.PA
Ground Water
Resource Assessment
U.S. Environmental Protection Agency
Office of Ground Water and
Drinking Water
October 1993
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ACKNOWLEDGEMENTS
This document was prepared for the U.S. Environmental Protection Agency, Office of
Water, Ground Water Protection Division. James Hamilton was the Work Assignment
Manager for this project.
This document was developed, in large part, through the contributions of a technical
committee, which consisted of:
Rob Adler, U.S. Environmental Protection Agency, Region I
Jim Bachmaier, U.S. Department of Energy, Office of Environment, Safety and Health
Assad Barari, South Dakota Geological Survey
John Barndt, Delaware Department of Natural Resources and Environmental Control
Richard Berg, Illinois State Geological Survey
Jerry Bernard, U.S. Department of Agriculture, Soil Conservation Service
Jim Brown, U.S. Environmental Protection Agency, Office of Solid Waste
Clay Chesney, U.S. Environmental Protection Agency, Region VI
Chuck Job, U.S. Environmental Protection Agency, Office of Water
Pat Costello, U.S. Environmental Protection Agency, Region VII
Dave Delaney, U.S. Environmental Protection Agency, Region I
Dennis Erinakes, U.S. Department of Agriculture, Soil Conservation Service
Marilyn Ginsberg, U.S. Environmental Protection Agency, Office of Water
Steve Gould, U.S. Environmental Protection Agency, Region II
Matt Hagemann, U.S. Environmental Protection Agency, Region IX
Jim Hamilton, U.S. Environmental Protection Agency, Office of Water
Al Havinga, U.S. Environmental Protection Agency, Office of Water
Glenn Hearne, U.S. Geological Survey, Water Resources Division
Paul Johnson, U.S. Environmental Protection Agency, Region V
Dru Keenan, U.S. Environmental Protection Agency, Region X
Evan Kifer, Missouri Department of Natural Resources, Division of Geology and Land Survey
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Ken Lovelace, U.S. Environmental Protection Agency, Superfund
James Marsh, U.S. Department of Defense, Office of Deputy Assistant Secretary of Defense
for Environment
Anna Miller, U.S. Environmental Protection Agency, Region V
Ed Miller, U.S. Department of Defense, Office of Deputy Assistant Secretary of Defense for
Environment
Robert Olive, U.S. Environmental Protection Agency, Region IV
Colleen Ostrowski, U.S. Department of Energy, Office of Environment, Safety and Health
Walt Schmidt, Florida Geological Survey
Dan Smith, U.S. Department of Agriculture
Gene Stallings, U.S Bureau of the Census
Peter Stevens, U.S. Geological Survey
Fred Swader, U.S. Department of Agriculture
Virginia Thompson, U.S. Environmental Protection Agency, Region III
Jerry Thornhill, U.S. Environmental Protection Agency, Robert S. Kerr Environmental
Research Laboratory
Joe Vorgetts, U.S. Department of Agriculture
Estella Waldman, U.S. Environmental Protection Agency, Office of Prevention, Pesticides and
Toxic Substances
Mike Wireman, U.S. Environmental Protection Agency, Region VIII
The Ground Water Protection Division wishes to thank the technical committee
members, without whom, this document could not have been produced.
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Table of Contents
Table of Contents
EXECUTIVE SUMMARY 5
CHAPTER 1: Introduction to Ground Water Resource Assessment
, 11
CHAPTER 2: Components of a Ground Water Resource Assessment ................ 23
Component #1 : Regional Hydrogeologic Setting ...... ... ........... 26
Component #2: Aquifer and Aquifer-System Occurrence .............. 36
Component #3: Water Table and Potentiometric Surface .............. 45
Component #4: Hydraulic Properties ............................. 52
Component #5: Confinement and Interaction Between Aquifers ......... 65
Component #6: Ground Water Recharge and Discharge Characterization . 72
Component #7: Ground Water and Surface Water Interaction .......... 81
Component #8: Ground Water Budget ............. .............. 94
Component #9: Chemical and Physical Characteristics of Aquifers
and Overlying and Underlying Materials ......... 1 02
Component #10: Ambient Ground Water Quality
CHAPTER 3: Approaches to Assessing Aquifer Sensitivity and
Ground Water Vulnerability ...............................
Approach #1 : Aquifer Sensitivity ................................ 128
1 42
Approach #2: Aquifer Use ....... . ............................
148
Approach #3: Land Use ......... ....... .....................
Approach #4: Ground Water Vulnerability ......................... 1 57
APPENDIX A: Comprehensive State Ground Water Protection Program
Priority-Setting Characteristics to be Addressed in
Ground Water Resource Assessments ...................... 1 67
APPENDIX B- Case Studies on the Development and Use of Ground Water Resource
Assessments at the State, Local, and Federal Level ............ 169
APPENDIX C: Sources of Hydrogeological Information ............... ...........
227
APPENDIX D: Glossary ..................................................
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List of Figures
List of Figures
Figure 1: Block Diagram Showing a Regional Hydrogeologic Setting
(Component #1)
Figure 2: Cross Section Depicting Regional Aquifer (Component #2) 38
Figure 3: Map and Cross Section Showing the Regional Aquifer Systems
of Kentucky (Component #2} 39
Figure 4: Schematic Showing Water Table and Potentiometric Surface
(Component #3) 46
Figure 5A: Calculation of Hydraulic Gradient in an Unconfined Aquifer
(Component #4)
Figure 5B: Difference Between Hydraulic Conductivity and Transmissivity
(Component #4)
Figure 6: Different Conditions of Aquifer Confinement and Interaction
(Component #5)
Figure 7A: Recharge Areas for a Confined and Unconfined Aquifer
(Component #6)
Figure 7B: Ground Water Recharge and Discharge Areas (Component #6) 75
Figure 8A: Cross Section Showing Ground Water Discharging to Surface Water
(Component #7)
Figure 8B: Cross Section Showing Surface Water Recharging to Ground Water
(Component #7)
Figure 9: Use of Ground Water Tracer to Check Source of Water
at Discharge Point in Streambed (Component #7) 89
Figure 10: Water Budget (Component #8) 95
Figure 11 A: Bar Diagrams Presenting Data From Chemical Analyses of Water
From Three Wells (Component #10) 119
Figure 11B: Circle Diagrams Presenting Data From Chemical Analyses of
Water From Four Wells (Component #10) 120
Figure 11C: Stiff Diagrams Presenting Data From Chemical Analyses of
Water From Four Wells (Component #10) 121
Figure 11D: Trilinear Diagram Presenting Data From Chemical Analyses of
Water From Four Wells (Component #10) '22
Figure 12: Map Depicting Relative Aquifer Sensitivity
for Lake Walcott Quadrangle, Idaho (Approach #1) >37
Figure 13: Example of DRASTIC Scoring Map of
Bureau County, Illinois (Approach #1) 138
Figure B-1: Big Sioux Aquifer and Drainage Basin (Appendix B) 192
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List of Tables
List of Tables
Table 1: Flow Diagram of Resource Assessment Information 19
Table 2: Format for Presenting Selected Aquifer and
Aquifer-System Information . 43
Table 3: Chemical Data Bases Containing Properties of Common
Ground Water Contaminants 108
Table 4: Comparison of Factors Used in DRASTIC and SEEPAGE 136
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Executive Summary
EXECUTIVE SUMMARY
This document is intended to provide guidance to State1 resource managers who are
conducting a ground water resource assessment. For the purposes of this document, EPA
defines a resource assessment as:
(1) the collection, analysis, and presentation of existing and new data on:
(a) geology and hydrogeology
(b) ground water vulnerability
(c) current and potential land use
(d) current and potential aquifer use, and
(2) the use of these data in making ground water protection decisions.
Why Should States Conduct Resource Assessments?
EPA encourages each State to develop and implement a Comprehensive State
Ground Water Protection Program (CSGWPP) that ties together its various efforts in ground
water protection. EPA has identified six strategic activities that together make up an
adequate and complete CSGWPP. The second strategic activity calls for establishing
priorities based, in part, on a characterization of ground water resources.
Resource assessments provide the information managers need to conduct a variety of
State and Federal ground water protection programs. The information produced from a
resource assessment will enable managers to understand their ground water resources,
identify existing and possible future problems, prioritize the problems for action, and act to
resolve those problems.
1 Includes States, Tribes, and local governments.
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Executive Summary
What is the Resource Assessment Process?
The resource assessment process as outlined by EPA begins with collecting and
analyzing data on the physical ground water system, followed by a consideration of the
ground water's use, value, and vulnerability to human activity. This process includes ten
Components that characterize the physical and chemical properties of the resource. These
Components are:
0) Regional Hydroqeoloqic Setting -- Hydrogeologic factors that control the regional
occurrence, movement, and availability of ground water: hydrogeology, topography,
regional climate, hydrography, soil, vegetative cover, regional recharge and discharge
patterns, ground water quality, geochemistry, and geophysical characteristics.
(2) Aquifer and Aquifer-System Occurrence - Areal distribution and three-dimensional
position of aquifers in the geologic sequence.
(3) Water Table and Potentiometric Surface -- Water table: the upper surface of the
saturated portion of an unconfined aquifer. Potentiometric surface: water surface
elevation to which water will rise in a well tapping a confined aquifer.
(4) Hydraulic Properties - The properties of soil, rock, sediment, and other geologic
materials that govern the movement of water into, through, and out of an aquifer.
(5) Confinement and Interaction Between Aquifers - Ease with which leakage
between aquifers can occur. The greater the confinement, the less the interaction.
(6) Ground Water Recharge and Discharge Characterization -- Where, and at what
rate, aquifers are recharged by infiltrating precipitation and ground water is discharged
to the land surface.
(7) Ground Water and Surface Water Interaction - Where, and at what rate, water
moves between an aquifer and a body of surface water.
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Executive Summary
(8) Ground Water Budget -- An accounting of all natural and anthropomorphic
removals from, and additions to, the ground water reservoir.
(9) Chemical and Physical Characteristics of Aquifers and Overlying and Underlying
Materials -- Materials that make up the aquifer and overlying unsaturated and
underlying zones. These materials have chemical and physical characteristics that
impact water quality and affect the fate and transport of contaminants.
(10) Ambient Ground Water Quality -- The quality of ground water at a baseline time
selected by the decision-making agency. Ambient quality may be the natural quality of
ground water or may be the quality as impacted by widespread historical
contamination. (Some aquifers may be naturally unsuitable for a variety of uses, while
others are unsuitable as a result of contamination.)
In addition, EPA identifies four Approaches to resource assessment that managers
can use to analyze how human activity might affect ground water resources now and in the
future. These four Approaches consider:
(1) Aguifer Sensitivity -- The relative ease with which a contaminant applied on or near
the land surface can migrate to an aquifer of interest. An aquifer's sensitivity is a
function of the intrinsic characteristics of the geologic materials in question and the
overlying saturated and unsaturated materials. Aquifer sensitivity is independent of
land use and contaminant characteristics.
(2) Aquifer Use - Quantification of ground water withdrawal rates and identification of
types of use. This information allows managers to determine future trends, to plan for
changes, or to modify existing practices.
(3) Land Use -- Uses of land may affect ground water resources. The type of land
cover, including vegetation and manmade alterations such as pavement, directly affect
the runoff and infiltration of precipitation.
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Executive Summary
(4) Ground Water Vulnerability -- The relative ease with which a contaminant applied
on or near the land surface can migrate to an aquifer under a given set of land use
management practices, contaminant characteristics, and aquifer sensitivity conditions.
EPA presents these various Components and Approaches as a "menu" from which
State resource managers can choose the elements that best fit their own needs and financial
and human resources. Although EPA does not expect that all States will choose to use all
fourteen Components and Approaches, this document presents the elements in a rational
order, where one Component or Approach might rely on information collected under a
previous one.
Many States have conducted some kind of assessment of ground water resources,
and most States already have available much of the information needed to begin a ground
water resource assessment. EPA encourages managers who conduct resource assessments
to acquire as much existing data as possible before incurring the expense of producing new
data. Managers should make an effort to contact State and Federal agencies, universities,
and other potential sources of ground water data before beginning their own data collection
program.
A resource assessment can and should be refined over time as more and better data
become available and as ground water management needs change. The fundamental
objective of this iterative assessment process is to provide a resource-based framework upon
which managers can make informed decisions.
Organization of the Document
Chapter 1 of this document provides an overview of EPA's resource assessment
concept and discusses how a resource assessment can be used in decision-making, how it
can benefit the user, and what types of data and analyses it produces. Chapter 2 describes
each of the ten Components of a resource assessment in detail. Chapter 3 describes each of
the four Approaches. For each Component and Approach the discussion includes:
a detailed definition
the Component's/Approach's objective
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10
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Executive Summary
data needs
methods for characterizing the Component/Approach
presentation of data
considerations
references
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Introduction to Ground Water Resource Assessment 11
CHAPTER 1:
Introduction to Ground Water Resource Assessment
Assessing the condition of ground water resources is an essential first step in
developing effective programs to protect those resources. This document summarizes the
general methods available for collecting and analyzing hydrogeologic data, for determining
land and aquifer use, and for establishing the sensitivity and vulnerability of ground water
supplies. Knowledge of these methods will assist State2 and Federal resource managers in
preparing a Comprehensive State Ground Water Protection Program (see below).
Many of the elements of a resource assessment are commonly found in other Federal
regulatory and nonregulatory programs.3 The resource assessment process will help
resource managers to integrate the various management strategies used in these different
programs and to set priorities for ground water protection. It also will allow managers to
address both existing problems (e.g., site remediation) and pollution prevention (e.g.,
wellhead protection). The process described in this document focuses on tools for protecting
ground water across a broad region rather than a specific site. EPA recognizes, however,
that the resource assessment process could be used for site-specific characterizations as
well.
The resource assessment process helps managers to make the best use of existing
ground water data, to identify gaps in critical data, and to consider all sources of information
and funding if new data collection is required. Ground water protection and management
programs do not have to cost more to work better: Resource managers can significantly
improve the economy and effectiveness of their programs by sharing information with other
Includes States, Tribes, and local governments.
3 Examples are the Resource Conservation and Recovery Act (RCRA); the Federal Insecticide,
Fungicide, and Rodenticide Act (FIFRA); the Toxic Substances Control Act (TSCA); the Comprehensive
Environmental Response, Compensation and Recovery Act (CERCLA or "Superfund"); the Underground
Storage Tank (UST) Program; the Wellhead Protection Program (WHPP); the Sole Source Aquifer (SSA)
Program; and the Public Water Supply Supervision Program (PWSSP).
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12 Chapter 1
government programs and avoiding needless duplication. The resource assessment process
encourages State and Federal regulatory and non-regulatory organizations to cooperate in
collecting new data. This type of collaboration already is underway for several regionally
important aquifers such as the Ogallala (Midwest/High Plains Area), Edwards (Texas), and
Biscayne (Florida) aquifers.
Each State will have to determine the extent of its own resource assessment efforts
and its priorities for ground water protection based on available financial, human, and
technical resources. That is, a State should decide which Components and Approaches
described in Chapters 2 and 3 will be undertaken, and which products it deems most critical
to its protection and management efforts.
Definition of Ground Water Resource Assessment
For the purposes of this document, ground water resource assessment is defined as:
(1) the collection, analysis, and presentation of existing and new data on:
geology and hydrogeology
ground water vulnerability
current and potential land use
current and potential aquifer use, and
(2) the use of these data in making ground water protection decisions.
This document does not discuss the assessment of ground water for ecological
purposes. EPA plans to prepare a technical assistance document providing guidance to
States on methods for delineating areas of ground water and surface water interaction. That
document will discuss the impacts of the ground water and surface water interaction
(hyporheic) zone on ecosystems.
Comprehensive State Ground Water Protection Program
In Protecting the Nation's Ground Water: EPA's Strategy for the 1990s (USEPA, 1991),
EPA stated its policy to promote the development and implementation of a Comprehensive
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Introduction to Ground Water Resource Assessment 13
State Ground Water Protection Program (CSGWPP) by each State. Resource assessments
are at the center of comprehensive State programs because of they are an important first step
in setting protection priorities. By encouraging the States in this initiative, EPA:
(1) recognizes that States have the primary responsibility for protecting
their ground water resources
(2) focuses on resource protection as the principal (but not the only) basis
for setting priorities across Federal, State, and Tribal ground water
programs
(3) integrates Federal, State, and Tribal ground water program functions to
more effectively and efficiently protect ground water resources
(4) recognizes its commitment to the concept of comprehensive resource
protection in Federal ground water programs
EPA's National Guidance for CSGWPP (USEPA, 1992a) identifies six strategic activities
of a comprehensive State program. These activities are as follows:
(1) Establishing the State's ground water protection goal to guide all
relevant Federal, State and local programs operating within the State
(2) Establishing priorities for meeting that goal, based on characterization of
the resource, programmatic needs, and identification of existing and
potential sources of contamination
(3) Defining authorities, roles, responsibilities, resources, and coordinating
mechanisms across relevant Federal, State, Tribal, and local programs
(4) Implementing the actions necessary to accomplish the State's ground
water protection goal, consistent with the State's priorities and
schedules
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14 Chapter 1
(5) Coordinating information collection to measure progress, re-evaluate
priorities, and support all ground water-related programs
(6) Improving public education and participation in all aspects of ground
water protection
The need for a resource assessment is addressed in the second strategic activity,
"Establishing priorities," which encourages States to set ground water protection priorities
based, in part, on a characterization of the ground water resource. This document will help
with that characterization.
Existing Resource Assessments
Many States have already made significant progress toward a Statewide resource
assessment. The Wisconsin and Ohio State Geological Surveys, for example, have produced
aquifer yield maps, while the Illinois State Geological Survey has prepared Statewide maps of
both aquifer sensitivity and vulnerability. Data on ground water resources can be obtained
from many sources, including State geological surveys, departments of agriculture, regulatory
and water resource agencies, universities, and regulated entities. These agencies may
already have characterized ground water resources in the State, and may also have collected
data about current and potential land use, aquifer sensitivity and vulnerability, and current and
potential aquifer use.
A thorough review of existing resource assessment data, including reports and maps
produced by other agencies, will allow managers to identify and prioritize areas where more
data are needed. In some States, such a review may show that sufficient information exists to
perform an initial assessment. It is likely, however, that the quality of existing data will vary
across the State, and that a complete resource assessment will require considerable
additional research. The State will need to find the funding and expertise to accomplish this
research.
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Introduction to Ground Water Resource Assessment 15
Role of EPA and Other Federal Agencies in State Ground Water Resource Assessments
EPA's primary role in State resource assessments is to assist States in conducting
technically sound, comprehensive, Statewide assessments that can serve as a basis for
setting CSGWPP priorities. EPA provides funds to States, through Section 106 of the Clean
Water Act, that can be used for resource assessments. In addition, EPA regional offices can
provide technical assistance and encourage the consistency of programs in areas where
different States share a common aquifer. Regional offices can also help identify sources of
data and information.
The recently published Handbook for State Ground Water Managers (USEPA, 1992b)
identifies Federal programs that may provide information and funding to States for conducting
ground water resource assessments. EPA also promotes cooperation in providing technical
assistance among its own programs and Federal agencies such as the U.S. Geological
Survey (USGS), Department of Defense (DOD), National Oceanic and Atmospheric
Administration (NOAA), Department of Agriculture (USDA), and Department of Energy (DOE)
in helping States to develop resource assessments. In addition, the Federal Interagency
Committee on Water Data's Subcommittee on Ground Water has prepared a comprehensive
Directory of Federal Ground Water Programs (in progress), which includes sources of
information useful in resource assessments.
Resource Assessment Process
By its nature, resource assessment is an iterative process. As new and better data are
collected, and as currently available resource descriptions or maps are used to make
decisions, managers will identify additional locations or parameters that should be studied.
The best professional judgement of ground water scientists and hydrologists plays a critical
role in this process, particularly during the data collection and interpretation stages. How a
resource assessment is ultimately used may also be a factor in determining the best way to
conduct the assessment.
This document identifies ten Components of a ground water resource assessment.
These Components address the physical and chemical characteristics of an aquifer. Together
they provide a comprehensive characterization of a State's ground water resources, including
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16 Chapter 1
a description of the quality and quantity of water underlying a State, the matrix through which
the water moves, and the recharge and discharge areas associated with the ground water
reservoir.
These ten Components are:
(1) Regional Hydrogeologic Setting - Hydrogeologic factors that control the regional
occurrence, movement, and availability of ground water: hydrogeology, topography,
regional climate, hydrography, soil, vegetative cover, regional recharge and discharge
patterns, ground water quality, geochemistry, and geophysical characteristics
(2) Aquifer and Aquifer-System Occurrence - Areal distribution and three-dimensional
position of aquifers in the geologic sequence
(3) Water Table and Potentiometric Surface -- Water table: the upper surface of the
saturated portion of an unconfined aquifer. Potentiometric surface: water surface
elevation to which water will rise in a well tapping a confined aquifer
(4) Hydraulic Properties -- The properties of soil, rock, sediment, and other geologic
materials that govern the movement of water into, through, and out of an aquifer
(5) Confinement and Interaction Between Aquifers - Ease with which leakage
between aquifers can occur. The greater the confinement, the less the interaction
(6) Ground Water Recharge and Discharge Characterization - Where, and at what
rate, aquifers are recharged by infiltrating precipitation and ground water is discharged
to the land surface
(7) Ground Water and Surface Water Interaction -- Where, and at what rate, water
moves between an aquifer and a body of surface water
(8) Ground Water Budget - An accounting of all natural and anthropomorphic
removals from, and additions to, the ground water reservoir
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Introduction to Ground Water Resource Assessment 17
(9) Chemical and Physical Characteristics of Aquifers and Overlying and Underlying
Materials - Materials that make up the aquifer and overlying unsaturated and
underlying zones. These materials have chemical and physical characteristics that
impact water quality and affect the fate and transport of contaminants
(10) Ambient Ground Water Quality -- The quality of ground water at a baseline time
selected by the decision-making agency. Ambient quality may be the natural quality of
ground water or may be the quality as impacted by widespread historical
contamination. (Some aquifers may be naturally unsuitable for a variety of uses, while
others are unsuitable as a result of contamination)
In addition to identifying these Components, the resource assessment process
includes four different Approaches to assessing ground water. These Approaches combine
the physical and chemical components with human activities to better explain the potential
impact of those activities on the ground water resource.
The four Approaches presented in this document are:
(1) Aquifer Sensitivity - The relative ease with which a contaminant applied on or near
the land surface can migrate to an aquifer of interest. An aquifer's sensitivity is a
function of the intrinsic characteristics of the geologic materials in question and the
overlying saturated and unsaturated materials. Aquifer sensitivity is independent of
land use and contaminant characteristics
(2) Aquifer Use - Quantification of ground water withdrawal rates and identification of
types of use. This information allows managers to determine future trends in ground
water use, to plan for changes, or to modify existing practices
(3) Land Use - Uses of land may affect ground water resources. The type of land
cover, including vegetation and manmade alterations such as pavement, directly affect
the runoff and infiltration of precipitation
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18 Chapter 1
(4) Ground Water Vulnerability - The relative ease with which a contaminant applied
on or near the land surface can migrate to an aquifer under a given set of land use
management practices, contaminant characteristics, and aquifer sensitivity conditions
Appendix A presents an initial list of characteristics to be considered when conducting
a ground water resource assessment. This list is from the National Guidance for CSGWPP.
The technical and hydrogeologic factors in the list have been incorporated, expanded, and
reorganized in this document.
States are encouraged to select those Components and Approaches that are most
relevant to their own needs. Explanations of the Components and Approaches in this
document were written to stand alone, with some overlap in the descriptions, because States
will most likely choose to perform some, but not all, of them. The Components and
Approaches are meant to apply everywhere, although certain modifications may be necessary
in unique areas of the country.
Table 1 shows the flow of information among data sources, resource assessment
providers, Components, Approaches, and the end users of resource assessments. The table
depicts all Components and Approaches as being part of a complete resource assessment,
but States may choose only those that they deem necessary. An aquifer sensitivity or ground
water vulnerability assessment is not necessary to the resource assessment process, but
either type of assessment would aid State ground water protection management efforts by
helping to determine the relative susceptibility of different geographic areas of a State to
contamination. If a State chooses to perform a sensitivity or vulnerability assessment, it will
first have to perform those Components it considers necessary to characterize its ground
water system.
Additionally, a vulnerability assessment requires that the State complete the Land Use
and possibly the Aquifer Use Approaches. A sensitivity or vulnerability assessment helps
managers use data from the resource assessment Components in making decisions about
ground water protection.
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20 Chapter 1
Use of Resource Assessments for Decision-Making
EPA recognizes that decision-making processes differ among States. For many
States, government agencies will conduct or may have already conducted the resource
assessment. In other States with ground water protection priorities based on a sound
resource assessment methodology, consultants or other non-government personnel may
conduct assessments that update or refine information for a given area.
States can begin the resource assessment process by using existing information as
well as data acquired from ongoing programs to develop a preliminary resource assessment
for setting initial protection priorities. These activities could be followed by data collection
and analysis for geographic areas where information is sparse or absent.
Under a CSGWPP, States can base their protection and management priorities partly
on the results of a Statewide resource assessment. Federal agencies can in turn use the
priorities established by States to manage Federal programs related to ground water.
Resource Assessment in Perspective
Due to the wide areal extent of ground water resources (as compared to surface
waters), the protection of ground water requires the setting of priorities, since resources (i.e.,
people and money) are always limited. The fundamental objective of ground water resource
assessment, therefore, is to provide a "resource-based" framework for making decisions and
setting priorities. States that assess their ground water resources will be able to better focus
the efforts of both Federal and State programs (e.g., Superfund, Underground Storage Tank,
Nonpoint Sources) aimed at protecting the resource.
"Resource-based" decisions consider ground water as an overall resource rather than
limiting consideration to ground water at or adjacent to a single site. This "resource-based"
approach recognizes the integral role of ground water in the hydrological/ecological system.
Organization of This Document
Chapter 1 gives an introduction to ground water resource assessment
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Introduction to Ground Water Resource Assessment 21
Chapters 2 and 3 describe the individual Components and Approaches
of a resource assessment. These chapters describe data gathering,
presentation, and analytical methods used to develop an overall
resource assessment
Appendix A is an initial list of characteristics to be considered when conducting
a ground water resource assessment
Appendix B presents five case studies that illustrate the implementation
of resource assessments and how they were used in decision-making
Appendix C lists sources of hydrogeological information
Appendix D provides a glossary of selected terms used in this
document
Citations
U.S. Environmental Protection Agency, 1992a. Final Comprehensive State Ground Water
Protection Guidance (EPA 100-R-93-001). Office of the Administrator, 135 p.
U.S. Environmental Protection Agency, 1992b. A Handbook For State Ground Water
Managers (EPA 813-B-92-001). Office of Water, 21 p.
U.S. Environmental Protection Agency, 1991. Protecting The Nation's Ground Water: EPA's
Strategy for the 1990's (21Z-1020). Office of the Administrator, 84 p.
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22
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Components of a Ground Water Resource Assessment 23
CHAPTER 2:
Components of a Ground Water Resource Assessment
A ground water resource assessment begins with an evaluation of the resource based
on a number of discrete Components, which are described in detail in this chapter. Resource
managers may choose to consider only those Components that are critical to State priorities.
Knowledge of the basic characteristics of ground water and the materials through
which it flows is important for understanding larger issues such as the quantity and quality of
the overall resource. The Components in this chapter deal with the collection, analysis, and
presentation of basic hydrogeologic data. These data give managers the background
information needed to assess aquifer sensitivity and ground water vulnerability as described
in Chapter 3. They also provide a basis for making decisions that affect the resource, such
as water supply development, siting of waste handling and disposal facilities, dealing with
existing aquifer contamination, and setting priorities for protection programs.
Establishing goals and objectives is an important first step in a resource assessment
that should not be overlooked. Resource managers also should develop a data collection
plan that considers data storage and retrieval capabilities, data format and quality, and
resources needed to analyze the data. Collection of hydrogeologic information should be
coordinated among government agencies to ensure efficiency.
The U.S. Geological Survey (USGS), State geological surveys, and other State water
research agencies have missions that include the evaluation of ground water resources.
Because of the technical nature of the required data, these agencies can provide managers
with resource evaluations, as needed. Reporting all the elements of the Minimum Set of Data
Elements for Ground Water Quality (USEPA, 1992) facilitates the sharing of information among
agencies and enhances the resource assessment process.
Defining a study area also is important. Because geologic conditions can vary over
short distances, collecting data in a small area is often necessary to determine local geologic
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24 Chapter 2
conditions. Because resource managers are often more concerned with ground water
resources on a regional level, it is recommended that managers consider the aquifer or
aquifer system as a whole. The manager should be aware, however, that a regional depiction
is based on information acquired from site-specific and well-specific data, which include their
own assumptions.
The limitations of existing data, and of data collected through new studies, affect how
the data can be used. Such limitations include geographic scale and reliability. It is often
necessary to collect new data to correlate and verify results of previous data collection efforts.
Hydrogeologists and other ground water professionals should be involved in determining the
adequacy of data or data collection methods and ensuring that sound scientific judgement
and techniques are used in the resource assessment process. The USGS, State geological
surveys, and other State water resource agencies have the relevant mission and expertise to
provide managers with ground water resource evaluations, as needed.
The resource assessment Components listed in this chapter, taken together, constitute
a rational, step-wise process for collecting hydrogeologic data and information. Information
produced for each Component will facilitate completion of the next Component.
The ten Components are:
(1) Regional Hydrogeologic Setting
(2) Aquifer and Aquifer-System Occurrence
(3) Water Table and Potentiometric Surface
(4) Hydraulic Properties
(5) Confinement and Interaction Between Aquifers
(6) Ground Water Recharge and Discharge Characterization
(7) Ground Water and Surface Water Interaction
(8) Ground Water Budget
(9) Chemical and Physical Characteristics of Aquifers and Overlying and
Underlying Materials
(10) Ambient Ground Water Quality
The discussion of each Component is broken into the following subsections:
Definition
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Components of a Ground Water Resource Assessment 25
Objective
* Data Needs
Methods
Presentation of Data/Information
Considerations
Citations
Citations
U.S. Environmental Protection Agency, 1992. Definitions for the Minimum Set of Data
Elements for Ground Water Quality (EPA 813/B-92-002). Office of Water, 98 p.
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26 Component #1
Component #1: Regional Hydrogeologic Setting
Definition
For the purposes of this discussion, regional hydrogeologic setting is an area of broad
extent (a county, State or multi-State area) with common geologic and hydrologic features
that control ground water movement in, through, and out of the area (Aller, et al, 1987).
These features include stratigraphy, the nature of water-bearing openings of the aquifers and
confining beds, major recharge and discharge characteristics, hydrogeologic divides, and
other physical, chemical, and hydrologic features.
Objective
The objective of this Component is to establish the regional hydrogeologic setting that
provides a general framework for the characterization of aquifers. This information helps
frame exploratory, evaluative, or management studies of ground water. This information also
improves the predictability of encountering any given geologic unit at specific sites and
improves confidence in the conclusions of ground water management studies. Obtaining and
evaluating regional hydrogeologic information is generally cost-effective because regional
information is typically collected, compiled, and distributed by government agencies.
Data Needs
Selected data such as those listed below are needed to describe the regional
hydrogeologic setting:
hydrogeology
topography
regional climate
hydrography
soil and vegetative cover
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Regional Hydrogeologic Setting 27
regional recharge and discharge patterns
ground water quality/geochemistry
When evaluated at a regional scale, these data contribute to the overall understanding
of the hydrogeologic setting. If managers desire a more localized study (i.e., one conducted
at a larger scale), it is more appropriate to collect data at more closely spaced points.
Because of the various constraints encountered in the collection of data, it is important to
determine data needs and carefully plan data collection activities at the beginning of a
resource assessment.
Hydrogeologic data form the basis for understanding hydrogeologic settings. These
data describe the major geologic and hydrologic factors that control ground water storage
and movement into, through, and out of an area. From these data, it is possible to make
generalizations about both ground water availability and pollution potential. Hydrogeologic
data include hydraulic conductivity, storativity, and transmissivity of the vadose zone and
aquifer; the mineral composition of the water-bearing matrix; and the geology of the
hydrologic unit(s) (i.e., both aquifers and confining beds).
Hydrologic parameters such as hydraulic conductivity, storativity and transmissivity
help define an aquifer's ability to store and transmit ground water and effect the rate of
movement of pollutants. For more information on the hydraulic properties of geologic
materials, see Component #4.
The nature of the water-bearing matrix relates to the kinds of openings, primary pores
and fractures in which ground water can be stored and transported; the solubility of the
matrix is in part determined by its mineral composition. These matrix characteristics influence
water storage and transmission, the dispersion and dilution of pollutants, and ambient water
quality. For more information concerning the physical and chemical characteristics of aquifer
materials, see Component #9.
Information about geology and landforms provides the framework for studying ground
water flow volume, direction, and quality. Information about geologic structures (e.g., faults,
folds, and intrusions) is critical in defining the location and extent of aquifers, especially in the
western United States. For example, faulting may truncate water bearing units or connect
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28 Component #1
them to other permeable units. Stratigraphic data describe the geometrical and age relations
(i.e., relative order of occurrence with depth) among geologic lenses, beds, and formations.
Stratigraphic data help identify the occurrence of water-bearing units and the spatial relations
that exist between the water-bearing and non-water-bearing units.
Topographic data help to determine the extent and direction of surface water flow
and are necessary to determine the elevation of the water table. In many hydrogeologic
settings, highlands are ground water recharge areas (i.e., areas where water enters the
ground water reservoir) and lowlands are ground water discharge areas (i.e., areas where
water exits the ground water reservoir). Diverse topographic features, even in basins
underlain by consistent and homogeneous geologic materials, can create a complex system
of ground water flow. Where local topographic relief is negligible, ground water flow systems
may be more regional. Where local relief is pronounced, ground water flow systems may be
more local (Freeze and Cherry, 1979). Topographic data can play a vital role in selecting the
appropriate scale for collecting, evaluating, and displaying hydrogeologic data. Figure 1
shows a regional hydrogeologic setting (USGS, 1992).
Data describing the regional climate are critical to assessing the regional
hydrogeologic system. Climatic data are necessary to evaluate the recharge, storage, and
occurrence of ground water. These data include the quantity and pattern of precipitation,
average and extreme temperatures, and evaporation rates. Both areal and temporal patterns
of climatic events are important.
Hydrographic data provide valuable information on the location, extent and flow of
surface water bodies (e.g., lakes, rivers, wetlands). This information is relevant to determining
ground water recharge and discharge areas and is necessary for defining areas of ground
water and surface water interaction. The information is critical for a complete evaluation of a
ground water budget (i.e., an accounting of water movement into and out of the ground water
system). For more information on the use of surface water data for determining ground water
characteristics, see Component #7.
Data on the soil and vegetative cover help identify recharge areas and infiltration and
transpiration rates. Soil characteristics are a major influence on infiltration rates. Types and
amount of vegetative cover determine the amount of precipitation intercepted and used
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Figure 1
Block Diagram Showing a Regional Hydrogeologic Setting
Gray Shale
Water
Table
Water
Table
Water Table
Well in ss
River
Source: After USGS, 1992
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30 Component #1
(transpired) and therefore, unavailable for recharge. Coefficients for soil and for vegetation
based on type and percent cover are necessary inputs to the equations and computer
models that calculate water balances of geographic regions. In addition to soil and
vegetation data in areas of karst topography, information on surficial features such as the
location and general characteristics of sinkholes, surface fractures (lineaments), solution
features (e.g., sinking streams, caves), and all possible points of direct recharge to karst
aquifers, should be obtained.
Regional recharge and discharge patterns identify where water enters (recharges)
and exits (discharges) ground water systems. Data defining recharge and discharge
locations help identify areas that contaminants can enter and exit the ground water system.
Recharge areas are typically areas where contaminants can more easily enter ground water.
Contaminants in the ground water are likely to exit in ground water discharge areas. For
further discussion of the characterization of ground water recharge and discharge areas, see
Component #6.
Ground water quality/geochemistry data describe the presence and concentration of
natural and human-induced biological, radiological, and chemical constituents in water and
provide information to help determine the appropriateness of the water for its intended
purpose: agriculture, industry, and domestic and municipal consumption. For example,
ground water quality/geochemistry data can be used for such purposes as determining the
safety of drinking water supplies. Baseline data can be used to establish ground water
quality trends. Constituents dissolved in ground water provide clues to its geologic history
and may yield information on the rocks and soils through which the water has flowed. For
information on ambient ground water quality, see Component #10.
Methods
Several methods can be used to obtain the data described above. The most cost-
effective initial method is a literature search. A search for existing data and information
frequently reduces the need for additional field work. The search could include both
published and unpublished materials, such as: maps, circulars, reports, monographs, and
aerial photographs. Existing data sources should be analyzed for level of detail, potential
applicability and representativeness. Soil, geologic, hydrographic, and topographic data are
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Regional Hydrogeologic Setting 31
often available from maps and reports published by government agencies (e.g., the U.S.
Geological Survey (USGS), State geological surveys, the U.S. Department of Agriculture's Soil
Conservation Service (SCS), the USGS Earth Resources Observation System (EROS) Data
Center, and the National Weather Service), and universities. Additionally, universities may
provide theses and dissertations containing relevant information and additional references.
County and local planning agencies often collect aerial photographs that may provide
supplementary information on the landforms, soils, and vegetation of their region. Climatic
information (e.g., precipitation, temperature, and weather patterns) can be obtained from the
National Oceanic and Atmospheric Administration (NOAA), the National Weather Service, and
universities having climatology or meteorology programs.
Several methods have been developed to organize and interpret hydrogeologic data
(see, for example, Heath, 1984; Johnston and Bush, 1988). In general, these methods use
hydrogeologic data to delineate and describe ground water regions across the United States.
Heath, for example, uses hydrogeologic data to divide the continental United States, Puerto
Rico, and the Virgin Islands into 15 distinct ground water regions. By referring to these and
similar regional studies, ground water resource managers can learn a great deal about the
hydrogeology of their region. Managers should understand, however, that these studies are
regional in scope, and will not reflect local variations in hydrogeology.
Site-specific data can be used to complement regional data where necessary. Existing
data bases or clearinghouses, such as those available through the USGS, State geological
surveys, and State Engineers' Offices, often provide site-specific data (e.g., test hole and well
data). Well logs are another useful source of site-specific data and are often readily available.
A comprehensive review of all available well logs may be highly resource intensive; however,
if well logs are computerized, careful screening and selection of logs for detailed review
reduces needed effort.
After a review of sources of existing data, a list of additional information needs can be
prepared to identify where field mapping activities are needed. This list should include the
exact nature of the data required, the applications and analyses that the data will be expected
to support, and the most efficient means of obtaining and managing the data. Depending on
the extent of previous geological field mapping activities, future mapping can be planned
according to State priorities. Geologic mapping is primarily the responsibility of State
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32 Component #1
geological surveys and the USGS. Additional mapping may be conducted by State and local
universities. Soil mapping is performed by the SCS. Once data are compiled, an
interpretation of the regional hydrogeologic setting is possible.
Presentation of Data/Information
Geologic maps are a fundamental vehicle for the display of geologic information.
Geology, topography, soils, hydrography, water table and potentiometric surfaces, water
quality, climatic variables such as precipitation, and other information are commonly displayed
on maps or cross-sections. Maps can also illustrate relationships such as between soils and
the stratigraphy of underlying geologic materials (including aquifers). Such representations
have numerous applications, including assessing the potential for aquifer contamination
(Soller and Berg, 1992). Because many combinations of soils and hydrogeology are
possible, overlays of different data sets that aid in focusing analyses may be particularly
useful. Computer applications, including the use of Geographic Information Systems (GIS),
may significantly ease the overlay process and, if the maps are in a digital format, may be
cost-effective. The use of GIS requires the careful checking of all output, particularly for
discrepancies in depiction of topography, evidence of input errors, and errors in site locations
of input data. Although GIS output from existing data sets is relatively inexpensive to obtain,
the time and expense to create new data sets and to maintain a GIS must be carefully
considered. Some personal-computer-mapping software also can be used to help in the
preparation of simple maps.
Geologic data may also be displayed three-dimensionally. For example, fence
diagrams illustrate a series of intersecting geologic cross-sections. Stack-unit maps show the
three-dimensional distribution of geologic materials in their order of occurrence of depth, over
a specified area and depth (Kempton, 1981). Block diagrams (see Figure 1) also present a
three-dimensional view of the hydrogeologic setting.
Considerations
Small-scale regional geologic maps are frequently available. For example, many
States publish a "State geologic map," often at a scale of 1:500,000. Data from these maps
are highly generalized and not intended for site-specific use. Small-scale studies are typically
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Regional Hydrogeologic Setting 33
based on regional settings ranging from counties to multi-State areas. Intermediate scales
ranging from 1:100,000 to 1:250,000 are also used for regional assessments. Data and
information on geology, soils, and topography are commonly compiled at these scales.
Regional maps are a very useful tool for identifying areas for more site-specific
investigations. A convenient scale for many site-specific investigations is 1:24,000, the scale
at which topographic information is available from the USGS for much of the United States.
In many States, less than ten percent of the area is adequately mapped at this scale.
1:24,000 is also the scale that will be used by many States to compile geologic information
under the recently passed Geologic Mapping Act of 1992 (P.L 102-285). The purpose of this
Act is to expedite the production of a geologic-map data base for the Nation to assist in the
resolution of issues related to land-use management, assessment, utilization and conservation
of natural resources, ground water management, and environmental protection. The Act
designates the USGS as the lead Federal agency responsible for overall management of this
national program.
As more site-specific data are collected over a large study area, the regional
interpretation based on site-specific data becomes increasingly accurate. This increasing
accuracy, in turn, results in better predictability when conducting site-specific studies. There
is, therefore, a continual feed-back process whereby site-specific information improves the
regional data base, and the improved regional data base increases the understanding of
hydrogeology at specific locations. The resources required to collect existing hydrogeologic
data are generally limited by the availability of staff. When collection of site-specific data is
required, field surveys, drilling or other field operations, and/or the obtaining of aerial
photographs will be needed. These activities are generally expensive and time-intensive.
