surfaces. It may be sufficient to apply
44
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correction factors to the evaporation rate calculated from lysimeters for
use in free-water surfaces.
Effluent from septic tanks and other wastes is commonly disposed of in
seepage pits or trenches which extend only a few feet beneath the land sur-
face. As such, these wastes usually are subject to the effects of evapo-
transpiration. Determination of evapotranspiration is difficult because of
varying soil conditions, septic tank disposal practices, vegetation type and
distribution, and other factors. Evapotranspiration is the sum of evapora-
tion from bare soil surfaces and transpiration by vegetation growing in the
area. Rooting depth would be a key factor in plant uptake of effluent from
trenches. If the land surface is irrigated this must also be considered.
Generally, if leach lines are placed at depths greater than about 5 feet
in most soils in the absence of deep rooted plants, seepage is virtually the
same as the waste discharge. If trenches are only a few feet beneath the
land surface, then a water budget analysis may be made. This analysis
would usually be done for groups of septic tanks, such as for a subdivision
in an Urban area. Precipitation is combined with waste discharge as the
input, while evapotranspiration and runoff are losses. The residual seepage
is subject to a soil moisture retention loss, depending on the depth to the
water table from the bottom of the trench.
Landfills pose a threat to groundwater quality depending on the volume of
leachate leaving the fill. This in turn is a function of the leachate control
methods in use for a particular landfill, such as clay liners, collection and
treatment, impermeable rubber or plastic barriers and caps. Many land-
fills have not been properly designed and as a consequence are almost cer-
tain to produce leachate.
The water budget method may be applied when estimating leachate pro-
duction from landfills. Precipitation volumes must be obtained and the por-
tion that infiltrates the landfill determined. This portion will first go into
meeting the moisture storage requirements of the solid waste. For this
reason the moisture content of the solid waste must be estimated. When the
solid waste reaches field capacity leachate will result. Whether this leach-
ate will reach the zone of saturation will depend on the leachate control
method in use.
The leachate produced from a landfill can be estimated using the follow-
ing relationship!
Leachate = P-R-ET-S
where
P = precipitation
R = runoff
45
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ET = evapotranspiration
and
S = the field capacity of the solid waste minus
its existing moisture content.
Step 8 — Evaluate Mobility of Pollutants
from the Land Surface to Water Table
The topsoil and materials of the vadose zone may have a significant capac-
ity to remove pollutants from downward-percolating waters. The extent of
groundwater pollution due to waste percolation from the land surface depends
strongly on the rate and volume of recharged water. In a semiarid or arid
climate, pollutants may be retained above the water table in a nearly perma-
nent fashion. On the other hand, in humid areas pollutants may be rapidly
carried downward from the land surface to the water table. Generally, in a
homogeneous porous media, percolating water will pass vertically through
the vadose zone. However, in a heterogeneous, stratified material, such as
most of the alluvial deposits of the western U. S. , percolating water may be-
come perched above layers of low permeability. In this situation, lateral
movement for substantial distances can occur above the water table.
The capacity for attenuation of many potential pollutants is greatly
limited by the amount and characteristics of the geologic materials present
in the vadose zone. This is especially true for the sorption capacity of
many organic chemicals, trace elements, and radionuclides. This limited
capacity for removal of some pollutants is in sharp contrast to the almost
unlimited ability of many unconsolidated materials- to remove bacteriological
pollutants. The existence of many documented case histories of ground-
water pollution indicates that the vadose zone may often not provide complete
protection. Problems can occur when the zone is bypassed during waste
discharge or when attenuation capacity is exceeded due to high waste load-
ings.
Pollutant attenuation in the subsurface commonly occurs due to the fol-
lowing processes: dilution, filtration, sorption, buffering, precipitation,
oxidation and reduction, volatilization, biological degradation and assimila-
tion, and radioactive decay. Each of these processes must be evaluated with
respect to specific pollutants.
DILUTION. Dilution above the water table can be substantial in humid
areas and almost nonexistent in arid areas. Sources of water for dilution
include precipitation, seepage from streams, lakes and canals, and artifi-
cial recharge. A water budget analysis can be used to evaluate the extent
of dilution. Generally, the analysis is done in a similar manner to that dis-
cussed in the previous step concerning evaluation of infiltration potential.
However, in this case, all items of recharge from the land surface are
46
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considered, such as canal seepage, percolation from streams and lakes, and
artificial recharge in the area. The quality of water from each source of
recharge must be determined. A comparison of the respective quantities of
water and constituents concentrations in a waste discharge at the land sur-
face can indicate the extent of subsequent dilution of pollutants.
An example is presented in the following discussion. Assume an agricul-
tural area in the West where irrigation is practiced in the dry summer
months and rainfall occurs in the wet winter months. Return flow over the
area averages 18 inches per year and the salinity of this water is 300 parts
per million (ppm). Rainfall is 12 inches per year and its salinity is 10 ppm.
Consideration of the water budget analysis at the land surface indicates
that 9 of the 12 inches of rainfall percolates to the water table. The subse-
quent dilution can be calculated by the equation:
AVA + BVB = C
where V^ and VB are the respective percentages of water from return flow
and precipitation. A, B, and C are the respective salinities of the return
flow, precipitation, and the mixture of the two. In this example:
C = 300(18/27) + 10(9/27)
C = 200 + 3 = 203 ppm
This dilution reduces the pollutant concentration by about one-third of the
original value. This simple concept can be expanded to encompass dilution
and a number of sources of pollution.
FILTRATION. Filtration removes virtually all of the suspended materi-
als that would be of more concern in surface water pollution. However, this
process is generally not effective for most of the inorganic chemical species.
Exceptions include iron and manganese, which may be present in aerated
waters as hydroxides in particulate matter. Similarly, as precipitates form
due to chemical reactions, they may be effectively filtered out as water
moves through porous media. For wastes with high iron or manganese
contents, laboratory tests can be performed on soils or geologic materials
of the vadose zone. However, other attenuation factors affecting the pollut-
ants would have to be evaluated.
SORPTION. Sorption is probably one of the most effective processes for
attenuating groundwater pollution. Clays, metallic oxides and hydroxides,
and organic matter can all be suitable materials for sorption of various pol-
lutants. With the exception of chloride, and to a lesser extent nitrate and
sulfate, most pollutants can be sorbed and removed to some extent under
favorable conditions. Under other circumstances, however, the pollutants
can move freely through the porous media. The pH and oxidation potential
47
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often govern the extent of sorption for specific constituents. The sorption
process depends on the type of pollutant and the physical and chemical prop-
erties of both solution and the containing materials.
When a pollutant in ionic form is sorbed, some other change must occur
to compensate for loss of the ion from solution. In ion-exchange processes,
a different ion is released by the solid to the water. However, this release
is not required if the pollutants are sorbed or electrically neutral, such as
most organics and neutral complexes of various metals.
The sorptive capacity can be estimated based on the density, clay content,
and cation exchange capacity of the soil and geologic materials above the
water table. Values for these parameters can be calculated from available
data in soils and groundwater reports on the area of interest. In exceptional
cases, these parameters can be determined from detailed onsite measure-
ments. For calculation purposes, the thickness of the vadose zone is known
or determined from water level data. For simplicity, the vertical path of
polluted water from the land surface beneath the waste disposal area to the
water table can be assumed to be the distance traveled.
As an example, assume the average density of materials in the vadose
zone is 1.6 grams per cubic centimeter, the clay content is 20 percent by
weight, and the clay has a cation exchange capacity of 70 milliequivalents
per 100 grams. Each gram of clay will have the ability to remove 0.70 mil-
liequivalents of the pollutant of interest. For example, for potassium
(equivalent weight of 39), each gram of clay will have the ability to remove
27. 3 (0. 70x39) milligrams of potassium from the percolated waste water.
Each gram of solid material will have the ability to remove 5. 5 (0. 20x27. 3)
milligrams of potassium from the percolated waste water. With a density
of soil of 1.6 grams per cubic centimeter, one acre-foot (1.2335x10^ cubic
centimeters) of soil would contain 1.97xl09 grams of solid material. This
soil could sorb 23,900 pounds of potassium. For a vadose zone 50 feet
thick, one acre of the vadose zone could sorb over one million pounds of
potassium.
To determine the actual extent of adsorption, laboratory tests can be per-
formed utilizing soils and geologic materials typical of the waste disposal
site. The actual waste discharge can be used or a similar synthetic solution
prepared. Hajek (1969) summarizes laboratory procedures for such tests.
It should be noted that percolating fluids may subsequently remobilize
species that have been sorbed. The sorptive capacity of soils and geologic
materials is finite for most inorganic substances which cannot be biode-
graded. However, for substances which are biodegradable, such as many
bacteriological constituents and nitrogen, the sorptive capacity may be re-
newed indefinitely.
48
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BUFFERING. The pH is a critical factor in many reactions involving pol-
lutants. Buffering is the resistance to a pH change of the soil solution. The
basis of buffer capacity lies in the adsorbed cations on the exchange complex
of the soil. The higher the exchange capacity, the greater will be the buffer
capacity. The portion of the cation exchange capacity occupied by exchange-
able bases is termed base saturation. There is a correlation between base
saturation and pH, with higher base saturation for higher pH. The degree of
buffering is lowest at the extremes of base saturation, and highest at inter-
mediate base saturation values.
The extent of buffering in most cases will be relatively unimportant if the
pH of the waste discharge is between 6 and 9. These pH values correspond
to those commonly found in natural groundwater. Wastes with a pH in this
range will generally be buffered to an extent that the percolating waste water
will present no unusual problem. Consideration of buffering is thus of fore-
most importance in cases of disposal of very acidic or basic wastes. De-
tailed considerations are presented in Buckman and Brady (1969).
CHEMICAL PRECIPITATION. It is theoretically possible to precipitate
almost any dissolved species from solution. However, in soil-groundwater
systems, the necessary species often are not present in sufficient quantities
to precipitate potential pollutants. Certain constituents are normally pres-
ent and available for reaction in most groundwater, soil, and geologic mate-
rials. Calcium, magnesium, sodium, potassium, bicarbonate, sulfate,
chloride, and silica are usually the major species in groundwater. Iron,
aluminum, nitrogen, and carbonate, in addition to the previous constituents,
may be found in soil and geologic materials.
There are important precipitation reactions for calcium, magnesium, bi-
carbonate, and sulfate. Calcite, aragonite, gypsum, and magnesium car-
bonates are major compounds which may precipitate in the soil and vadose
zone. In arid areas, virtually all major constituents could be precipitated
at or near the land surface in some situations; however, in this case virtual-
ly all of the waste has evaporated and percolation is minimal. The following
trace constituents have important precipitation potential: arsenic, barium,
cadmium, copper, fluoride, cyanide, iron, lead, mercury, molybdenum,
zinc, and radium.
No rigorous procedure is given herein to evaluate chemical precipitation.
However references such as Hem (1970), Stumm and Morgan (1970), Faust
and Hunter (1967), and Gould (1967), detail thermodynamic calculations
which may be used to evaluate this phenomenon. In many field situations
data are commonly lacking on some parameters of importance, thus judgment
is often necessary.
OXIDATION AND REDUCTION. The oxidation of organic matter in the
topsoil is one of the most important pollutant attenuation mechanisms.
49
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Oxidation and reduction reactions often work in conjunction with other mech-
anisms for pollutant attenuation. Besides those reactions causing precipita-
tion, reducing conditions can also theoretically cause the formation of native
elements such as arsenic, copper, mercury, selenium, silver, and lead,
which are quite insoluble. Reducing environments can convert dissolved
sulfate to sulfide and dissolved nitrate to nitrogen gas. Sulfides can react
with certain metals to produce highly insoluble precipitates, such as sulfides
of arsenic, cadmium, copper, iron, lead, mercury, molybdenum, nickel,
silver, and zinc.
Oxidation and reduction reactions are also susceptible to analysis by
thermodynamic considerations. These reactions are also subject to labora-
tory experimentation and no further detail is presented here.
VOLATILIZATION. Volatilization and loss as a gas can be effective for
sulfate and nitrate. Mercury in solution can be volatilized in anaerobic
environments or by reaction with dissolved humic acids. Several organic
compounds of arsenic are volatile, and the escape of arsenic as a gas has
been demonstrated for both aerobic and anaerobic soils. Selenium may be
subject to volatilization, because of its chemical similarity to sulfur. The
microbial reduction of nitrate to gaseous forms of nitrogen is well docu-
mented. No quantitative procedure is proposed to evaluate the extent of this
phenomenon. It is more important to be aware of the pollutants that may be
affected.
BIOLOGIC DEGRADATION AND ASSIMILATION. These processes are
very important in the removal of organic and biologic pollutants. Many
organic chemicals can be attenuated or removed by biological activity in
the vadose zone. Sulfate, nitrate, arsenic, cyanide, mercury, and sele-
nium are likely candidates for biologic fixation or volatilization. Molyb-
denum is strongly assimilated and concentrated by plants. Crop uptake can
remove many of the nutrients in waste waters, particularly nitrogen, phos-
phorus, and potassium. However, the crop has to be removed or the pol-
lutants may be introduced into the soil-groundwater system. Previous ref-
erences, given under the step for identification of pollution sources and
causes, contain relevant information as to evaluations of the extent of this
phenomenon. Again, a general knowledge of the pollutants likely to be af-
fected is of most use.
RADIOACTIVE DECAY. This mechanism is of great potential value in
the attenuation of radioactive wastes by subsurface storage. Storage may
be possible for thousands or tens of thousands of years, during which time
the wastes would lose much of their activity through decay. Half-lives of
many radionuclides are presented in references such as Davis and DeWiest
(1966) and Hem (1970). The half-life represents the time required for a
given quantity of the radionuclide to decay to one-half the original quantity.
Consideration of this phenomenon is unnecessary for most cases of
50
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groundwater pollution monitoring, as radioactive pollutants are relatively
uncommon.
In summary, attenuation above the water table is greatest for biological
constituents. Many organic chemicals and trace elements and some radio-
nuclides and inorganic chemicals will not generally reach the water table.
The most mobile constituents would generally be the major inorganic chemi-
cal constituents and tritium. Chloride, nitrate, sulfate, sodium, and boron
can be fairly mobile. Other major chemical constituents in the topsoil or
vadose zone can be mobilized during waste disposal operations. Changes in
pH, oxidation potential, and ion-exchange can cause this mobility. Potas-
sium and phosphorus are ordinarily immobile in alluvial sediments, but
could be mobile in flow-through consolidated rocks. Iron and manganese
are often found in groundwater and are thus fairly mobile. Trace elements
such as chromium, cadmium, arsenic, molybdenum, and selenium, which
form anions in water, appear to be fairly mobile in some cases. Others
such as barium, mercury, and cobalt are relatively immobile in most soil-
groundwater systems. Some pesticides are mobile under certain conditions.
Bacteriological pollutants are generally removed above the water table un-
less this zone is bypassed.
The evaluation of pollutant mobility above the water table requires con-
siderable judgment on soils physics and chemistry, hydrogeology, and water
chemistry. Such an evaluation is essential in order to accurately select
what portion of the system should be monitored, and to what degree. This
judgment may often require a team of specially trained investigators. Ex-
perience gained from case histories may be combined with this judgment to
effectively perform this step.
Step 9 — Evaluate Attenuation of
Pollutants in the Saturated Zone
Many of the attenuation processes which occur in the vadose zone can also
occur below the water table, but in a modified manner. For example, the
lower oxygen content below the water table reduces the possibility of oxida-
tion of organic nnatter. Some pollutants, such as iron, may be more mobile
in the reduced state. Reducing conditions are favorable, however, in some
cases for pollutant removal from water, particularly(for sulfate and nitrate.
Another major consideration is that organic matter, common in the topsoil,
is virtually absent in many types of geologic materials comprising the aqui-
fer. This would ordinarily decrease the extent of sorption as well as reac-
tions such as denitrification. In addition, certain geologic materials, such
as granite or limestone, may lack many of the common substrates for sorp-
tion. The dilution process below the water table differs greatly from that
operative in the vadose zone.
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PROCESSES OTHER THAN DILUTION. The attenuation processes
other than dilution do not generally have to be considered in detail if there is
an adequate thickness of the vadose zone for treatment. In cases where the
water table is shallow or a large part of the vadose zone is bypassed during
waste disposal, detailed consideration of these processes may be necessary.
Filtration and sorption are discussed in Step 8; however, in saturated flow,
pollutant movement is generally horizontal. Thus, instead of utilizing a
thickness of vadose zone beneath a waste disposal site, a volume of the aqui-
fer is selected. Generally this will correspond to the projected volume and
location of recharged waste water plume at a specific time. This volume
can be estimated by utilizing flow net analysis to determine the vertical and
horizontal direction of groundwater movement from beneath the waste dis-
posal site. Specific distances from the waste discharge site, such as 100
feet, 500 feet, and 1000 feet, can be chosen and volumes of material calcu-
lated for each.
Buffering can be handled as discussed in Step 8. Generally, this is not of
great concern unless extremely acidic or alkaline wastes are disposed of
directly to the saturated zone, i. e. , the vadose zone is bypassed. Chemi-
cal precipitation can be handled as described in Step 8. One major differ-
ence in this process compared to that occurring in the vadose zone is the
general lack of evapotranspiration as a factor in concentrating solutions.
In addition, the materials are continuously saturated below the water table
and are usually not exposed to drying. Oxidation and reduction can be han-
dled as discussed in Step 8. However, in the saturated case, oxidation is
generally less important and reduction is more important than in the vadose
zone. Volatilization and radioactive decay can be handled as discussed in
Step 8.
DILUTION AND RELATED FACTORS. Once percolating wastes reach
the zone of saturation, in most dynamic groundwater systems there will be
a physical attenuation of pollutant concentrations with distance from the in-
tersection with the water table. This attenuation is generally of much
greater magnitude than that due to the previously discussed factors. This
attenuation is one of the primary factors that mitigates against widespread
groundwater pollution. In one sense, this restricted dilution is analogous
to that of a plume of polluted air. The attenuation occurring in most cases
is determined by the following factors:
• The volume of waste water reaching the water table
• The waste loading, i. e. , the weight per unit area of pollutant
reaching the water table
• Areal hydraulic head distribution, as indicated by water-level
elevation contour maps
• Transmissivity of aquifer materials
52
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• Vertical hydraulic head gradients and vertical permeabilities
through confining beds which are present
• Quality of native groundwater in a three-dimensional sense
• Quantity of recharge reaching the water table from other
sources at the land surface
• Quality of recharge reaching the water table from other sources
• Well construction
• Pumpage volumes and patterns.
The first two factors determine the concentration of pollutants reaching
the water table. The third and fourth factors, along with porosity, deter-
mine the direction and magnitude of horizontal groundwater inflow and out-
flow from the area. The fifth factor determines the direction and magnitude
of vertical groundwater flow in the area. The sixth factor comprises the
quality of groundwater with which the recharged waste water will mix. The
seventh and eighth factors determine the effect of recharge from other
sources on pollutant concentration. Lastly, well construction can allow
short-circuiting of aquifer materials and well pumping can drastically alter
the hydraulic head distribution.
A first approximation of dilution can be obtained by assuming that the re-
charged waste enters a certain part of the aquifer; for example, the upper
10 feet, 50 feet, or 100 feet, over a certain area. Knowledge of the extent
of groundwater pollution in historical situations in the area or a comparable
area can be used to make this evaluation. Secondly, water reaching the
water table from other sources of recharge and groundwater inflow from
nearby areas usually tends to dilute the recharged wastewaters. The dilu-
tion can be calculated if the volume and quality of the various sources of
water are known. Conservative constituents, such as chloride, can be used
for a first approximation of dilution. In most cases, the pollutant of interest
will be less mobile and thus occupy a smaller plume than a mobile constit-
uent such as chloride. Groundwater outflow tends to carry pollutants away
from the waste disposal site.
Water level elevation maps and flow nets can be used to consider whether
the waste discharge is in an area of converging or diverging groundwater
flow, which affects dilution. Vertical head gradients indicate whether
wastes could move to deeper levels of the aquifer or whether deeper aquifer
water could move up and dilute the wastes. Both cases tend to accentuate
mixing or dilution. Aquifer transmissivity can be used to calculate ground-
water flow rates into and out of an area. The quality of sources other than
the waste discharge and native groundwater will obviously affect dilution as
the lower concentration waters will exert relatively more dilution. The
foregoing factors can be integrated into a mass balance analysis, both for
the recharged wastewater and for the individual pollutants.
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Wells affect dilution in several ways:
• Gravel packs or perforations in certain situations can act to
short-circuit confining beds and allow vertical movement of
pollutants near the well
• Well pumping can drastically alter flow patterns, both
horizontally and vertically
• Well pumping can remove pollutants from groundwater and
expose them to subsequent loss at the land surface or in the
topsoil, by processes such as volatilization, crop uptake, and
precipitation.
Most of these factors are significant for all types of pollutants that reach
the water table, whether they are inorganic chemical, physical, organic
chemical, bacteriological, or radiological. In some cases, certain factors
do not attenuate the pollutant concentration, but rather increase it. An
example is the development of a large depression cone in an agricultural
area, whereby pollutants are drawn into the area from many directions but
are effectively prohibited from leaving by the depression. The factors
leading to attenuation or concentration of pollutant concentrations in the
saturated zone have seldom been analyzed in case histories.
