GUIDELINES FOR DELINEATION OF
WELLHEAD PROTECTION AREAS
OTFICE OF WATER
OFHCE OF GROUND-WATER PROTECTION
U.S. ENVIRONMENTAL PROTECTION AGENCY
JUNE 22, 198?
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ACKNOWLEDGEMENTS
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This document was prepared by the U.S. Environmental Protection Agency, Office
of Ground-Water Protection (OGWP) under the overall direction of Ron Hoffer, Chief
Hydrogeologist arid Director of the Guidelines Implementation Staff. The efforts of the
Technical Committee on Hydrogeologic Aspects of the SOW A Amendments deserve a
special note. The communal knowledge and experience of this group, from both technical
and administrative viewpoints, provided the foundation upon which these guidelines are
based. The activities of this group, which worked cooperatively to provide a balanced
perspective, allowed OGWP to meet its statutory directives in a timely and sound manner.
Special appreciation from OGWP is extended to key members from outside EPA, and in
particular to: Keros Cartwright (Illinois Geological Survey), Charles Kreitler (Texas
Bureau of Economic Geology), Albert Ogden (formerly with the Idaho Department of
Health and Welfare, now with Tennessee Technological University), Hugo Thomas
(Connecticut Department of Environmental Protection), and 3ohn Vecchioli (U.S.
Geological Survey).
OGWP extends its thanks to the technical consultants on this effort, the firm of
Dames &. Moore, with Alberto G. Morilla serving as Project Manager. The input of key
staff is appreciated, both at OGWP (including at Headquarters: Bill Stelz, Carey
Carpenter, Paul Violette, Joyce Edwards, and Delores Furman; and in the Regions: Jerri-
Anne Garl and Doug Heath), and at Dames & Moore (including Roberto L. Sanchez, John
Osgood, Robert McDonough, Bob Kalinski, Harch Gill, Theresa Thomas, and Valerie Orr).
Gordon Everett, consultant to OGWP, also provided valuable insight and overall
inspiration.
Last, but certainly not least, go our thanks to Georg Matthess of Kiel University in
West Germany, and Hubert Van Waegeningh of the National Institute of Public Health and
Environmental Hygiene -in the Netherlands. These two gentlemen have been at the
forefront of the in-place wellhead protection efforts of Europe. Through their
publications and their very effective participation in our Hydrogeology Workshop, they
have demonstrated that wellhead protection can be carried but while balancing the
sometimes conflicting demands of good science and implementable policy.
Marian Mlay
Of f ice of Ground-Water Protection
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FOREWORD
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* These guidelines are provided as technical assistance to State and .local governments
in their efforts to protect ground-water resources supplying public wells used for drinking
water. The document is one in a continuing series of publications on the hydrogeologic
aspects of ground-water protection^ prepared in response to the 1986 Amendments to the
Safe Drinking Water Act. Policies regarding applications by States for financial support
are addressed in separate grant guidance and application documents. Additional
information on the Wellhead Protection Progratn is available from the Office of Ground-
Water Protection in Washington, D.C., and from the ten EPA Regions.
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EXECUTIVE SUMMARY
V The Amendments to the Safe Drinking Water Act (SDWA), which were passed in
June 1986, established the first nationwide program to protect ground-water resources
used for public water supplies from a wide range of potential threats. Unlike previous
Federal programs, which have tended to focus on individual contaminant sources, this new
effort approaches the assessment and management of ground-water quality from a more
comprehensive perspective. The SDWA seeks to accomplish this goal by the establishment
of State Wellhead Protection (WHP) Programs w,hich "protect wellhead areas within their
jurisdiction from contaminants which may have any adverse effect on the health of
persons."
One of the major elements of WHP is the determination of zones within which
contaminant source assessment and management will be addressed. These zones, denoted
as Wellhead Protection Areas (WHPA's), are defined in the SDWA as "the surface and
subsurface area surrounding a water well or wellfield, supplying a public water system,
through which contaminants are reasonably likely to move toward and reach such water
well or wellfield." Hence, the law establishes the concept of protecting some of the
recharge areas to these points of public drinking water withdrawal. The States are given
flexibility in determining appropriate operational approaches to WHPA delineation. The
Environmental Protection Agency (EPA), in addition, is required by the SDWA to release
technical guidance on the hydrogeologic aspects of this task. These Guidelines for
Delineation of Wellhead Protection Areas are provided to meet this need. Apart from this
requirement, issuance of this guidance does not affect or inhibit EPA regulatory
programs.
WHPA delineation policy is generally based upon the analysis of criteria, criteria
thresholds, and delineation methods. The criteria and criteria thresholds define the
general technical basis of the WHPA. The WHPA delineation methods are used to
translate or apply these criteria, to develop on-the-ground or on-the-map WHPA
boundaries. In preparation for criteria and method selection, most States will assess the
availability of hydrogeologic data and the institutional capability of the State to perform
such technical assessments.
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HYDROGEOLOGIC AND CONTAMINANT CONTROLS OVER WHPA DEUNEAT^
Th«jse delineation guidelines provide a discussion of the basic concepts of ground-
,water flow and contaminant transport,. as they apply to the itask of WHPA delineation.
Differences among the major aquifer types are emphasized.
Approximately half the U.S. population is dependent on ground-water sources-wells
and springs-for its domestic water. Though springs are occasionally used for water
supplies, exploitation of ground water normally requires the drilling and installation of
wells or well fields. Under natural conditions, ground water is in equilibrium and flows
from areas of higher head to areas of lowe'r head. Ground-water pumping or discharge
alters the natural equilibrium and causes the lowering of water levels around the pumping
well. This effect, called drawdown, affects an area referred to as the zone of influence
(ZOI) of the well. This expression is generally synonymous with the commonly
encountered term "cone of depression." Part of the ZOI is contained within the zone of
contribution (ZOC), which includes all areas that recharge or contribute water to the well
or well field. The guidance notes that both technical and nontechnical specialists -
commonly (though incorrectly) assume that the ZOI is always completely contained within
the ZOC. Understanding the differences between these concepts is essential to fostering
more precise WHPA delineation.
The concept of a WHPA can be applied to a variety of aquifer types under both
confined and unconfined conditions. Uncpnfined aquifers, also known as "water-table
aquifers," are in direct hydrogeologic connection with the surface, and hence are
generally more vulnerable to contaminants originating at or near the surface than
confined aquifers. Confined aquifers, sometimes known as "artesian aquifers," occur
beneath less permeable materials, and are under pressure conditions greater than
atmospheric. Despite this generally less vulnerable basic condition, confined aquifers are
susceptible to contamination from a variety of factors-the relative difference in head
between the aquifer and other aquifers, natural or human-induce.^I breaks in confinement
such as fault zones or abandoned and corroded well casings, and the physical conditions of
the confining unit itself. The guidance provides technical information to help States
evaluate the extent of specific WHPA's needed for wells under confined conditions. More
tailored WHPA techniques for conduit karst, fractured bedrock, and other "exceptions" to
the basic aquifer types are also noted.
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The delineation guidelines assume that WHPA delineation and protection will be
targetted to three general threats. The first is the direct introduction.of contaminants to
the area immediately contiguous to the-well through improper casing, road runoff, spills,
and accidents. A second basic threat is from microbial contaminants such as bacteria and
viruses, the third major threat is the broad, range of chemical contaminants, including
inorganic and naturally occurring or synthetically-derived organic chemicals. The
transport characteristics of these classes of contaminants are reviewed briefly in the
guidance document.
WHPA DELINEATION CRITERIA
There are several operational goals the States may use to meet the delineation
elements of the statutory goals for WHP. Three of these are: provide a remedial action
zone to protect wells from unexpected contaminant release; provide an attenuation zone
to bring the concentrations of specific contaminants to desired levels by the time they
reach the wellhead; and provide a well-field management zone in all or part of a well or
well field's existing or potential recharge area. Some conceptual standard is needed,
however, to meet these goals.
The conceptual standards oh which WHPA delineation may be based are referred to
in this document as criteria. They may include distance, drawdown, travel time, flow
system boundaries, and the capacity of the aquifer to assimilate contaminants. Choice of
the criteria to be applied will likely be based on both technical and nontechnical
considerations.
The technical merits of a criterion depend on the degree to which it incorporates
physical processes affecting ground-water flow and contaminant transport. Nontechnical
considerations include a State's institutional capabilities for implementing a program,
together with economic and demographic realities in the State. After selection of
criteria for WHPA delineation, appropriate thresholds must be chosen. These are values
that represent the limits above or below which a criterion will cease to provide the
desired degree of protection.
A distance criterion defines the WHPA by a radius or dimension measured from a
pumping well to encompass the area of concern. A drawdown criterion defines the WHPA
as the area around the pumping well in which the water table (in an unconfined aquifer) or
the potentiometric surface (in a confined aquifer) is lowered by the pumping; this involves
mapping all or part of the zone of influence. The time of travel (TOT) criteria bases the
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WHPA boundary on the time required for contaminants to reach the water supply. A flow
boundaries criterion incorporates the known locations of ground-water divides and other
physical^ hydrologic features that control ground-water movement. The assimilative
'capacity criterion is based on the subsurface formation's capacity to dilute or otherwise
attenuate contaminant concentrations to. acceptable levels before they reach public
drinking-water wells.
Each of the criteria has advantages and disadvantages in meeting these goals
depending largely on the hydrogeologic settings within a State, as well as the
administrative and technical resources ..available. Selecting appropriate criteria
thresholds will be another key decision point, although it will be done in conjunction with
establishing the management elements of the WHP.
WHPA DELINEATION METHODS
Following selection of WHPA delineation criteria, it is necessary to choose the
specific methods for mapping the selected criteria. Six methpds have been identified as
having been used in WHPA delineations, These are, in increasing order of cost and
sophistication: arbitrary and calculated fixed radii, simplified variable shapes, analytical
methods, hydrogeologic mapping, and numerical flow/transport models. They range from
simple techniques to highly complex and comprehensive ones.
The arbitrary fixed radius method involves circumscribing a zone around the water
supply that is based on a distance criterion threshold. Though simple and inexpensive, this
method may tend to over-protect or under-protect. A significant improvement over no
delineation, the method is often used for microbial protection, or in the early phases of a
WHP Program for chemical contaminants.
The calculated fixed radius method applies an analytical equation to calculate the
radius of a circular WHPA based on a time-of-travel criterion. Though still relatively
simple and inexpensive to apply, this method provides more accuracy, depending on site
conditions.
Simplified variable shapes are standard outlines of WHPA's, generated using
analytical models, and generally based on a combination of flow boundary and time-of-
travel criteria. The appropriate shapes are then chosen to match or approximate
conditions encountered at specific wellheads, well fields, and springs. This is another
inexpensive yet somewhat more accurate technique. v
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Analytical methods may be used to define ground-water flow boundaries and
contaminahfaransport dynamics through the application of empirically derived equations.
This is perhaps the most commonly used method where greater precision is needed.
Hydrogeologic mapping can be used to map flow boundaries and to implement other
criteria through use of geological, geomorphic, geophysical, and dye tracing methods. The
method is particularly appropriate in some types of aquifers.
Numerical models use mathematical approximations of ground-water flow and/or
contaminant transport equations that can take into account a variety of hydrogeologic and
contamination conditions. These models offer possibly the most accurate delineations,
though at considerable cost.
Comparisons of the results of specific methods in "case study" applications can be
used, to evaluate and then choose WHPA delineation techniques. In such comparative
analyses, the output from more expensive, complex methods is generally compared with
the results from less expensive, simpler techniques to determine the cost and benefit
tradeoffs in given hydrogeologic settings. These case analyses will also be useful for
evaluating, on a generic basis, the spatial extent of different WHPA's based on different
criteria and criteria thresholds. Such information could be very useful in the early phases
of a State WHP Program, to begin the assessment of potential contamination threats to
public water supplies. /
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CONTENTS
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FOREWORD .
ACKNOWLEDGEMENTS
EXECUTIVE SUMMARY ...1........................... ES-1
CONTENTS ...... .....................i............. i
1 INTRODUCTION ...^...... 1-1
1.1 LEGISLATIVE AUTHORITY............................^.......... l'1
1.2 PURPOSE AND SCOPE OF DOCUMENT .4.......................... 1-3
1*3 EPA'S IMPLEMENTATION APPROACH 1-5
1.4 ORGANIZATION OF DOCUMENT.......... . ... 1-6
2 HYDROGEOLOGIC AND CONTAMINANT CONTROLS
OVER WHPA DELINEATION ..........i........................... 2-1
2.1 BASICS OF GROUND-WATER FLOW SYSTEMS 2-1
2.1.1 Natural Flow System ..................->.................... 2-1.
2.1.2 Pumping of Ground Water 2-3
2.2 OTHER AQUIFER CONSIDERATIONS 2-6
2.2.1 Confined Aquifers... 2-6
2.2.2 Karst and Fractured Bedrock Aquifers 2-11
2.3 CONTAMINANT PROPERTIES. 2-13
2.3.1 Inorganic Chemicals........................................ 2-13
2.3.2 Organic Chemicals 2-14
2.3.3 Bacteria and Viruses 2-15
2.4 DELINEATION ZONE PROPERTIES AND TERMINOLOGY. ............ 2-19
3 DELINEATION CRITERIA 3-1
3.1 CRITERIA DEFINITION AND CHARACTERISTICS .................... 3-1
3.1.1 Distance........... 3-2
3.1.2 Drawdown *... 3-4
3.1.3 Time of Travel (TOT).... 3-4
,3.1.4 Flow Boundaries 3-8
3.1.5 Assimilative Capacity *... 3-8
3.2 CRITERIA THRESHOLD EXAMPLES 3-11
3.3 CRITERIA SELECTION CONSIDERATIONS. * 3-17
3.3.1 Overall Protection Goals..... 3-17
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CONTENTS (cont'd)
*» 3.3.2 Technical Considerations oft -_2Q
3.3.3 Policy Considerations ,,.... \_-5-?
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4 WHPA DELINEATION METHODS 4-1
4.1 INTRODUCTION TO WHPA DELINEATION METHODS.,,. 4.]
4.2 WHPA DELINEATION METHOD ASSESSMENTS ....
4.2.1 Arbitrary Fixed Radii .
4.2.2 Calculated Fixed Radii 'I
4.2.3 Simplified Variable Shapes .
4.2.4 Analytical Methods.. .... .
4.2.5 Hydrogeologic Mapping ...
4.2.6 Numerical Flow/Transport Models .
4.3 WHPA DELINEATION METHOD COSTS
4.4 WHPA COMPARATIVE ANALYSIS
4.5 METHOD SELECTION CONSIDERATIONS 4_37
4.5.1 Technical Considerations
4.5.2 Policy Considerations 9%
5 EXAMPLE OF CRITERIA AND METHOD SELECTION 5.1
5.1 PROBLEM STATEMENT: THE HYPOTHETICAL STATE
5.2 EXAMPLE OF CRITERIA SELECTION .
5.2.1 Overall Protection Goals
5.2.2 Technical Considerations
5.2.3 Policy Considerations ,....- 5.5
5.2.4 Summary of Panel's Decision on Criteria Selection. -5-7
5.3 EXAMPLE OF METHOD SELECTION 5.7
REFERENCES __ R A
APPENDIX ASTATE, COUNTY, AND LOCAL
DELINEATION APPROACHES
A.I STATE EXAMPLES A_j
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CONTENTS (cont'd)
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A.1.1 ^State of Florida...................... .................. A-l
A.1.2 Dade County, Florida.......:;.............................. A-3
A.1.3 Massachusetts.......... A-4
A.1.4 Vermont... ..;.. ....:... ...i.... A-6
A.2 EUROPEAN DELINEATION APPROACHES. A-7
A.2il The Netherlands..........*. A-7
A.2.2 West Germany A-9
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APPENDIX B-COMPARATIVE ANALYSIS B-l
Bil CAPE COD, MASSACHUSETTS........... *... .....- .B-4
B.1.1 Hydrogeology of Study Area B-4
B.1.2 Method Application
B.1.3 Data Requirements....................
B.I.* Comparison of Resulting WHPA's. B-5
B.2 SOUTHERN FLORIDA..... . B-13
B.2.1 Hydrogeology of Study Area B-l3
B.2.2 Method Application B-13
B.2.3 Data Requirements. B-13
B.2.4 Comparison of Resulting WHPA's. .......>......... B-14
B.3 CENTRAL COLORADO. ......' B-18
B.3.1 Hydrogeology of Study Area...................... B-18
B.3.2 Method Application ..............*.............. .......... B-19
B.3.3 Data Requirements B-19
B.3.4 Comparison of Resulting WHPA's..... B-19.
B.4 SOUTHWESTERN CONNECTICUT B-24
B.*.l Hydrogeology of Study Area....... P -.:. '
B.4.2 Method Application ........................................
B.4.3 Data Requirements..........
B.*.« Comparison of Resulting WHPA's.....*. B-25
B.5 SUMMARY AND CONCLUSION
APPENDIX C-GLOSSARY................. C-l
APPENDIX DMODEL ASSESSMENT FOR DELINEATING WELLHEAD
PROTECTION AREAS................ « D"1
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FIGURES
Figure No.
page
1-1
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
3-1
3-2.
3-3
3-4
3-5
4-1
4-2
4-3
4-4
General approach to State WHPA delineation ............ ..... . . "
Ground-water flow system (stream valley) under
natural conditions ..... ..... , ..... ....................... .... 2-2
Ground-water flow system (stream valley) affected
by a pumping well ......* ................... ^ . . ,.. ........... . 2-4
Confined aquifer with upward leakage ..... . ..... ..... ....... . 2-7
Confined aquifer with downward 'leakage ... ...... , ............ .. 2-8
Elimination constant and 99.9% elimination of some
relevant bacteria and viruses in ground water ..... , ............ . 2-18
Terminology for wellhead protection area
delineation (hypothetical pumping well
in porous media) ................. ............. .......... ..... 2-20
Terminology for wellhead protection area delineation
(hypothetical contaminant transport in porous media) .......... . . 2-21
Terminology for wellhead protection area delineation
(hypothetical ground-water basin in mature karst) . . . . .. . ..... . . 2-23
Terminology for wellhead protection area delineation
(hypothetical ground-water basin in fractured rock) ,, . . ......... . . 2-24
Terminology for wellhead protection area delineation
(hypothetical confined aquifer in porous media) ..... ........... . . 2-25
Relationship between WHPA delineation criteria
and physical processes .............. ... ......... ,. ...... . ..... 3-3
Aquifer with flat water table and high rainfall
conditions, where boundaries of ZOI and ZOC
approximately coincide (conceptual) .............. ............. 3-5
Flow velocity ranges ................... ..................... 3-7
Flow boundaries criteria (conceptual) ........ ..... ............. 3-9
Assimilative capacity criteria (conceptual) .. ...... . . ........... 3-10
Consideration factors that may affect process of
criteria selection ....... ...... ...... .......... ... . . . . . ....... 3-18
Interrelationships of WHPA methods ......... . ................ . 4-3
WHPA delineation using the arbitrary fixed radius method ........ 4-5
WHPA delineation using the calculated fixed radius method ....... 4-7
WHPA delineation using FDER volumetric flow equation
for well in Florida. ........ .................................. 4-9
IV
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FIGURES (cont'd)
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4-J WHPA delineation using simplified variable shapes method. 4-11
4-6 Examples of standardized forms of WHPA deUneation
using simplified variable shapes..* ...........I.. 4-13
4-7 WHPA delineation using the uniform flow analytical model ....... 4-15
4-8 WHPA delineation using arbitrary fixed radiii
analytical model, and hydrogeologic mapping
(example from Massachusetts)
4-9 WHPA delineation using analytical models, step 1:
Determination of downgradient null point using «
pumping test data (example from Cape Cod, '
Massachusetts)..... .....;.. - 4-1&
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4-10 WHPA delineation using analytical models, step 2:
Identify upgradient null point based on Strahler
prism model (example from Cape Cod, Massachusetts) ..... i..... 4-20
4-11 WHPA deUneation using analytical models, step 3: ,
WHPA delineation using upgradient and downgradient
null points (example from Cape Cod, Massachusetts)............. 4-21 I
4-12 WHPA delineation using hydrogeologic mapping
(use of geologic contacts) 4-22
4-13 WHPA delineation using hydrogeologic mapping
(use of ground-water divides) , i... 4-23
4-14 WHPA delineation using hydrogeologic mapping
(example from Vermont) 4-25
4-15 WHPA delineation using hydrogeologic mapping: dye I
tracing (example from Kentucky)................... 4-26
4-16 Simulation procedure used in WHPA delineation
with numerical modeling 4-31
4-17 Numerical modeling application to Biscayne
aquifer well field 4-33
4-18 WHPA comparative analysisWhat is accuracy? 4-36
5-1 Procedure for WHPA delineation 5-2 |
5-2 Consideration factors that may affect process of - ,
criteria selection 5-12
A-l European protection areas. A-8
B-l Data requirements for WHPA comparative analysis .............. B-3
B-2 WHPA comparative analysis, example for well #1, n,
Cape Cod, MA, 10-Year TOT « B"7
B-3 WHPA cpmparative analysis, example for well Y/l,
Cape Cod, MA, 25-year TOT B-8
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FIGURES (cont'd)
WHPA comparative analysis, example for well #1,
B-5
B-6
B-7
B-8
B-9
B-10
B-ll
B-12
B-13
B-14
B-15
B-16
t-ape v-oa, M/\, ;>u-year TOT: * ....