Typically, geologists must visit the site in question and appraise the surficial and subsurface
hydrogeologic characteristics. Drilling rigs may be required to drill test holes and to install
ground water monitoring wells to obtain the additional data desired.
The use of a GIS to assist in data interpretation requires a sophisticated computer
system and additional staff time to manage the data. GIS may be used to assist ground
water scientists by producing initial estimates of the positions of hydrogeologic boundaries
and features, and the positions of parameter contours; the limitations of such interpretations
must be recognized.
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34 Component #1
In most States, much of the information referred to above is available. The information
used to describe the regional hydrogeologic setting provides the larger framework for making
decisions on additional data needed for a resource assessment to support State ground
water policy.
Citations
Aller, L.T., T.W. Bennett, J.H. Lehr, and R.J. Petty, 1987. DRASTIC: A Standardized System for
Evaluating Ground Water Pollution Potential Using Hydrogeologic Settings (EPA/600/2-
87/035). U.S. Environmental Protection Agency Robert S. Kerr Environmental
Research Laboratory, Ada, OK, 622 p.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated, Englewood
Cliffs, NJ, Chapter 8, pp. 304-307.
Heath, R. C., 1984. Ground-Water Regions of the United States. U.S. Geological Survey
Water Supply Paper 2242. U.S. Geological Survey, Washington, DC, 78 p.
Johnston, R.H., and Bush, P.W., 1988. Summary of the Hydrology of the Floridan Aquifer
System in Florida and in Parts of Georgia. South Carolina, and Alabama. U.S.
Geological Survey Professional Paper 1403-A. U.S. Geological Survey, Washington,
DC, 24 p.
Kempton, J.P., 1981. Three-dimensional Geologic Mapping for Environmental Studies in
Illinois. Illinois State Geological Survey Environmental Geology Note 100, 43 p.
Seller, D.R., and R.C. Berg, 1992. "A Model for the Assessment of Aquifer Contamination
Potential Based on Regional Geologic Framework." Environmental Geology and Water
Sciences. 19 (3), pp. 205-213.
U.S. Geological Survey, 1992. Geologic Maps: Portraits of the Earth. U.S. Government
Printing Office, p. 6.
For More Information
For more information on this subject see the following references:
Berg, R.C., J.P. Kempton, and K. Cartwright, 1984. Potential for Contamination of Shallow
Aquifers in Illinois. Illinois State Geological Survey Circular 532, 30 p.
Berg, R.C., J.P. Kempton, and A.M. Stecyk, 1984. Geology for Planning in Boone and
Winnebago Counties. Illinois State Geological Survey Circular 531, 69 p.
Davis, S.N., and R.J.M. De Wiest, 1966. Hydroqeology. John Wiley and Sons, New York, NY,
463 p.
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Regional Hydrogeologic Setting 35
Dobrin, M.B., 1960. Introduction to Geophysical Prospecting. McGraw-Hill, New York, NY
446 p. '
Hem, J.D., 1992. Study and Interpretation of the Chemical Characteristics of Natural Water.
U.S. Geological Survey Water Supply Paper 1473, 363 p.
Stumm, W., and J.J. Morgan, 1970. Aquatic Chemistry. John Wiley and Sons New York NY
583 p. '
U.S. Environmental Protection Agency, 1990. Handbook: Ground Water. Volume |- Ground
Water and Contamination (EPA/625/6-90/016a). Office of Research and Development
Washington, DC, Chapter 1, pp. 1 -49.
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36 Component #2
Component #2: Aquifer and Aquifer-System Occurrence
Definition
An aquifer is a geologic formation, group of formations, or part of a formation that
contains sufficient saturated, permeable material to yield significant quantities of water to wells
or springs. An aquifer system is a combination of permeable and less permeable materials
that function regionally as a water-yielding unit (USGS, 1989). Aquifer and aquifer-system
occurrence refers to the areal distribution and position of an aquifer or aquifer system,
including its depth below the ground surface, thickness, areal extent, and hydrologic
boundaries (i.e., the natural geologic and hydrologic characteristics that define the aquifer).
Objective
The objective of this Component is to focus the resource assessment on geologic
units that are logical ground water management units. Knowledge of the geometry and
geology of an aquifer or aquifer system facilitates protective resource planning (e.g.,
appropriate siting of facilities that are potential sources of contamination) and prioritizing the
remediation of contaminated sites.
Data Needs
Geologic and hydrologic data are needed to define the occurrence of aquifers and
aquifer systems in three dimensions. These data include:
saturated thickness of the aquifer system
depth to top and bottom of individual aquifers
areal extent
geophysical characteristics
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Aquifer and Aquifer-System Occurrence
37
Knowledge of the lithology (i.e., composition and texture) of geologic units provides
general information about the potential of those units to function as an aquifer The
stratigraphic arrangement of geologic units is needed to define the relationship between
aquifers and aquitards. Knowledge of the regional geologic sequence will assist investigators
in identifying the types of aquifers throughout the region or study area. Figures 2 and 3 (after
Moody, et al, 1988) illustrate the influence of geologic structure on the occurrence of regional
aquifers. For example, in areas where geologic materials have low primary porosity and
primary permeability (e.g., igneous or metamorphic rocks), aquifer hydraulic conductivity is
controlled by the presence of fractures, faults, or other conduits.
Saturated thickness of the aquifer system is defined as the entire zone of saturation
of unconfined and/or confined aquifers. The upper surface of the zone of saturation of an
unconfined aquifer is called the water table. In general, the water table is a subdued reflection
of the surface topography and lies at greater depth under hills than under valleys; however,
the depth to the water table in an unconfined aquifer is subject to seasonal variation causing
a change in the thickness of the saturated zone (USEPA, 1987). The saturated thickness of
an unconfined aquifer is the distance between the water table and the top of the first
underlying confining unit. The potentiometric surface of a confined aquifer, which is the
surface defined by the level to which water would rise in wells penetrating a confined aquifer,
can also vary seasonally, but this variation does not cause a change in saturated thickness
unless the water level drops below the aquifer's upper confining bed.
Saturated thickness is used with other parameters to determine the transmissivity of an
aquifer system and to estimate the volume of ground water in storage. Transmissivity is the
total amount of water that can be transmitted horizontally through the aquifer system's full
saturated thickness (Freeze and Cherry, 1979).
The depth to the top and bottom of individual aquifers defines aquifer thickness. In
unconfined aquifer settings, the depth to the top of the aquifer is often important in defining
surface water occurrence and connection with ground water. Locations of confining layers
and aquifers help define interrelationships within an aquifer system and the extent of regional
continuity of aquifers.
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Figure 2
Cross Section Depicting Regional Aquifer
Potentiometric Surface
Unconfined Regional Aquifer
Confining Layer
///////// Limestone'' / / / /
rv ////////// and Shale-' ' x x '
Salt Member
Horizontal Distance is Approximately 10 Miles
Source: After Moody et al, 1988
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Figure 3
Map and Cross Section Showing the Regional Aquifer
Systems of Kentucky
Feet
1,000
Coastal
1 Plain 1
m.
Interior Low Plateaus
Appalachian
\ 1
A -A1 Trace of hydrogeologic section
PRINCIPAL AQUIFERS
(1) Alluvial
(2) Tertiary and Cretaceous aquifers
(3,4) Pennsylvanian aquifer system
Eastern Kentucky Pennsylvanian aquifers (3)
Western Kentucky Pennsylvanian aquifers (4)
(5) Mississippi aquifer system
(6) Ordovician aquifer system
Source: After Moody et al, 1988
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40 Component #2
The areal extent of an aquifer or aquifer system is directly related to its geology.
Aquifer/aquifer system are composed of those portions of a geologic formation(s) that can
provide significant water to wells. The extent of geologic formations is finite due to the
intrinsic characteristics of their environment of deposition and their modification by natural
geologic processes. For example, formations may thin out or "pinch out", crop out at the
surface, or may be truncated by faulting, plutonic intrusions, or erosion. Areas of significant
water yield may be considerably smaller than the full extent of the geologic formation(s) due
to lithologic variability within the formation(s),
Geophysical data may enhance understanding of the three-dimensional geometry of,
and relationships among, aquifers and aquitards. Geophysical techniques are sometimes
employed to locate ground water resources and to assess spatial characteristics of aquifer/
aquifer systems. Techniques frequently used to gather geophysical data include seismic
refraction, electrical resistivity, electrical conductivity, and ground penetrating radar (GPR).
Analysis and interpretation of these data can provide an estimate of the extent of water-
bearing materials. Hydrogeologists can then verify their interpretations with well information
and plot the extent of the aquifers.
Methods
Similar to all other Components, data for characterizing the occurrence of aquifers and
aquifer systems can be obtained from existing sources and from collecting new field
information. In some cases, existing information will be sufficient to delineate the geometry
and lithology of aquifers and aquitards. Aerial and satellite imagery, if available, may provide
cost effective information on the areal extent of aquifers. If sufficient data are lacking, geologic
mapping and lithologic analyses or other techniques will be required to define the occurrence
of aquifers.
The U.S. Geological Survey (USGS), State geological surveys, State water quality and
water research agencies, and universities commonly collect the types of hydrogeological data
needed to assess the occurrence of aquifers and aquifer systems. Once collected, these
data are relatively inexpensive for other agencies to obtain and are usually highly reliable.
The data may be interpreted in the form of maps, cross-sections, fence diagrams, or
stratigraphic columns showing the relative age and location of geologic formations in the
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Aquifer and Aquifer-System Occurrence
41
study area. Also, numerous published and unpublished reports exist for local and regional
aquifers located throughout the United States.
Most major aquifers and aquifer systems in the United States have been identified and
mapped. However, many glacial drift aquifers in the Midwest are poorly documented. The
USGS's Regional Aquifer System Analysis (RASA) program is systematically studying the
major aquifers and aquifer systems in the United States. The program consists of studies of
28 aquifer systems across the U.S.; more than three-fourths of the program studies are
completed. The studies present an assessment of regional geology, discharge and recharge
dynamics, hydrogeology, and geochemistry. The USGS is also publishing a "Ground Water
Atlas of the United States," which is a series of regional atlases presenting text, maps and
other figures that synthesize information from the RASA program and related studies. The
Atlas is scheduled for completion in 1994.
If significant data gaps are identified, additional test drilling and geologic field mapping
may be necessary. Test drilling and well drilling provide an opportunity to: compile logs of
geologic materials, core or otherwise sample the materials, identify the presence of aquitards,
characterize overlying soil and unsaturated (i.e., vadose) zone materials, and measure depth
to water.
Detailed geologic mapping provides information on the lithology, structure, and
stratigraphy of the geologic formations. The process of geologic mapping requires developing
detailed notes on geologic formations, formation bedding trends, structures, and other
geologic information. Field notes and field maps provide the information for the development
of surface and subsurface geologic maps and cross-sections. These products, combined
with information about hydraulic properties can be used to define aquifer and aquifer system
occurrence.
Geophysical techniques may provide site-specific or regional data. The nature of the
information obtained depends on the technique applied. For example, gamma and electrical
resistivity logging allow interpretations of the physical properties of the subsurface geologic
materials for a specific borehole. Surface-based geophysical techniques can sometimes be
used to interpolate between areas of ground truth (e.g., boreholes, wells). These techniques
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42 Component #2
may be relatively rapid to perform, and can be very cost effective (Zohdy, et al, 1974; Keys,
1990).
Presentation of Data/Information
The areal extent and thickness information collected for a specific aquifer or aquifer
system may be compiled into maps, fence diagrams or geologic cross-sections. Contour
maps can also be developed to present such information as the elevation of the water table
and top or base of an aquifer. The saturated thickness of unconfined aquifers may vary with
season and well pumpage, and therefore, more than one saturated-thickness map or water-
table map may be desired. Where hydraulic properties are fairly uniform, aquifer thickness
can be used to evaluate the areas of greatest potential for well-field development; elsewhere,
transmissivity maps should be used for well-field siting.
For ground water protection purposes, it may be appropriate to develop thickness
maps of confining materials. The thicker the confining materials, the less likely the aquifer is
to become contaminated. Table 2 presents the formats used to depict selected information on
aquifer and aquifer-system occurrence. A Geographical Information System (GIS) may be
used to assist ground water scientists by producing initial estimates of aquifer or aquifer-
system boundaries in three dimensions. Some computer software can also assist in the
preparation of simple maps. Maps showing depth to aquifer or confining layer thickness over
a geographical area are particularly useful products for ground water protection purposes.
Considerations
The scale of aquifer or aquifer-system delineation depends on the size of the aquifer
or aquifer system being mapped. Well logs and test holes provide site-specific information
that may be extrapolated over large areas. Although published reports and maps are
generally based on numerous data points, more data (ground truth) may be available for
some parts of the study area than for others.
Data in published reports and maps are available from many agencies. Collection and
accurate interpretation of well-drilling logs reported by private well drillers requires
-------
Aquifer and Aquifer-System Occurrence 43
Table 2
Format for Presenting Selected
Aquifer and Aquifer-System Information
Information Presented
Presentation Format
Areal Extent
Map
Fence Diagram
Block Diagram
Thickness
Geologic Cross-Section
Fence Diagram
Block Diagram
Isopach Map
Stack-Unit Map
Depth to the Top of Aquifer or Confining
Layer
Geologic Cross-Section
Fence Diagram
Block Diagram
Stack-Unit Map
professional staff with an in-depth knowledge of the local geologic setting. Drillers' logs from
the installation of wells, however, may lack sufficient detail or accuracy to provide worthwhile
information. In addition, the location of the drill site as indicated on a private driller's log is
often inaccurate and must be verified.
In spite of these drawbacks, drilling logs are an important source of geologic
information, particularly if several logs are available for the same general location. Drill
cuttings and core samples taken during drilling may help confirm some of the driller's entries
or provide necessary detail. It is particularly helpful if information is available from nearby
exploratory holes or test holes logged by a geologist to confirm the well driller's log.
The drilling of test holes requires expensive equipment and technical staff to log the
test hole and collect samples of the geologic materials. Downhole geophysical techniques
can be used to accurately delineate formation changes. Experienced technicians and
specialized equipment are required to produce the logs, and geologists/geophysicists are
needed to interpret test-hole and geophysical data.
Geologic field mapping requires the judgement of a geologist. It is recommended that
a geologist familiar with the State or region of interest conduct the mapping and interpret the
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44 Component #2
results. Relationships shown by geologic maps, cross-sections, and columns are interpolated
from field data and should be used carefully with consideration of the uncertainties inherent in
gathering and interpreting the information presented.
Citations
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated, Englewood
Cliffs, NJ, 604 p.
Keys, W.S., 1990. Borehole Geophysics Applied to Ground-Water Investigations. U.S.
Geological Survey Techniques of Water Resource Investigations, Book 2, Chapter E-2,
150 p.
Moody, D.W., and others, Compilers, 1988. National Water Summary 1986-. U.S. Geological
Survey Water Supply Paper 2325, p. 263 and 266.
U.S. Environmental Protection Agency, 1987. Handbook: Ground Water (EPA/625/6-87/016).
Office of Research and Development, Washington, DC, Chapter 4, p. 73.
U.S. Geological Survey, 1989. Federal Glossary of Selected Terms: Subsurface-Water Flow
and Solute Transport. Office of Water Data Coordination, Washington, DC, 38 p.
Zohdy, A.A.R., G.P Eaton, and D.G. Mabey, 1974. Application of Surface Geophysics to
Ground-Water Investigations. U.S. Geological Survey Techniques of Water Resource
Investigations, Book 2, Chapter D-1.
For More Information
For more information on this subject see the following references:
American Water Works Association, 1989. Groundwater. American Water Works Association,
Second Edition, 151 p.
Bowen, R., 1986. Groundwater. Applied Science Publishers Ltd., London, 427 p.
Brassington, R., 1988. Field Hydrogeology. John Wiley and Sons, New York, NY, 175 p.
Driscoll, F.G., 1986. Groundwater and Wells. Second Edition, Johnson Division, St.
Paul, MN, 1089 p.
Hamill, L, and Bell, F.G., 1986. Groundwater Resource Development. Butterworths, Boston,
MA, 344 p.
Senay, Y., 1988. Aquifer Analysis. The Association of Ground Water Scientists and
Engineers.
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Water Table and Potentiometric Surface 45
Component #3: Water Table and Potentiometric Surface
Definition
A water table is the upper surface of the saturated zone of an unconfined (i.e., water
table) aquifer. At this surface, hydrostatic pressure approximately equals atmospheric
pressure. Under unconfined conditions, the static water level in a well represents the water
table. A water table can occur in almost any type of material.
An aquifer is confined if it is overlain by low-permeability materials. Ground water in a
confined aquifer exists between low-permeability layers and is generally under hydrostatic
pressure greater than atmospheric. A potentiometric surface is defined as an imaginary
surface representing the elevation to which water will rise in wells penetrating the confined
aquifer. Well discharge from a confined aquifer can cause the potentiometric surface to fall
below the confining layer, particularly near the well. Figure 4 (USEPA, 1991) is an illustration
of a water table and a potentiometric surface.
Objective
The objectives of mapping the water table or potentiometric surface are to understand
(1) the general direction of lateral ground water flow, (2) the location of recharge and
discharge areas, (3) the hydraulic gradient and (4) the hydraulic effects due to pumping, and
to obtain information to determine the flow direction and degree of interconnection between
an aquifer and adjacent hydrogeologic units and the flow direction and degree of
interconnection between ground water and surface water.
Data Needs
To achieve the objectives of this component, the following types of data should be
collected:
-------
Figure 4
Schematic Showing Water Table and Potentiometric Surface
t
'''.''''/.''.''.''' -1
'.'/'.''/' .'V.'V.
VX.'X'X'X1
"^N
r ". ". ", *. *, ".
1
s
=
B
1
,"1
'':''' :''' :'J
/Ground surface
xWater table
'"Pote^
Uncc
Apuitsrd
/;.;/V-V Lea
b"mefrfc~su"tac«
infined aquifer
ky aquifer/VvVv
Source: USEPA, 1991
-------
Water Table and Potentiometric Surface 47
ground water level
ground water well location
Water-level data from standing wells can be used for a variety of purposes, including:
(1) construction of water-table/potentiometric-surface maps, (2) location of recharge and
discharge areas, and (3) determination of ground water flow direction and velocity. Water-
level data are also needed to determine hydraulic gradient. Data from a well where the water
level has been disturbed by pumping must be used with care. Water-level data should be
compared only among wells in the same aquifer, because water levels measured in different
aquifers at the same geographic location will vary. Therefore, information such as the depth
of well screens and other well construction details should be collected.
Well-location data are needed so that the positions of wells can be plotted on a
topographic map. Without topographic elevations of wells it is not possible to accurately plot
water-level data on a map or draw reliable water-table/potentiometric-surface contours. The
accuracy of well-location data is more critical for smaller study areas than for larger areas.
Well logs and well registration information collected by Federal, State, and local regulatory
programs usually include information on well location and water level. Locations of private
wells are often available from well drilling companies, although this source often provides less
accurate information. Plotting well locations on topographic maps during field investigations
is highly recommended.
Methods
Data collection, management, and analyses for this Component are generally
straightforward. Potential data sources include the U.S. Geological Survey (USGS), State
geological surveys, State natural resource regulatory and research agencies, local
universities, and well drillers' logs. These data sources should be searched to obtain water-
level data from existing wells (e.g., monitoring, municipal, or private) installed in the aquifer(s)
of interest. If existing wells do not provide adequate water-level data, additional observation
wells or piezometers can be installed. Water-level data can be collected using appropriate
techniques (e.g., steel tape and chalk, electric probes, downhole pressure sensors,
transducers, automated data-collection equipment). Water-level elevations are expressed as
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48 Component #3
feet above some reference point -- generally mean sea level. Wellhead elevations can be
obtained by surveying or by approximating from 1:24,000-scale topographic maps.
Once water-level data are obtained for an aquifer of interest, a water-level contour map
depicting lines of equal hydraulic head (water level) can be drawn. Data selected for the
construction of a water-level contour map should be obtained only from wells screened in the
aquifer of interest. If two aquifers are present, a separate map should be drawn for each.
The direction of ground water in an aquifer can then be approximated by drawing ground
water flow lines perpendicular to contour lines of equal hydraulic head; flow is in the direction
of decreasing hydraulic head.
The magnitude of the hydraulic gradient (or change in hydraulic head) can be
determined by measuring the change in water-level elevation over a given distance. For
example, if the water-level elevation decreases 10 feet in one mile, then the hydraulic gradient
is 10 feet per mile. The water level of a given geographic location often varies with depth
within an aquifer. In such aquifers, determination of vertical gradients within the aquifer is
facilitated by installing clusters of observation wells or piezometers, with each well in the
cluster screened at a different depth. A comparison of water levels measured in these wells,
in conjunction with well-screen depth, permits calculation of the magnitude of potential vertical
water movement in the aquifer. Clusters of wells at the same geographic location but
screened in different aquifers can be used to help determine potential interaction between
aquifers and potential leakage through confining beds (see Component #5).
Presentation of Data/Information
The common output resulting from an investigation of water levels is a map of the
water table/potentiometric surface in an aquifer. Using well-location data, the wells can be
plotted on a map with their associated water levels. A contour map of the water table or
potentiometric surface is developed by drawing lines of equal water-level elevation. Computer
contouring software may provide an initial estimate of contour positions, however, because
interpretation between data points is generally required, final maps should be developed by
ground water scientists. Directional-flow maps may then be developed from the water-
table/potentiometric-surface maps. The scale of data presentation can vary widely depending
on the size of the area of interest.
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Water Table and Potentiometric Surface 49
Considerations
Delineating accurate water tables or potentiometric surfaces requires a substantial
amount of data. This effort may require the installation of piezometers or observation wells to
collect additional data if available data are insufficient. Using steel tape and chalk to collect
water-level data from existing wells or piezometers is an economical data collection
technique; data loggers with transducers have higher equipment costs but low associated
personnel costs. Labor, time, and equipment used to collect and record information will vary
according to the size of the particular region or study area, available data and/or data
collection points, and the needs of the resource manager.
Four issues should be considered before conducting water-table or potentiometric-
surface and ground water flow direction studies.
(1) Collection of water-level data during a single data collection event cannot
characterize temporal changes in water-table/potentiometric-surface elevations.
Water levels vary with changing seasons and climatic conditions. Therefore,
for some purposes, data may have to be collected and analyzed at various
times during the year (e.g., wet season and dry season). Regional and local
ground water flow directions may vary due to tidal and barometric influences,
pumping, irrigation, and impacts from adjacent aquifers and surface water
bodies.
(2) Because of seasonal and long-term climatic influences on water levels, water-
level contours should be drawn from data collected within a short time period.
Comparisons of water-level contours constructed for different measuring
periods can then be made to determine possible climatic influence on water
levels.
(3) Well installation costs increase not only with an increase in the number of wells
drilled but also with well depth. The cost of installing a well will also vary with
the local geology and primary purpose of the well, which dictate such factors
as well diameter, casing and screen material. The cost of data collection and
well installation rises dramatically as the size of the study area, geologic
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50 Component #3
complexity, or stringency of State and/or local well construction requirements
increase. Using existing wells screened at, and only at the depth of interest,
can significantly reduce the cost of collecting water-level data,
(4) The concept of a water table/potentiometric surface is strictly valid only for
water levels obtained from wells screened in the same horizon in an aquifer
that has horizontal flow (Freeze and Cherry, 1979). Most water-table and
potentiometric-surface maps, however, are constructed (1) using water-level
data obtained from wells installed at different depths throughout an aquifer,
and (2) for aquifers that do not have horizontal flow. These factors lead to
additional uncertainty in the maps.
Citations
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated, Englewood
Cliffs, NJ, 604 p.
U.S. Environmental Protection Agency, 1991. Wellhead Protection Strategies for Confined
Aquifer Settings. Office of Water, p. 6.
For More Information
For more information on this subject see the following references:
Driscoll, F.G., 1986. Groundwater and Wells. Second Edition, Johnson Division, St.
Paul, MN, 1089 p.
Fetter, C.W., 1988. Applied Hydrogeology. Second Edition, Merrill Publishing Company,
Columbus, OH, 592 p.
Heath, R.C., 1989. Basic Ground-Water Hydrology. U.S. Geological Survey Water
Supply Paper 2220, 84 p.
Nielsen, D.M., ed., 1991. Practical Handbook of Ground-Water Monitoring. Lewis Publishers,
Chelsea, Ml, 717 p.
Robson, S.G., 1987. Bedrock Aguifers in the Denver Basin. Colorado-A Quantitative Water-
Resources Appraisal. U.S. Geological Survey Professional Paper 1257, 73 p.
Thornhill, J., 1989. Accuracy of Depth to Water Measurements (EPA/540/4-89/002).
Superfund Ground Water Issue Paper, U.S. Environmental Protection Agency, Robert
S. Kerr Environmental Research Laboratory, Ada, OK.
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Water Table and Potentiometric Surface 51
U.S. Environmental Protection Agency, 1987. Handbook: Ground Water (EPA/625/6-87/016).
Office of Research and Development, 212 p.
U.S. Geological Survey, 1989. Federal Glossary of Selected Terms: Subsurface-Water Flow
and Solute Transport. Office of Water Data Coordination, Washington, DC, 38 p.
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52 Component #4
Component #4: Hydraulic Properties
Definition
Hydraulic properties refers to attributes of rock, sediment, and other materials that
govern the capacity of materials to hold, transmit, and deliver water. These attributes include
effective porosity, maximum and minimum hydraulic conductivity, transmissivity, specific yield,
and storativity.
Objective
The objective of this Component is to define the hydraulic characteristics of geologic
material. Information about hydraulic characteristics can be used to describe and quantify the
occurrence and movement of ground water in aquifers and confining units. Hydraulic data
are also necessary to determine well-yield characteristics and determine the movement of
contaminants.
Data Needs
The information needed to assess ground water occurrence and flow includes:
hydraulic gradient
porosity/effective porosity/fracture porosity
grain-size distribution
structural-geology factors
hydraulic conductivity
transmissivity
storativity and specific yield
ground water velocity
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Hydraulic Properties 53
These data are used to estimate amounts of ground water stored in aquifers and other
geologic units, quantities of water flowing between surface water and ground water, the
amount of ground water flowing between aquifers, and general rates of ground water flow.
Hydraulic gradient is a measure of the change in hydraulic head over a given
distance (i.e., the slope of the water table or potentiometric surface). For a graphical
illustration of the calculation of hydraulic gradient, see Figure 5A. The direction of the
hydraulic gradient is the direction of maximum decrease. Hydraulic head is a general term
used to describe the elevation of water above a known datum. Hydraulic head is composed
of three parts: (1) the elevation head, or water level above a datum; (2) the pressure head
with reference to atmospheric pressure; and (3) the velocity head. Because ground water
moves relatively slowly, velocity head can generally be ignored.
Porosity is the maximum amount of water a volume of geologic material can contain.
Porosity depends on grain size, sorting, packing, and cementation. Porosity is expressed as
the percentage of pore space (i.e., voids) contained in a total volume of material. For
example, a porosity of 10 percent means that 10 percent of a volume of porous material is
composed of voids. Typical aquifer porosities range from approximately 40 percent (e.g.,
well-sorted gravel deposits) to near zero in unfractured igneous rocks (Freeze and Cherry,
1979). Porosity, however, "does not indicate how much water the aquifer will yield" as it is not
a measure of the size or inter-connectivity of the pores (Driscoll, 1986). For example, the
porosity of clay may be higher than that of gravel, yet clays yield little water (see "specific
yield" below). Effective porosity is the amount of interconnected voids in a material through
which water or other liquids can travel divided by the total volume of material (Fetter, 1988).
The size and shape of individual particles, how they are arranged relative to each other, and
deposition of any cementing material determines the volume of interconnected void spaces.
Fracture porosity is a measure of the void space caused by fracturing or dissolution of rocks.
In crystalline (igneous) rocks, fractures may provide the only pore space. In porous rock,
fractures provide porosity additional to inter-grain porosity.
The grain-size distribution of aquifers influences the porosity, effective porosity, and
permeability of aquifers. Poorly sorted materials tend to have relatively low porosity because
smaller particles fill voids between larger particles. Sediments that are well-sorted, such as
dune sand deposits, tend to have high porosities and large water-holding capabilities.
-------
Figure 5A
Calculation of Hydraulic Gradient in an Unconfined Aquifer
Hydraulic Gradient =
Where Ah = difference in hydraulic head
d = distance
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Hydraulic Properties 55
Structural geology factors can also influence the amount of void space in a
formation and the ability of water to flow through an aquifer. Folds, fractures, and faults can
control the presence and flow of ground water. Typically, fracture trends follow regional
structural features such as folds or faults. The folding of rock formations, whether on a local
or regional scale, can cause fracturing of geologic materials. Faulting of rocks can also
create fractures adjacent to the fault. Fractures and faults may be filled with impermeable
material, or they may act as conduits for ground water flow. Where fractures intersect in the
subsurface, ground water may be plentiful. Fracture-trace analysis, the use of aerial
photographs to locate surface manifestations of subsurface fractures, can provide an
indication of successful well locations by identifying areas of intersecting fractures. Ground
water flow through fractures in porous materials can be locally significant, as it is in recharge
areas along subsidence-induced fractures in the alluvial valleys of the southwestern United
States.
Hydraulic conductivity is a measure of the ability of a porous medium (or a fractured
rock that approximates a porous medium) to transmit water or other liquid. It is expressed as
the volume of water that will move in a unit time under a unit hydraulic gradient through a unit
cross-sectional area of the medium. Hydraulic conductivity can be expressed in units of
feet/day and can be derived from gallons per day (gpd)/unit cross-sectional area (square
feet). The hydraulic conductivity of a particular porous medium is dependent on the size,
distribution, and degree to which water-transmitting openings are connected, and the
presence of joints, faults, and macropores. Although the nature of the ground water (e.g.,
temperature, contaminants) also affect hydraulic conductivity, for the purposes of conducting
a resource assessment, these elements of hydraulic conductivity can generally be ignored.
Most aquifers are heterogeneous, that is, hydraulic conductivity varies from point to point.
Transmissivity is a measure of an aquifer's ability to transmit water through a given
saturated thickness. Transmissivity is the weighted average of horizontal hydraulic
conductivities at various depths in the aquifer, multiplied by the saturated thickness of the
aquifer (Nielsen, 1991). Transmissivity is expressed in terms of volume/time/length (area/time)
of saturated thickness. Transmissivity is helpful in calculating flow rates and aquifer yield.
The transmissivity of a typical sandstone aquifer may be less than 400 square feet/day to over
2,100 square feet/day, while the transmissivity of alluvial aquifers along stream beds can be
more than 13,000 square feet/day (Robson, 1987). In practice, transmissivity of a formation is
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56 Component #4
commonly measured whereas hydraulic conductivity is estimated from the transmissivity value
or determined from slug tests. See Figure 5B (Heath, 1984) for an illustration of the difference
between hydraulic conductivity and transmissivity.
For confined aquifers, storativity is defined as the volume of water that an aquifer
releases from storage per unit surface area of the aquifer per unit decline in the component of
hydraulic head normal to that surface (Freeze and Cherry, 1979). For unconfined aquifers,
the term specific yield is used instead of storativity and is defined as the amount of water
that a specific volume of saturated aquifer material will release by gravity drainage. Storativity
and specific yield are dimensionless (unitless) quantities. Storativity values for confined
aquifers (which range from 0.005 to 0.00005) are usually much lower than specific yield
values for unconfined aquifers (which range from 0.01 to 0.30) (Freeze and Cherry, 1979).
Specific yield and specific retention are related hydraulic properties of an unconfined
aquifer. The specific yield reveals how much water will drain due to gravity and can be
expressed as the following (Fetter, 1988):
volume of water a material will yield by gravity drainage
total volume of the material
When water is drained by gravity, some of the water is retained by the material. Specific
retention, the amount of water that is retained, can be expressed as the following ratio (Fetter,
1988):
volume of water retained by the material
total volume of the material
Clay materials typically exhibit high specific retention ratios, while sand and gravel typically
exhibit high specific yield ratios.
The velocity of ground water flow in porous media and finely fractured media is
generally low and is frequently measured at rates of feet/year. The macroscopic (i.e., average
linear) velocity of flow under ideal hydrological conditions is equal to the discharge of a
volume of water over a measured time (e.g., cubic feet/second) divided by the cross-sectional
-------
Figure 5B
Difference Between Hydraulic Conductivity and Transmissivity
Hydraulic conductivity defines the water-
transmitting capacity of a unit cube (A) of the aquifer.
Transmissivity defines the water-transmitting capacity of a
unit prism (8) of the aquifer.
Source: Heath, 1984
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Component #4
area of the flow divided by the volumetric porosity. Ground water velocity in porous media
can be determined from the equation that is a form of Darcy's Law:
q = Kl
where q = ground water velocity
K = hydraulic conductivity of the porous medium
I = hydraulic gradient
Calculated velocities are average values because K varies throughout most aquifers.
Ground water flow in finely fractured rocks that approximate porous media can be
determined using the above equation. Flow of ground water in rocks with large diameter
fractures and/or solution conduits, however, often cannot be calculated with this equation.
Flow rates in such settings are often quite high; rates of one mile/day are not uncommon.
Methods
Data on hydraulic properties can be collected through a literature search of existing
data and by using a combination of field and laboratory methods. Porosity is generally
measured in the laboratory; transmissivity and storativity are generally calculated from data
collected in the field. Hydraulic conductivity can be either measured or estimated in the
laboratory or from field data. Laboratory measurements provide estimates of hydraulic
conductivity at specific locations. Disturbance of the sample during collection and the nature
of the laboratory equipment may cause errors in the estimation of hydraulic conductivity (and
other hydraulic properties). Because hydraulic conductivity is dependent on geologic
materials whose characteristics usually vary over relatively short distances, laboratory values
frequently do not provide information applicable to broad areas. Field observations are
generally more representative of the hydraulic conductivity throughout the aquifer. Values of
hydraulic conductivity measured in the lab are often one to two orders of magnitude lower
than field-measured values (Herzog and Morse, 1986).
A literature search may significantly reduce the time, effort, and cost required to
adequately characterize hydraulic properties. It is important to identify existing local, regional,
and national sources of hydrogeologic data. State geological surveys, the U.S. Geological
Survey (USGS), and State natural resource regulatory and research agencies are excellent
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Hydraulic Properties 5g
sources of hydrogeologic data and technical reports. U.S. Environmental Protection Agency
(EPA) offices such as those that oversee the Resource Conservation and Recovery Act
(RCRA), Comprehensive Environmental Response, Compensation and Liability Act (CERCLA),
Underground Storage Tank (UST), and Underground Injection Control (UIC) regulatory
programs may require hydrogeologic data from permittees and petitioners that include
information about hydraulic properties. Local regulatory agencies with responsibility for
ground water protection will also collect and maintain hydrogeologic data. Other sources of
data that should be considered include Federal agencies such as the U.S. Department of
Agriculture's Soil Conservation Service (SCS), and private businesses that have conducted
site characterization investigations.
Information obtained through a literature search may include well-log data and tables
of hydraulic properties of geologic materials. Detailed reports and computerized data bases
may also be available. Some data may be used directly in a resource assessment while other
data can be used to derive various hydraulic properties. For example, descriptions of the
grain size (e.g., sand, silt, clay) of porous media are recorded in drilling logs. Hydraulic
conductivities can be estimated from these descriptions of texture using empirical
relationships that have been developed for this purpose (Cartwright and Hensel, 1992; Freeze
and Cherry, 1979). Porosity can also be estimated from these logs. An approximation of
transmissivity can be estimated from specific capacity, which is a measure of the productivity
of a well. Specific capacity is obtained by dividing the rate of well discharge by the
drawdown of the water level in the well.
Field methods may be used to determine saturated hydraulic conductivity. Well tests
(i.e., bail or slug tests) and aquifer tests may be used to collect water-level data over a period
of time. Analytical methods can then be applied to these data to determine values of
hydraulic conductivity, transmissivity, and storativity. Transmissivity and storativity can be
estimated in the field from bail or slug tests, aquifer tests, and tracer tests. In addition,
borehole geophysical methods may be used to estimate hydraulic conductivity.
Bail tests involve the removal of a known volume of water from a single well and
careful measurement of the subsequent recovery of the water level over time (Nielsen, 1991).
Slug tests measure the water level decline in a well over time after a measured amount of
water has been added to a well (or a slug used to displace water is placed in the well)
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£2 Component #4
(Freeze and Cherry, 1979). Analytical methods can be applied to these data to estimate the
hydraulic conductivity of the aquifer. Horizontal hydraulic conductivity is measured as water
travels horizontally to or from the well through the aquifer; the vertical component of flow from
adjoining confining layers and from within the aquifer is a function of the vertical hydraulic
conductivity of the aquifer or confining layer.
Aquifer tests are a field method for determining transmissivity and storativity of porous
media (and in finely-fractured rocks that approximate porous media). An aquifer test is
performed by pumping a well at a constant rate over a period of time ranging from several
hours to several days and measuring the change in water level in observation wells or
piezometers located at different distances from the pumping well. Time versus water-level-
drawdown data are then interpreted using graphical and analytical methods. The hydraulic
conductivity can be estimated from these data if the thickness of the confined aquifer or
saturated zone of an unconfined aquifer are known. Two common methods are used to
analyze the data to determine transmissivity and storativity. The Theis method involves curve
matching on a log-log plot while the Jabob method interprets the data with a semi-log plot
(Freeze and Cherry, 1979; Walton, 1962).
Tracer tests can be used to estimate the degree of hydraulic connection along
potential flow conduits, such as fractures or solution channels in non-porous media, and can
be used to estimate average flow velocities in porous media. In this field method, a tracer
(e.g., a salt, radioactive isotope, or fluorescent dye) is added to the ground water reservoir;
monitoring piezometers or wells are used to determine the increase in the concentration of
the tracer over time at selected monitoring locations (Freeze and Cherry, 1979). Tracer tests
can also measure arrival times of ground water at points known to be in hydraulic connection
with the tracer-source site.
Geophysical methods for determining hydraulic properties may involve surface or
subsurface investigations. Borehole geophysical data can be used to identify areas in the
stratigraphic section where high porosity and permeability rocks (i.e., rocks with high potential
yield) occur. Several types of logs, including resistivity, spontaneous potential, neutron, and
gamma, provide detailed information about the subsurface. Effective porosity can be
determined from calibrated log-normal resistivity logs; permeability can be estimated from
porosity and injectivity data (Fetter, 1988).
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Hydraulic Properties 61
Laboratory measurements of hydraulic properties of geologic materials rely on
samples taken in the field and transported to the laboratory. These samples must be
carefully collected and maintained to minimize disturbance of the material. Porosity, hydraulic
conductivity, and grain-size distribution can all be determined from laboratory measurement of
samples.
Porosity is generally measured in the laboratory by obtaining values for the oven dried
mass of the sample, field volume, and solid particular volume (see Freeze and Cherry, 1979).
Another method used in laboratories for determining porosity is the gas pycnometer method.
The gas pycnometer method measures gas-filled volumes in porous media based on the
volume-pressure relationships of gasses.
Laboratory methods for determining hydraulic conductivity include direct measurement
methods using constant- or falling-head permeameters or indirect estimates using particle-size
analyses of material. The direct methods involve measuring the volume of water that flows
through a fixed cross-section of saturated porous media under an applied hydraulic gradient.
These methods use many types of devices in which flow may be directed either up or down
through the core sample, the hydraulic gradient may be high or low, and the hydraulic head
may be constant or falling (Fetter, 1988).
Particle-size analysis of drilling-core samples supplies information on the size
distribution of the particles that comprise unconsolidated porous media. As previously
described, hydraulic conductivities can be estimated from textural information using
established empirical relationships. Using laboratory determinations of grain-size distributions
from drilling cores, however, is preferable to textures (grain size) recorded in well logs,
because textures noted in well logs are usually determined from subjective visual estimates
and "feel" tests.
Presentation of Data/Information
Information on hydraulic properties may be most easily understood and interpreted
when presented in maps, charts, or figures. Maps are useful to show the areal distribution of
hydraulic properties within a hydrogeologic unit. If the area to be mapped contains significant
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Component #4
variation in hydraulic properties, a large amount of data may be needed to adequately
describe the hydraulic characteristics of the area.
Charts or figures may show such information as the depth and thickness of
hydrogeologic units. Data presented in tables or data bases may be useful for modeling the
hydrogeoiogic setting.
If data are digitized, a Geographic Information Systems (GIS) may be used to assist
ground water scientists by producing initial drafts of maps of hydraulic parameters. Maps
may be overlain (manually or with use of a GIS) to develop derivative maps. Mapping
software for personal computers is also available to assist in the preparation of simple maps.
It is important to recognize, however, that professional expertise and judgement are
necessary in the development of any maps of hydraulic properties.
Considerations
The collection and interpretation of hydraulic data will assist resource managers in
evaluating the quality and quantity of ground water within their jurisdiction. The results of this
collection and interpretation of data will often depend on the resources available to perform
the study, the methods used, and the selection of study areas or sites. The data collection
process should be organized to meet the objectives of the study and provide the best use of
available resources.
Adequate assessment of hydraulic properties for a hydrogeologic setting requires a
substantial amount of data. Collection of large amounts of data may be very costly,
especially if new wells must be installed. Therefore, it is especially important to first conduct
a literature search first to determine and locate existing hydrogeologic data.
Data to determine aquifer characteristics may be collected from "point"-type tests (slug
or bail) and/or aquifer tests. In general, slug or bail tests provide information for a specific
point, while aquifer tests provide generalizations across the area of influence of the pumping
well. Managers should be aware that water pumped during an aquifer test must be diverted
to surface waters or a collection area and that discharge permits may be required. Managing
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Hydraulic Properties 63
the pumped water can be especially difficult and costly if the pumped water is contaminated.
Sites for data collection activities must be chosen carefully to maximize the
applicability of the new data. New data collection sites should be selected only after
considering all presently available hydrogeologic information. If aquifer tests are planned, it is
necessary to ensure that the screened intervals of the pumping and monitoring wells are in
the same hydrogeologic unit. A reliable stratigraphic framework, as described in Components
#1 and #2, will help determine which tests should be conducted and which data should be
collected.