Plumes or zones of polluted groundwater may behave as a slow-moving
viscous mass, but they may also be quite dynamic, especially where in-
fluenced by recharge and/or well pumping.
Evaluation of pollutant attenuation mechanisms in the saturated zone re-
quires considerable hydrogeologic judgment. Such an evaluation is essen-
tial in order to properly determine the location and construction of monitor
wells. Hydrogeologic judgment combined with experience gained from case
histories may be effectively used to perform this step.
Step 10 — Prioritize Sources and Causes
The monitoring methodology presented thus far consists of a sequence of
monitoring objectives or steps which must be performed in order to priori-
tize the identified sources and causes of groundwater pollution for monitor-
ing within each of the selected monitoring areas. These monitoring objec-
tives are presented not only in a chronologically preferred order for ac-
complishment but also occur in an order of increasing difficulty, both in
terms of the monitoring methods available to accomplish these objectives
and in terms of capability to interpret the data obtained from using these
methods. Concomitantly the costs increase with implementation of these
methods and the analytical procedures used in their evaluation.
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In the early stages of a monitoring program it will not be possible to make
an accurate prioritization of the pollution sources because of incomplete data
and knowledge regarding the fate and transport of pollutants in site-specific
situations, unless considerable monitoring is already underway. The priori-
tization scheme is dynamic in nature and with time will tend toward an opti-
mum as more information is gained from a monitoring program.
Each objective of the methodology has been carefully selected to identify
and build up the prioritization scheme which follows. In Step 1 criteria for
selecting the monitoring areas are set forth. Step 2 prescribes that each
monitoring area should be fully inventoried for known or potential sources
and causes of groundwater pollution, and the method of waste disposal asso-
ciated with each source determined. Completion of Step 3 will result in the
identification of the biological, chemical, physical, and radiological charac-
teristics of the pollutants associated with each source and as a result will
allow a trial ranking to be made of the sources and causes in terms of the
potential of the various pollutants to violate drinking water standards. Com-
pletion of Step 4, which has as its objective identification of groundwater
usage in the vicinity of each source will allow a further refinement of the
trial ranking of the sources and causes made in Step 3, based this time on
their threat to existing groundwater usage.
The various uses of groundwater including the applicable water quality
standards are discussed in Section III of this report under the heading
Quality in Relation to Water Use. Of the possible uses of groundwater, it
is apparent that usage for potable water supplies stands out as paramount.
Therefore, sources and causes which pose a health threat to potable water
supplies will have priority over nonhealth-related damages to potential users.
Of foremost concern then in the prioritization will be pollution sources ex-
pected to result in the presence of pollutants exceeding the U. S. Public
Health Service mandatory drinking water limits. For other sources of pol-
lution the damage to users can be estimated on a monetary basis and the
prioritization carried out based on the cost of anticipated damages to exist-
ing or potential users. The cost of groundwater quality degradation has been
estimated, in areas such as the Los Angeles Basin in Southern California, in
terms of the following considerations:
• Quality-related consumer costs, i. e. , the cost of various treat-
ments such as water softening or chlorination
• The cost of removing the pollutant to the background level of
the groundwater resource
• The cost of removing the pollutant in the groundwater to the
limits of drinking water standards.
In another instance a detailed investigation was made of an incident where
a freshwater aquifer has been polluted by accepted disposal of oilfield brine
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through an "evaporation" pit and later a faulty disposal well (Fryberger,
1972). Several rehabilitation methods were evaluated in detail, including
controlled pumping to the Red River and deep-well disposal. Although real
economic damage both present and future resulted from this brine pollution,
rehabilitation was determined to not be economically justified.
With completion of Steps 2, 3, and 4 of the methodology a much improved
appreciation of the potential for groundwater quality degradation at the land
surface will be realized.
One of the more difficult tasks facing a DMA charged with monitoring
groundwater pollution sources will be to gain an accurate understanding of
the fate and transport of pollutants associated with particular sources in
site-specific situations. The presence of a pollutant at the land surface does
not necessarily demonstrate a threat to groundwater quality. In most situa-
tions important data deficiencies will exist relative to pollutant mobility.
The application of generalizations regarding the fate and transport of pollut-
ants subsurface should be used with great care. Sometimes under tight
budgetary constraints no other choice will exist. In such cases the applica-
tion of rule of thumb generalizations should be left only to the specialist.
The objectives of Steps 5 and 6 are to gain a site-specific appreciation of
the hydro geology and existing water quality in relation to the pollution
sources. In general, it will not be an objective of Steps 5 and 6 to require
that regional appraisals of hydrogeology and groundwater quality be con-
ducted, unless a diffuse source covering many square miles is involved.
Regional appraisals of hydrogeology are outside the overall objective of the
groundwater pollution monitoring methodology described in this report.
This does not preclude that regional studies will be conducted by other agen-
cies in cooperation with the DMA.
Steps 7, 8, and 9 comprise the basis for estimating pollutant mobilities
and their ultimate presence at a point of groundwater discharge. Based on
the estimations of pollutant mobilities determined as a result of the analyses
carried out in these three steps, it will be possible to make a more accurate
revision of the prioritization made in Step 4. The final three-phase adjust-
ment in the prioritization will be made by considering first the potential pol-
lutants at the land surface (Step 7), secondly, pollutants potentially reaching
the water table (Step 8), and lastly, pollutants potentially reaching water
supply wells (Step 9).
The refinement in the prioritization carried out as the result of Step 8
will have particular significance in terms of the nondegradation mandates of
PL 92-500 and for the protection of sole source aquifers as required under
PL 93-523. The refinement in the prioritization carried out as the result
of Step 9 will have particular significance in demonstrating whether or not
existing users are being threatened and for estimating potential damages to
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these users. Solute transport models will play an increasingly important
role in the years to come as a means for estimating the damage potential to
the groundwater users.
Prioritization of potential pollutants at the land surface (Step 7) will re-
quire an estimation of the annual volume of liquid waste or weight of solid
waste subject to leaching, pollutant concentration, solid or liquid waste
loading per unit area, and pollutant loading per unit area.
Completion of the procedural steps and resulting prioritization scheme
suggested above will allow a DMA to direct its monitoring resources in a
most effective manner toward the primary goals of PL, 92-500 and PL 93-
523. The prioritization obtained will need to be reevaluated on at least a
yearly basis as pollution controls are implemented and as new sources of
pollution are detected.
Step 11 — Evaluate Existing Monitoring Programs
Every effort should be made to incorporate these ongoing activities in a
new monitoring program. In fact, such inclusion is essential if the program
is to be both comprehensive and cost-effective.
Existing monitoring activities in an area may be carried on by the follow-
ing agencies or organizations:
• U. S. Geological Survey — groundwater and surface water
quality data
• State geologic and water agencies — groundwater and surface
water quality data
• Local water districts (flood control, irrigation, water con-
servation, etc) — groundwater and surface water quality data
• Health departments (city, county, and State) — data on quality
of groundwater from water supply wells
• Sanitation districts — data on quality of treated waste water
effluent before disposal on land
• Industries — data on quality of self-supplied groundwater and
of treated waste water effluent before disposal on land
• Local consulting firms working in the water resources field.
It should be noted that many of the existing monitoring programs are not
specifically oriented toward monitoring groundwater pollution. Thus, their
value is often limited. With the review of existing monitoring programs
completed, it will be possible to determine monitoring deficiencies. This
is accomplished by noting the availability of existing monitoring activities
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serving the high priority sources and causes. Clearly, if the surveillance
systems for these are inadequate or incomplete, monitoring deficiencies
exist.
The final result of this step will be a priority listing of sources and
causes having monitoring deficiencies. The sequence of this listing will be
identical to that developed in Step 10, except that sources which are ade-
quately monitored will be eliminated from the list.
Step 12 — Establish Alternative Monitoring Approaches
As a result of making a first pass through the first 11 steps of the meth-
odology a DMA will have a good appreciation of those sources and causes of
groundwater pollution which hold the highest priority for monitoring. Al-
though in some cases the accuracy of this first-cut prioritization will be
questionable, an important objective will have been accomplished — that of
identifying data and information deficiencies.
In Step 11 the existing monitoring programs were checked to ascertain if
it would be possible to modify these existing monitoring activities to collect
the needed data. Whether or not this can be accomplished will usually be
determined on legal or institutional grounds. In some instances it may be a
least-cost approach to pay to have specific data collected during the course
of ongoing monitoring programs.
Based on the data and information deficiencies identified in the prioriti-
zation of Step 10, it will be possible to identify the required alternative
monitoring approaches. To establish the alternative monitoring approaches
it will be necessary to first identify and develop pollutant-specific technical
monitoring objectives for the pollutants known to emanate from each source.
For example, consider a landfill producing leachate high in dissolved solids.
A pollutant-specific technical monitoring objective could be to determine
total dissolved solids (TDS). A first step would then be to identify the moni-
toring zone (surface, vadose, or saturated zone), the monitoring methods
that could be used to monitor TDS in each zone, the sample analysis tech-
niques for each monitoring method, and sampling frequencies.
Since it is possible to have several combinations of monitoring zones,
monitoring methods, sample analyses, and sample frequencies to meet the
same technical objective, more than one monitoring approach may exist for
each technical objective. By definition, a monitoring approach consists of
a mix of monitoring methods. If only one method is feasible for meeting the
technical objective, it follows that this method will be the preferred moni-
toring approach. When several monitoring approaches exist it will be nec-
essary to make a cost-effective comparison between them in order to select
the preferred approach.
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SELECTION OF PORTION OF SYSTEM TO BE MONITORED. The por-
tion or portions of the system to be monitored for each source depends on the
method of waste disposal, infiltration potential, travel time of waste waters
from the land surface to the water table, and the mobility of pollutants in the
topsoil and vadose zone. Obviously, no monitoring is required in the topsoil
or vadose zone if they are bypassed during waste disposal. If pollutants un-
dergo significant attenuation above the water table, little monitoring may be
necessary in the saturated zone. For example, in the case of phosphorus,
which is readily adsorbed on soil particles, little monitoring in the saturated
zone would be necessary for most diffuse sources. However, where over-
loading may occur, such as at point sources of wastes with a high phosphorus
concentration, monitoring in the zone of saturation would often be necessary.
In cases where significant storage capacity exists in the vadose zone and
travel times of pollutants to the water table are long (decades or centuries),
sampling in the vadose zone may be stressed. Likewise, in cases where
waste water application and infiltration rates are very small (several milli-
meters per year), monitoring in the vadose zone may be emphasized.
In cases where there is rapid movement through the vadose zone and high
waste water application and infiltration rates (tens or hundreds of feet per
year), sampling in the vadose zone is minimal and water well sampling is
maximal. Where sources are highly variable in potential pollutant composi-
tion or in cases where the composition is poorly known, intense source sam-
pling may be necessary. In cases where the composition is fairly constant
or relatively well known, little source sampling may be required. Selection
of the portion or portions of the system to be monitored requires judgment
on the soils, hydrogeology, and water chemistry.
It is also necessary to determine the area over which to sample. This is
self-explanatory for land surface monitoring. In the case of the vadose zone,
generally, sampling can be confined to the area beneath the pollution source.
This is particularly true in cases where geologic materials allow primarily
vertical movement to the water table. In cases where layers of low permea-
bility inhibit vertical flow, significant lateral flow may take place. If this
factor is predominant, sampling in parts of the vadose zone only under the
source of pollution may be ineffective. In this case sampling of a much
larger area may be warranted, and batteries of piezometers and tensiome-
ters may be necessary to determine this area.
In the saturated zone, the area to sample depends largely on pollutant at-
tenuation factors in the aquifer. These factors have been discussed previ-
ously in Step 9 of the methodology. Application of the methodology of Step 9
will allow estimation of the horizontal extent of pollutant travel in the aquifer.
SELECTION OF NONSAMPLING METHODS. Nonsampling methods at
the land surface almost always will include the waste load inventory. The
testing of liners, pipelines, and tanks for leakage is obviously only
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applicable to cases where the type of waste disposal involves these items.
Aerial surveillance is generally useful when sources of pollution methods of
waste disposal are poorly known or when the method of waste disposal is
highly variable. Nonsampling methods in the vadose zone largely comprise
in-place measurements of moisture characteristics, such as by neutron log-
ging, tensiometers, and moisture blocks. These methods are most useful
for point sources of pollution. Experienced soils scientists and hydrologists
can best select the appropriate tool. In the saturated zone, most nonsam-
pling methods are of direct use only in special cases, for example, resistiv-
ity surveys which are generally applicable only to cases of high salinity
waste disposal.
DETERMINATION OF SAMPLING PROCEDURES. A determination must
be made of the required sampling in each portion of the system, namely the
land surface, the topsoil and vadose zone, and the saturated zone. This
sampling primarily involves liquids and solids. Solids at the land surface
comprise stockpiles and other items subject to leaching. Solids in the sub-
surface comprise soils and geologic materials. The liquids at the land sur-
face are primarily waste waters or polluted surface water. Liquids to be
sampled in the subsurface include native waters and polluted waters.
The determination of the required sampling is based on what data are al-
ready available, the purpose of monitoring, the type of pollution source and
pollutants, and the method of waste disposal. This probably requires more
judgment relative to soils and hydrogeology than any other part of the moni-
toring methodology. Sampling of solids at the land surface is often unneces-
sary if the composition is generally known. An exception would be the ra-
dium content in byproduct gypsum from phosphorus fertilizer production,
especially if this content is not well known or is highly variable. In general,
waste waters of highly variable composition (many industrial wastes) will
require much more sampling than those of more consistent composition
(many municipal wastes). As an example, the composition of septic tank
effluent is generally well known if the composition of the water source is
known. Sampling of waste waters in the case of toxic materials and highly
variable composition is a major tool in monitoring groundwater pollution.
In the topsoil and vadose zone, the tools required to retrieve water and
soil samples will vary greatly with geographic area due to differences in
soil, geological, and climatic conditions. In many situations, the type of
augering or drilling depends highly on the nature of subsurface deposits, the
moisture characteristics, and the depth of exploration. The specific reason
for monitoring and pollutants to be monitored often dictate the tools for sam-
ple retrieval. For example, moisture cups may have important limitations
with regard to bacteriological sampling. Many of the limitations of specific
sampling devices have been discussed by Everett et al. (1976).
In the case of the saturated zone, significant data may be obtained by
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sampling existing wells, tile drains, springs, and baseflow of streams. For
wells with fixed pumps, water samples may be taken directly from the well
discharge if it is freely discharging or a faucet or other opening is provided.
In the case of wells without pumps, submersible pumps may be installed.
Open wells can be sampled by a number of down-the-hole devices. The de-
termination of which wells to sample, and the extent of additional test wells
that need to be drilled depends on the purpose of monitoring, aquifer charac-
teristics, and mobility of pollutants in the aquifer. The portion of the aqui-
fer to be monitored must be determined; for example, the upper 10 feet, the
lower 50 feet, or a composite of the entire aquifer. The construction of
monitor wells requires consideration of subsurface geology, aquifer charac-
teristics, and hydraulic head distribution. In local areas well construction
techniques must be determined by persons experienced in the area. Down-
the-hole sampling generally supplies a sample representative of a very small
area in the aquifer. Small-capacity wells pumped for short time periods also
reflect fairly local conditions. High-capacity wells pumped for long time
periods can indicate regional conditions and integrate quality data over large
areas.
DETERMINATION OF REQUIRED ANALYSES. The pollutants in the ma-
jor sources have been previously described. For the determination of re-
quired analyses, consideration is given to liquid wastes, solid wastes, soil
and geologic materials, and water in the soil-groundwater system.
Liquid Wastes. In general, the analyses of liquid wastes can be based on
known compositions from the literature. Specific parameters of importance
to groundwater pollution can be selected. In general, the more mobile con-
stituents would have priority, as well as those of greatest importance in sub-
sequent reuse of polluted water. There are great advantages to running rela-
tively complete chemical analysis for the major species commonly found in
groundwater, namely calcium, magnesium, sodium, potassium, carbonate,
bicarbonate, chloride, sulfate, nitrate, and silica. Electrical conductivity,
total dissolved solids, and pH are also routinely determined. With the de-
termination of other major ionic species in polluted waters, such as ammo-
nium and fluoride, certain procedures can be used to check the chemical
analyses. Determination of these parameters also allows for limited chemi-
cal equilibrium calculations. In case of a drinking water supply, fluoride
and arsenic would also be important parameters. For agricultural supply,
boron would also be important. Some of the more common trace elements in
polluted groundwater are arsenic, chromium, cadmium, molybdenum, iron,
and manganese. With respect to nitrogen, phosphorus, and sulfur, various
forms may have to be determined, such as ammonia, organic nitrogen, ni-
trite, and nitrate in the case of nitrogen. Oxidation potential is also impor-
tant in this case.
Electrical conductivity monitored on a regular basis can be used as an
indicator for concentration changes in major constituents. Monitoring for
total salinity in salt balance studies may only require determination of
electrical conductivity. Another widely used measurement is chloride
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content. Chloride is common in many types of liquid waste, is extremely
mobile in the soil-groundwater system, and is therefore of special value as
a tracer. Representative constituents of interest in groundwater pollution
are given by Everett et al. (1976). If wastes have certain characteristics
and insufficient attenuation occurs, secondary effects of crucial importance
to groundwater pollution monitoring could result. For example, acidic
wastes, which if not buffered sufficiently above the water table, could mobil-
ize certain trace elements in minerals in the aquifer.
Bacteriological determinations are not generally of great importance in
waste water, unless specific pollutants have been found in groundwater near
a pollution source. The bacteriological composition of most waste waters is
generally known from the literature. Radiological determinations are very
important in selected cases. The composition of organic chemicals possibly
entering groundwater could assume a major role in the future. At present
most organic chemicals are generally known and will rarely have to be sam-
pled in waste liquids. Again if a problem is found in well samples, a spe-
cific pollutant may need to be monitored in waste waters.
Solid Wastes. Analyses to be run on solid wastes are highly variable.
In general, the major chemical constituents are well known from the litera-
ture (for example, gypsum stockpiles). Thus analyses usually focus on
trace element content and radioactivity.
Soil and Geologic Materials. The physical analyses on soil are generally
performed in order to monitor moisture characteristics and water move-
ment in the vadose zone. The selection of these parameters is based on
soil and hydrogeologic judgment. Chemical analyses will generally be lim-
ited to materials absorbed on or precipitated in the materials. Trace ele-
ments and radionuclides would be commonly analyzed. Trace elements and
radionuclides in geologic materials which might be mobilized by disposal of
certain toxic wastes may also be analyzed.
Water. In general, the analyses for water in the vadose zone and aquifer
are related to those for waste water at the land surface. However, analyses
of wastes at the land surface can considerably narrow down the required
analyses for water beneath the land surface. The relative immobility of
some pollutants in the topsoil often renders analysis of water for these con-
stituents in the vadose zone unnecessary. For example, many bacteriologi-
cal constituents and trace elements can be removed in the topsoil under a
favorable set of circumstances. Sampling in the vadose zone indicates addi-
tional attenuation of pollutants. Thus, in most respects, analyses for aqui-
fer water may require the least determinations, since many potential pollut-
ants will not reach the aquifer. In any case, the major inorganic species
commonly found in groundwater should generally be determined. This is
primarily for the sake of checking chemical analyses, equilibrium calcula-
tions, and providing data for the use of trilinear diagrams and other analyti-
cal tools.
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Generally in the early part of a monitoring program, sampling for de-
tailed determinations is made. This decision is based on the knowledge of
trace elements, radionuclides, bacteriological constituents, and organic
chemicals in the aquifer of the selected area. In general, nationwide, there
is a dearth of data on these substances. The substances of major concern
will be elucidated by source monitoring, and secondarily by monitoring in the
topsoil and vadose zone.
DETERMINATION OF SAMPLING FREQUENCIES. The selection of
sampling frequencies often involves a trial and error procedure. In general,
the fluctuations with time in composition over short periods (days or weeks)
are greatest for waste water at the land surface and least for groundwater
samples. In general, passage of pollutants through the topsoil and vadose
zone will tend to smooth out fluctuations in composition at the land surface.
In sampling at the land surface, the foregoing should be kept in mind. Often
the extremes in concentration are not desired, but rather an integrated or
typical value. For waste water sampling, open pond water subject to mixing
processes can often be sampled monthly to determine the major characteris-
tics. Compositing may be advisable, but is usually done on the waste
stream. A trial and error procedure is often used, and the main idea is to
establish seasonal changes or patterns in quality. Chemical hydrographs can
be plotted and used as an aid in selection of optimal sampling frequencies.
Geologic and soil samples are generally analyzed less frequently than
waters. In many cases geologic sampling may only be done once. Easily
retrievable soils samples (upper 5 to 10 feet) may be analyzed several times
a year or annually. Water in the vadose zone in areas of rapid percolation
should generally be done monthly or quarterly. The frequency of sampling
in this case is limited by the slowness of water movement into sampling de-
vices. In areas of slow percolation to the water table, measurements may
be made only every 5 or 10 years.