WHPA comparative analysis, example for well //2,
Cape Cod, MA, 10-year TOT. . . '.
WHPA comparative analysis, example for well #2,
Cape Cod, MA, 25-year TOT
WHPA comparative analysis, example for well #2,
Cape Cod, MA, 50-year TOT
WHPA comparative analysis, example from Southern
Florida, 30-day travel time
WHPA comparative analysis, example from Southern.
Florida, 210-day travel time
WHPA comparative analysis, example from Southern
WHPA comparative analysis, example from Colorado,
1-year TOT
WHPA comparative analysis, example from Colorado,
WHPA comparative analysis, example from Colorado,
20-year TOT and buffer zone
WHPA comparative analysis, example from Connecticut,
1-year TOT
WHPA comparative analysis,' example from Connecticut,
Comparative analysis nomenclature
B-9
B-10
B-ll
B-12
B-15
B-16
B-17
B-21
. . , B-22
B-23
B-26
B-27
B-30
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TABLES
Ta1>le No. . Page
2-1 Persistence of organic substances in ground
water and soils 2-16
3-1 Distance: WHPA criterion threshold values 3-12
3-2 Drawdown: WHPA criterion threshold values 3-13
3-3 Time of travel: WHPA criterion threshold values 3-14
3-4 Physical boundaries: WHPA criterion threshold values 3-16
3-5 Example relationships between overall protection goals .
and criteria for delineating wellhead protection areas 3-19
3-6 WHPA criteria selection versus technical considerations.......... 3-21
3-7 WHPA criteria selection versus policy considerations ......'. 3-23
4-1 WHPA delineation methods and example applications '.'-. 4-2
4-2 Geophysical techniques 4-28
4-3 Costs of delineation associated with various WHPA methods 4-34
4-4 Relationship between WHPA delineation methods and criteria 4-38
4-5 WHPA methods selection versus technical considerations ;... 4-39
4-6 WHPA method selection versus policy considerations. 4-41
5-1 WHPA criteria selection versus technical considerations
(water table aquifer in porous media for the hypothetical
State example) 5-3
5-2 WHPA criteria selection versus policy considerations 5-6
5-3 WHPA methods selection versus technical considerations
(water table aquifer in porous media for the hypothetical
State example) 5-8
5-4 WHPA method selection versus policy considerations
(water table aquifer in porous media for the
hypothetical State example) *'............ 5-9
A-l State WHPA delineation methodologies and criteria A-2
B-l Hydrogeologic parameters used in comparative analyses B-6
B-2 Summary of results of comparative analysis examples B-29
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GUIDELINES FOR WELLHEAD PROTECTION AREA DELINEATION
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CHAPTER 1 -
INTRODUCTION
Nearly half the population in the United States uses wells or springs to obtain
drinking water (U.S. Geological Survey, 198*). Improper management of contamination
sources resulting from human activities of ten .causes degradation of these supplies. One
solution to this problem is to prevent contaminated ground water from reaching wells and
springs by establishing areas of protection around them.
A new provision in the 1986 Amendments to the Safe Drinking Water Act (SOWA) is
the Wellhead Protection (WHP) Program. This program is designed to assist States in
protecting areas surrounding wells within their jurisdiction against contaminants that may
have adverse effects on human health (SOWA, Section 1428(a)). The Amendments
mandated that, among other provisions, the U.S. Environmental Protection Agency (EPA)
Administrator issue technical guidance that States may use in determining the extent of
such areas of protection (Section 1428(e)). This document has been prepared to furnish
such guidance. Another document, Guidance for Applicants for State WHP Program
Assistance Funds, is also available to aid States and Territories in applying for program
support.
1.1 LEGISLATIVE AUTHORITY
The 1986 Amendments to the SOW A authorized two new provisions for ground-water
protection. These were the WHP Program and the Sole Source Aquifer (SSA)
Demonstration Program. Both are designed to support the development of State and local
efforts to protect ground-water resources. The statutory language creating these
programs is in Section 1427 (SSA Demonstration Program) and Section 1428 (State
Programs to Establish Wellhead Protection Areas). The intent of Section 1428 is to
establish a State program that adequately protects the wellhead areas of all public water
systems from contaminants that may have adverse human health effects.
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The SOW A incorporates the fundamental definition of a WHP A in Subsection
1428(e):
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SfS£?°N .°F,,KWEi'LHEAD PROTECTION AREA-As used in this
ion, the term 'wellhead protection area' means th« surface and subsurface
Jrea surrounding a water well or wellfield, supplying a public water system,
through which contaminants are reasonably likely to move toward and reach
such water well or wellfield. The extent of a wellhead protection area,
within a State, necessary to provide protection from contaminants which may
l!?Vf ^yj^61'86 «««« on the health of persons is to be determined by the
State In the program submitted under subsection (a). Not later than 1 year
after tte enactment of the Safe Drinking Water Act Amendments of 1986,
the Administrator shall issue technical guidance which States may use in
making such determinations. Such guidance may reflect such factors as the
radius of influence around a well or wellfield, the depth of drawdown of the
water table by such well or wellfield at any given point, the time or rate of
travel of various contaminants in various hydrologic conditions, distance from ?
the well or wellfield, or other factors affecting the likelihood of :
contaminants reaching the well or wellfield, taking into account available
engineering pump tests or comparable data, field reconnaissance, topographic
Information, and the geology of the formation in which the well or weilf ieid
is located. _ . |1. ,
The statute furthermore defines a WHP Program as one that incorporates the
following elements: .
Duties of State and local agencies and public water supply systems in
implementing the program
Determination of WHPA's for each public well or well field
Identification of all potential anthropogenic sources within the protection area
A program that contains, as appropriate: technical assistance, financial [
assistance, implementation of control measures, education, training, and
demonstration projects to protect wellhead areas from contaminants
Contingency plans for alternative water supplies In cases of contamination
Siting considerations for all new wells
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Public participation. j
This program must be submitted to the Administrator of EPA within 3 years after
enactment. States are expected to make every reasonable effort to implement this
program within 2 years after it has been submitted to the Administrator. The only impact
on a State for failing to participate in the WHP Program, however, is the loss of grant
funds. EPA is not authorized to establish a WHP Program in a State that does not choose *
to participate. , I
1-2
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JU2 PURPOSE AND SCOPE OF DOCUMENT
\-.' ' ' '-'.. '.''.,
Instituting WHP in the United States will present two major challenges. First will.
be* to resolve successfully the technical problems of delineating meaningful protection
\ areas to prevent ground-water contamination. The second will be to resolve the vast
.complex of management problems that will accompany attempts tp implement the
WHPA's. States will face major institutional hurdles, for example, in controlling
industrial, commercial, and agricultural activity and land usage within the delineated
WHPA's. The scope of this document is to provide general guidance in solving the initial
problems of actually delineating the protection areas. The document does not prescribe
specifio mechanisms or approaches that must be strictly followed. Instead, the document
describes a variety of technical approaches, from the simple to the sophisticated, that
may be used singly or in combinations., The issuance of this guidance, in and of itself,
furthermore does not affect or Inhibit Agency regulatory programs.
Ground-water protection is primarily a State responsibility. Accordingly, EPA
intends to ensure that States and localities have flexibility in developing their programs,
while ensuring that the goals and objectives of the law are met^ EPA expects that there
will be several stages in a State program for WHPA delineation, shown in general terms in
Figure 1-1. Initially, the States will probably establish technical committees or work
groups to review relevant technical materials (including this delineation guidelines
document) and conditions within the State. After analysis by program personnel, often
including "test case" applications, "criteria" and "methods" will be adopted, and the actual
' . * '
delineation and mapping of the areas will commence.
Determination of State WHPA criteria and appropriate WHPA methods (Stages 3 and
4 in Figure 1-1) are the two major topics covered in this guidance document. Criteria
refer to the primary delineation factors mentioned in the statute (Subsection 1428(e))
(e.g., "radius of influence, depth of drawdown, time or rate of travel"). The term criteria
is used here because these factors can be used as conceptual standards on which to base
WHPA delineations. The methods are the techniques that can be used to map the WHPA's.
These methods range from simple "cookie-cutter" approaches to complex computer
'i . . ^
models.
Only a few States have been active in wellhead protection. However, numerous
European nations have been involved in such programs (Van Waegeningn, 1985).
Information based on their experiences has been incorporated into this document.
1-3
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Figure 1-1
V General Approach to State WHPA Delineation
STAGE
MM
1
WORKING GROUPS
OR COMMITTEES
ESTABLISHED
I
TECHNICAL STUDIES
AND
INSTITUTIONAL
ANALYSIS
I
DETERMINE
STATE WHPA
CRITERIA
1
DETERMINE
APPROPRIATE
WHPA METHODS
1
DELINEATE BOUNDARIES
OF PROTECTION AREA
FOR SPECIFIC
WELLS/WELL FIELDS
1
CONDUCT
ADDITIONAL
STUDIES
1
REFINE
DELINEATION
OF BOUNDARIES
AS APPROPRIATE
-------
EPA expects that delineation of WHPA's will be implemented so as to protect wells
from three general categories of threatsthe direct introduction of contaminants through
and around the well casing, microbial contaminants, and chemical contaminants. The
immediate vicinity of the well or well field, is a primary area to be protected from
accidental spills, road runoff, and similar incidents. The management of this area may
include standards for well casing, grouting, housing, surface grading, buffer zones, and
well abandonment procedures. Microbial contamination, especially from bacteria and
viruses,, is of significant concern, since micro-organisms may persist in drinking water
even after treatment and delivery to consumers.
An important element of the amended SDWA, however, is to provide protection
from the broader range of threats to ground-water quality posed by a variety of chemical
contaminants. While a few hundred feet of buffer zoning is usually adequate to address
microbial threats, many toxic chemicals persist for long time periods and may travel
great distances in the subsurface environment. This constitutes the major technical and
administrative challenge of the WHP programs. Addressing these threats, particularly the
third one, should greatly reduce the incidence of well contamination in the United States.
1.3 EPA»S IMPLEMENTATION APPROACH
The SDWA provisions represent a significant change in the roles and
interrelationships of Federal, State, and local governments in ground-water protection.
For -the first time there is statutory basis at the Federal level for protecting ground-water
resources, rather than efforts aimed at controlling specific contaminants or
contamination sources. The programs will foster new approaches to resource assessment
and protection, and support, the State's overall ground-water protection activities. EPA's
goals in implementing the WHP Program are tos
Meet the goals of the statute _ -
Recognize the diversity of hydrogeologic settings and sources of
contamination
Maximize State creativity and flexibility in program design and
implementation
Be sensitive to concerns regarding Federal involvement in the related areas of
land use and water allocation
1-5
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States in achieving comprehensive ground-water protection through
^coordination with State ground-water protection plans and strategies, thus
ensuring safe public water supplies.
The Agency's approach during development of these and related guidances has been
to encourage the active participation of those who will implement WHP Programs, and of
those who will be affected. This has been accomplished by the formation of technical
committees, comprising State representatives, academic specialists, and EPA
Headquarters and regional staff.
A technical committee on the hydrogeologic aspects of WHP met four times from
September 1986 through April 1987. It reviewed proposed criteria and methods for WHPA
delineation and made numerous recommendations that were used in subsequent revisions
of the draft guidelines. In addition, a 2-day workshop, attended by more than 50 leading
technical and policy specialists and State and local officials, was held in January 1987 in
Bethesda, Maryland. Detailed presentations of the proposed criteria and methods were
followed by group discussions of specific topics in which the participation of all attendees
was encouraged. Most of the recommendations and issues raised by the discussion groups
were incorporated in subsequent drafts of this guidance document.
EPA established two other technical committees on WHPone on the grants and
financial aspects of the program and the second on the management and control aspects.
As a result of their efforts, a series of documents will be available to help the States in
developing and implementing WHP, as well as in applying for financial assistance from
EPA. Technical specialists involved with the hydrogeologic asipects of WHP delineation
must consult the relevant technical section of the "grant guidance'1 package for insights
into EPA's approach for determining program "adequacy" under the SDWA. These
. , :, ' .-,p f'l .',, ;;j!'.»u ' i .,..' ".' : ,..",. <: .':, I ^i,-'f!';^ ";:r--;!!"
requirements are outlined in Sections IV and V of the Guidance for Applicants for State
WHP Program Assistance Funds, a document available from the Office of Ground-Water m
Protection in EPA Headquarters and the Regions.
1.4 ORGANIZATION OF DOCUMENT
The main body of this guidance document provides a concise review of WHPA
delineation issues. Supporting appendices contain background technical information and
examine relevant case studies.
i
1-6
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Chapter 2 of this guidance provides basic information on hydrogeologic and
contaminanHcontrols aver ground-water flow and contaminant transport, as these relate
to''WHPA delineation. Chapter 3 presents criteria that can be used to establish
conceptually the extent of a WHPAj it also provides guidance in the process of selecting
a criterion. Chapter 4 identifies the methods available for delineating WHPA's and
discusses advantages and disadvantages of each method. Chapter 5 provides a general
approach to the WHPA delineation process and examples of criteria and method
selections.
Appendix A provides background information on several WHP efforts in the United
States and Europe. Appendix B depicts several case studies where the specific criteria
and methods are applied, and the resulting WHPA delineations shown. A glossary defines
both common hydrogeologic terms and definitions specific to the subject of WHPA
delineation.
1-7
-------
V '
I
-------
I
CHAPTER 2
HYDROGEOLOGIC AND CONTAMINANT CONTROLS OVER WHPA DELINEATION
«* " ' .'. . . ..-.-
This chapter provides general information on basic hydrogeologic principles
governing ground-water flow under natural and pumping conditions, as well as information
on contaminant transport and its relevance to the delineation of wellhead protection areas
(WHPA's), For the sake of simplicity, the early discussion in this chapter focuses on flow
through porous media under unconfined conditions.
For more elaborate discussion of ground-water flow and contaminant transport,
readers may refer to textbooks by Bear (1979), Bouwer (1978), DeWiest (1965), Driscoll
(1986), Fetter (1980), Freeze and Cherry (1979), and Todd (1980). Other references by
Fried (1975), Matthess, et al.(1981), and Yates, et al. (1984) focus on contaminant
transport.
2.1 BASICS OF GROUND-WATER FLOW SYSTEMS
2.1.1 Natural Flow System ;
Under natural conditions, an aquifer is in a state of dynamic equilibrium. That is,
the total recharge to the aquifer is equal to the total discharge, with no change over, time
in the volume of water stored in the aquifer (Fetter, 1980). The motion of ground water
through an aquifer is controlled by differences in energy levels. Ground water moves
from areas of higher energy to areas of lower energy in order to reach or maintain a state
of equilibrium. '
In 1738, Bernoulli developed a fundamental equation that expresses the underlying
concept governing ground-water flow, He proved that the "total head" (h) of a unit
volume of fluid at a location is equivalent to the sum of the "pressure head" and the
"elevation head." This concept introduced the idea that if the total heads at two points in
an aquifer differ, ground-water flow will occur from the high-head point to the low-head
point. For example, as illustrated in Figure 2-1 for a stream valley system, ground-water
flow would occur from the ground-water divide (high head) to the stream (low head). The
"equipotential lines" shown in the figure represent lines along which the total head is
constant. The "flow lines" represent the paths that ground water would follow under a
state of equilibrium. The velocity at which ground water would move through a porous
media aquifer can be determined by the following relationship
2-1
-------
: If11:,""' Wl ,' 'J:L!
V-
Figure 2-1
Ground-water .Flow System (Stream
Valley) Under Natural Conditions
Recharge
^Ground-water
Divide
^^=s^^^ss:=^^ tl^^ I
>^,VuwpTOibi«wW.^
fa) VERTICAL
Stream
Ground-
water
Divide**
100
90 BO 70
60 70 80
HEAD (FT)
90 100 110 120 110
(bl PLAN VtEW~"FLOW NET'
LEGEND:
Ground-Water Divide
Equipotential Lines
** Flow Lines
Z Water Table
SOURCE: Modifttd from Oritcoll. 1986
NOT TO SCALE
2-2
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'. .v .= **- '.'.. - ' '. ' '. . .
where
v = average interstitial velocity "
k = hydraulic conductivity
n = porosity
i = hydraulic gradient = Ah/Al
Ah = change in head between two points of concern in the aquifer
Al = distance between these points.
2.1.2 Pumping of Ground Water
The use of ground water as a source of drinking water normally requires the
installation and operation of a well or well field. Ground-water pumpage alters the
natural state of equilibrium in an aquifer. The withdrawal of water by a well causes a
lowering (drawdown) of water levels in an area around the well. From a spatial
perspective, this is referred to as the "area of influence" of a well, or its "zone of
influence" (ZOI). In cross-section, this is commonly referred to as the "cone of
depression." Within the ZOI, flow velocities increase toward the well, due to increased
hydraulic gradients.
Figure 2-2 illustrates the effects of a pumping well on the ground-water flow
system of the same hypothetical stream valley introduced earlier. The ZOI of the well is
shown in Figure 2-2a. Figure 2-2b shows that the equipotential and flow lines for the
"natural" (nonpumping) conditions have been distorted, and are directed toward the well.
This distortion causes an area of ground-water recharge to the well. The pumping does
not affect the flow lines outside of that area. It should also be noted that the pumping of
the well causes some of the ground water that previously flowed directly to the stream to
reverse its path and flow back toward the well. The entire area recharging or
contributing water to the well or well field is defined in this document as the zone of
contribution (ZOC). Other authors use similar terminology (e.g., Morrissey, 1987), or
refer to this as the "capture zone" (Keely and Tsang, 1983). The areal extent of the ZOC
can increase with time as the well continues to pump. These transient zones are referred
to as "time-related capture zones."