When using historical data, it is important to consider the accuracy and reliability of
the information. This can be accomplished by examining what types of methods were used
to collect the data and the expertise in the organization that collected them.
Citations
Cartwright, K. and B.R. Hensel, 1992. Chapter 4, "Hydrogeology": in D.E. Daniel ed.,
Geotechnical Practice for Waste Disposal. Chapman and Hull, New York, NY, 683 p.
Driscoll, F.G., 1986. Groundwater and Wells. Second Edition, Johnson Division, St.
Paul, MN, 1089 p.
Fetter, C.W., 1988. Applied Hydrogeology. Second Edition, Merrill Publishing Company,
Columbus, OH, 592 p.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated, Englewood
Cliffs, NJ, 604 p.
Heath, R. C., 1984. Ground-Water Regions of the United States. U.S. Geological Survey
Water Supply Paper 2242. U.S. Geological Survey, Washington, DC, p. 8.
Herzog, B.L. and W.J. Morse, 1986. "Hydraulic Conductivity at a Hazardous Waste Disposal
Site: Comparison of Laboratory and Field-Determined Values." Waste Management
and Research. 4, p. 177-187.
Nielsen, D.M., ed., 1991. Practical Handbook of Ground-Water Monitoring. Lewis Publishers
Chelsea, Ml, 717 p.
Robson, S.G., 1987. Bedrock Aguifers in the Denver Basin. Colorado - A Quantitative Water-
Resources Appraisal. U.S. Geological Survey Professional Paper 1257, 73 p.
Walton, W.C., 1962. Selected Analytical Methods for Well and Aguifer Evaluation.
Illinois State Water Survey, Bulletin 49, 81 p.
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64
__ Component #4
For More Information
For more information on this subject see the following references:
Hanks, R.J., and G.L Ashcroft, 1980. Applied Soil Phvsics Springer-Verlag, New York, NY,
I oy p.
Heath, R.C., 1989. Basic Ground-Water Hydrology U.S. Geological Survey Water
Supply Paper 2220, 84 p.
Klute, A., 1986. Methods of Soil Analysis. Part 1. Physical and Mineraloqical MPthnH^
Second Edition. ASA. Madison, Wl, 1188 p. ' l
U.S. Geological Survey, 1979. Ground-Water Hydraulics. U.S. Geological Survey
Professional Paper 708. U.S. Government Printing Office, Washington, DC, 70 p.
U.S. Geological Survey, 1976. Introduction to Ground Water Hydraulics. US
Geological Survey Techniques of Water Resource Investigations Book 3
Chapter B2.
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Confinement and Interaction Between Aquifers 65
Component #5: Confinement and Interaction Between Aquifers
Definition
Confined aquifers are located between confining layers, or aquitards, that impede the
vertical flow of ground water. Aquitards are geologic formations with significantly lower
hydraulic conductivity than aquifers. Examples of aquitards include unfractured shale and
siltstone. Natural interaction between aquifers occurs when aquitards are absent or
permeable enough to transmit some ground water to underlying or overlying aquifer units.
The movement of water through ground water systems is controlled by vertical and horizontal
hydraulic conductivity, thickness of the aquifers, thickness and degree of continuity of
confining beds, and the hydraulic gradient. The degree of hydraulic connection between
aquifers and aquitards is primarily a function of the hydraulic properties of the aquitard and
the vertical hydraulic gradients as shown in Figure 6 (Heath, 1989).
Objective
The objective of analyzing the degree of interaction between aquifers is to determine
the quantity of water that is flowing through the confining layer to the aquifer, both under
natural conditions and as a result of well discharge. Knowledge of relative confinement
and/or interconnection between aquifers is essential to siting water supply wells and well
fields, and assessing the vulnerability of deeper ground water to sources of surface
contamination. Interconnection of aquifers often complicates efforts for siting waste disposal
facilities or locating potable water supplies.
Data Needs
To achieve the objectives of this Component the following data should be collected:
lithology and stratigraphy
geophysical properties
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Figure 6
Different Conditions of Aquifer Confinement and Interaction
Land surface
Discharging welk
QnfLnjng feed IirBperrneaJ>]eL
Unconfined aquTfeF "" ""
Source: Heath, 1989
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Confinement and Interaction Between Aquifers 67
hydraulic properties
water quality
Freeze and Cherry (1979) define aquitards as those layers in a stratigraphic sequence
that have insufficient permeability to allow wells completed in them to yield an economically
significant amount of water. Although water flows very slowly within aquitards, their capacity
to store ground water can be quite high (Driscoll, 1986). Thus, the permeability of aquitards
(confining layers) and the degree to which they allow flow or leakage of ground water
between aquifers vary according to the aquitards' lithology, stratigraphy, and hydraulic
properties. Knowledge of these attributes of the confining layer(s) leads to a better
understanding of the aquifer and aquitard relationship and can assist in identifying highly
confined areas and areas where the greatest potential for aquifer interaction may occur. See
Figure 6 for an illustration of this concept. Figure 6a depicts horizontal flow to a well
discharging from a confined aquifer. Figure 6b depicts leakage from an upper, unconfined
aquifer into a confined aquifer from which a well is withdrawing water.
Confining layers between aquifers impede the exchange of water and contaminants;
the thicker the confining layer (or lower the permeability) the greater the impedance.
Similarly, a thicker confining layer (or lower permeability) above a shallow confined aquifer,
reduces susceptibility of the aquifer to surface contamination. Thickness, permeability,
lithology, and hydraulic conductivity of confining layers may vary within short distances.
Fractures, higher permeability zones, and man-induced breaches such as boreholes are
conduits between aquifers. Over large distances, confining layers may disappear completely
as a result of environmental conditions at the time of their deposition.
Geophysical data can be used to determine the extent of confining layers and
permeabilities of geologic materials. Hydraulic property data, such as hydraulic conductivity
of aquifers and aquitards, storativity, and hydraulic gradient, combined with information on
continuity of the aquitard and the presence of artificial penetrations (e.g., boreholes and
poorly constructed wells), assist in the determination of aquifer confinement and interaction.
Vertical leakage occurs through most confining layers; that is, they are not "tight".
According to Meinzer (1942), a well pumping from a confined aquifer (except one overlain by
a very impermeable layer) receives water from four major sources:
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68
(1) water moving through the aquifer toward the well
(2) water forced from the aquifer by compaction due to the weight of overlying
materials
(3) the expansion of water in the aquifer as its pressure decreases due to pumping
(4) water that is forced from surrounding aquitards by compaction
Over time, a significant portion of water pumped from a confined aquifer may originate
as "leakage" from overlying and/or underlying aquitards.
Water quality is an important factor in determining the presence and nature of
interconnection between aquifers. Similar water quality in adjacent aquifers is often an
indication of good hydraulic connection. Water of different qualities frequently indicates poor
connection. Information on the geochemistry, presence and type of radionuclides and even
contaminants in ground water from each aquifer can be used to help determine the presence
or absence of inter-aquifer flow. A comparison of water temperatures may also provide
information regarding hydraulic connection.
Methods
Data on hydraulic properties of aquifers and aquitards can be collected through a
search of existing data and by using a combination of laboratory and field methods. For
more information about analytical methods to determine hydraulic properties of aquifers, see
Component #4. Application of analytical methods to aquifer-test data can be used to
determine the effects of leakage from aquitards to the water pumped from an aquifer and to
the recovery of water levels in the aquifer after pumping (Kruseman and De Ridder, 1990).
Geophysical methods of determining hydraulic properties may involve surface or
subsurface investigations. Borehole geophysical data can be used to interpret areas in the
stratigraphic column where low-permeability rocks (those rocks that limit aquifer interaction)
occur. Several types of logs, including resistivity, spontaneous potential, neutron, and
gamma logs provide detailed information concerning the subsurface. Comparison of
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Confinement and Interaction Between Aquifers 69
geophysical data from different well-logging sites assists in the determination of the presence
and position of confining units.
Confining layers often contain areas of higher permeability or man-made breaches,
that permit significant ground water flow to the underlying aquifer. This flow can be estimated
from the saturated thickness and hydraulic conductivity of the aquifer and the hydraulic
resistance of the confining layer (Kruseman and De Ridder, 1990). Hydraulic resistance of an
aquitard is the ratio of its saturated thickness to its vertical hydraulic conductivity. High
values indicate large resistance to upward or downward leakage.
Finally, geochemical methods can also be used to determine interaction between
aquifers. An understanding of the overall geochemistry of water, including the absence or
presence of common constituents, can assist in characterizing the degree of aquifer
interconnection. See Components #9 and #10 for more information about the geochemical
characterization of ground water.
Presentation of Data/Information
Information on geologic materials, as it relates to the confinement and interaction of
aquifers, may be presented in table or chart form to show the depth and thickness of aquifers
and aquitards and their associated hydraulic data. Geologic cross-sections depict a
geologist's or ground water scientist's interpretation of aquifer-aquitard relationships that
improve understanding of the interconnections between aquifers. Maps displaying the
thickness (isopach maps) and extent of aquifers and aquitards are typically used to present
such information. Components #1 and #2 discuss the use of maps in more detail.
Graphical displays and maps showing areas of high aquifer interconnection or
confinement are often produced from site-specific data. Geographic Information Systems
(GIS) may be used to assist ground water scientists by producing initial estimates of aquifer
and aquitard attributes such as potentiometric surface elevation, hydraulic conductivity,
transmissivity, composition, and unit thickness. The maps developed may be manually
overlain to allow the creation of derivative maps of relative aquifer connection or relative
aquifer confinement. If the maps developed are digitized as separate coverages, a GIS may
be used to superimpose the map layers and aid in the development of derivative maps.
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70 Component #5
However, it is important to recognize that professional expertise and judgement are necessary
in the development of any maps that interpret aquifer data.
Considerations
All available hydrogeologic data should be considered when determining the degree
and lateral extent of aquifer interaction across a region. To properly interpret this data, a
ground water scientist should have a good understanding of the nature of the hydrogeologic
setting (see Components #1 and #2) and be cautious when correlating site-specific
information across the region.
Aquifer-test and drilling-core data are helpful in the determination of properties needed
to assess the confinement and interaction of aquifers. These data may exist in local or State
government offices. If few data are available, field investigations, including the installation of
pumping wells and piezometers, may be needed to collect the necessary information. Such
data collection could prove to be costly. Geophysical investigations may reduce costs and
rapidly provide data on some subsurface characteristics but the data may be difficult to
interpret.
Citations
Driscoll, F.G., 1986. Groundwater and Wells. Second Edition, Johnson Division, St.
Paul, MN, 1089 p.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated, Englewood
Cliffs, NJ, 604 p.
Heath, R.C., 1989. Basic Ground-Water Hydrology. U.S. Geological Survey Water
Supply Paper 2220, p. 8.
Kruseman, G.P., and N.A. De Ridder, 1990. Analysis and Evaluation of Pumping Test
Data. International Institute of Land Reclamation and Improvement, Publication
#40, 345 p.
Meinzer, O., ed., 1942. Hydrology. McGraw-Hill, New York, NY, 712 p.
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Confinement and Interaction Between Aquifers 71
For More Information
For more information on this subject see the following references:
Bredehoeft, J.D., 1983. Regional Flow in the Dakota Aquifer: A Study of the Role of Confining
Layers. U.S. Geological Survey Water Supply Paper 2237. U.S. Government Printing
Office, Washington, DC, 45 p.
Fetter, C.W., 1988. Applied Hvdrogeoloqy. Second Edition, Merrill Publishing Company,
Columbus, OH, 592 p.
Theis, C.V. 1940. "The Source of Water Derived from Wells, Essential Factors Controlling the
Response of an Aquifer to Development." Civil Engineering. 10 (5), pp. 277-280.
Todd, D.K., 1980. Ground Water Hydrology. Second Edition, John Wiley and Sons, New York,
NY, 535 p.
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72 Component #6
Component #6: Ground Water Recharge and
Discharge Characterization
Definition
Ground water recharge and discharge are components of the hydrologic cycle.
Recharge is the water that enters the ground water reservoir; discharge is the water that exits.
Characterizing recharge and discharge includes identifying their rates and areas of
occurrence.
Objective
The objectives of characterizing ground water recharge and discharge are: (1) to
protect recharge areas from contamination, (2) to gain knowledge about changes in ground
water levels, and (3) to gain insight into the nature of the impact of ground water on the
quality of the surface water resources into which ground water discharges, the flow of
streams, and the size of lakes.
It is important to recognize that ground water recharge and discharge are processes
that are separate from, but related to, aquifer recharge and discharge. For example, in
hydrogeologic settings with deep confined aquifers, only a small fraction of ground water
recharge may contribute to the recharge of a specific aquifer of interest. The remaining
recharge may be discharged to local surface water bodies or be intercepted by shallower,
overlying aquifers.
Data Needs
The data needed to characterize ground water recharge and discharge in a resource
area are:
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Ground Water Recharge and Discharge Characterization 73
location of recharge and discharge areas
recharge and discharge rates
precipitation
geologic and soils data
water levels from wells completed in area aquifers and confining units
interaction of ground water with surface water
Recharge and discharge areas are the ground surface areas in which water enters or
exits the ground water system. Ground water flow in a recharge area is downward; ground
water flow in a discharge area is upward. Figures 7A and 7B (Baldwin, 1963; Heath, 1989)
present a basic depiction of recharge and discharge characteristics. From the recharge area,
the water moves through the ground water reservoir and exits (perhaps after flowing through
more than one aquifer) through a discharge area, such as a spring, a seep, or surface water
body. Ground water in recharge areas is usually more susceptible to surficial contamination
than in other areas. Contaminants entering through the recharge area may exit through the
discharge area. Thus, the locations of recharge and discharge are essential to a thorough
understanding of the hydrologic cycle and the routes for contamination.
For some purposes, such as the development of management priorities, it may be
important for a State or local authority to distinguish between recharge to, and discharge
from, a ground water reservoir. Recharge or discharge at a given geographic location may
not be to or from a particular aquifer of interest. In some settings, little or no local ground
water recharge and/or discharge may be to or from the locally-used aquifer.
Recharge and discharge rates are affected by a number of factors, including the
duration and quantity of precipitation events, the duration and quantity of irrigation, surface
evaporation, soil moisture content, soil infiltration rates, hydraulic conductivity of geologic
materials, vegetative cover, water demand of plants, land use, depth of the water table, and
distance and direction to a stream or river (Walton, 1965). Recharge and discharge are
generally estimated as annual average rates and for the ground water reservoir as a whole.
Precipitation is often thought of as the first step in the hydrologic cycle. Rainfall and
snowmelt that does not run off, evaporate, or transpire from plants, infiltrates the soil and
unsaturated zone and recharges the subsurface hydrogeological systems. Although the
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Figure 7A
Recharge Areas for a Confined and Unconfined Aquifer
I I
I I
Recharge Area '
Source: After Baldwin, 1963
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Figure 7B
Ground Water Recharge and Discharge Areas
Source: After Heath, 1989
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76 Component #6
annual recharge rate is directly related to the annual precipitation rate, recharge is usually
less than precipitation because not all precipitation infiltrates the soil.
Geologic and soils data, are important in locating recharge and discharge areas and
in estimating recharge and discharge rates. Of particular importance are data on the
infiltration rates of soils, and the hydraulic conductivity and stratigraphy of the unsaturated
zone. Low-conductivity layers in the unsaturated zone may laterally deflect, or prevent the
recharge of, precipitation. Unconfined aquifers generally receive significant recharge from
direct percolation of precipitation into the aquifer. Confined aquifers, however, are usually
separated from the surface by relatively impermeable strata (See Figure 7A, Baldwin, 1963).
Recharge areas for confined aquifers may be some distance from the area of confinement.
Recharge to the confined area is primarily from lateral flow within the aquifer, although some
recharge is from vertical flow through confining layers. For more information on the types of
data needed to characterize geologic materials and aquifer confinement, see Components
#1, #4, and #5.
Because ground water flows from higher water level to lower water level, a comparison
of water levels from closely spaced wells, installed at different depths, provides the direction
of vertical flow. Upward flow indicates discharge area, downward flow, recharge areas.
Little ground water enters an aquifer where it is confined. Although some leakage
through the confining bed often occurs, confined areas are usually not considered to be
either recharge or discharge areas.
The principle governing ground water flow to or from a stream is the same as that
described above. If the elevation of the water surface of a stream is lower than the elevation
of the water level in a well screened either in the stream-bed sediments or in the ground
water below, then the stream is gaining water from the ground water reservoir and vice versa.
Interaction with surface water should also be considered in characterizing recharge
and discharge. Streams and wetlands are usually ground water discharge areas; however,
these surface features may also recharge aquifers depending on surrounding geology and
hydraulic and climatic conditions. Lakes frequently have recharge and discharge areas along
their length. The location of surface waters and their impact on ground water are, therefore,
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Ground Water Recharge and Discharge Characterization 77
important in determining overall recharge and discharge characteristics. For more information
on the types of data needed to assess ground water and surface water interaction, see
Component #7.
Methods
Methods employed to characterize ground water recharge and discharge include
literature searches and field methods. Frequently, information characterizing recharge and
discharge for a study area may already exist. Some data are easily obtainable. For example,
precipitation data are available from the National Oceanic and Atmospheric Administration
(NOAA). Soil survey information describing the upper 60 inches of material for most counties
in the United States is available from the U.S. Department of Agriculture, Soil Conservation
Service (SCS). SCS soil survey maps are often updated and maintained by local county soil
scientists or agricultural extension offices. Geologic information is available from the U.S.
Geological Survey (USGS) or State geological surveys.
One can often identify potential recharge and discharge areas based on a few factors,
such as the composition and areal distribution of geologic materials, on relevant water-level
data and/or infiltration rates. Where available, aerial photographs and satellite imagery,
particularly near infrared imagery, can provide insight into the location of ground water
discharge areas. For example, Keefer and Berg (1990) produced a map of potential aquifer
recharge areas in the State of Illinois by evaluating depth to the aquifer, the occurrence of
major aquifers, and the potential infiltration rate of the surficial soil materials. Computerized
Geographic Information Systems (GIS) may be useful in performing this type of analysis.
The data required to perform recharge and discharge analyses may be available from
the existing sources described above, or obtained through field methods that provide more
precise, site-specific information. For example, surface geophysical methods, such as
seismic reflection or refraction, electromagnetics, ground-penetrating radar, and electrical
resistivity/conductivity may be applied to a study area to examine the subsurface geology.
Similarly, well logs, core samples, test holes, and borehole geophysical logging provide
information about the soils, geology, and water level at a point of interest. The data may be
expanded to cover a study area by sampling at several selected points and correlating the
data. Monitoring wells, installed in clusters (i.e., groups of wells screened at various depths
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78 Component #6
in aquifers), can provide valuable information on the vertical component of ground water flow
within geologic deposits. The American Society for Testing and Materials (ASTM) publishes
methods for obtaining geologic data and applying them to ground water recharge mapping
(Andres, 1991).
The introduction of manmade tracers or use of natural tracers may aid in evaluating
and identifying recharge and discharge areas. For example, a tracer may be injected into an
aquifer to determine the flow rates within the aquifer and where the aquifer discharges into a
stream. Tracers may also be used to locate areas of ground water recharge from surface
water sources.
Recording and non-recording rain gauges can measure precipitation and provide
information on precipitation quantity and duration. Numerical estimates of average ground
water recharge rates begin with an analysis of precipitation data, and are developed either
through a flow-net analysis, a hydrologic budget, or use of a computer model.
Presentation of Data/Information
Recharge and discharge areas are usually displayed using two-dimensional maps.
Three-dimensional representations or figures showing recharge from and discharge to
aquifers or surface waters may also be useful in more detailed, site-specific studies. Relative
rankings of potential recharge rates or estimates of actual recharge rates can also be shown
on maps. If substantial amounts of data are available, a GIS may be useful to manage the
information (if digitized) and assist ground water scientists in developing initial drafts of
recharge and discharge maps. If numerical estimates of recharge rates are available, it may
also be beneficial to present this information in tables or in graphs, which are better suited to
displaying seasonal changes.
Considerations
Identifying recharge areas allows environmental planners to focus attention on areas
that may be particularly susceptible to contamination. Armed with information about recharge
areas, managers and planners may choose to provide more protection for these critical areas
rather than implement uniform protection policies across much larger areas.
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Ground Water Recharge and Discharge Characterization 79
In terms of scale, recharge and discharge have been characterized for areas ranging
in size from individual counties (Berg, Kempton, and Stecyk, 1984) to sections of States
(Rehm, Groenewold, and Peterson, 1982; Andres, 1991) to entire States (Keefer and Berg,
1990). Quantitative estimates of recharge and discharge are available in some cases, such
as Walton (1965) and O'Hearn and Gibb (1980). The resources required to characterize
recharge and discharge vary depending on the scale of the study, the level of detail required,
and the availability of existing information.
Using existing studies and maps to locate recharge and discharge areas requires
some effort; determining recharge and discharge rates is more difficult. Evaluation of ground
water recharge rates requires fairly detailed subsurface information. Use of a GIS may
simplify the process of assembling, storing, and managing georeferenced information and
may assist ground water scientists in developing initial maps if the data are available in digital
format. However, the costs of computer systems and staff time required to set up and
maintain a GIS, if one is not already available, can be significant. Mapping packages
available for personal computers can assist in developing simple maps.
If sufficient information does not exist for the study area, additional data collection will
probably be necessary. Data collection may include test-hole drilling and logging, log
interpretation, and water-level measurement and interpretation. Geophysical techniques
provide additional information but require sophisticated equipment and may be difficult to
conduct. Surface geophysical investigations can be performed rapidly but provide data that
are difficult to interpret. Tracer methods also have substantial labor and equipment demands,
although interpretation is much simpler. The presence of isotopes or other naturally
occurring tracers in ground water may reduce the costs of conducting tracer tests.
Estimation of actual ground water recharge rates generally requires existing field data
to be supplemented with additional information. Flow-net analysis is based on water-level
data and estimates of the hydraulic conductivity of the near-surface geologic formations. If
flow nets have not been constructed, information on the hydraulic head at various locations
and water-level depths throughout the study area should be collected and compiled. The
hydraulic conductivity of the surficial materials may be determined from actual measurements,
estimated from samples obtained from drilling cores or cuttings from test holes, or estimated
from geophysical data and well logs.
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80 Component #6
Citations
Andres, A.S., 1991. Methodology for Mapping Ground Water Recharge Areas in Delaware's
Coastal Plain. Delaware Geological Survey, Open File Report No. 34, 18 p.
Baldwin, H.L, 1963. A Primer on Ground Water. U S Geological Survey, p 8.
Berg, R.C., J.P. Kempton, and A.N. Stecyk, 1984. Geology for Planning in Boone and
Winnebaqo Counties. Illinois State Geological Survey, Circular 531, 69 p.
Heath, R.C., 1989. Basic Ground Water Hydrology. U.S. Geological Survey Water
Supply Paper 2220, p. 22.
Keefer, D.A. and R.C. Berg, 1990. Potential for Aquifer Recharge in Illinois (Appropriate
Recharge Areas). Illinois State Geological Survey, Map with discussion.
O'Hearn, M., and J.P. Gibb, 1980. Ground Water Discharge of Illinois Streams. Illinois State
Water Survey, Contract Report 246.
Rehm, B.W., G.H. Groenewold, and W.M. Peterson, 1982. Mechanisms. Distribution, and
Frequency of Ground Water Recharge in an Upland Area of Western North Dakota.
North Dakota Geological Survey, Report of Investigations 75, 72 p.
Walton, W.C., 1965. Ground Water Recharge and Runoff in Illinois. Illinois State Water
Survey, Report of Investigation 48, 55 p.
For More Information
For more information on this subject see the following references:
Berg, R.C., J.P. Kempton, and K. Cartwright, 1984. Potential for Contamination of Shallow
Aquifers in Illinois. Illinois State Geological Survey, Circular 532, 30 p.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated, Englewood
Cliffs, NJ, Chapter 6, pp. 203-217.
Kempton, J.P., 1981. Three-dimensional Geologic Mapping for Environmental Studies in
Illinois. Illinois State Geological Survey, Environmental Geology Note 100, 43 p.
U.S. Environmental Protection Agency, 1990. Handbook: Ground Water. Volume I: Ground
Water and Contamination (EPA/625/6-90/016a). Office of Research and Development,
Washington, DC, 144 p.
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Ground Water and Surface Water Interaction 81
Component #7: Ground Water and Surface Water Interaction
Definition
Ground water and surface water interaction refers to the movement of water between
a geologic unit and a surface water body. The volume and direction of that movement will
vary with time and geologic setting.
Objective
The objective of assessing ground water and surface water interaction is to determine
the qualitative and quantitative impacts of surface water and ground water on each other and
any potential human health and ecological impacts that may result. In some hydrogeologic
settings, it is necessary to assess shallow ground water and surface water as a single
system, because of the high degree of interaction between the two.
Data Needs
The data needed to assess ground water and surface water interaction are:
surface water and ground water hydrology (i.e., direction, quantity, and rate of
flow)
hydraulic properties, lithology, and mineralogy of geologic materials
surface water and ground water quality
ecological data (both for ground water and surface water)
sediment quality and type
precipitation and temporal changes
Surface water and ground water hydrology control the extent of ground water and
surface water interaction. The specific parameters of importance are direction of flow (from
ground water to surface water or vice versa), and rate and quantity of flow between ground
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82 Component #7
and surface water. These characteristics help determine the impact of surface water on the
quality and supply of ground water, and vice versa. Information on the boundaries of surface
water features such as rivers, streams, and wetlands, areas of ground water interaction with
surface water, and hydraulic connections is also necessary to completely understand surface
and ground water hydrology.
The U.S. Geological Survey (USGS) estimates that 40 percent of average annual
streamflow in the United States is derived from ground water (Moody, 1988). The interaction
of ground water and surface water, however, is not limited to ground water discharges to
surface water; surface water can also infiltrate to recharge the ground water reservoir. When
ground and surface waters are hydraulically connected, a change in the water level of either
affects the other. For example, during the beginning of dry periods that follow periods of
extended rainfall, streamflow may decrease substantially while the water table adjacent to the
stream may remain high allowing ground water discharges to the stream, adding to its flow.
After prolonged dry periods, both the stream and the water table would be low. Analogously,
following large or successive rainfall events, stream levels may rise more rapidly than ground
water levels, causing streamflow to enter the stream's banks. Figures 8a and 8b illustrate the
interaction between ground water and surface water (Heath, 1989). Human-induced impacts
may also affect the ground water/surface water relation. In a situation similar to that shown in
Figure 8b, Barari and others (1993) reported that the loss of water from a river to an aquifer,
due to pumping of municipal wells, was so great in 1988 that the river ceased flowing in the
vicinity of the municipal wellfield.
Ground water/surface water interactions can also be significant in areas where lakes
occur. Some wetlands may obtain a substantial portion of their water from ground water. The
hydrologic behavior of lakes is often strongly influenced by the ground water flow system
underlying them (Freeze and Cherry, 1979). Furthermore, interaction with underlying ground
water can be an important factor in determining the water budget of a lake. Lakes that have
well-defined inflowing and outflowing streams receive most of their water from surface water
contribution, while other lakes receive most of their water from discharges of underlying
ground water (Fetter, 1988). The degree and type of interaction between lakes and ground
water flow systems primarily depend on factors such as: the relative water level in each, the
nature of the sediments underlying the lake, and climate. In general, large lakes are typically
areas of net discharge of regional ground water systems (i.e., net water flows from the ground
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Figure 8A
Cross Section Showing Ground Water Discharging to Surface Water
Ground
Surface
Ground Water Flow
Source: After Baldwin, 1963
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Figure 8B
Cross Section Showing Surface Water Recharging to Ground Water
Source: After Heath, 1989
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Ground Water and Surface Water Interaction 85
water system to the lake), and small lakes in the upper portions of watersheds are usually
areas of net recharge for local ground water flow systems (Freeze and Cherry, 1979).
The hydraulic properties, lithology, and mineralogy of geologic units affect the
direction, quantity and quality of flow between ground water and surface water. The hydraulic
properties (e.g., hydraulic conductivity and porosity) of the geologic materials that comprise
the saturated and unsaturated zones influence the rate of interchange between ground water
and surface water (Seller and Berg, 1992). These hydraulic properties are a function, in part,
of lithology. The mineralogy of geologic units also affects water quality. For example, ground
water from calcareous aquifer materials that discharges to surface water may increase surface
water alkalinity. For more information on the types of data needed to characterize the
hydraulic properties of geologic units, see Component #4.
Information on the water quality of ground water and surface water is important in
understanding how ground water and surface water affect each other. For example, water-
quality data have been used to determine the flow between surface and ground water (e.g., in
a 1991 study of aquifers in the Nashua River Basin in Massachusetts) by deducing the extent
of the interchange of water from an analysis of the quality of two water bodies (USEPA, 1992).
Water-quality data could include information on the presence and concentration of natural
constituents, radionuclides, manmade contaminants, temperature, and pH. For more
information on the types of data needed to assess ground water quality, see Component
#10.
Ecological data may include inventories of: microorganisms, plants, animals, and
insects (e.g., measurements of the population or the relative abundance of various species).
For the purposes of determining ground water/surface water interaction, ecological data of
interest are those data related to the biota in and overlying the zone of interchange. These
ecological data may help define the boundaries of this zone, can be used as an indicator of
the ecological health of ecosystems and, indirectly, provide ground and surface water quality
information.
Sediment quality and type are factors affecting surface water quality, and, therefore,
may affect ground water quality through the interaction of surface and ground water
resources. Individual sediment particles, suspended in surface water or settled on stream
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86 Component #7
and lake bottoms, can carry thousands of molecules of pesticides, organic wastes, and other
chemicals (U.S. Department of Agriculture, 1989), Some organic chemical constituents of
ground water may also be adsorbed onto channel sediments. Fine-grained sediments that
accumulate on lake and stream bottoms create low-permeability layers that decrease the rate
of interchange between ground water and surface water. Positive correlations between
ground water chemistry and stream sediment chemistry may indicate interchange.
Knowledge of precipitation and resulting temporal changes are critical in assessing
surface and ground water interaction. Precipitation is directly or indirectly, the source of
ground and surface water recharge. As such, precipitation directly impacts ground and
surface water levels and quality. The transport of contaminants and contaminated sediments
by overland flow to streams impacts surface water quality. Surface water infiltration can
transport these contaminants into the ground water. Temporal changes, due in large part to
seasonal fluctuations in precipitation or climate, but also to daily fluctuations such as tidal
cycles, may impact the relation between ground and surface water levels, and thus affect the
direction, quantity and quality of interaction. For example, as discussed earlier, seasonal
fluctuations in hydrological and meteorological conditions can result in cyclical variation in
exchanges of water. Understanding temporal variations is helpful for a comprehensive
assessment of the interaction of ground water and surface water.
Methods
A number of methods can be used to assess the extent of ground water and surface
water interaction. These methods include:
literature search
geological characterization
direct field measurement
indicator studies
hydrograph separation
numerical flow models
Some information on ground water and surface water interaction for any given area
may already exist. Therefore, a search of available literature is advisable. The literature
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Ground Water and Surface Water Interaction 87
search should include both published and unpublished materials, such as maps, reports, and
monographs. Some types of data, including information on geologic units and climate (e.g.,
precipitation), may be available from sources, such as the USGS, the U.S. Department of
Agriculture, or the National Oceanic and Atmospheric Administration (NOAA). Federal, State,
and local agencies with responsibility for ground water or surface water protection may have
additional information. Where available, aerial and satellite imagery may provide cost-effective
information on the locations of areas of ground water/surface water interaction.
Other methods exist for obtaining data. The magnitude of ground water and surface
water flow at specific points can be determined in the field with equipment such as seepage
meters and piezometers. These devices are inserted into and/or through the sediments of a
lake or stream or along a profile from uplands through a stream. The instruments may
provide a rough estimate of ground water/surface water exchange. There are, however,
numerous field-related problems associated with the use and collection of reliable data with
these devices. Data collected from these devices, from observation wells, or from water table
contour maps, along with estimates of the hydraulic conductivity and the cross-sectional area
of the aquifer that is hydraulically connected to a stream, can form the basis for ground water
flow measurement. Applying Darcy's Law to this information can provide an estimate of the
ground water flow rate.
Ecological data can be collected using field methods that measure populations and
other ecologic variables. These data can then be used to measure ecologic health. For
example, the Ohio EPA has developed an index, the Qualitative Habitat Evaluation Index, that
reports a stream's water quality as estimated by a survey of relevant habitat parameters (U.S.
Department of Agriculture, 1992). In general, an ecological assessment of surface water
quality is performed either by measuring the population of specific indicator organisms or
assessing the health of the ecosystem as a whole by measuring the diversity and relative
abundance of the species present. The similar use of ground water fauna to assess ground
water quality has also been suggested in the literature, although not utilized extensively (Ward
and Stanford, 1989; Ward, Voelz, and Harvey, 1989). As methods for assessing the
importance of ground water ecosystems become available, they can be incorporated into the
overall resource assessment.
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Component #7
Indicator studies that measure ground water and surface water interchange include
isotopic studies and tracer investigations. These techniques can provide information on flow
velocity and direction and can be adapted to cover sizeable streams and lakes Isotopic
methods rely on the comparison of the concentrations of such naturally-occurring isotopes as
oxygen or hydrogen in the ground water and in the stream to estimate the share of
streamflow derived from ground water.
Tracer studies, such as those described by Bencala (1984) or Castro and Hornberger
(1991) may yield approximations of the "mixing" of stream water with the adjacent and
underlying ground water in alluvium. An example of the use of ground water tracers is shown
in Figure 9 (USEPA, 1987). In this Figure, the tracer (T) is placed into the surface water at the
sinking stream. The tracer will flow with the ground water and may be detected at
downgradient sampling locations. Once the tracer is identified through sampling, ground
water scientists can determine the direction and velocity of the ground water flow and any
interaction between surface and ground water. Depending on the relationship of the
interaction between the ground water and surface water bodies, tracers may also be used to
estimate time of travel from specific points in the aquifer to the discharge point in a stream, or
from the stream to a specific point in the aquifer. Tracers may include anions such as
chloride and bromide; cations such as strontium, potassium, sodium, and lithium; dyes such
as fluorescein and rhodamine WT; and naturally occurring substances.
Ground water and surface water interaction can also be assessed on a wider scale,
often indirectly. For example, during the dry season, ground water discharge (i.e., base flow)
may account for the entire flow of a stream. When streamflow has contributions from both
surface water runoff and base flow, the portion that is base flow can be estimated using a
variety of techniques. One such technique is hydrograph separation, which is the analysis of
streamflow over time to estimate the relative contributions of surface runoff, ground water
discharge, and shallow lateral subsurface flow above the water table (i.e., interflow). Soil
interflow can account for a large percentage of runoff in watersheds having thin, permeable
soils overlying low-permeability, fractured bedrock (Fetter, 1988). Hydrograph separation may
be applied to a range of watersheds, from those of small streams to major river basins
(USEPA, 1990).
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Figure 9
Use of Ground Water Tracer to Check Source of Water at Discharge
Point in Streambed
Sinking Stream
Sampling Point
f
Stream
Source: USEPA, 1987
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90 Component #7
Regression analysis and numerical flow models use watershed data to estimate
ground water and surface water interaction, usually on a watershed-wide scale. Regression
analysis correlates the base flow with stream-basin characteristics, such as the drainage area
of the watershed or the flow duration ratio. The flow duration ratio is a comparison of the
frequency of the low flow rate of the stream with the frequency of its higher flow rate.
Numerical flow models generally divide flow systems into a finite set of geographic cells with
differing hydrologic properties. The models can generate an estimate of ground water
discharge for each cell. Seepage studies can also be used to determine the quantity and
quality of ground water discharging to a surface water body at multiple points. In a seepage
study, measurements of streamflow are used to construct water balances for reaches
between measurement sites. Calculation of ground water discharge is used to identify
gaining or losing reaches.
Presentation of Data/Information
Data and information produced by the methods mentioned above can be presented in
various forms. Maps can illustrate the locations of significant ground water and surface water
interaction, and indicate flow direction. Tables or graphs may be more appropriate for
presenting quantitative information and for illustrating temporal changes. For example, water
quality information for specific sample points may be presented in tables. These forms of
presenting data may also be used together. A map might show collection points and trends
in the quality of ground and surface water in a region, while a table might display the relative
abundance of various biological species in a specific water body. If substantial amounts of
georeferenced data area available, a Geographic Information System (GIS) may be useful to
assemble, store, and manage the information and assist ground water scientists in the
development of maps.
Considerations
Managers need to consider the fact that all methods of assessing ground water and
surface water interaction have limitations. Also, not all methods are universally applicable.
For example, direct measurement of ground water flow using seepage meters may provide
acceptable data for a specific point over a period of time, but may introduce large errors
when extrapolated over extended time frames or a large area. Hydrograph separation and
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Ground Water and Surface Water Interaction 91
numerical methods may be effective for larger areas, but these methods generally provide
little information on local areas of ground water and surface water interaction.
The applicability of individual methods is also dependent on the hydrogeologic setting.
The application of some methods may be inappropriate in areas: with karst geology and
variable base flow, with peaking after rainfall or snowmelt events, or with numerous seeps.
For example, applying typical hydrograph separation techniques in these areas may provide
gross underestimates of the ground water discharge component of the hydrograph.
In applying all of the methods discussed above, careful attention should be given to
determining the temporal fluctuations. Data covering only a snapshot in time will not
accurately depict temporal variations in ground water and surface water interaction. At
different times throughout the year, the direction, quantity, and quality of flow between ground
water and surface water may differ. Also, the intermittent pumping of nearby wells can have a
pronounced effect on local water levels. Unless the effects of well pumpage on the
potentiometric surface are specifically desired, personnel responsible for collection of water-
level data should avoid collection of data from or near a well that is pumping or has recently
been pumped. Pumping artificially lowers the potentiometric surface, which may take some
period of time to return to equilibrium. Tides may also affect water levels in wells. Managers
should consider this effect when interpreting water-level data in tidal areas.
The methods described above may require investment in equipment ranging from 55-
gallon drums (used as seepage meters) to sophisticated electrical probes (for geophysical
investigations) and expensive mainframe or minicomputers (for numerical flow models).
Isotope or tracer studies covering large areas can similarly require a significant commitment
of resources. The presence of naturally-occurring chemicals that can be used as tracers,
however, can help reduce this resource demand. More generalized methods may be
appropriate for larger areas. Application of numerical flow models may be extremely
resource-intensive, but may provide the most reliable results for large study areas. Clearly,
the resource commitment will vary depending on the method selected and the scope of the
study.
One final consideration is that the interaction of ground water and surface water and
the significance of this interaction in terms of water quality and ecological effects is an
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92 Component #7
emerging field of study. Therefore, existing information may be limited, and some older
information may be based on outdated methods and have limited usefulness. Thus, any
assessment of ground water and surface water interchange should examine the implications
of new developments in this area.
Citations
Barari, A., D.L lies, and T.C. Cowman, 1993. Chapter 4, "Wellhead Protection and Monitoring
Options for the Sioux Falls Airport Wellfield, South Dakota": in B.A. Moore (co-author
and editor), Case Studies in Wellhead Protection Area Delineation and Monitoring.
Environmental Monitoring Systems Laboratory, Office of Research and Development,
U.S. Environmental Protection Agency, Las Vegas, NV.
Bencala, K.E., 1984. "Interactions of Solutes and Streambed Sediment: A Dynamic Analysis
of Coupled Hydrologic and Chemical Processes that Determine Solute Transport."
Water Resources Research. 20(12), pp. 1804-1814.
Castro, N.M. and G.M. Hornberger, 1991. "Surface-Subsurface Water Interactions in an
Alluviated Mountain Stream Channel." Water Resources Research. 27, pp. 1612-1621.
Fetter, C.W., 1988. Applied Hydrogeology. Second Edition, Merrill Publishing Company,
Columbus, OH, 592 p.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated, Englewood
Cliffs, NJ, pp. 217-229.
Heath, R.C., 1989. Basic Ground Water Hydrology. U.S. Geological Survey Water
Supply Paper 2220, p. 22.
Seller, D.R., and R.C. Berg, 1992. "A Model for the Assessment of Aquifer Contamination
Potential Based on Regional Geologic Framework." Environmental Geology and Water
Sciences. 19 (3), pp. 205-213.
U.S. Department of Agriculture, 1992. Water Quality Tool Inventory. National Water Quality
Technology Development Staff, Fort Worth, Texas.
U.S. Department of Agriculture, 1989. Water Quality Indicators Guide: Surface Waters. A
Teacher's Handbook. U.S. Department of Agriculture and National Council for
Agricultural Education, 129 p.
U.S. Environmental Protection Agency, 1992. Review of Select State and Local Ground Water
Resource Assessments. U.S. Environmental Protection Agency, Region VIII, Water
Management Division, 58 p.
U.S. Environmental Protection Agency, 1990. Handbook: Ground Water. Volume I: Ground
Water and Contamination (EPA/625/6-90/016a). Office of Research and Development,
Washington, DC, 144 p.
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Ground Water and Surface Water Interaction 93
U.S. Environmental Protection Agency, 1987. Handbook: Ground Water (EPA/625/6-87/016).
Office of Research and Development, Washington, DC, Figure 7-6 C, p. 131.
Moody, D.W., and others, Compilers, 1988. National Water Summary - 1986. U.S. Geological
Survey Water Supply Paper 2325, p. 3,
Ward, J.V., and J.A, Stanford, 1989. "Ground Water Animals of Alluvial River Systems: A
Potential Management Tool." Proceedings of the Colorado Water Engineering and
Management Conference, pp. 393-399.
Ward, J.V., N.J. Voelz, and J.H. Harvey, 1989. Groundwater Faunas as Indicators of
Groundwater Quality: The South Platte River System. Colorado Water Resources
Research Institute, Colorado State University, 32 p.
For More Information
For more information on this subject see the following references:
Dunne, T, and LB. Leopold, 1978. Water in Environmental Planning. W.H. Freeman and
Company, New York, NY, 818 p.
Goodman, J., J.M. Collins, and K.B. Rapp, 1992. "Nitrate and Pesticide Occurrence in
Shallow Groundwater During the Oakwood Lakes -- Poinsett RCWP Project": in The
National Rural Clean Water Program Symposium --10 Years of Controlling Agricultural
Nonpoint Source Pollution: The RCWP Experience (EPA/625/R-92/006), U.S.