Water samples in the aquifer can often be collected on a semiannual basis
for large-capacity wells once seasonal trends are established. In the early
part of sampling programs, analyses on a weekly, daily, hourly, or more
frequent schedule may be necessary. In cases of point sources, monthly
analyses may be necessary. For diffuse sources, annual sampling of wells
pumping long time periods will generally suffice, but only when seasonal
trends have been established. For low-capacity wells, more frequent sam-
pling of a greater number of wells is necessary, and monthly sampling may
be necessary in many cases. Chemical hydrographs can also be used in this
case as an aid in selection of optimal sampling frequencies.
Specific examples which illustrate the selection and application of alterna-
tive monitoring approaches using the stepwise procedure outlined in this re-
port are given in Section II of a companion report in this series entitled
Monitoring Groundwater Quality; Illustrative Examples (Tinlin, 1976).
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Step 13 — Select and Implement the Monitoring Program
In Step 12 a procedure for developing pollutant-specific preferred moni-
toring approaches based on cost-effectiveness was discussed. When working
with a source containing many pollutants it will not be unusual to go through
several suboptimizations before a source-specific preferred monitoring ap-
proach can be selected. By definition, a source-specific preferred monitor-
ing approach consists of the set of pollutant-specific monitoring approaches.
The reason for this suboptimization is that in many cases it will be possible
to measure more than one pollutant using the same method. The normal
procedure when dealing with several pollutants from a single source will be
to examine each in terms of the available methods for sampling and analyses
and select the one best suited.
After a source-specific preferred monitoring approach has been selected
for the highest priority source, the cost of implementing this monitoring ap-
proach will need to be computed and compared against the monitoring budget.
If funds remain, the procedure for selecting a source-specific preferred ap-
proach and its implementation will be repeated for the next highest priority
source and so on to each lower priority source until the budget is depleted.
A preferred monitoring program will consist of the set of selected
source-specific preferred monitoring approaches. Monitoring approaches,
e. g. , remote sensing, which provide information pertaining to more than
one source may assist in achieving cost-effectiveness at the program level.
Certain other economies of scale will also exist at the program level when
discounts for materials and chemical analyses are available and by spreading
the cost of personnel and equipment over many sources.
The principal action in implementing a monitoring program for an area
by a DMA will be to see that the necessary monitoring activities are carried
out. This will involve making personnel assignments, purchasing monitor-
ing equipment and data handling supplies, and letting contracts for services,
such as drilling, performing well tests, and performing chemical analyses.
A most important action on the part of a DMA will be to insure that a strong
quality assurance program is carried out. A key consideration in this pro-
gram will relate to a capability by the DMA to provide valid data to support
enforcement actions in situations where environmental harm is projected.
It is important to recognize that additional monitoring may not imply
large expenditures. Innovative techniques may produce useful quality data
at low cost. For example, consider a large sanitary landfill, which poten-
tially could be a major pollution source, that is not being monitored. If the
DMA decides that monitoring of this source is important, then the first move
should be to search for existing wells near and on the downgradient side of
the landfill. Assume that three wells — two domestic and one irrigation —
are found which satisfy the locational conditions. The appropriate action
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then would be for the DMA to arrange for regular sampling and analysis of
the three well waters. If no wells were available then a more expensive
alternative would be to drill one or more monitoring wells.
A data management system applicable to groundwater quality is described
in a companion report. Monitor ing Groundwater Quality: Data Management
(Hampton, 1976). The selection of a system for a given area requires con-
sideration of several factors. One is the volume of data to be handled by the
system. A second is the use and distribution that will be made of the data.
Third, the compatibility of a system with others that may be in use in the
area must be considered. Fourth, decisions may already have been made
at a higher administrative level, such as by a State, which will specify the
monitoring system to be employed. And fifth, the cost of the system is an
important factor. In general, where the monitoring program is small, as
in an undeveloped rural area, the data management system can be extremely
simple — perhaps only xeroxing and filing of a few data sheets. But in a
large urban area which is heavily pumped, a sophisticated system involving
digital computers may be essential to handling the input of monitoring data.
Step 14 — Review and Interpret Monitoring Results
A key function of a DMA after the implementation of a monitoring pro-
gram is underway will be to collect and to review all current monitoring data
in its area. The data should be analyzed and interpreted so as to define
quality trends, new pollution problems, regions of improvement, and effec-
tiveness of pollution control activities. Assessments such as those portions
of the groundwater resource not meeting water quality standards and pre-
dictions of future quality under projected population and land use conditions
should be prepared.
The responsibility of analyzing monitoring data to convert it to water
quality information will be a continuing activity for a DMA. As new data are
received, they should be studied promptly in order to detect changes rapid-
ly, particularly those requiring immediate attention or action.
Step 15 — Summarize and Transmit Monitoring Information
The final result of a monitoring program organized in an area by a DMA
is information on groundwater quality. Thus, the final task of a DMA is to
disseminate the information gained in usable forms to the agencies and
organizations concerned with such information.
Monitoring should be summarized in appropriate forms for convenient
study before distribution outside of the DMA. This may involve preparation
of tables showing averages and/or changes in water quality. Similarly,
graphs prepared to readily display long-term trends may be helpful. Maps
showing, for example, locations of major known sources of pollution, areal
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distributions of concentrations of key pollutants, and regions having ground-
water with qualities not meeting drinking water standards, can also be shown
to be both useful and effective.
Monitoring information should be distributed regularly to appropriate
public agencies — local, State, and Federal. Major industries in the area
should also receive the material as well as cooperating agencies and organi-
zations that contribute monitoring data. In addition, the general public
should be informed of the results of the monitoring program; therefore, re-
ports should be sent to local newspapers, citizens' groups, Chambers of
Commerce, and conservation and environmental organizations. It can be
expected that the public awareness of groundwater quality created by such
publicity efforts will indirectly act to encourage individuals and organizations
to preserve and to protect the underground resource which they, perhaps for
the first time, more fully understand.
Finally, a DMA has the responsibility to alert action and enforcement
agencies of critical problems or situations which are discovered -within the
monitoring program. This may involve, for example, detection of hazardous
or toxic pollutants which could imminently affect a nearby municipal well
field. Prompt reporting of such instances is essential as well as following
up with specialized monitoring efforts for documenting and controlling emer-
gency situations.
EXAMPLE 1 - TABULAR PRESENTATION OF GROUNDWATER
QUALITY. Table 5 illustrates a format for presenting groundwater quality
data in tabular form. With the exception of temperature, only chemical
quality data are included. Note that the ionic constituents are presented
both in milligrams per liter and milliequivalents per liter and that hardness
includes both total and noncarbonate values. The well-numbering system is
based on township and range designations so that the well location is known
from the table to the nearest quarter-quarter section. In this table some
wells have been sampled semiannually in the spring (for high groundwater
level conditions) and in the fall (for low groundwater conditions), while
others have been sampled only once a year.
EXAMPLE 2 - GRAPHICAL PRESENTATION OF GROUNDWATER
QUALITY. Graphical representations of analyses of the chemical quality of
groundwater are useful for display purposes, for comparing analyses, and
for emphasizing similarities and differences. Graphs can also aid in de-
tecting the mixing of waters of different composition and in identifying chem-
ical processes occurring as groundwater moves through the underground. A
variety of graphical techniques is available; some of the more useful ones
are described and illustrated in the following paragraphs.
Figure 8 illustrates the most widely used bar graph in the United States.
Each analysis appears as a vertical bar graph whose total height is
66
-------
TABLE 5. ANALYSES OF CHEMICAL QUALITY OF GROUNDWATER PRESENTED IN TABULAR FORM
(California Department of Water Resources, December 1974)
Owner and Use Sources;
Stole Wellond Other
Numbers; Dates Sampled
Temp
(°F>
Specific
Conductance
(micromhos
<.t25°C)
Mineral Constituents In mg 1
pH
Calciimi
(Co!
Magnesium
(«9>
Sodium
(No)
Potassium
'Kl
Carbonate
(C03I
Bicarbonate
IHCO3>
Sulfote
(S
-------
Figure 8« Vertical bar graph of chemical quality expressed in milliequivalents
per liter (Hem, 1970).
proportional to the total concentration of anions or cations, expressed in
milliequivalents per liter. The left half of the bar represents cations and the
right half anions. These segments are divided horizontally to show the con-
centrations of major ions or groups of closely related ions, which are shown
by distinctive patterns. Numbers at the tops of the bars serve to identify
the analyses.
Figure 9 shows the same bar graph as Figure 8 but with addition of a bar
for hardness. Values of hardness are expressed in milligrams per liter as
CaCO3, which is equivalent to the sum of the calcium and magnesium seg-
ments, in milliequivalents per liter, multiplied by 50.
Figure 10 also shows the same bar graph as Figure 8 but with the addi-
tion of a horizontal bar for silica. Here the concentration of silica is given
in millimoles per liter because milliequivalents cannot be used for uncharged
solutes.
68
-------
Figure 9. Vertical bar graph of chemical quality expressed in milliequivalents
per liter which also shows hardness as CaCOo in milligrams per
liter (Hem, 1970).
Figure 10. Vertical bar graph of chemical quality expressed in milliequivalents
per liter which also shows silica in millimoles per liter (Hem/ 1970).
69
-------
Figure 11 illustrates a system of plotting quality by radiating vectors in
which the lengths of the six vectors from the center represent ionic concen-
trations in milliequivalents per liter.
No + K
12'6
Co~ ^ 15-1
'N^r"
sO^TN
Cl%
Na + K
i.
10
No + K
17-3
•O
J>
Cl
10
MILLIEQUIVALENTS PER LITER
Figure 11. Radial vector diagram of chemical quality expressed in milliequiv-
alents per liter (Hem, 1970).
Figure 12 shows a method for presenting analyses using four parallel
axes extending on each side of a vertical zero axis. Concentrations of ca-
tions are plotted to the left and anions to the right, all in milliequivalents
per liter. The resulting points are connected to form an irregular polyg-
onal pattern; waters of similar quality define a distinctive shape.
Figure 13 indicates still another graphical representation of water quali-
ty. Here a circular "pie" diagram is drawn with a scale for the radii which
makes the area of the circle represent the total ionic concentration. Sub-
divisions of the area show the proportions of the different ions as percent-
ages of the total milliequivalents per liter.
70
-------
Na
Ca
Mg|-
Feh
HCI
HHCO,
ICO
12-6
15-1
17-3
30 25 20 15 10 5 0 5 10 15 20 25
CATIONS (milliequfvalenrs per liter) ANIONS (milliequivalents per liter)
Figure 12. Pattern diagram of chemical quality expressed in milliequivalents
per liter (Hem, 1970).
71
-------
15-1
50 100
SCALE OF RADII
(TOTAL OF MILLIEQUIVALENTS PER LITERS
Figure 13. Circular diagram of chemical quality with subdivisions showing percentages
of total milliequivalents per liter (Hem, 1970).
Figure 14 illustrates a trilinear diagram, which is a useful method for
representing and comparing water quality analyses. Here cations, ex-
pressed in percentage of total cations as milliequivalents per liter, plot as
a single point on the left triangle; while anions, similarly expressed as a
percentage of total anions, appear as a point in the right triangle. These
points are then projected into the central diamond-shaped area parallel to
the upper edges of the central area. This single point is thus uniquely re-
lated to the total ionic quality, and at this point a circle can be drawn with
an area proportional to the total dissolved solids concentration. The tri-
linear diagram is a convenient way to distinguish similarities and differ-
ences among various groundwater samples as waters with similar qualities
will tend to plot together as groups. Also, simple mixtures of waters can
be identified; for example, an analysis of any mixture of waters A and B
will plot on the straight line AB on the diagram, where A and B are the
analyses of the two component waters.
72
-------
CATIONS PERCENT OF TOTAL
MILLIEQUIVALENTS PER LITER
Figure 14. Trilinear diagram of chemical quality expressed in percentages of cations
and anions as milliequivalents per liter and represented by two points and
a circle (Hem, 1970).
Figure 15 is modification of the trilinear diagram which is convenient
where a large number of analyses are to be graphically displayed. The tri-
angle and diamond areas are the same as in Figure 14 except that they are
shifted in position. The difference is that analyses are shown as points
rather than circles on the diamond area and total dissolved solids are plot-
ted to the right on a parallelogram with a logarithmic scale. In addition,
hardness as CaCC^ is plotted on a second parallelogram to the right of the
cation triangle.
EXAMPLE 3 - QUALITY VARIATION WITH TIME. Figure 16 shows
graphically the variation in chloride concentration with time for groundwater
at Burlington, Massachusetts. The increase in chlorides is associated with
the advent of road salting in the area. Salt was first stored uncovered in
1961, approximately 400 feet upgradient from the town's well field. At that
73
-------
HARDNESS AS CoCO3, mg/l
Cl
+
N03
100
S04
103 104
TOTAL DISSOLVED SOLIDS, mg/l
105
Figure 15. Comprehensive frilinear diagram of chemical quality in which five points represent the propor-
tions of cations and onions together with total dissolved solids in milligrams per liter and
hardness as CaCC>3 in milligrams per liter.
-------
300 - •
;
1955
1960
1965
1970
Figure 16. Variation in chloride concentration with time for groundwater at Burlington, Massachusetts
(Terry, 1974).
-------
time the chloride concentration was less than 15 mg/1; by 1963 the concen-
tration began to increase notably. Remedial measures by Burlington in-
cluded construction of a salt-storage shelter in 1968, when the chloride
reached 170 mg/1, and banning the use of deicing chemicals on city streets
in 1970, when the concentration exceeded the 250 mg/1 upper limit recom-
mended by the U. S. Public Health Service. Chlorides decreased after 1970
and were down to 85 mg/1 in 1972, perhaps assisted by abnormally high rain-
fall that year. The deicing ban was lifted in December 1972.
Figure 17 illustrates another change of groundwater quality with time.
Here seasonal variations in nitrate measured in groundwater near a sewage
treatment plant in Fresno, California, are plotted. A significant annual
cycle is apparent with a maximum in the fall and a minimum in the spring.
This fluctuation can be attributed to the discharge of high nitrogen content
wastes from wineries in the area during the fall of each year. It is clear
that frequent sampling is necessary to define these short-term changes.
50
Q.
Q.
z
o
z1
o
U
30
20
WINERY
SEASON
WINERY
SEASON
ASONDJ FMAMJ J A S O N D
Figure 17. Seasonal variation in nitrate concentration for groundwater at Fresno,
California (Schmidt, 1972).
76
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EXAMPLE 4 - QUALITY VARIATION WITH DISTANCE. Figure 18
presents the variation in electrical conductivity of groundwater along the
length of the Santa Ana River Basin in California. Electrical conductivity
(EC) is an inexpensive measure of total dissolved solids; normally TDS is
about 60 percent of EC. The pronounced increase in conductivity in a down-
stream direction can be attributed to a combination of urbanization, waste-
water disposal, and artificial recharge of poorer quality imported water.
EXAMPLE 5 - QUALITY VARIATION WITH DEPTH. Figure 19 shows
the variation of total dissolved solids with depth for groundwater in one por-
tion of the Santa Clara-Calleguas area, Ventura County, California. At this
location there are three distinct aquifers present. The samples from wells
penetrating the aquifers indicate that there is little significant difference in
quality in the two lower aquifers; however, the shallow perched water has
been appreciably degraded, probably from waste disposal or seawater
sources.
EXAMPLE 6 - AREA VARIATION IN QUALITY. Figure 20 is a map
of total dissolved solids in groundwater of the Santa Clara-Calleguas area,
Ventura County, California. Isosalinity lines cover the water-bearing por-
tions of the area and are drawn on the basis of quality analyses from well
water samples gathered throughout the basin.
EXAMPLE 7 - VERTICAL CROSS SECTION OF QUALITY. Figure 21
presents a vertical cross section of an alluvial aquifer in Michigan. Pollu-
tion resulted from disposal of industrial wastewaters into disposal ponds;
chloride is used as an indicator of the pollution. Control of spread of the
pollutant underground was accomplished by a combination of recharge ponds
for cooling water and purge wells, both shown in Figure 21. These pro-
vided an effective hydraulic barrier to the spread of the pollution. Monitor-
ing wells throughout the area enabled hydraulic and quality variations of the
groundwater to be evaluated.
EXAMPLE 8 - MAPS OF POLLUTION PLUMES. Figure 22 outlines
the plume of pollution in groundwater resulting from an oilfield brine dis-
posal pit in southwestern Arkansas. This map shows that highly saline wa-
ter, expressed by contours of chloride concentration, has spread generally
southward in the direction of groundwater flow. The irregular shape of the
pollution zone may be attributed to variations in permeability within the aqui-
fer and to irregularities in the top surface of the shale which forms the bot-
tom of the alluvial aquifer.
Figure 23 shows a long narrow plume of groundwater pollution produced
by a landfill near Munich, West Germany. Some 70 monitoring wells were
measured biweekly at this site for chloride, electrical conductivity, and
temperature. Only chloride concentrations are shown in Figure 23; how-
ever, all three indicators of pollution display nearly identical configurations,
suggesting that they are conservative and hence useful parameters for detec-
tion of subsurface pollution. 77
-------
SANTA ANA RIVER BASIN
1500
1000
500
"
O
t£
o
ELECTRICAL CONDUCTANCE
i i i I I I i I i i I I I I I i i I I i I i MI i I i i I i
65 60 55 50 45 40
35 30 25
MILES
20 15 10
Figure 18. Variation in electrical conductivity of groundwater along the length of the Santa Ana
River Basin, California (California Department of Water Resources, December 1974).
-------
too
•00
u too
o
IMO
SIPI*
atoi
3162
ERCHCO WATER-
rtCFI
•UN2
OXNARO
AND
MUGU AQUIFERS
10
•ITOI
«ITLI
I4AT»
• IMS
ITNZ*
.1401
•Ml
•«KT
• Mil
HUENEME,
FOX CANYON.
AND SRIME9 CANTON
AQUIFERS
•IMS
•lORI
•lIAt
ises
• 1704
•am
woo
MOO
MOO
4000
TOTAL DISSOLVED SOLIDS IN MILLIGRAMS PER LITER
Figure 19. Variation of total dissolved solids with well depth in a portion of the Santa
Clara-Calleguas groundwater basin, Ventura County, California (California
Department of Water Resources, August 1974).
79
-------
X
:
•f
H i
• &%i&$te*&M '--
X
BOUNDARY OF STUDY AREA
INTRA BASIN BOUNDARY
] WATERBEARING AREA
mH WON WATERBEARING AREAS
—20O— LINES OF ISOSALINITY ( mg/l )
Figure 20. Isosalinity map of groundwater in the Santa Clara-Calleguas groundwater
basin, Ventura County, California, as of 1966 (California Department of
Water Resources/ August 1974).
-------
WASTE
PONDS
RECHARGE
PONDS
PW 4
16
WATERBEARING
SAND
£
13
ui
_
_
!
z
_
LEGEND
WATER LEVEL ELEVATIONS
FLOW LINES
VERTICAL EXAGGERATION = 10
PW = PRODUCTION WELL
P = PURGE WELL
OB = OBSERVATION WELL
'CLAY'
CHLORIDES IN PPM
I ~] 1000 & ABOVE
T"7"^ 500-1000
I! 100-500
D 0-100
Figure 21. Vertical cross section showing groundwater pollution movement from
waste disposal ponds and control by cooling water recharge ponds and
purge wells (Burt, 1972).
-------
OBSERVATION WELL LOCATION AND NUMBER
CHLORIDE CONCENTRATIONS IN mg/l
LOCATION OF CROSS SECTION DEPICTED IN
FIGURE 7
Figure 22. Contours of chloride concentration in groundwater surrounding a brine
disposal pit in southwestern Arkansas (modified after Fryberger, 1975).
82
-------
,'
/
GROUNDWATER
SAMPLING BORES
SPRING
TERRACE EDGE
BUILT UP AREA
CHLORIDE VALUE
— LINES OF EQUAL
-CHLORIDE VALUE
^ 100 (mg/l)
100 - 200 (mg/l)
200-300 (mg/l)
300-400 (mg/l)
400-500 (mg/l)
500 (mg/l)
500
(mg/l)
1000m
Figure 23. Plume of groundwater pollution from a landfill near Munich, West
Germany, shown by lines of chloride concentration (Cole, 1975).
83
-------
SECTION III
GROUNDWATER QUALITY
HYDROGEOLOGIC FRAMEWORK
Geologic Formations as Aquifers
Permeable rock formations which store and transmit significant quantities
of water are known as aquifers. A variety of geologic formations can act as
aquifers.
The most widely developed aquifers in the United States consist of uncon-
solidated alluvial deposits, chiefly gravels and sands. These geologic fea-
tures occur as water courses, buried valleys, plains, or intermontane val-
leys.
Limestone, a consolidated sedimentary rock, serves as an important
aquifer when sizable proportions of the original rock have been dissolved and
removed. Openings may range from microscopic pores to large solution
caverns forming subterranean channels large enough to carry entire streams.