2-3
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Figure 2-2
Ground-water Flow System (Stream Valley)
Affected by a Pumping Well
Recharge
J I
Ground-water
Divide
Water Table
^
a) CROSS SECTION
Ground-water
100 90 80 70 60 70 80 90
HEAD (FT) '
110 120 110 100
b) PLAN VIEW
LEGEND:
Pumping Well
Equipotential Lines
______ Ground-water Divide
» Flow Line
SOURCE: Modifitd from Driscoll. 1986
A Z
Drawdown at Well
Zone of Contribution to the Well
Water Table
-------
The two zones described above (ZOC, ZOI) are referred to extensively throughout
this document because of their significance to WHPA development. The ZOC is of
greater importance because contaminants, introduced within this zone could reach a we'lL
The contaminants would travel very rapidly toward the well once they enter the portion of
a ZOC where ground-water levels are significantly lowered by pumping.
The historic confusion over these two concepts, and perhaps the overemphasis in
.some ground-water protection efforts on the ZOI or cone of depression, is stated
succinctly by Morrissey (1987):
The fallacious idea that contributing area and area of influence
are identical persists. ...(This confusion may have contributed to the
use of circular areas around wells as buffer zones for ground-water-
quality protection.) Actually these areas can be the same only in the
hypothetical circumstances where the pre-pumping water table is
perfectly flat and all aquifer properties are uniform within the area of
influence. When the pre-pumping water table has a gradient, as it
does under most natural conditions, the contributing area to a well will
be distorted to extend to a greater distance on the upgradient side and
to a lesser distance on the downgradient side.
Recharge that enters the aquifer through the area of influence
of a well will not necessarily travelto the well, and recharge that
enters the aquifer outside the area of influence may travel to the well.
Generally, the most significant process controlling the movement of contaminants
within the ZOC is called "advection," in which contaminants are carried toward a well by
the bulk motion of the flowing ground water. Chemical, biological, and physical processes
other than advection may affect the fate of contaminants in ground water. Retardation
and dispersion are two processes that respectively slow and accelerate the movement of a
contaminant toward a pumping well. Relevant properties of contaminants that could
affect their movement toward a well or spring are briefly discussed in Section 2.3.
Finally, it should be noted that while many surface bodies serve as boundaries to
flow (the situation depicted in Figures 2-1 and 2-2), many do not. Pumping can induce
flow not only from the surface water bodies themselves, but (due to underflow) also from
areas on the opposite side of the surface water body from the well. In such situations,
Contaminants within surface waters or from other aquifer segments can be induced to
move toward the pumping well. Analyses of the extent and occurrence of this
2-5
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phenomenon, and the impacts on WHPA delineation, will be an important factor in some
hydrogeologic settings and in some State programs.
OTHER AQUIFER CONSIDERATIONS
Aquifers in porous, granular materials are commonly divided into two types, . I
unconf ined and confined, on the basis of stratigraphic setting and hydraulic pressure
(head) relationships. Unconfined aquifers have an upper water surface (water table) that
rises and falls freely in response to the volume of water in storage in the aquifer. The
water table is a free surface open to, and in pressure equilibrium with, the atmosphere.
The upper water surfaces of such aquifers mSy lie a few feet or tens of feet beneath the ' ". '
surface in humid regions. In arid or semi-arid alluvial settings;, the water table may be I
several hundred feet below the surface. The depth to the water table and the nature of
the unsaturated zone above an unconfined aquifer can be significant in controlling how
rapidly contaminants are able to reach the aquifer. Much is known about unconfined,
granular aquifers. These aquifers have received the bulk of attention in the scientific
literature Other aquifer types such as confined, karst, and fractured rock settings are
less well understood. The remainder of this section is therefore directed to a review of I
hydrogeologic factors of these settings relevant to WHP.
2.2.1 Confined Aquifers
Confined aquifers occur beneath a lower permeability "confining unit" of rock or
sediment. Pressure in the aquifer is greater than atmospheric, so that water will rise
above the base of the confining unit in a well penetrating that confining horizon (Figures ^
2-3 and 2-4). This situation is also commonly known as "artesian.11 The relative head
relationships across the confining unit are key factors in understanding the required
extent of a WHPA, as well as the need for particular management strategies. If the head
' ' 'T> . ....... ; i :.',;" '.. ' .
(as expressed by the potentiometric surface) of a confined aquifer is above that of the
overlying unconfined aquifer (i.e., the water table), contaminants would likely remain in
the unconfined aquifer, due to the tendency for upward flow across the confining unit (as u
shown in Figure 2-3). Conversely, should the potentiometric surface in the confined
aquifer be lower than the water table, downward leakage of water and contaminants is
possible (Figure 2-4).
i *
Apart from these hydraulic head relationships, the low permeabilities of confining
units overlying confined aquifers can reduce both the travel times to and contaminant n
concentrations in the aquifer, so that the contaminant may pose a reduced threat to the "
2-6
i .
'-. " ' ; '! . ' B
-------
§
Ul
Ul
i
O
w
o
N
Figure 2-3
Confined Aquifer with Upward Leakage
Abandoned or Inadequately
Cased or Cemented Wells
Water Production Well
Potentiometric
Direction of Ground-water Flow
SOURCE: Everett. 1987
NOT TO SCALE
2-7
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*> .*
V'
Figure 2-4
Confined Aquifer with Downward Leakage
Abandoned or Inadequately
Water Production Well
Potentiometric
Surface
Cased or Cemented Well
Direction of Ground-water Flow
i
SOURCE: Everett. 1987
NOT TO SCALE
2-8
I
-------
aquifer. Major areas of concern, however, lie with natural or manmade breaches in
confinement,*such as incised channels in confining beds or abandoned wells. Relative head
relationships in these situations may permit inward flow or leakage of contaminants from
overlying units. .
As a result of pumping over a period of time, confined aquifers may have their
hydraulic pressure lowered until the surface of water adjacent to the well bore is no
longer in contact with the base of the confining unit. Thus, the water surface is in a
water table condition in the cone of depressi9n, although it is still "stratigraphically"
confined. , . ,
Most confined aquifers are actually semiconfined, being leaky to some extent.
Leakage is not in itself evidence of contamination; many confined aquifers derive a
significant amount of recharge from this source. Rather, leakage indicates an influent
. - / f.m ,
condition that could introduce contaminants into an aquifer where they are able to reach
the leakage pathway.
As relative heads change to permit inflow to the confined aquifer, it can be
presumed that the relative risk of contamination to the aquifer will increase. The
potential for introduction of contamination is roughly proportional to the difference in
\ . . , . . .
heads and hydraulic conductivity of the confining unit. The area most subject to rapid
contaminant inflow would thus be in the area of lowest relative aquifer head; that is, low
elevation in the aquifer's potentiometric surface. Analysis of hydraulic head differentials
and identification of potential pathways should provide a basis for evaluating the risk to
wells or well fields in confined aquifers.
Shallow, Poorly-Confined Conditions. Fractures in fine-grained confining sediments under
near-surface conditions can provide significant natural pathways for contaminant
migration. Although fractures have been observed to penetrate to depths of about 60 feet
in glacial till, they are usually restricted to much shallower depths under shallow water
table conditions (Cartwright, personal communication, 1987). The permeability resulting
from near-surface fracturing is significantly greater than similar fracturing at depth.
This is because the effect of increasing horizontal in-situ stress is to decrease both the
aperture width and spacing frequency of fractures. Permeability of unconsolidated
sediments (due to primary porosity) is also greatest near the surface, decreasing with
depth.
2-9
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Conditions of increased fracture permeability in fine-grained sediments and higher
near-surface primary-porosity permeability combine to cause; the zone of greatest risk of
contaminant transport into a confined or semiconfined aquifer to be near the surface. As
a result, it can be considered that shallpw, poorly-confined aquifers (100 feet or less
below the surface) have approximately the same risk of contamination as do unconfined
aquifers. If data exist to indicate that such aquifers are as effectively confined from
surface and shallpw subsurface contaminants as are deeper confined aquifers, a less
stringent approach may be considered.
Intermediate Confined Conditions. Between depths of 100 and 300 feet, confinement
characteristics are difficult to predict because they are; very dependent on local
circumstances. In this intermediate zone, some confined aquifers are very leaky. Fluids
may move downward with ease through poorly consolidated sediments, fracture-prone thin
siltstones, carbonate rocks, and sandstones of low permeability. In other settings,
aquifers of this depth can be well confined by fine-grained sediments or consolidated
rocks. !
The intermediate zone lies below depths where good soils and engineering data on
permeability are frequently available (usually only for the range from the surface to 20
feet). It is also beyond the depth range for which most laboratory and field test data are
developed. Intermediate-depth confined aquifers are so subject to the specific
characteristics of individual sites that generalizations relative to WHPA delineation are
difficult to support. Approaches should therefore be developed on a class-by-class (where I
regional similarities exist) or well-by-well basis.
Deep Confined Conditions. Aquifers that are deeper than 300 feet below the surface are
at the upper (shallow) end of the data sets showing field or laboratory measurements of
fracture hydraulic conductivity and permeability, or else are sufficiently close to such
data that reasonable extrapolations of properties can be made. In addition, the extent of r
contaminant attenuation that can occur during vertical transport to the deep units adds to
the margin of safety. Except in such settings as the coastal plains and deep alluvial
basins, confined porous granular aquifers are frequently consolidated below 300 feet. This
means that permeabilities are greatly reduced in comparison with their unconsolidated
analogues. In such circumstances, the cone of depression can be a significant indicator of
relative head and potentiometric surface relationships between a confined aquifer, its £
confining units, and adjacent aquifers.
2-10
B
-------
Where leakage occurs through adjacent strata, recharge is generally greater in the
deepest parts.ipf depression cones, decreasing with distance from a pumping center. The
recharge rate increases as the potentiometric surface declines and the vertical head loss
increases (Walton, 1970). Neuman and Witherspooh (1969) and subsequent studies have
discussed some of the complexities of assumptions and their consequences in the analysis
of leakage. Nonetheless, Walton's generalizations appear valid.
The volumetric extent of aquifer leakage occurs over a wide range* Some poorly
confined aquifers can produce a high ratio of water from leakage relative to that from
storage. More tightly confined aquifers will'have a small ratio of leakage to storage
water. As was indicated previously, leakage only indicates the possibility of
contamination, should contaminants enter a leakage path into a confined aquifer. In cases
where leakage is from water stored in the confining unit, it may be that no discrete
leakage path exists across the, confining unit to an overlying aquifer.
Deep confined aquifers should be evaluated on the basis of various factors. The
effectiveness of natural confinement is a major consideration, taking into account natural
breaches (such as fractured or eroded confining units) and changes in hydraulic
conductivity from changes in facies of confining horizons. Manmade breaches, such as
active and abandoned well bores, are quite significant to the possibility of contamination
threats. Relative differences in head between the aquifer, confining units, and adjacent
aquifers are also important.
2.2.2 Karst and Fractured Bedrock Aquifers '
Although there is a broad range in flow velocities among granular, porous aquifers,
it is apparent that flow conditions in other types of aquifers need to be considered. Both
karst and fractured bedrock aquifers can be in either unconfined or confined settings. In
unconfined and poorly confined conditions, these aquifers can have very high flow (and
N ' .,.-.
contaminant transport) rates under rapid recharge conditions such as storm events.
" - ' - : -
Transport times across entire karst or fractured bedrock flow systems may be as short as
hours to weeks, much briefer than in porous, granular.aquifers. For this reason, these
susceptible aquifers should be evaluated differently from the more common porous,
granular aquifers.
Solution enhancement of bedding plant joints and fractures in karst aquifers creates
'
range over several orders of magnitude between high-flow and normal-flow conditions.
2-11
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Because karst aquifers can include both conduit and diffuse flow paths, different flow
mechanisms can supply water to well and spring discharges concurrently. Diffuse flow
,, systems can frequently be modeled and evaluated using the methods for porous, granular
aquifers, but conduit flow situations are not effectively analyzed in the same manner.
Karst aquifers can be divided into diffuse flow, mixed diffuse and conduit flow, and
conduit flow. Under conduit flow conditions, contaminants can be transported quite
rapidly in the system from their point of introduction to the point of delivery, with only
minimal dilution or dispersion. Similarly, conduit karst can often undergo rapid flushing
of contaminants from the system. As a fesult of different conducting channels within
conduit flow systems, contaminants in .one set of channels may not interconnect with
adjacent channels. Thus, the pattern of water quality during a contamination event can
differ considerably from that which would occur in porous, granular aquifers.
Fractured bedrock aquifers share many characteristics with conduit karst aquifers.
However, they often cannot match the higher flow velocities in karst, because fracture
apertures have not been enlarged to the same extent by dissolution. Fractured bedrock
aquifers generally have relatively little storage capacity in'the pore space of the aquifer
compared to that in porous, granular aquifers. If they are capable of significant water
supply, this is usually the result of interconnections with alluvial aquifers, saturated
saprolites, or surface water bodies. They are characterized by rapid and large rises in the
water table during recharge/maximum flow events, and can be influenced by recharge
from a large portion of the effective drainage Jbasin.
As discussed in Chapters 3 and 1, unconfined and poorly confined, conduit flow,
karst, and bedrock aquifers that are characterized by high-flow events will likely be
delineated initially by mapping the general physical boundaries of their drainage basins.
Water table elevations under normal and high-flow conditions will also provide relevant
data. Subsequently, more precise delineation of flow can be conducted to determine those
portions of the drainage basin that actually contribute to a well or spring. This effort can
be based upon use of dye or other tracing techniques.
Finally, the approach to WHPA delineation in more effectively confined karst and
fractured bedrock aquifers that are isolated from both surface water and shallow, rapid-
flow-response aquifers can be the same as that for other deep, confined aquifers.
2-12
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2.3 CONTAMINANT PROPERTIES
Subjection 142S(a) of the SDWA requires States to adopt programs "to protect
Wellhead areas...from contaminants which-may have any adverse affects on the health of
persons/1 Subsection 1428(a)(3) further states that these programs must as "a
minimum...identify within each wellhead protection area all potential anthropogenic
sources of contaminants which may have any adverse effect on the health of persons."
Based on the current knowledge of contaminant characteristics, ground-water
management strategies, and other WHP factors, there is no one operational approach that
will be suitable for meeting this general goal. Each State will likely choose its own
approach and rationale. It is clear, however, that some knowledge of contaminant
properties is essential for understanding the adequacy of WHP delineation.
Many different types of contaminants exist; those of most concern can generally be
classified as inorganic and organic chemical compounds and elements, bacteria, and
viruses. It is important to identify what is known about specific contaminant types in
assessing their significance in WHP A delineation. The remainder of this chapter reviews
some of the major properties that affect the persistence and mobility of contaminants in
these groups. These properties form the basis for understanding WHP A criteria, the
subject of Chapter 3.
2.3.1 Inorganic Chemicals
s=- . "
Some of the most common and mobile contaminants result from the release of
inorganic chemicals into ground water. Such constituents as nitrate, ammonia, sodium,
and chloride often cause persistent problems due to their high solubility in ground water.
For example, nitrate contamination from sewage and agricultural practices occurs over
large areas in many shallow aquifers. Salt water problems from highway deicing storage
depots, seawater infiltration, and brine upwelling have degraded ground-water supply
sources that have been stressed due to overpumping. -
The primary mode, of inorganic contaminant movement is through advection.
Retardation processes occur through denitrif ication, adsorption, bacterial decomposition,
precipitation, and chelationall of which are considerably less effective under saturated
conditions. The most effective mechanisms of concentration reduction in ground water
are dispersion and dilution.
A relative ranking of the mobility of common inorganic chemical pollutants that are
characteristic of municipal waste leachates shows very significant attentuation of heavy
2-13
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tnetals moving through clay, whereas there is only slight retardation of water-soluble
organictjonstituents exerting a chemical oxygen demand (Griffin and Shimp, 1978; Griffin,
»»et al., 1976). The comparative effectiveness of different cJlay minerals and of iron and
aluminum oxyhydroxides in removing heavy metals has been demonstrated (Griffin and
Shimp, 1976; Kinninburgh, et al., 1976). Oxidizing conditions in soils and water lead to
precipitation of iron, manganese, and aluminum oxyhydroxides, scavenging other metals as
well. On the other hand, oxidizing conditions in water can maintain dissolved nitrate
concentrations that can be readily reduced under biological or chemical reduction
conditions. ' ' " .. ' .;' , . ^ p '.'' ^ \\ ';'' \
._.- _ : . .' i, - . .
Although certain metals may persist for long periods in iground water, their mobility
is generally lower than other more "conservative" inorganics, such as nitrates and
chlorides. This is due to the relative low solubilities of many metals under most ground-
water conditions and to their tendency to be adsorbed on clay minerals, on hydrous oxides
of iron and manganese, and on organic matter. Isomorphous substitution or
coprecipitation with minerals or amorphous solids can also be important (Freeze and
Cherry, 1979). ' i ' ' ''_ _ ' p , ' ' "/''.._! , .' ". '
The solubility of metals is generally controlled by the most abundant anions in
natural ground water. These are hydroxyl, bicarbonate, sulfate, chloride, nitrate, and (in
reducing environments) sulf ide ions. The mobility of metals depends on the solubilities of
their hydroxides, carbonates, sulfates, chlorides, sulfides, and organic complexes
(Matthess, et al., 1985). The movement of metals, as with other inorganic species, is
primarily by advection.
2.3.2 Organic Chemicals .
Although many organic chemicals occur naturally in the subsurface environment, the
effects of certain synthetic organic chemicals are becoming of concern in most State
ground-water protection efforts. These chemicals include, among others, solvents,
pesticides, and synthetic hydrocarbons. Organic chemicals may be removed from ground
water by a variety of means. Chemical reactions, microbial iactiyity, and cometabolism
either reduce the concentrations of organics or metabolize and destroy the chemicals by
transformation or consumption. The rate of degradation is influenced by such factors as
the volume of contaminant, its miscibility and solubility in water, temperature, pH,
oxygen content, the availability of certain organic and inorganic materials, and
character of the substrate (Helling, 1971; Iwata, et al., 1973; Griffin, et al., 1979).
2-14
the I
I
-------
Decomposition is especially enhanced by micro-organisms, which are most active in
soils and inWerobic, shallow, unconfined aquifers. It is uncertain whether this is the result
of,transformation to secondary organic compounds or complete mineralization. However,
decomposition rates are much slower in ground water than in the soil. Consequently,
organic chemicals can be quite persistent after ground-water contamination has occurred.
Table 2-1 lists the persistence of several organic materials in ground water and
soils. Some pesticides may contaminate ground water due to their higher leaching
potentials. It can be seen from this table that certain organic contaminants are very
persistent, especially in ground water. For example, DBCP has a half-life of about 10
weeks in the soil, in contrast with up to 140 years in ground water.
A growing concern lies with a phenomenon called "facilitated transport" (Tomson, et
al., 1987). Contaminants that have been considered relatively immobile, such as dioxin
and metals, have been discovered at great distances from their sources. It appears that
organic solvents can greatly affect the mobility of these contaminants. Recent
information also indicates that colloids and macromolecules appear to facilitate
movement of contaminants, enabling them to disperse faster than the average ground-
water flow rate. The full impacts of this phenomenon on the transport of metals and
organic chemicals are not yet known. Implications on selecting WHPA criteria thresholds
are discussed in Chapter 3.
2.3.3 Bacteria and Viruses
The survival of pathogenic micro-organisms (e.g., parasitic and enterotoxiri-
producing bacteria) in the subsurface environment has been a key component of public
health concerns for drinking water protection for many decades. Allochthonic bacteria
(those artificially introduced) are usually eliminated in the subsurface environment,
generally faster than organic chemicals. In oxygen-rich environments, bacteria can
survive for fairly long periods (greater than 6 months) in the deeper parts of the
unsaturated zone and in ground water.