Environmental Protection Agency, Office of Research and Development, and Office of
Water, Washington, DC, 400 p.
Jennings, J.N., 1971. Karst. MIT Press, Cambridge, MA, 252 p.
Nield, S.P. and LR. Townley, in press. "A Framework for Quantitative Analysis of Surface
Water-Ground Water Interactions: Flow Geometry in Vertical Section." Water
Resources Research.
U.S. Environmental Protection Agency, 1991. A Review of Methods for Assessing Nonpoint
Source Contaminated Ground Water Discharge to Surface Water (EPA 570/9-91-010).
Office of Water, Washington, DC, 99 p.
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94 Component #8
Component #8: Ground Water Budget
Definition
A ground water budget is a quantification of all the natural and anthropogenic gains of
water to, and losses of water from, the ground water reservoir.
Objective
A ground water budget can be used to make a qualitative and/or quantitative
assessment: of ground water flow into or out of the ground water reservoir, of ground water
storage in the reservoir, and of the response of water levels to varying amounts of recharge
and discharge. Ground water budgets assist managers in assessing the current extent of
ground water recharge and in forecasting possible supply inadequacies resulting from
increased ground water use.
Data Needs
The information needed to develop a ground water budget should include all the
available data regarding the amounts of water traveling through the different parts of the
hydrologic cycle. Components of the hydrologic cycle that should be included in developing
a ground water budget are shown in Figure 10 (Walker, 1993). The following data are
essential in preparing a ground water budget:
hydrologic data
quantity of evapotranspiration
aquifer and overlying and underlying material characteristics
anthropogenic additions to and withdrawals from the ground water reservoir
Hydrologic data, including precipitation and streamflow information, are needed to
estimate the amount of water reaching the ground surface and, potentially, ground water
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Figure 10
Water Budget
Evapotranspiration From
Surface-Water Bodies, Land
Surface and Vegetation
Atmospheric Moisture
/ / Precipitation / /
Evaporation
From Oceans
Source: After Waller, 1993
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96 Component #8
Precipitation infiltrating through the soil and reaching the zone of saturation becomes part of
the ground water flow system.
A number of factors determines the rate of runoff and infiltration of precipitation,
including permeability of soils, rate of precipitation, vegetative cover, time of year, and the
slope of the receiving area. Urban and other developed surfaces, soils with low permeability,
and unvegetated open tracts of land tend to produce less infiltration and more runoff than
naturally vegetated, undisturbed areas. Runoff also occurs once soils reach field capacity
and can no longer accept water into storage. The rate, intensity, and duration of precipitation
are also important factors in determining the amount of runoff. Storms producing moderate
amounts of rainfall over extended periods of time generally supply significantly more recharge
than short duration, intense storms, because precipitation from heavy storms is introduced
more rapidly than it can infiltrate the ground surface. Finally, land slope (i.e., topography)
influences the amount of water entering the soil or surface water; for the same surficial-
sediment type, steep slopes or mountainous regions produce more runoff than areas of lower
relief. Refer to Component #6 for further discussion characterizing ground water recharge
and discharge.
Evapotranspiration is the total amount of water traveling from the land to the
atmosphere by (1) evaporation of open waters, (2) evaporation from soil surfaces and shallow
water tables, and (3) transpiration of water from the soil by plants (Freeze and Cherry, 1979).
Evapotranspiration is affected by the local climate, amount and types of vegetation, and the
local soil characteristics. With respect to the water budget, evapotranspired water is
unavailable to ground water reservoirs. Measurement of evapotranspiration is extremely
complex and estimates for a given region will vary widely.
Aquifer and overlying and underlying material characteristics influence the rate of
ground water recharge and discharge. An aquifer may be in equilibrium, meaning that the
amount of recharge equals the amount of discharge, with the potentiometric surface for
confined aquifers and the water table for unconfined aquifers remaining constant over time.
Most often, however, recharge and discharge are unequal and the water-table
surface/potentiometric surface fluctuates over time. This fluctuation, as measured by changes
in water levels in wells, can be used to estimate changes in the volume of water stored in the
aquifer, a factor that must be accounted for in the water budget.
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Ground Water Budget 97
Anthropogenic additions and withdrawals of ground and/or surface water (i.e.,
imported and exported water) should be taken into account when preparing a ground water
budget. Localized surface water extractions may have a negative impact on the ground water
system if the surface water feature is a source of ground water recharge. Extraction of water
by wells reduces the amount of available ground water. Conversely, water may be added to
the ground water system by sewage discharges, return flow from irrigation, and recharge via
wells to control subsidence or salt water intrusion.
Methods
Once estimates for all factors have been obtained, a ground water budget can be
calculated through the use of a simple arithmetic equation. The equation may be solved for
any of its variables if the other quantities are known. Results of the equation should be used
with caution, however, because errors can occur in estimating some of the variables. The
equation is as follows:
Net ground water recharge (change in ground water in storage) =
(infiltrated precipitation + surface water inflow +
imported water + ground water inflow)
- (evapotranspiration + surface water outflow +
exported water + ground water outflow)
For the purpose of the ground water budget, each of these terms is defined as follows:
Infiltrated precipitation is the quantity of precipitation that reaches the
saturated zone
Surface water inflow is the quantity of surface water that recharges the
ground water reservoir via ground water/surface water interaction
Imported water is the quantity of water that is recharged to the aquifer
artificially (i.e., by man) for such purposes as storage, disposal, or
replenishment of ground water resources
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98 Component #8
Ground water inflow is the quantity of ground water that enters the ground
water reservoir from areas upgradient of the region of consideration
Evapotranspiration is the combined quantity of water entering the atmosphere
through evaporation from soil surfaces and shallow water tables, transpiration
from the soil by plants, and evaporation from open bodies of surface water
hydraulically connected to the ground water reservoir
Surface water outflow is the quantity of ground water discharged to wetlands
lakes, streams, drainage ditches, and/or rivers that are hydraulically connected
to the ground water reservoir
Exported water is ground water that is removed from the aquifer by man via
wells
Ground water outflow is the quantity of ground water that exits the ground
water reservoir to areas downgradient from the region of consideration
Various methods can be used to obtain the data necessary to complete a ground
water budget. These methods, including literature searches and field/laboratory techniques
discussed under other Components, can be used to collect the following data:
precipitation data
aquifer characteristics
stream discharges
anthropogenic additions and withdrawals
soil maps and profiles
evapotranspiration
Precipitation data, stream discharges, and soil information can be readily obtained by
contacting Federal, State and local agencies. The National Oceanic and Atmospheric
Administration (NOAA) maintains rainfall records for reporting stations throughout the United
States, as well as pan evaporation data for selected stations. The U.S. Geological Survey
(USGS), and State and local agencies often maintain stream discharge data. Soil maps and a
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Ground Water Budget 99
soils data base are maintained by the Soil Conservation Service (SCS) for many localities and
are updated by county soil scientists familiar with local conditions.
Evapotranspiration can be measured in a traditional (non-suction) lysimeter. This
device is a field apparatus containing soil and vegetation that is used to approximate
evapotranspiration under actual field conditions. Pan-evaporation rates in the field can also
be used to estimate evaporation. Alternatively, evapotranspiration can be estimated using
empirical methods that assume an upper limit to the amount of evapotranspiration possible,
and assign a quantity to potential loss of water by evapotranspiration that relies on climatic
variables (Fetter, 1988). One of these methods, devised by Thornthwaite, uses air
temperature as an index of the amount of energy available for evapotranspiration (Dunne and
Leopold, 1978). Potential evapotranspiration is expressed as a function of mean monthly air
temperature and average monthly sunlight, expressed as a function of month and latitude.
This method is fairly accurate for estimated annual potential evapotranspiration, particularly in
humid areas; however, because it does not account for types or rates of growth of
vegetation, the method is inadequate for estimating potential evapotranspiration in the spring
and early summer growing seasons (Fetter, 1988).
Aquifer characteristics effect the amount of ground water that can be held in storage in
the ground water reservoir. Aquifer characteristics may be determined from existing data from
subsurface investigations, or if no data exist, from aquifer tests, well logs, and samples of
geologic materials.
Records of anthropogenic influences on ground water systems are often scarce in
some regions of the United States. Records of the number of pumping wells within the
ground water reservoir can often be found in local health department files, State geologic
surveys, State agency well registration programs, or water regulatory or research agencies.
Records of industrial discharge into surface and ground water may be scarce and/or
inaccurate. Anthropogenic additions or withdrawals may be negligible in comparison to the
amount of natural ground water recharge and discharge in humid areas. However,
particularly in arid and semi-arid climates, these additions or withdrawals may be significant.
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100 Component #8
Presentation of Data/Information
Identifying local and regional recharge and discharge areas, which are important in
determining a ground water budget, should be a goal of the presentation of data. This
presentation would be similar to those for the recharge and discharge characterization found
in Component #6. Topographic, geologic, and soils information are usually displayed on
two-dimensional maps. These data are helpful in locating recharge and discharge areas.
Hydrologic information, aquifer characteristics and related data can be compiled into tables
and charts. Geographical Information Systems (GIS) may be helpful to ground water
scientists in assembling, storing, and managing georeferenced information and in producing
initial estimates of the positions of map contours and hydrologic boundaries. For each
parameter in the ground water budget equation, values obtained for different ground water
study areas can be presented in tabular, graphical or matrix form for ease of comparison.
Considerations
Quantification of the parameters in a ground water budget may rely primarily on
existing data. Special care should be exercised, however, in correlating the ground water
budget of one area to that of another or to a large region because hydrologic, geologic, and
anthropogenic parameters can vary over small distances.
Managers will find calculations of the amounts of ground water recharge and
discharge important in planning for the future use of ground water resources. Expected and
future withdrawals from an aquifer can be compared to the existing recharge to determine the
availability of, and impact on sustainable ground water supplies.
Managers should be aware that pumping water from an aquifer will lower the aquifer's
potentiometric surface or water table even if the amount of water withdrawn is less than the
natural recharge. This occurs because the natural (i.e., predevelopment) potentiometric
surface or water table of an aquifer depends on the equilibrium conditions of natural recharge
and discharge. Removing water stored in an aquifer lowers aquifer water-levels and reduces
the natural flow of ground water to those surface water bodies that are in connection with the
aquifer. Withdrawal of ground water may induce additional recharge from surface sources,
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Ground Water Budget
lowering lake levels and reducing wetlands and stream flows. Ground water withdrawals from
one aquifer can induce leakage from adjoining stratigraphic layers.
Error in the result of the water-budget equation is the result of all the errors
incorporated into the individual components^ Several of the components are particularly
difficult to accurately estimate. Calibration of a computer model of ground water flow
produces a balance between ground water recharge and discharge, plus or minus changes in
storage. Oftentimes, recharge is estimated as part of the calibration process.
Citations
Dunne, T. and LB. Leopold, 1978. Water in Environmental Planning W.H. Freeman and Co
San Francisco, CA, pp. 136-138.
Fetter, C.W., 1988. Applied Hvdroaeoloqy Second Edition, Merrill Publishing Companv
Columbus, OH, pp. 433-448.
Freeze, R.A., and JA Cherry, 1979. Groundwater. Prentice-Hall, Incorporated Enqlewood
Cliffs, NJ, pp. 203-217. '
Waller, P.M., 1993. Ground Water and the Rural Homeowner. U.S. Geological Survey, p. 5.
For More Information
For more information on this subject see the following references:
Andres, A.S., 1991. Methodology for Mapping Ground Water Recharge Areas in Delaware's
Coastal Plain. Delaware Geological Survey Open File Report No. 34, 18 p.
Burch, S.L, 1991. The New Chicago Model: A Reassessment of the Impact of Lake
Michigan Allocations on the Cambrian-Ordovician Aquifer System in Northeastern
Illinois. Illinois State Water Survey Research Report 119, 52 p.
Roadcap, G.S., S.J. Cravens, and E. Smith, in press. Meeting the Demand for Water- An
Evaluation of the Shallow Ground Water Resources in Will and Southern Cook
Counties. Illinois. Illinois State Water Survey Research Report
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102 Component #9
Component #9: Chemical and Physical Characteristics of
Aquifers and Overlying and Underlying Materials
Definition
Chemical characteristics of an aquifer and its overlying and underlying units are
distinguishing attributes that describe the chemical composition of these geologic materials.
Physical characteristics refer to the texture and structure of these geologic materials.
Objective
The objective of this element is to provide basic information on the chemical and
physical properties of the geologic materials that are in contact with ground water, in order to
better understand their impact on water quality and the fate and transport of contaminants.
Data Needs
To assess these characteristics, data relating to each of the following three zones
should be collected:
(1) soil material (weathered surface layer that supports plant growth)
(2) unsaturated geologic materials underlying the soil
(3) saturated geologic materials (confining units and aquifers)
These data should include the following:
overall mineralogy of the material
overall chemistry of materials
content and distribution of organic matter, plant material, and bacteria
physical characteristics (texture and structure) of materials
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Chemical & Physical Characteristics of Aquifers & Overlying & Underlying Materials 103
depositional nature of sedimentary materials and degree of fracturing
climatic variables
moisture content
hydraulic characteristics of the material in each layer
advection and hydrodynamic dispersion characteristics
degradation characteristics
cation and anion exchange capacity
Information about the overall mineralogy of the geologic material comprising a zone
can provide a better understanding of the zone's chemical and physical characteristics
(Freeze and Cherry, 1979). For example, minerals may be relatively soluble, leading to the
formation of conduits or karst conditions that result in rapid transport of contaminants into or
through the aquifer. Mineralogy also affects the type and amount of small chemical charges
present on the surface of geologic particles. These charges determine the cation and anion
exchange capacity of the material, i.e., the capacity of the material to retain charged particles
such as contaminants (Fetter, 1988). Pore water chemistry of subsurface geologic units is
greatly affected by the mineralogy of the geologic materials (Pucci, et al, 1992). Swelling
clays, which expand when wetted and are of low permeability, exhibit highly variable
infiltration capacities. During drying, they contract and may develop dessication cracks.
Precipitation following dry periods readily infiltrates the cracks before they swell, and provides
rapid potential recharge and a transport mechanism for contaminants. Although the rate of
dissolution of silica is extremely small, in bedrock aquifers composed of igneous and/or
metamorphic rocks, the width of fractures can increase as recharge water dissolves silica
from fracture walls (Freeze and Cherry, 1979). Chemical characteristics of materials of an
aquifer and its overlying and underlying formations also affect the interactions, conversions,
and degradation of constituents migrating toward or through the aquifer.
Naturally-occurring, non-living organic matter is relatively insoluble and tends to
accumulate near the surface of the soil. This organic matter, generally in the form of humus
(i.e., partially decomposed plant and animal material), may have very high cation and anion
exchange capacities and tends to capture some portion of potential contaminants before they
enter the ground water (Fetter, 1988). Organic matter may also be found in underlying
paleosols (i.e., buried soils). A total organic carbon analysis can determine the amount of
organic matter in a representative sample of soil. Living material may affect aquifer
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104 Component #9
susceptibility to contamination by temporarily immobilizing contaminants through biological
uptake. Plants growing on the soil layer can also affect susceptibility by modifying the
hydrologic balance. Soil water uptake by plants decreases the amount of water recharging
the aquifer, thereby decreasing the potential contaminant transport mechanism to the aquifer.
Absence of vegetation is conducive to runoff, regardless of the soil permeability (Hanks and
Ashcroft, 1980).
Information on the physical characteristics (texture and structure) of materials is
important for determining their hydraulic properties (Taylor and Ashcroft, 1972). As discussed
in Component #4, texture and structure determine the porosity of unconsolidated media.
Texture is a measure of the size distribution of particles that compose sedimentary geologic
material. Geologic material comprised of well-sorted (fairly equal-sized) particles generally is
more porous than poorly sorted material. Structure is defined by the arrangement of particles
within the material. The arrangement (packing) of particles controls the ability of fluids to
travel through the material. Loose packing can correspond with little resistance to flow (even
with small particle size) and tight packing can indicate a restriction of flow (Hanks and
Ashcroft, 1980). Preferred pathways, such as macropores that develop when large plant
roots are removed or when desiccation cracks form can develop in surficial materials and
"short circuit" the flow of water through these materials.
The degree of fracturing in igneous, metamorphic and sedimentary rocks can
indicate the potential for fluid to flow through these materials. Porosities of unfractured
igneous and metamorphic rocks are generally very low; however, fractures that have
developed in these rocks and in consolidated sedimentary rocks, because of structural
activity (e.g., folding and faulting), can, if interconnected, dramatically increase hydraulic
conductivity and increase the flow of ground water and migration of contaminants. Fractures
can be widened through the dissolution of silica in the rock matrix by recharging ground
water, thereby further increasing permeabilities. The depositional nature of volcanic rocks can
provide information on their physical characteristics of a zone. For example, lava often
covers gravels deposited by streams flowing over previously deposited lavas, thus creating
rock masses with gravel interbeds that can have high bulk permeability (Freeze and Cherry,
1979).
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Chemical & Physical Characteristics of Aquifers & Overlying & Underlying Materials
105
The depositional nature of sedimentary materials can provide insight into the
physical characteristics of the materials. For example, rivers and streams tend to deposit
their coarsest materials near streambanks and increasing amounts of finer materials at
increasing distances from the stream. Stream-deposited materials also are often seasonally
layered as the result of flooding and erosive storm events. Sedimentary materials formed by
lake deposition tend to be fine and tightly-packed, while airborne sedimentary materials tend
to be fine and loosely-packed (Ritter, 1986),
The fate and transport of contaminants in the subsurface is also related to the area's
climatic variables. In particular, precipitation and subsequent infiltration have an important
effect on the movement of contaminants through the subsurface. See Component #8 for a
discussion of the ground water budget and the importance of climate.
Moisture content is an indication of the water-storage capability of the soil layer.
Moisture content is related to the physical characteristics of the soil, the hydraulic pressure
head in the soil and whether the soil is drying or being wetted (Freeze and Cherry, 1979).
The hydraulic characteristics of a geologic material are a measure of the material's
capacity to hold and transmit water. A discussion of hydraulic characteristics can be found in
Component #4.
Two physical processes that determine contaminant migration through porous
geologic media are advection and hydrodynamic dispersion (Freeze and Cherry, 1979).
Advection is the transport of contaminants by flowing ground water. Hydrodynamic
dispersion is the spreading of dissolved contaminants due to both molecular diffusion and
mixing caused by ground water flow. As a contaminant is dispersed through the ground
water, the concentration of the contaminant may decrease (through dilution) below detection
limits. Decreases in contaminant concentrations due to dilution do not indicate a decrease in
the total mass of contaminants.
Organic contaminants are subject to the process of degradation that may change the
chemical constituents of contaminants into other hazardous or non-hazardous constituents.
The primary form for degradation is microbial action in aerated porous media. As conditions
for microbial action in an aerobic environment are more likely to exist near the soil surface,
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Component #9
degradation will occur primarily in the soil layer. Organic contaminants vary greatly in the rate
at which they microbially degrade. The rate at which an organic contaminant degrades
depends on the concentration of the contaminant and the chemical properties of constituents
within the contaminant. Organic-contaminant degradation rates tend to decrease
exponentially with decreasing contaminant concentration. Degradation rates for organic
chemical constituents are expressed in terms of the number of days required to degrade one-
half of the constituent mass (i.e., half-life).
As previously discussed, the cation and anion exchange capacity of organic matter
and geologic media tend to retard the migration of contaminants. The combined effect of
these advection-resisting forces is a contaminant concentration that decreases with distance
(i.e., attenuation) from the point of contamination (Fetter, 1988).
Methods
To meet the objective of this Component, the methods discussed herein include not
only methods to compile information on chemical and physical characteristics of geologic
materials, but also methods to use this information to predict the extent and concentration of
contaminants within aquifers and their overlying and underlying materials. Data on the
chemical and physical characteristics of geologic materials can be collected through a
literature search of existing data and by using a combination of field and laboratory methods.
The collected chemical and physical characteristics data can then be used in chemical fate
and transport models to predict the extent and concentration of contaminants.
A literature search for existing data may significantly reduce the resources required to
adequately define the chemical and physical characteristics of the aquifer and its
overlying/underlying materials. A large amount of data on the study area may exist in
published and unpublished reports (see Components #1, #2 and #4). The U.S.
Environmental Protection Agency (EPA) offices, such as those that oversee the Resource
Conservation and Recovery Act, Superfund, Underground Storage Tank, and Underground
Injection Control regulatory programs, require hydrogeologic data from facility owners and
operators including information about chemical and physical characteristics of aquifers and
their overlying materials. Sources of data obtained through a literature search may include
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Chemical & Physical Characteristics of Aquifers & Overlying & Underlying Materials 107
well logs, geologic information (including maps and cross-sections), soil surveys, ground
water reports, and computerized data bases.
Data on the chemical and physical characteristics of geologic media can be obtained
from such publications, institutions, and agencies as:
U.S. Geological Survey (USGS) and State geological surveys (geologic and
hydrogeologic maps and reports)
U.S. Department of Agriculture's Soil Conservation Service (SCS) (soil surveys
and data bases)
State land grant and other universities and their extension services, geology
departments, and soil science departments
EPA Environmental Research Laboratories in Ada, Oklahoma and Athens,
Georgia.
It is important to note that the fate and transport of contaminants are greatly affected
by interactions between the contaminant and geologic materials. To fully understand fate and
transport, therefore, it is also necessary to know the specific chemical and physical
characteristics of the contaminant(s). Once contaminants of interest have been identified,
information on their characteristics can be obtained through various chemical data bases.
For a listing of such data bases see Table 3.
Due to the number of potential contaminants and the potentially complex interactions
between these contaminants and geologic materials, a discussion of the chemical and
physical characteristics of specific contaminants is beyond the scope of this document.
However, further information can be obtained from the U.S. Department of Energy's
Multimedia Environmental Pollutant Assessment System (MEPAS) (Pacific Northwest
Laboratory, 1987) or from the American Chemical Society's Handbook of Chemical Property
Estimation Methods (Lyman et al., 1990). Soil-water partition coefficients for organic
pollutants are found in Fetter (1988). The Data Collection Handbook Supporting Modeling
the Impacts of Radionuclide Material in Soil (Argonne National Laboratory, 1993), prepared for
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108
Component #9
Table 3
Chemical Data Bases Containing Properties
of Common Ground Water Contaminants
Data Base
CHEMEST
DATALOG
CHEMFATE
QSAR
ENVIROFATE
Description
Properties of organic compounds,
including water solubility, soil adsorption
coefficient, vapor pressure, water
volatilization rate, liquid viscosity, and
Henry's Law Constant
Properties of 12,000 organic compounds
and metals, including water solubility,
octanol/water partition coefficient, vapor
pressure, ultraviolet spectra, dissociation
constant, soil adsorption coefficient,
evaporation rate, Henry's Law Constant,
biodegradation, and photoxidation
Properties of 1 ,730 chemicals including
chemodynamic properties (e.g., log
octanol/water partition coefficient, log
acid dissociation constant, soil
adsorption coefficient), transport
properties (e.g., bioconcentration,
evaporation from water, Henry's Law
Constant, soil column transport),
degradation data (e.g., microbial
degradation, oxidation, and photolysis),
and water and soil monitoring data
Properties of 56,000 chemicals, including
water solubility, pKa (expression of
strength of organic acids and bases),
log octanol/water partition coefficient,
and 1 1 structure-activity-relationship
(SAR) models that can be used to
calculate physical-chemical properties
Transport and degradation properties of
more than 800 chemicals, including
biodegradation, oxidation, hydrolysis,
water solubility, and vapor pressure
Vendor
Technical
Database
Services,
Inc.
Technical
Database
Services,
Inc.
Technical
Database
Services,
Inc.
Technical
Database
Services,
Inc.
Chemical
Information
Systems,
Inc.
Address
10 Columbus
Circle
New York, NY
10019
10 Columbus
Circle
New York, NY
10019
10 Columbus
Circle
New York, NY
10019
10 Columbus
Circle
New York, NY
10019
7215 York Rd.
Baltimore, MD
21212
* Maintained by Chemical Information Systems, Inc. for U.S. EPA's Office of Pollution
Prevention and Toxics
-------
Chemical & Physical Characteristics of Aquifers & Overlying & Underlying Materials 109
the U.S. Department of Energy, provides useful information on chemical and hydrogeological
parameters.
Data that cannot be obtained from existing sources may be obtained from field
sampling and testing. The mineralogy, chemical makeup, content and distribution of organic
matter, bacteria and plant material, moisture content, and hydraulic characteristics of
geologic materials can often be determined in the laboratory from field samples. The
physical characteristics of sedimentary, igneous, and metamorphic rocks are often
determined directly from field observations. To avoid additional field investigations, samples
should be collected whenever possible from on-going operations that require drilling or
collection of geologic material. Samples can be taken from cores made during the
construction of wells or from cores taken for general construction or excavation purposes. In
addition, surface and subsurface geophysical methods such as seismic refraction, electrical
resistivity/conductivity, and borehole geophysics can be used to determine the physical
characteristics of geologic materials.
Chemical and physical characteristics of aquifers and their overlying and underlying
materials can often be determined in the field. As mentioned in Component #4, field
measurement of hydraulic conductivity is representative of the geologic materials throughout
the area of influence of the aquifer test well; laboratory determinations are only valid for the
site of the sample. Methods and considerations for using field tests such as aquifer and
tracer tests are discussed in more detail in Component #4.
Geographic location (e.g., township, range, section, or, preferably, latitude and
longitude) should be assigned to data collection sites. If precise locations are available using
latitude and longitude, data can be input to a Geographic Information System (GIS) that can
be used to combine the data, interpolate values between sampling points, and provide rough,
initial estimates of chemical and physical characteristics across a study area.
Presentation of Data/Information
Information on the chemical and physical characteristics of aquifers and their
overlying/underlying materials may be most easily understood and interpreted when
presented in map, chart, or graphical format. Maps are useful to show the geographic
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110 Component #9
distribution of hydraulic properties over a region. Separate maps can also be prepared for
different aquifers or zones. If the area to be mapped contains significant variations in
chemical and physical characteristics, mapping may require a large amount of data to
adequately delineate where these changes occur.
Vertical column and cross-sectional profiles can also be prepared to show the depth
and thickness of each aquifer or zone and its associated chemical and physical
characteristics.
Data on aquifer (and overlying and underlying material) characteristics can be
correlated to geographic locations and then put into a GIS for preparation of graphical
displays or preliminary drafts of maps.
It is important to preserve the original data in tables or data bases. These tables or
data bases may be needed for subsequent manipulation of the data or modeling of the
hydrogeologic setting. Even when data are presented using a graphical format, the raw or
complete numerical data set should also be made available.
Considerations
The scale at which one assesses chemical and physical characteristics of aquifers and
their overlying and underlying materials depends on the specific application. More data will
be needed where geologic conditions change significantly within short distances. Adequate
characterization of chemical and physical characteristics of materials in these settings
generally requires a vast amount of data. Collection of large amounts of data may be very
costly, especially if new test wells are to be installed. For this reason, it is especially
important to conduct a literature search to determine and locate existing hydrogeologic data.
When using existing data, it is important to consider their accuracy and reliability.
Often this can be accomplished by examining the methods that were used to collect the data.
The age of the data should also be considered, because detection methods and detection
limits have improved over time.
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Chemical & Physical Characteristics of Aquifers & Overlying & Underlying Materials
Choosing sites for data collection activities must be done carefully to maximize the
applicability of the new data. New data collection sites should be selected only after
considering all available hydrogeologic data including terrain- and boundary-forming features
such as faults, low permeability formations, and recharge and discharge areas Well depths
must also be considered when planning aquifer tests that require pumping.
Citations
Argonne National Laboratory, 1993. Data Collection Handbook Supporting Modeling
the Impacts of Radionuclide Material in Soil. ANL/EAIS-8.
Driscoll, F.G., 1986. Groundwater and Wells. Second Edition, Johnson Division St
Paul, MN, 1089 p.
Fetter, C.W., 1988. Applied Hvdroaeology. Second Edition, Merrill Publishing Company
Columbus, OH, 592 p.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Incorporated Enqlewood
Cliffs, NJ, 604 p.
Hanks, R.J., and G.L Ashcroft, 1980. Applied Soil Phvsics. Springer-Verlag, New York NY
159 p.
Lyman, W.J., W.F. Reehl, and D.H. Rosenblatt, 1990. Handbook of Chemical Property
Estimation Methods. American Chemical Society.
Pacific Northwest Laboratory, 1987. Multimedia Environmental Pollutant Assessment System
(MEPAS). Addendum D: Constituent Data Base U.S. Department of Energy Office of
Environment, Safety, and Health.
Pucci, A.A., T.A. Ehlke, and J.P. Owens, 1992. "Confining Limit Effects on Water Quality in the
New Jersey Coastal Plain." Ground Water. 30(3), p. 415-427.
Ritter, D.F., 1986. Process Geomorpholoav. Second Edition, Wm. C Brown Co Dubuaue
IA, 603 p. - M -
Taylor, S.A., and G.L Ashcroft, 1972. Physical Edaphology. W.H. Freeman and Companv
San Francisco, CA, 533 p.
For More Information
For more information on this subject see the following references:
Aller, L, T.W. Bennett, J. Denne, G. Hackett, J.H. Lehr, D.M. Nielsen, R.J. Petty, and H.
Sedoris, 1989. Handbook of Suggested Practices for the Design and Installation of
Ground Water Monitoring Wells (EPA/600/4-89/034). 221 p.
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112 Component #9
Heath, R.C., 1989. Basic Ground Water Hydrology. U.S. Geological Survey Water
Supply Paper 2220, 84 p.
Klute, A., 1986. Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods.
Second Edition. ASA. Madison, Wl, 1188 p.
U.S. Environmental Protection Agency, 1987. Handbook: Ground Water (EPA/625/6-87/016).
Office of Research and Development, 212 p.
U.S. Geological Survey, 1979. Ground Water Hydraulics. U.S. Geological Survey
Professional Paper 708. U.S. Government Printing Office, Washington DC, 70 p.
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Ambient Ground Water Quality
113
Component #10: Ambient Ground Water Quality
Definition
Ambient ground water quality is the quality of ground water at a baseline time selected
by the decision-making agency. Ambient quality may be the natural quality of ground water or
may be the natural quality as impacted by widespread historical contamination. Ground
water quality is assessed by means of extensive tests that measure physical, chemical,
biological, and radiological constituents of representative samples.
Objective
Ambient ground water quality is the existing condition on which future resource
management should be based. Ground water quality data can play a key role in developing
resource protection policies and should be collected to assess local ground water quality
conditions in shallow as well as deeper, confined aquifers. The data may provide an
assessment of the status of available drinking water supplies or may serve as a baseline for
future comparisons of ground water quality. Ground water quality data are often used by
resource managers to encourage compliance with existing protection policies, as in the case
of drinking water standards, and in the development of new standards. Ground water quality
data also improve the understanding of the ground water flow system. A fundamental
knowledge of ground water quality should be considered an integral part of any ground water
resource assessment.
Data Needs
To assess the ambient ground water quality of an aquifer, managers should collect
data and information on:
sampling location (areal extent and depth)
climatic and infiltration characteristics
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114 Component #10
mineralogy of geologic and soil materials
chemical parameters (i.e., constituents and their concentrations)
organic parameters
radiological parameters
biological parameters (i.e., species and their concentrations)
Sampling location and sample depth are essential data when collecting ground
water quality samples. The depth from which samples are drawn is needed because it is
usually important to know the aquifer from which the sample is obtained. The dates samples
are taken are important for determining trends in ground water quality, especially for shallow
aquifers that respond to seasonal variations.
Climatic and infiltration characteristics can affect ground water quality. Chemical
quality of ground water supplies can be directly related to precipitation and infiltration.
Shallow aquifers are influenced more directly by precipitation than are deeper, confined
aquifers. Confined aquifers receive recharge water from leaky confining layers, through
fractures that enhance interaction between aquifers, or from direct recharge where the aquifer
outcrops or is close to the land surface. Refer to Components #6 and #8 for a more detailed
discussion of climatic variation and recharge and discharge.
The quality of ground water is also affected by the mineralogy of geologic and soil
materials. The mineral composition of aquifers, aquitards, and overlying unsaturated material
has a substantial influence on the quality of ground water. Ground water quality within a
particular region may vary greatly as a result of spatial differences in the abundance of the
different minerals comprising the geologic materials. The geochemical interrelationships
between water and rock are complex and beyond the scope of this Component; however,
additional information can be found in Component #9. The hydrogeologic setting of the
aquifer may also impact water quality. For example, salt water intruding into aquifers in
coastal areas may severely impact water quality. Also, shallow aquifers, which are
hydrologically connected to surface water bodies, may reflect surface water quality.
Drinking water standards established by the Safe Drinking Water Act (SDWA) serve
both as a basis for appraisal of the results of chemical, radiological, and biological analyses
of water and to establish the suitability of the water for drinking water. Chemical parameters
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Ambient Ground Water Quality -I -j 5
listed in the drinking water standards include both inorganic and organic parameters. The
listed parameters, both naturally occurring constituents and contaminants introduced by man
are found in ground water supplies of drinking water. Primary and recommended limits for
inorganic constituents in drinking water have existed for many years. The major inorganic
constituents that are used in assessing ground water quality and for which the U.S.
Environmental Protection Agency (EPA) has set recommended limits are nitrate, sulfate, and
chloride. These and other inorganics should be monitored to detect the presence of
excessive levels of potential contaminants. Each parameter is unique and may have
standards based on aesthetic qualities (i.e., appearance and taste) as well as health effects.
Total dissolved solids, an EPA secondary standard, may be of concern in some settings and
may, therefore, have to be monitored.
Other inorganic parameters often measured in ground water samples include calcium
and magnesium, which are used to characterize the hardness. A variety of metals such as
iron and manganese could cause household nuisances with precipitates, stains, and bad
taste. The most common increases in concentrations of inorganics observed through
monitoring programs are in sodium chloride and nitrate levels, but changes in other inorganic
and organic constituent levels may also exist. The EPA has established maximum permissible
concentrations for such inorganic parameters as: nitrate-nitrite, arsenic, lead, mercury, silver
and fluoride. These constituents are considered to have significant potential for harm to
human health at concentrations higher than permissible levels.
EPA has set recommended limits for organic constituents in drinking water, such as
pesticide residues. Small amounts of naturally occurring dissolved organic substances are
normally found in ground water, and pose little concern to human health. However, synthetic
organic compounds are of much greater concern, as sewage treatment plants have difficulty
in removing many of these compounds from waste streams. In addition, these compounds
are more resistant to biological degradation. Examples of synthetic organic compounds
include aromatic hydrocarbons (e.g., benzene, styrene, and toluene), industrial solvents (e.g.,
trichloroethane and tetrachloroethane), and pesticides. Synthetic organic compounds can
enter ground water from the downward migration of contaminants released from a variety of
sources including chemical spills, agricultural application of pesticides, and sanitary landfills.
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116 Component #10
The drinking water standards also include radiological parameters. Measurements of
Radium 226 and Radon 222 are conducted to establish natural levels of radioactivity present
in geologic materials. Gross alpha and gross beta are measures of radioactivity from natural
uranium deposits or from manmade sources such as radioactive wastes. Testing for gross
alpha activity is an efficient way to determine the existing radioactivity in ground water and is
a qualitative measure most useful for screening purposes.
Changes in the biological quality of ground water are detected through sampling and
analysis of biological parameters. For ground water quality, sampling and analysis of
biological parameters is usually limited to the measurement of total coliform bacteria. Total
coliform is used as an indicator of the presence of disease-causing viruses, protozoans, fungi,
worms, and other bacteria associated with human or animal wastes. Positive total coliform
test results are not necessarily indicative of the presence of harmful biological organisms.
However, if a sample tests positive for total coliform bacteria, fecal or E. coli bacteria tests
should be conducted to determine if either of these more harmful bacteria are present.
Methods
The methods used for collecting and assessing data will be determined by the
objectives of the ground water quality assessment. Before designing and establishing a
ground water sampling and monitoring program, a thorough search of existing data should
be conducted. Sources of data include soil maps and reports, geologic and water-quality
maps, geologic cross-sections, well logs, and published reports. This information is available
from State geological survey offices, U.S. Geological Survey (USGS), the U.S. Department of
Agriculture's Soil Conservation Service (SCS), State and local universities, State water
research, quality and appropriations agencies, and local and regional planning agencies.
Existing data, including chemical analyses of selected parameters may be available through
local government health departments and planning agencies. The ecological description of
ground water is a newly emerging science; ecological data are difficult to obtain, but may be
available from academic sources.
Following a search and analysis of existing data, and the identification of data gaps,
managers will need to consider a ground water monitoring program to fill the gaps. The
following are generic steps for planning such a program (after Fetter, 1988):
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Ambient Ground Water Quality 117
define the purpose and objectives of the program
define locations of, and procedures for sampling (e.g., how many samples are
needed, are there existing sampling points, are new sampling locations
needed)
determine the chemical constituents to be evaluated
determine if constituents to be analyzed necessitate special well casing
materials and/or sampling requirements
develop a quality assurance/quality control (QA/QC) program
Such planning is essential to ensure the utility of the data collected. The above procedures
should be followed to ensure that ground water quality data collected from the same sample
points can be compared over time.
To evaluate the existing water quality of an area, the most appropriate sources of data
may be existing wells and springs; the aquifers from which the water quality samples are
collected should be determined. The distribution of these existing wells and springs should
be evaluated to identify gaps in coverage. Sampling should occur throughout the study area,
including any recharge and discharge areas. The design of the sampling program should
consider the effects of anthropogenic sources on localized ground water quality.
If an adequate distribution of reliable, existing, sampling points does not exist,
dedicated monitoring wells may have to be installed. These monitoring wells should be
placed at points that are strategically selected, based on estimates of flow direction and travel
time, to better monitor ground water quality in susceptible or remote areas. For example,
dedicated ground water monitoring wells are often installed in the vicinity of wastewater-
treatment sites, waste-disposal sites, or agricultural areas to monitor changes in ground water
quality.
There are two general approaches for sampling ambient ground water quality: (1)
sampling existing sites where ground water is accessible, including public and private wells
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118 Component #10
and natural springs; and (2) sampling dedicated ground water monitoring wells if they are
needed to supply additional information. For some purposes, for example determining the
water quality of a highly transmissive aquifer after a recharge event, synchronizing the timing
of the two sampling approaches is necessary. The timing of sampling is critical for aquifers
with rapid ground water flow and for shallow aquifers with rapid recharge after storm events
or when discrete events such as pesticide application occur. Sampling frequency should be
considered when long-term monitoring is needed.
Sampling procedures and subsequent analyses of water samples should be well
documented and should follow accepted standard methods. Ground water should be
extracted from the source, tested for field parameters (such as pH, temperature, and specific
conductance), containerized, treated with preservatives if needed, and analyzed on-site or
off-site for targeted parameters. On-site, real-time analysis is a developing technology.
Targeted parameters are defined by the specific objectives of the study. It is important to
note that samples collected to establish trends over time should be taken from the same
location and depth to ensure the comparability of results.
Presentation of Data/Information
Once ground water quality data are collected, the constituent parameters may be
reported in a tabular format or on maps. The use of bar and line graphs, pie charts, and box
charts may facilitate the interpretation of voluminous complex data, or data collected over
time. Chemical characteristics of water quality can be presented graphically in geochemical
diagrams such as bar, circle, Stiff, and trilinear diagrams (Driscoll, 1986). Examples of these
diagrams are shown in Figures 11A through 11D (Hem, 1992).
A Geographic Information System (GIS) is a helpful tool to store, assemble, and
manipulate different sets of georeferenced water-quality data for graphical presentation and
statistical data analysis. Presentation of water quality data using a GIS can enhance the
understanding of multiple parameters over a large area.
Interpretation of water quality data by ground water scientists, in conjunction with
other hydrogeologic information, permits the development of water quality maps with lines of
equal parameter concentration and boundaries of water quality types. Separate maps could
-------
Figure 11A
Bar Diagrams Presenting Data From Chemical Analyses
of Water From Three Wells
14
12
10
= 4
12-6
EXPLANATION
Na
NO.
S0
Ca C0
S.O.
15 -'
17 3
12-6 = Well Number
Source: Hem, 1992
-------
Figure 11B
Circle Diagrams Presenting Data From Chemical Analyses
of Water From Four Wells
15-1
Mg
Na
HCO-
Mg
12-6
Na + K
HCO, /'/
Mg
Na+K \
Cl
HCO,
SO,
01 5 10
50
IOC
SCALE OF RAD
(TOTAL OF MILLIEQUIVALENTS PER LITER i
12-6 = Well Number
Source: Hem, 1992
-------
Figure 11C
Stiff Diagrams Presenting Data From Chemical Analyses
of Water From Four Wells
Ni -t- K K
Ci -
-IHCC.
30 25 K 15 10
CATIONS M MILLIEQUIVAIENTS
PER LITEP
C 5 10 15 2C
AWONS. IN MULIEQUIVALE1TS
PER UTEP
12-6 = Well Number
Source: Hem, 1992
-------
Figure 11D
Trilinear Diagram Presenting Data From Chemical Analyses
of Water From Four Wells
DISSOLVED SOLIDS
MILLIGRAMS PER LITER
I i L
SCALE OF DIAMETERS
CATIONS
PERCENT OF TOTAL
MILLIEQUIVALENTS PER LITER
ANIOflS
12-6 = Well Number
Source: Hem, 1992
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Ambient Ground Water Quality
123
be made for each constituent of interest for individual aquifers. A GIS may assist ground
water scientists in the development of draft maps. Mapping software available for personal
computers can assist in the development of simple maps.
Historical data of acceptable quality may be used to identify temporal trends in ground
water quality. Geographic trends in ambient ground water quality, or contaminant
concentrations, can be analyzed and compared over time to identify areas of decreasing
ambient quality due to anthropogenic contamination. Trends in ground water quality may
also be used to justify and apply ground water protection policies in specific areas.