Within large openings in limestone aquifers, groundwater can flow rapidly
under turbulent conditions. Fractures and faults may allow limestones to
serve as significant aquifers. Springs are frequently found in limestone
areas.
Volcanic rocks such as basalt flows can form highly permeable aquifers.
Flow breccias, porous zones between lava beds, lava tubes, shrinkage
cracks, faults, and joints are other permeable zones in volcanic rocks.
Most of the largest springs in the United States originate in basalt.
Sandstones and conglomerates represent cemented forms of sand and
gravels. Sandstones function best as aquifers where they are only partially
cemented or where joints, fractures, or faults are present. Crystalline and
metamorphic rocks are usually relatively impermeable; however, ground-
water may be developed by shallow wells under fractured or weathered con-
ditions.
The following underground situations include most field conditions. The
differences among them are important to waste disposal practices and to
management of pollution problems.
84
-------
• Unconsolidated granular materials extending downward from the
ground surface to great depths: Beneath the ground surface in
many places are loose granular materials, chiefly clays, silts,
and sands, which may represent soil near the ground surface and
sedimentary material below. Water and dissolved waste materi-
als move en masse through pores surrounding the mineral par-
ticles.
• Unconsolidated granular materials at the ground surface under-
lain at shallow depths by dense rocks with linear openings: In
many places the soils, loose sedimentary materials, or residual
weathered materials are only a few feet or a few tens-of-feet
thick and are underlain by dense rocks, the only openings in
which are joints or solution channels. Water and waste mate-
rials move through both types of media.
• Dense rocks at the ground surface: The only movement is through
interconnecting joints or solution channels.
The permeability of underground strata may vary by several orders of
magnitude, and large variations can often be found over short distances.
Some generalizations regarding permeability follow:
• In the vertical direction, the contrast in permeability between
loose granular soil and underlying jointed rock can be very
large.
• Zones of uniform permeability tend to be associated with partic-
ular rock strata.
• Where interbedded sedimentary rocks are flat or gently inclined,
the changes of permeability in the vertical direction are frequent
and large.
• Changes of permeability in the horizontal direction, although
common, are in many cases more gradual than in the vertical
direction.
An unconfined aquifer is one where a water table forms the upper surface
of the zone of saturation (see the upper aquifer in Figure 24). A water table
is a surface representing the level of atmospheric pressure within an aqui-
fer. Fluctuations in the water table correspond to changes in the volume of
water in storage within an aquifer.
A confined (or artesian) aquifer is one where groundwater is confined,
under pressure greater than atmospheric, by overlying less permeable
strata. If a well penetrates a confined aquifer, the water level will rise
above the bottom of the confining bed, as shown in Figure 24. Variations of
water levels in wells penetrating confined aquifers result from pressure
85
-------
RECHARGE
AREA
WATER
TABLE WELL
ARTESIAN
WELL
PIEZOMETRIC SURFACE
WATER
TABLE
GROUND
SURFACE
.FLOWING
/ WELL
WATER TABLE
UNCONFINED
AQUIFER
CONFINING STRATUM
CONFINED AQUIFER
IMPERMEABLE STRATA
Figure 24. Unconfirmed and confined aquifers (Todd, 1959).
changes within the aquifer. The piezometric surface of a confined aquifer
(see Figure 24) is an imaginary surface defining the hydrostatic pressure
of the water in the aquifer.
Groundwater Movement
Most groundwater moves in accordance with Darcy's Law, which states
that the velocity is directly proportional to the permeability of the aquifer
and the hydraulic gradient. Typical groundwater flow velocities fall in the
range of 5 feet per year to 5 feet per day; however, exceptionally higher
velocities have been measured in highly permeable outwash glacial deposits,
in fractured basalts and granitic rocks, and in cavernous limestones.
Essentially all groundwater is in motion from its source of recharge to
its point of discharge. Natural recharge occurs from precipitation and sur-
face water bodies; artificial recharge results from acts of man, such as by
irrigation. Groundwater discharges naturally to springs, surface water
bodies, and the ocean. Wells and drains function as manmade discharge
points for groundwater.
Pollutants tend to move in the direction of flow of the surrounding
groundwater. Within confined aquifers water movement is roughly horizon-
86
-------
tal because of the negligible vertical movement within the confining strata.
There may be in certain situations, however, large vertical head gradients
which induce vertical flows from one strata to another. In unconfined aqui-
fers the groundwater also flows generally horizontally beneath a gently
sloping water table. In the unsaturated zone above a water table, water
usually percolates vertically downward to the water table. Less permeable
layers may cause saturated conditions (perched groundwater) and allow
horizontal movement.
Water in the saturated zone (below the water table) tends to move faster
at relatively shallow depths than that at great depths. Where groundwater
occurs to great depths, it is reasonable to consider an upper zone of rapid
circulation, a middle zone of delayed circulation, and the lowest zone of
very slow water circulation.
Natural Chemical Quality
All groundwater contains natural chemical constituents in solution. The
kinds and amounts of constituents depend upon the geochemical environment,
movement, and source of the groundwater. Typically, concentrations of
dissolved constituents in groundwater exceed those in surface water. Also,
salinities tend to be higher in arid regions and where drainage is poor.
Chemical constituents originate primarily from solution of rock materi-
als. The geologic history of groundwater governs its salinity. Common
chemical constituents of groundwater include:
Cations Anions Undissociated
Calcium Carbonate Silica
Magnesium Bicarbonate
Sodium Sulfate
Potassium Chloride
Nitrate
An abundance classification of dissolved solids in fresh water is shown
in Table 6. Frequency distributions of various constituents are shown in
Figure 25.
Table 7 provides a convenient summary of the major natural chemical
constituents in groundwater in terms of their sources and their effects upon
the usability of water.
The chemical quality of groundwater is often conveniently described for
domestic and industrial use in terms of its salinity and its hardness. Salin-
ity refers to the concentration of total dissolved solids present in the water.
Hardness is a measure of the calcium and magnesium content and is usually
expressed as the equivalent of calcium carbonate. Table 8 lists classifica-
tions of water by salinity and hardness.
87
-------
TABLE 6. RELATIVE ABUNDANCE OF DISSOLVED SOLIDS
IN POTABLE WATER (Davis and DeWIest, 1966)
Major Constituents
(1.0 to 1000 ppm)
Sodium
Calcium
Magnesium
Bicarbonate
Sulfate
Chloride
Silica
*These elements occupy an
Secondary Constituents
(0.01 to 10.0 ppm)
Iron
Strontium
Potassium
Carbonate
Nitrate
Fluoride
Boron
uncertain position in the list.
Minor Constituents
(0.0001 to 0. 1 ppm)
* Antimony
Aluminum
Arsenic
Barium
Bromide
* Cadmium
* Chromium
Cobalt
Copper
* Germanium
Iodide
Lead
Lithium
Manganese
Molybdenum
Nickel
Phosphate
* Rubidium
Selenium
* Titanium
Uranium
Vanadium
Zinc
Trace Constituents
(generally less than 0,001 ppm)
Beryllium
Bismuth
* Cerium
Cesium
Gallium
Gold
Indium
Lanthanum
* Niobium
Platinum
Radium
* Ruthenium
* Scandium
Silver
* Thallium
* Thorium
Tin
* Tungsten
Ytterbium
* Yttrium
* Zirconium
Besides solution of rock materials, other natural sources of salinity in
groundwater include:
• Water of volcanic origins
• Evapotranspiration through native vegetation
• Airborne salts.
Within a large body of groundwater the natural chemical composition of
the water tends to be relatively consistent, although the concentration of
minerals in solution may be variable. However, where geologic differences
or multiple sources exist, significant salinity differences occur. Time var-
iations of groundwater quality under natural conditions are minor in compar-
ison with surface water quality changes.
Groundwater under natural conditions tends to increase in salinity with
depth. Most of the geologic formations containing groundwater in the United
States are underlain by waters varying from brackish to highly saline. Den-
sity and permeability differences act to maintain a separation between these
waters and the overlying fresh groundwater.
-------
-
<
0.01
100
1000
mgA
Figure 25. Cumulative curves showing the frequency distribution of various constituents in potable water
(modified after Davis and DeWiest, 1966).
-------
TABLE 7. MAJOR NATURAL CONSTITUENTS IN GROUNDWATER - THEIR
SOURCES AND EFFECTS UPON USABILITY (modified after Miller et al.,
1974)
Silico
Sources: Feldspars, ferromagnesium and clay minerals, amorphous silica, chert, opal.
Effect:
In the presence of calcium and magnesium, silica forms a scale in boilers and on
steam turbines that retards heat; the scale is difficult to remove. Silica may
be added to soft water to inhibit corrosion of iron pipes.
Iron (Fe)
Sources (natural): Igneous Rocks — amphiboles, ferromagnesian micas, ferrous sulfide (FeS),
ferric sulfide or iron pyrite (FeS2), magnetite (Fe3C>4) — and
Sandstone Rocks — oxides, carbonates, and sulfides or iron clay minerals.
Effect: More than 0.1 ppm precipitates after exposure to air; causes turbidity, stains
plumbing fixtures and laundry and cooking utensils, and imparts objectionable tastes
and colors to foods and drinks. More than 0.2 ppm is objectionable for most
industrial uses.
Manganese (Mn)
Sources: Manganese in natural water probably comes most often from soils and sediments.
Metomorphic and sedimentary rocks and mica biotite and amphibole hornblende
minerals contain large amounts of managanese.
Effect: More than 0.2 ppm precipitates upon oxidation; causes undesirable tastes, deposits
on foods during cooking, stains plumbing fixtures and laundry, and fosters growths
in reservoirs, filters, and distribution systems. Most industrial users object to
water containing more than 0.2 ppm.
Calcium (Co) and Magnesium (Mg)
Sources: Calcium — Amphiboles, feldspars, gypsum, pyroxenes, aragonite, calcite, dolomite,
clay minerals.
Magnesium — Amphiboles, olivine, pyroxenes, dolomite, magnesite, cloy minerals.
Effect: Calcium and magnesium combine with bicarbonate, carbonate, sulfate, and silica to
form heat retarding, pipe-clogging scale in boilers and in other heat-exchange
equipment. Calcium and magnesium combine with ions of fatty acid in soaps to form
soapsuds. A high concentration of magnesium has a laxative effect, especially on
new users of the supply.
Sodium (No) and Potassium (K)
Sources: Sodium — Feldspars (albite); clay minerals; evaporites, such as halite (NaCI) and
mirabilite (No2SC>4 • 10H2O).
Potassium — Feldspars (orthoclase and mic roc line), feldspathoids, some micas,
clay minerals.
Effect- More than 50 ppm sodium and potassium in the presence of suspended matter causes
foaming, which accelerates scale formation and corrosion in boilers. Sodium and
potassium carbonate in recirculating cooling water can cause deterioration of
wood in cooling towers. More than 65 ppm of sodium can cause problems in ice
manufacture.
Carbonate (€03) and Bicarbonate (HCCfo)
Sources: Bicarbonate — Biosphere; limestone; dolomite.
Effect; Upon heating, bicarbonate is changed into steam, carbon dioxide, and carbonate.
The carbonate combines with alkaline earths — principally calcium and magnesium —
to form a crust I ike scale of calcium carbonate that retards flows of heat through
pipe wells and restricts flow of fluids in pipes. Water containing large amounts
of bicarbonate and alkalinity are undesirable in many industries.
(continued)
90
-------
Table 7. (Continued)
Sulfote (SO4)
Sources: Oxidation of sulfide ores; gypsum; anhydrite.
Effect: Sulfate combines with calcium to form an adherent, heat-retarding scale. More
than 250 ppm is objectionable in water in some industries. Water containing
about 500 ppm of sulfate tastes bitter; water containing about 1,000 ppm ma/ be
cathartic.
Chloride (Cl)
Sources- Sedimentary rocks and evaporites; ocean tides force salty water upstream in tidal
estuaries.
Effect: Chloride in excess of 100 ppm imparts a salty taste, while concentrations of the
order of 1000 or more may cause physiological damage. Food processing industries
usually require less than 250 ppm. Some industries — textile processing, paper
manufacturing, and synthetic rubber manufacturing — desire less than 100 ppm.
Fluoride (F)
Sources: Amphiboles (hornblende), apatite, fluorite, mica.
Effect: Fluoride concentration between 0.6 and 1.7 ppm in drinking water has a beneficial
effect on the structure and resistance to decay of children's teeth. Fluoride in
excess of 1.5 ppm in some areas'causes "mottled enamel" in children's teeth.
Fluoride in excess of 6.0 ppm causes pronounced mottling and disfiguration of
teeth.
Nitrate (NOg)
Sources: Atmosphere; legumes, plant debris, and animal excrement.
Effect: Water containing large amounts of nitrate (more than 100 ppm) is bitter tasting
and may cause physiological distress. Water from shallow wells containing more
than 45 ppm has been reported to cuase methemoglobinemio in infants. Small
amounts of nitrate help reduce cracking of high-pressure boiler steel.
Dissolved Solids
Sources: The mineral constituents dissolved in water constitute the dissolved solids.
Effect: More than 500 ppm is undesirable for drinking and many industrial uses. Less than
300 ppm is desirable for dyeing of textiles and the manufacture of plastics, pulp,
paper, and rayon. Dissolved solids cause foaming in steam boilers; the maximum
permissible content decreases with increases in operating pressure.
OCCURRENCE OF GROUNDWATER POLLUTION
Definition
Groundwater pollution is the degradation in the natural quality of ground-
water produced by acts of man. Pollution may inhibit the use of the water
or may create hazards to public health through toxicity or the spread of
disease.
This definition follows that appearing in the Federal Water Pollution Con-
trol Act of 1972, and quoted in the Introduction to this report.
Distribution of Pollutants
If it were possible to see zones of groundwater pollution from an aerial
vantage point, most would appear so small in relation to the total areas as
to be termed scattered points of pollution. Areally extensive sources such
91
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TABLE 8. CLASSIFICATIONS OF WATER
(Davis and DeWiest, 1966)
Based on Concentration of
Total Dissolved Solids (TDS)
Name
Fresh
Brackish
Salty
Brine
Concentration of TDS
(parts per million)
0-1,000
1,000-10,000
10,000-100,000
More than 100,000
Based on Hardness
Name
Soft
Moderately Hard
Hard
Very Hard
Hardness as CaCO3
(parts per million)
0-60
61-120
121-180
More than 180
as irrigation return flows and seawater intrusion would be identified as non-
point sources. A line source would result, for example, from recharge of
sewage effluent in an ephemeral stream channel.
Figure 26 suggests by small dots on a map the distribution of ground-
water pollution in a drainage basin. As indicated by the profile view at the
top of Figure 26, most point sources of pollution will not penetrate through
the zone of aeration; this is particularly true where the volume of pollutant
is relatively small and where the water table is some distance below ground
surface. The profile view of Site 5 in Figure 26 shows a pollutant that has
reached the water table and has begun to migrate down-gradient with the
groundwater flow.
Mechanisms of Pollution
Shallow aquifers are usually the most important sources of groundwater
for water supply purposes, but the upper portions of these aquifers are al'so
the most susceptible to pollution. The entry of pollutants to shallow aqui-
fers occurs (1) directly through wells, (2) by downward percolation through
the zone of aeration, (3) by induced recharge from surface water bodies, (4)
by interaquifer flow, and (5) by upconing of deeper saline water due to over-
pumping of wells.
It should be recognized that the configuration of pollution entry into and
movement within the underground is unique for each individual pollution
92
-------
PROFILE VIEW
WATER TABLE
PROFILE VIEW OF SITE 5 ENLARGED
^-DISPOSAL SITE
LAND SURFACE.
Figure 26. A hypothetical drainage basin in a humid region showing in plan view
the distribution of zones of polluted water in the upper part of the zone
of saturation. Line AA1 shows profile view across basin. At disposal
sites 1 and 5 pollutants extend through zone of aeration and cause a
polluted zone beneath the water table. Disposal sites 2, 3, 4, and 6
do not pollute the groundwater (modified after LeGrand, 1965b).
93
-------
source. Furthermore, because there are many millions of groundwater
pollution sources in the United States, it becomes apparent that the possibil-
ities in terms of pollutant movement and distribution are virtually limitless.
Notwithstanding this fact, typical flow patterns of groundwater pollutants for
a variety of common situations can be described.
The diagrams on the following pages depict some of the frequently occur-
ring pollution geometries. These emphasize vertical cross sections at pol-
lution sources; horizontal pollution movement thereafter is discussed later.
Whatever the particular source of pollution may be, these diagrams indicate
the hydraulic relationships for a given situation. Where the local hydro-
geology is known, paths of probable pollutant movement can be defined.
With estimates of permeability, hydraulic gradient, and porosity available,
rates of groundwater movement can be ascertained. Rates of pollutant
movement are based on groundwater flow rates, chemical interactions with
aquifer materials, and changes in water chemistry. Thus, pollutants travel
at velocities equal to or less than that of the groundwater.
Figure 27 shows the local movement of effluent from a domestic septic
tank system. The waste water flows vertically downward to the water table
and then is distributed laterally within the groundwater body.
PRODUCTION
7\
WELL
PRETREATMENT
DISPOSAL
EVAPOTRANSPIRATION
ZONE OF POLLUTED
GROUNDWATER
Figure 27. Disposal of household wastes through a conventional septic rank
system (modified after Miller et al., 1974).
-------
SOURCE OF
^POLLUTANTS
=1
'VADOSE ZONE
•S^i:^'^-'--"^RECHARGE
' '^^'^-•':.'-:ijfr$ ^OU.ND :';
- --^•^•"i-^^'T T^Si'^li'." '' *•,*•'•-'.'••.'.' ' • •'•'•
^^i*!^:^.^:
-I CONFINING BED
Figure 28. Diagram showing percolation of pollutants from a disposal pit to a
water table aquifer (modified after Deutsch, 1963).
Figure 28 illustrates the flow of pollution from a surface source such as
a disposal pit, lagoon, or basin. Note that the polluted water flows down-
ward to form a recharge mound at the water table and then moves laterally
outward below the water table. If significant layering exists above the water
table, horizontal movement may occur in the vadose zone as suggested by
Figure 29.
Figure 30 shows cross-sectional and plan views of groundwater pollution
caused by a leaking sewer. The pollution drains downward to the water table
and then flows laterally thereafter to form a line source of pollution beneath
the sewer.
Figure 31 indicates how salt leached from a salt stockpile moves down-
ward to the water table and thereafter laterally and vertically to a nearby
pumping well. Figure 32 indicates pollution movement from a surface
stream or lake to a nearby pumping well. The drawdown of the water table
induces recharge of surface water to groundwater. Many municipal water
supply wells are located adjacent to rivers in order to insure continuous
water supplies. This is an important ground-water pollution mechanism
where rivers are polluted. In arid areas where water tables are relatively
deep, polluted surface water can percolate to groundwater regardless of
pumping patterns.
95
-------
DISPOSAL PIT
GROUND SURFACE
V
L-
I I \
CLAY LENS
UNCONFINED AQUIFER
Figure 29. Diagram showing the horizontal movement of pollutants beneath a
disposal pit as a result of clay lenses in the vadose zone above the
water table.
CROSS SECTION
GROUND SURFACE
M
LEAKING SEWER
WATER TABLE
'ZONE OF POLLUTION
PLAN VIEW
[
t'V. V-'
* •.'• -.;'
§'•""••- •'•
K$i
i
^LEAKING SEWER
ZONE OF POLLUTION
I
Figure 30. Illustration of a line source of groundwater pollution caused by a
leaking sewer. The water table is situated below the sewer and is
assumed to be horizontal.
96
-------
;«?.;::'.::-.:-'tv-;.:''-;::0|:;^::.; FRESH WATER .'"/y;..-.:
' AQUICLUDE
Figure 31. Diagram showing pollution of an aquifer by leaching of surface solids
(modified after Deutsch, 1963).
POLLUTED
•SURFACE WATER
Figure 32. Diagram showing how polluted water can be induced to flow from
a surface stream to a well (modified after Deutsch, 1963).
97
-------
RIVER IN FLOOD
GRAVEL PACK
TOO CLOSE TO
SURFACE
KJV^V.v. FRESH WATERV.v£::
AQUICLUDE
Figure 33. Diagram showing floodwater entering a well through an improperly
sealed gravel pack (modified after Deutsch, 1963).
Figure 33 suggests how temporary flooding of a well can lead to ground-
water pollution. Downward flow of polluted surface water occurs around the
well casing if the well has been improperly sealed at the ground surface.
Figure 34 indicates how the disposal of pollutants into one well can be
transported through the aquifer and lead to pollution of a nearby pumping
well. Because a pumping well is a convergence point for groundwater over
a large area, this collection mechanism increases the opportunity for ob-
taining polluted water from a pumping well.
Figure 35 outlines the flow patterns of pollutants entering a water table
aquifer and a confined aquifer from an injection or recharge well. Note that
the pollution tends to spread through the entire thickness of an aquifer and
then move radially outward from the well.