The elimination of pathogens results from the combined effects of the physical
(including temperature), biological, and chemical conditions that exist at a site. The
availability of nutrients and biological factors is most important for the survival of
pathogenic bacteria. Elimination is faster at high temperatures (37° C), at pH values of
about 7, at low oxygen concentrations, and at high levels of dissolved organic carbon.
2-15
-------
TABLE 2-1
Persistence of Organic Substances in Ground Waiter and Soils
Organic Chemical
Estimated Half-Life (years)
In Ground Water
Hydrocarbons
Benzene
Toluene
Xylene
Ethylbenzene
03 Benzene
Napthalene
In Soils
1
0.3
0.3
0.3
0.6
0.6
Halogenated Hydrocarbons
Dichloromethane
Trichloroethane
1,1,1 -Trichloroethane
Dichlorobenzene
10
2
1
1
Pesticides* (solubility in
water)
Chlordane
DDT
Dieldrin
Heptachlor
Toxaphene
DDVP
Methyl demeton S
Thimet
2 to 4
3 to 10
1 to 7
7 to 12
10
0.047 (17 days)
0.071 (26 days)
0.005 (2 days)
Pesticides** (high solubility
in water)
EDB 5.8
DBCP .28.5 to 140
Aldicarb 0.2 to 12.5
Atrazine 0.2 to 2
Carbofuran 0 to 1
0.04-0.35 (2-18 weeks)
0.2 (10 weeks)
0.08-0.15 (4-8 weeks)
0.08-1.1 (4-57 weeks)
0.02-0.7 (1-37 weeks)
Source:
*Matthess, et aL, 1985
**Cohen, et al., 1984
2-16
-I
-------
Under these conditions, naturally occurring bacteria are activated, which act,
antagonistically towards pathogenic microorganisms in the waste materials.
* Elimination is specific for different microbial species (Figure 2r5). For example,
Coliform bacteria will reach a 99.9 percent elimination in less than 8 days, while it takes
50 days for E. Coli to attain the same level of elimination. Under oligotrophic conditions
and at temperatures below 15° C, Salmonella typhi can survive more than 100 days,
Salmonella typhimurium approximately 230 days, and Yersinia sp. approximately 200 days
(Matthess and Pekdeger, 1981). Several factors control the survival and migration of
viruses once they have been introduced into the subsurface environment. In general, the
climate, clay content and moisture-holding capacity, and virus type are the major
elements in determining virus fate. Viruses can migrate considerable distances
underground; virus penetrations to depths as great as 67 meters and horizontal migrations
as far as 408 meters have been reported (Keswick and Gerba, 1980).
Considerable emphasis has been placed on examining the persistence of viruses in .
ground water. A recent study determined that temperature was the only variable
significantly correlated with the extended survival of three viruses examined. In addition,
it was observed that the viruses persisted for longer periods in well water samples than in
surface waters incubated at similar temperatures. At the lower temperatures
characteristic of ground water in most areas of the United States, Poliovirus 1 and
Enchovirus 1 persisted for very long periods, up to 28.8 days, before a significant
reduction was achieved (Yates, et al., 1985). Figure 2-5 indicates that 0.1 percent of
Poliovirus, Hepatitisvirus, or Enterovirus can survive after a 140-day period in ground
water, which is considerably longer than the survival of E. Coli bacteria. Under favorable
oligotrophic conditions and at temperatures less than 15° C, Poliovirus can survive for
over 250 days (Matthess and Pekdeger, 1981). ,
From these and similar findings based on field studies, it has been recommended in
Europe that delay times of at least 50 to 60 days, and where possible as much as 1 year,
should be provided to protect wellheads from virus and pathogenic bacteria
contamination. In addition, due to scale dependency factors and regardless of delay
times, a minimum 100-meter (325-foot) distance is required (Matthess, personal
communication, 1987). These conclusions have been derived from an extensive* multi-
year research program (Matthess, et al., 1985).
2-17
-------
Figure 2-5
Elimination Constant and 99.9% (Elimination
of Some Relevant Bacteria and
Viruses in Ground Water
99.9% Elimination | | | | |
in Water After 2751 70 35 23
140 t
50 Days
16 14 12
Shigella sp.
10 9
10 Days
Coliform bacteria
Salmonella faecal is
E. coli
More Persistent than E. coli -*-
Mean of Evaluated Investigations
-j »- Less Persistent than E. coli
S. typhi
Elimination
Viruses (Polio-, Hepatitis-, Entero-)
S. paratyphi
S. typhimurium
, - , - , - , - , - , - , - ... _ - -
Constant (I/day) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
SOURCE: Mitthea.etal., 1985
2-18
-------
2.4 DELINEATION ZONE PROPERTIES AND TERMINOLOGY
The concepts of natural ground-water flow, the influence of pumping, the rates' of.
travel, and contaminant transport are introduced in the earlier sections of the chapter.
At present, these concepts form the elementary principles used in most' WHP programs.
As will be discussed in Chapter 3, existing WHP programs are generally aimed at one of
the following overall protection goals:
Provide a remedial action zone to protect wells from unexpected contaminant
releases.
Provide an attenuation zone to brine concentrations of specific rontaminantc
to desired levels at the time they reach the wellhead.
Provide a well-field management zone in all or part of a well's present or
future recharge area.
Several approaches have been utilized to accomplish the goals listed above. The
approaches require operational procedures for delineating WHPA's for a variety of
settings. Five hypothetical situations in different hydrogeologic settings are described
below to illustrate the applications of these generalized approaches. The application of
each approach is based on specific criteria (such as time of travel or drawdown) that form
the basis for several delineation methods. The criteria and methods used in WHP A
delineation are discussed extensively in the chapters following. The purpose of this
discussion, however, is to depict the differences in criteria and method application based
on a range of aquifer types.
The first example is depicted in Figure 2-6. A pumping well is shown to have
created a cone of depression within an unconfined ground-water flow system. The aquifer
consists of an unconsolidated porous media overlying bedrock. The ZOI of the well is the
area overlying the cone of depression. The ZO'C is the entire flow system that supplies
water to the well, including in this case a large portion of the ZOI. The full extent of the
ZOC would represent a more accurate appraisal of the area in which ground water
actually flows to the pumping well.
The second illustration (Figure 2^-7) depicts (by shading) zones of hypothetical
transport of a contaminant in the same aquifer. The time for a contaminant to travel
from a point to a well is identified by contours of equal travel time (isochrones). The
zones within the isochrones are referred to as "zones of transport" (ZOT's). Large ZOT's
2-19
-------
: :i :"
Figure 2-6
Terminology for Wellhead Protection
Area Delineation (Hypothetical
Pumping Well in Porous Media)
GROUNDWATER
DIVIDE
PREPUMPING
WATER LEVEL
(A)| VERTICAL PROFILE
(B) PLAN VIEW
LEGEND:
V Water table
' Ground-water Flow Direction
Pumping Well
ZOI Zone of Influence
ZOC Zone of Contribution
NOT TO SCALE
2-20
-------
Figure 2-7
Terminology for Wellhead Protection
Area Delineation (Hypothetical
^Contaminant Transport in Porous Media)
GROUND-WATER
DIVIDE,
I PUMPING I
1 WELL
PREPUMPING
WATER LEVEL
CONE OF
DEPRESSION
BEDROCK
SURFACE
(A)| VERTICAL PROFILE
PUMPING WELL
(B) PLAN VIEW
LEGEND:
₯ Water Table
i
10 Year Zone of Transport
- Direction of Ground-water Flow
ZOC Zone of Contribution
ZOI Zone of Influence
ZOT Zone of Transport
NOT TO SCALE
2-21
-------
are shown for areas near the ground-water divide far from the pumping well. The larger
the ZOT^(i.e., the larger the TOT threshold), the more protective the WHPA. Very small
4 ZOTs are shown within the area of influence of the well, where contaminant travel tinies
are significantly accelerated due to the high hydraulic gradients and flow velocities in this
area. The 2OT is part of the 2OC, however.
The third situation (Figure 2-8) depicts a ground-water flow system in a mature
karst setting. The discharge is to a spring used as a public water supply source. The flow
is generally confined to a complex network of solution channel and cavernous conduits
that is extremely difficult to infer from the surface. An approach in such a situation
might be to delineate WHPA's based on the boundaries of the 2OC being inferred as the
divides or drainage boundaries of the setting.
The fourth example (Figure 2-9) presents a pumping well in a fractured bedrock
aquifer that has been placed at the intersection of two fractures. This well location takes
advantage of the higher permeability and storage provided by the fracture zone. Flow to
the well is controlled by the distribution and degree of interconnection that exists
between fractures and by the variations in aquifer recharge due to rainfall. It is
extremely difficult to define the actual recharge area of a well in a fracture setting. An
assumption that the topographic divides or drainage boundaries of the setting represent
the 2OC may be the basis for WHPA delineation here.
The final example (Figure 2-10) illustrates a pumping well in a confined aquifer in
porous media. In this case, the prepumping potentiometric surface of the confined aquifer
has been lowered below the water table of the overlying unconfined aquifer. The
confining layer may provide some protection to the water source. However, the dominant
vertical direction of potential contaminant flow in the area where the potentiometric
surface is lower thai) the unconfined water tabte suggests that this shouldi be examined as
an area of concern for WHPA delineation. This would focus the search for abandoned
wells, fractures, and other features that could penetrate the confining layer. Another
" ,^ , ' . ; , i ;'",:; :;. .;: ;:::;;: ,-.:;\x ::; ° ,-,.., ., , i
approach might focus on a portion of the contributing area, based upon .some TOT
threshold within the aquifer.
1
2-22
1
-------
Figure 2-8
Terminology for Wellhead Protection Area Delineation
(Hypothetical Ground-water Basin in Mature Karst)
.WATER SUPPLY
/ SPRING
VERTICAL PROFILE
PLAN VIEW
NOTE: The "ZOC" shown was delineated with purpose of
including all principal areas contributing to the cave
based on inferred surface and subsurface drainage
areas.
SOURCE: Modified from Quintan and Ewers. 1985
LEGEND:
O Sinkhole
Water Supply Spring
*<** Surface Stream
Conduit System
V Water Table
Limestone
NOT TO SCALE
2-23
-------
Figure 2-9
Terminology for Wellhead Protection Area
Delineation (Hypothetical Ground-water
Basin in Fractured Rock)
Ground
water
Divide
A'
\
VERTICAL PROFILE
Stream
PLAN VIEW
SOURCE: Modified from Otton. 1981
LEGEND:
X Water Table
">£ Fractures
_ Ground-water Divide
-I
NOT TO SCALE
2-24
-------
Figure 2-10
Terminology for Wellhead Protection Area Delineation
(Hypothetical Confined Aquifer in Porous Media)
zoi
| Abandoned or Inadequately
I Cased or Cemented Well)
Area of Net Downward Leakage-
Water Production Well
Pre-pumping
Level
NOTE: ZOI is larger than area of downward leakage.
LEGEND:
^*~ Direction of Water Flow
^- Contaminant Flow
ZOI' Zone of Influence
S. Water Table
SOURCE: Everett, 1987.
NOT TO SCALE
2-25
-------
-------
CHAPTERS
DELINEATION CRITERIA
.,**''. > .
As discussed in the first chapter, the SDWA Amendments refer to "factors" that
may be reflected in this guidance to the States (Section 1428(e)):
Such guidance may reflect such factors as the radius of influence around a
well or wellfield, the depth of drawdown of the water table by such well or
wellfield at any given point, the time or rate of travel of various
contaminants in various hydrologic conditions, distance from the well or
wellfield, or other factors affecting the likelihood of contaminants reaching
the well or wellfield.
Many of these factors have been used in Europe and by State and local agencies in the
United States to protect wellheads against different types of threats, including:
Direct introduction of contaminants into well casings ,
Microbial contamination
Chemical contamination. *4
This chapter focuses on a discussion of these factors, here termed "criteria" because
they can be used as conceptual standards on which to base the actual delineation of a
WHPA. A distinction is made between the terms "criteria" and "criteria thresholds." In r
using a criterion for WHPA delineation, a value or set of values must be selected to l
' '
represent the limits above or below which a given criterion will cease to provide the
desired degree of protection. Throughout this document these values are referred to as
"criteria thresholds." Definitions and examples to clarify this distinction are provided in a
later section. Later sections also provide guidance on the selection of criteria and
criteria thresholds. Chapter ft will describe how criteria and criteria thresholds can be i
mapped using specific techniques or methods.
3.1 CRITERIA DEFINITION AND CHARACTERISTICS
The term "criteria" is used in this document to group all conceptual standards that
form the technical basis for WHPA delineation. In this chapter, five types of criteria are
identified and described:
Distance
Drawdown
3-1
-------
,";!:, I1'
Time of travel
H" Flow boundaries
*' Assimilative capacity.
It is important to note that the SDWA language of protecting WHPA's from '"contaminants
which may have any adverse effect on the health of persons" may'be met in many ways by
the State. The selection of WHP criteria and methods is only one input to this analysis of
WHP Program "adequacy."
A State's choice of a criterion will likely be based on a combination of technical and
nontechnical (e.g., administrative) considerations. The "technical merits of a criterion
depend on the degree to which a criterion incorporates the processes affecting ground-
water flow and contaminant transport. For example, as shown in Figure 3-i, a criterion
such as "drawdown" considers solely the physical process controlling contaminant
movement due to ground-water flow (advection). Other technical criteria such as time of
travel (TOT) can consider more processes, such as advection, hydrodynamic dispersion,
and solid-solute interaction.
In some instances, nontechnical considerations (such as a State's institutional
capabilities to implement a program) would dictate the choice of criteria. This could
mandate use of a simpler criterion, such as distance, rather than a more technically
sophisticated one that might be more suitable if the capability existed to implement it.
3.1.1 Distance
* The distance criterion is the concept of delineating a WHPA using a radius or
dimension measured from a pumping well to a point of concern'. Any "WHP A criterion
selected must eventually be mapped. The distance criterion is the most direct way of
delineating a WHPA. Since by definition a WHPA is an area., mapping it would require
that a selected distance be measured from the well to the point of concern. The use of a
distance criterion by itself may present a disadvantage, isince it does not directly
incorporate the processes of ground-water flow or contaminant transport. Therefore, the
resulting WHPA could provide insufficient or ineffective protection. The latter condition
might be a consequence of trying to administer an inappropriate WHPA with limited
resources for contaminant source control.
Selection of distance as a criterion generally has been based on past experience with
ground-water pollution control, or on nontechnical considerations. Commonly, it is an
arbitrary policy decision. Distance has frequently been selected as a "first step" in WHPA
3-2
,,
1.1! '";! 11,
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*
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U1
i__
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HYDRODYNAI
DISPERSION
(MECHANICAL
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. & . ..,.. :-..;.'-''
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3-3
-------
delineation; it offers significant advantages over the absence of a WHPA. Further
refinement of the WHPA's may later be based on a more sophisticated or tailored
criterion^ Distance .has been used for "generic" delineation of microbial protection zones,
''and for establishing setbacks from pesticide applications.
3.1.2 Drawdown
Drawdown refers to using, as the WHPA criterion, the extent to which well pumping
lowers the water table of an unconfined aquifer, or the potentiometric surface of a
confined aquifer. This is the criterion that defines the commonly used "cone of
depression" or "area of influence" concept. As discussed iin Chapter 2, the greatest
drawdown occurs at the well, and decreases with distance, until a point is reached where
the water level is not affected by the pumpage. This is illustrated conceptually in Figure
3-2. As a result of the drawdown created by a pumping well, the hydraulic gradients and
ground-water flow velocities toward the well increase. Drawdown can accelerate
contaminant migration toward a well. The actual extent of the ZOI can vary enormously,
from a few tens of feet in highly prolific water-table aquifers ito tens of miles in confined,
consolidated, regional aquifers.
An approach to protecting the wellhead is to delineate the boundaries of the area of
pumping influence (ZOI). This can be accomplished by selecting a small threshold value
for a drawdown criterion and then determining the distances from the well(s) to the points
where the specified criterion is satisfied. For example, in the flat water table condition
shown in Figure 3-2, the ZOI is.likely to coincide with the zone of contribution (ZOC).
Therefore, protecting the ZOI would achieve a degree of protection similar to the results
of protecting the entire ZOC. As noted earlier, however, the more common setting of a
sloping water table implies a potentially significant difference between the ZOI and ZOC.
,| , ' , .' . 'i. '!' ' I,1" '.' . ! ,' ' - I ,' ' .'
Reliance on the ZOI may therefore lead to inappropriate protection in many settings.
3.1.3 Tim* of Travel (TOT)
TOT is a WHPA delineation criterion based on the maximum time for a ground-
water contaminant to reach a well. As shown by Figure 3-1, TOT conceptually
incorporates a more comprehensive evaluation of the physical processes of contaminant
transport than most of the other criteria identified. Of these physical processes,
advection is the best understood, and hence TOT calculations for WHPA delineation have
usually been carried out on this basis. If only advection is considered, the time required
I
-------
Figure 3-2
Aquifer with Flat Water Table and High
L . .Rainfall Conditions, Where Boundaries of
v ZOI and 2OC Approximately Coincide
(Conceptual)
ZOI « ZOC
RECHARGE
PUMPING
WELL
RECHARGE
DRAWDOWN
CONTOURS
(A) VERTICAL PROFILE
LAND SURFACE
PREPUMPING
WATER LEVEL
(B) PLAN VIEW
, BEDROCK-SURF ACE
NOTE:
For the case of small hydraulic
gradient, the ZOI»ZOC
LEGEND:
Direction of Ground-water Flow
-Water Table
NOT TO SCALE
3-5
-------
for a contaminant to reach a well would be affected not onlly by the distance to the well
but also,by ihe increase in hydraulic gradient near the well.
For most well fields, particularly those where flow velocities are relatively high,
advection accounts for most of the movement of contaminants toward the well(s). In'
aquifers where the velocities are high, it is likely that a contaminant would travel quickly
toward the weMs). Relatively high threshold values for a TOT criterion may be selected
in these cases if possible, though some concerns over implenwntability may be raised.
For aquifers with low flow velocities, other physical processes, such as
hydrodynamic dispersion, should be considered. Under such conditions, dispersion becomes
more important, since it can cause a contaminant to reach a well sooner than would be
predicted by the hydraulic TOT equation shown above. Detailed discussions on the effects
of dispersion on contaminant transport can be found in Anderson (1984), Bear (1979), and
Fried (1975). In addition, the concept of "facilitated transjwrt" presented in Chapter 2
may further reduce the actual travel time of contaminants to the well. Dispersion and
facilitated transport provide further scientific evidence that short TOT thresholds (based I
on uncontaminated ground-water flow rates) may be problematic.
. . ^ . 'i ..
TOT is an operational measure of overall ground-water flow velocities. Such
velocities vary enormously based on hydrogeologic setting. Selected examples depicting
this link are shown in Figure 3-3. It is apparent that, first, there is great similarity in
hydraulic conductivities in a variety of types of porous granular aquifers, and second, very
high flow rate environments-in fractures, solution-enlarged fractures, boulder '
conglomerates, and fractured volcanic rocks and lava tubes-function effectively as either
open- or closed-channel (pipe) flow. In the geologic settings for such high flow velocities,
which operate under peak conditions for only short periods of maximum recharge, travel
times are extremely rapid. For the entire flow system, they are in terms of hours to days
or weeks, rather than the years and multiples thereof characteristic of laminar flow in
porous, granular aquifers. Whether confined or unconfined, the high-flow-velocity ^
geologic settings require separate consideration from those appropriate to either
consolidated or unconsolidated porous, granular media.
As a result of the focus on only maximum velocities of contaminant transport, the *
numerous factors operating along the contaminant's flow path (into as well as within the
aquifer) to reduce, disperse, or dilute the maximum concentration become factors of I
3-6
I
-------
-------
(Ill III 111
safety for the vast majority of contaminants. The consequence is that arrival times may
be more accurately estimated than contaminant concentrations.