Considerations
The monitoring of ground water quality can be highly resource intensive, particularly if
new monitoring wells are installed. Labor and equipment necessary to collect samples can
be expensive. For most areas, geologic and hydrogeologic assessment programs are
conducted in tandem. Therefore, holes drilled for geologic characterization of materials can
also be used for installation of dedicated ground water monitoring wells. See Components
#1, #4, and #9 for further discussion. Samples should be collected over time and
geographic area by identical methods. This will help ensure accurate results and
comparability of data. Analysis of ground water samples can be costly, depending on the
targeted parameters. Increasing the number of samples or monitoring wells will decrease the
level of uncertainty associated with the findings but increase the costs. Developing maps
showing lines of equal parameter concentration is interpretive and should rely heavily on the
understanding of the flow system. GIS availability may aid ground water scientists in
developing such maps.
Background ground water quality monitoring is helpful in determining trends in ground
water quality. These trends are useful in forming sound protection policies. Related historical
data may provide additional information, but the reliability of the data should be evaluated.
Citations
Driscoll, F.G., 1986. Groundwater and Wells Second Edition, Johnson Division St Paul
MN, 1089 p. '
-------
124 Component # 10
Fetter, C.W., 1988. Applied Hydrogeology. Second Edition, Merrill Publishing Company,
Columbus, OH, 592 p.
Hem, J.D., 1992. Study and Interpretation of the Chemical Characteristics of Natural Water.
U.S. Geological Survey Water Supply Paper 1473, pp. 174-176 and 179.
U.S. Environmental Protection Agency, 1990. Handbook: Ground Water. Volume I: Ground
Water and Contamination (EPA/625/6-90/016a). Office of Research and Development,
Washington, DC, 144 p,
For More Information
For more information on this subject see the following references:
Aller, L, T.W. Bennett, J. Denne, G. Hackett, J.H. Lehr, D.M. Nielsen, R.J. Petty, and H.
Sedoris, 1989. Handbook of Suggested Practices for the Design and Installation of
Ground Water Monitoring Wells (EPA/600/4-89/034). 221 p.
Barcelona, M. J., J. P. Gibb, J. A. Helfrich, and E.E. Garska, 1985. Practical Guide for Ground
Water Sampling. Illinois State Water Survey Contract Report 374, 94 p.
Bowen, R.f 1986. Groundwater. Applied Science Publishers Ltd., London, 427 p.
Everett, L.G., 1984. Groundwater Monitoring. Genium Publishing Corp., Schenectady, NY,
440 p.
Hamill, L, and Bell, F.G., 1986. Groundwater Resource Development. Butterworths, Boston,
MA, 344 p.
Matthess, G., and Harvey, J.C., 1982. The Properties of Groundwater. John Wiley and Sons,
New York, NY, 406 p.
Scott, N.R., 1985. Groundwater Quality and Management. Cornell University, New York, NY.
U.S. Environmental Protection Agency, 1991. Handbook: Ground Water. Volume II:
Methodology (EPA/625/6-90/016b). Office of Research and Development, Washington,
DC, 141 p.
Ward, R.C., J.C. Loftis, and G.B. McBride, 1990. Design of Water Quality Monitoring Systems.
Van Nostrand Reinhold, New York, NY, 231 p.
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Approaches to Assessing Aquifer Sensitivity and Ground Water Vulnerability 125
CHAPTER 3:
Approaches to Assessing Aquifer Sensitivity and
Ground Water Vulnerability
As water moves through the hydrologic cycle, its quality changes in response to the
environments through which it passes. The changes may be either natural or human-
influenced. In some cases they cannot be controlled, but in many instances the changes can
be managed so as to limit adverse impacts on water quality.
An understanding of the relationship between aquifers and their recharge areas is
critical to evaluating the condition of ground water resources and designing programs for
their protection. One means of identifying options for resource managers is to conduct
aquifer sensitivity and/or ground water vulnerability assessments. For the purposes of this
document, EPA defines aquifer sensitivity as:
the relative ease with which a contaminant applied on or near the land surface
can migrate to the aquifer of interest. Aquifer sensitivity is a function of the
intrinsic characteristics of the geologic materials in question and the overlying
saturated and unsaturated materials. Aquifer sensitivity is not dependent on
land use and contaminant characteristics.
Ground water vulnerability is defined as:
the relative ease with which a contaminant applied on or near the land surface
can migrate to the aquifer of interest under a given set of land-use
management practices, contaminant characteristics, and aquifer sensitivity
conditions.
Resource managers can use the various methods identified in this chapter to assess
aquifer sensitivity and ground water vulnerability. By conducting such assessments,
managers can prioritize which areas and which potential sources of ground water
contamination need special management attention. Establishing these priorities will allow
States to use their often limited financial and personnel resources to achieve maximum
environmental benefits.
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126 Chapters
There are many different sources of ground water contamination. The type of land
use in a recharge area may be the most important, as well as the most controllable factor in
determining ground water quality. Residential, commercial, and industrial development may
pose serious threats to ground water quality due to drastically altered infiltration rates caused
either by reducing recharge areas with impermeable pavement or by degrading the quality of
water that does recharge.
Residences can contaminate ground water through faulty septic systems, over-
application of lawn chemicals, and the improper disposal of household hazardous wastes.
Industrial areas may produce chemicals that can percolate to ground water if not managed
properly. Accidental spills also can occur, and depending on the contaminant(s) involved
and the quantity of the spill, these can seriously contaminate ground water environments.
Intensive use of chemicals on agricultural land in areas vulnerable to those chemicals also
can pollute ground water. Less intensive land uses and wise, conservative use of chemicals
can minimize this contamination.
Management efforts to protect ground water quality may be ineffective in areas with
leaking or poorly constructed water wells and abandoned or improperly sealed wells. In
either case, properly applied chemicals may leak directly along the well casing, causing rapid
degradation of the ground water and posing the more serious problem of
cross-contamination of adjacent aquifers.
An analysis of land use, aquifer use, and the relationship of aquifers and their
recharge areas can help determine the sensitivity and vulnerability of an aquifer when
considered along with the hydrogeologic and hydraulic properties discussed in Chapter 2.
The four Approaches to assessing ground water described in this chapter expand on the
Components discussed in Chapter 2 by taking into account the use and vulnerability of
ground water resources.
These four Approaches follow a rational progression that managers typically use to
improve their understanding of ground water sensitivity and vulnerability. That progression is
reflected in the organization of this chapter:
Approach #1 - Aquifer Sensitivity
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Approaches to Assessing Aquifer Sensitivity and Ground Water Vulnerability 127
Approach #2 - Aquifer Use
Approach #3 - Land Use
Approach #4 - Ground Water Vulnerability
-------
128 Approach #1
Approach #1: Aquifer Sensitivity
Definition
Aquifer sensitivity is the relative ease with which a contaminant applied on or near the
land surface can migrate to an aquifer. An aquifer's sensitivity is a function of the intrinsic
characteristics of the geologic materials and the overlying saturated and unsaturated
materials. Aquifer sensitivity is not dependent on land use or contaminant characteristics.
Objective
The objective of an aquifer sensitivity assessment is to estimate the relative ground
water pollution potential of specific hydrogeologic settings. An aquifer sensitivity assessment
provides a means to screen a broad geographic area, and to characterize or rank the intrinsic
potential for the ground water to become contaminated. Sensitivity assessment methods help
resource managers identify critical areas where more detailed mapping or assessments
(including vulnerability assessments) may be warranted, select monitoring sites, choose
ground water protection management practices, and prioritize areas for enhanced protection.
Areas that are assessed as sensitive and that have been subjected to applications of
contaminants, spills, or discharges, could be further assessed with a vulnerability method (see
Approach #4), and evaluated with a monitoring program.
Data Needs
The specific data needed to assess aquifer sensitivity are dependent on the
sensitivity method selected and the scale of the assessment. Typical hydrogeologic factors
needed for such assessments include the following (modified from Aller et al., 1987):
depth to aquifer
aquifer recharge
aquifer media
-------
Aquifer Sensitivity 129
confining-layer media
soil media
surface features
unsaturated zone
hydraulic conductivity
Depth to aquifer is the measured distance between land surface and the top of the
aquifer. The depth to aquifer is an important element for assessing aquifer sensitivity,
because depth measures the thickness of materials through which a contaminant must pass
before reaching the aquifer. While not always the case (especially in the semi-arid areas of
the Midwestern United States), greater depths to aquifers often imply longer travel times in the
unsaturated media, and thus offer a greater distance through which contaminant attenuation
may occur. For confined aquifers, the depth is calculated through the overlying material to
the top of the aquifer. For unconfined aquifers, the depth is calculated to the water table.
Aquifer recharge is the total amount of water that is applied to the ground surface
that infiltrates to the aquifer. Recharge can transport contaminants to the aquifer. The
greater the recharge, the greater the potential for ground water to become contaminated;
however, recharge may also dilute contamination. The effects of recharge should be
evaluated individually for different contaminant sources and hydrogeologic settings.
Aquifer media is the type of material that constitutes an aquifer (e.g., limestone, sand,
or gravel) . The aquifer medium determines the path length, route, and rates of travel that
water and contaminants would follow, and thus affects the attenuation process. The type of
flow path (e.g., conduit, fracture, intergranular) is a significant attribute of the medium that
contributes to the aquifer's sensitivity to contamination.
Confining layer media refers to the low permeability geologic materials above and
below confined aquifers. The confining layer's thickness, composition, and permeability
define the path length, route, and the rate of travel of ground water and potential
contaminants through the confining layer to the aquifer. Confined aquifers are less likely to
become contaminated by pollutants infiltrating from the unsaturated zone than are unconfined
aquifers. The lowest probability of a contaminant reaching an aquifer, or contaminants being
transported from one aquifer to another, will occur where confining beds are thick, of very low
-------
Approach #1
permeability, not compromised by human activity, and not subjected to fracturing or
dissolution features.
Soil media is the upper weathered zone of the earth's surface. Soil media thickness,
composition, and permeability have significant impact on the amount of recharge that
infiltrates into the ground. In addition, soil organic matter and clays may adsorb some
contaminants, reducing the threat of contamination. Slope can also impact the amount of
recharge. For a given surficial sediment type, shallow slopes are more conducive to recharge
than steep slopes.
Surface features are the geologic and geomorphic features (e.g., sinkholes, fractures,
etc.) of the land surface that act as open conveyances to the aquifer. Such features are
generally portions of an area's natural infiltration system that can provide easy access of
contaminants to the underlying aquifer.
The unsaturated zone is the zone of geologic material above the water table and, for
purposes here, below the soil zone. The characteristics of the unsaturated zone media affect
the path length and attenuation time for contaminants moving through this zone.
Hydraulic conductivity is a quantitative term that refers to the ease with which a fluid
(e.g., water) can pass through a given medium. The rate at which the ground water flows
also affects the rate at which a contaminant can spread through an aquifer. As the hydraulic
conductivity increases, the potential for more ground water to become contaminated also
increases.
Methods
Specific hydrogeologic factors, as detailed in Components #1 througb #10 above,
provide the preliminary basis upon which ground water scientists conduct sensitivity
assessments. It is the completeness, accuracy, and detail of these hydrogeologic data that
will affect not only the accuracy of the sensitivity assessment method employed, but also the
selection of which method is most appropriate.
-------
Aquifer Sensitivity 131
Methods for assessing aquifer sensitivity use only hydrogeologic factors, such as soil
and aquifer physical characteristics. Methods for obtaining these hydrogeological data range
from simple searches of published data to complex field data-collection efforts. Typically, the
data required to conduct sensitivity assessments already exist and can be collected through a
literature search and review of data such as well logs. The literature search should include
published and unpublished materials, such as maps, reports, data bases, well logs and
monographs. The U.S. Geological Survey (USGS), State geological surveys, State water
research and resource agencies, State engineers' offices, the U.S. Department of
Agriculture's Soil Conservation Service (SCS), and local and State universities are all good
sources of hydrogeological data and may also be able to provide information about available
modeling results. County and local planning agencies may also provide supplementary
information that may be helpful for site-specific assessments.
A review of available data will help a resource manager determine if more site-specific
field data collection efforts are warranted. If further data collection efforts are necessary, an
evaluation of the data requirements, the applications and analyses that the data will support,
and consideration of the most efficient means of collecting and managing the data will help
maximize the use of often limited financial and human resources.
Sensitivity assessments may be conducted using one of two categories of methods -
hydrogeologic setting classification or aquifer sensitivity scoring methods. Hydrogeologic
setting classification methods assess sensitivity by delineating subareas within a management
area, based on inherent hydrogeologic characteristics (e.g., permeability and texture of
geologic materials). Sensitivity characteristics are usually similar within a given subarea.
Hydrogeologic classification methods usually use two or more hydrogeologic factors to
delineate sensitivity classes. Most hydrogeologic classification methods result in the
delineation of between two to five classes of relative sensitivity (e.g., highly sensitive,
moderately sensitive). Advantages in using hydrogeologic setting methods to determine
sensitivity include the following:
these methods are based on easily obtainable information from a wide
variety of local sources, often without reconnaissance
these methods are relatively simple to use
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132 Approach #1
these methods allow comparisons to be made across State boundaries
because intrinsic parameters of aquifers and confining beds form the
basis of mapping, rather than political boundaries.
Hydrogeologic setting classification methods are most frequently used as a screening
tool for broad geographic areas (such as a county); however, the methods can also be used
for smaller areas if data sets are of sufficient detail and accuracy. Classification methods are
particularly helpful in assessing areas with great variation in the completeness, accuracy, and
detail of hydrogeologic data. The user should be aware, however, that results may reflect the
biases and capabilities of those conducting the assessment. The shortcomings of the
method titled DRASTIC noted by Soller, and discussed at the end of this Approach, also
apply to hydrogeological classification methods.
The steps involved in using a hydrogeologic setting classification method generally are
as follows:
(1) determine the availability of data for the factors used in the method. Based on
the availability, the user may choose to collect additional data, modify the
method, or select another method
(2) select the number of aquifer sensitivity classes desired. The selection should
be based on the number of plausible management options to be considered
and the variety (or range and magnitude) of hydrogeologic settings
(3) specify classification decision rules that define how to assign an overall
sensitivity rating to an area with mixed ratings for key factors (e.g., recharge is
rated high, soil texture is medium, and depth-to-ground water is low). Decision
rules focus on the number of factors, with like-sensitivity ratings necessary to
place an area within a class. Because of the relative nature of the class
determination, a judgement must be made as to whether all, some, or only one
of the classification criteria must be met. The rule-makers should select
decision rules that will identify sensitive areas that seem most consistent with
ground water protection needs and the local hydrogeology
-------
Aquifer Sensitivity -j 33
The following example of a hydrogeologic classification method considers leachability
characteristics in Kansas soils. The data base for the study, the National Cooperative Soil
Survey, is very detailed. Therefore the method may be used accurately at the field (small
area) level. This example has been excerpted from EPA, (in press).
According to Kissel et al. (1982), many soil materials that overlie aquifers in
Kansas offer protection from contaminants that might be transported by
infiltrating waters In some areas of the State, soil materials allow contaminants
to reach ground water more easily than in other areas, and the authors devised
a classification system to account for the spatial variation in the attenuation
potential of these overlying soils.
In general, the greater the percentage of sand in soils (coarse-textured soils),
the more susceptible they were judged to be to pesticide leaching.
Accordingly, this method grouped Kansas soils into four classes of leaching
susceptibility based on soil texture and soil permeability (expressed as the
water infiltration rate).
The classification decision rule focused on the limiting soil horizon in the soil
profile. For example, a soil with a top layer (horizon) permeability of 1 inch per
hour and a subsoil horizon permeabiiity of 4 inches per hour will be placed in
leaching susceptibility Class 2, where permeabilities range from 2 to 6 inches
per hour.
The final class determination is based on the factor most limiting to pesticide
leaching losses -- either texture or permeability. For example, a loam soil with
a texture listed in Class 3 but a permeability listed in Class 2 would be
classified as Class 3, since Class 3 is less susceptible to leaching.
A leaching susceptibility map of Kansas soils was prepared based on the
general soils map available from the National Cooperative Soil Survey at a
scale of 1 cm:40 km. An initial attempt was made to classify only those soils
with more than approximately 50,000 mapped acres published in Soil Survey
reports through May 1981. However, some soils with less acreage were
included if they were known to be highly cultivated, particularly if they were
Class 1 or 2 soils.
The second method category for assessing aquifer sensitivity is aquifer sensitivity
scoring. Scoring methods are an extension of hydrogeologic setting classification methods in
that they use relative rankings or ratings to classify the subject area based on hydrogeologic
parameters. In the literature, aquifer sensitivity scoring methods are referred to as ranking
systems or numerical rating systems. Scoring methods involve calculating a rating or
numerical score for subareas within a subject area. The scores provide a relative measure of
-------
134 Approach #1
the aquifer sensitivity among subareas, by translating and then comparing physical
information to a factor rating.
Because scoring methods recognize a discrete continuum of aquifer sensitivity, they
facilitate differential management measures based on relative hydrogeologic sensitivity. This
scoring, or ranking, helps in the evaluation of the relative ground water pollution potential of
different hydrogeologic settings. Additional applications for sensitivity scoring methods
include prioritizing monitoring programs, identifying data gaps, and evaluating land-use
activities.
The steps involved in using an aquifer sensitivity scoring method generally are as
follows:
(1) determine the availability of data for the factors used in the method.
Based on the availability of these data, the user may choose to collect
additional data or select another method
(2) score each factor. The range of each factor is subdivided into discrete
hierarchical increments. Unlike hydrogeologic setting classification
methods where the increments are assigned one descriptive class, each
increment is assigned a numerical value reflecting the relative degree of
sensitivity
(3) combine scores to produce an overall sensitivity score for the setting.
Each method may use either additive or multiplicative mathematical
approaches for combining factor scores into a final score for a setting.
Multiplicative approaches are used to weight factor scores relative to
the assumed importance of each factor. Output for a sensitivity scoring
method typically is a numeric score.
Currently, there are over thirty different documented scoring methods for assessing
aquifer sensitivity. Some of these methods allow the user to vary factor input values based
on landforms or structural zones of interest. Many of these methods, such as DRASTIC (Aller
-------
Aquifer Sensitivity 135
et al., 1987), include modifications that have been designed to target specific geological or
aquifer characteristics of a particular geographic region.
Similar to hydrogeologic setting classification methods, different scoring methods are
based on an evaluation of a set of hydrogeologic factors described in the Data Needs section
above. Generally, it is preferable that spacially representative data be available for each
hydrogeologic factor, although this is seldom possible. It is likely that the accuracy and
spatial distribution of data vary according to the factor. As a result, the validity of and
confidence about sensitivity classifications or scores will vary spatially. The user must
recognize that the level of uncertainty associated with the classifications or scores is generally
unknown. Because these methods are primarily for screening purposes, users should
conservatively estimate parameter values in the absence of accurate or sufficient
hydrogeologic data. For a more extensive discussion of sensitivity methods, including case
studies, the reader is referred to (EPA, in press).
Presentation of Data/Information
The output of a hydrogeologic setting classification is typically several class
designations of geographic areas (e.g., high sensitivity, moderate sensitivity, low sensitivity)
based on the most significant factors affecting contamination potential. These factors may
include depth to aquifer, hydraulic conductivity of the aquifer and confining layers, and aquifer
recharge (Berg, et al., 1984; Lusch, et al., 1992; Seller and Berg, 1992). Each method may
generate a different number of these classes. These outputs can be presented in map, list, or
matrix form.
The output for sensitivity scoring methods is typically a numerical score. These
scores are dimensionless (that is, not related to an actual physical measurement) and are
only a means for developing a hierarchy of relative sensitivity. Resulting scores indicate
qualitative rather than quantitative differences in aquifer sensitivity over an area. Two
sensitivity scoring methods in use, DRASTIC and SEEPPAGE, use relative ranking systems for
seven soil/aquifer parameters to form a numerical i,.Jex representing an area's relative degree
of pollution potential. SEEPPAGE (Moore, 1989) is a relative ranking procedure that assesses
the degree of aquifer sensitivity of a site. Table 4 presents a comparison of factors used in
DRASTIC and SEEPPAGE.
-------
136
Approach #1
Table 4
Comparison of Factors Used in DRASTIC and SEEPPAGE
Factors Used in DRASTIC
Factors Used in SEEPPAGE
D - Depth to Water
R - Recharge (Net)
A - Aquifer Media
S - Soil Media
T - Topography (Slope)
I - Impact of the Vadose Zone
C - Conductivity (Hydraulic) of the Aquifer
Aquifer Net Recharge
Depth to Water Table
Horizontal Distance from Site and Point
of Water Use
Land Slope
Soil Attenuation Potential
Soil Depth
Vadose Zone Media
Regardless of whether a hydrogeologic setting classification or a scoring method is
employed, a user may prepare a map overlay for each factor using, e.g., different patterns or
shades of gray. Superimposing the overlays for all factors will produce a cumulative
sensitivity map depicting relative hydrogeologic sensitivity in various patterns or shades of
gray. This process can be facilitated by digitizing the factor data into an existing Geographic
Information System (GIS). The use of the GIS may also facilitate presentation of several or all
of the factors by providing ground water scientists with initial drafts of sensitivity-factor
overlays. Figures 12 and 13 present examples of aquifer sensitivity and DRASTIC maps
respectively (EPA, in press).
Considerations
Aquifer sensitivity methods are generally used for screening purposes for relatively
large geographic areas (e.g., counties). Screening is often performed because the availability
of data is limited. Broad-area assessments frequently cannot address the sensitivity of
localized aquifers. However, even after large areas with limited data have been screened,
resource managers can make conservative assumptions and identify critical areas where
future, more detailed studies can be conducted.
Aquifer sensitivity evaluations should be conducted by using a logical hierarchical
approach. Regional studies should be conducted first, followed by more detailed
investigations, as needed, in those areas designated on regional maps as being potentially
sensitive. Sensitivity mapping should be performed at a scale corresponding to the scale of
evaluation.
-------
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-------
Figure 13
Example of DRASTIC Scoring Map of Bureau County, Illinois
SOW 45
sew 15'
- 41 N 30'
41 N 15
Legend
Hydrogeologic Setting
Sedimentary Rocks
Pesticide
DRASTIC Score
mm
^
r i
ZZ2
CZI
7Ba
71
7C
70
7Aa
- Outwash
- Swamp/Marsh
- Moraine
- Burled Valley
- Glacial Till Over Bedded
206
149
134
*
126
108
Source: USEPA.1993
-------
Aquifer Sensitivity 13g
Sensitivity classification methods may have inherent drawbacks The user of any
method should be aware that:
the relations between factors may not be directly reflected in the assessment
methods
factors may overlap, causing some parameters to be represented twice (e.g.,
including aquifer thickness, permeability and aquifer transmissivity is redundant
because transmissivity is the product of an aquifer's thickness and its hydraulic
conductivity)
the capabilities and biases of those conducting the assessment may
significantly affect results (e.g., decision rules used to classify areas that have
characteristics of more than one class are developed by the user and therefore
the user could interject bias into the results).
Resource managers tend to use scoring methods to screen larger rather than smaller
areas. As with classification methods, scoring methods allow for the subdivision of
assessment areas into subareas, each with its own level of sensitivity. Seller (1992)
discusses problems with using scoring methods. He evaluated the DRASTIC scoring method
model for the U.S. Environmental Protection Agency (EPA). The following shortcomings of
DRASTIC noted by Seller also apply to other aquifer sensitivity scoring methods:
opportunities for the modeler to err are numerous, because the
literature often states that the modeler does not have to be a
hydrogeologist. Computation of scores is often complex, involving the
gathering and subjective interpretation of sparse data
source information, upon which factor values are based, commonly are
not available, and when available, may not provide adequate source
data
often these methods produce isolated products with little consideration
for regional context or consistency from one area to another
-------
-(40 Approach #1
Scoring methods are also limited by the fact that they may not include all the
significant factors that determine sensitivity. The weights assigned to the various factors have
been a subject of controversy in the use of this type of method. The objective of weighting is
to acknowledge the importance of the contribution of each factor to overall sensitivity to
contamination. However, the exact relationship between factors is seldom fully understood.
As with the user of classification systems, the user of scoring systems should be aware of
their subjectivity. Results may reflect the capabilities and biases of those conducting the
assessment. A final difficulty associated with scoring methods is the uncertainty associated
with establishing a score that will trigger the need for ground water protection management
responses. Because of the uncertainties associated with aquifer sensitivity methods,
managers may choose to be conservative in selecting ground water protection and
management practices and in prioritizing areas for enhanced protection when basing
decisions on sensitivity assessments.
The resources required to determine the availability of existing data depends on the
sensitivity assessment method selected, but consist primarily of professional staff time.
Assessments at the 1:24,000 or larger scale (i.e., a small area) often require more data than
are generally available. Regional data, however, usually exist to satisfy the data requirements
of many of the methods. Because the sensitivity assessment process is used to screen
broad areas, additional field collection of localized data, which can be costly, is not usually
necessary.
Citations
Aller, L.T., T. Bennett, J.H. Lehr, and R.J. Petty, 1987. DRASTIC: A Standardized System for
Evaluating Ground Water Pollution Potential Using Hydroqeoloqic Settings (EPA/600/2-
87/035). U.S. Environmental Protection Agency Robert S. Kerr Environmental
Research Laboratory, Ada, OK, 622 p.
Berg, R.C., J.P. Kempton, and K. Cartwright, 1984. Potential for Contamination of Shallow
Aquifers in Illinois. Illinois State Geological Survey Circular 532, 30 p.
Kissel, D.E., O.W. Bidwell, and J.F. Kientz, 1982. Leaching Classes of Kansas Soils. Kansas
State University, Kansas Agricultural Experiment Station, Manhattan, KS, Bulletin 641,
10 p.
Lusch, P.P., C.P. Rader, LR. Barrett, and K. Rader, 1992. Aquifer Vulnerability to Surface
Contamination in Michigan. Center for Remote Sensing and Department of
Geography, Michigan State University, East Lansing, Ml, map, 1:1,500,000 scale.
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Aquifer Sensitivity 141
Moore, J.S., 1989. SEEPPAGE: A System for the Early Evaluation of the Pollution Potential of
Agricultural Ground Water Environments. Technical News Note 5, Revision 1. U.S.
Department of Agriculture, Soil Conservation Service, NE National Technical Center
Chester, PA.
Seller, D.R., 1992. Applying the DRASTIC Model - A Review of County Scale Maps. U.S.
Geological Survey Open File Report 92-297, 36 p.
U.S. Environmental Protection Agency, in press. A Review of Methods for Assessing Aquifer
Sensitivity and Ground Water Vulnerability to Pesticides. Office of Water, 181 p.
For More Information
For more information on this subject see the following references:
Bowen, R., 1986. Groundwater. Applied Science Publishers Ltd., London, 427 p.
Driscoll, F.G., 1986. Groundwater and Wells. Second Edition, Johnson Division St
Paul, MN, 1089 p.
Everett, L.G., 1984. Groundwater Monitoring. Genium Publishing Corp. Schenectadv NY
440 p.
Page, G.W., 1987. Planning for Groundwater Protection. Harcourt Brace Jovanovich
Publishers, New York, NY, 387 p.
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142 Approach #2
Approach #2: Aquifer Use
Definition
Aquifer use is defined as the human activities for which water in an aquifer, or the
ground water reservoir as a whole, is used and the quantities of water withdrawn for those
activities. Unlike aquifer characteristics, aquifer uses are dynamic and can change
significantly over time.
Objective
The objective of describing aquifer use is to account for all existing uses of water from
a specific aquifer or the ground water reservoir, quantify ground water withdrawal rates, and
identify types and geographic areas of water use. This information is useful for projecting
future use trends. Knowledge of current and future use patterns allows managers to plan for
changes such as new or modified: operating rules, regulations, ground water allocations, or
water resource facilities. Additionally, aquifer-use information can be considered along with
aquifer sensitivity and vulnerability characteristics to develop water-use strategies that protect
aquifer quality.
Data Needs
The data needed to characterize aquifer use and to make projections for future use
center on a comprehensive inventory of all wells. The data needs include:
»
number and areal distribution of wells for each aquifer
withdrawal rates of wells
uses of the water
economic and demographic characteristics and trends
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Aquifer Use 143
The number and areal distribution of wells can be coupled with demographic data to
provide a rough estimate of aquifer-use rates. Because a well that is improperly installed
and/or poorly maintained can act as a vertical conduit for the migration of contaminants to
the ground water, ground water in areas with a high density of wells may be particularly at
risk from contamination.
The withdrawal rates of wells, (i.e, quantity of water pumped over time), can be
combined with information on the areal distribution of wells to identify withdrawal-rate density
throughout the reservoir or for specific aquifers. It is important for ground water managers to
understand the effects that pumping characteristics can have on ground water quality. For
example, excessive pumping of a coastal, fresh-water aquifer lowers the potentiometric
surface or water table, and enables saltwater to intrude into the aquifer.
Pumping can draw not only ground water, but also contaminants, within the zone of
influence of a well, towards the well. This migration of contaminants can extend a
contaminant plume in both the horizontal and the vertical directions.
Major water uses can be categorized as follows:
public supply (can include some of the uses below)
rural, residential, and domestic (generally pumped from individual wells
for household purposes)
commercial (e.g., for hotels, restaurants, office buildings)
irrigation (e.g., for crop production, parks, golf courses)
livestock (e.g., for stock wells, feedlots, dairy operations, agriculture)
industrial (e.g., for fabrication, processing and cooling)
mining (e.g., for extraction of minerals, coal, gas, petroleum, etc., and
for quarrying, dewatering, milling, etc.)
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144 Approach #2
power generation (water used in the process of generating power)
In addition, ground water can be used to support aquatic ecosystems, a use that does
not involve water withdrawals.
Coupling current and historical water-use information with location information can
facilitate understanding of water-quantity demands across the areal extent of an aquifer or the
ground water reservoir as a whole. In forecasting future water-use patterns, information on
economic and demographic characteristics and trends is essential. Such information
includes growth statistics on population, the economy, per-capita energy consumption, food-
production demands, manufacturing, mining, government programs (e.g., environmental
protection, agricultural subsidies), technological changes, and the price of water to users
(Viessman and Welty, 1985). Some of these trends are discussed in Approach #3.
Methods
Methods available to assess aquifer use can be divided into the following two
categories: (1) methods to establish current use patterns; and (2) methods to identify trends
in future use.
Well permit records represent a key source of data for aquifer-use characterization.
Health departments, State geological surveys, and/or State water research or resource
agencies, typically maintain a file of permits for wells. These permits may stipulate the
maximum withdrawal rate for a well, and/or may specify the type of use for the water. This
information can be used to develop a relatively comprehensive characterization of aquifer-use
patterns.
In addition to permit files, some States maintain well data bases. Such data bases are
often routinely updated, but the level of detail contained in them varies significantly. For
example, some user classes may be exempt from permit or reporting requirements (e.g., small
users using less than 5,000 gallons/day), or the source aquifer may not be specified.
It is virtually certain that aquifer-use patterns will change with time. Historical use data
help to project future trends. These data highlight the principal factors influencing water use
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Aquifer Use
and indicate how changes in these factors have effected use in the past. To aid in
developing aquifer-use strategies, estimates of future demands should be coupled with
current and historical use data.
Changes in use patterns will differ by use type. For example, suburban population
changes will significantly affect residential water use; change in a regional economic base
from agricultural to manufacturing will change the amounts of irrigation and industrial water
demand.
Projecting future use trends usually involves the use of growth models that incorporate
information on economic and demographic growth trends. The simplest model would
associate an economic or demographic indicator element (e.g., population) that is assumed
to be directly, linearly related to a specific water-use type. A growth multiplier of the indicator
element, for a specified time span, is then applied to the water-use type. More complex
models are based on mathematical relationships between economic and demographic
indicator elements and the types of aquifer uses.
Presentation of Data/Information
A variety of formats can be used to present aquifer-use information, including tables,
graphs, maps, or reports. The elements presented under any of these formats parallel those
outlined in the Data Needs section of this Approach. Graphs and maps provide a good
format for easy interpretation of aquifer-use data. Place markers of various size circles can
be assigned to wells according to their withdrawal rate. These place markers can also
differentiate water-use types by color. Maps of this information depict water-use and
withdrawal patterns.
In addition to displaying well-discharge and water-use information, maps can integrate
aquifer-use data with other aquifer and demographic data. Geographic Information Systems
(GIS) can integrate these data, and provide initial displays of withdrawal patterns in relation to
demography, industrial activity, land use, etc.
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146 Approach #2
Considerations
Managers should consider data availability, limitations of trend projections, and
resources required, when characterizing use patterns. Characterizing aquifer use by
inventorying all wells may be extremely resource intensive. Moreover, it is unlikely that
information is available about all wells, and available water-well permit information may be
unreliable If multiple aquifers exist, it may be very difficult to discern the aquifer in which a
well is completed. Geologic and hydrologic characterization of the aquifer or aquifer system
(See Components #1 and #2} should be initiated prior to determining water-use trends.
When defining data needs and developing aquifer-use information, it may be useful to
first identify critical geographic areas. The determination of such areas can be made based
on aquifer vulnerability and sensitivity mapping (See Approaches #1 and #4), preliminary
information about general use patterns, and expected regions of industrial or population
growth, etc. Using this approach, use patterns in areas of concern can be addressed first.
Numerous data gaps exist in water withdrawal information. Reasons for these gaps
include: use classes being exempted from reporting requirements, small-quantity users not
needing a permit, and some land uses (e.g., parks) receiving little investigative attention.
Estimates of those economic and demographic trends that influence aquifer use may
not adequately account for future changes in regulations, technology, behavior, available
resources, etc. Modelers should use data from outside their study area with discretion,
understanding that national or regional trends may not be analogous to local trends. Further,
the underlying assumptions used to develop trend projections must be met.
One option that may reduce the risk of erroneously projecting future use trends is to
develop a series of projections based on a range of scenarios. Some of the scenarios may
then be eliminated at an early stage when actual behavior and activities are observed. This
approach, however, may require greater initial resources.
Estimating future use trends is dependent on the availability: of adequate data, of
staff with expertise in economics and demographics, and of appropriate computer equipment
and models.
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Aquifer Use 147
Citation
Viessman, W., Jr., and C. Welty, 1985. Water Management: Technology and Institutions.
Harper and Row, New York, NY, 618 p.
For More Information
For more information on this subject, especially for projection models of water use,
see the following references:
Solley, W.B., R.R. Pierce, and H.A. Perlman, 1992. Estimated Use of Water in the United
States in 1990. U.S. Geological Survey Circular 1081, 76 p.
Solley, W.B., C.F. Merk, and R.R. Pierce, 1988. Estimated Use of Water in the United
States in 1985. U.S. Geological Survey Circular 1004; 82 p.
U.S. Environmental Protection Agency, in press. A Review of Methods for Assessing Aquifer
Sensitivity and Ground Water Vulnerability to Pesticides. Office of Water. 181 p.
U.S. Water Resources Council, 1978. The Nation's Water Resources: 1975-2000. U.S.
Government Printing Office, Volumes 1-4.
Viessman, W., Jr. and C. DeMoncada, 1980. State and National Water-use Trends to the Year
2000: A Report to the U.S. Senate Committee on Environment and Public Works.
U.S. Congress, 96th, 2nd session, Committee Print Serial No. 96-12.
Wollman, N. and G.W. Bonem, 1971. The Outlook for Water Quality. Quantity, and National
Growth. Johns Hopkins Press, Resources for the Future, Baltimore, MD, 286 p.
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148 Approach #3
Approach #3: Land Use
Definition
Land use is the altering, or maintaining, of existing natural features of the land to meet
human needs. Features that may be part of a land-use inventory include hydrologic units
(e.g., wetlands, streams, rivers, and lakes), vegetative cover (e.g., croplands, forests and
grasslands), and urbanized areas as shown on contour maps.
Objective
Information on past and present land cover, and past, present, and planned future
land use is needed to establish land-use trends over time. Determining land-use trends is
essential for evaluating future demands on, and degradation of, ground water resources. For
example, as land is converted from rural to urban use, the amount of precipitation runoff
increases, because more land surfaces become paved and less permeable. Surface water,
and potentially ground water, may become contaminated by non-point source contaminants if
the runoff is not properly controlled and managed. In addition, the water supply needed to
support the increased population must be evaluated to determine what, if any, water will have
to be imported to meet the new demand.
Data Needs
The data and information needed to establish land-use trends include the following:
land cover
land uses
demography
Land cover data describe the appearance of the land surface, that is, whether the
surface is covered by: forests, croplands, grasslands, or water, etc. Comparing past and
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Land Use 14g
present land cover provides information on the effect of natural and human changes on the
landscape.
Land-use data reflect anthropogenic uses of the land surface. Land uses can be
subdivided into four broad categories: urban, rural, agricultural, and open space (e.g., forests,
lakes) not included in the other uses. Subcategories, dependent on the purpose of the data
gathering, are frequently specified. Industrial development (see below) can be located in any
of the other categories.
Urban areas usually consist of core cities, containing high-density residential,
commercial, and industrial areas, surrounded by suburbs with lower-density residential and
commercial areas. While many urban areas in the United States depend on surface water for
the majority of their drinking water supply, a combination of surface and ground water
sources is often used. Some cities such as Miami, San Antonio, and Memphis rely on ground
water as their primary drinking water source (Spirn, 1984). With population increasing in
urban areas and surface water availability remaining constant, ground water will probably
become more important as a source of drinking water.
Urban land use produces more runoff of precipitation than any other type of use.
Roads, parking lots, buildings, and sidewalks all decrease the permeability of the land
surface, and therefore decrease the amount of infiltration, and ultimately ground water
recharge to an underlying aquifer that would occur under natural conditions. This decrease
in recharge could affect future availability of ground water.
Rural areas contain low-density residential land-use areas and open spaces intermixed
with slightly higher densities of residences at crossroads and small towns. A majority of
people in rural areas rely on ground water as a primary source of water (USEPA, 1990).
Ground water supplies are usually adequate to support an individual water well in sparsely
populated areas. However, the individual sewage disposal systems found in rural areas are
conducive to contamination of shallow aquifers.
Agricultural areas have low residential density and can be described as cropland,
livestock, silviculture, or fallow. Agricultural activities can result in the alteration of surface-
drainage patterns. For example, forests or grasslands that are cleared for agricultural
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150 Approach #3
purposes produce more runoff of precipitation than would occur under natural conditions
(Marsh, 1983). Agriculture can also impact water quality; application of agricultural fertilizers
and pesticides can contaminate both ground and surface water.
Industrial land use usually occurs near available natural resources (e.g., metals, fossil
fuels, or water) needed by the industry, or near major transportation corridors (i.e., highways,
rivers, lakes, airports). Point-source pollution (e.g., leakage from chemical storage, or
untreated water discharged into surface water) from industrial sites may impact the quality of
local ground water (USEPA, 1989a). In addition, industry often uses large quantities of
ground water for manufacturing. For more information about aquifer use, see Approach #2,
Demography is the study of the size, density, distribution, and characteristics of
human populations. Census data show areas of gaining or losing population at small to
regional scales. As population grows, so do the conflicts between supply and demand for
water, and residential versus industrial development. Each land use has associated with it a
potential for ground water contamination. Ground water protection policies and strategies
should be developed in growth areas prior to the realization of degraded water quality or
insufficient water supplies to meet demands.
Methods
Analysis of land-use trends should rely on collection and interpretation of existing
data. Land-cover and land-use data are typically available from various Federal, State, and
local agencies. Demographic data can be obtained from local governments or directly from
the Census Bureau. Other data can be collected from the following:
the U.S. Geological Survey (USGS) and State geological surveys
(topographic and land-use maps, aerial photographs and *
satellite imagery)
the U.S. Bureau of Land Management (land-status maps)
the U.S. EPA (contaminant-source information)
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Land Use 151
U.S. Department of Agriculture's Soil Conservation Service (SCS) (soil-
survey data and maps)
U.S. Bureau of Census (census information)
relevant State agencies (land-use maps and data bases)
local planning agencies (zoning maps and comprehensive plans)
Topographic maps from the USGS provide elevation, cultural, and hydrographic data
at a variety of scales. The scale of the most detailed and common USGS map is 1:24,000.
The maps may also identify areas of vegetative cover. Topographic maps should be used for
outlining vegetative areas only in the absence of more reliable and detailed sources such as
recent aerial photographs. Topographic maps also show the extent of urban development;
however, they are updated infrequently and should not be used for this purpose. The USGS
also produces land-use maps. These maps show land use and land cover (as polygons) for
regional areas at a scale of 1:100,000 or smaller (i.e., larger geographical area). These maps
can be used for regional assessment of land-use characteristics, but should not be used to
evaluate local land uses. More detailed information for local assessments may be available
from local planning agencies.
State agencies, sometimes in cooperation with Federal agencies, may maintain land-
use maps for parts of their State. For example, Nebraska's Natural Resources Commission,
Databank Section, in cooperation with the SCS, is developing State land-use maps for
individual counties. The Databank Section maintains computerized copies of the maps and
SCS maintains the actual data. Land-use maps currently exist for 61 of Nebraska's 93
counties. The information contained on the maps includes different types of crop lands,
pasture land, forests, urban areas, and surface water bodies. Also, Florida's State Planning
Law of 1986 requires all counties to develop comprehensive plans that include land-use
maps. Florida has five water-management districts all or some of which have developed land-
use maps for their own districts.
Aerial photographs and satellite imagery can be used to identify land uses. These
remotely sensed images can be particularly useful for quickly surveying the land cover and
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152 Approach #3
land use of relatively large geographic areas. Conventional aerial photography is typically
used to obtain relatively large-scale, land-use assessments of such features as: forests,
agricultural lands, paved or roofed areas, and industrialized areas. The U.S. Department of
Agriculture's Agricultural Stabilization and Conservation Service (ASCS), and the USGS,
through their National High Altitude Aerial Photography (NHAAP) program, regularly take
aerial photographs on a county-by-county basis. The USGS NHAAP program takes
photographs on an approximate five-year basis to update 7,5-minute topographic maps The
ASCS aerial-photography program generally takes photographs on a county-by-county
rotational basis for use with the SCS soil-series maps. The scale of aerial photographs in the
range of 1:12,000 to 1:50,000 are often used for mapping land use and may be obtained from
the USGS or the Aerial Photography Field Office of the ASCS. Digitized cultural data are
available for roads, utilities, county boundaries, and other manmade structures, in computer
files that may be used in a Geographic Information System (GIS). Some local-planning
agencies also maintain aerial photographs of their jurisdiction.