Figure 36 illustrates the reversal of underground flows due to pumpage
from one aquifer and hence the possibility to degrade the groundwater
quality by interaquifer flow. Under natural conditions shown in the upper
diagram, the water table of Aquifer A is higher than the piezometric surface
of Aquifer B; therefore, groundwater tends to move downward through the
98
-------
. POLLUTANTS
INTRODUCED
AQUIFER
WATER SURFACE
POLLUTED WATER
POLLUTED
GROUNDWATER
AQUICLUDE
Figure 34. Diagram showing movement of pollutants from a recharge well to a
nearby pumping well (modified after Deutsch, 1963).
semipermeable zone separating the two aquifers. In the lower diagram,
however, pumping has interchanged the relative positions of the two water
levels. As a result, the greater pressure in Aquifer B causes water to
migrate upward into Aquifer A. If, as is often the case, the lower aquifer
is more saline, this will cause the salt content of the upper aquifer to in-
crease.
Figure 37 presents two situations of interaquifer flow through a nonpump-
ing well penetrating more than one aquifer. In Figure 37(a) the water table
stands above the piezometric surface so that water flows down the well into
the deeper aquifer. But in Figure 37(b) the situation is reversed so that
water rises through the well and invades the upper zone.
Figure 38 shows plan and profile views of a recharge pond overlying an
unconfined aquifer with a sloping water table and with groundwater flowing
from left to right. Under these conditions pollution from the pond extends
a short distance upstream and is stabilized. The bulk of the pollutant moves
away from the pond in a downgradient direction within clearly defined
99
-------
LIQUID POLLUTANTS
AQUICLUDE
A. WATER TABLE AQUIFER
.LIQUID POLLUTANTS
AQUICLUDE
ORIGINAL-
GRADIENT .
.AQUIFER
-NEW PIEZOMETRIC SURFACE
•OLD PIEZOMETRIC SURFACE
SCREEN
AQUICLUDE
B. ARTESIAN AQUIFER
Figure 35. Diagrams showing spread of pollutants injected through wells into
water table and artesian aquifers (modified after Deutsch, 1963).
100
-------
NATURAL (
A
;PIEZOMETRIC SURFACE
OF AQUIFER B
AQUIFER A ....
-.-• .- -- -:-- '
:i
:ONDITIONS
STATIC WATER TABLE
OF AQUIFER A
' : ' i " i ' " ': 'j " - ' • • '
;,
. •••'_, SCREEN.
^ ' •'•
/..CONFINING ' '
BED;,;, -'.••:
1 •• • • '^- •;---"; •••'•£
AQUIFER B
'^i^^^^^
SCREEN
.".'>^
'^
•—
.- ••
i>
PUMPING CONDITIONS
A
WATER TABLE OF'
AQUIFER A
: AQUIFER A
PIEZOMETRIC SURFACE;
OF AQUIFER B
SCREEN
Figure 36. Diagrams showing reversal of aquifer leakage
by pumping (Deutsch, 1963).
101
-------
.,":.;:..'.•.'; GROUND SURFACE
. WATER TABLE
UNCONFINED AQUIFER
•PIEZOMETRIC SURFACE
CLAY LAYER
CONFINED AQUIFER
(a) WATER TABLE ABOVE THE PIEZOMETRIC SURFACE
•GROUND SURFACE
I PIEZOMETRIC SURFACE
WATER TABLE
UNCONFINED AQUIFER
CLAY LAYER
CONFINED AQUIFER
(b) PIEZOMETRIC SURFACE ABOVE THE WATER TABLE
Figure 37. Diagrams showing aquifer leakage by vertical movement of water
through a nonpumping well.
102
-------
FLOWLINES
PLAN VIEW
:••; -j.w TE TABLE ;.v.'.y
.^ORIGINAL WATER TABLE
•.-.: .•:.:;.::>• 1/1 y-r •j'-;-'
'•.:.::-'-::.'::'-...v :• ':• '•• •'•' ••'.::'-\^
Figure 38. Diagrams showing lines of flow of pollutants from a recharge pond
above a sloping water table (modified after Deutsch, 1963).
103
-------
boundaries. For given aquifer and recharge conditions, the lateral spread
of the pollution ae it moves downstream can be determined (Todd, 1959).
Waste water from a disposal well penetrating an aquifer having the same
conditions would move in a similar flow pattern.
Figure 39 suggests how underlying saline groundwater can rise due to
deepening of a stream channel. This intrusion of saline water occurs be-
cause of the reduced head of fresh water.
Attenuation of Pollution
Pollutants in groundwater tend to be removed or reduced in concentration
with time and with distance traveled. Mechanisms involved include decay,
chemical processes, and dilution. The rate of pollution attenuation is a
function of the type of pollutant and of the local hydrogeologic framework.
Predicting the degree to which pollutants will become attenuated is one of
the most difficult, but also one of the most important, problems in the de-
sign of waste disposal systems utilizing the underground.
• DECAY. The reduction in the strength or potency of a pol-
lutant with time constitutes a decay mechanism. This may
involve oxidation of organic wastes in the zone of aeration,
the decrease in concentration of a radioactive waste as a
function of its half-life, or death of micro-organisms in un-
suitable geologic environments.
• CHEMICAL PROCESSES. Adsorptive and other physical-
chemical interfacial forces combine to remove pollutants from
solution and to concentrate them on fine-grained soil and aqui-
fer materials, particularly clays. Soils have a large capacity
to adsorb organic materials. Many radioactive wastes, in *
addition, are strongly adsorbed by alluvial aquifers. Sorp-
tion may also include ion-exchange. Furthermore, cations
such as potassium and ammonium, anions such as phosphate,
and many trace elements tend to be adsorbed by soils and
granular porous media.
Salts can be precipitated from solution under certain condi-
tions of temperature, pH, oxidation potential, and concentra-
tion. Thermodynamic relations can be used to determine if
precipitation of mineral phases should be occurring under a
given set of- conditions. Anions most affected by precipitation
are carbonate, bicarbonate, sulfate, and phosphate; cations
most affected are calcium and magnesium.
• DILUTION. Pollutants in groundwater flowing through porous
media tend to become diluted in concentration due to hydro-
dynamic dispersion. Microscopic dispersion is mixing caused
104
-------
ORIGINAL CHANNEL
DREDGED CHANNEL
^^^*^T*™»*W^WP*T*T7
XV" "" yyvJ^T^^l:':V.-'oRIGiNALJVATEVTABLE ;••'.'•:.'•:'•.:'
X.—-/W^^^-T^ v^^Tv.-^vT. ~ ^.vvT'v-
-—— •— x Xr -.v; •>•'•IVfrVv:*:"-:. '.•'•':;:••'•:'.•' L'OWE'RE D"WA leV f AB?P'*.':'!.'»''.' •
Figure 39. Diagram showing migration of saline water caused by lowering of water levels
in a gaining stream.
by the tortuous flow around individual grains as water
moves through an aquifer. Macroscopic dispersion is
mixing resulting from heterogeneities of geologic forma-
tions, such as variable permeability, which cause flow
lines to deviate and to converge. The result of these
mechanisms is a longitudinal and lateral spreading of a
pollutant within the groundwater so that the volume af-
fected increases and the concentration decreases down-
gradient. An analogous effect would be the dissipation
of smoke from a smokestack as it drifts downwind in the
atmosphere.
It is important to emphasize the role of aquifers in these attenuation
processes. Aquifers composed of fine-grained materials possess very large
surface areas which promote sorption processes. These same aquifers also
encourage dilution by dispersion because of the large number of small inter-
stices through which the groundwater must flow. On the other hand aquifers
with large openings, whether from large-sized materials, cracks, or solu-
tion openings, permit a pollutant to advance rapidly underground with little
105
-------
or no reduction in concentration. Thus, in general, adsorption is greater
in fine-grained aquifers, while dilution by mixing is greater in coarse-
grained aquifers.
Specific statements cannot be made about the distances that pollution
will travel because of the wide variability of aquifer conditions and types of
pollutants. Yet certain generalizations which are widely applicable can be
stated. For fine-grained alluvial aquifers, pollutants such as bacteria,
viruses, organic materials, pesticides, and most radioactive materials,
are usually removed by adsorption within distances of less than 100 meters.
But most common ions in solution move unimpeded through these aquifers,
subject only to dilution by mixing and chemical processes.
Distribution of Pollution Underground
Given the above attenuation processes, pollution from a point source
moves outward until a harmless or very low concentration level is reached.
Because each constituent of a pollution source may follow a different attenu-
ation rate, the distance to which pollution is effective will vary with each
quality component.
A hypothetical example of a waste-disposal site is shown in Figure 40.
Here groundwater flows toward a river. Zones A, B, C, D, and E represent
essentially stable limits for different contaminants resulting from the
steady release of wastes of unchanging composition. Pollutants, once en-
trained in the saturated groundwater flow tend to form plumes (again analo-
gous to smoke in the atmosphere) of polluted water extending downstream
from the pollution source until they attenuate to some minimum quality
levels. Only Zone E reaches the river in Figure 40 and is subsequently
diluted by surface water.
The shape and size of a plume depends upon the local geology, the ground-
water flow, the type and concentration of pollutant, the continuity of waste
disposal, and any modifications of the groundwater system by man, such as
well pumping (LeGrand, 1965b). Examples of various types of plumes are
shown in Figure 41 and explained in Table 9. These are illustrative of the
diversity of forms that plumes may assume. Where groundwater is moving
relatively rapidly, a plume from a point source will tend to be long and
thin; but where the flow rate is low, the pollutant will tend to spread more
laterally to form a wider plume. Irregular plumes can be created by local
influences such as pumping wells and nonuniformities in permeability.
Plumes ordinarily tend to become stable areas where there is a constant
input of waste into the ground. This occurs for two reasons: the tendency
106
-------
, WA.SU SITE
DOWNSTREAM LIMIT
. OF POLLUTANT E
Figure 40. Plan view of a water table aquifer showing the hypothetical areal extent
to which specific pollutants of mixed wastes at a disposal site disperse
and move to insignificant levels (modified after LeGrand, 1965b).
a
2
O
az
o
Q
PERENNIAL STREAM
Figure 41. Types of pollution plumes in the upper part of the zone of saturation
(plan view). An "X" marks the core of contamination beneath a waste
site and "Z" the point downstream at which some plumes terminate
(LeGrand, 1965b).
107
-------
TABLE 9. EXPLANATION OF PLUMES SHOWN IN FIGURE 41 (modified after LeGrand, 1965b)
o
CO
Plume Governed By
Site
A
B
C
D
£
F
G
H
t
J
K
L
M
N
O
P
O
R
Dilution
Nci appreciable In ground;
some in streams
Not cpp( eel-able
Improbable
No molenclave formed
(See Remarks)
Slight near waste vte;
tome at greater distance
Yes; suggestive of nearly
homogeneous porous materials
Not appreciable in ground;
tome near and in stream
Yes: suggestive of nearly
homogeneous porous materials
Yes
Slight
Yes; suggestive of nearly
homogeneous porous materials
Yes; suggestive of nearly
Homogeneous poroui materials
Some in ground and stream
Yes
Yei
Some
Some-
Yes
Decoy Sorpti on
No No
Either decoy or torpfion or bath
Perhaps Perhaps
Either decoy or sorption or both
Possibly Possibly
improbable Improbable
Not appreciable Not appreciable
Probably either decay or sorption
or both
Perhaps Perhaps
Not appreciable Probably not
appreciable
Either decay or sorption or both
Either decay or sorption or both.
Not appreciable Not appreciable
Either decay or sorption or both
Either decay a* vwptian. a* both
Either decay or sorption or both
Either decoy or sorplion or both
Either decay or lorptian or botfi
Liquid Waste
Recharge Form-
log Water-
lable Mound
Ho
No
Mo
No
No
No
No
No
No
No
Yes
Yes
Y*«
Yes
No
No
No
No
Composite
Water
Sites
No
No
No
No
No
No
No
No
No
No
No
No
No
Ye*
Yes
Yes
No
Examples of Types
of
Pollutarf
Chloriaev nitrores
Sewage, radio-
active wastes
Sewage, radio-
active wastes
Chlorides, nitrates
Chlorides, nitrates
Sewage,, radio-
acttve wastes
.._
Chlorides, nitrates
Sewage, radio-
active wastes
Sewage, radio-
active wastes
Chlorides, nlrrates
Sewage, radio-
active wattes
Sewage, iod\o-
active wastes
Sewage, radio-
active wastes
Sewoge, radio-
octfve wastes
Sewage., radio-
active wastes
Remarks
Probably small waste release or good
attenuation In zone of aeration.
Pollutant is completely attenuated in zone
of aeration and does not reach zone of
saturation.
Lack oF dispersion near waste *tt« typical
of linear openings m rock; po Muted water
downgradient cflspertes into different type
of material.
Irregularities in permeability cause
deviation in plume.
Downgradient split in plume may be due to
dense impermeable rock or great increase
in sorprive materials.
Downgradfent plume ii due to shunting of
pollutant to land surface at tail of upper
plume and reinfllrrotion of pollutant.
Irregularities in plume caused by changes
*n permeability and /or sorption.
Deviation in plume due to impermeable zoo*.
Polluted water from three waste sites at
right angles to groundwater flow, merging
to form a composite plume .
Polluted water from Vwo waste wV*s paral-
lel to groundwater flow, forming a com-
posite lite.
Polluted water from two waste sitesot an
angle with groundwater flow, forming a
composite plume.
large composite plume Formed by several
waste s'tes.
Pumping well drgws plume reward it; pel-
luted water is greatly d" luted at the well.
-------
WASTE SITE
FORMER
BOUNDARY
PRESENT
-BOUNDARY
WASTE SITE
PRESENT
BOUNDARY
FORMER
BOUNDARY
WASTE SITE
FORMER
BOUNDARIES
PRESENT
BOUNDARY
WASTE SITE
PRESENT
BOUNDARY
FORMER
-BOUNDARY
ENLARGING
PLUME
1. INCREASE IN RATE OF
DISCHARGED WASTES
2. SORPTION ACTIVITY
USED UP
3. EFFECTS OF CHANGES
IN WATER TABLE
REDUCING
PLUME
1. REDUCTION IN WASTES
2. EFFECTS OF CHANGES
IN WATER TABLE
a. MORE EFFECTIVE
SORPTION
b. MORE EFFECTIVE
DILUTION
c. SLOWER MOVEMENT
AND MORE TIME FOR
DECAY
NEARLY STABLE
PLUME
1. ESSENTIALLY SAME WASTE
INPUT
2. SORPTION CAPACITY NOT
FULLY UTILIZED
3. DILUTION EFFECT FAIRLY
STABLE
4. SLIGHT WATER TABLE
FLUCTUATION OR EFFECTS
OF WATER TABLE FLUCTUA-
TION NOT IMPORTANT
SHRUNKEN
PLUME
WASTE NO LONGER
DISPOSED AND NO
LONGER LEACHED AT
ABANDONED WASTE
SITE
Figure 42. Changes in plumes and factors causing the changes (modified after
LeGrand, 1965a).
for enlargement as pollutants continue to be added at a point source is coun-
terbalanced by the combined attenuation mechanisms, or the pollutant
reaches a location of ground-water discharge, such as a stream, and emerges
from the underground. When a waste is first released into groundwater, the
plume expands until a quasi-equilibrium stage is reached. If sorption is im-
portant, a steady inflow of pollution will cause a slow expansion of the plume
as the earth materials within it reach a sorption capability limit.
An approximately stable plume will expand or contract generally in re-
sponse to changes in the rate of waste discharge. Figure 42 shows changes
in plumes that can be anticipated from variations in waste inputs.
An important aspect of groundwater pollution is the fact that it may per-
sist underground for years, decades, or even centuries. This is in marked
contrast to surface water pollution. The average residence time of ground-
water is on the order of 200 years; consequently, a pollutant which is not
109
-------
readily decayed or sorbed underground can remain as a degrading influence
on the resource for indefinite periods. The comparable residence time for
water in a stream or river is on the order of 10 days; thus, surface water
pollution can be rapidly eliminated. Reclaiming polluted groundwater is
usually much more difficult and time consuming than reclaiming polluted
surface water. Underground pollution control is usually best achieved by
regulating the pollution source, and secondarily by physically entrapping
and, when feasible, removing the polluted water from the underground.
Evaluation of Pollution Potential
To provide guidance in evaluating the potential pollution of a given site,
LeGrand (1964) developed an empirical point-count system. The concept is
applicable to locations of waste disposal sites and to wells; water table aqui-
fer conditions are presumed.
Local factors influencing pollution include:
• Depth to water table
• Sorption
• Permeability
• Water table gradient
• Distance.
The rating chart shown in Figure 43 illustrates the evaluation procedure for
sites in unconsolidated alluvial materials. A numerical value is read above
the line for each of the five factors based upon the corresponding data below
the line.
The pollution potential of a given site is the sum of the numerical ratings
of the five factors in Figure 43. Total point values may be interpreted in
terms of possibility of pollution as follows:
Total Points Possibility of Pollution
0-4 Imminent
4-8 Probable or possible
8-12 Possible but not likely
12-25 Very improbable
25-35 Impossible
LeGrand (1964) emphasized that his index system for evaluating pollution
was imperfect and only a beginning. Certainly refinements can and should
be made in the future, but for the present his approach is useful and sound.
110
-------
WATER TABLE
7 8
I i
10
I
10
\
20
30
I
I
150
I
I
300
40 50 75 100 150 200
DISTANCE BELOW BASE OF DISPOSAL UNIT (ft)
500
I I
750 1000
SORPTION
0
COARSE
GRAVEL
*
1
1
1
COARSE CLEAN
SAND
12 3 2
I
I
CLAY SILT OR CLAYEY
2 3
I 1
1 1
SMALL SILT
AMOUNTS
OF CLAY
IN SAND
PERMEABILITY
1
1
1
FINE SAND
4 4.5 5
1 1 1
1
EQUAL AMOUNTS
OF CLAY
AND SAND
SANDY SAND
6
CLAY
0
I
COARSE COARSE
SAND GRAVEL
CLAY
GRADIENT
1-
0
I
1
60
1
30
1
1
1
20
1
10
2
1
3
I
(
4
i
)
5
I
6
1
10
6
PERCENTAGE
DISTANCE
3 1
) 25 50
2 :
) 4 5 <
1 1
75 100 150 2C
CCCT
i
0 3C
7 f
X) 5C
} <
0 10
? 10 1
1
1 1
00 2500 1 1
K_< U«-MIIF<;-».
'UNACCEPTABLE RANGES
Figure 43. Rating chart for pollution potential in unconfmed aquifers of uncon-
solidated alluvial materials (modified after LeGrand, 1964).
Ill
-------
Trends in Groundwater Pollution
Because of the many millions of groundwater pollution sources in the
United States, comprehensive data defining the extent of the problem are
almost nonexistent. Thus, although an overview of the magnitude of the
problem is difficult to obtain, basic trends of pollution can be suggested
from a demographic approach.
Recognizing that groundwater pollution results from activities of man,
one can relate the magnitude of pollution to population and other demographic
factors. As an example, Figure 44 shows the estimated growth of under-
ground pollution for the United States during the 20th century. The ordinate
is the percent of current (1974) pollution levels. The curve preceding 1974
is based upon the growth of urban population adjusted by a factor of two to
account for industrial development, increased per capita water use, devel-
opment of irrigated agriculture, and introduction of agricultural fertilizers
since 1900. The cumulative aspect of pollution, whereby pollution dating
from say 1954 may still be underground in 1974, has been neglected.
The curve in Figure 44 has been extended from 1974 to 2000 based on
estimated urban population growth only without adjustment. What this analy-
sis suggests is a tenfold increase in groundwater pollution from 1900 to the
present, and — assuming no future efforts to control groundwater pollution
— a further 60 percent increase by the end of the century. Hopefully, with
the implementation of the Federal Water Pollution Control Act of 1972 (PL
92-500) and the Safe Drinking Water Act (PL 93-523) this dire forecast will
not become reality.
CONSTITUENTS IN POLLUTED GROUNDWATER
Quality Categories
Water quality is normally expressed in terms of four basic categories:
chemical, biological, physical, and radiological. Within each category a
large number of individual parameters and constituents can be identified.
Table 10 lists a wide range of possible pollutants which may be found by
analysis of groundwater samples. The possible potential pollutants in the
chemical and biological categories are, of course, virtually limitless. On
the other hand most analyses of groundwater include only a few key param-
eters and constituents because they are sufficient to serve as indicators of
pollution.
Effects of Water Use
The sources and causes of groundwater pollution are by definition related
to man's use of water. The diversity of impacts of man's activities on the
hydrologic cycle create a complex and interrelated series of modifications
to natural water quality. The sources of water and the effects of man on
112
-------
160
£
u.
o
80
z
i
_J
2
oc
UJ
<
o
at
O
140
120
100
60
40
20
1900
1920
1940 1960
YEAR
1980
2000
Figure 44. Estimated trend of groundwater pollution in the United States during
the 20th Century.