<3.JU* Flow Boundaries
A WHPA delineation criterion based pn f tow boundaries applies the concept of using
determined locations of ground-water divides and/or other physical/hydrologic features
that control ground-water flow. Use of ftow boundaries &*^^fa..,fa$ffWl&$M.Jhe
approach of protecting the well's ZOC. This assumes that a contaminant entering the
, ' !""i '.. . . ;, , " v1-!1' i ' ,. '.« L. '.,.«».,; »,*,-,'. j V! ..';.,. ';:!. .. r i, , (JP. ,, ,.
ZOC would eventually reach the well under the prevailing hydraulic gradient. Examples
of surface features that in some hydrogeologic settings act as flow boundaries are ridges,
rivers, canals, and lakes. The limits of an aquifer and a fixed regional ground-water
divide are examples of subsurface boundaries, as illustrated in Figure 3-4. This criterion
is also useful for initial delineation of WHPA's for fractured bedrock and conduit-flow
karst aquifers. As noted in Chapter 2, however, flow beneath surface waters due to
pumping can occur. In such circumstances, the flow boundaries criterion is much less
relevant. . - ' , , \' f.^ ....'...,,., ...
The flow boundaries criterion is especially useful for small aquifer systems, where
TOT to the boundaries may be very brief, or where the ZOI created by well pumping is
rapidly affected by proximity to the physical limits of the aquifer. Moderate to larger
aquifers, with boundary separations of tens to hundreds of miles, may be less amenable to
this criterion due to problems of implementing protection over very large geographic
areas. Exceptions should be expected, however, such as where the well is situated
relatively close to these boundaries.
3.1.5 Assimilative Capacity
wj'1'1 , , . , ' ,,",, '" ', ' |,,!|! I1:,!,;:,,,:,,,',",,; ,,,,:',', , ' ,,.,, ', , "" ;, .,
The assimilative capacity criterion for WHPA delineation applies the concept of
using the ability of the saturated and/or unsaturated zones of a formation to attenuate
the concentrations of contaminants) to acceptable levels before they reach a well.
A hypothetical illustration of how the assimilative capacity of a subsurface
formation could be used as a criterion in WHPA delineation is shown in Figure 3-5. The
figure indicates that the subsurface formation will attenuate concentrations of
'si ' ." ', " , ' ,! i .' ' ', " '.i' i , -,"' i',1'1" ,': «."ul1",!;:;.. 'ii'.!.!*?^'1"'''''.]!:!1 'U"1'/1!! : "t /if,, if1'1 " 'n"1 !''!,l> ,; ','. ],«? '^\.
contaminants generated by continuous sources located at points (1) and (2). By the time
these contaminants reach the well, a desired standard or "threshold concentration" (Ca)
would be satisfied.
3-8 s
I
, i /",",' ;'.'.. , , >-,
:-.::".,;:.<'-,:, '- i a
-------
.Vi
Figure 3-4
Flow Boundaries Criteria
(Conceptual)
(a)
River Discharging to Ground-water
Low-permeability rock
(b)
NOTE:
(a) The ground-water divide induced by the river is an example
of the type of surface feature that may be used as a physical
boundary criterion [Figure (a) modified from Driscoll (1986) ].
(b) The boundary between the "single valley system" and "the ,
regional system" is an example of the type of subsurface
feature that may be used as a physical boundary criterion
[Figure (b) modified from Fetter (1980) ].
^ Water Table
v Direction of Ground-water Flow
3-9
I
NOT TO SCALE
-------
3-10
-------
There are no known examples of the use of an assimilative capacity criterion to
delineate a^HPA for a wide range of contamination threats. The existence and the
kinetics of attenuation processes are closely tied td specific contaminants and soil and
aquifer matrix composition and conditions, they are not easily modeled or quantitatively
determined. Site-specific data for particular contaminants are needed for evaluations;
for most contaminants, little specific information on reactions Is available. As a result,
the attenuation mechanisms are generally considered too complex for selection as WHPA
criteria. The degree to which they retard contaminant transport rates or diminish
concentrations becomes an unstated facto!' of safety in some methods of WHPA
delineation, however.
Where contamination threats are limited to one or two types, there have been some
attenuative-capacity analyses. Examples include evaluations of nitrate loadings from
septic tanks in certain northeastern U.S. communities, and buffer zone concepts for
guarding against Aldicarb contamination in Florida.
3.2 CRITERIA THRESHOLD EXAMPLES
Development of a WHP Program will require that one or more of the WHPA
delineation criteria discussed above be selected. In addition, a threshold value, or a set of
them, must be chosen to implement the actual protection area delineation. Thresholds
may be chosen for all three categories of threats (direct, microbial, and chemical), though
the first two are often combined. A threshold value selected to implement an appropriate
criterion that is overly or insufficiently conservative might not achieve the WHP goals.
This subsection presents examples of threshold values that have been used by
national, state, regional, and local governing bodies. Tables 3-1 through 3-4 present
threshold values for distance, drawdown, TOT, and physical boundaries criteria,
respectively. The information is presented for illustrative purposes only, though it does
indicate the range of thresholds that are currently being examined. In general, protection
from chemical threats is being reviewed over the following criteria threshold ranges:
TOT5 to 50 years (within the aquifer); less than 5 years in high-flow settings
DistanceI,000 feet to more than 2 miles
Drawdown0.1 to 1.0 foot
« Flow BoundariesPhysical and hydrologic
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^Assimilative CapacitySingle-constituent only; targeted to drinking water
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3.3 CRITERIA SELECTION CONSIDERATIONS
Three major considerations, shown schematically in Figure 3-6, can affect the
delineation of WHPA's in a State. The relative importance of each consideration will vary
from State to State. The considerations are:
Overall protection goaKs)
Other technical considerations
Other policy considerations.
Policy issues are comprehensively addressed under parallel efforts by EPA. This
subsection emphasizes the technical considerations and the overall protection goals that
affect criteria selection. However, a brief discussion of the effects of policy issues is
also included. Policy and technical considerations will not always lead to the selection of
the same criterion. For example, policy considerations for a specific geologic setting may
lead to the selection of distance as the criterion, while technical considerations may lead
to selecting a criterion such as flow boundaries. Similarly, technical evaluations of
ground-water flow may suggest TOT thresholds of 50 years or more, whereas policy
considerations may favor TOT thresholds of 10 to 20 years.
3.3.1 Overall Protection Goals
As noted previously, three general goals have been identified as relevant to the
process of selecting WHPA delineation criteria:
Reaction Time. Provide a remedial action zone to protect wells from
unexpected contaminant releases.
Attenuation of Contaminants. Attenuate the concentrations of specific
contaminants to desired levels at the time they reach the wellhead.
Protect All or Part of ZOC. Provide a well-field management zone in all or a
major portion of a well's existing or potential recharge area.
\, ,
Relationships between the criteria and these goals, along with a brief assessment of the
goals, are shown in Table 3-5.
3-17
-------
Figure 3-6
Consideration Factors That May Affect
Criteria Selection
POLICY ISSUES
REACTION TIME
ATTENUATION
CONTAMINANTS
SITE-SPECIFIC
CONSIDERATIONS
PROTECT ALL
OR PART OF
ZOC
(Hydrogeologic Setting,
Technical Capabilities,
Sources of Contamination,
Other Technical
Considerations) ^&
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3-18
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' ' '
Technical Considerations
, - . , i
This subsection identifies the technical factors that am be used to evaluate and
»ultimately select the delineation criteria; A matrix of technical evaluation factors versus
criteria is presented as Table 3-6. The matrix cells have been left blank so thaj an
appropriate ranking of each criterion may be made by a State or locality in the selection
process. It should be noted that the relative importance of these evaluation factors
depends on the hydrogeologic setting as well as the goals of the protection program in
which they are applied. The technical factors are described below.,
Ease of Application. A factor in evaluating a criterion is how easily a technical user can f
apply it. For valid WHPA delineations, the State must have technical specialists capable
of implementing the delineation criteria chosen. The more technologically demanding
criteria require more advanced and specialized user abilities.
Ease of Quantification. The ability to place a numerical value or threshold on a criterion
has a major influence on its suitability for use in guidelines or regulations. Some criteria,
such as distance and TOT, are easily expressed in numerical terms. Others, most notably !
assimilative capacity, are difficult to quantify. Consequently, the clarity of
communicating or legally defining criterion values can vary widely.
Variability Under Actual Conditions. Another consideration is ithe ability of a criterion to
reflect changes in hydrologic conditions. These changes may be due to pumping rates,
recharge rates, and flow boundary effects, and will likely affect movement of a r
contaminant toward a well. For example, a criterion such as TOT will allow a user to
modify the size of a WHPA to reflect an anticipated increase in pumping rates. In such
case, the hydraulic gradients near a well will be increased, and the distance that a
contaminant will travel in a given time (i.e., a specified criterion threshold) will also
increase.
Ease of Field Verification. Often it is quite difficult to reproduce accurately in the field B
values that have been previously calculated. The ability to confirm criterion threshold
values through onsite testing or inspection thus becomes significant in evaluating criteria
for selection. For example, in a porous media aquifer it would be considerably more
difficult to verify estimated TOPs than drawdowns. " .. '"
Ability to Reflect Ground-Water Standards. Another consideration for selecting a WHPA ' .
delineation criterion is the potential for relating it to an overall water quality standard (in
the well or ground water). For example, selecting assimilative capacity as a delineation
3-20
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criterion implies that the attenuation characteristics along flow paths in the saturated
and unsaturated zones are known. Knowledge of how, where, and when the concentrations
«of a specific contaminant are reduced would be helpful in determining whether a standard
can be met. . ,. ', ,,,, . ' '
Suitability for a Given Hydrogeologic Setting. Hydrogeologic controls over ground water
vary widely under natural conditions. The ability to apply a criterion to the hydrogeologic
setting being considered is, from a technical perspective, an essential evaluation factor.
Among the major physical controls that may influence the appropriateness and ease of
criteria application are the location of aquifer boundaries, extent of confinement, degree
of consolidation, amount of fracturing, and extent of solution channel development.
Ability to Incorporate Physical Processes. Selection of a criterion should include
consideration of whether the physical processes controlling contaminant transport at the
specif ic site are incorporated by the criterion.
3.33 Policy Considerations
Because a parallel effort by EPA is addressing poliqr/management issues, this
subsection will describe only a few basic policy considerations for illustration. The
discussion is not intended to be comprehensive.
'I " '' ' ' ' " " ' { ' ' .',,' ', j ., ,
To aid in the process of selecting a criterion, an evaluation matrix of criteria versus
policy considerations is presented as Table 3-7. The matrix cells have been left blank, so
that an appropriate ranking of each criterion may be made by a State or locality in the
selection process. The policy considerations in the matrix are described below. In
general, it should be noted that the primary policy consideration, which cuts across the
four separate considerations, is the applicability of the criterion to the overall WHP goal.
Ease of Understanding. How easily a criterion can be understopd by the general public is
considered to be a significant measure of its usefulness, and may affect the decision to
use the criterion in a WHPA delineation program. For example, prior to establishing a
delineation program, the policy of a State may be to conduct a public
outreach/information program, for which purposes ease of understanding will be relevant.
Economy of Criteria Development. The economics of developing a criterion and related
threshold values are also significant considerations. The costs of applying a criterion, and
of developing the technical resources to support this application, may do much to inhibit
or encourage its use. Generally, criteria that are highly complex, rely on a detailed data
3-22
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3-23
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base, or are labor intensive to apply will be expensive. This inay deter their selection and
acceptance, even though their technical validity is unquestioned.
Defensibility. Enforcement and permitting considerations will require that the boundaries
of a WHPA be clearly defined and defensible against potential challenges and litigation
from the parties affected by the delineation. Some criteria are more contestable in legal
disputes than others. Therefore, policymakers may prefer to use the most technically
defensible criteria for those areas in a State where the potential for litigation or
challenge to the delineation is likely to occur.
, ii >* , , , i
Usefulness for Implementing Phasing. Some States may prefer to initiate their WHPA
programs using the simplest and/or most economic criteria. For example, a criterion such
as distance could be selected at the initial phase. The concept of "phasing" is to initiate
the program in this way, moving toward more sophisticated criteria at a later time.
Relevance to Protection Goal. A final deciding factor in criteria evaluation is the degree
to which specific criteria can meet or support the protection goal selected by the State.
As mentioned in subsection 3.3.1, with examples in Table 3-5, these goals include providing
a remedial action zone, an attenuation zone, and a well-field management zone.
i
3-24
-------
^ CHAPTERS
WHP A DELINEATION METHODS
This chapter describes the techniques or "methods" used to translate the selected
criteria and criteria thresholds described in the previous chapter to actual, mappable
delineation boundaries. Information has been assembled on the methods used in various
ground-water protection programs in the United States and Western Europe to delineate
WHPA boundaries. From this information, six primary methods were examined. Each has
inherent strengths and weaknesses, depending upon hydrogeologic conditions and the
overall goals and objectives of the WHPA program. This chapter reviews these methods
and provides examples at different-levels of sophistication. Since WHP is a relatively new
concept, however, new methods or modifications of existing methods will undoubtedly
>; .-'_-
surf ace in the next few years.
*.l INTRODUCTION TO WHPA DELINEATION METHODS
The six primary methods are listed below in order of increasing technical
sophistication:
Arbitrary fixed radii ,
Calculated fixed radii
Simplified variable shapes
Analytical methods
Hydrogeologic mapping
Numerical flow/transport models.
The methods range from simple, inexpensive methods to highly complex and costly
ones, table 4-1 presents the WHPA delineation methods, together with places where they
have been or are being applied. In any WHP program, however, it is important to
remember that more than one method can be used to delineate a WHPA for a single well
or well field. '
The various methods of delineating WHPA's can be represented conceptually in a
triangular diagram, Figure 4-1. The vertices (three corner points) represent pure
applications of the three major method types. These allow a range in sophisticationfrom
1 the selection of arbitrary values (e.g., a simple fixed radius with no scientific basis), to
the application of highly quantified techniques (e.g., analytical and numerical models
based on extensive site-specific data), to mapping physical features which determine the
4-1
-------
TABLE*-!
WHPA Delineation Methods and Example Applications
Method
Arbitrary Fixed Radii
Example Locations Where Used
Nebraska
Florida
Cape Cod!, Massachusetts
Calculated Fixed Radii
Florida
Vermont
Simplified Variable Shapes
Analytical Methods
Southern England
Cape Cod, Massachusetts
West Germany
Holland
Hydrogeologic Mapping
Vermont
Connecticut
Cape Cod, Massachusetts
Numerical Flow/Transport Models
Southern Florida
Cape Cod, Massachusetts
4-2
-------
Figure 4-1
Interrelationships of WHPA Methods
QUANTITATIVE
ANALYTICAL, NUMERICAL
MODEL
CALCULATED
FIXED
RADIUS
ARBITRARY,
FIXED
RADIUS
CALCULATED AREA
EXTENDED TO
BOUNDARY
HYDROGEOLOGIC
MAPPING
ARBITRARY
FIXED RADIUS
WITH EXTENSION TO
BOUNDARIES
(PHYSICAL OR HYDROLOGIC)
PHYSICAL
FEATURES
4-3
-------
geologic or geomorphic controls on ground-water flow. Intermediate methods lie
somewhere between these three "corners."
fc * , t ; ' « i
* WHPA's delineated by a calculated radius based on generalized regional flow
equations would be a combination of arbitrary and quantitative methods. Regional flow
models can be developed and used by combining th* quantitative and physical features
methods. An approach that starts with a fixed radius and then extends the area to a basin
divide would combine the arbitrary and physical features methods. Numerous
permutations can be developed by combining the methods represented by the endpoints.
4.2 WHPA DELINEATION METHOD ASSESSMENTS
: . ' .; s ,'' ,,: _ . . ,/' f _ : "i .:' . t: , ^. - ; r,» ,,.,., ,,n>;:'. it* J: <,..i .:(' f< i i;..;; w- :-' : i..:, :"-.. i, >" -KJ
Various aspects and specific examples of the WHPAr*^^^,!|^^ 'are'''
discussed in the following subsections. Brief indications of Jh^ cp^js inyolyed in
implementation and application of each method are presented here, though more
quantitative cost estimates are provided in Section 4.3.
4^.1 Arbitrary Fixed Radii
In ii i i 11
Delineation of a WHPA using the arbitrary fixed radii method involves drawing a
circle of a specified radius around a well being protected. The radius of the WHPA may
be an arbitrarily selected distance criterion threshold value (Figure 4-2). Although it may
appear that protection areas delineated by this method are not based on scientific
principles, the distance criteria threshold may be based on very generalized hydrogeologic
considerations and/or professional judgement. For example, the distance threshold
selected-the radius or set of radii-could be based on, averaging; the distances which
correspond to a TOT threshold under various hydrogeologic settings across the State.
Advantages. The arbitrary fixed radii method is an easy techni(?ue for applying a distance
criterion, can be very inexpensive, and requires relatively Jlittle technical expertise.
Using this method, WHPA's for a large number of wells can be delineated in a relatively
-short time. The approach can be protective if large thresholds are chosen, overriding
somewhat its lack of hydrogeologic precision. The method can also be used to initially
define WHPA's until a more sophisticated approach can .be adopted, as the need for
accurate protection increases or more hydrogeologic data become available. The concept
of gradually implementing more sophisticated approaches is called "phasing" in this
document. ." \ ',,, , .'!' .'',''
I
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-------
Figure 4-2
WHPA Delineation Using the
Arbitrary Fixed Radius Method
WHPA BOUNDARY
NOT TO SCALE
4-5
-------
Disadvantages. -'A high degree of uncertainty complicates the application of the arbitrary
fixed radii method, due to the lack of scientific basis for the criteria threshold values
«used with the method. This can be particularly true in areais of heterogeneous and rion-
isotropic hydrogeology or where significant hydrologic boundaries are present. This
method may also tend to over- or under-protect well recharge areas. This could add to
costs of procuring or controlling land use in areas that arent needed. Conversely,
recharge areas that should be protected may lie outside of the fixed radius, and thus
outside the protection area. If large thresholds are chosen, however (perhaps 2 or more
miles), a significant amount of protection could be afforded in most settings.
Costs. The costs of developing and implementing a WHPA program using the arbitrary
fixed radii method are relatively low. A minimum amount of data collection is required
to draw a circular WHPA based on a distance criterion threshold. In addition, WHPA's can
be delineated for a large number of wells in a relatively short time.
,
! ' ' ' ' j
4.2.2 Calculated Fixed Radii ',
\ '
Delineation of a WHPA using the calculated fixed radiii method involves drawing a
circle for a specified TOT criterion threshold. A radius is calculated using an analytical
equation that is based on the volume of water that will be drawn to a well in the specified
time (Figure 4-3).
The input data required by the equation includes the pumping rate of the well and
hydrogeologic parameters such as porosity and hydraulic conductivity. The time period
used is one considered adequate to allow cleanup of ground-water contamination before it
reaches a well, or that allows adequate dilution or dispersion of contaminants.
Advantages. The method is easy to apply and relatively inexpensive; it requires a limited
amount of technical expertise. In addition, WHPA's can be delineated for a large number
of wells in a short period of time. Conceptually, it offers a significant increase in WHPA-
specific accuracy over the fixed-radius method. However, this approach requires more
money than using arbitrary fixed radii, since time and costs may be greater, and data
must be developed to define the criteria thresholds and parameters used in the equation.
Disadvantages. The calculated fixed radii method may be inaccurate, since it does not
account for many factors that influence contaminant transport. This can particularly be
true in areas of heterogeneous and non-isotropic hydrogcology or where significant
hydrologic boundaries are present.