Satellite or other remotely sensed images typically are used for defining large features
such as slopes, drainage, and geology, and for assessing spatial relations of natural and
anthropogenic features on a broad range of scales (Marsh, 1983). These images can be
used to enhance field surveys. Satellite images provide the user with the ability to observe
relatively large areas (e.g., 115 square miles for Landsat MSS) and to observe the spectral
reflectance of several bands or wavelengths of electromagnetic energy. The various bands of
spectral reflectance recorded on the image allow the user to "highlight" various physical
features on the land surface. For example, if the image is displayed in the near Infrared
(band 6 Landsat TM), vegetation will appear darker than the surrounding features, while
developed areas will appear very bright.
Satellite imagery generally comes in digital (i.e., electronic tape or diskette) format, but
may also be purchased in picture scenes. Image processing software can be used for both
aerial photography (if scanned into digital format) and satellite images. Image processing
software can be used to enhance the image to highlight various features and to digitize
different spatial land-use patterns for use in a GIS.
Zoning ordinances and corresponding zoning maps can provide a wealth of
information on land use in developed areas. In their simplest form, zoning ordinances aim to
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Land Use
control the general types of activities that can occur within a specified area (USEPA, 1989b).
For example, an area may be zoned for open spaces, agricultural, residential, commercial,
light industrial, or heavy industrial use. Zoning maps may present existing development or
areas legally planned for development that has not yet occurred. Comprehensive plans
designed by local planning agencies establish goals for, and define the geographical area of,
future development. These plans often contain generalized maps that highlight areas of
potential growth. Parcels of land within a growth area that is presently zoned for rural use
may be rezoned to a use compatible with a comprehensive plan.
Survey plat maps of property boundaries are very useful in showing urban land-use
changes. These maps are available for most cities in the United States and were developed
for tax-assessment purposes. Survey plats show streets and historical uses, making these
maps very helpful in locating sites where potential contaminants may be buried, but not
readily apparent because land-use changes have masked former uses. By comparing current
and past plat maps, new development can usually be identified. Local property records also
document past and present land uses. Such records include land titles, deeds, property
transfers, and building permits. Property transfer records typically are maintained at the
county level. These records should also provide good information on past, present, and
future land uses.
For many years, the SCS has been providing technical and scientific support to local
governments in producing soil-survey maps and reports. Soil boundaries are often mapped
on aerial photographs that show land cover and uses. The land-use and land-cover
information contained on the photos may be outdated, but may provide historical information
in establishing land-use trends. The soil information is also helpful in identifying
environmentally sensitive areas such as hydric soils that may indicate the presence of
wetlands. Many local governments have updated original soil surveys with new field
information and put the surveys on new base maps.
Federal and sometimes local floodplain maps depict floodplain boundaries and can be
used to protect these sensitive areas. Other environmentally sensitive areas, such as
wetlands, riparian zones, and ground water recharge areas, can be identified and mapped.
These maps could be consulted in the development or modification of zoning regulations and
comprehensive plans.
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-154 Approach #3
Some jurisdictions peripheral to urban areas, have developed methods of ensuring an
adequate supply of ground water, as their population expands. For example, in addition to
customary approval of wells and on-site sewage disposal systems, officials in Loudoun
County, Virginia review detailed hydrogeoiogical studies of available ground water before they
will approve of plans for subdivisions of ten or more lots (Cooper, et al, 1989). This
development standard has been an effective means of ensuring available ground water
supply prior to development.
Presentation of Data/information
Information obtained from land-use and land-cover assessment methods should be
assembled onto a base map. Most urban jurisdictions maintain detailed base maps of their
land areas, but in the absence of a detailed base map, USGS topographic maps can be
used. Data on: existing land cover, land uses, environmentally sensitive areas, zoning, and
potential growth areas, could be mapped. Maps could be overlain (manually, or with a GIS if
the data are digitized) for management planning and protection purposes. The overlays are
easy to read and can serve as excellent exhibits for presenting information to decision-
makers.
Considerations
Existing aerial photography and satellite imagery are excellent tools for determining
land-use distribution, and are very inexpensive. Aerial photographs can be purchased from
Federal agencies (e.g., ASCS or USGS) for regional studies. Satellite imagery can also be
purchased from private firms and distributors. Many universities possess the necessary
image-processing software, hardware, and expertise to assist States in assessing land-use
patterns and trends.
Although zoning information provides local land-use data of significant detail on
current and past land uses and is easy to obtain, local planning agencies should be
consulted to ascertain that the information is not out of date. Zoning ordinances and
comprehensive plans are updated approximately every ten years by local planning agencies,
or more frequently as local conditions warrant. Zoning maps are usually updated after a
rezoning occurs for a given property.
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Land Use
The ultimate products of an assessment of land cover and land use are informed
predictions regarding land-use trends and better planning for future land-use protection
measures. Ground water protection policies aimed at controlling land use can be
implemented using a variety of tools, including comprehensive plans to define goals and
zoning ordinances to set development standards. These planning tools can help protect
ground water resources by targeting land uses that have a high potential to contaminate the
ground water.
Citations
Cooper, B., A. Blackburn, and J. Widmeyer, unpublished. "Use of Geographic Information
System (GIS) to Support Local Groundwater Ordinances and Research in Loudoun
County, Virginia." Presented at the Conference of Groundwater in the Piedmont of the
Eastern United States, October 16-18, 1989. 8 p.
Marsh, W.M., 1983. Landscape Planning: Environmental Applications. John Wiley and Sons
New York, NY, 356 p.
Spirn, A.W., 1984. The Granite Garden: Urban Nature and Human Design Basic Books
Inc., New York, NY, 334 p.
U.S. Environmental Protection Agency, 1990. Citizen's Guide to Ground-Water Protection
(EPA 440/6-90-004). Office of Ground Water Protection, 33 p.
U.S. Environmental Protection Agency, 1 989a. A Local Planning Process for Groundwater
Protection. Office of Drinking Water, 58 p.
U.S. Environmental Protection Agency, 1989b. Wellhead Protection Programs: Tools for
Local Governments (EPA 440/6-89-002). Office of Water, 50 p.
For More Information
For more information on this subject see the following references:
Aronoff, S., 1989. Geographic Information Systems: A Management Perspective. WDL
Publications, Ottawa, Ontario, Canada, 294 p.
Chen, W.T., G.W. Freas, Jr., G.D. Hickman, D.A. Pemberton, T.D. Wilkerson, I. Adler, and V.J.
Laurie, eds., 1978. Application of Remote Sensing to the Chesapeake Bay Region,
Proceedings. NASA Scientific and Technical Information Office, Conference
Publication 6, 417 p.
Drury, S.A., 1987. Image Interpretation in Geology. Allen and Unwin, London England 243
p. '
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156 Approach #3
Jenson, J.R., 1986. Introductory Digital Image Processing: A Remote Sensing Perspective.
Prentice-Hall, Incorporated, Englewood Cliffs, NJ, 379 p.
Last, FT., M.C.B. Hotz, and B.G. Bell, eds., 1986. Land and Its Uses - Actual and Potential.
Plenum Press, New York, NY, 597 p.
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Ground Water Vulnerability 157
Approach #4: Ground Water Vulnerability
Definition
Ground water vulnerability is the relative ease with which a contaminant applied on or
near the land surface can migrate to the aquifer of interest under a given set of land-use
management practices, contaminant characteristics, and aquifer sensitivity conditions. The
concept of vulnerability focuses on the vertical migration of contaminants into the ground
water reservoir, rather than on the direct placement of contaminants into the reservoir (e.g.,
backflow of chemicals down the well during chemigation practices). Ground water
vulnerability assessment methods assess hydrogeologic characteristics, contaminant
characteristics, and management practices related to the use of contaminants. For example,
aquifers with a high degree of sensitivity and located in agricultural areas with high pesticide
use are likely to be vulnerable to contamination.
Objective
Assessing ground water vulnerability provides a means of accounting for the
interrelated processes governing the movement and degradation of contaminants in the
saturated and unsaturated zones. Vulnerability assessment methods are used to identify
ground water resources that are at risk of being contaminated and serve as an aid in the
selection of appropriate ground water protection and management practices.
Data Needs
The data needed to assess ground water vulnerability include the following:
aquifer sensitivity (i.e., hydrogeologic characteristics)
potential sources of ground water contamination and their
characteristics
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158 Approach #4
land use
Analyzing an aquifer's sensitivity is a useful preliminary step in assessing the
vulnerability of ground water resources. An analysis of aquifer sensitivity provides ground
water managers with information concerning the intrinsic characteristics of the materials
comprising the aquifer and its overlying materials. That information provides a basis upon
which ground water scientists can perform ground water vulnerability assessments to estimate
the relative ease with which specific contaminants can migrate to an aquifer. For more
information on aquifer sensitivity analysis, including the uncertainties associated with its use,
see Approach #1.
To estimate the vulnerability of an aquifer, managers need to know the locations and
types of potential sources of ground water contamination. In the absence of current or
potential sources of contamination, ground water is not considered vulnerable.
Potential sources of ground water contamination can be categorized as point and
non-point sources. Point sources are any discernable or discrete conveyance from which
pollutants are or may be discharged (USGS, 1989). Point sources include: municipal and
hazardous-waste landfills, underground storage tanks, septic-tank drainfields, accidental
spills, leakage from chemical-storage areas at industrial and commercial facilities, and leakage
of petroleum products from underground storage tanks.
Non-point sources are releases of contaminants that occur over a wide area.
Contamination from dispersed sources cannot be traced back to a single point of release.
Non-point sources include pesticides and fertilizers applied in agricultural areas, and runoff
from city streets and parking lots.
The toxicity and quantity of potential contaminants from point and nor>point sources
determine the severity of ground water contamination. Common ground water contaminants
include:
organic chemicals
inorganic chemicals (including metals)
radionuclides
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Ground Water Vulnerability 159
microorganisms
Common organic chemical contaminants include: trichloroethylene and
trichloroethane used as industrial solvents; benzene, a solvent and additive in gasoline and
diesel fuels; pesticides such as insecticides, fungicides, herbicides, rodenticides, and
nematicides; RGB's used in insulating fluids in closed electrical systems; and other chemicals
used for lubricants, dyes, and adhesives. Inorganic contaminants include aluminum, arsenic,
cadmium, lead, and mercury, used in paints, protective coatings, alloys, and photography.
Other inorganic contaminants include nitrates from human and animal waste and commercial
fertilizers, and chlorides from chemical manufacturing, highway de-icing, water-purification
processes, and salt-water intrusion.
Radionuclides commonly found in ground water include uranium, radium, radon,
cesium, and tritium. Most occurrences of radionuclides in ground water are from natural
sources, but in some instances radionuclides are derived from human activities such as
medical applications, nuclear fuel-cycle and power-plant operations, mineral extraction
processes, and weapons production and testing. Microorganisms that can contaminate
ground water include giardia, salmonella, typhoid, and viral hepatitis. Any agricultural activity
involving animal wastes has the potential to contaminate ground water with microorganisms.
Because of synergistic effects, mixtures of contaminants may provide a greater
potential for pollution than individual contaminants. The chemical and physiochemical
reactions among contaminants, water, and geologic materials are not well understood and
add a complicating factor to vulnerability assessments.
To a large extent, land use determines the number and type of potential sources of
contamination. Ground water managers can identify, on a broad basis, where potential
sources of contamination are likely to exist by considering land uses. For more information
on land use and its impact on ground water, see Approach #3.
Methods
Methods for assessing ground water vulnerability can be divided into the following four
major categories:
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160 Approach #4
(1) simulation methods
(2) pesticide leaching methods
(3) contaminant loading methods
(4) mapping methods
For an extensive discussion of the vulnerability assessment methods in categories (1),
(2), and (3), including case studies, the reader is referred to EPA's document A Review of
Methods for Assessing Aquifer Sensitivity and Ground Water Vulnerability to Pesticide
Contaminants (EPA, in press).
Most methods used to assess ground water vulnerability are simulation models that
utilize computers. Simulation models are theoretically-based, mathematical expressions of
one or more processes or phenomena related to the transport and fate of contaminants in the
soil/aquifer systems. Simulation models can be effective in identifying best management
practices and in understanding the fate and transport processes that lead to the
contamination of specific sites. They can also be used to predict contaminant
concentrations, loadings, and the time it takes specific contaminants to travel various
distances through the aquifer. Vulnerability simulation models vary primarily by the number of
processes incorporated into the computer programs and the number and kinds of input
required. Some relatively simple ground water simulation methods incorporate only a few fate
and transport processes and can be used on personal computers without extensive technical
support. Other ground water simulation models might be referred to as research tools,
because they require powerful computers, substantial technical support, and several data
bases to operate.
Pesticide leaching assessment methods, the second group of vulnerability assessment
methods, are a narrowly-defined subcategory of vulnerability assessment methods that
incorporate both hydrogeologic and chemical factors. These methods require both
compound-specific and soil-specific information. Pesticide leaching methods allow users to
compare the relative leachability of various compounds for a given soil series and set of field
conditions. These methods are similar to scoring methods for aquifer sensitivity analyses
(see Approach #1), because they calculate a relative index, score, or classification. However,
chemical leaching assessment methods incorporate chemical characteristics such as the half-
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Ground Water Vulnerability 161
life of the compound and are considered a blend of aquifer sensitivity and ground water
vulnerability assessment methods.
The third group of ground water vulnerability assessment methods provides estimates
of contaminant loading. Contaminant loading methods combine chemical use (i.e., loading)
data with an aquifer sensitivity assessment. Contaminant loading methods can be used to
screen large study areas
The fourth ground water vulnerability assessment method is mapping. Mapping can
be used to determine the potential for contamination from point or from non-point sources of
contamination. Vulnerability mapping methods are relatively simple, use verified and easily
obtainable data, and have as output maps that are easy to interpret. For assessing
vulnerability to agricultural chemicals, agrichemical sales data or data on the percent of
intensely farmed land per political division can be used and reflect agricultural management
practices. For assessing vulnerability to point sources of contamination, the locations of, for
example, waste generators, landfills, and abandoned hazardous waste sites are needed.
Shafer (1985), and Bhagwat and Berg (1991) present a procedure for using the
mapping method to determine ground water vulnerability. Under this procedure, geologic
sensitivity based on a classification method is combined with information detailing the
distribution of waste sources per unit area (e.g., county, zip code). Highly vulnerable areas
have aquifers located at or near the land surface and contain either numerous contaminant
sources or are intensively agricultural. Low-vulnerability areas contain few contaminant
sources or are less intensively agricultural, and have either deep or no aquifers. For each
study area, the percent of land in each vulnerability ranking is calculated to obtain a weighted
vulnerability average. This method is particularly useful for assessing regional vulnerability
and for comparing the vulnerability of regions. The method can also be used to identify
potential "hot spots" that warrant more detailed investigations. Environmental officials in
Illinois used this mapping method to delineate ground water protection planning regions (see
the case study on Illinois in Appendix B for more information on this application).
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162 Approach #4
Presentation of Data/Information
Information developed from vulnerability assessment methods can be presented in
tabular, graphic, map, or report form. Tables are especially useful for reporting numerical
values, such as model output, that represent various degrees of ground water vulnerability.
Results from vulnerability assessment methods such as pesticide leaching methods that
generate a vulnerability score, classification, or relative index, typically are presented in
tabular form. Graphs can be used to illustrate vulnerability assessment outputs for such
important relationships as contaminant concentrations in soil versus soil depth.
The results of ground water vulnerability assessments may also be displayed on maps.
Small-scale maps (e.g., 1:100,000 or 1:250,000) are often used by managers who (1) are
responsible for ground water resources on a county or region-wide basis, (2) need a
screening assessment before proceeding to more detailed studies of priority areas, (3) expect
to encounter only a limited range of hydrogeologic conditions within a region, or (4) do not
have data to conduct a more detailed assessment. The scale of these maps is critical to
ensuring that the maps can provide support for their intended uses. Managers should be
cautioned that maps may have inherent limitations with respect to their accuracy of
representation.
As discussed above, assessing ground water vulnerability requires the synthesis of
different types of data, such as:
aquifer sensitivity (hydrogeologic characteristics)
land-use and zoning maps identifying potential sources of contamination
property boundaries
contaminant (e.g., pesticides) use and physical/chemical property information
If the data are georeferenced, a Geographic Information System (GIS) can help synthesize
and overlay the data and provide the ground water scientist with initial drafts of vulnerability
maps.
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Ground Water Vulnerability
163
Considerations
Managers should be aware of a number of considerations in the use of ground water
vulnerability assessments. Most important are: the uncertainty related to mapping, the
inherent limitations on models, and the resources required to implement vulnerability
assessment methods.
Mapping uncertainty is a consideration in the use and development of all maps,
including vulnerability maps. This uncertainty is often related to the scale of the map. The
accuracy of maps is also significantly reduced when a map compiled at a smaller scale (i.e.,
large geographical area) is displayed at a larger scale (i.e., small geographical area). This is
a particularly important consideration when using a GIS, due to the ease with which these
systems enable users to enlarge maps. When selecting a map scale to display results, it is
important to carefully consider the scale necessary for the intended use, the scale at which
data was calculated, and the density of data points.
Assessment methods that rely on simulation models have a number of limitations of
which managers need to be aware. The most important of these limitations, and the related
questions that managers should discuss with ground water scientists, are as follows:
Assumptions - On what assumptions is the model based? Have the
model's assumptions been met? What is the range in application of the
model, physiographically and with regard to specific parameters?
Input parameters - How reliable are the estimates of the input
parameters? Are the input parameters quantified within accepted
statistical bounds?
Quality control and error estimation - Has the model been checked
against direct applications or simulation of controlled experiments?
(USEPA, 1987)
The costs of staff, computing facilities, and specialized data-presentation equipment
needed to support assessment models can be significant. Vulnerability simulation models
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164 Approach #4
generally require a high level of expertise, although some models are less complicated than
others. Comprehensive simulation models may require a multidisciplinary team of highly-
skilled specialists. Even with less complicated simulation models, the use of personnel
familiar with them is necessary. Although data requirements vary by the complexity of the
model, most simulation models require site- and contaminant-specific values. For the most
accurate results, users should have a good basic knowledge of soil science, geology,
chemistry, and the hydrogeology of the study area. As a result of these personnel needs,
costs are generally greater for technical staff than for equipment or software.
The cost of conducting an assessment using the vulnerability mapping method can
also be high, because the method involves many steps, including the gathering of information
on hydrogeology and ground water quality (i.e., Components 1 through 10), inventorying
potential sources of contamination, and integrating the information. The cost is directly
related to the amount of data that are readily available.
Citations
Bhagwat, S.B., and R.C. Berg, 1991. Benefits and Costs of Geologic Mapping Program in
Illinois. Case Study of Boone and Winnebago Counties and its Statewide Applicability.
Illinois State Geologic Survey Circular 549, 40 p. .
Shafer, J.M., 1985. An Assessment of Ground Water Quality and Hazardous Substances for a
Statewide Monitoring Strategy (AA B3 1268). Illinois State Water Survey Contract
Report 367, 119 p.
U.S. Environmental Protection Agency, in press. A Review of Methods for Assessing Aquifer
Sensitivity and Ground Water Vulnerability to Pesticides. Office of Water, 181 p.
U.S. Geological Survey, 1989. Federal Glossary of Selected Terms. Subsurface-Water Flow
and Solute Transport. Office of Water Data Coordination, 38 p.
U.S. Environmental Protection Agency, 1987. Handbook. Ground Water (EPA/625/6-87/016).
Robert S. Kerr Environmental Research Laboratory, Ada, OK, p. 181.
For More information
For more information on this subject see the following references:
Berg, R.C., J.P. Kempton, and K. Cartwright, 1984. Potential for Contamination of Shallow
Aquifers in Illinois. Illinois State Geological Survey Circular 532, 30 p.
Bowen, R., 1986. Groundwater. Applied Science Publishers Ltd., London, 427 p.
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Ground Water Vulnerability
Driscoll, F.G.,1986. Groundwater and Wells Second Edition, Johnson Division St
Paul, MN, 1089 p.
EVerett44f^"1984' Groundwater Monitoring. Genium Publishing Corp., Schenectady, NY,
Hamill, L, and Bell, F.G., 1986. Groundwater Resource Development Butterworths, Boston
MA, 344 p, ' '
Page, G.W., 1987. Planning for Groundwater Protentinn Harcourt Brace Jovanovich
Publishers, New York, NY, 387 p.
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166
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CSGWPP Characteristics to be Addressed in Ground Water Resource Assessments
167
APPENDIX A:
Comprehensive State Ground Water Protection Program
Priority-Setting Characteristics to be Addressed in
Ground Water Resource Assessments
The Final Comprehensive State Ground Water Protection Program Guidance (USEPA,
1992) identified the characteristics below to be used in setting priorities, determining
appropriate remediation methods, and making siting decisions. The Ground Water Resource
Assessment Document incorporates these characteristics and reorganizes and expands on
them where appropriate to provide a comprehensive approach to assessing the resource.
This list is included only for reference purposes It is acknowledged not to be exhaustive but
rather suggestive of the kinds of information useful in resource assessment as one of the
bases for setting priorities for State ground water protection activities.
intrinsic sensitivity, hydrogeologic regimes and flow patterns (e.g., recharge
and discharge areas), geologic and hydraulic parameters and local
hydrogeologic setting
quantity and potential yield
ambient and/or background water quality as determined by monitoring
potential for remediation where contamination already exists
current use
reasonably expected future use based on demographics, land use,
remoteness, quality, and availability of alternative water supplies
values attributed to ground water resources
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168 Appendix A
the interactions and potential contamination impacts between surface and
ground water and the value of ground water quality to the maintenance of
ecosystem integrity
inter-jurisdictional characteristics
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Case Studies on the Development and Use of Ground Water Resource Assessments
169
APPENDIX B
Case Studies on the Development and Use of Ground Water
Resource Assessments at the State, Local, and Federal Level
This appendix presents five case studies that illustrate the nature of resource assessment and
the variety of approaches for conducting resource assessments in the field. Each case study
demonstrates how a State (or as in one case study, the U.S. Department of Energy [DOE]) actually
conducted a ground water resource assessment, identifies the parameters included in the State's
resource assessment, and demonstrates how the resource assessment was or will be used for
decision-making. Each case study includes the following sections:
Purpose of the Resource Assessment. This section briefly discusses the
State's/DOE's purpose in undertaking the resource assessment
Overview of State Ground Water Protection Efforts. This section places the resource
assessment technique in the context of ground water protection efforts
Administration and Organization of the State's Resource Assessment. This section
provides an overview of the resource assessment and of the agencies that
participated in the assessment
Conducting the Resource Evaluation. This section discusses which resource
assessment Components and Approaches the State/DOE used. This discussion ties
the State's/DOE's efforts back to Components and/or Approaches outlined in this
Technical Assistance Document. This section also describes how the State/DOE
collected, managed, and synthesized data for the resource assessment and prepared
the final product of the assessment
Decision-Making Based on the Resource Evaluation. This section discusses how
information from the resource evaluation was used as part of resource assessment to
achieve the most prudent decision-making for ground water protection management
by the State/DOE. The discussion focuses on how the information was or is being
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170 Appendix B
employed in making land-use decisions and in influencing other policy related
decisions
Other Sources of Information. This section includes the sources of information used in
the development of this case study and where additional sources of information on the
case study can be located
This appendix includes the following case studies:
Arizona Department Of Water Resources Hydrologic Map Series
Potential for Contamination of Shallow Aquifers in Illinois
Sensitivity Assessment of Major Aquifer Systems of Allen County, Indiana
Big Sioux Aquifer Assessment in South Dakota
Hydrologic Assessment of U.S. Department of Energy's Oak Ridge, Tennessee
Reservation
The DOE case study on the Oak Ridge Reservation follows a slightly different format than the
other case studies. The DOE case study discusses DOE ground water protection requirements, the
resource assessment undertaken at Oak Ridge, and DOE cooperative relationships with relevant State
agencies.
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Case Studies on the Development and Use of Ground Water Resource Assessments
171
ARIZONA
Department of Water Resources
Hydrologic Map Series
Overview of State Ground Water Protection
Efforts
More than 60 percent of the water resources
supplied in Arizona comes from ground water. Most
of the ground water supplies, especially in the
central and southern sections of the State, are
found in unconsolidated alluvial and valley fill
deposits between 800 and 1200 feet thick. Depth to
water ranges from a few feet to several hundred feet
below ground surface.
PURPOSE OF THIS RESOURCE
ASSESSMENT:
The Arizona Department of Water
Resources (ADWR) hydrologic map
series is a cooperative effort with the
U.S. Geological Survey to study and
evaluate the ground water resources of
the State as an essential element in
planning, management, and policy
development processes.
The semi-arid climate with summer temperatures often exceeding 100F and low annual
precipitation of between 7 and 8 inches can place limits on the adequate availability of surface water
in the State. As a result, Arizonans rely heavily on ground water resources for domestic and
commercial purposes. The principle uses of water resources are:
municipal (including domestic drinking water and urban irrigation)
industrial
agricultural irrigation
By the year 2025 the percent of consumptive use by category is expected to shift dramatically.
Municipal use may more than double while agricultural use may be reduced by half (ADWR, 1991).
Many areas in the State have experienced severe ground water overdrafts. Overdraft
conditions exist when ground water extraction exceeds recharge. Ground water withdrawals in central
and southern Arizona have exceeded recharge by approximately two million acre-feet per year and
have resulted in the lowering of ground water levels by up to 600 feet in some areas. Ground water
levels in the Phoenix Active Management Area (AMA) have declined up to 450 feet at certain locations,
averaging a decline of 2.7 feet per year between 1923 and 1983 (ADWR, 1991).
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172 Appendix B
The lowering of ground water levels can create three significant problems in addition to the
depletion of water resources:
increased well drilling and pumping costs
decline in water quality resulting from the use of deeper, more highly mineralized
ground water
earth subsidence resulting in cracks and fissures at the earth's surface
In many areas, these conditions have made it economically unfeasible to extract ground water for
some uses (ADWR, 1991).
Arizonans, seeking to address the growing problems associated with ground water overdrafts,
and recognizing the necessity of wise planning and management of water resources, joined in a
comprehensive effort to formulate a resource protection plan. Those involved included State and local
leaders and legislators, private commercial interests such as industrial and development concerns,
special interest groups, and the general public. The result was Arizona's Groundwater Management
Code (Code) enacted in 1980. The Code has three important goals:
control severe overdraft
provide a means to allocate the limited ground water resources
augment ground water usage through water supply development
In addition, the Code created the ADWR and charged it with the responsibility to administer the
Code's provisions.
A key provision of the Code was to target regulations to areas of the State with the most
severe ground water problems. To accomplish this, the Code established three levels of water
management. The most regulated level is the Active Management Area which includes 80 percent of
the State's population and 70 percent of ground water overdrafts. The second management level is
the Irrigation Non-expansion Area (INA) where, depending on when ground water was first used for
irrigation, limitations are imposed on additional ground water withdrawn for agricultural purposes. The
lowest level of regulation includes provisions that apply Statewide where ground water concerns are
less critical. To assist management efforts further, ground water resources are organized
geographically by ground water basins and sub-basins rather than geopolitical boundaries.
Recognizing that ground water resources must be of suitable quality as well as of sufficient
quantity for intended uses, the legislature enacted the Environmental Quality Act (EQA) of 1986. The
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EQA created the Arizona Department of Environmental Quality (ADEQ), effective July, 1987, "to
administer State programs for water quality, air quality, solid waste, and hazardous waste" (ADWR,
1991). Because ground water quantity and quality are interrelated issues, both the ADWR and ADEQ
have authority to regulate ground water quality and the two agencies coordinate efforts to achieve
ground water resource protection goals.
In the Phoenix AMA, the goal of the Ground Water Quality Management Program, which is
principally administered by ADWR, is to control ground water quality and maximize the quantity
available for beneficial use. To meet this goal, four objectives are recognized by ADWR:
(D
(2)
(3)
(4)
protect ground water quality from degradation
collect ground water quality data on a regular basis
identify those areas with ground water of poor quality
correct problems
Although both ADWR and ADEQ are responsible for studying and characterizing the State's ground
water resources, ADWR assumes much of the data compilation activities with technical support
provided by ADEQ.
Administration and Organization of the State's Resource Assessment
A characterization of the State's ground water resource is the initial step in, and becomes the
basic tool to achieve ground water quantity and quality goals. ADWR has been gradually assuming
ground water resource characterization responsibilities from the U.S. Geological Survey (USGS) which
has been conducting characterizations for many years. Ground water resource characterization
remains a cooperative effort among the USGS, ADWR, and ADEQ, however. Collected information
and data bases are shared between the three agencies with lead responsibility resting with ADWR.
A Memorandum Of Understanding (MOU) has been developed between ADWR and ADEQ
specifically stating the roles of each agency including responsibilities, staff and financial resource
allocation, and coordination of activities. Although the current MOU expired in June, 1992, a verbal
agreement between the two agencies continues the MOU virtually unchanged.
The product of the joint agreement and the agencies' collaborative efforts is the Hydrologic
Map Series. These maps were produced to incorporate ground water quality concerns into
management programs. The subject of this case study is Hydro.ogic Map Series Report Number 12
Maps Showing Groundwater Conditions in the West S..t River. East S.lt River. Lake
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174 Appendix B
Carefree and Fountain Hills Sub-Basins of the Phoenix Active Management Area. Maricopa. Final, and
Yavapai Counties. Arizona-1983 (Report Number 12) (Reeter and Remick, 1986). The report typifies
ground water resource evaluations conducted in Arizona.
Report Number 12 combines data compiled from multiple sources by ADWR hydrogeologists.
Specifically, the principle sources of data are:
USGS's WATSTORE data base
EPA's STORET (Storage and Retrieval) data base containing data collected by ADEQ
and other local, State, and Federal agencies
ADWR's GWSI (Ground Water Site Information) system
consultant reports
The information in the data bases was compared to and used to fill data gaps and update and
confirm other published reports. Data on certain water quality parameters such as volatile organic
compounds were provided by ADEQ.
Conducting the Resource Evaluation
The goal of the assessment program is to provide the information necessary to combine
ground water quality and quantity concerns into ADWR management programs. Hydrologic Map
Series Report Number 12 includes three maps, each presenting data essential to meeting the goal.
Map number one presents depth to water and the elevation of the water table. Water level
contours with a contour interval of 50 feet are included as are the locations of known water wells and
springs. The location and extent of valley fill deposits and bedrock are presented. Accompanying text
describes the hydrogeologic conditions of the area. Background information on the legislative and
organizational structure and a synopsis of the existing ground water problems are also provided.
Map number two presents changes in ground water levels between 1976 and 1983. Water
levels were measured in selected wells; declines and increases are notated by a "-" or"+" respectively,
with the corresponding value. Hydrographs for selected wells are included showing water level
fluctuations measured from ground surface for the years between 1945 and 1985. A table containing
ground water pumpage in acre-feet per year from 1915 to 1983 completes the data presented on map
two.
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Case Studies on the Development and Use of Ground Water Resource Assessments 175
Map number three presents the chemical quality of water in the management area. Numerical
data from selected wells indicate dissolved solids and fluoride concentrations in the ground water. In
addition, diagrams showing cation/anion concentrations for major constituents (i.e., sodium, chloride,
calcium, bicarbonate, magnesium, and sulfate) are given for selected wells. The diagrams provide "a
means of comparing, correlating, and characterizing similar or dissimilar types of water" (Reeter and
Remick, 1986).
Each of the maps presents certain information in common with the others. The information
presented is:
boundaries of the study area
Public Land System grid (Township and Range)
prominent natural surface features (e.g., surface water and mountain ranges)
urban areas
the location and extent of valley fill deposits and bedrock
The combination of data presented in the maps along with accompanying text, provide a very
useful means of evaluating the ground water resources in detail fine enough for overall planning and
management purposes. The data components are relatively congruent with the following Technical
Assistance Document Components:
Aquifer and Aquifer System Occurrence (Component #2)
Water Table and Potentiometric Surface (Component #3)
Hydraulic Properties (Component #4)
Chemical and Physical Characteristics of Aquifers and Overlying Materials
(Component #9)
Ambient Ground Water Quality (Component #10)
However, not every Component is necessarily applicable or utilized. For example, a detailed
description of lithology is not included because the alluvial deposits, which contain the majority of
ground water resources, are fairly homogeneous throughout the area and need be described only
once in text format. Likewise, the movement and flow of ground water is relatively consistent and can
be determined by changes in the water table elevation above the datum (mean sea level).
As previously mentioned, the data presented on the maps were compiled from a variety of
sources utilizing the data bases and technical expertise of local, State, and Federal agencies. In
addition, the data collection process is an ongoing cooperative effort. As new information becomes
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176 Appendix B
available, it is input to the appropriate data base. ADWR and ADEQ monitor thousands of wells
annually and attempt to update the information in targeted areas (areas in greatest need) every three
years. Maps are updated as needed as sufficient new data become available.
Decision-Making Based on the Resource Evaluation
The hydrologic map series is intended and designed to assist ADWR and ADEQ in their
respective missions to manage ground water quantity and quality. In so doing, the maps are used to
identify areas potentially requiring special well construction methods or spacing. This helps protect
ground water from degradation. To assist ADWR with long-range ground water requirement planning,
the maps can be compared with land use, urban growth projection, wildlife, and other similar types of
maps. In areas identified as having ground water unsuitable for drinking water, other water supplies
can be utilized instead, thus protecting the public health. Where public supply wells produce water
unsuitable for drinking purposes, the type and level of contaminants can be addressed with
appropriate treatment technologies.
Water quantity planning decisions also rely on accurate and current supply information. In
areas where ground water overdrafts occur, or where supplies are insufficient to meet projected
demand, ground water pumping can be reduced and future well development minimized by placing
limits on extraction and restricting the number of permits issued. Additional programs such as
incentives to conserve existing supplies; reduce demand, encourage reuse, and to secure new
supplies or augment current supplies could also be implemented. If necessary, residential and
industrial development plans can be required to directly address and mitigate adverse conditions
affecting ground water quantity and quality before being approved to allow development.
Other Sources of Information
Arizona Department of Water Resources, Undated. Arizona Water Conservation Requirements: 1980-
1990.
Arizona Department of Water Resources, 1991. Management Plan for the Second Management Period
1990 - 2000 Phoenix Active Management Area.
Arizona Department of Water Resources, Undated. Overview of Arizona's Groundwater Management
Code.
Meeks, G. Jr., 1987. Arizona Groundwater: Negotiating an Environmental Quality Act. National
Conference of State Legislators, Denver, CO.
Reeter and Remick, 1986. Maps Showing Groundwater Conditions in the West Salt River. East Salt
River. Lake Pleasant. Carefree and Fountain Hills Sub-Basins of the Phoenix Active
Management Area. Maricopa. Final, and Yavapai Counties. Arizona-1983.
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Case Studies on the Development and Use of Ground Water Resource Assessments 177
Wallace, Greg. Hydrologist. Arizona Department of Water Resources.
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178
Appendix B
ILLINOIS
Potential for Contamination of
Shallow Aquifers in Illinois
Overview of State Ground Water Protection
Efforts
Approximately 80 percent of the people
residing in the State of Illinois, excluding the
Chicago metropolitan area, depend upon ground
water for their drinking water. In addition to
household uses, the ground water resource serves
industry, business, and agriculture in the State.
Ground water also contributes a large portion to the
surface water flows in Illinois through discharge to streams. The ground water input contributes to
many surface water uses and is important in maintaining surface water flow, especially during low to
normal precipitation periods.
Ground water used for public water supplies in Illinois is usually obtained from high-yielding
wells in unconsolidated glacial drift materials or from consolidated rock formations that may underlie
the drift deposits. These shallow water-bearing bedrock aquifers are limestone or dolomite and the
deeper aquifers are sandstone. The potential for ground water resources to become contaminated is
a critical concern in Illinois, particularly for the shallow aquifers occurring throughout the State.
PURPOSE OF THIS RESOURCE
ASSESSMENT:
The purpose of this study was to
describe and map geologic materials to
a depth of 50 feet throughout the State.
Such an understanding and
representation of geologic materials
allowed the ISGS and others to
determine the potential sensitivity of
underlying aquifers to contamination.
Understanding the importance of the ground water resource and the potential for its
contamination from diverse sources, the Illinois Legislature and Governor enacted the Illinois
Groundwater Protection Act (IGPA) in 1987. The Act seeks to "restore, protect and enhance the
ground water... as a natural and public resource." It also establishes a unified cjfound water
protection program including ground water protection policy, cooperation across State agencies,
water well protection zones, resource mapping and assessment, recharge area protection, and ground
water quality standards.
The IGPA created the Interagency Coordinating Committee on Groundwater (ICCG) to direct
efforts of State agencies and facilitate implementation of the IGPA. Ten State agencies participate in
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Case Studies on the Development and Use of Ground Water Resource Assessments 179
the ICCG. The Illinois Environmental Protection Agency (IEPA) and the Department of Energy and
Natural Resources (ENR) are very active in the implementation of the Act. ENR is responsible for
developing a comprehensive ground water evaluation program, including resource assessments, data
collection and automation, and ground water monitoring. The Illinois State Geological Survey (ISGS)
and Illinois State Water Survey (ISWS), divisions of ENR, developed a long-term ground water
evaluation plan, which is being implemented as funds become available.
Administration and Organization of the State's Resource Assessment
The Illinois State Geological Survey has been studying the State's ground water resources for
over fifty years. During that time, the ISGS has published numerous ground water resource
evaluations at both the county and State level and has provided valuable information to the IEPA and
ENR on the hydrogeologic characteristics of the State's ground water resources. The Illinois State
Water Survey has been conducting ground water studies even longer. The agency performs aquifer
tests across Illinois and maintains an extensive data base on aquifer properties. The ISWS was
organized specifically as the State's water resource research agency and primarily deals with water
quantity and quality issues.
Ground water evaluations conducted in Illinois provide the foundation for a number of
activities. For instance, the ISGS has studied areas sensitive to landfilling of wastes and the potential
for contamination of unconsolidated and bedrock aquifers. The ISGS has mapped and demonstrated
the potential for contamination of aquifers at both the State and county level. These studies and
others continue to provide important hydrogeologic information for environmental decision making. Of
particular note is the ISGS Statewide study on the Potential for Contamination of Shallow Aquifers in
Illinois, completed in 1984. The purpose of this study, initiated and supported by the IEPA, was to
describe and map geologic materials to a depth of 50 feet throughout the State. Such an
understanding and representation of geologic materials allowed the ISGS and others to determine the
potential vulnerability of underlying aquifers to contamination. This mapping increased awareness
regarding the contamination potential of Illinois' shallow aquifers by showing that about 50 percent of
the State was characterized as having an aquifer within 50 feet of the surface. The study was a key
element for promoting ground water protection legislation in the State.
As part of the study, the ISGS produced maps of the entire State at a scale of 1:500,000 that
are unique in their detail of geologic information. The maps' intended uses are to:
suggest areas, not specific sites, where disposal of wastes will have the minimum
potential for contaminating ground water resources
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180 Appendix B
screen areas with low contamination potential, as part of the process of locating new
disposal sites
The Potential for Contamination of Shallow Aquifers in Illinois study relied almost entirely on
geological and hydrogeological information already compiled by the ISGS and ISWS. The study
coordinated and synthesized information collected as part of other county and State level studies. In
addition, thousands of water well logs were evaluated for purposes of identifying potential aquifer
materials. This approach demonstrates how existing data often form a base of information that can be
used in future resource assessments. This approach also avoids duplication of effort in collecting
baseline geologic and hydrogeologic data and information.
Conducting the Resource Evaluation
The Potential for Contamination of Shallow Aquifers in Illinois study describes and maps
geologic materials on the basis of thickness, texture, permeability, and stratigraphic position. Since
waste effluent travels through different materials at different rates, the contamination potential of
aquifers depends on the protection afforded by overlying and underlying less permeable materials.
As a result, the combination of hydrogeologic properties and stratigraphic position of geologic
materials provides the basis for mapping the potential for the contamination of aquifers. The general
premise of the mapping exercise is that the deeper the aquifer, and the thicker and finer-grained the
overlying confining materials, the lower the potential that the aquifer will become contaminated. A
rating scheme that addresses the potential for contamination allows officials to compare sequences of
geologic materials in any area of the State.
The ISGS was interested in collecting and synthesizing the following information to determine
the potential for contamination of shallow aquifers:
distribution of geologic materials (see Component #1)
Bedrock
Glacial and other surficial deposits
source, movement, and availability of ground water
Location and areal distribution of aquifers (see Component #2)
Hydraulic properties and aquifer materials (see Component #4)
Aquifer confinement and interconnections (see Component #5)
Recharge characterization (see Component #6)
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Case Studies on the Development and Use of Ground Water Resource Assessments 181
physical properties that reduce concentration of contamination (see Component #9)
Dilution, dispersion, and filtering
Attenuation
An understanding of the distribution of geologic materials in Illinois allows the ISGS to assess
the potential movement of contaminants through vertical sequences of different geologic materials.
Knowledge of the source, movement, and availability of ground water provides important information
on the location of aquifers, the movement and flow of water within aquifers, and the potential
movement of contaminants into and within aquifers. An understanding of the contaminants and the
physical properties that reduce concentrations of contamination provides further insight into how
contaminants move through geologic settings and aquifers.
Through a detailed search of previously conducted ISGS and ISWS studies and maps, as well
as an evaluation of water well logs on file, the ISGS pieced together a 20-foot and a 50-foot depth
geologic stack-unit map (Berg and Kempton, 1988) to demonstrate how geologic materials are
distributed both horizontally and vertically throughout Illinois. A stack-unit map shows the areal
distribution of geologic materials over a specified area in their order of occurrence to a specified
depth. Sources of information used to construct these stack-unit maps included:
general ISGS publications and maps such as the Geologic Map of Illinois and
Quaternary Deposits of Illinois
other ISGS studies including subsurface stratigraphic data from maps, field notes, test
drilling, and water well logs
evaluation of more than 25,000 well logs and sample-set descriptions
From this work, the ISGS developed two contamination potential maps. The map for land
burial of municipal waste, with a depth limit of 50 feet, was constructed first. Then the map for surface
and near surface disposal of wastes, with a depth limit of 20 feet, was made by transferring some unit
boundaries from the land-burial map.