113
-------
TABLE 10. PARAMETERS AND CONSTITUENTS WHICH MAY BE INCLUDED IN
ANALYSES OF GROUNDWATER QUALITY*
Chemical - Organic
Biochemical Oxygen
Demand (BOD)
Carbon Chloroform
Extract (CCE)
Chemical Oxygen
Demand (COD)
Chlorinated Phenoxy
Acid Herbicides
Detergents
(Surfactants)
Organic Carbon (C)
Organophosphorus
Pesticides
Phenols
Tannins and Lignins
Chemical - Inorganic
Acidity
Alkalinity
Aluminum (Al)
Ammonia (Nfy)
Antimony (Sb)
Arsenic (As)
Barium (Ba)
Beryllium (Be)
Bicarbonate (HCO3)
Boron (B)
Bromide (Br)
Cadmium (Cd)
Calcium (Co)
Carbonate (CO3)
Chloride (Cl)
Chromium (Cr)
Cobalt (Co)
Conductance, specific
Copper (Cu)
Cyanide (CN)
Fluoride (F)
Hardness
Hydroxide (OH)
Iodide (1)
Iron (Fe)
Lead (Pb)
Lithium (Li)
Magnesium (Mg)
Manganese (Mn)
Mercury (Hg)
Molybdenum (Mo)
'This list is illustrative rather
as well as different analytic
Units
mg/l
M9/I
mg/l
M9/I
mg/l
mg/l
Mg/l
mg/l
mg/l
mg/l
mg/l
M9/I
mg/l
M9/I
Mg/l
Mg/l
Mg/l
mg/l
Mg/l
Mg/l
M9/I
mg/l
mg/l
mg/l
Mg/l
Mg/l
umhos/cm
at 25 °C
M9/I
M9/I
Mg/l
mg/l
mg/l
M9/I
ug/l
M9/I
M9/I
mg/l
ug/l
ug/l
ug/l
Chemical - Inorganic
Nickel (Ni)
Nitrite (NO2)
Nitrate (NO3)
Nitrogen (N)
Oil and Grease
Oxygen (©2)
PH
Phosphate (PO^
Potassium (K)
Selenium (Se)
Silver (Ag)
Silica (SiO2)
Sodium (Na)
Solids, dissolved
Solids, suspended
Strontium (Sr)
Sulfate (SO4)
Sulfide (S)
Sulfite (SO3)
Tin (Sn)
Titanium (Ti)
Vanadium (V)
Zinc (Zn)
Biological
Coliform Bacteria
Fecal Coliform
Bacteria
Fecal Streptococci
Bacteria
Physical
Color
Odor
Temperature
Turbidity
Radiological
Barium- 140 (140Ba)
Cerium - 141 and 144
(HlCe/ 144Ce)
Cesium - 134 and 137
(134cs, 13?Cw)
Gamma Spectrometry
Gross Alpha
Gross Gamma
Iodine- 131(131I)
Neptunium - 239(239Np)
Radium (Ra)
Thorium (Th)
Tritium (3H)
Uranium (U)
than comprehensive. Various ionic forms of
expressions for
certain constituents have not
Units
M9/I
mg/l
mg/l
mg/l
mg/l
mg/l
pH units
mg/l
mg/l
M9/I
Mg/l
mg/l
mg/l
mg/l
mg/l
M9/I
mg/l
mg/l
mg/l
M9/I
Mg/l
M9/I
M9/I
Coliforms/100 ml
Fecal Coliforms/
100ml
Fecal Streptococci/
100ml
PCU
TO
°C
TU
pc/l
pc/l
pc/l
pc/l
pc/l
nc/l
pc/l
pc/l
pc/l
Mg/l
pc/l
Mg/l
some constituents
been included.
114
-------
water quality are suggested in the water quality cycle of Figure 45. Note
that there are four main uses of water — agricultural, industrial, commer-
cial, and domestic; each of these in turn exerts an influence on groundwater
quality.
AGRICULTURAL USES. The various agricultural uses of water and
their effects on water quality are shown schematically in Figure 46. Chemi-
cal constituents from agricultural activities are added at the land surface, as
it moves downward through the soil, and as it passes through disposal sites
for solid agricultural wastes. In particular, irrigation degrades the quality
of water due to evapotranspiration, which concentrates salts in irrigation
return water. Addition of fertilizers, soil amendments, pesticides, and
other additives applied to the soil also contribute to groundwater pollution.
Solid wastes produced by agricultural activities, particularly dairies and
feedlots, are in part deposited in sanitary landfills. Leachates and gases
generated by the decomposition of solid wastes may affect the quality. The
effect and the areal extent of such leachates vary depending upon the volume
of leachate, the rate of mixing with groundwater, the volume of groundwater
available, and the rate of groundwater movement.
INDUSTRIAL USES. The major uses of water in industrial plants are for
cooling, manufacturing and processing, and sanitation.
Figure 47 shows industrial uses of water and their effects on water qual-
ity. As could be expected, the quality of waste water varies with respect to
the type of industry and water use.
Water cooling systems vary from "open once-through" to "closed recir-
culating. " The first method requires large volumes of water, and waste
water is disposed of after one use; a closed recirculating system uses less
water but generates wastes with higher salinities. Softening of water before
use in cooling, to inhibit scale formation, results in generation of brine
wastes. Water returned to the underground after use for cooling will pos-
sess a higher salt content and a higher temperature.
Boiler feed systems have similar "open" and "closed" designs and yield
waste waters with increased salinities and temperatures. Industrial organic
wastes other than sewage generally possess a higher COD than domestic
wastes. Nonreclaimable industrial waste water may be disposed into deep
injection wells, whereas reclaimable waste water may be artificially re-
charged to groundwater after treatment.
COMMERCIAL USES. Figure 48 diagrams commercial uses of water and
their effects on water quality. Outside water use includes irrigation of
lawns, shrubs, and landscaping as well as activities such as car washes.
115
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IMPORTED WATER
CHEMICAL CHARACTER AND QUALITY
VARY GREATLY BETWEEN THESE SOURCES.
ATMOSPHERE
_ EVAPOTRANSPIRATION
RESERVOIRS
STRATIFICATION PROBLEMS
PRECIPITATION
PARTICLES: NUCLEI: GASES:
DUST No, Co, Mg, Cl, S, O2, COj, SO2,
SMOKE F, Hg, RADIONUCLE- H2S, N,, NO,
BACTERIA IDES, ETC. NH3, O3, ETC.
GROUNDWATER RECHARGE
PERCOLATION TO GROUND-
WATER BASINS (NATURAL
RECHARGE)
1. LEACHING OF EVAPORITES AND
SOLUTION OF MINERALS IN
SEDIMENTS (GEOCHEMISTRY).
2. FILTRATION OF SUSPENDED
MATTER AND BACTERIA .
3. ION EXCHANGE (ADSORPTION
AND DESORPTION) REACTIONS.
4. OXIDATION-REDUCTION (AVAIL-
ABILITY OF O2) REACTIONS.
5. PRECIPITATION OF SALTS - pH,
CO2p, Eh, T, ETC.
6. BIOCHEMICAL REACTIONS
MOST REACTIONS OCCUR IN
THE SOIL ZONE, FEWER IN
SATURATED ZONE. WATER PER-
COLATING TO SATURATED ZONE
MIXES SLOWLY. WELLS ARE MIXING
TOOLS.
QUALITY OF PUMPED WATER DE-
PENDS ON (1) WELL DEPTH AND PER-
FORATIONS, (2) RATE AND DURA-
TION OF PUMPING.
GROUNDWATER
EXTRACTIONS RECHARGE OF
GROUNDWATER
BASINS
RUNOFF ON
PAVED OR
IMPERVIOUS
LAND
STORM DRAIN WATER
SUSPENDED MATTER,
ORGANIC DEBRIS,
BACTERIA,
E VAPOR IT E SALTS
ARTIFICIAL
RECHARGE OF
GROUNDWATER
BASINS
LOW TDS, TURBIDITY
GROUNDWATER RECHARGE
TO SUPPLY POOL
SURFACE WATER
STREAMS
TURBIDITY, DO, ORGANIC LOAD,
BOD, BACTERIA, SALINITY, ALGAE,
NO3, PO4, PESTICIDES, DETERGENTS,
SUSPENDED MATTER
SURFACE WATER RESERVOIR
STRATIFICATION:
SOLUTION OF SALTS IN RIVER 6ED
MIXING WITH AGRICULTURAL RETURN
WATER AND EFFLUENT GROUNDWATER
t. ZONE OF CIRCULATION (AEROUC)
2. ZONE OF THERMOCLINE
3. ZONE OF STAGNATION (ANAEROBIC)
VARIABLE QUALITIES IN THESE ZONES
IN TERMS OF DO, BOD, pH, TASTE,
ODOR, GASES, Mn. Fe, SULFIDES,
PHOSPHORUS, ETC.
LAKE, SEA, OR
OCEAN
HIGH TDS, NUTRIENT
LEVELS, BOD, ALGAE,
BACTERIA, ETC.
SEE FIGURE 46
SEE FIGURE 47
SEE FIGURE 48
SEE FIGURE 49
Figure 45. Water quality cycle — sources and uses of water and effects on water quality
(modified after Hassan, 1974).
-------
AGRICULTURAL USES
(INCLUDING FEED LOTS AND DAIRIES)
AGRICULTURAL
SOLID WASTES
(SOURCE OF
NITRATES)
o. PLANT & CROP
RESIDUES
b. MANURE
c. DEAD ANIMALS
EVAPOTRANSPIRATION
(CONSUMPTIVE USE)
SALTS IN APPLIED WATER
ARE CONCENTRATED (2
OR 3 TIMES, DEPENDING
ON IRRIGATION EFFICIENCY)
APPLICATION OF
ADDITIVES
(ORGANIC AND INORGANIC)
PESTICIDES, SOIL CONDITIONERS
AND AMENDMENTS, AND FERTILIZERS.
SOIL REACTIONS
INCLUDE DEPOSITION
OF SALTS, ION EX-
CHANGE, OXIDATION,
REDUCTION, ETC.
SANITARY LANDFILL
EFFECTS ON GROUNDWATER
DEPEND ON CONTROL AND
DEPTH TO WATER TABLE, RAIN-
FALL AND MOISTURE CONTENT
IN WASTE, HYDRAULIC GRADIENT
OF WATER TABLE, GEOMETRY OF
SITE, ETC.
TAIL WATER
(SEEPAGE OFF LAND
SURFACE) HIGH TDS,
ORGANICS, BOD, SILT,
PESTICIDES, ETC.
CHANGES IN SOIL ZONE
ORGANIC CHANGE TO INORGANICS.
NITROGENOUS COMPOUNDS CHANGE
TO NITRATE. PHOSPHORUS COM-
POUNDS CHANGE TO PHOSPHATE.
NUTRIENT UPTAKE BY PLANT ROOTS,
DENITRIFICATION, NITROGEN FIXA-
TION, ION EXCHANGE AFFECTS
PESTICIDES, BIOCHEMICAL REACTIONS,
AND DEGRADATION OF ORGANIC
COMPOUNDS.
FACTORS: Eh, pH, AEROBIC OR
ANAEROBIC MEDIUM, ETC.
IEACHATES
(IF WATER IS EXCESSIVE IN
FILL). EFFECTS: ORGANIC
ACIDS, ALCOHOLS, OTHER
VOLATILES. TASTE, COLOR,
ODOR, HIGH BOD, LOW DO,
HIGH TDS, ft, AND OTHER
MINERALS.
SURFACE WATER
EFFECTS: LOW DO, HIGH
BOD, HIGH TDS, HIGH
NUTRIENT LEVELS, ALGAE,
BACTERIA, FISH KILLS.
(STREAM CYCLE)
PERCOLATION
TO GROUNDWATER
EFFECT: HIGH TDS, NO3,
Cl, S04, No.
GASES
CH4, H2S, NH3, CO2
EFFECT OF CO2 ON
GROUNDWATER: ALKALINITY
(SCALE-FORMING), ACIDITY
(CORROSIVITY), INCREASE
IN HARDNESS, TDS, ft AND
Mn, COLOR, TURBIDITY, ETC.
Figure 46. Agricultural uses of water and their effects on water quality
(modified after Hassan/ 1974).
117
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INDUSTRIAL USES
EVAPORATION
SANITATION USE
EFFECTS: PICK-UP OF TDS,
BACTERIA AND VIRUSES, B,
MBAS, NITROGEN AND
PHOSPHORUS COMPOUNDS,
HIGH BOD, TOXIC DISINFEC-
TANTS, ETC.
MANUFACTURING 8. PROCESSING USE
MANUFACTURING: TOXIC HEAVY METALS
AND CHEMICALS FROM INDUSTRIES SUCH
AS MINING, METAL PLATING, IRON,
FERTILIZERS, PESTICIDES, AND PAPER.
PROCESSING: SUCH AS PICKLING, FOOD,
FRUIT PACKING AND WASHING.
EFFECTS: HIGH TDS, ACIDITY OR ALKA-
LINITY, HEAVY METALS SUCH AS Cr^,
Cd, As, Hg, Ni, Fe, Mn, PESTICIDES,
HIGH COD, BRINES FROM SOFTENING.
COOLING USES
ALGAE INHIBITORS AND pH
ADJUSTORS ARE USED.
EFFECTS: HIGH T (THERMAL
POLLUTION), TDS, ACIDITY,
ALKALINITY, ETC.
NONRECLAIMABLE
WASTEWATER
LOW TDS, FREE OF TOXICITY
REUSE
(BACK TO
RESOURCE
POOL)
RECHARGE
OF
GROUNDWATER
BASINS
SURFACE
WATER
STREAMS
Figure 47. Industrial uses of water and their effects on water quality
(modified after Hassan, 1974).
118
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COMMERCIAL USES
INSIDE USE
SOFTENING: ADDITION OF
BRINES FROM SOFTENER
REGENERATION.
SANITATION: PICK-UP OF
TDS, N, P, MBAS, BACTERIA,
VIRUS, DISINFECTANTS, HIGH
BOD, COD, ETC.
WASTEWATER
TREATMENT
PLANT
PRIMARY, SECONDARY OR TERTIARY.
(QUALITY OF EFFLUENT DEPENDS
ON LEVEL OF TREATMENT).
TO
STREAMS
EVAPOTRANSPIRATION
OUTSIDE USE
IRRIGATION OF LAWNS &
SHRUBS. EVAPOTRANSPIRA-
TION AND FERTILIZATION
CAUSE INCREASE IN SALINITY,
N, AND P OF PERCOLATE TO
GROUNDWATER.
SOLID WASTES
SANITARY LANDFILL
RECYCLING
OF TREATED
WATER
RECHARGE OF
GROUNDWATER
BASINS
EFFECTS DEPEND ON
SALINITY OF IRRIGATION
RETURN
OCEAN
OUTFALL
SLUDGE
LAGOONS
SANITARY
LANDFILL
Figure 48. Commercial uses of water and their effects on water quality
(modified after Hassan, 1974).
119
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Irrigation effects are similar to those previously mentioned for irrigated
agriculture.
Inside uses embrace water softening plants, sanitation uses in schools
and public buildings, laundries, and commercial laboratories, among others.
Most of the waste water generated from commercial uses is disposed of in
sewer systems; from there, after treatment, it may return to groundwater
via recharge basins or sanitary landfills.
DOMESTIC USES. Domestic uses of water include drinking and cooling,
cleaning and bathing, laundry, sanitary needs, air conditioning, garden wa-
tering, and for swimming pools. The flow of water used domestically and
the effects on water quality are outlined in Figure 49. Inside domestic water
uses are basically nonconsumptive uses. Per capita water use varies widely
between city and suburban areas and with income levels of households. Wa-
ter softening may also be a quality consideration of domestic use. Effects
of outside water uses are similar to those for irrigated agriculture.
SOURCES AND CAUSES OF POLLUTION
Groundwater pollution results from the activities of man; consequently,
the various sources and causes of pollution would conceptually form a long
and complex list. However, in terms of basic causes and of primary in-
fluences on groundwater quality, the list can be condensed to a reasonable
size. Table 11, therefore, contains the principal causes and sources of
groundwater pollution grouped into four general categories. Each item
listed is discussed in the following sections with respect to its magnitude,
locations, and effect on groundwater quality.
Agricultural Sources and Causes
IRRIGATION RETURN FLOW, Approximately one-half to two-thirds of
the total water applied during irrigation is used consumptively. The re-
mainder is termed irrigation return flow, which returns to surface streams
or groundwater. Irrigation degrades the quality of applied water. The in-
crease in salinity of irrigation return flow results from the addition of salts
by dissolution during the irrigation process, from salts added to irrigation
water as fertilizers or soil amendments, and from the concentration of salts
by evapotranspiration of applied water. The salinity of irrigation return
flow due to these processes may range from three to ten times that of the
applied water (Jenke, 1974).
The principal cations of return flow are calcium, magnesium, sodium,
and potassium. Minor amounts of iron, aluminum, manganese, and other
cations may also be present. The dominant anions include carbonate, bi-
carbonate, sulfate, chloride, and nitrate.
-------
DOMESTIC USES
EVAPOTRAN5PIRATION
INSIDE USE
(ABOUT 50%)
PICK-UP OF TDS, N, P, DIS-
INFECTANTS, BACTERIA,
VIRUSES, TOXIC MATERIALS,
BRINE FROM SOFTENING,
MBAS, ETC.
OUTSIDE USE
(ABOUT 50%)
LAWN WATERING,
(FERTILIZERS, PESTICIDES,
AND SOIL AMENDMENTS),
CAR WASH, SWIMMING POOLS.
PRIMARY, SECON-
DARY, OR TERTIARY.
{QUALITY OF EFFLUENT
DEPENDS ON TREAT-
MENT).
SLUDGES
RECHARGE OF
GROUNDWATER
BASINS
HIGH TDS, NO-,
S04. 3
CI4
STORM
DRAINS
IOW TDS,
HIGH ORGANIC
CONTENT, DUST
REUSE OF
WATER
IRRIGATED AGRI-
CULTURE, INDUSTRI-
AL AND/OR SPREAD-
ING FOR GROUND
WATER RECHARGE .
SURFACE WATER
STREAMS
HIGH BOD, NUTRIENTS,
MBAS, ALGAE, ETC.
SANITARY
LANDFILLS
Figure 49. Domestic uses of water and their effects on water quality {modified after
Hassan, 1974).
121
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TABLE 11. PRINCIPAL SOURCES AND CAUSES OF
GROUNDWATER POLLUTION
Agricultural
1. Irrigation return flow
2. Animal wastes
3. Fertilizers
4. Crop residues and dead animals
5. Pesticide residues
Municipal and Industrial
1. Surface disposal of solid wastes
2. Surface disposal of liquid wastes
3. Sewer leakage
4. Tank and pipeline leakage
5. Disposal wells
6. Injection wells
7. Stockpiles
8. Mining activities
9. Oilfield brines
Groundwater Basin Management
1. Saline water intrusion
2. Aquifer interchange through wells
Miscellaneous
1. Spills and surface discharges
2. Septic tanks and cesspools
3. Highway deicing
Irrigation return flow is a nonpoint source of groundwater pollution be-
cause of its large areal extent. The problem has been identified as the ma-
jor cause of pollution in the Southwestern United States (Fuhriman and Bar-
ton, 1971) and is significant throughout the arid and semiarid portions of
the entire Western United States where irrigated agriculture is practiced.
ANIMAL WASTES. In recent years the feedlot has become an important
method for beef production. For the 120 to 150 days that a beef animal re-
mains in a feedlot, it will produce over a half-ton of manure on a dry weight
basis. With thousands of animals in a single feedlot, the natural assimila-
tive capacity of the receiving soil is heavily overtaxed. Runoff from rain-
fall that comes in contact with manure may carry high concentrations of pol-
lutants into ponds, streams, and groundwater.
Animal wastes release salts, organic loads, and bacteria into the soil.
Investigations have shown that nitrate-nitrogen is the most important
122
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persistent pollutant that reaches the water table (Fuhriman and Barton,
1971). Where permeability is moderate and the depth to water table is large,
most biological feedlot pollutants are removed in the vadose zone before
reaching the groundwater.
Feedlot operations are largest in Texas and California; however, they can
be found throughout the western and central portions of the United States.
FERTILIZERS. The application of fertilizers to agricultural land usually
results in a portion of the fertilizer being leached through the soil and into
the underlying groundwater. The most important constituents are com-
pounds of nitrate and phosphorus. Most phosphate fertilizers, however, are
readily adsorbed on soil particles so that they seldom constitute a ground-
water problem. But nitrogen in solution is only partially used by plants and
also may be adsorbed to only a limited extent by the soil or lost in gaseous
form to the atmosphere; consequently, nitrogen has been found to be the pri-
mary fertilizer element related to groundwater pollution (Fuhriman and Bar-
ton, 1971).
The use of fertilizers is extensive in the United States and will increase
in the future. Therefore, fertilizer usage leading to the potential for nitro-
gen pollution of groundwater on a nonpoint source basis can be expected to
continue. Furthermore, high nitrate concentrations observed in ground-
waters of suburban areas suggest the possibility of lawn fertilizers as a
source (Miller, 1974).