'I! i':, , " '" < ii1 ii-ll
4-6
"I; » , ii; iiiLiii KJ'ii' ;
-------
Figure 4-3
WHPA Delineation Using the
Calculated Fixed Radius Method
LAND SURFACE
Radius (r) is (calculated using a simple equation that incorporates
well pumping rate and basic hydrogeojogic parameters.
-Radius determines a volume of water that would be pumped from
well in a specified time period.
H = Open interval or length of well screen.
NOT TO SCALE
-------
Costs. Costs of developing and implementing a WHPA program using calculated fixed
radii are^relatively low. Some initial costs may be encountered in developing the criteria
thresholds and in hydrogeologic data collection. The costs of actually mapping the
WHPA's thereafter, however, is relatively low, in that a large number of WHPA's can be
delineated with a small investment of time. In general, the calculated fixed radius
method is more expensive than the arbitrary fixed radius method, because of more
extensive data requirements.
Example 1: Florida. The Florida Department of Environmental Regulations (FDER)
requires that Zone D of a WHPA be defined as a circle of a radius (r) calculated using a
volumetric equation with a 5-year time of travel criterion. Figure 4-4 shows the FDER
equation and an application to a well in the Biscayne aquifer in Florida. The volumetric
equation is shown on the figure.
Example 2: Vermont. As ah additional example, Vermont used a calculated fixed radius
equation to delineate WHPA's based on a drawdown criterion threshold of 0.05 foot
(Vermont Department of Water Resources, 1985). If pump test data are available for an
unconfined unconsolidated aquifer, then the radius of the primary zone of protection is
determined using the Theis nonequilibrium equation (Theis, 1935)
u4Tt
Where
T =
t =
S =
aquifer transmissivity
time to reach steady state
storativity or specific yield of aquifer
and u is a dimensionless parameter related to the well function
: w(U)= M§ ; "'" !;i '"""""'' i--i^':*":'i---^"''
1111 ,' , ' ' ' ' l"il I. " u, ' i i ' ... V ',!!,,'
i I11- , " , , ' : ' i.iiii »!,,. :,,i!!'"' 'i ' ' ' .' ,' ,' ',. .
Where s = drawdown at the maximum radius of influence
Q= pumping rate
To calculate the radius, the well function is calculated and u is obtained from a table.
This value of u is then used to calculate the radius.
In the case of an aquifer in Vermont, the input'data are
T « 200ft2/day
t * 1 day ' / '. ' i '^ ' _ [ " """'^ ' ' ^''y
S = 0.02
Q s 25 gpm
s s 0.05 feet
4-8
-------
' %.-
Figure 4-4
WHPA Delineation Using FDER Volumetric Flow
Equation for Well in Florida
PUMPING
WELL
irnH
1138ft
WHERE
Q= Pumping Rate of Well 694.4 gpm = 48,793,668 ft3/yr
n = Aquifer Porosity «= 0.2
H = Open Interval or Length of Well Screen = 300 ft
t* Travel Time to Well (5 Years)
(Any consistent system of
units may be used.)
\
VOLUME VOLUME OF
PUMPED CYLINDER
4-9
-------
and the radius of the primary protection zone is 315 feet. To provide a more accurate
WHPAj^ this calculated radius is then skewed in the direction of ground-water flow
patterns.
"' 4.Z3 Simplified Variable Shapes
In the simplified variable shapes method, "standardized forms" are generated using
analytical models, with both flow boundaries and TOT used as criteria. This method
attempts to simplify implementation by selecting a few representative shapes from the
large array of potential possibilities. The appropriate ^standardized form" is then
selected for hydrogeologic and pumping conditions matching or similar to those found at
the wellhead (Figure 4-5). The standardized form is then oriented around the well
according to ground-water flow patterns. The variable shapes are calculated by first
computing the distance to downgradient and lateral extent!; of the ground-water flow
boundaries around a pumping well (i.e., the ZOC), and then using a TOT criterion to
calculate the upgradient extent. Standardized forms for various criteria are calculated
for different sets of hydrogeologic conditions. Input data for the standardized shapes
include basic hydrogeologic parameters and well pumping rates. [
'' , '" »"'"' ,',,"' , .1 , III lilt
, ;i » .' '" " '-: t
Advantages. Advantages of the simplified variable shapes method are that it can be
easily implemented once the shapes of the standardized forms are calculated, and that it
, i" i1 , ' .. i: , ., .; " I'll 11 ||i I i i | Mi H in i
requires a relatively small amount of field data. In addition, relatively little technical
, : :' , - . ' ., ' ' i; ".. I ' III I li I I I I I I
expertise is required to do the actual delineations. Generally, the only information
required to apply the shapes to a particular well or well field, once the standardized forms
1,.' ii , : . i i n i i i i i j i H i i i ' i in i
are delineated, are the well pumping rate, material type, and the direction of ground- *
water flow. This method offers a more refined analysis than.the fixed-radius method,
with only a modest increase in cost.
Disadvantages. The simplified variable shapes method may not be accurate in areas with
T .1 ,|. , I I , , , T J|! H
many geologic heterogeneities and hydrologic boundaries. There are some conceptual
problems if flow directions near a well differ from those inferred from regional or |
subregional assessments.
Costs. Costs of initially developing the standardized forms for a specific State or locality
i r . , ,- , ; V,;' :'/: *.»>;», i 11 « i i i
may be moderate, although the costs of implementation (i.e., selecting the appropriate
< . v'i ' . ; : . :.' '.f.1-'1.:.. TM .. ji i i i in I i ji
standard shape for a well site) are relatively low. Significant data collection is required
(compared to calculated fixed radii) in order to obtain the set of representative
11 ; " ' , , ,!'"" ,J ''.'',. * P
hydrogeologic parameters needed to calculate the shapes of the standardized forms and to |
' , ,11 , : . ,';' fi t,' ' .,,:",' " "'', III! I I I I I III II
determine the overall ground-water flow directions in the vicinity of specific wells.
4-10
-------
Figure 4-5
V WHPA Delineation Using Simplified
Variable Shapes Method
STEP 1: DELINEATE STANDARDIZED FORMS FOR CERTAIN AQUIFER TYPE
I.
Ql > Q2
Pumping Rite -
I
3
o
02
Q3
-Various standardized forms are generated
using analytical equations using sets of
representative hydrogeologic parameters.
Upgradient extent of WHPA is calculated
with TOT equation; downgradient with
uniform flow equation.
STEP 2: APPLY STANDARDIZED FORM TO WELLHEAD IN AQUIFER TYPE
Standardized form is then applied to
well with similar pumping rate and
hydrogeologic parameters.
LEGEND:
Pumping Well
I Direction of Ground-water Flow
NOT TO SCALE
-------
Examples Southern England. In England, the shapes of "standardized forms" used in the
simplified variable shapes method are developed using uniform flow equations (Todd, 1980)
and a TOT equation. The concern in Southern England is protection of the highly prolific,
. high-flow Chalk aquifer. Areas are generated for various sets of representative
hydrogeologic conditions. The standardized forms are then oriented around the well
according to ground-water flow patterns (Southern Water Authority, 1985).
The uniform flow equations (subsection 4.2.4) are used to calculate the zone of
contribution to a pumping well. These equations describe the ZOC for a confined, porous
media aquifer under uniform flow and steady-state conditions. For unconfined aquifers,
thickness is replaced by the uniform saturated aquifer thickness, provided that the
drawdown at the well is small in relation to the aquifer thickness. These equations do not
determine the upgradient limits of the ZOQ. Therefore, another technique is necessary to
dose the upgradient boundary of the ZOC. The Southern Water Authority in England
utilizes a TOT equation.
The distance (rx) defining the upgradient extent of the ZOC is determined by
substituting a 50-day TOT criterion for tx and solving by trial and error the equation
+ (rx-rw) + Z In (Z ± r«,)
*«««»A ft £ *»&«». *4.«».«.l &«.._*1 .._:_.«. ^
= whether point x
Standardized forms, such as those shown in Figure 4-6, were developed using data
from approximately 75 different possible sets of hydrogeologic parameters with varying
pumping rates, hydraulic gradients, storativities, and aquifer thicknesses. When a WHPA
is to be delineated for each well, the standardized form that most closely matches the
pumping rate and parameters at the well is used. The standardized form is drawn over the
well in the appropriate direction of ground-water flow.
i
4-12
-------
*..' Figure 4-6
Examples of Standardized Forms of WHPA Delineation
Using Simplified Variable Shapes
(Example from Southern England for Chalk Aquifers)
i
0.5
Natural Springs
U-1.0k
Pumping Rate <5MI/d
Pumping Rate 5 to 15 Ml/d
LEGEND:
Pumping Well
-1.5km »
Pumping Rate >15MI/d
DIRECTION OF GROUND WATER FLOW
f.
SOURCE: Southern Water Authority, 1985
-------
4.2.* Analytical Methods
With analytical methods, WHPA's can be delineated through the use of equation(s) to
define ground-water flow and contaminant transport. The uniform flow equations (Tpdd,
* 1980) shown in Figure it-7 are often used to define the area of contribution to a pumping
well in a sloping water table.
Analytical methods, such as the uniform flow equations, require the input of various
hydrogeologic parameters to calculate the distance to the downgradient divide, or
,,.': ' ' v.v . , .: ;. :;';< ,i 31:;;;..,"»;; ' i i n I ° ii I i
stagnation point, and the width of the ZOC to the well. The upgradient extent of the
WHPA can then be calculated based on either a TOT or flow boundaries criterion. For
example, the location of a hydrogeologic boundary such as a ground-water divide or
lithologic contact, can determine the upgradient boundary of the WHPA. Site-specific
hydrogeologic parameters are required as input data for each well at which the method is
applied. These parameters can include the transmissivity, porosity, hydraulic gradient,
hydraulic conductivity, and saturated thickness of the aquifer.
. i, ; I : . '''; t-y t '.'':' ' ;;., : - v.; - v""! !>'.«'';{; :'t: Ii i«: |' K';,;' \' --;.;;' i' '*;'*;'; .< i; \f ^.'H,'"'. '.';.', i, .illil i ,'Slf W f If il
The uniform flow model can be used to calculate distances that define the ZOC of a
.' 'i " '" . ' i!" , '; ',' ' ;":; .'.: J; .i-'1 - 'i:,:'' ,.; i;' i :v;;,: :..' \&: ]: ^ \>: i'lMl1 v P .; ji^.i' i: ^ ,i> w; *^; :;,:«:i:: \ ^ WM i ti,,, lasK-i »
well pumping in a sloping water table, but generally will not calculate drawdown, which [
determines the area of the ZOI. For flat water tables, however, analytical models can be
used to calculate both the ZOC and ZOI of a well because in these cases the boundaries of
. '> ' , ' ;">,= i1, i ,.;,'i!Vi " ,., ;!.,;>. v.T'.iWf.'fC.'iii fsiiiii'iif'C'H'!.!:',':!1, ^::f~,"..'liii11 " -'"'"i .1 "Jf.i i1 I;".". i:.,;;:: is.1.';.1 ;:.~;v,",-,!;-;
the two could closely coincide (see Chapter 3). These calculations can be performed with
the aid of computers. An assessment of available computer-assisted analytical flow and
transport models that may be appropriate for WHPA delineation is included in van der
Heijde and Beljin (1987). An excerpt from the draft of this report is included as Appendix [
D to this document.
, ' " , ' ': " ', ': 'V i '' i I
*.' « . ' '; . .(..-' " MI i in i I i i i ' i ii ii
Advantages. The method uses equations that are generally easily understood and solved
by most hydrogeologists and civil engineers. In addition, it takes into account some site-
specific hydrogeologic parameters. It is, furthermore, the most widely used method,
allowing comparisons with other WHPA programs. Finally, it is considered an especially
valid approach for assessing drawdown in the area closest to a pumping well.
Disadvantages. The methods use models that generally do not take into account
hydrologic boundaries (e.g., streams, canals, lakes, etc.), aquifer heterogeneities, and non-
uniform rainfall or evapotranspiration.
Costs. Costs of using analytical methods to delineate WHPA's are relatively low, although
implementation costs can be high if site-specific hydrogeologic data must be developed
-------
Figure 4-7
WHPA Delineation Using the
Uniform Flow Analytical Model
ORIGINAL
P1EZOMETRIC
SURFACE
GROUND
Q /SURFACE
DRAWDOWN CURVE
(a)
IMPERMEABLE
EQUIPOTENTIAL LINES S
UNIFORM-FLOW
EQUATION
LEGEND:
Pumping Well
SOURCE: Todd, 1950
x.---
o
2rrKbi|
2Kb!
DISTANCE TO
DOWN-GRADIENT
NULL POINT
BOUNDARY
LIMIT
Where:
Q*= Well Pumping Rate
K= Hydraulic Conductivity
b = Saturated .Thickness
i = Hydraulic Gradient
ir = 3.1416
NOT TO SCALE
-------
r! fi' ** f
for each WHPA. The data may be derived from pertinent locral or regional hydrogeologic
reports^. If reports are not available or more accuracy is desired, data collection may
involve site studies, "including test hole drilling and pump tests.
Example Is Massachusetts. A town in Massachusetts has applied an analytical method to
define a WHPA. The distance to -the downgradient stagnation point and the envelope of
the area of contribution were calculated using the uniform flow equations, as shown in
Figure 4-8 (Anderson-Nichols & Co., 1985). The distance to the downgradient divide (X).
or stagnation point at the well, was calculated using the equation
feet
where
Q = pumping rate of the well = 134,760 ft3/day
i = hydraulic gradient of the water table = 0.00125
T s aquifer transmissivity = 14,700 ft2/day.
The maximum width of the influx zone (Y) is calculated using the equation
Y = - = 7,334 feet.
, .
The distance to the upgradient limit was set as the distance; to the upgradient regional
ground-water divide, which in this case was equal to 3,800 ft.
Example 2s Massachusetts. Another town in Massachusetts delineates the key WHPA
zone using the uniform flow model to calculate the distance to the downgradient
stagnation point and the envelope of the area of contribution (Horsley and Whitten, 1986).
The upgradient limit is drawn as the geologic contact between the unconsolidated aquifer
and low permeability bedrock. r
' , ' : ;u> , '., ..... , . - .;._. .:;^.;.'*j.V.:j:1/' i; ;..: ':'"i:- : ..: ........ " '. ..... i" 'l ....... r" l I .,
Example 3s Cape Cod. Distance-drawdown curves, analytical models, and data on local
hydrogeology have been used to delineate WHPA's by the Cape Cod Planning and
Economic Development Commission (Horsley, 1983). An example is shown below for a 1
MGD well; delineation is accomplished in a three-step process.
Step 1 involves identifying the distance to the downgradient drainage divide from a
well by a graphical technique that involves the use of distance-drawdown curves (Figure
4-9). Three plots are shown in Figure 4-9. Plot A represents the sloping water levels |
near the well prior to the start of pumping. Plot B represents the cone of depression *
(drawdown) created around the pumping well. These two plots are used to construct Plot
C by substracting the drawdowns from the sloping water levels. The distance to the
downgradient divide is then determined* from the shape of Plot C, the adjusted cone of
influence, to be about 850 feet.
Step 2 involves identifying the distance criterion threshold to the upgradient
drainage divide. The basis for this step is the Strahler prism model for ground-water flow
on Cape Cod (Strahler, 1966). In this step, the well is assumed to be drawing water from i
the top 75 feet of the aquifer, which is 225 feet thick. Because the ratio of the well
depth to aquifer thickness is Is3, the distance to the upgradient null point is assumed to
4-16
-------
v Figure 4-8
WHPA Delineation Using Arbitrary Fixed Radii,
Analytical Model, and Hydrogeologic Mapping
(Example from Massachusetts)
WELL
APPROXIMATE DOWN-
GRADIENT NULL POINT
r = 2500 FEET
^ /
REGIONAL GROUND-WATER DIVIDE
LEGEND:
Pumping Well
WHPA Delineated with
Analytical Method
WHPA Delineated with
Arbitrary Fixed Radii
Method
SOURCE: Anderson-Nichols & Co., 1985
4-17
NOT TO SCALE
-------
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-------
equal one-third the distance to the regional ground water divide, which is 10,500 feet in
the example (Figure 4-10).
>* . ' ' '
4 Step 3 consists of outlining the WHPA. This is done by determining the area
required to supply ground water to a well based on the annual average ground-water
recharge rate. Once the area is determined, it is drawn on a map using a planimeter and
the downgradient and upgradient divides as guidelines. The final WHPA delineation for
the well is shown in Figure 4-11. For this well, the area of the WHPA was calculated by
dividing the well pumping rate (1 million gallons per day) by the ground-water recharge
rate (13 inches per year), and the area of the WHPA was determined to be 45,046,500 ft*.
4.2.5 Hydrogeologic Mapping
: \ ,
In many hydrogeologic settings, flow boundary and TOT criteria can be mapped by
geological, geophysical, and dye tracing methods. The flow boundaries are defined by
lithologic variation or permeability contrasts within the aquifer. Geological observations
may provide surface indications of litholdgy changes, which will correlate with WHPA
boundaries (Figure 4-12). Surface geophysical data can be used to map the spatial extent
or thickness of unconfined aquifers. Hydrogeologic mapping may also include mapping of
ground-water levels in order to identify ground-water drainage divides, as shown in Figure
4-13.
Delineation of upland carbonate aquifers having rapid recharge into conduit karst
during storm events can be done initially by topographic analysis of drainage basin divides,
supplemented by mapping the water table using water levels in wells and springs.
Subsequent refinement of conduit recharge patterns is possible by using dye tracing
techniques, especially during high-flow conditions. Under such conditions, sub-basins can
become integrated or even spill over into other basins, reflecting the complex nature of
karst systems. Although less frequently reported in scientific literature, these methods
can also be used to delineate recharge and flow systems in non-carbonate fractured
bedrock aquifers.
Advantages. Hydrogeologic mapping is well suited to hydrogeologic settings dominated by
near-surface flow boundaries, as are found in many glacial and alluvial aquifers with high
flow velocities, and to highly anisotropic aquifers, such as fractured bedrock and conduit-
flow karst.
Disadvantages. The method requires specialized expertise in geologic and geomorphic
mapping, plus significant judgment on what constitute likely flow boundaries. This
method is also less suited to delineating WHPA's in large or deep aquifers.
4-19
-------
Figure 4-10
WHPA Delineation Using Analytical Models
Step 2: Identify Upgradient Null Point
Based on Strahler Prism Model
(Example from Cape Cod, Massachusetts),
REGIONAL GW Dp-Gradient
./DIVIDE Mull poinf
(EXAGGERATED PROFILE)
WELL DEPTH
SEA
LEVEL
-400
SOURCE: Hor»ley, 1983
2 - Wall Depth - SO FEET
b - SatiiHttd Thickness - 225 FEET
RATIO-?*25' " 0-33
' D
LEGEND:
ZONE OIF CONTRIBUTION
AQUIFER SATURATED THICKNESS
DIRECTION OF GROUND-WATER
FLOW
^. WATER TABLE
2 - WELL DEPTH
NOT TO SCALE
B
-------
Figure 4-11
WHPA Delineation Using Analytical Models
Step 3: WHPA Delineation Using Upgradient
and Downgradient Null Point
(Example from Cape Cod, Massachusetts)
UP-GRADIENT NULL POINT
DOWN-GRADIENT NULL POINT
2000 Feet
ZONE OF CONTRIBUTION - WHPA
SOURCE: Hartley, 1983
LEGEND:
Contour Line
Pumping Well
4-21
-------
Figure 4-12
WHPA Delineation Using Hydrogeologic Mapping
(Use of Geologic Contacts)
STREAM
PUMPING WELL
BEDROCK (NON-AQUIFER
MATERIAL)
ALLUVIAL AQUIFER
.__ Primary WHPA Boundary Drawn as Contact
Between Aquifer and Non-Aquifer Material
NOTE: A secondary protection zone could be delineated based on
the larger area of recharge derived from surface runoff, and
inferred from topography and basin boundaries.