Within map boundaries for both maps, related stack units or vertical sequences of materials
were combined into sets of geologic sequences. Unique sets were identified and then described by
relating type, texture, and permeability of materials to depth, thickness, and the position in the
geologic sequence. These sets of vertical geologic sequences were then rated by comparing the
capacities of earth materials to accept, transmit, restrict, or remove potential contaminants from waste
effluent. Finally, assigned ratings were added to each specific map unit. The two maps show the
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182 Appendix B
distribution of sequences of geologic materials and their comparative ratings. Resulting products are
aquifer sensitivity maps (see Approach #1).
The ISGS faced a number of difficulties in preparing the stack-unit maps for the entire State
(Berg and Kempton, 1988). In general, the availability and accuracy of data decreases as depth
increases. Many of the maps used in this study relied on a variety of different scales. Because the
final map product was at a scale of 1:500,000, some detail on smaller units was lost. Also units less
than three feet thick were too small to be included unless they were continuous over a relatively large
area (i.e., three to four square miles).
Decision-Making Based on the Resource Evaluation
The map for land burial of municipal wastes and the map for surface and near surface
disposal of wastes provide a sound basis for preliminary appraisals of earth materials and geological
sequences on a regional scale for:
selecting new waste disposal sites
assessing the suitability of existing waste disposal sites and operations by relating
their location to the rating indicators on the maps
The maps can also be used to show the generalized geology of the State of Illinois to a depth
of 50 feet and can be used in evaluation projects to describe and rate sequences of geologic units for
sand and gravel resources, shallow drinking water supplies, and general construction conditions.
The Potential for Contamination of Shallow Aquifers in Illinois study maps have been used
widely by local and county authorities to support zoning and siting decisions. IEPA has applied the
maps to assist in the selection process for new waste management facilities and to gauge the
potential for contamination from existing facilities.
These maps, with the addition of deeper aquifer information and contamination source data,
also allowed IEPA, with the assistance of the ICCG, to select Ground Water Protection Planning
Regions. These Regions consist of multi-county areas initially chosen because of their high potential
vulnerability to ground water contamination.
In addition, the ISGS maps from this study, along with deeper aquifer information, were used
by the Illinois Department of Nuclear Safety to screen the State for a low-level radioactive waste
disposal site.
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Case Studies on the Development and Use of Ground Water Resource Assessments 183
The ISGS maps have two limitations as waste management decision-making tools. First, these
maps cannot be used to evaluate sites for wastes that require long periods of containment, such as
high-level radioactive wastes. Second, these maps can only be used to assess the regional
appropriateness for waste management activities, and cannot be used as substitutes for site-specific
evaluations because of local complexities in geologic materials, A number of site-specific factors and
seasonal factors must be considered in determining an appropriate site for waste management
activities. Many of these factors were beyond the scope of this project and the scale of these maps.
Other Sources of Information
State Richard C. Berg
Contact: Illinois State Geological Survey
Natural Resources Building
615 East Peabody Drive
Champaign, IL 61820
(217) 244-2776
Berg, R.C and J.P Kempton, 1988. Stack-unit Mapping of Geologic Materials in Illinois to a Depth of 15
Meters: Illinois State Geological Survey, Champaign, IL, Circular 542, 23 p.
Berg, R.C., Kempton, J.P., and Cartwright, K., 1984. Potential for Contamination of Shallow Aquifers in
Illinois. Illinois State Geological Survey, Champaign, IL, Circular 532, 30 p.
Berg, R.C., Kempton, J.P., and Stecky, A.N, 1984. Geology for Planning in Boone and Winnebaoo
Counties- Illinois State Geological Survey. Champaign, IL, Circular 531, 69 p.
Burch, S-L" 1991- The New Chicago Model: A Reassessment of the Impact of Lake Michigan
Allocations on the Cambrian-Ordovician Aquifer System in Northeastern Illinois. Research
Report 119, Illinois State Water Survey, Champaign, IL, 52 p.
The Illinois Ground Water Protection Act, 1987. P.A. 85-0863.
Illinois Environmental Protection Agency, 1988. A Primer Regarding Certain Provisions of the Illinois
Ground Water Protection Act. Illinois Environmental Protection Agency, Springfield, IL, 48 p.
Illinois Interagency Coordinating Committee on Ground Water, 1990. Illinois Ground Water Protection
Program: Biennial Report. Illinois Environmental Protection Agency, Springfield, IL, 65 p.
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184
Appendix B
INDIANA
PURPOSE OF THIS RESOURCE
ASSESSMENT:
The purpose of this study was to identify
the distribution of major aquifer systems
and their sensitivity to contamination in
Allen County, Indiana.
Sensitivity Assessment of Major
Aquifer Systems of Allen County
Overview of State Ground Water Protection
Efforts
Indiana depends on its ground water
resource for a number of beneficial uses. Nearly 60
percent of the State's five million residents use
ground water for drinking water purposes. Ground
water is also vital for Indiana's industrial and agricultural growth and development. Ground water
consumption and use in Indiana is expected to increase in the foreseeable future.
The availability and quality of ground water varies widely across Indiana. Indiana relies on
bedrock aquifers in the southwest and glacial outwash aquifers beneath and adjacent to major rivers
and tributaries for ground water. Most fresh or potable ground water in Indiana occurs at depths of
40 feet to 300 feet. Highly mineralized waters are usually found at greater depths. Much of Indiana's
ground water is moderately to excessively hard as a result of the presence of dissolved calcium, and it
locally contains high levels of iron, manganese, or hydrogen sulfide. Conventional water treatment
can correct these problems for normal uses.
Even though there is an abundance of high quality ground water to provide for the State's
needs, Indiana recognizes that its continued economic growth and quality of life will depend on the
actions taken to maintain this vital resource. Indiana's ground water protection policy requires that
existing and potential beneficial uses of ground water be protected. The policy allows for limited
degradation of some ground waters, if beneficial uses are not affected and the degradation is judged
to be economically or socially justifiable. The policy, however, also prohibits degradation of ground
water whose quality exceeds existing standards (Indiana Administrative Code, Title 330, 1987).
The responsibilities of implementing Indiana's ground water protection policy falls on three
separate State agencies. The Indiana Department of Environmental Management (IDEM) administers
applicable State and Federal laws through regulatory programs to protect the quality of ground water
from potential pollution sources. The Indiana Department of Natural Resources (IDNR) is responsible
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185
Case Studies on the Development and Use of Ground Water Resource Assessments
for management of oil, gas, and mining activities, water well drilling, ground water information, and
aspects of water quality. Within the IDNR, the Division of Water and Indiana Geological Survey
provide valuable information on ground water resources to the other State agencies. Finally, the
State Board of Health administers septic system regulations and ensures that public water supplies
provide safe drinking water. Indiana's Inter-Agency Ground Water Task Force coordinates the
implementation of ground water protection activities across the three agencies.
Administration and Organization of the State's Resource Assessment
Indiana recognizes that one of the most important features of a ground water protection
program is the development of detailed maps and descriptions of the State's major aquifer systems.
As part of its Ground Water Protection Strategy, Indiana identified the following ground water resource
assessment needs:
delineation of the lateral distribution and thickness of aquifers
identification and delineation of aquifer recharge and discharge areas
information on ground water flow rates and direction
data on the physical properties of aquifers and confining units, such as permeability,
porosity, and grain size
The IDNR's Division of Water and the Indiana Geological Survey have gathered and
synthesized much information on Indiana's ground water resources. As part of the State's ground
water resource assessment efforts, IDNR has initiated a phased regional study approach. These
regional studies use river basins as boundaries and map aquifer environments, computerize well
records, and collect water quality data for each basin. Through this approach, IDNR is seeking to
delineate and name aquifer systems in a standard fashion.
In addition to assisting the State in conducting a comprehensive assessment of its ground
water resources, the Indiana Geological Survey (IGS) conducts ground water resource assessments
for individual counties. An example of such an assessment is a study to identify the distribution of
major aquifer systems and their sensitivity to contamination in Allen County. At the request of Allen
County, IGS conducted a study that resulted in the preparation of 90 open-file maps at a scale of
1:24,000 showing hydrogeologic settings and their sensitivity to contamination, and a county report
that describes the bedrock geology, glacial geology, hydrogeological framework, general ground
water availability, and sensitivity of aquifers to pollution. The county report will be accompanied by
nine maps of the entire county, each at a scale of 1:63,360. These county maps will include:
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186 Appendix B
distribution and types of data points
bedrock geology and topography
total thickness and sequence characteristics of unconsolidated materials
geology and topography of the buried surface of the late Wisconsin Trafalgar
megasequence
stratigraphy and distribution of aquifers and aquifer systems
near surface geologic sequences and thickness of surface till between the land
surface and mapped aquifers
potentiometric surface of the bedrock aquifer system, including recharge and
discharge areas
potentiometric surface of shallow sand and gravel aquifer systems, including recharge
and discharge areas
sensitivity to contamination of mapped aquifers
The report and accompanying maps are expected to be published by Allen County by mid-1994.
Conducting the Resource Evaluation
Allen County is located in northeastern Indiana and is situated between three different
geologic-physiographic regions. Within the county, limestone, dolomite, and shale bedrock are
overlain by glacial deposits that range in thickness from less than 30 feet in the east to more than 340
feet in the northwest. The bedrock and the unconsolidated deposits contain three aquifer systems
that supply the majority of water for most ground water uses in the county. Allen County's interest in
protecting its ground water resources led county officials to request and fund IGS to study the
distribution of major aquifer systems and their sensitivity to contamination.
IGS compiled the county report and maps from sets of detailed hydrogeologic and
stratigraphic maps constructed on USGS 7.5-minute topographic quadrangles. Each set of maps for
each of Allen County's twenty quadrangles includes:
distribution and types of data points
bedrock topography and geology (see Component #1)
stratigraphy of aquifer systems and confining units (see Components #2 and #5)
near surface geologic sequences and thickness of till confining units (see Component
#2 and #5)
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Case Studies on the Development and Use of Ground Water Resource Assessments 187
potentiometric surfaces of major aquifer systems, showing recharge and discharge
areas and the locations and approximate zones of influence of registered high
capacity wells (see Components #3 and #6)
sensitivity of ground water to contamination (see Approaches #1 and #3)
IGS employed a variety of new and existing information to develop these maps, including:
6,400 water well and test boring records
200 down-hole gamma-ray logs
75 down-hole sample sets
samples collected from 15 surface exposures
340 seismic shots
soil maps developed by the Soil Conservation Service
geomorphic relationships
The maps were derived from the above data through a number of methods. For example, cross-
sections and fence diagrams representing more than 1,350 linear miles were constructed and utilized
to interpret the depositional environments, facies relations, and three-dimensional geometry of aquifers
and confining units. Stratigraphic correlations of these units was based chiefly upon their physical
properties, including textural, mineralogical. geotechnical, and down-hole geophysical characteristics.
The identification of aquifer systems was made on the basis of both Stratigraphic relationships as well
as hydrodynamic considerations, such as analysis of physical and hydrogeochemical characteristics
of till confining units, detailed contouring of potentiometric surfaces based on Stratigraphic position,
and recognition of distinct flow regimes in adjacent or subjacent geologic units.
Due to the irregular distribution and variable quality of data points, the maps are not suitable
for detailed site-specific evaluations. The maps are intended for comparative purposes such as site
screening and general planning activities. These maps, however, are unique, because they show the
distribution of different kinds of data points. An understanding of the distribution of data points allows
the user to make a direct inference regarding the reliability of the maps for any region or point of
interest. For example, there are specific sites that may have as many as 50-75 high-quality data
points, all within an area as small as one square mile. On the other hand, areas of similar size
elsewhere in the county may contain few or no data points, meaning that hydrogeologic relationships
were inferred from nearby areas within the same hydrogeologic settings that have more data. While
the maps are not a substitute for site-specific investigation, the maps provide an extremely useful local
and regional perspective for such investigations.
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188 Appendix B
The ground water sensitivity maps indicate the relative potential for contamination of a
particular aquifer system as it varies across the landscape. The sensitivity maps are very generalized
because of the wide variety of contaminants and the variety of pathways into the ground water. IGS
developed a numerical index to evaluate ground water sensitivity. This approach allows:
a direct comparison among differing geologic regions
an interpretation of the relative sensitivities of the many areas that fall into intermediate
sensitivity classes
IGS used four basic factors to formulate the sensitivity index:
the type and hydraulic conductivity (relative) of aquifer media
the type and thickness of material overlying the aquifer and the degree of confinement
of the aquifer
the position within the ground water flow system (i.e., recharge and discharge areas)
the characteristics of the surface soil
These factors directly influence the rate at which a potential contaminant can migrate into an aquifer,
the potential for attenuation of the contaminant, the fate of the contaminant once it reaches an aquifer,
and the potential impact on overall water quality within the aquifer system. The sensitivity index also
contains three key components for each of the four factors listed above:
weights
ranges
ratings
The sensitivity index for each map unit was determined by summing the products of the weight and
rating for each factor. It must be emphasized that individual index numbers have no absolute
meaning in and of themselves. The index numbers are not indicators of absolute contamination
potential, and should only be interpreted relative to one another.
Decision-Making Based on the Resource Evaluation
The ground water sensitivity maps for Allen county provide a sound basis for preliminary
appraisals of earth materials and geological sequences on a county scale and for a generalized
understanding of the potential for contamination of the County's aquifer systems. These quadrangle
maps can be particularly useful for:
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Case Studies on the Development and Use of Ground Water Resource Assessments 189
zoning decisions to limit the potential adverse impacts to ground water
screening of potential sites for hazardous and solid waste disposal facilities
prioritization of aquifers and geographic areas for protection
The. maps and reports have other uses including showing the generalized glacial geology and
hydrogeology of Allen County, as well as wellhead protection areas, foundation conditions, mineral
resources, and generalized ground water availability.
In Allen County, the Department of Planning Services, the Office of Environmental
Management, and the Fort Wayne/Allen County Board of Health use the maps as a basis for
management decisions. The Department of Planning Services uses the maps to:
evaluate land-use proposals from the Planning Commission and the Board of Zoning
Appeals
establish urban service areas as part of a long-term comprehensive planning strategy
for Allen County (Service areas are those parts of Allen County where development of
many types is encouraged)
review appropriateness of speculative siting proposals for industrial parks and
commercial areas
Specifically, the county report and maps have been used to protect ground water recharge
areas in the Huntertown Urban Service Area. The maps identified the regional importance of the
ground water recharge area in Huntertown. As a result, the areal extent of the Huntertown Urban
Service Area was reduced to ensure the protection of the recharge area from development.
The Allen County ground water resource assessment maps are very useful as a comparative
tool for screening sites for solid and hazardous waste facilities, industrial development, and related
activities, because the maps indicate the range of geologic variability that can be expected within
each map unit as well as between map units. However, these maps have some limitations as
decision-making tools. These maps cannot be used for site-specific evaluations because of local
complexities in geologic materials. These maps can only be used to assess the regional
appropriateness for certain activities. A number of site-specific factors and seasonal factors must be
considered in determining appropriate uses for specific sites. Many of these factors were beyond the
scope of this project and the scale of these maps and must be completed on a case-by-case basis.
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190 Appendix B
Other Sources of Information
State Tony Fleming Local Dennis Gordon, Director
Contact: Indiana Geological Survey Contact: Allen County
611 N. Walnut Grove Department of Planning Services
Bloomington, Indiana, 47405 630 City-County Building
(812) 855-7428 One Main Street
Fort Wayne, IN 46802-1804
(219) 428-7607
Fleming, A.M., (in preparation). The Hydrogeologic Framework of Allen County. Indiana Geological
Survey Special Report, Bloomington, IN, Report and 9 plates (1:63,360).
Fleming, A.M., 1992. Explanation of Hydrogeologic Quadrangle Maps of Allen County: Technical
Appendix to The Hydrogeologic Framework of Allen County. Indiana Geological Survey Open
File Report, 55 p. plus 90 geologic and hydrogeologic quadrangle maps (1:24,000).
Indiana Interagency Ground Water Task Force, 1988. Annual Status Report on Implementation of the
Indiana Ground Water Protection and Management Strategy.
Indiana Interagency Ground Water Task Force, 1986. Protection of Indiana's Ground Water: Strategy
and Draft Implementation Plan.
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Case Studies on the Development and Use of Ground Water Resource Assessments 191
SOUTH DAKOTA
Big Sioux Aquifer Assessment
Overview of State Ground Water Protection Efforts
South Dakota is largely dependent on its
ground water for water supply. Approximately 66
percent of the 674 million gallons of water used per
day in South Dakota is taken from the ground. The
uses of ground water include domestic purposes,
livestock watering, irrigation, and industrial use. The
majority of the State's public water supplies rely on
ground water, and virtually everyone not supplied by
public water systems is dependent on ground water
from private wells.
The Big Sioux aquifer of glacial origin is the
most utilized source of ground water for drinking
water purposes in South Dakota and serves ^^^^^^^^^^^^^^^^^^^m^^i^mm
approximately one-third of the State's population (see Figure B-1). Additional major sources of ground
water for South Dakota's population are the other glacial aquifers in the eastern half of the State and
alluvial and bedrock aquifers throughout the State. Surficial aquifers and the bedrock aquifers that
outcrop in areas of the Black Hills are vulnerable to contamination. The three most significant
categories of potential ground water contamination are:
PURPOSE OF THIS RESOURCE
ASSESSMENT:
The original intent of the ground water
resource assessment of the Big Sioux
aquifer (Fig. B-1) was to delineate the
areal extent, thickness, and water quality
for use in making water development
decisions for domestic, municipal, and
irrigation purposes. However, because
of increasing demands for water and
realization of the vulnerability of this
aquifer to contamination, the
hydrogeologic data are now extensively
used for water management, including
various ground water protection
activities.
contamination from petroleum, fertilizer, pesticides, and other chemicals from releases
due to equipment failure and mishandling
contamination of domestic wells due to poor well construction and the well's location
relative to point sources of pollution, such as septic systems, barn yards, feed lots,
and lagoons
contamination from non-point sources of pollution
Recognizing the immeasurable value of ground water, the Governor-sponsored Centennial
Environmental Protection Act of 1989 was passed by the South Dakota Legislature. This act
establishes the State's ground water goal to "conserve and protect the ground water of the State and
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Figure B-1
Big Sioux Aquifer and Drainage Basin
N
Big Sioux aquifer
Big Sioux drainage
basin
Miles
50
0 50
Kilometers
South Dakota
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Case Studies on the Development and Use of Ground Water Resource Assessments 193
to protect, maintain and improve the quality thereof for present and future beneficial uses through the
prevention of pollution, correction of ground water pollution problems and close control of limited
degradation parameters permitted for necessary economic or social development." [South Dakota
Codified Law 34A-2-104]
The South Dakota Department of Environment and Natural Resources (DENR) has the
responsibility for evaluation, appropriation, and development of guidelines for protection of the State's
water. The Division of Water Rights deals with the appropriation of water. The Division of Water
Resources Management deals with the funding of water projects. The Ground Water Quality Program
in the Division of Environmental Regulation, coordinates most of the programs, activities, and funds
relating to ground-water protection. The South Dakota Geological Survey (SDGS), a nonregulatory
division of DENR, is charged with conducting scientific research for use in developing the State's
natural resources and protection of the environment. Hydrogeologic studies and research at the
SDGS are varied and serve as a sound basis for the State's ground water protection activities. DENR
developed a comprehensive ground water protection strategy in 1987 which is updated each year.
This strategy establishes a ground water prioritization process based on the potential for
contamination and the impacts contamination would have on aquifers or specific portions of aquifers.
According to the strategy, the following criteria are used to prioritize DENR's protection and planning
activities:
areas that will affect public health
wellhead protection areas/public water supplies
private water supplies
ambient water quality with Total Dissolved Solids (TDS) value of 10,000 mg/L or less
giving it the beneficial use of drinking water
vulnerability of the aquifer
documented water quality problems
special considerations
Based on these criteria, the Big Sioux aquifer has the highest priority rating.
The State's wellhead protection program has been approved by the U.S. Environmental
Protection Agency (EPA). However, prior to approval of the State's plan, significant wellhead
protection measures were implemented for a large portion of the Big Sioux aquifer in eastern South
Dakota. These protection measures were formulated and implemented under the auspices of city,
county, and water-development district authorities working with DENR.
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194 Appendix B
Administration and Organization of the State's Resource Assessment
As part of natural resource assessments, the SDGS and other Federal, State, and
local-government entities conduct a variety of ground water related studies, including ground water
resource assessments. The SDGS's resource assessment program covers the entire State, and nearly
all of the ground water resources of eastern South Dakota have been characterized. The process of
resource assessment is not new to South Dakota. The SDGS has been locating, mapping, and
evaluating water resources of the State for approximately 100 years. Also, the Division of Water Rights,
has been assessing ground water availability for purposes of water appropriation for 37 years. Current
resource assessment efforts are merely a continuation of standard practices which have, over the
years, resulted in a large data base of hydrogeologic information for many aquifers in the State. Data
gathering techniques typically include:
mapping of surface and subsurface geology
extensive drilling of test holes
geophysical logging
installation of monitoring wells
monitoring of water levels and water quality
conducting well inventories
performance of aquifer tests
Some studies have focused on entire counties or regions while others have concentrated on only a
few square miles. As a result of these investigations, numerous reports and maps have been
produced. The SDGS maintains a computerized data base containing approximately 32,000 lithologic
logs, 3,400 water-quality analyses, and 197,000 water levels. The U.S. Geological Survey (USGS) and
the EPA data bases contain additional ground water data.
Conducting the Resource Evaluation
The SDGS and other government agencies have been examining the Big Sioux aquifer in eastern
South Dakota for many decades. Studies have shown that the Big Sioux aquifer is a surficial, glacial
outwash unit that covers about 770 square miles and is hydraulically connected to the Big Sioux River.
Knowledge of the Big Sioux aquifer is primarily based on:
systematic reconnaissance investigations of the geologic and hydrologic resources of
most counties in eastern South Dakota
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Case Studies on the Development and Use of Ground Water Resource Assessments 195
a study, conducted jointly by SDGS and USGS, that focused specifically on the entire
extent of the Big Sioux aquifer
studies by SDGS to locate water sources or improve water quality for cities and rural
water systems
systematic gathering of data on nitrates and pesticides over the areal extent of the
aquifer through a permanent network of monitoring wells
research to better quantify surface and ground water interaction between the Big
Sioux River and the Big Sioux aquifer
Funding of investigations of the Big Sioux aquifer has been through the South Dakota DENR,
including SDGS, as well as through the East Dakota Water Development District, individual
communities, rural water systems, counties, USGS, EPA, and the South Dakota Department of
Agriculture. Different projects have utilized various combinations of these funding sources but State
and local funds have been involved in every project. Work on these investigations has been performed
by the SDGS and USGS, although USGS has usually participated only in large areal assessments.
Field activities related to these studies have taken from a few weeks to several years to complete and
have utilized one or two geologists and hydrologists per project and drilling and well-installation crews
ranging in size from three to six people.
An extensive data base is available for the Big Sioux aquifer and includes records for 5,667
test holes and 2,187 wells. In addition, the State has 656 monitoring wells in the Big Sioux aquifer.
These data and water level and water quality records are maintained in a computerized data system
(see Components #3, #8, and #10). Numerous aquifer tests have also been performed. This data
base plus the numerous ground water studies provide the basis for an overall resource assessment of
the aquifer.
Mapping of surface and subsurface geology has defined the regional geologic setting and
allowed delineation of three-dimensional spatial relationships of all sediments (see Component #1).
The Big Sioux aquifer occurs at or near land surface, is highly permeable, and occurs primarily under
unconfined conditions. Thus, the entire aquifer is extremely susceptible to contamination. Good
regional characterization of ground water flow directions allows an understanding of recharge and
discharge areas.
Data indicate that throughout much of its course, the Big Sioux River and the Big Sioux aquifer
have extensive interaction. In fact, pumping in the Sioux Falls well field has caused cessation of flow in
certain portions of the Big Sioux River (see Component #7). Hydrologic testing and computer
modeling have refined this relationship in certain areas. These studies have also identified
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Appendix B
recharge-discharge relationships, determined potential yield, and ground water time of travel (see
Component #6).
There are currently 1 ,030 water-quality analyses in SDGS's computerized data base for the Big
Sioux aquifer. Additional analyses are available from public water suppliers. The majority of available
water quality data deals only with general inorganic parameters, however, limited information is also
available on pesticides and volatile organic compounds. The information base on pesticides and
volatile organic compounds is growing as wellhead protection efforts proceed and as research
continues on the quality of water in the aquifer.
Each investigation conducted by the SDGS or the USGS is accompanied by a report of
findings which typically includes tabular data, information on water quality, and map presentations of
data and interpretations, which include the areal extent and thickness of the aquifer, water table
contours, and ground water flow directions. These reports are available from the respective
organizations. The DENR is developing a Geographic Information System (GIS) which will include all
pertinent hydrogeologic data. The use of a GIS will enhance decision making regarding aquifer issues
and should allow for more rapid and widespread use of aquifer-related information.
Decision-Making Based on the Resource Evaluation
While most of the work done on the Big Sioux aquifer relates only to the first part of EPA's
definition for a resource assessment (i.e., a classical, scientific resource evaluation), some of the
hydrogeologic study results regarding this aquifer are being used by planners and water managers for
a number of purposes, including:
the appropriation of water rights
management of water use for municipal, industrial, and irrigation purposes
prioritization of public water supplies for wellhead protection
the delineation of wellhead protection areas
vulnerability assessment of public water supplies to determine monitoring frequency
Existing aquifer maps and other hydrogeologic information, such as data on the hydraulic
properties of the aquifer, are regularly used by the Division of Water Rights, to estimate the potential
impact of one water right upon another as part of the decision-making process regarding the
appropriation of water rights. Any large-scale development of the aquifer is directly dependent upon
the granting of water rights. Also, the hydrogeologic information is used by the city of Sioux Falls
(population 105,000) to manage the pumping of water from its well field and was the basis for the
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Case Studies on the Development and Use of Ground Water Resource Assessments 197
development of contingency plans to deal with a major contamination incident in the aquifer as part of
the city and county wellhead protection efforts.
The East Dakota Water Development District and the First District Association of Local
Governments are developing a comprehensive ground water protection program in most of the Big
Sioux aquifer area, including the coordination of wellhead protection programs in eleven counties.
Known as the East Dakota Comprehensive Ground Water Protection Program, this effort includes
standardizing county maps of aquifers, delineating wellhead protection areas, contingency planning,
and public education in the eleven-county area. This effort also includes formulation of measures to
reduce non-point source pollution of critical ground water areas and to change land uses that may be
identified as having the potential to contaminate the ground water. The city of Sioux Falls and
surrounding Minnehaha County have also developed and implemented wellhead protection measures
for the Big Sioux aquifer. In addition, wellhead monitoring options are being researched and
implemented in the Sioux Falls area. These efforts are already altering land-use practices over the
aquifer. Experience with the Big Sioux aquifer shows that cooperation of State and local government,
as well as input from the public, are essential for developing achievable and comprehensive ground
water protection.
Other Sources of Information
State Contact: Assad Barari
South Dakota Geologic Survey
University of South Dakota Science Center
Vermillion, South Dakota
(605) 677-5227
South Dakota Department of Environmental and Natural Resources, 1991. South Dakota Ground
Water Strategy 1991-1992.
East Dakota Water Development District. Program Description of the East Dakota Comprehend
Ground Water Protection Program. "
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198
Appendix B
U.S. DEPARTMENT
OF ENERGY
DOE Ground Water Resource Assessment
at the Oak Ridge Reservation
This case study describes efforts by the
Department of Energy's (DOE) Oak Ridge
Reservation (ORR) to classify ground water in the
vicinity of the ORR facilities consistent with
Tennessee's Comprehensive Ground Water
Management Program and in the context of DOE
ground water protection program policy and
requirements.
Overview of DOE Ground Water Protection
Program Requirements
THE PURPOSE OF THIS RESOURCE
ASSESSMENT
The purpose of this study was to
conduct an assessment of the ground
water resource at DOE's Oak Ridge
Reservation in an effort to assist the
State of Tennessee in completing its
development of a ground water
classification system and to help guide
DOE ground water protection efforts at
the Reservation.
Ground water protection at DOE sites nationwide is achieved by complying with applicable
Federal and State regulations and with internal DOE orders. Order DOE 5400.1, entitled General
Environmental Protection Program, establishes two basic ground water protection requirements for all
DOE sites. One requirement is to develop and implement a Ground Water Monitoring Program to
collect information on how DOE activities affect on-site and off-site environmental and natural
resources. The second requirement is to develop and implement a site-wide Ground Water Protection
Management Program to ensure that ground water remediation activities are coordinated and to
establish systems to prevent future ground water contamination. Results of ground water monitoring
activities are presented in an Annual Site Environmental Report, along with all other site environmental
protection activities.
-------
Case Studies on the Development and Use of Ground Water Resource Assessments 199
The Oak Ridge Reservation
ORR occupies 35,300 acres of Federally-owned land in eastern Tennessee. The site contains
three major operating facilities: the Y-12 Plant, the K-25 Site, and the Oak Ridge National Laboratory
(ORNL). The Y-12 Plant fabricates nuclear weapons components, processes nuclear materials, and
provides technical support to other DOE facilities and laboratories. The K-25 Site had been involved
in enrichment of uranium for use as a fuel in nuclear reactors prior to 1987, and is currently
developing and demonstrating advanced enrichment technology and performing additional technical
support. The ORNL is a multi-purpose research laboratory whose mission is to expand basic and
applied knowledge in energy-related areas.
The geology of the ORR is typical of the Appalachian foreland fold and thrust belt. Lower
Paleozoic sedimentary lithologies (shales and carbonates) are structurally repeated along regional
thrust faults. From a hydrologic perspective, the ORR is underlain by alternating aquifer (carbonate)
and aquitard (shale) units. The principal aquifer in the area is the Knox aquifer, which is composed of
fractured dolomite and limestone. Although the Knox aquifer has not been fully evaluated, it appears
that at the Y-12 plant, ground water may become saline (TDS >30,000 mg/L) below a depth of
approximately 1,100 feet.
The depth of the vadose zone ranges from 45 to 90 feet from the surface. It is estimated that
approximately 90 percent of the infiltration from the surface does not reach the water table, due to
lateral migration along short flow paths to surface water, seeps, and springs.
To ensure that ground water resources are protected and to comply with applicable
regulations and DOE Orders, ORR staff have developed a Ground Water Protection Management
Program (GWPMP) for each of ORR's three major facilities. The GWPMP is a management tool
designed to ensure that ground water activities are complete and comprehensive, and that lines of
responsibility and communication mechanisms are established and functioning properly. Each facility
has developed its own ground water monitoring program that is designed to identify existing ground
water contamination, detect future contamination at the earliest possible point, and to ensure that
standard methods for sampling, analysis, QA/QC. and reporting are used throughout ORR. Ground
water coordinators at each ORR facility participate in a sitewide Ground Water Coordination
Committee, which meets regularly to ensure consistency, exchange information, and report on the
status of site investigations and technology evaluations.
-------
200 Appendix B
Administration and Organization of Resource Assessment at ORR
It is DOE policy to comply with all applicable environmental statutes, regulations, and
standards, and to incorporate national environmental protection goals into all DOE programs. DOE is
committed to good environmental management at all of its facilities: to correct existing environmental
problems, to minimize risk to public health and the environment, and to anticipate and address
potential environmental problems before they pose a threat. In the course of carrying out DOE
environmental protection policy, close coordination and interaction with State environmental agencies
by each DOE site is strongly encouraged. An example of this coordination is provided by the ORR's
efforts to classify ground water at ORR according to a classification system under development by
Tennessee's Department of Environmental Conservation (TDEC). While ground water of drinking
water quality is generally available throughout Tennessee, most residents in the vicinity of ORR receive
their drinking water from a public water supply system that uses surface water. However, some rural
residents rely upon private ground water wells.
Tennessee has begun to develop a Comprehensive Ground Water Protection Program that
identifies Statewide goals, including developing a Statewide ground water data base, establishing
formal coordination mechanisms with Federal, State, and local agencies, and classifying ground water
resources throughout the State. Due to the complexity of the issue of ground water classification at
the State level, TDEC is considering several alternative ground water classification schemes as part of
the State's Ground Water Protection Program. Recently, the State has developed a preliminary
classification system that would allow for differential management of ground water based on various
ground water uses, with ground water that is of drinking water quality receiving the greatest
protection.
A salient feature of the classification systems under consideration is the recognition of different
levels of ground water protection for drinking water and other beneficial uses. According to a recently
proposed classification scheme, TDEC could establish four ground water classes:
(1) current or potential drinking water supplies
(2) non-drinking water supplies, (i.e., water that is neither currently nor expected to be
drinking water supplies but are protected for other purposes)
(3) ground water that may be used for the underground injection of fluids, as per State
regulation
(4) ground water managed to assure the protection of the State's surface water, as per
State regulation
-------
Case Studies on the Development and Use of Ground Water Resource Assessments 201
The classification schemes currently under consideration reference water quality criteria for
distinguishing ground water classes. For example, the Tennessee Primary Drinking Water Standards
are used to classify drinking water supplies. In some cases, a ground water classification could be
made following considerations of the yield of the well and whether the well water can be treated to
meet State drinking water standards by conventional treatment methods.
At present, the State of Tennessee is reviewing various ground water classification options.
To assist the State in completing development of its classification system, and to enable DOE to base
ground water protection activities on the most complete and accurate understanding of subsurface
conditions, DOE at Oak Ridge is implementing an approach that allows its staff to move forward with
the development of a conceptual or preliminary framework for the classification of ground water at
ORR, and to assemble a data base on subsurface conditions needed to perform preliminary
classifications. The approach that the DOE at Oak Ridge is using has the following characteristics:
Compatibility: The preliminary classification framework will be conservative and in
general accord with the principles of Federal guidance on ground water classification
(i.e., that the classification is protective of human health and the environment, and that
the classification recognizes present and potential future use of the resource). When
possible, DOE staff will strive to infuse the preliminary classification framework with
timely and appropriate State input
Utility: The activity of ground water classification will generate a data base that could
provide technically useful information for on-going ground water protection activities
Flexibility: The preliminary classification framework should serve as a basis for the
implementation of Tennessee's classification, when Tennessee completes its Statewide
system
ORR and the TDEC expect to rely on the system in the future to assist in making decisions regarding
implementation of ground water protection program activities.
-------
202
-------
Sources of Hydrogeological Information 203
APPENDIX C:
Sources of Hydrogeological Information
Source: U.S. Environmental Protection Agency, 1992. RCRA Ground Water Monitoring: Draft
Technical Guidance EPA/530-R-93-001 (NTIS # PB 93-139-350).
-------
204
Appendix C
GENERAL DATA SOURCES
Source
Libraries
Information
Obtainable
Earth science
bibliographic indices
Computer literature
searches
Bibliographic indices
Dialog
Subscriptions and
information:
1-800-3-DIALOG.
Accesses over 425 data
bases from a broad
scope of disciplines
including such data
bases as GEOREF and
GEOARCHIVE.
Comments
Many of the types of information
discussed below can be obtained from
libraries. Excellent library facilities are
available at the U.S. Geological Survey
offices (USGS) in Reston, VA; Denver,
CO; and Menlo Park, CA. Local university
libraries can contain good collections of
earth science and related information and
typically are repositories for Federal
documents. In addition, local public
libraries normally have information on the
physical and historical characteristics of
the surrounding area.
Perhaps one of the most useful and cost
effective developments in the
bibliographic indexes has been the
increased availability of computerized
reference searches. On-line computer
searches save significant time and money
by giving rapid retrieval of citations of all
listed articles on a given subject and
eliminate manual searching of annual
cumulated indexes. A search is done by
use of keywords, author names, or title
words, and can be delimited by ranges of
dates or a given number of the most
recent or oldest references. The average
search requires about 15 minutes of
online searching and costs about $50 for
computer time and offline printing of
citations and abstracts.
Provides indexes to book reviews and
biographies; directories of companies,
people, and associations; and access to
the complete text of articles from many
newspapers, journals, and other original
sources.
-------
Sources of Hydrogeological Information
205
Source
Master Directory
(MD)
User Support Office
Suite 300
Hughes SIX Corp.
7601 OraGlen Drive
Greenbelt, MD
20771
(301) 513-1687
Span: BLAND
NSSDCA.
GSFC.NASA.GOV
THIEMAN.NSSDCA.
GSFC.NASA.GOV
Master Directory
(continued)
Information
Obtainable
The MD is a multidis-
ciplinary data base that
covers earth science
(geology, oceanography,
atmospheric science),
space physics, solar
physics, planetary
science, and astronomy/
astrophysics. It
describes data
generated by NASA,
NOAA, USGS, DOE,
EPA, and other agencies
and universities, as well
as international data
bases.
Comments
MD is a free on-line data information
service. Data available include personnel
contact information, access procedures to
other data bases, scientific campaigns or
projects, and other data sources.
Access Procedures: MD resides on a
VAX at NSSDC and may be reached by
several networks. MD is option #1 on the
menu of NSSDC's On-line Data
Information Services (NODIS) account.
From span nodes: SET HOST NSSDA.
USERNAME:NSSDC (no password).
From Internet: TELNET
NSSDCA.GSFC.NASA.GOV or TELNET
128.183.36.23.
Via Direct Dial: Set modem to 8 bits, no
parity, 1 stop bit, 300,1200 (preferable), or
2400 baud. Dial (301) 286-9000 ENTER
NUMBER: MD, CALL COMPLETE: [CR],
USERNAME: NSSDC (no password). For
assistance or more information, contact
the MD User Support Office (301) 513-
1687.
-------
206
Appendix C
Source
Information
Obtainable
Comments
Alternative
Treatment
Technology
Information Center
(ATTIC)
4 Research Place
Suite 210
Rockville, MD
20850
(301) 670-6294
(voice)
(301) 670-3808
(on-line)
Earth Science
Data Directory
USGS
801 National
Center
Reston, VA 22092
(703) 648-7112
The ATTIC system is a
collection of hazardous
waste databases that
are accessed through a
computerized bulletin
board system (BBS).
The BBS features news
items, bulletins, and
special interest
conferences. ATTIC
users can access
several databases
including the ATTIC
Database, which
contains over 2,500
records dealing with
alternative and
innovative technologies
for hazardous waste
treatment; and the RREL
Treatability Database,
which provides data on
characteristics and
treatability of a wide
variety of contaminants.
Information from these
sources consists of
treatability information,
case histories, transport
and fate data, and other
technical information.
Also included are the
abstracts of Superfund
Innovative Technology
Evaluation (SITE)
reports, many Records
of Decisions (RODs),
State agency reports,
international programs,
and industry studies.
ESDD is a data base
that contains information
related to the geologic,
hydrologic, cartographic,
and biological sciences.
ATTIC is free of charge to all members of
the Federal, State and private sectors
involved in site remediation. ATTIC can
be accessed directly by a modem.
Abstracts of reports can be downloaded
from the system. Copies of complete
reports are available on request. (Users
register online the first time they access
ATTIC.) A User's Manual is available and
may be obtained by calling the ATTIC
System Operator or leaving a message
on the bulletin board.
Also included are data bases that
reference geographic, sociologic,
economic, and demographic information.
Information comes from worldwide data
sources and data includes that from
NOAA, NSF, NASA, and EPA.
-------
Sources of Hydrogeological Information
207
Source
Information
Obtainable
Comments
Local, State,
Federal, and
Regional Agencies
University sources
Comprehensive
dissertation index
AGI Directory of
Geoscience
Department
DATRIX II University
Microfilms
International
300 North Zeeb Rd.
Ann Arbor, Ml
48106
(800) 521-3042
ext. 732
(313) 761-4700
(in Alaska, Hawaii,
and Michigan)
Site specific assessment
data for dams, harbors,
river basin
impoundments, and
Federal highways, soils,
land-use, flood plains,
ground water, aerial
photographs, well
records, geophysical
borehole logs
Engineering and
geology theses
Doctoral dissertations
Faculty Members
Dissertations and
Masters theses
Many States maintain a department of the
environment or natural resources.
Reports can be obtained by contacting
the responsible agency Surface water
and geological foundation conditions
such as fracture orientation, permeability,
faulting, rippability, and weathered
profiles are particularly well covered in
these investigations.
College and university geology theses, in
most instances, are well-documented
studies dealing with specific areas,
generally prepared under the guidance of
faculty members having expertise in the
subject under investigation. Most theses
are not published.
Citations began in 1861 and include
almost every doctoral dissertation
accepted in North America thereafter.
The index is available at larger library
reference desks and is organized into 32
subject volumes and 5 author volumes.
Specific titles are located through title
keywords or author names. Ph.D.
dissertations from all U.S. universities are
included.
Regular updates of faculty, specialties,
and telephone date.
Using title keywords, a bibliography of
relevant theses can be compiled and
mailed to the user within two weeks. In
addition, the DATRIX Alert system can
automatically provide new bibliographic
citations as they become available.
-------
208
Appendix C
Source
Information
Obtainable
Comments
United States
Geology: A
Dissertation
Bibliography by
State
Ph.D. dissertation or
Masters theses
Dissertation
Abstracts
International.
Volume B - Science
and Engineering, a
monthly publication
of University
Microfilm
International
Extended abstracts of
dissertations from more
than 400 U.S. and
Canadian universities
Free index from University Microfilms
International. Some universities do not
submit dissertations to University
Microfilms for reproduction or abstracting,
however, and the dissertations from these
schools do not appear in the United
States Geology index. Citations for
dissertations not abstracted must be
located through DATRIX II or
Comprehensive Dissertation Index.
Once the citation for a specific
dissertation has been obtained from the
Comprehensive Dissertation Index or from
DATRIX II, the abstract can be scanned to
determine whether it is relevant to the
project at hand. Since some universities
do not participate, some theses indexed
in the two sources listed above must be
obtained directly from the author or the
university at which the research was
completed.
Abstracts of Masters theses available
from University Microfilms are summarized
in 150-word abstracts in Masters
Abstracts and are indexed by author and
title keywords.