CROP RESIDUES AND DEAD ANIMALS. Crop residues are those por-
tions of a plant left in the field or processing shed after harvest. For every
pound of food marketed, from 2 to 5 pounds of residues are left in the field
or in the packing shed (Fuhriman and Barton, 1971). Although such wastes
can create groundwater pollution problems, there is little evidence available
to show that they do.
Larger farm animals, when dead, are usually disposed of by rendering
plants, and seldom affect groundwater quality. Similarly, dead sheep or
wildlife on the range are usually quickly disposed of by other forms of wild-
life. Bodies of animals used in laboratory experiments, particularly those
subjected to radioactive treatments, must be disposed of with special care.
The disposal of dead poultry is probably the only source which can create
a serious groundwater pollution hazard. Poultry producers today often han-
dle flocks exceeding 100,000 fowl. The death rate in such an operation can
average 35 fowl per day (Fuhriman and Barton, 1971). Many producers dis-
pose of dead birds by burial in a large trench; consequently, with percolat-
ing water in the vicinity of such a mass of decaying organic matter, the
groundwater pollution potential is considerable.
123
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PESTICIDE RESIDUES. The term "pesticide" is here broadly inter-
preted to embrace any material used to control, destroy, or mitigate pests,
including insecticides, herbicides, fungicides, nematocides, rodenticides,
bactericides, growth regulators, and defoliants. Whenever these materials
occur in groundwater, even in minute concentrations, the consequences are
serious in terms of the potability of the water.
The magnitude of the threat of pesticides to groundwater quality depends
upon the properties of the pesticide residue; the frequency and rate of rain-
fall or irrigation; the hydrologic characteristics of the soil; and the volume,
the state (liquid or solid), and the persistence of the pesticide applied (Todd
and McNulty, 1974). Many pesticides are relatively insoluble in water;
many also are readily adsorbed on soil particles.
Municipal and Industrial Sources and Causes
SURFACE DISPOSAL OF SOLID WASTES. The land disposal of solid
wastes constitutes an important source of groundwater pollution. A landfill
may be defined as any land area used for the deposit of urban, or municipal,
solid waste. Estimates of the production of solid wastes indicate a total of
about 1 ton per capita per year, equal to almost 6 pounds per person per
day (Meyer, 1973). Because wastes are generated and disposed of where
people are living, the pattern of urban population distribution gives an indi-
cation of the location and intensity of landfill practice.
There are two basic types of landfills: one is the sanitary landfill, de-
signed and constructed according to engineering specifications, while the
other is simply a refuse dump. Of the more than 100,000 landfills in the
United States, probably no more than 10 percent can be classed as sanitary
landfills.
Leachate from a landfill can pollute groundwater. For this to occur,
however, a source of water moving through the fill material is required.
Possible sources include precipitation, moisture content of refuse, surface
water infiltrating into the fill, percolating water entering the fill from adja-
cent land, or groundwater in contact with the fill (Meyer, 1973). Leachate
is not produced in a landfill until a significant portion of the material has a
moisture content equal to field capacity. Ordinary mixed refuse contains a
high paper content and usually has a moisture content far below that of field
capacity.
It follows, therefore, from the above reasoning that leachate from a
landfill can be prevented if refuse can be compacted and covered without be-
coming saturated, if rainfall and surface runoff can be diverted from the
landfill material, and if the fill material can be isolated from nearby
groundwater. These are esentially the goals of a well-designed sanitary
landfill. With a properly constructed landfill, any leachate generated can
124
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be controlled and prevented from polluting groundwater. Accomplishment
of these objectives is possible by proper site selection, by placement of ap-
propriate cover material, and by surface and subsurface leachate collection
systems. The problem of pollution from landfills is greatest in the Eastern
United States where high rainfalls and shallow water tables occur. Con-
versely, the problem is minimal in portions of the arid Southwest where
deep water tables are found.
Analyses of leachate show that its quality can vary widely. The most im-
portant pollutants are COD, BOD, iron, chloride, and nitrate. In addition,
hardness, alkalinity, and total dissolved solids are often increased. Gases,
including methane, carbon dioxide, ammonia, and hydrogen sulfide, are a
further byproduct of landfills; these may cause subsurface chemical reac-
tions which can degrade groundwater quality.
SURFACE DISPOSAL OF LIQUID WASTES. There are few, if any, in-
dustries which do not make use of water, either directly as part of the prod-
uct, such as in beverage industries and in steam generation, or indirectly as
for cooling water and as a transporting medium (paper industry). Water is
often used as a solvent either as a medium for chemical reactions or for
washing products and containers, or machines, apparatus, factory floors,
etc. Much of the water is subsequently discharged as waste water, the com-
position of which differs according to the usage and nature of the process
used.
Wastes from a particular type of industry are usually similar enough
from factory to factory to be compared directly. The waste composition and
volumes are often correlated with production rates,, Industrial wastes may
be broadly classified as:
• Nonfermentable inorganics and other inert wastes
• Fermentable, mainly organic wastes
• Toxic wastes.
Waste pickling-bath solutions from sheet-metal or galvanizing shops are
examples of nonfermentable wastes, however they may also be toxic due to
low pH and the presence of trace elements. Many food industries discharge
readily fermentable wastes; for example, meat-packing plants and canneries,
However, these wastes may also be toxic due to low pH from sulphurous
acid, or because of plating shop wastes which are discharged along with
packing shop wastes. Industries which commonly discharge toxic wastes
include dyehouses and electroplaters (cyanides, sulfides, chromium, or
copper) and chemical factories manufacturing chlorinated hydrocarbons,
etc. DyehouHe wastes are usually mineralized and may also contain signif-
icant amounts of fermentable organic matter. Waste waters from the use
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of water for cooling purposes may be relatively unpolluted, except for tem-
perature (Imhoff et al. , 1971).
Several major types of industrial waste of importance to groundwater pol-
lution are cooling water, process wastes, boiler blowdown, washdown water,
storm runoff, stockpiles, water treatment plant effluent, tank and pipeline
leakage, and hydrocarbon storage. These wastes are disposed of by a vari-
ety of methods and often in combination.
Cooling Water. Cooling water comprises the greatest industrial use of
water. Cooling water is often disposed of in percolation ponds and disposal
wells, and is sometimes used for irrigation.
Process Wastes. Process wastes probably present the most serious
threat to groundwater quality of all types of industrial wastes. These wastes
include spent fluids, catalysts, byproducts, and other wastes. These
wastes are commonly disposed of in wells and percolation ponds.
Boiler Blowdown. Boiler blowdown is one of the common types of indus-
trial wastes, and may commonly be combined with other types of wastes be-
fore disposal.
Washdown Water. Water for floor washing is often highly polluted from
acids, solid wastes, and other substances. This waste is also commonly
combined with other types of waste prior to disposal.
Storm Runoff. Precipitation on uncovered surfaces at industrial sites
may pick up significant levels of pollutants. This water may be gathered
and disposed of in a percolation pond, dry stream bed, disposal well, or
used for irrigation. The quality largely depends on housekeeping procedures
of the industry and the type of material that may be spilled or leaked at the
land surface.
Stockpiles. The piling of solid raw materials, products, byproducts,
and waste materials on the ground without protection from precipitation can
cause groundwater pollution.
Water Treatment Plant Effluent. Varying amounts of treatment may be
required for various industries depending on the quality of source water.
Water treatment commonly involves filtration and clarification, water soft-
ening, and demineralization or deionization. Disposal is commonly by per-
colation ponds or disposal wells. This waste may present a substantial pol-
lutant load in the case of waste brines.
Tank and Pipeline Leakage. One of the sources of groundwater pollution
currently receiving considerable attention is small leaks in tanks and pipe-
lines.
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Hydrocarbon Storage. Facilities for hydrocarbon storage or disposal are
often constructed so as to permit inadvertent groundwater pollution.
The disposal of municipal and industrial liquid wastes on the ground sur-
face involves not only a wide range of potential groundwater pollutants but
also several methods of release of effluents. The topic can be discussed
under three basic techniques of disposal — into land depressions, by spray-
ing, and into stream beds.
Natural or artificial depressions in the ground surface for waste disposal
are usually referred to as lagoons, basins, or pits. These may be lined or
unlined, but in either case, leakage to groundwater is a possibility. These
structures are intended to serve any of a variety of purposes; to name a few,
storage, processing, waste treatment, cooling, evaporation, and disposal.
It is now widely recognized that many so-called "evaporation" ponds are in
reality essentially percolation ponds. The once common practice of dis-
charging oilfield brines into open pits is now largely past as a result of
State regulatory practices; however, the effects on groundwater quality re-
main in many localities.
The type of pollution created clearly depends upon the type of waste ma-
terial, its volume and concentration, the soil and aquifer conditions, and
the location of groundwater. Sewage disposal into a lagoon usually results
in the removal of bacteria and suspended organic matter after only a few
feet of movement underground; however, dissolved organic matter can per-
sist for longer distances. Removal of pollutants may be minimal for perco-
lation through cavernous or highly fractured rocks. The increase in min-
eral content of groundwater can be considerable, as shown by Table 12.
Urban runoff collected in storm sewers can contribute BOD, COD, nitrate,
lead, gasoline, oil, and grease, among other pollutants.
TABLE 12. NORMAL RANGE OF MINERAL PICKUP IN
DOMESTIC SEWAGE (Todd, 1970)
Mineral Constituents
Total Dissolved Solids
Boron
Percent Sodium
Sodium
Potassium
Magnesium
Calcium
Total Nitrogen
Phosphate
Sulfate
Chloride
Total Alkalinity
Normal Range in mg/l
(except as noted)
100-300
0.1-0.4
5-15%
40-70
7-15
15-40
15-40
20-40
20-40
15-30
20-50
100-150
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Effluents percolating from industrial lagoons or basins have a greater
potential to degrade groundwater from a constituent standpoint than does
domestic sewage effluent, but not volumetrically. These industrial liquids
may contain brines, arsenic compounds, heavy metals, acids, petroleum
products, phenols, radioactive substances, as well as other miscellaneous
chemicals (Todd and McNulty, 1974; Meyer, 1973). And some of these
materials are capable of traveling long distances in groundwater.
Spray irrigation has become a common practice for disposal of waste
water by fruit and vegetable processors and of treated sewage by municipal-
ities. Studies of the effect of spray effluents on groundwater have indicated
that vegetation often takes up a substantial fraction of the nitrogen as com-
pared to percolation beneath a bare soil. Thus, the adverse effect on
groundwater quality may be limited to an increase in total dissolved solids.
Compared to lagoons, however, spray irrigation differs in that it provides
a greater opportunity for waste water to contaminate surface runoff during
rainfall periods (Meyer, 1973).
Because spraying is basically a method of waste water disposal, nutrient
removal, and water reclamation, it can be expected to increase in the fu-
ture. The practice should be limited to predominantly organic wastes that
can be readily assimilated in the soil zone so that any effect on quality of
groundwater is minimized.
Disposal of partly treated sewage and industrial wastes into the beds of
intermittent and ephemeral streams is practiced mainly in the arid and
semi-arid regions of the Southwestern United States (Meyer, 1973). Storm-
water runoff is also similarly discharged in many parts of the country. The
benefit of these procedures is the replenishment of groundwater resources.
Pollutants that enter an aquifer beneath a stream bed depend on the
character of the wastes, the type of stream-bed material, the depth to the
water table, and the type of treatment given to the wastes. For domestic
wastes the potential pollutants include chloride, organic compounds, nitro-
gen compounds, phosphates, boron, synthetic detergents, bacteria, viruses,
and perhaps pesticides. For industrial wastes, the spectrum of possible
pollutants becomes much broader; in general, those of greatest concern in-
clude heavy metals and organics such as phenols and polychlorinated biphen-
yls.
SEWER LEAKAGE. Conceptually, a sanitary sewer is intended to be
watertight and thus to present no hazard to groundwater quality. In reality,
however, leakage, especially from old sewers, is a common occurrence.
Leakage from gravity sewers may result from poor workmanship, defective
sewer pipe sections, breakage by tree roots or other causes, ruptures from
heavy loads, rupture by soil slippage, fractures by seismic activity, loss of
foundation support due to washouts, shearing due to differential settlement
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at manholes, and infiltration causing sewage to flow into abandoned sewer
laterals (Meyer, 1973).
Sewer leakage releases raw sewage into the ground, often close to ground-
water. This can introduce high concentrations of BOD, COD, chlorides, un-
stable organics, and bacteria into groundwater. On the other hand suspended
solids tend to clog sewer cracks, and the surrounding soils tend to become
clogged due to anaerobic conditions; therefore, the actual effect of sewer
leakage may be less than the theoretical potential.
TANK AND PIPELINE LEAKAGE. Underground storage and transmis-
sion of a wide variety of fuels and chemicals is a.common practice for com-
mercial, industrial, and individual uses. These tanks and pipelines are sub-
ject to structural failures from several causes, and the subsequent leakage
becomes a source of groundwater pollution.
Petroleum and petroleum products, because of their large usage, are re-
sponsible for most of the pollution. Thus, 90 percent of the interstate liq-
uid pipeline accidents reported in 1971 involved crude oil, gasoline, lique-
fied propane gas, or fuel oil (Meyer, 1973). Major causes of these pipeline
leaks were corrosion, equipment rupturing the pipelines, defective pipe
seams, or incorrect operations by handling personnel.
Leakage is particularly frequent from small installations such as home
fuel oil tanks and gasoline stations, where installation, inspection, and
maintenance standards may be low. In Maryland some 60 instances of
groundwater pollution were reported in a single year from gasoline stations;
and in northern Europe, where most homes are heated by oil stored in sub-
surface tanks, oil pollution has become the major threat to groundwater
quality (Meyer, 1973).
Liquid radioactive wastes are sometimes stored in underground tanks.
Leakage has been reported from an installation at Hanford, Washington.
Leakage of an immiscible liquid such as oil into the ground will cause the
oil to move downward in relatively permeable soils or, if the leak is from a
pipeline in relatively impermeable soil, the oil will tend to remain in the
trench and move in the down-slope direction. Oil coats soil particles as it
advances; therefore, if the quantity of leaked liquid is sufficiently small, the
total flow may become immobilized. Subsequent infiltrating water will tend
to transport the pollutant from the soil particles downward to the water
table, Once oil reaches a water table it spreads to form a thin layer on top
of the water table and then to migrate laterally with the groundwater body.
DISPOSAL WELLS. Many thousands of wells throughout the United
States are used for disposal of pollutants into freshwater aquifers. Exam-
ples include electronic industries disposing of metal-plating wastes in
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Arizona; domestic sewage disposal from individual homes in Florida and
Texas; low-level radioactive wastes at one location in Idaho; and heated wa-
ter from cooling systems in New York, California, and several midwestern
States (Meyer, 1973).
In recent years considerable attention has been given to the possibility of
injecting treated municipal sewage into wells penetrating freshwater aqui-
fers. Several of the proposed schemes not only would solve a sewage-
disposal problem but also would help to recharge freshwater aquifers or to
establish hydraulic barriers against saltwater encroachment in freshwater
aquifers. Advanced pilot plant experiments are being conducted in Long Is-
land and in California (Meyer, 1973). Sewage must be given at least second-
ary treatment and preferably tertiary treatment to prevent clogging of the
disposal wells and to reduce or prevent significant chemical and bacteriologi-
cal pollution of the aquifer.
Modification of the quality of groundwater caused by subsurface disposal
of wastes through wells depends on a variety of factors, including the com-
position of the native water, the amount and composition of the injected waste
fluid, the rate of injection, the permeability of the aquifer, the type of well
construction, and the kinds of biological and chemical degradation that may
occur. Most wells used for disposal of polluted liquids are, for economic
reasons, located in the shallowest available aquifer.
INJECTION WELLS. Deep injection wells are employed for disposal of
industrial wastes and oilfield brines. At present there are fewer than 300
industrial disposal wells in the United States (Meyer, 1973), but there are
more than 70, 000 brine disposal wells.
It has been common practice in the past to use abandoned oil production
wells for brine disposal. Because the wells were not designed, cased, or
cemented for brine injection, there have been numerous instances of injec-
tion wells with undetected ruptures beneath the surface where injected brines
have seeped into freshwater aquifers for many years before being discovered.
Some State regulatory agencies have alleviated this problem by requiring an
injection tubing inside a casing. The space between the tubing and casing is
filled with a fluid which is monitored to detect ruptures.
Currently, most oilfield brines are returned to subsurface formations
either for secondary recovery in an oil-producing formation or just as a dis-
posal method. However, even with properly designed and constructed injec-
tion wells, brine disposal presents pollution problems because of the numer-
ous oil, gas, injection, and test holes, which for many years were simply
abandoned without proper plugging. Unplugged wells provide vertical path-
ways for injected brines to rise into overlying freshwater aquifers.
Because of the limited number of industrial waste injection wells and the
careful attention given to their siting, design, and operation by State
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regulatory agencies, there have been few reported cases of groundwater pol-
lution from this source; however, the potential for this to occur at distances
from such wells should not be minimized.
STOCKPILES. Stockpiles of solid materials are a commonly found sight
around industrial plants and at construction sites. These may be raw ma-
terials awaiting use, or they may be solid wastes placed for temporary or
permanent storage. Precipitation falling on unsheltered stockpiles causes
leaching to occur which may then transport heavy metals, salt, and other
inorganic and organic constituents as pollutants to the groundwater. Only
by storing solid wastes in bins or shelters can this source of groundwater
pollution be effectively controlled.
MINING ACTIVITIES. A variety of groundwater pollution problems can
be associated with mining activities. Mines fall into two basic categories —
surface mines and underground mines. Pollution effects depend on the ma-
terial being extracted and the milling process; coal mines are a major con-
tributor; metallic ores for production of iron, copper, zinc, and lead are of
secondary importance; while stone, sand, and gravel quarries are numerous
but chemically much less important.
Both surface and underground mines invariably extend below the water
table so that dewatering to further mining activity is common. The water so
pumped, either directly from the mine or from nearby wells, may be highly
mineralized and is frequently referred to as "acid mine waters. " Although
there is no typical analysis of mine drainage water, normal characteristics
include low pH, high acidity, high ferrous or ferric iron, high aluminum,
and high sulfates (Miller, 1974). The magnitudes of the various constitu-
ents vary with the extent of oxidation and/or neutralization of the drainage
water.
Many economic deposits of coal and other minerals found in bedrock are
associated with sulfide minerals, pyrite (FeS2) being one of the most prom-
inent. Pyrite and most other sulfides are stable under the conditions that
exist below the water table. However, if the water table is lowered, oxida-
tion of the sulfides occurs in the dewatered zone. Oxidation of pyrite fol-
lowed by contact with water produces ferrous sulfate (FeSO^ and sulfuric
acid (f^SO,^) in solution. This situation may arise where a mine is aban-
doned and dewatering activities cease or by downward percolating rain-
water. The net result is that this solution is introduced into the ground-
water system, causing a drop in pH, and a rise in sulfate and iron content
(Miller, 1974).
In the mining and milling of ores groundwater pollution can result from
a variety of processes. With copper ore, for example, reagents are added
during milling; these include lime, arsenic, cyanide, kerosene, and organ-
ic materials. The crushing of sulfide-related ores can release copper
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sulfate, molybdenum, potassium, and high total dissolved solids. The
leaching of ores in oxide form with acids can contribute iron, manganese,
low pH, copper, molybdenum, and high total dissolved solids. The use of
explosives in fracturing overburden or ore has potential to introduce ammo-
nium nitrate to groundwater.
Pollution of groundwater can also result from the leaching of old mine
tailings and from settling ponds. Uranium mill tailings are radioactive so
that this could become a source of localized pollution. Serious pollution
problems can be associated with both active and abandoned mines.
OILFIELD BRINES. The production of oil and gas is usually accompa-
nied with the production of waste water in the form of brines. The ratio of
brine to oil or gas varies with location and with the age of a well. A recent
study in the Southcentral States (Scalf et al. , 1973) reported about three bar-
rels of brine were produced for each barrel of oil. The chief constituents
of brine typically include sodium, calcium, ammonia, boron, chloride, sul-
fate, trace metals, and of course, high total dissolved solids.
Until recently the common methods of oilfield brine disposal consisted of
discharge to streams or to "evaporation" ponds. In both cases brine-
polluted aquifers became commonplace in oil production areas as infiltrating
water from streams and ponds moved to the groundwater. Thousands of un-
lined brine pits were in use in the Southcentral States until only a few years
ago when they were prohibited by the oil regulatory agencies of the various
States. Despite this ban and the fact that few of the brine-affected areas
have been mapped, enough have been located to indicate a serious ground-
water pollution problem for many years to come (Todd and McNulty, 1974;
Scalf et al. , 1973). Because of the slow movement of groundwater, brine-
polluted groundwater is only now being discovered in many areas of oil
development abandoned 20 or 30 years ago.
With the ban on unlined evaporation pits, oil companies were forced to
construct pits lined with impervious material or to inject brines back into
the oil-bearing formation or into another formation sufficiently removed
from freshwater aquifers to prevent contamination (see previous subsection
on Injection Wells). Nevertheless, there are numerous reported and sus-
pected violations of these regulations, primarily in the form of bypassing
brine pits, by accidental or deliberate rupture of pit liners, by overflowing
waste pits, or by leakage from broken lines.