I
NOT TO SCALE
4-22
B
-------
V -;
Figure 4-13
WHPA Delineation Using Hydrogeologic Mapping
(Use of Ground-water Divides)
LAND SURFACE
WHPA
STREAM
VALLEY
STREAM
I
WHPA
DRAWDOWN
CONTOURS
/
GROUND-WATER
DIVIDE
LEGEND:
Water Table
Pumping Well
Ground-water Divide
Direction of Ground-waiter Flow
WHPA
4-23
-------
Costs. tCosts of developing and implementing a wellhead protection program using
hydrogeologic mapping are variable. Costs may be relatively low if considerable data are
already available or if the general hydrogeology of the ground-water system is known.
The particular type of hydrogeologic mapping technique used wiill also determine costs. In
general, geophysical techniques are the most costly, followed by mapping of geologic
contacts, dye tracing, regional water level mapping, and basin delineation using
topographic mapping. Costs may be high if little hydrogeologic information is available in
an area and if test holes and/or pump tests are necessary to confirm the mapping.
Example: Vermont. Vermont utilizes a method in which mapping of geologic contacts is [
combined with simplified fixed-ring calculations (subsection 4.2.2) (Vermont Department
Water Resources, 1985). In an example from Vermont (shown in Figure 4-14), a primary
protection area is delineated using hydrogeologic calculations while a secondary area is
delineated with hydrogeologic mapping of the well's recharge area. Hydrogeologic
mapping in this case is based on physical boundaries and the prevailing topography, with
assumption that shallow local ground-water flow mirrors topography.
Hydrogeoiogic mapping has also been used to delineate parts of WHPA's in a town in *
Massachusetts, where the upgradient extent of the WHPA is formed by the regional I
ground-water divide, as shown in Figure 4-8.
Other Hydrogeologic Mapping Tools
Tracer Tests. Tracing techniques can be used to map underground conduits by injecting
dyes or tracers into a ground-water system. The dye is introduced into a sinkhole or
stream that flows into ground water suspected to flow to the supply source for which the r
WHPA is being delineated. Water from the supply well or stream is then monitored and/or
observed for a period of time that is adequate for the tracer to reach the supply. If the
tracer is detected in the supply, the source from which the tracer was injected becomes
part of the WHPA. Existing contaminants in ground water can also be used as tracers to
delineate flow to water supply wells. If the source of contamiinants to a well is known,
the infprmation can be used to better understand ground-water flow in the area, and the g
specif ic sources of water in the well. " ' ' '"" '"' ' " "
'.'.; , , - "'I ':. "' '. : ", ''" >ii;'r'i.':>""'I 'f!!"!'li'L .«' i ;.>.' .,'' ">, '. "': **'(". y,1-1 '.,'',',: ,;',' Bi:1"1:!11';1 i npi^rWrf
'; " i. . iii;,-|ll. .. ' : .. ;, " " . [ ' .. IM ,' .;".*.,; ':,.!.!'.;,,' ,'' '* .''j' 1.!MJifflK'r I V1^1 i'!''':''':'( i ' '.'/:ij '^ .-','!,'>'f'V; V'" S' '*,' t '.''.'"li SR ';'$$
Example: Kentucky. Dye tracing has been used to delineate ZOC's to water supply
springs in Kentucky (Quinlan and Ewers, 1985). In the example shown (Figure 4-15), the
ZOC tp a spring supplying a town differs from a ZOC that would be interpreted from
observing topography and mapping potentiometric surfaces. In this example, although the
spring was hydraulically downgradient from a contaminated pond, dye tracing revealed
that the spring would not be affected.
.'': ' . ;"..» " - :::,:: ', ' . ' . , ' ,' ' ' ''I ' i '"' I
Geophysics. Surface geophysical techniques have also been applied in aquifer mapping
investigations. These techniques measure the surface response of subsurface elastic,
' , ... " Hi i ' i i I i i
4-24
I
-------
Figure 4-14
WHPA Delineation Using
Hydrogeologic Mapping
(Example from Vermont)
* Primary Area
(Secondary Area-
Topographic Divi
PRIMARY AREA (STRATIFIED DRIFT)
SECONDARY AREA (TILL AND BEDROCK)
SOURCE: Vermont Dept. of Water Resources. 1985
4-25
-------
Figure 4-15
VWH PA Delineation Using Hydrogeologic Mapping:
Dye Tracing (Example From Kentucky)
Potentiometric surface
Traced flow route
Sinking spring
Spring-fed stream
Intermittent stream
Sinking stream
. . ZOC of spring A based on
mapping of potentiometric surface
A Municipal water supply spring
-*»- Inferred direction of ground-water flow
Sinking stream B was found to not be in ZOC of spring A,
although this would be inferred from potentiometric surface.
i
Modifttd from Quintan and Ewert. 1985
NOT TO SCALE
4-26
i
-------
density, electrical, or magnetic contrasts. The resulting subsurface interpretations can
provide information on the lithologic and hydrologic characteristics of unconfined aquifer
systems.
The nature of the hydrogeologic setting, deter mines the applicability of a particular ,
geophysical method. In many ground-water studies, several different geophysical methods
are applied to the same survey area. In general, the selection of a geophysical technique
depends on: the physical nature of the survey area, the desired depth of penetration, the
data resolution requirements, and the available resources.
v ' '.'"'''...'.» .''..'; ."..-" ' .
Geophysical methods model the subsurface environment according to simplifying
assumptions. Subsurface interpretations are generally improved when information from
test borings or observation wells are available to constrain the data sets. One common
strategy is to use surface geophysical data to correlate between boreholes or to
extrapolate borehole information into new terrain. In these surveys, surface geophysics
functions as a rapid, inexpensive alternative to test drilling.
WHPA delineation programs can use surface geophysics to map the subsurface
boundaries in unconfined aquifer systems. In these boundary delineation studies, seismic
refraction and electrical resistivity techniques have been applied most consistently, with
gravity and magnetic methods having only secondary applications. However, recent
technological advances have resulted in the development of new techniques that have
ground-water applications. Table 4-2 summarizes some of the technical characteristics,
applications, advantages, and limitations of the geophysical techniques that have been
used in ground-water investigations, based on a report by the Office of Ground-Water
Protection (1987).
Age Assessment, (Tritium). An indication of recent leakage or paths of rapid recharge into
a confined aquifer is the presence of tritium in concentrations greater than atmospheric
background, a consequence of the presence of post-1954 tritium from atmospheric testing
of nuclear weapons. In precipitation, tritium from cosmic ray bombardment of the upper
atmosphere has a quite low concentration and is variable with latitude, season, and local
meteorological parameters. Thus ground water from atmospheric precipitation prior to
1952 has quite low concentrations relative to the enhanced levels subsequent to 1954.
The presence of tritium in ground water at higher concentrations (unless it results
from radioactive waste disposal) can be used to determine roughly ground-water age and
origin. In confined aquifers, for example, the existence of leaks in pathways could be
4-27
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determined and the extent of WHPA's could thus be modified according to the locations of
Lf'T * ' ' - _ | t'i\ . >.--.-
such pathways. Ground water is frequently a. mixture of waters of different ages and
sources, which can complicate age-determination of the major portion of recharge.
Because leakage into a confined aquifer can short-circuit into ground water from other
recharge paths, water having a much greater isotopic age (as can be measured by carbon
1* dating) may be present also.
Trichlorofluoromethane (CC13F) is Of anthropogenic origin and has been in the
atmosphere for about fifty years. It is an additional possible tracer of leakage into
confined aquifers (Thompson and Hayes, 1979), although it does not have well-defined
chemical and physical behavior during ground water flow as does tritium. CCl^F is
subject to adsorption and desorption phenomena that affect its concentrations in ground
water (Russell and Thompson, 1983).
It appears that detection of significant tritum concentrations in confined aquifers
may be one of the most expedient initial methods of evaluating the leakiness of confining
strata in the short term. It must be kept in mind that mere leakiness of an aquifer is not
equivalent to finding contamination by a pollutant, merely an indication of the existence
of a possible pathway should a contaminant subsequently be introduced to that part of the
flow system.
4.2.6 Numerical Flow/Transport Models
> v , . =
WHPA's can be delineated using computer models that approximate ground-water >
flow and/or solute transport equations numerically. A wide variety of numerical models is
presently available both commercially and through organizations such as the U.S.
Geological Survey (USGS), Holcomb Institute's International Ground-Water Modeling
Center (IGWMC), and the National Water Well Association (NWWA).
Numerical flow/transport models are particularly useful for delineating WHPA's
where boundary and hydrogeologic conditions are complex. Input data may include such i
hydrogeologic parameters such as permeability, porosity, specific yield, saturated
thickness, recharge rates, aquifer geometries, and the locations of hydrologic boundaries.
Solute transport parameters such as dispersivity may also be incorporated in these models.
Depending upon the size of the area to be modeled and the number of cells or
elements, these models can be run on a mainframe or microcomputer. Intermediate-type i
models that use combinations of analytical methods to generate head field distributions *
and numerical methods to generate particle tracing maps are also available. Such models
may not account for all boundary conditions at a site, however.
' ' '' . . 4-29 ' ' v '
-------
Criteria such as drawdown, flow boundaries, and TOT may be mapped using
^ numerical methods, typically in a two-step procedure. First, a hydraulic head field
* distribution is generated with a numerical flow model under a prescribed set of
hydrogeologic parameters and conditions, and with a selected flow boundaries criterion to
determine the extent of the modeling domain. Second, a 'rui^ri^'wauim transport model
that uses the generated head field as input calculates the WHIPA based on the preselected
criterion. Figure 4-16 illustrates a flow chart of some typical components of this
procedure. Some information from a draft report on available numerical models that may
be appropriate for WHPA delineation |s included as Appendix D to this report (van der
Heijde and Beljin,1987). An additional, useful guide for model selection |s provided in a
report by the EPA Office of Research and Development (1987).
Advantages. This method provides a very high potential degree of accuracy and can be
applied to nearly all types of hydrogeologic settings. The models can also be used to
predict the dynamic aspects of the WHPA such as changes in the size of the WHPA
resulting from natural or man-caused effects. .Specific ..advantages and disadvantages
associated with individual models are reviewed ii, the report "Model Assessment for
WHPA Delineation" by IGWMC (Beljin and van derHeijde, i987).
Disadvantages, Costs for this method are usually relatively higher than others.
Considerable technical expertise in hydrogeology and modeling is required to use this
method. However, the cost may be warranted in areas where a high degree of accuracy is
desired. Due to limitations on model grid spacing and density, numerical models are less
suitable than analytical methods in assessing drawdowns close to pumping wells. For this
reason, WHPA delineation in The Netherlands in recent years has focused on combining
analytical methods for the near-field and numerical models for the bulk of the protection
area. ' ,
Costs. Costs of developing and implementing a numerical model to delineate WHPA's can
be relatively high, depending upon the availability and quality of data, the number of
wells, and the complexity of the hydrogeplpgy. However, if .adequate data bases exist and
the hydrogeology of the area is known, numerical models can be cost effective.
Numerical modeling can also be less expensive if relatively homogeneous hydrogeologic
conditions exist and extensive data input is not necessary. In this case, a large number of
"default Values" for some of the hydrogeologic parameters can be used, while using
better-known values for the more sensitive parameters.
4-30
i i
B
-------
Figure4-16
Simulation Procedure Used in WHPA
Delineation with Numerical Modeling
INPUT PARAMETER/
BOUNDARY CONDITIONS
FOR A GIVEN PERIOD
I
RUN HEAD
SIMULATION
FOR ABOVE
CONDITION
I
OUTPUT"
HEAD FIELD
7
CHOOSE MODEL
DEPENDING ON:
PROPERTIES OF SYSTEM
AVAILABLE DATA
AVAILABLE RESOURCES
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MEASURED
WATER LEVEL
FOR SAME PERIOD
4-31
-------
Example: Florida. The Counties of Broward, Dade, and Palm Beach in Florida use
numerical ground-water models to delineate WHPA's. Figure 4-17 shows a map with the
^numerically generated 30-day, 210-day, and 500-day TOPs (based on the multiple WHPA
zone approach) for a well field in the Biscayne aquifer. . -
4.3 WHPA DELINEATION METHOD COSTS
,! >>>!! i III
Estimates of potential costs for each of the six WHPA delineation methods are
shown in Table 4-3. These are rough estimates on a per-well basis, considering labor costs
and level of expertise required for each method. The table also includes potential
overhead costs that may be encountered with each method, Jilthough dollar figures have
11 . ! ' '. , :';*!;; '.. ,, ,:'..; i n , i i fHi1 nI IM i,n i in i i,i\
not been assigned to overhead. Labor costs for the various levels of expertise are based
on a survey by the National Water Well Association on salaries of ground-water scientists
in the United'States (NWWA, 1985). The costs are expressed in uninflated dollars.
Several assumptions built into the figures in Table 4-3 include:
WHPA's will be delineated by personnel and staff at the agency in charge of
the WHPA program, possibly aided by consulting firms.
Each method requires a different level of technical expertise to apply.
Data on hydrogeology of the areas in which WHPA's are being delineated are
relatively available, although some data collection and searching may be
required. , "' '
Manhour requirements for each method have been projected in ranges of hours. The
higher end of the range may apply If a relatively large amount of data collection is
required or the data are not readily available. It may also apply if the personnel are
unfamiliar with WHPA delineation methods and/or have not reached a level on the
"learning curve*1 where WHPA's can be delineated efficiently. The lower end of the range
of manhours may apply if data are generally easily available and/or the personnel doing
the delineation are familiar with and have used the delineation methods. For estimates in
Table 4-3, it was assumed that the average annual salary estimated from that survey was
roughly equivalent to that of a mid-level hydrogeologist. Salaries of other levels were
then estimated from that figure.
: * » *
, , . , , ,
Potential overhead costs include those for equipment to collect hydrogeologic data,
iM& S8\ >,
computer hardware and software, and the costs associated with report preparation,
including typing and creating maps and figures. In general, if many of these items are
already available to the agency or organization doing the delineation, potential overhead
4-32
-------
\; Figure 4-17
Numerical Model Application to Biscayne Aquifer Well Field
500 Day Travel Time
30 Day Travel Time
210 Day Travel Time
Wellhead
4-33
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costs become less significant. .These figures do not reflect costs for consulting firms
-'*' " ' ' - ' -
potentially engaged in.this work. It should be noted that the greatest expenses are
typically related to data acquisition, and these are clearly State- and WHPA-specific.
4.4 WHPA COMPARATIVE ANALYSIS ....."'
1 - , \ .
Once a desired criterion and criterion threshold have been selected, one or more
WHPA delineation method(s) will be chosen to "map" the criterion. To aid in method
selection, a comparative analysis of delineated areas resulting from different methods
may be performed. Results of this comparison should consider relative accuracy, ease of
implementation, and costs. For example, if a fixed radius method were being considered
for delineating WHPA's in an entire State, a comparative analysis for a limited number of
wells using more sophisticated (and presumably more accurate) methods could help
determine if the simpler and less costly method provides adequate results. Examples of
comparative analyses of WHPA delineations done for actual wells in several locations are
described in detail in Appendix B.
Two approaches can be used in WHPA comparative analyses. One approach is to
compare areas of protection that result from applying the same method of delineation to
different hydrogeologic settings. A second approach is to compare areas of protection
that result from applying different methods of delineation to the same hydrogeologic
setting.
With any analysis, a basic assumption is made that there is one method that provides
results most indicative of actual conditions. Once the various areas have been delineated
in the comparative analysis, the tradeoffs of accuracy versus costs versus speed of
implementation, can be more fully considered in any given State or hydrogeologic setting
within a State.
Figure 4-18 conceptually illustrates' the effects of accuracy on the degree of
protection and ease of implementation. If the area delineated by a method is smaller than
that delineated by the method assumed to be the most accurate, under-protection may
occur. This may result in possible degradation of water supplies. If the area is too large
relative to the accurate method, over-protection may occur and result in implementation
problems. The common European "rule" for determining the extent of WHPA's is "as large
as necessary, as small as possible."
4-35
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4.5 METHOD SELECTION CONSIDERATIONS
' ,\:. -1 ' ''-'' ' ' ' . ' '
The amount of effort required to select a method is largely reduced once the desired
criterion has been selected/That is, the method selected must be suitable to map or
delineate the selected criterion or criteria. For example, if the criterion selected is
' ' - . - .
distance, then the only appropriate methods to map distance are arbitrary fixed radii and
hydrogeologic mapping. Table 4-4 shows the suitability of each method to map each
criterion, A detailed technical discussion of the approaches to selecting analytical or
numerical models (either two-dimensional or three-dimensional) for a typical glacial,
stratified-drft, river-valley aquifer In New England is provided by Morrissey (1987).
As in the case of criteria selection (Section 3.4), choosing a method depends on
various technical and policy considerations. The choice of method is tied less to the
protection goal, however, than to the accuracy of delineation desired, and the financial
resources available for delineation.
4.5.1 Technical Considerations
To guide the States in the process of selecting a method, a matrix of technical
evaluation factors versus methods is presented as Table 4-5. The matrix is blank to allow
the States or local agencies to assign their own rankings according to site-specific
' ' '' ' \ ', ' , . '
conditions. An "H" (High) ranking implies that the method is relatively useful or
beneficial in satisfying the technical consideration. The factors that might be used to
evaluate the method are described below. Understanding the basis of the method and the
input data requirements, applying the method, and evaluating the method's results are all
significant considerations.
Extent of Use. It is useful to identify how commonly the method is used (e.g., whether it
is presently used by regulatory agencies or is in the process of being adopted).
Simplicity of Data. The amount and types of data required for method application are
quite significant. The data required may be site-specific (i.e., developed specifically for
method application) or regional (i.e., approximate and already available).
Suitability for a Given Hydrogeologic Setting. An important consideration is the
capability of a method to be applied to the hydrogeologic setting in the State. It may be
important to evaluate how suitable the method would be to incorporate the effects of
"sources" and "sinks," boundary conditions, variable aquifer parameters, and other
technical factors. .
4-37,
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Accuracy. It is important to consider the degree to which the results from method
application can be expected to compare with actual field conditions.
**" . . .' ......... '..;!
4.5.2 Policy Considerations
To aid in the process of selecting a method, an evaluation matrix of methods versus
policy considerations is presented as Table 4-6. The matrix has 'been teft blank,' so that an
appropriate ranking of each method may be made by a State or locality in its selection
process. The policy considerations are described below.
' '" " "
Ease of Understanding. It is important to consider the degree to which the principles
underlying the method can be readily understood by nontechnical people.
Economy of Application. The relative cost incurred in applying a method to one wellhead,
, ,..''.. ".'. , ... , ........ .. ...... . ., ' , , .... ,,, '. ..... ; . . |. ,, ........ , :
well field, or the main fields in a .State may do much to inhibit or encourage its use.
Factors that may affect costs include data acquisition, professional labor, computer time,
graphics, and reporting.
Def ensibility. Enforcement and permitting considerations will require that the boundaries
of a WHPA be clearly defined and defended against potential challenges and litigation
from parties affected by the delineation.
Relevance to Protection Goal. As mentioned in subsection 3.3.1, WHPA delineation will
reflect an overall policy/protection goal. The relevance to this goal of the methodology
under consideration by the State is a key factor in program success.