Both Dissertation Abstracts International
and Masters Abstracts are available at
many university libraries.
A hard (paper) or microform (microfilm or
microfiche) copy of any dissertation or
thesis abstracted can be purchased from
University Microfilms.
-------
Sources of Hydrogeological Information
209
Source
Information
Obtainable
Comments
USGS Publication
Manuscripts
System
(PUBMANUS)
Earth Science
Information Center
507 National
Center
Reston, VA 22092
(703) 648-6045
U.S. Geological
Survey (USGS)
Earth Science
Information Center
(ESIC)
Reston, VA
(703) 648-6045
1-800-USA-MAPS
Electric Power
Research Institute
(EPRI)
ATTN: EPRI
Technical
Information
Specialists
3412 Hillview Ave.
Palo Alto, CA
94304
(415) 855-2411
(510) 934-4212
(distribution
center)
This data base provides
referral to all U.S.
Geological Survey
publications.
Detailed topographic,
geologic, and hydrologic
information is available
from the USGS through
the Earth Science
Information Center.
United States historical,
physical divisions,
Federal-aid highways,
national atlas and
scientific maps.
Up-to-date compilation
of research relevant to
utilities.
Flexible searching techniques enable
users to find information in numerous
ways. Currently, search requests are
accepted through the USGS Earth
Science Publication Office at no charge.
(800) USA-MAPS. The "Guide to
Obtaining USGS Information" (circular
900) is also an excellent source. It
describes the services provided by USGS
information offices. Includes addresses
and telephone numbers, and lists types
of publications and information products
and their sources. Publication is free and
may be ordered from USGS Book and
Report Sales. This guide can be
obtained from USGS, Book and Report
Sales, Box 25286, Denver, CO 80225,
(303) 236-7477.
ESIC can be contacted to determine
which map best meets your needs. Maps
can be purchased from:
USGS Map Sales
Box 25286
Denver, CO 80225
(303) 236-7477
The EPRI manages a research and
development program on behalf of the
U.S. electric power industry. Its mission
is to apply advanced science and
technology to the benefits of its members
and their customers.
-------
210 Appendix C
Information
Source Obtainable Comments
RCRA/Superfund Information on RCRA. Team of information specialists maintains
Hotline CERCLA, SARA, and up-to-date information on the various
Office of Solid UST statutes and regulations and rulemakings in progress.
Waste (OS-305) corresponding Hours of operation 8:30 a.m. to 7:30 p.m.
U.S. EPA regulations. Also (EST) Monday through Friday. Answer
401 M Street, SW provides document questions from wide range of callers -
Washington, DC distribution service, consultants, attorneys, generators,
20460 including relevant transporters, facility owner/operators,
(800) 424-9346 Federal Register notices. State and Federal regulatory agencies,
(toll free) trade associations, and the general
(Washington, DC public.
metropolitan area)
(703) 920-9810
-------
Sources of Hydrogeological Information
211
TOPOGRAPHIC DATA
Source
Branch of
Distribution
U.S. Geological
Survey
Maps Sales
Box 25286, Federal
Center
Denver, CO 80225
(303) 236-7477
Commercial map
supply houses
Topographic
Database
National
Geophysical Data
at NOAA
Code E/GCI
325 Broadway
Boulder, CO 80303
(303) 497-6764
U.S. Geological
Survey
Topographic Map
Names Database
Attn. of Chief:GNIS
USGS
523 National
Center
Reston, VA 22092
(703) 648-4544
Information
Obtainable
Index and quadrangle
maps for the eastern
U.S. and for States west
of the Mississippi River,
including Alaska, Hawaii,
and Louisiana. Other
scales are available.
Topographic and
geologic maps.
A variety of topography
and terrain data sets
available for use in
geoscience applications.
This database contains
descriptive information
and official names for
approximately 55,000
topographical maps
prepared by the USGS,
including out-of-print
maps. Data includes the
names of topographic
maps, along with SE
coordinates of the States
in which they are
located.
Comments
A map should be ordered by name,
series, and State. Mapping of an area is
commonly available at two different
scales. The quadrangle name is, in some
instances, the same for both maps; where
this occurs, it is especially important that
the requestor specify the series
designation, such as 7.5 minute
(1:24,000), 15 minute (1:62,500), or two-
degree (1:250,000),
Commercial map supply houses often
have full State topographic inventories
that may be out of print through national
distribution centers.
The data were attained from U.S.
government agencies, academic
institutions, and private industries.
Printouts and searches are available on a
cost recovery basis.
-------
212
Appendix C
Source
Information
Obtainable
Comments
U.S. Geodata
Tapes
Dept. of the
Interior
Room 2650
18th & C Sts., NW
Washington, DC
20240
(202) 208-4047
Geographic
Information
Retrieval and
Analysis System
(GIRAS)
USGS
Earth Science
Information Center
(ESIC)
507 National
Center
Reston, VA 22092
(800) USA-Maps
(703) 648-6045
Topographic Maps
Users Service
Geographic Names
Information
System
(GNIS)
Reston, VA 22092
(703) 648-7112
National
Geophysical
Data Center
NOAA, Code E/GCI
325 Broadway
Boulder, CO 80303
(303) 497-6764
These computer tapes
contain cartographic
data in digital form.
They are available in two
forms. The graphic form
can be used to generate
computer-plotted maps.
The topologically-
structured form is
suitable for input to
geographic information
system for use in spatial
analysis and geographic
studies.
Land-use maps, land
cover maps, and
associated overlays for
the United States.
Organized and
summarized information
about cultural or
physical geographic
entities.
This system contains a
variety of topography
and terrain data sets
available for use in
geoscience applications.
Tapes are available for the entire US,
including Alaska, and Hawaii, and are
sold in 4 thematic layers: boundaries,
transportation, hydrography and US
Public Land Survey System. Each of the
four layers can be purchased individually.
US Geodata tapes can be ordered
through Earth Science Information (ESIC)
Center, as well as through the following
ESIC offices. Anchorage, AK - (907) 786-
7011; Denver, CO - (303) 236-7477 and
7476; Menlo Park, CA - (415) 329-4309;
Reston, VA - (703) 860-6045; Rolla, MO -
(314) 341-0851; Salt Lake City, UT - (801)
524-5652; Spokane, WA - (509) 456-2524;
and Stennis Space Center, MS - (601)
688-3541 or (601) 353-2524.
These maps have been digitized, edited
and incorporated into a digital data base.
The data is available to the public in both
graphic and digital form. Statistics
derived from the data are available also.
Users are able to search for either
locations or attributes. To obtain
information from this data base, contact
ESIC.
GNIS provides a rapid means of
organizing and summarizing current
information about cultural or physical
geographic name entities. The data base
contains a separate file for each State,
the District of Columbia, and territories
containing all 7.5-min. maps published or
planned.
The data were obtained from U.S.
Government agencies, academic
institutions, and private industries. Data
coverage is regional to worldwide; data
collection methods encompass map
digitization to satellite remote sensing.
-------
Sources of Hydrogeological Information
213
GEOLOGIC DATA
Source
Geological
Reference Sources:
A Subject and
Regional
Bibliography of
Publications and
Maps in the
Geological
Sciences. Ward
and others (1981)
A Guide to
Information
Sources in Mining.
Minerals, and
Geosciences.
Kaplan (1965)
Bibliography and
Index of Geology
KWIC (Kevword-in-
Contents) Index of
Rock Mechanics
Literature
Information
Obtainable
Bibliographies of
geologic information for
each State in the U.S.
and references general
maps and ground water
information for many
sites.
Describes more than
1,000 organizations in
142 countries. Its
listings include name,
address, telephone
number, cable address,
purpose and function,
year organized,
organizational structure,
membership categories,
and publication format.
Federal and State
agencies are listed for
the U.S. as well as
private scientific
organizations, institutes,
and associations.
Includes worldwide
references and contains
listings by author and
subject.
Engineering geologic
and geotechnical
references.
Comments
Provides a useful starting place for many
site assessments. A general section
outlines various bibliographic and
abstracting services, indexes and
catalogs, and other sources of geologic
references.
An older useful guide. Part II lists more
than 600 worldwide publications and
periodicals including indexing and
abstracting services, bibliographies,
dictionaries, handbooks, journals, source
directories, and yearbooks in most fields
of geosciences.
This publication is issued monthly and
cumulated annually by the American
Geological Institute (AGI), and replaces
separate indexes published by the U.S.
Geological Survey through 1970 (North
American references only) and the
Geological Society of America until 1969
(references exclusive of North America
only). Both publications merged in 1970
and were published by the Geological
Society of America through 1978, when
AGI continued its publication.
The KWIC index is available in two
volumes at many earth science libraries
(Hoek, 1969; Jenkins and Brown, 1979).
-------
214
Appendix C
Source
Information
Obtainable
Comments
GEODEX Retrieval
System with
Matching
Geotechnical
Abstracts
GEODEX
International,
Inc.
P.O. Box 279
Sonoma, CA 95476
U.S. Geological
Survey
Branch of
Distribution
604 S. Pickett St.
Alexandria, VA
22304
Engineering geological
and geotechnical
references.
U.S. Geological
Survey Library
Database
USGS Main Library
National Center
MS 950
12201 Sunrise
Valley Drive
Reston, VA 22092
(703) 648-4302
Geologic Names of
the United States
(GEONAMES)
Geologic Division
USGS
907 National
Center
Reston, VA 22092
The U.S. Geological
Survey (USGS)
produces annually a
large volume of
information in many
formats, including maps,
reports, circulars, open-
file reports, professional
papers, bulletins, and
many others.
The Reston library
contains more than
800,000 monographs,
serials, maps, and
microforms covering
chemistry, environmental
studies, geology,
geothermal energy,
mineralogy,
oceanography,
paleontology, physics,
planetary geology,
remote sensing, soil
science, cartography,
water resources, and
zoology.
GEONAMES is an
annotated index of the
formal nomenclature of
geologic units of the
United States. Data
includes distribution,
geologic age, USGS
usage, lithology,
thickness, type locality,
and references.
The GEODEX is a hierarchically organized
system providing easy access to the
geotechnical literature and can be used
at many university libraries. The GEODEX
system can be purchased on a
subscription basis.
To simplify the dissemination of this
information, the USGS has issued a
Circular (No. 777) entitled A Guide to
Obtaining Information from the USGS
(Clarke, et al.f 1981).
This library system is one of the largest
earth science libraries in the world.
Library staff and users may access the
online catalog from terminals at each of
the 4 USGS libraries. The data base can
be searched by author, title, key words,
subjects, call numbers, and corporate/
conference names. The general public is
welcome to conduct literature searches
using various data bases. Regional
libraries are located in Denver, CO;
Flagstaff, AZ; and Menlo Park, CA.
Printouts are not available. Diskettes
containing data for 2 or more adjacent
States are available from USGS Open-File
and Publications, Box 25425 Federal
Center, Denver, CO 80225. Magnetic
tapes can be obtained from NTIS.
-------
Sources of Hydrogeological Information 215
Information
Source Obtainable Comments
USDA Soil maps and
Soil Conservation description are available
Service (SCS) for about 75% of the
(202) 720-1820 country through the U.S.
Soil Conservation
Service office located in
each State capital
-------
216
Appendix C
GEOPHYSICAL DATA
Source
U.S. Geological
Survey Water
Supply Papers
Well Log Libraries
Electric Log
Services
P.O. Box3150
Midland, TX 79702
Tel: (915) 682-7773
Geophysical
Survey Firms
Information
Obtainable
The most common types
of geophysical data are
available from seismic
and resistivity surveys.
Electric logs for many
petroleum wells can be
obtained from one of
several well log libraries
in the U.S.
Specific geophysical
logs
Comments
Water Supply Papers for an area can be
located by any of the computer searches
or published indexes described in the first
section of this paper. In addition, the
USGS also publishes geophysical maps
of various types at relatively small scales
for many areas of the U.S. Aeromagnetic
maps have been completed for much of
the U.S., although the flight altitude of
several thousand meters and scale of
1:24,000 make these maps too general
for most site specific work.
The geophysical logs are indexed by
survey section. To obtain information on
wells in a given area, it is necessary to
compile a list of the townships, ranges,
and section numbers covering the area.
Proprietary geophysical data can
sometimes be obtained from private
survey firms. In general, the original
client must approve the exchange of
information, and preference is given for
academic purposes. If the information
cannot be released, firms may be willing
to provide references to published
information they obtained before the
survey, or information published as a
result of the survey.
-------
Sources of Hydrogeological Information
217
Source
Information
Obtainable
Comments
NOAA
National
Geophysical
Data Center
(NGDC)
Chief, Solid Earth
Geophysics
325 Broadway
Boulder CO 80303
(303) 497-6521
Fax (303) 497-6513
Geomagnetism
(GEOMAG)
Branch of Global
Seismology and
Geomagnetism
USGS
Box 25046
Federal Center
Mail Stop 968
Denver, CO 80225
(303) 273-8440 or
(303) 273-8441
NGDC maintains a
computer database
which contains
information on
earthquake occurrences
from prehistoric times to
the present. Historic
U.S. earthquakes are
included for the period
starting in 1638. NGCD
also maintains
databases on other
parameters, such as
topography, magnetics,
gravity, and other topics.
GEOMAG contains
current and historical
magnetic-declination
information for the
United States. It
provides historical and
current values of
declination.
Site studies for many projects now
require information regarding the
seismicity of the region surrounding the
site. The National Geophysical Data
Center (NGDC) of the National Oceanic
and Atmospheric Administration (NOAA)
is a focal point for dissemination of
earthquake data and information for both
technical and general users, except for
information on recent earthquakes.
(Information about recent earthquakes
can be obtained by contacting the
USGS.)
For a fee, a search can be made for one
of the following parameters:
- Geographic area (circular or
rectangular area)
- Time period (staring 1638 for U.S.)
- Magnitude range
- Date
- Time
- Depth
- Intensity (Modified Mercalli)
Current or historical values back to 1945
can be obtained over the telephone at no
charge by calling (800) 358-2663. To
access the full program via modem,
contact the listed office for hook-up
instructions. There is no subscription fee.
-------
218
Appendix C
REMOTE SENSING
Source
USGS Earth
Resources
Observation
Systems (EROS)
Data Center
User Service
EROS Data Center
U.S. Geological
Survey
Sioux Falls, SD
57198
(605) 594-6151
Landsat Data
Information
Obtainable
The EROS Program
provides remotely-
sensed data. To obtain
publications, request
further information, or
place an order, contact
the EROS Data Center.
Landsat satellites sensor
images are found in
spectral bands:
- Band 4 (emphasizes
sediment-laden and
shallow water)
- Band 5 (emphasizes
cultural features)
- Band 6 (emphasizes
vegetation, land/water
boundaries, and
landforms)
- Band 7 (as above,
with best penetration
of haze)
- Band 5 gives the best
general-purpose view
of the earth's surface.
Black and white
images and false-color
composites are
available.
Comments
The EROS Data Center, near Sioux Falls,
South Dakota, is operated by the USGS
to provide access primarily to NASA's
Landsat imagery, aerial photography
acquired by the U.S. Department of the
Interior, and photography and multi-
spectral imagery acquired by NASA from
several satellite data systems sources.
The primary functions of the Data Center
are data storage and reproduction, user
assistance, and training.
The Landsat satellites were designed to
orbit the earth about 14 times each day
at an altitude of 920 km, obtaining
repetitive coverage every 18 days. The
primary sensor aboard the satellites is a
multi-spectral scanner that acquires
parallelogram images 185 km per side in
four spectral bands.
-------
Sources of Hydrogeological Information
219
Source
Information
Obtainable
Comments
EOSAT
4300 Forbes Blvd.
Lanham, MD 20706
(301)552-0500
SPOT Image
Corporation
1897 Preston White
Dr.
Reston, VA 22091
(703)620-2200
U.S. Department of
Commerce
NOAA/NEDIS/
NSDC
Satellite Data
Services Division
(E/CCGI)
World Weather
Building, Rm 10
Washington, DC
20233
NASA Aerial
Photography
The Thematic Mapper
provides data in 7 bands
including one band of
emitted infrared
(thermal)
SPOT (Satellite
Probatoire I'Observation
de la Terre) is the
European counterpart of
LANDSAT. The data is
essentially the same as
that produced by
LANDSAT.
Advanced Very High
Resolution Radiometer
(AVHRR) is particularly
useful for regional
geologic analysis
because of its wide
scene size (2100 km).
The data are collected in
five spectral (including
one thermal) bands at a
resolution of 1100
meters.
Photography is available
in a wide variety of
formats from flight at
altitudes ranging from
one to 18 km.
Photographs generally
come as 230 mm by 230
mm prints at scales of
1:60,000 or 1:120,000,
and are available as
black and white, color,
or false-color infrared
prints.
Thematic Mapper images are identical in
scene size as LANDSAT MSS but have a
30 meter resolution. Repetitive coverage
(revisit time) is reduced from 18 to 16
days. In addition, the detectors are
placed directly at the focal planes of the
optical system.
SPOT gathers data in four spectral
bands. Three bands are in 20 meter
resolution and one is in 10 meter
resolution. The system was designed to
produce stereo pairs of images by
pointing the detection system off-nadir
(the ground area directly underneath the
platform).
The orbits are sun-synchronous (cross
the same ground area repeatedly at the
same local time). This line-scanning
system sweeps through 56 degrees either
side of nadir. This feature, together with
an orbital altitude of 833 km produces the
relatively large ground resolution. The
ground resolution size distorts the image
toward its edges and must be corrected
geometrically by computer.
NASA aerial photography is directed at
testing a variety of remote-sensing
instruments and techniques in aerial
flights over certain preselected test sites
over the continental U.S.
-------
220
Appendix C
Source
Information
Obtainable
Comments
Aerial Mapping
Photography
Aerial Photography
Field Office
U.S. Department of
Agriculture
P.O. Box30010
Salt Lake City, UT
84130
(801) 975-3503
Photogrammetry
Division of NOAA
National Oceanic
and Atmospheric
Administration
6001 Executive
Blvd.
Rockville, MD
20852
(301) 443-8601
FTS 443-8601
U.S. Bureau of
Land
Management
Aerial Photo
Section Slyia
Gorski
(SC-67-C)
P.O. Box 25047
Building 46
Denver, CO 80225-
0047
(303) 236-7991
Coverage obtained by
USGS and other Federal
agencies (other than
SCS) available as 230
mm by 230 mm black
and white prints taken at
altitudes of 600 m to 12
km. Scales range from
1:20,000 to 1:60,000.
Conventional aerial
photography scales of
1:20,000 to 1:40,000.
The Coastal Mapping
Division of NOAA
maintains a file of color
and black and white
photographs of the tidal
zone of the Atlantic,
Gulf, and Pacific coasts.
The scales of the
photographs range from
1:20,000 to 1:60,000.
The Bureau of Land
Management has aerial
photographic coverage
of over 50 percent of its
lands in 11 western
States.
Because of the large number of individual
photographs needed to show a region on
the ground, photomosaic indexes are
used to identify photographic coverage of
a specific area. The Data Center has
more than 50,000 such mosaics available
for photographic selection.
Aerial photographs by the various
agencies of the U.S. Department of
Agriculture (Agricultural Stabilization and
Conservation Service [ASCS], Soil
Conservation Service [SCS], and Forest
Service [USFS]) cover much of the U.S.
An index for the collection can be
obtained by contacting the Coastal
Mapping Division at (301) 443-8601 or the
address listed.
For an index of the entire collection
contact the U.S. Bureau of Land
Management at (303) 236-7991 or the
address listed.
-------
Sources of Hydrogeological Information
221
Source
Information
Obtainable
Comments
National Archives
and Records
Admin.
Cartographic and
Architectural
Branch
8 Pennsylvania
Ave.,
N.W.
Washington, DC
20408
(703) 756-6700
National Air
Photograph
Library
615 Booth St.
Ottawa, Ontario
K1A OE9
Canada
(613) 995-4560
Fax (613) 995-4568
Canada Center for
Remote Sensing
588 Booth Street
Ottawa, Ontario
K1A OW7, Canada
(613) 990-8033
Commercial Aerial
Photo Firms
American Society
for
Photogrammetry
and Remote
Sensing
5410 Grosvenor
Lane
Suite 210
Bethesda, MD
20814
(301) 493-0290
Airphoto coverage from
the late 1930's to the
1940's obtained for
portions of the U.S.
Also, foreign airphoto
coverage for the World
War II period is
available.
This service may be important for early
documentation of site activities.
Canadian airphoto coverage can be
obtained from the National Aerial
Photograph Library at (613) 995-4560 or
the address listed.
Canadian satellite imagery can be
obtained from the Canada Center for
Remote Sensing at (613) 990-8033 or
from the address listed.
In many instances, these firms retain the
negatives for photographs flown for a
variety of clients and readily sell prints to
any interested users.
For a listing of nearby firms specializing in
these services, consult the yellow pages.
-------
222
Appendix C
HYDROLOGIC DATA
Source
Water Publications
of State Agencies,
Giefer and Todd
(1972, 1976)
Local Assistance
Center of the
National Water
Data Exchange
(NAWDEX)
U.S. Geological
Survey
421 National Ctr.
Reston, VA 22092
(703) 648-5663
Information
Obtainable
This book lists State
agencies involved with
research related to water
and also lists all
publications of these
agencies.
In general, hydrologic
data can be classified
into four primary
categories: stream
discharge, stream water
quality, ground water
level, and ground water
quality.
NAWDEX identifies
organizations that collect
water data, offices within
these organizations from
which the data may be
obtained, alternate
sources from which an
organization's data may
be obtained, the
geographic areas in
which an organization
collects data, and the
types of data collected.
Information has been
compiled for more than
1,700 organizations, and
information on other
organizations is added
continually. More than '
450,000 data collection
sites are indexed.
Comments
The trend for the past decade has been
to compile such basic data in
computerized data banks, and a number
of such information systems are now
available for private and public users.
Many data now collected by Federal and
State water-related agencies are available
through computer files, but most data
collected by private consultants, local and
county agencies, and well drilling
contractors remain with the organization
that gathered them.
NAWDEX, which began operation in 1976
and is administered by the U.S.
Geological Survey consists of a computer
directory system which locates sources of
needed water data. The system helps to
link data users to data collectors. For
example, the NAWDEX Master Water Data
Index can identify the sites at which water
data are available in a geographic area,
and the Water Data Sources Directory
can then identify the names and
addresses of organizations from which
the data may be obtained. In addition,
listings and summary counts of data,
references to other water data systems,
and bibliographic data services are
available.
-------
Sources of Hydrogeological Information
223
Source
Information
Obtainable
Comments
WATSTORE
Branch of
Computer
Technology
USGS
Reston, VA 22092
(703) 648-5686
Published Water-
Supply Studies and
Data
Catalog of
Information on
Water Data
WATSTORE maintains
the storage of: 1)
surface water, quality-of-
water, and ground water
data measured on a
daily or a continuous
basis; 2) annual peak
values of stream flow
stations; 3) chemical
analyses for surface
and ground water sites;
4) water-data
parameters measured
more frequently than
daily; 5) geologic and
inventory data for
ground water sites; and
6) summary data on
water-use.
Stream discharge,
ground water level, and
water quality data have
been obtained during
short-term, site-specific
studies, and these data
are typically available
only in published or
unpublished site reports.
Data related to lakes,
reservoirs, and wetlands
are commonly found
only in such reports.
The reference consists
of four parts:
- Part A: Stream flow
and stage
- Part B: Quality of
surface water
- Part C: Quality of
ground water
- Part D: Aerial
investigations and
miscellaneous
activities.
Data can be retrieved in machine-
readable form or as computer printed
tables or graphs, statistical analyses, and
digital plots. To retrieve WATSTORE
data, contact:
National Water Data Exchange
(NAWDEX)
Branch of Computer Technology
USGS
Mail Stop 421
Reston, VA 22092
(703) 648-5664
Although significant progress has been
made in computerizing surface- and
ground water data, the majority remains
available only through published and
unpublished reports.
Bibliographic publication indexes USGS
sampling and measurement sites
throughout the U.S. Maps are available
that show a numeric code for each river
basin and has information on drainage,
culture, hydrography, and hydrologic
boundaries for the 21 regions and 222
subregions designated by the Water
Resources Council. Maps depict
boundaries and codes of 352 accounting
units within the National Water Data
Network.
-------
224
Appendix C
Source
Information
Obtainable
Comments
Geologic and
Water-Supply
Reports and Maps
(available for each
State)
Water Resources
Investigations, by
State
Office of Water
Data
U.S. Geological
Survey
417 National Ctr.
12201 Sunrise
Valley Drive
Reston, VA 22092
Federal Flood
Insurance Studies
National Stream
Quality Accounting
Network (NASQAN)
USGS
Branch of
Distribution
1200 South Ends
St.
Arlington, VA 22202
Listed are all agencies
cooperating with the
USGS in collecting water
data, information on
obtaining further
information, and a
selected list of
references by both the
USGS and cooperating
agencies.
To meet the provisions
of the National Flood
Insurance Act of 1968,
the USGS, with funding
by the Federal Insurance
Administration, has
mapped the 100-year
floodplain of most
municipal areas at a
scale of 1:24,000.
Regional and nationwide
overview of the quality of
our streams.
This publication lists references for each
USGS division for each State or district,
the listing, however, is by report number,
requiring a scan of the entire list for
information on a particular area.
This booklet describes the projects and
related publications for all current USGS
work in a State or group of States. Also
available is a useful summary folder with
the same title that depicts hydrologic-data
stations and hydrologic investigations in a
district as of the date of publication.
Additional assistance can be obtained by
contacting: Hydrologic Information Unit,
U.S. Geological Survey, 420 National
Center, 12201 Sunrise Valley Drive,
Reston, VA 22092.
Floodplain maps can be obtained from
the nearest USGS district office and other
agencies, such as the city, town, or
county planning office, or the Federal
Insurance Administration. Some areas
have more detailed "Flood Insurance
Studies" completed for the Federal
Emergency Management Agency (FEMA);
these include 100-year and 500-year
floodplain maps. Complete studies are
available at the nearest USGS office, city,
town, or county planning office, or FEMA.
Consists of over 400 sampling sites. Data
collection sties are located at or near the
downstream end of hydrologic accounting
units or at representative sites along
coastal areas and Great Lakes.
-------
Sources of Hydrogeological Information
225
Source
Information
Obtainable
Comments
Office of Water
Data Coordination
(OWDC)
USGS
417 National
Center
Reston, VA 22092
(703) 648-5016
National Ground
Water Information
Center (National
Ground Water
Association)
6375 Riverside
Drive
Dublin, OH 43017
(800) 332-2104
(614) 761-3446
(fax)
Publications including
the "National Handbook
of Recommended
Methods for Water-Data
Acquisition," indexes to
the "Catalog of
Information on Water
Data," and other
publications.
Computerized, on-line
bibliographic database
that provides a variety of
information on the
quantity and quality of
ground water resources
worldwide. Also
includes references on
such ground water
topics as ground water
protection, waste
remediation, well design
and construction, drilling
methods, water
treatment, and flow and
contaminant transport
models. Photocopying
service of most
database references and
interlibrary loan service
available. Public
information brochures
on ground water
available.
OWDC is the focal point for inter-agency
coordination of current and planned
water-data acquisition activities of all
Federal agencies and many non-Federal
organizations
Databases are accessible through
computer, modem, and
telecommunications software. Members
and nonmembers can gain access.
Abstracts are relatively short and
nontechnical.
-------
226
Appendix C
CLIMATIC DATA
Source
National Climatic
Data Center
(NCDC)
Federal Building
37 Battery Park
Ave.
Asheville, NC
28801-
2733
(704) 259-0682 or
(703) 259-0871
Information
Obtainable
Readily available are
data from the monthly
publication
Climatological Data.
which reports
temperature and
precipitation statistics for
all monitoring stations in
a given State or region.
An annual summary is
also available.
In addition to collecting
basic data, NCDC
provides the following
services:
- Supply of publications,
reference manuals,
catalog of holdings,
and data report
atlases
- Data and map
reproduction in
various forms
- Analysis and
preparation of
statistical summaries
- Evaluation of data
records for specific
analytical
requirements
- Library search for
bibliographic
references, abstracts,
and documents
- Referral to
organizations holding
requested information
- Provision of general
atmospheric sciences
information.
Comments
The National Climatic Data Center
(NCDC) collects and catalogs nearly all
U.S. weather records. Climatic data
(which are essential for construction
planning, environmental assessments,
and conducting surface and ground
water modeling) can be obtained from the
NCC.
NCC can provide data on file in hard
(paper) copy, in microfiche, on magnetic
tape, and on diskette.
For general summary statistics and maps,
the publication Climates of the States -
NOAA Narrative Summaries. Tables, and
Maps for Each State, by Gale Research
Company (1980) is helpful.
-------
Glossary 227
APPENDIX D
Glossary
Adsorption - The attraction and adhesion of a layer of ions from an aqueous solution to the solid
mineral surfaces with which it is in contact.
Advection - The process by which solutes are transported by the bulk motion of flowing ground water.
Aerial Photography - Photographs of the earth taken from either high or low altitudes and used to
interpret natural and manmade surface features.
Aquifer - Rock or sediment in a formation, group of formations, or part of a formation that is saturated
and sufficiently permeable to transmit economic quantities of water to wells or springs.
Aquifer Discharge Areas - An area of land where the zone of saturation is in direct contact with the
ground surface. Discharging ground water may appear as springs, seeps, or as baseflow of streams.
Aquifer Recharge Areas - An area of land above or remote from an aquifer that allows infiltration of
water to that aquifer.
Aquifer Test - Pumping of a well at a constant rate for a fixed period of time with concurrent water-
level measurements in one or more nearby observation wells. The time-drawdown data are analyzed
to yield quantitative aquifer parameter values.
Aquitard - A geologic unit of low permeability that can store and slowly transmit ground water from
one aquifer to another. Aquitards act as confining units of aquifers.
Attenuation - The process by which a compound is reduced in concentration over time through one
or more of the following processes: adsorption, degradation, dilution, or transformation.
Bail Piezometer Test - A single well test to determine the in-situ hydraulic conductivity of an aquifer
by the instantaneous removal of a known quantity of water from a well, and the subsequent
measurement of the recovery as a function of time.
Baseflow - That part of stream discharge that originates as ground water seeping into the stream.
Borehole Geophysical Logging - A general term that encompasses all techniques in which a sensing
device is lowered into a borehole for the purpose of characterizing the associated geologic formations
and their fluids. The results can be interpreted to determine lithology, geometry, resistivity, bulk
density, porosity, permeability, and moisture content.
Bulk Density - The mass of dry soil including air space, per unit volume of material.
Chromatographic - Pertaining to a method for separating mixtures that makes use of the different
tendencies that substances have for being adsorbed onto the surface of some stationary support.
Coefficient of Storage - See Storativity.
-------
228 Appendix D
Confined Aquifer - An aquifer that is bounded above and below by low permeability formations or
aquitards.
Cross-Section - A profile depicting the geologic materials and structures through a vertical slice of
the earth.
Darcy's Law - An equation for the computation of the quantity of water flowing through porous media.
Darcy's Law assumes that the flow is laminar and that inertia can be neglected. The law states that
the rate of viscous flow of homogenous fluids through isotropic porous media is proportional to, and in
the direction of, the hydraulic gradient.
Decay - The process by which a substance is broken down by either biotic or abiotic processes or
through radioactive emission.
Degradation - The transformation over time of a compound into one or more similar chemicals.
Diffusion - The process by which both ionic and molecular species dissolved in water move from
areas of higher concentration to areas of lower concentration.
Dilution - To reduce the concentration of a component in a mixture by increasing the amount of one
or more other components.
Dispersion - The spreading and mixing of chemical constituents in ground water caused by diffusion
and mixing due to microscopic and macroscopic variations in velocities within and between pores.
Drawdown - The amount that a pumping well lowers the water table or potentiometric surface as
water is removed. The amount of drawdown is a function of the discharge rate and the physical
properties of the aquifer, such as hydraulic conductivity, storativity, and its boundaries.
Electrical Resistivity - Measurement of subsurface electrical resistance. Electrical resistivity is a
function of the physical and mineralogical properties of soil and rock and the chemistry of pore fluids.
Electromagnetics - Method that measures subsurface conductivity through the use of low-frequency
electromagnetic induction.
Equipotential - Lines of equal pressure; lines connecting points of equal hydraulic head.
Evaporation - The process by which water passes from the liquid to the vapor state. Water loss to
the atmosphere (e.g., from surface water bodies, soil, etc.).
Evapotranspiration - Loss of water from the soil both by evaporation and by transpiration from the
plants growing in the soil.
Fence Diagram - A projection of known stratigraphic columns to show the lateral thicknesses and
interrelationships of geologic units.
Flow-Direction - The vector in which the water in an aquifer moves.
Flow-Net Analysis - Study to determine a set of interacting equipotential lines and flow lines
representing a two-dimensional steady flow through porous media.
Gamma Logging - A borehole logging technique that measures the natural gamma radiation emitted
by the formation rocks. It is used to delineate subsurface rock types, their positions, and thicknesses.
-------
Glossary 22g
Geographic Information System (GIS) - A computerized data base/mapping system that may be
used to store, retrieve, and analyze information, such as soil and hydrogeologic data, based on
geographic location.
Geologic Cross-Section - Method of extrapolating surface geologic observations to the relationships
of geologic units under the surface. A cross-section is a two-dimensional presentation of a study area
and can be either of large or small scale.
Geologic Structure - The form, symmetry, and geometry of geologic units. Structural geology may
include the study of folds, faults, and joints, as well as the mechanical properties of rocks.
Geophysical Methods - Means of obtaining data on subsurface conditions. Includes use of
electromagnetics, ground-penetrating radar, electrical resistivity, magnetics, seismic refraction and
reflection, gravity, and borehole measuring techniques.
Ground-Penetrating Radar (GPR) - A surface geophysical technique based upon the transmission of
repetitive pulses of electromagnetic waves into the ground. Some of the radiated energy is reflected
back to the surface and the reflected signal is captured and processed. GPR is useful for defining the
boundaries of buried trenches and other subsurface installations.
Ground Water Withdrawal - Removal of water from an aquifer by pumping.
Half-Life - The time required for a pollutant to be reduced by 50 percent of its original amount.
Hydraulic Conductivity - A coefficient of proportionality that describes the rate at which a fluid can
move through a permeable medium. It is a function of both the media and of the fluid flowing through
it
Hydraulic Gradient - A measure of the change in ground water head over a given distance.
Hydraulic Head - The height above a specific datum (generally mean sea level) that water will rise in a
well.
Hydrogeologic Setting - The composite description of the regional geology of a specific area that
characterizes the stratigraphy, structure, and lithology of the materials, and the occurrence and
chemistry of the ground water.
Hydrograph - A graph that shows the elevation of ground water in a well, or surface water level,
above a particular datum point, against time.
Hydrologic Cycle - The endless circulation of water between the ocean, atmosphere (by evaporation)
land (by precipitation), and back to the ocean (by stream and subsurface flow).
Hydrology - The study of the occurrence, distribution, circulation, and chemistry of water.
Impermeable Strata - Layers of rock or sediment that do not allow the transmission of water.
Infiltration Test - Field or lab tests used to measure the permeability or hydraulic conductivity of a
porous media as a liquid passes through it. These tests are usually used to analyze a soil profile.
Interflow - The lateral movement of water in the unsaturated zone during and immediately after a
precipitation event. The water moving as interflow discharges directly into a stream or lake.
Intrusive Borehole Tests - Techniques that measure resistivity, conductivity, radioactive properties
velocity, density and other physical properties, depending on the tool used. The specific borehole'
-------
230 Appendix D
tools are lowered downhole and the data are recorded continuously either digitally and/or by hard
copy.
Isopach Map - A map showing areas of an aquifer or geologic formation of the same thickness.
Isotropy - The condition in which the property or properties of interest are the same when measured
along axes in any direction.
Karst - Areas underlain by soluble bedrock (e.g., limestone, dolomite) that are generally characterized
by surface and subsurface features (e.g., sinkholes, caves) formed by the dissolution of rock by
ground and surface water. These landscapes can describe an area containing specific solutionally-
modified landforms as well as well as areas underlain by solutionally-derived conduit aquifer systems.
Leaky Aquifer - A low-permeability layer that can transmit water at sufficient rates to furnish some
recharge to a well pumping from an adjacent aquifer.
Lithologic Correlation - Verifying results of an analytic method through direct study of the
macroscopic features of a rock (e.g., its texture or petrology).
Macropores - Spaces within a geologic material above the water table that are too large to hold water
by capillary action. Macroporosity may result in enhanced migration of contaminants into ground
water.
Organic Matter - The material of a living organism and/or the remains or a key byproduct of a living
organism.
Particle Density - The mass per unit volume of soil particles, usually expressed in grams per cubic
centimeter.
Partition Co-Efficient - The ratio of concentration of a chemical sorbed to the solid phase to its
concentration in the aqueous phase (Kd).
Permeability - The ability of a porous medium to transmit fluids under a hydraulic gradient. Highly
permeable soils are more likely to result in the leaching of contaminants than soils of lower
permeability.
pH - A measure of the acidity or alkalinity of a liquid or solid material.
Piezometer - Generally a small-diameter, non-pumping well used to measure the elevation of the
water table or potentiometric surface.
Plume - The area of a measurable discharge of a contaminant from a given point of origin.
Porosity - The ratio of the volume of small openings in soil or rock to its total volume, usually
expressed as a percentage.
Potentiometric Surface - A surface that represents the total head of ground water in a confined
aquifer that is defined by the level to which water will rise in a well.
Redox - A chemical reaction in which an atom or molecule loses electrons to another atom or
molecule. Also called oxidation-reduction. Oxidation is the loss of electrons; reduction is the gain in
electrons.
Retardation - Preferential retention of contaminant movement in the subsurface zone. Retention may
be the result of adsorption processes or solubility differences.
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Glossary 231
Runoff - The total amount of water flowing into a body of water. It includes overland flow, return flow
and interflow.
Salt Water Encroachment - The movement, as a result of human activity, of saline ground water into
an aquifer formerly occupied by fresh water. Passive saline water encroachment occurs at a slow rate
owing to a general lowering of the fresh water potentiometric surface. Active saline water
encroachment proceeds at a more rapid rate owing to the lowering of the fresh water potentiometric
surface below sea level.
Satellite Imagery - Images that are produced from the reflected electromagnetic radiation as recorded
by satellites. These images are used to identify and assess cultural, geographic, climatic and qeoloqic
features of the earth.
Saturated Zone - The subsurface zone where pore spaces are completely filled with water.
Seepage Meter - A device used to measure leakage from underlying aquifers into stream beds or
through emergence of ground water into a stream channel.
Seismic Methods - Exploration of subsurface geologic structures by means of seismic waves that are
induced at the surface.
Slug Piezometer Test - A single well test to determine the in-situ hydraulic conductivity of an aquifer
by the instantaneous addition of a known quantity (i.e., slug) of water into a well, and the subsequent
measurement of the resulting recovery time.
Soil - The natural, weathered, unconsolidated, mineral and organic matter on the surface of the earth-
it is a medium for the growth of plants.
Specific Retention - The ratio of the volume of water that a given body of rock or soil will hold against
the pull of gravity to the volume of the body itself. It is usually expressed as a percentage.
Specific Yield - The ratio of the water drained from a rock under the influence of gravity, or removed
by pumping, to the total volume of the rock voids or pore space in the drained rock.
Stack-Unit Maps - A map showing the areal distribution of geological materials based on their order
of occurrence to a specified depth.
Stiff Diagram - A graphical means of presenting the chemical analysis of the major cations and anions
of a water sample.
Storatlvity (Coefficient of Storage) - The volume of water an aquifer releases from or takes into
storage per unit surface area of the aquifer per unit change in head. In unconfined aquifers it is equal
to the specific yield, but in confined aquifers, the storage coefficient depends on elastic compression
of the aquifer and is usually less than 10".
Subsidence - Sinking or settling of the ground surface due to natural or anthropogenic causes
Surface material is displaced vertically downwards with little or no horizontal movement. One
anthropogenic cause of subsidence is ground water pumpage from unconsolidated aquifers that
greatly exceeds the recharge rate and depletes the aquifer.
Temporal Variations - Some characteristics of ground water vary depending upon the time of year
For example, water levels in shallow aquifers in the Eastern United States for the summer and winter
months will be lower than levels in the spring and fall when most of the yearly precipitation occurs
Ground water managers need to be aware of these variations when assessing ground water
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232 Appendix D
Topography - The physical features of a surface area including relative elevations and the position of
natural and manmade features.
Total Organic Carbon - The amount of carbon existing as part of organic compounds in a sample.
Excludes inorganic forms of carbon such as CO2 and CaCOS.
Tracer Tests - Tests that measure the reduction over time of the concentration of a tracer as well as
the arrival times of ground water flow at a known point. Possible tracers include salt, radioactive
isotopes, and fluorescent dyes.
Transformation - The physical, chemical, and biological processes by which a molecule of a chemical
is altered to form a higher- or lower-molecular-weight chemical.
Transmissivity - The rate at which water of a prevailing density and viscosity is transmitted through a
unit width of an aquifer or confining bed under a unit hydraulic gradient. It is a function of the
properties of the liquid, the porous media, and the thickness of the porous media.
Trilinear Diagram - A method of graphically plotting the chemical composition of the major anions and
cations of a water sample.
Unconfined Aquifer - An aquifer characterized by the absence of an aquitard above it, so that the
water table forms the upper boundary of the aquifer and is free to move with atmospheric influences
such as atmospheric pressure. Also referred to as a water table aquifer.
Vadose Zone - The subsurface zone where pore spaces are not completely filled with water.
Volatile Organic Compound - Any organic compound that participates in atmospheric photochemical
reactions except for those designated by the EPA Administrator as having negligible photochemical
reactivity.
Water Budget - A method of assessing the size of future water resources in an aquifer, catchment
area, or geographical region that involves evaluating all the sources of supply or recharge in
comparison to all known discharges or abstractions.
Water Table - The level below which the soil or rock is saturated with water. It is also the upper
boundary of the saturated zone. At this level, the hydraulic pressure is equal to atmospheric pressure.
Also used to refer to an aquifer that exists in unconfined conditions (e.g., a water table aquifer).
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