In oil-producing areas brines represent one of the major causes of
groundwater pollution. Case studies of the problem have been extensively
documented (Todd and McNulty, 1974; Scalf et al. , 1973).
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Ground water Basin Management
SALINE WATER INTRUSION. Saltwater may invade freshwater aquifers
to create point or nonpoint sources of pollution. In coastal aquifers sea-
water is the pollutant; in inland aquifers any of several sources of saline
water may be responsible.
Under natural conditions fresh groundwater in coastal aquifers is dis-
charged into the ocean. If, however, localized pumpage becomes suffi-
ciently large, the seaward flow is decreased or even reversed, thereby
causing seawater to advance inland within the aquifer. Almost all of the
coastal States of the United States have some coastal aquifers polluted by the
intrusion of seawater (Meyer, 1973). Florida is the most seriously affected
State, followed by California, Texas, New York, and Hawaii.
The usual cause of seawater intrusion in coastal aquifers is overpumping.
In flat coastal areas, drainage channels or canals can also cause intrusion.
They can contribute to the problem in two ways — one by reducing the water
table elevation and its associated freshwater flow, and the other by permit-
ting seawater during periods of high tide to advance long distances inland
where it can infiltrate into the ground. On oceanic islands freshwater from
rainfall percolates to form a lens overlying seawater. If a well penetrating
the lens is pumped at too high a rate, the underlying seawater will rise and
pollute the water supply of the well.
At the boundary between freshwater and seawater underground, disper-
sion and diffusion, together with external influences such as recharge from
precipitation, pumping of wells, and tidal action, combine to create a tran-
sition zone of brackish water. Figure 50 shows a vertical cross-section of
a coastal aquifer together with the transition zone and associated circula-
tions.
In inland aquifers saline water can be found at increasing depths from
seawater which entered aquifers during deposition or during a high stand of
the sea in geologic time. Approximately two-thirds of the United States is
underlain in part by saline groundwater, often referred to as connate water.
In addition, localized saline zones may occur from unique geologic forma-
tions or topographic features or from saline wastes contributed by man.
The most common mechanism of intrusion is that caused by overpumping
of a well which causes an upconing of underlying saline water toward the
well. This upward movement is illustrated in Figure 51. Where freshwater
and saline aquifers are connected, a lowering of the water table can induce
an upward movement of saline water. Thus, dewatering operations, as for
quarries, roads, or excavations, or the dredging of a stream channel can
contribute to the encroachment of saline water into aquifers.
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GROUND SURFACE
Figure 50. Schematic vertical cross section through a coastal aquifer showing
freshwater and seawater circulations with a transition zone (Meyer, 1973).
AQUIFER INTERCHANGE THROUGH WELLS. Because wells form
highly permeable vertical connections between aquifers, they can serve as
important means for groundwater pollution. This usually happens, however,
only where attention is not given to the proper construction, sealing, or
abandonment of wells.
Pollution occurs where well screens, perforated casing, or an open bore-
hole interconnects two separate aquifers, or where the surface casing has
not been adequately sealed. In these instances water wells can serve as
mechanisms for transmission of pollutants from one aquifer to another or
from land surface to an aquifer. Interaquifer exchange occurs where there
are vertical differences in hydraulic head between aquifers.
A common problem of this type is the vertical movement of saline water
into a freshwater aquifer. Abandoned and corroded well casings allow the
saline water to enter either from an overlying or underlying saline water
aquifer or from an adjacent saline surface water body. The problem is well
illustrated by situations in Baltimore, Maryland, (Miller, 1974) and Ala-
meda County, California, (Meyer, 1973).
If a well is improperly sealed in the annular space between the casing
and the borehole and connects aquifers of different water quality, polluted
water can move along the exterior of the well casing and enter the well.
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GROUND SURFACE
s
FRESHWATER
L
INITIAL WATER TABLE
WATER TABLE
IINMIAL W
J WATER
INTERFACE REACHING
THE WELL
SALINE WATER
INITIAL INTERFACE
Figure 51. Schematic diagram of upconing of underlying saline water
to a pumping well.
In addition, if provisions are not made to divert surface water away from a
well, it can drain downward into a well. Most public water supply wells are
properly sealed, inspected, and maintained, but surveys by health authori-
ties have revealed that private wells serving individual residences often are
not protected against pollution from overland runoff containing septic fluids,
barnyard wastes, or storm waters.
In most States today, regulations exist requiring plugging of abandoned
wells. But there are many thousands of abandoned wells which remain un-
plugged either because they cannot be located or because changes in proper-
ty ownership with time make the responsibility for plugging indeterminate.
The problem is particularly serious in oil and gas areas where numerous
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exploration and production wells have been abandoned (Scalf et al. , 1973).
These holes serve as avenues for brine from injection wells to rise into
overlying freshwater aquifers.
Miscellaneous
SPILLS AND SURFACE DISCHARGES. Groundwater pollution can result
from hazardous and nonhazardous liquids that are discharged onto the ground
surface in an uncontrolled manner and then seep into the underlying soils.
If the volume of the fluid is sufficiently large, the pollutant can migrate down
to the water table and degrade the groundwater quality. Any of a variety of
activities can lead to spills and surface discharges that may serve as pollu-
tion sources.
Poor housekeeping at large industrial plants and airports is a contributory
pollution cause. At industrial sites, causal activities may include boilovere
and blowoffs, overpumping during transfer of liquids to or from storage and
carriers, leaks from faulty pipes and valves in product distribution systems,
and poor control over waste discharges and storm-water runoff. At airports
the washing of planes with solvents and spills of fuel can form an extensive
body of hydrocarbons floating on the water table (Miller, 1974).
Pollution of groundwater also occurs from the intermittent dumping of
fluids on the ground, especially at gasoline stations and other types of
small commercial establishments. Automotive waste oil is disposed of on
the ground by car owners, by commercial garages and gasoline stations,
and at construction sites; the total of these many small contributions runs
to millions of gallons of oil annually (Miller, 1974). Small industries often
dispose of lubricating, hydraulic, and cutting oils-by local dumping. It is
not uncommon to find small commercial facilities/discharging liquid wastes
onto undeveloped land, the reasoning being that it is uneconomic to store and
to haul the wastes to municipal treatment plants or landfills and that the
liquids may be harmful to local septic tanks or cesspools.
Finally, accidents involving aboveground pipes and tanks, railroad cars,
and trucks can cause the release of large quantities of a pollutant at a par-
ticular site. The use of water to flush spilled fluids, as from a highway,
may actually aid in transporting the pollutant down to the water table.
SEPTIC TANKS AND CESSPOOLS. Of all the sources and causes of
groundwater pollution, the most numerous and widely distributed is that of
septic tanks and cesspools. It is estimated that approximately 40 million
persons, or nearly 20 percent of the total population, are served by individ-
ual household waste water treatment systems. This means that some 2. 5
billion gallons of partially treated sewage is discharged from residences
directly into the underground every day. In addition, stores, laundries,
small office buildings, hospitals, and industries employ septic tanks in
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areas where community sewer systems are not available. Furthermore,
innumerable summer cabins, Forest Service campgrounds, and organized
group camps depend upon subsurface disposal of waste water, primarily
during the summer season.
The heaviest concentrations of septic systems are to be found in the sub-
urban subdivisions that developed on the fringes of major cities after World
War II. A septic tank is a watertight basin intended to separate floating
and settleable solids from the liquid fraction of domestic sewage and to dis-
charge this liquid together with its burden of dissolved and particulate solids
into the biologically active zone of the soil mantle through a subsurface per-
colation system such as a tile field, a seepage bed, or an earth-covered
sand filter (Meyer, 1973). A cesspool is a large buried chamber which is
walled with a porous material, such as concrete blocks, and designed to re-
ceive raw sewage. Although new installations of this latter kind are no
longer approved, many thousands of cesspools remain in operation in the
United States today wherever soil conditions are favorable.
Domestic sewage adds minerals to groundwater, as indicated in Table 12.
Bacteria and viruses are normally removed by the soil system. Phosphorus
is generally retained by the soil, but significant quantities of nitrogen can,
depending upon local soil and vegetation conditions, be added to groundwater.
The degree of groundwater pollution has been shown to be related to the den-
sity of septic tank installations (Miller, 1974) and to the local hydrogeologic
framework.
HIGHWAY DEICING. A recent and unique problem that has attracted
considerable attention is the pollution of groundwater resulting from appli-
cation of deicing salts to streets and highways in winter. The region most
largely affected includes the Northeastern and Northcentral States. The
salt reaches the groundwater both from surface stockpiles and from solution
of salt that has been spread on roadways.
Salt application quantities by State highway departments of the Northeast-
ern States range from 3 to 20 tons per single-lane mile during a single win-
ter season (Miller, 1974). More than 95 percent of this is sodium chloride,
the remainder being calcium chloride. Furthermore, the demand to main-
tain highways and roads for vehicular use in winter has caused a steady
growth in the use of salt for deicing. Data from the State of Massachusetts
shows that applied salts increased 700 percent in the 15-year period from
1955 to 1970.
Widespread and long-term degradation of groundwater quality has been
the experience with highway deicing salts (Meyer, 1973). In addition, cas-
ings and screens of wells have been corroded, necessitating replacement of
many wells. The gradual increase in salts has led to some town ground-
water supplies exceeding salt limits for persons on low-sodium diets (Todd
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and McNulty, 1974). Salt concentrations have been found to be highest in
areas where salting has been practiced longest, in wells closest to roadways,
and during April, the month of greatest snow melt.
QUALITY IN RELATION TO WATER USE
Water Quality Standards
The quality of groundwater is most commonly evaluated relative to its
existing or potential use. Because water quality criteria vary with the type
of use, a groundwater may be satisfactory for one use but not for another.
Thus, pollution, which is the manmade degradation of water quality, may or
may not restrict a given groundwater for a particular use. On the other
hand increasing pollution leads to increasing impairment for use of water.
The concept of water quality criteria, or standards, can be illustrated by
reference to the diagram in Figure 52. Here pollution is related to impair-
ment for use. Up to a threshold level of pollution, water is satisfactory for
a given use (such as irrigation, drinking, etc. ). This level then defines a
water quality criteria or standard. With increasing pollution above this
THRESHOLD (WATER QUALITY CRITERIA)
OPTIMAL
IMPAIRMENT FOR USE
Figure 52. Diagram illustrating the relation of water pollution to impairment
for a given water use (modified after McGauhey, 1968a).
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level, a relatively narrow cautionary band can be defined. But this termi-
nates at the limiting level of pollution, beyond which increases in pollution
constitute a danger for that particular use. Another way of stating this re-
lationship is that pollution up to the threshold level may be regarded as a
reasonable impairment, whereas pollution beyond the limiting level becomes
an unreasonable impairment. A pollutant may here be defined as any chemi-
cal constituent, any biological organism, or any physical characteristic
which can adversely affect the use of the water.
Standards or guidelines have been established for all types of water use.
Those applicable to the major uses of groundwater are briefly described in
the following subsections.
Drinking Water
The most important use of groundwater is for drinking water purposes.
Drinking water standards have in the past been set by the U.S. Public Health
Service in the United States, and most States have adhered closely to these
requirements. The standards are summarized in Table 13. These criteria
are under continual review so that new constituents and revised levels of
constituents are to be expected with time.
Industrial Water
Quality requirements of waters used in different industrial processes
vary widely. For example, makeup water for boilers must meet exacting
criteria, whereas water of the quality of seawater can be employed for many
cooling purposes. Recommended water quality tolerances for certain indus-
trial applications have been prepared (Todd, 1970) as guidelines.
For industrial purposes the relative constancy of various constituents is
as important as the quality itself. A relatively poor quality water can be
treated so as to be suitable for a given process, but if the quality fluctuates
widely, continual problems and added costs may be involved. From this
standpoint groundwater sources are preferred to surface water sources be-
cause variations in chemical and physical quality are normally much smaller.
Irrigation Water
The suitability of a groundwater for irrigation depends upon the effects of
chemical constituents in the water on the plant and the soil (Todd, 1959).
Salts can restrict plant growth physically by modifying osmotic processes
and chemically by causing undesirable metabolic reactions. Salts can pro-
duce changes in soil structure, permeability, and aeration.
Specific limits of permissible salt concentrations for irrigation water
cannot be stated because of variations in salinity tolerance among different
plants, as well as in soil type, climatic conditions, and irrigation practices.
139
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TABLE 13. DRINKING WATER STANDARDS OF THE U.S. PUBLIC HEALTH
SERVICE (McGauhey, 1968b)
PHYSICAL STANDARDS
Turbidity
Color
Threshold Odor Number
Units
5
15
3
CHEMICAL STANDARDS
Substance
Recommended Limits
of Concentrations,
in mg/l
Mandatory Limits
of Concentrations/
in mg/l
A Iky I Benzene
Sulfonote (ABS) 0.5
Arsenic (As) 0.01 0.05
Barium (Ba) --- 1.0
Cadmium (Cd) — 0.01
Carbon Chloroform
Extract (CCE) 0.2
Chloride (CD 250
Chromium (hexavalent)
(Cr+o) 0.05
Copper (Cu) 1.0
Cyanide (CN) 0.01 0.2
Fluoride (F) I.Tt 2.2*
Iron (F«) 0.3
Lead(Pb) — 0.05
Manganese (Mn) 0.05
Nitrate (NO3)* 45
Phenols 0.001
Selenium (Se) — 0.01
Silver (Ag) — 0.05
Sulfate (SO4) 250
Total Dissolved Solids
(TDS) 500
Zinc (Zn) 5
*ln areas in which the nitrate content of water is known to be in excess of the
listed concentration, the public should be warned of the potential dangers of
using the water for infant feeding.
tVaries with average maximum air temperature.
BIOLOGICAL STANDARDS
Sample Examined
Standard 10-ml portions
Standard 100-ml portions
Ljmits
Not more than 10 percent in one month
shall show coliforms.t
Not more than 60 percent in one month
shall show coliformj.*
tSubject to further specified restrictions.
RADIOACTIVITY STANDARDS
Source
Rodium-226
Strontium-90
Gross Batn Activity
Recommended Limits,
Picocuries per Liter
3
10
1,000
140
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TABLE 14. GUIDE FOR EVALUATING THE QUALITY OF WATER USED FOR IRRIGATION (Todd, 1970)
[MPN is most probable number. Sodium adsorption ratio is defined by the formula SAR = Na/CCa + Mg)/2, where the con-
centrations are expressed in milliequivalents per liter. Residual sodium carbonate is the sum of the equivalents of normal
carbonate and bicarbonate minus the sum of the equivalents of calcium and magnesium.]
Quality Factor Threshold Concentrations* Limiting Concentrationt
Coliform Organisms, MPN per 100 ml 1000* §
Total Dissolved Solids (TDS), mg/l 500* 1500*
Electrical Conductivity, /^mhos/cm 750* 2250*
Range of pH 7.0-8.5 6.0-9.0
Sodium Adsorption Ratio (SAR) 6.0* 15
Residual Sodium Carbonate (RSC), meq 1.25* 2.5
Arsenic, mg/l 1.0 5.0
Boron, mg/l 0.5* 2.0
Chloride, mg/l 100* 350
Sulfate, mg/l 200* 1000
Copper, mg/l 0.1* 1.0
threshold values at which irrigator might become concerned about water quality and might consider using additional
water for leaching. Below these values, water should be satisfactory for almost all crops and almost any arable soil.
tLimiting values at which the yield of high-value crops might be reduced drastically, or at which an irrigator might be
forced to less valuable crops.
*Values not to be exceeded more than 20 percent of any 20 consecutive samples, nor in any three consecutive samples.
The frequency of sampling should be specified.
§Aside from fruits and vegetables which are likely to be eaten raw, no limits can be specified. For such crops, the
threshold concentration would be limiting.
-------
Quality classifications of water for irrigation usually stress certain ranges
for sodium, total dissolved solids, and boron. A general guide for evaluat-
ing the quality of water used for irrigation is shown in Table 14.
Livestock Water
Poultry and farm animals can live on water of considerably lower quality
than human beings. Quality criteria depend on factors such as the type of
animal and its age, climate, and feeding regimen. A general guide for eval-
uating the quality of water used by livestock is shown in Table 15.
TABLE 15. GUIDE FOR EVALUATING THE QUALITY OF
WATER USED BY LIVESTOCK (Todd/ 1970)
Qua I it-/ Factor
Threshold
Concentration*
Limiting
Concentrationt
Total Dissolved Solids (IDS), ma/liter
Cadmium, mg/l
Calcium/ mg/l
Magnesium, mg/l
Sodium/ mg/l
Arsenic/ mg/l
Bicarbonate/ mg/l
Chloride/ mg/l
Fluoride/ mg/l
Nitrate/ mg/l
Nitrite/ mg/l
Sulfate, mg/l
Range of pH
2500
5
500
250
1000
1
500
1500
1
200
None
500
6.0-8.5
5000
1000
500*
2000*
500
3000
6
400
None
1000*
5.6-9.0
"Threshold values represent concentrations at which poultry or sensitive animals might
show slight effects from prolonged use of such water. Lower concentrations are of little
or no concern.
I1 Limiting concentrations based on interim criteria/ South Africa. Animals in lactation
or production might show definite adverse reactions.
* Total magnesium compounds plus sodium sulfate should not exceed 50 percent of the
total dissolved solids.
142
-------
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Zanoni, A. E., "Ground-Water Pollution and Sanitary Landfills —A Critical
Review, " Proceedings of the National Ground Water Quality Sympo-
sium. U. S. Environmental Protection Agency, Water Pollution Control
Research Series 16060 GRB 08/71, pp 97-110, 1971.
Zenone, C. , D. E. Donaldson, and J. J. Grunwaldt, "Groundwater Quality
Beneath Solid-Waste Disposal Sites at Anchorage, Alaska, " Ground
Water. Vol. 13, No. 2, pp 182-190, 1975.
153
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APPENDIX
METRIC CONVERSION TABLE*
Non-Metric Unit
inch (in)
feet (ft)
miles
acres
grains
gallons (gal)
pounds per square inch (psi)
parts per million (ppm)
gallons per minute (gpm)
gallons per hour (gph)
Multiply by
25.4
0.3048
1.60934
0. 404686
64.79891
3.7854
0.0680460
1
3.7854
3.7854
Metric Unit
millimeters (mm)
meters (m)
kilometers (km)
hectares (ha)
milligrams (mg)
liters (1)
atmospheres (atm)
milligrams per liter
(mg/1)
liters (1) per minute
liters (1) per hour
*English units were used in this report because the data obtained were not
available in metric units.
154
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TECHNICAL REPORT DATA
(Please read lnufurn.ms on the reverse before completing}
1. REPORT NO.
EPA-600/4-76-026
2.
4. TITLE AND SUBTITLE
MONITORING GROUNDWATER QUALITY:
MONITORING METHODOLOGY
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
June 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
D. K. Todd, R. M. Tinlin. K. D. Schmidt,
L. G. Everett
8. PERFORMING ORGANIZATION REPORT NO.
GE75TMP-68
9. PERFORMING ORGANIZATION NAME AND ADDRESS
General Electric Company— TEMPO
Center for Advanced Studies
P. O. Drawer QQ
10. PROGRAM ELEMENT NO.
1HA326
11. CONTRACT/GRANT NO.
68-01-0759
nta RavKnr
Califnrni
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U. S. Environmental Protection Agency
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
T.a
RQ114.
EPA-ORD Office of Monitor
ing and Technical Support
IB. SUPPLEMENTARY NOTES
This is one of the 5 final reports in a series of 11 documents prepared on
monitoring groundwater quality.
16. ABSTRACT
The first section of this report describes the needs, objectives, and constraints
of monitoring groundwater quality with particular emphasis on the problem as
viewed by the United States Environmental Protection Agency, given its legis-
lative mandates in the Federal Water Pollution Control Act Amendments of
1972 (PL 92-500), and the Safe Drinking Water Act of 1974 (PL 93-523). The
second section develops a methodology for monitoring groundwater quality
degradation resulting from man's activities. The methodology is presented in
the form of a series of procedural steps arranged in chronological order. By
so doing, a straightforward sequence of actions is outlined which can lead to a
groundwater pollution monitoring program in a given area. The third and final
section of the report provides information on groundwater quality. A descrip-
tion is given of the geologic framework governing the movement of groundwater,
and natural underground water quality. The occurrence of groundwater pollu-
tion, including its distribution, mechanisms, attenuation, evaluation, and
trends is presented. The constituents in polluted groundwater and the various
sources and causes of pollution are reviewed. The section ends with a discus-
sion of water quality in relation to water use.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Aquifers
Aquifer Characteristics
Aquifer Management
Groundwater Management
Groundwater Methodology
Groundwater Monitoring
Grqtvnd writ o r_ Oun 1 i ty
Hydrogeology
Hydrology
Pollution Con-
trol
Groundwater Monitoring
Methodology, Ground-
water Quality Monitoring
Program
•13 B.
08 D.
08 G.
08 H.
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
172
20. SECuni TY CLASS I This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
601.427-1976
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