I
4-40
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CHAPTER 5
, t - , - . - '?-. "
1 ' . .. ki. - '- ' - ' . ' ' ', '. ''
EXAMPLE OF CRITERIA AND METHOD SELECTION
'**' : ' . .- '
An example of the steps that a regulating agency might consider in a WHPA
delineation is provided in this chapter. The example is not meant to be the only
appropriate procedure. The approach eventually selected must reflect the specific
protection goal and other technical and policy considerations that a State might use in
meeting the requirements of the Safe Drinking Water Act.
1 * ,
Variations and diversities exist in both hydrogeologic settings and State regulatory
programs in the United States. Certain programs may find that their environmental
policies and resources lend themselves to one procedure, while those elsewhere make
another approach more suitable. Consequently, numerous issues should be thoroughly
examined and evaluated. These include water supply well construction regulations and
practices in use; organizational and institutional capabilities of State and local agencies
to provide appropriately skilled personnel, equipment, materials, and implementation
funding; and type and complexity of the hydrogeologic settings in the State. A careful
examination of these matters will greatly facilitate selection of the most appropriate
delineation criteria, methodologies, and strategies for implementation. Guidance on these
management-related issues is provided in other resource documents prepared by EPA.
The example of the criteria and method selection process for the hypothetical State
is organized in the following manner:
Description of the WHPA delineation problem
Evaluation matrices for degree of protection, technical, and policy
considerations
Summary of final decision reached by the hypothetical State.
' ' / . .
5.1 PROBLEM STATEMENT: THE HYPOTHETICAL STATE
The hypothetical State is establishing a wellhead protection program under the
SDWA. A panel of experts has been established with both technical and nontechnical
expertise. The panel's work was conducted under the following assumptions, developed by
previous State planning and research:
Aquifers requiring the greatest protection are mostly unconfined aquifers
comprised of unconsoiidated sands or sands and gravels.
5-1
-------
Certain industries will be affected by the WHPA program, and the threat of
V litigation has been raised. The technical basis of the WHPA delineation
program may, therefore, be challenged.
It is estimated that available technical personnel from State agencies will be
able to perform all analyses and mapping of the WHPA* in an expedient
manner.
'\ ' - ' /.' !i; ' :i.. ''. ^'-;i':'v'^;^;;;!fl
Degree of protection considerations have established ^at tije goal of WHPA
delineation will be to provide management of the well-field area. It is
,ii, ,! " ' "!' i! ' | ' " " ' '" ' '"" ....... "'' "' ...... ''"' ' ' ..... ' ........ : dl '-" ' ' '"ll ' " ' ! .........
expected that three different protection zones will be established to protect
against each type of threat (physical, microbial, and chemical). These will be
labeled Zones I, II, and HI, respectively.
Tn ,, , , ,
Approximately 900 wellheads will be in the first phase for delineation relative
to chemical threats (i.e., Zone IH).
A program to inform the general public of the developing wellhead protection
efforts will be implemented.
The State, in cooperation with county and local agencies, has the authority to
impose land use controls within the zones.
5.2 EXAMPLE OF CRITERIA SELECTION
5.2.1 Overall Protection Goals
As noted in the problem statement, the hypothetical State's goal is to provide
management of the well-field area. The panel was asked to examine and recommend
delineation criteria based on both technical and policy considerations. These separate
analyses, in addition to the panel's final recommendations, are outlined below.
i, , , "., " i ''''" i ' ' " « "'
5.2.2 Technical Considerations
As noted in the problem statement (subsection 5.3.2),' most of the aquifers requiring
i . ;. , a T,I », - i , i 7* . ..: , , ^ , P
protection in the hypothetical State are unconfined, porous media units. Based On this,
the panel evaluated the technical merits (subsection 3.4.3) of the delineation criteria,
focusing primarily on the 900 high-priority wells. The completed evaluation matrix is «
illustrated as Table 5-1.
Based on this evaluation, the panel decided that the criterion providing the strongest |
technical basis for WHPA delineation was TOT, with a threshold value of 15 years. The
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relationships between the TOT criterion (and the other criteria) and each of the technical
considerations are summarized by the rankings in Table 5-1 and are detailed below.
Ease of Application. Ease of application was not judged to be a significant impediment in
'the hypothetical State. The State's technical staff was deemed capable of understanding i
: : , ' , , 'in I'M .«' . ., i, " ; ' - i ." .. ||,,, , ij i . i in ,,,'i , ,',,,, ,, , , |i»'..Mi!'11!.,.1" 'JtJh,1! n liJ I11 , illllllllllllimL'lllil'il Ii lllliilll ii!i,> i!1'1"1'", i,,!'1!: I'lCl.iittii',,',!, i,! ,'!, 'i:,'!,U , /'J'JiyiiA»libllij JiiyilJi.il lililUl " HAM. iliHliiCnilMliiif |
and applying TOT information as a delineation criterion. Though the application will be
relatively complex (rated "M" in the matrix), the panel determined it to be within the
State's capabilities and allotted time.
Ease "of "Quantification. Although" TOT is "more 'difficult to quantify than" 'other" criteria,'
the hypothetical State's panel of experts believed that workable, technically defensible
." I . ' ! . I'll " , .' ' ' - "': ' ' .;.. ' !:':l'./w.i';;*''i*:':'- '"; ".I.'ViW:1 hiliiS'!i^
thresholds for the TOT criteria can be established and applied. These will focus on the f
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need to protect wellheads from microbial and chemical threats. The panel concluded that
a minimum of a 50-day TOT (along with a minimum distance of 500 feet) is needed to
protect against microbial contamination (Zone n). A 15-year TOT was seen as an
appropriate threshold to protect the well against the threat of chemical contamination
(Zone in). Most water purveyors purchase the land immediately contiguous to the well,
typically up to 100 feet away, which effectively delineates Zone I). |
Variability Under Prevailing Conditions. The panel recommended that the WHPA
delineation effort should accommodate future changes in pumping patterns. The panel
concluded that selected criteria should allow adjustments to the size of the WHPA to
allow for the effects of future increases in pumping rates; a TOT criterion will allow for
this adjustment. The projected maximum pumping capacity of existing wells under some _.
drought conditions will therefore be factored into the analysis to reduce the need to *
expand the WHPA's in the near future.
.; '!!' "'''', i'1"" i i i i i j i 11 i i i
Ease of Field Verification. It is not anticipated that field verification of zones of TOT's
will be undertaken for the whole State. Measurements will be done at several test case
sites. These measurements will be extrapolated to other WHPA's with similar
hydrogeologic conditions in the State. 1
Ability to Reflect Ground-Water Standards. The panel recognized that the attentuation
capacity of the aquifers for specific contaminants could theoretically be assessed. The
panel felt this criterion was impractical to implement, except for some experimental
studies. They also doubted that high-flow sand and sand and gravel aquifers within the
State could be protected by this criterion.
I" in111 *''
ii MI' i,
I
-------
Suitability for Hydrogeologic Settings. Use of a TOT criterion to delineate WHPA's in a
.water table aquifer in porous media was deemed appropriate, since most of the
approaches developed to estimate TOPs are based on assumptions that are generally met ..
in these aquifers within the State.
Ability to Incorporate Physical Processes. 'Most physical processes involved in the
transport of contaminants in a porous media aquifer, such as advection and dispersion, are
incorporated in TOT. This criterion is thus quite applicable for this type of aquifer.
5.2.3 Policy Considerations
'.''' ' , .
The hypothetical State's panel also evaluated the five criteria with respect to
several policy considerations and a composite ranking was established, as illustrated in
Table 5-2. For these considerations, a distance criterion was actually judged to be
somewhat superior to TOT. The panel's rationale for this ranking is discussed below, and
the resolution of this issue provided in subsection 5.2.4.
Ease of Understanding. The ability of the general public to understand the criterion was
considered important. Distance was judged to be the easiest to understand ("H" rating on
the matrix). However, it was believed that more technical concepts such as TOT could be
explained to the public.
Economy of Criteria Development. Development of a distance criterion would be very
economical. However, the panel concluded that, were this criterion ultimately selected
for the State, the threshold values selected should have some scientific basis. It was also
considered desirable to be somewhat "over-protective" (i.e., larger dimensions), given the ',
problems with the scientific basis. Implementation problems due to extension of
regulating authority over large geographic areas were a related concern.
Defensibility. The panel was concerned by the lack of technical justification for a
distance criterion. Since the thresholds required to provide adequate protection would
likely be overly "conservative" (i,e., overprotected), challenges from affected parties *
were considered possible.
Usefulness for Implementing Phasing. The panel concluded that the distance criterion
would be very useful for the State as an initial step if a phasing approach were to be used.
In a few years the State could move to a more sophisticated criterion. However, phasing -
had already been eliminated to avoid enforcement problems and the difficulties of
defending arbitrarily determined areas. I
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Relevance to Protection Goal. Given the hydrogeologic: settings in the State, and the
other assumptions outlined above, most criteria were acceptable. The key decision was
believed to be the selection of criteria thresholds.
5.2.* Summary of Panel's Decision on Criteria Selection
The example for thie hypothetical State illustrated can various considerations affect
the ultimate selection of criteria. A TOT criterion was eventually chosen after weighing
technical and policy considerations together. Though policy issues might have led to the
selection of distance as a criterion, TOT was rated nearly as high. The deciding factors
for this State were the concern over legal challenges, the relatively "simple"
hydrogeologic settings (enhancing the utility of TOT), and the fact that technical
resources in the State were deemed adequate. Therefore, the ultimate decision was to
select "a TOT criterion as the basis for WHPA delineation. The State established a
minimum of 15 years TOT as the threshold value. Municipalities and counties were urged
to adopt more protective thresholds (e.g., 20- to 50-year TOT's) where feasible.
5.3 EXAMPLE OF METHOD SELECTION
This section presents an example of how the panel of experts from the hypothetical
State evaluated the choices of available methods for mapping WHPA's. Given the panel's
previous recommendations on WHPA criteria, evaluations and rankings were only made ifor
methods that could map a TOT criterion (Table *-3).
1 . ,"'-'-- /
The panel again assessed the choices with respect to both technical and policy
considerations. The four methods that would map the selected criterion (TOT) were
evaluated with respect to technical evaluation factors, described in subsection *.5.1. The
results of their rankings are presented in Tables 5-3 and 5-4. As shown in these matrices,
the panel preferred analytical flow and transport models. The technical reason for this
method preference was based largely on the absence of flow boundaries near the pumping
wells. If the effects of boundaries on WHPA delineation had been considered, the panel
would have ranked numerical flow/transport models higher than the selected method. An
additional factor influencing the panel's ranking was the conclusions obtained by the State
, through comparative studies of WHPA delineations, performed at a few selected test
sites. These studies indicated that the results from analytical flow/transport models
correlated well with results from the more sophisticated methods (such as numerical
flow/transport models and hydrogeologic mapping). Therefore, the less complex and more
economical method was selected.
5-7
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From the csj^ndpoint of policy considerations, and in particular relevance to the
protection goal, analytical models were clearly preferred over numerical procedures. The
!***&* if used for all wells, would be prohibitively expensive and would prevent the State
from meeting its statutory responsibilities.
5-10
2
-------
^ REFERENCES
v '" '
(.-.'' / , ' ' '\
Anderson, M.P. 1984. Movement of Contaminants in Groundwater: Groundwater
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Everett, A.G., 1987. Some Significant Attributes of Aquifers as Related to Wellhead
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Freeze, R.A., and J.A. Cherry. 1979. Groundwater. Prentice Hall, Inc. 604 p.
Fried, 3.3. 1975. Groundwater Pollution. Elsevier Scientific Publishing Company. New
York, New York.
Griffin, R.A., and N.F. Shimp. 1976. Effect of pH on Exchange-Adsorption or
Precipitation of Lead from Landfill Leachates by Clay Minerals. Environment.
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Griffin, R.A., et al. 1976. Attenuation of Pollutants in Municipal Landfill Leachate by
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Griffin, R.A., A.K. Au, and Esk Chian. 1979. Mobility of Poly chlorinated Biphenyls and
Dicambia in Soil Materials: Determination by Soil Thin-Layer Chromatography.
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Heij, B.3. 1987. Personal communication. National Institute of Public Health and
Environmental Hygiene, Bilthoven, The Netherlands.
Helling, C.S. 1971. Pesticide Mobility in Soils III. Influence of Soil Properties. Soil
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r
R-2
-------
HorsJey, Scptt W. 1983. Delineating Zones of Contribution for Public Supply Wells to
t Protect Groundwater. Proceedings of the National Water Well Conference.
National Water Well Association. Worth ing ton, Ohio.
Horsley, S.W., and T.C. Cambareri. 1984. Delineating Zone of Contribution for Public
Supply Wells to Protect Ground Water in New England. Journal NEWWA. pp. 19-43.
Horsley, S.W., and J.D. Witten. 1986. The Town of Duxbury, Massachusetts Aquifer
Protection Plan: A Case Study in Innovative" Water Quality Protection Strategies.
Proceedings from the Third Annual Eastern Regional Ground Water Conference.
National Water Well Association. Dublin, Ohio.
iwata, Y., W.E., Westlake, and F.A. Gunther. 1973. Varying Persistence of
Polychlorinated Biphenyls in Six California Soils Under Laboratory Conditions.
Bulletin of Environmental Contamination Toxicology. Vol. 9. Pp. 204-211.
Keely, J.R., and Tsang, C-F.Y. 1983. Velocity Plots and Capture Zones of Pumping
Centers for Ground-Water Investigations. Ground Water. Vol. 21. No. 6. Pp. 701-
714.
Keswick, B.H., and C.P. Gerba. 1980. Viruses in Groundwater. Environmental Science and
Technology. Vol.14. Pp. 1290-1297.
Kinniburgh, D.G., M.L. Jackson, and J.K. Sykes. 1976. Adsorption of Alkaline Earth,
Transition, and Heavy Metal Cations by Hydrous Oxide Gels of Iron and Aluminium.
Soil Science Society of America Journal. Vol. 40. Pp. 796-799.
Lattman, L.A., and R.R. Parizek. 1964. Relationship Between Fracture Traces and the
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73-91.
Matthess, G. 1987. Personal communication. Institute of Geology and Paleontology, Kiel
University, Kiel, West Germany.
Matthess, G., and A. Pekdeger. 1981. Survival and Transport of Pathogenic Bacteria and
Viruses in Ground Water. Geological-PaleOntological Institute of Kiel University,
Kiel, Federal Republic of Germany.
Matthess, G., S.S.D. Foster, and A.C. Skinner. 1985. Theoretical Background,
Hydrogeology and Practice of Groundwater Protection Zones. International
R-3
-------
Contributions to Hydrogeologv. Vol.6. UNESCO-IUGS. International Association
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Matthess, G., et al. 1985. Der Stofftransport im Grundwasser und die Wasserschutz-
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Verlag, Berlin, West Germany.
McDonald, M.G., and A.W. Harbaugh. 1984. A Modular Three-Dimesional Finite-
Difference Ground-Water Flow Model. USGS Open File Report 83-875.
,;: i . | ' ' j, "i; i i' , " ";;!n j. i ;, | , i,, ^ ' ,; ' | | nil" |
Meade, D.B., and R.3. Knowlton. 1985. Ground-Water Availability in Southeastern I
Connecticut, Cannondale Aquifer, Wilton Falls Pond Aquifer, Redding. Connecticut
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Milanovic, P.T. 1981. Karst Hvdrogeology. Water Resources Publications. 434 p.
Milde, G., K. Milde, P. Friesel, and M. Kiper. 1983. Basis and New Development of the
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International Conference on Groundwater and Man; Volume 2, Groundwater and the '
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Morrissey, D.3. 1987. Estimation of the Recharge Area Contributing Water to a Pumped
Well in a Giadal-Drift, River-Valley Aquifer. U.S. Geological Sunrey Openipile
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National Water Well Association. 1985. The Survey Says: Average Ground Water I
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leaky Aquifers. Water Resources Research. Vol." 5.' Pp. 8T7-829 ' ' ' ' ' ''''' "" -" '"' ' ' ' ''"'
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" !, '" " I i' : , : ' ' n " l!*1 |i M! »!»." .'! ' ii ' "',11, i '. '.y.,,,11'! "I,," il* "|!":i|.| < m'! A'l|||, i..!i!i Pi, I ,""l, i* A :l, ^ ' ,. i'1 ! ,i ' in '"i,,, * 'iHI! ,'! ,'H ''.,, , i1, || n ,.|i,'i, '.''f ,', |il|i , "; WMi 'Hpill I i, 'll!|
-------
Office of Ground-Water Protection, U.S. Environmental Protection Agency. 1987.
>;..' - -'' . ' - - , ,
Geophysical Techniques for Aquifer and Wellhead Protection Area Delineation.
> - -' ,'" '
** (unpublished draft report). ..
.
Office of Ground-Water Protection, U.S. Environmental Protection Agency. 1987.
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, " ' . - - '
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'' ' ' ' 1 '
, . . , , , . . .... . . ..
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'"' " ,! ;' ;", i '! ":[.'. _ ..... I
Vermont Department of Water Resources. 1985. Vermont Aquifer Protection Area
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!'!!«','i I1,;*«! if I'M'' hii^'fr
R-6
-------
Vorhees, M.L. 1985. User's Reference Guide for an Interactive Solute Transport Model.
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.%>-. . ' -.''-.
Walton, W.C. 1970. Groundwater Resource Evaluation. McGraw-Hill Book Co., New
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Walton, W.C. 1984. Practical Aspects of Ground Water Modeling. National Water Well
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; ^ '
Yates, M.V., S.R. Yates, A.W. Warrick, and C.P. Gerba. 1986. Predicting Virus Fate to
Determine Septic Tank Setback Distances Using Geostatistics. Report by Robert
S. Kerr Environmental Research Lab, Ada, Oklahoma.
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.»,; ; ' v .j -»:,;;:]"'}: ? jjpj1"!' ,7; fFfi'JFf '','' ';l '-|""!"'"''l"! !''! S'fJ" ;T' ' 2?'f'tl'
-------
V -; APPENDIX A
^ .;-: - . .. . -. . ;., ,- - "
WHPA DELINEATION APPROACHES
There are many examples of wellhead protection programs in the United States and
Europe. The structure and scope of these programs vary and reflect differing
demographic, political, and hydrogeologic conditions. Some states and municipalities have
developed wellhead protection as part of overall ground-water protection programs. The
main focus of these programs is the delineation* of wellhead protection areas that impose
land use controls to protect public water supply wells. [
A.1 STATE EXAMPLES
As part of EPA's research on wellhead protection, numerous state programs were
. ' " i " . '"..'' ' " V'
examined for technical aspects of their WHPA delineation effort. Six common methods
for WHPA delineation were identified, as well as many specific techniques for applying
them to local situations. These methods are listed together with associated criteria and 1
locations where they are applied.
The methods identified in Table A-l range in sophistication from those that can be
applied by non-technical professionals (e.g., arbitrary fixed radius) to very complex
methods that require technical specialists (e.gn numerical flow/transport models). The
following is a brief review of wellhead protection activities in four selected states. While
not exhaustive, this review gives an indication of existing State and local programs. [
A.1.1 State of Florida
Several of Florida's County governments have sophisticated ground-water protection
programs. The State has also passed amendments to Chapter 17-3 of the Florida
Administrative Code that establishes a State-wide wellhead protection program for
vulnerable aquifers. The program would require wellhead protection zones to restrict I
activities that could contaminate the ground water.
The proposed law establishes two protection zones around public drinking water
supplies that have an average daily withdrawal of at least 100,000 gallons of ground
water. The zones are defined as two concentric areas around the major public water
supply well(s) or well field(s) of 200 feet and 5 years ground-water travel time,
respectively. The 5-year TOT zone is defined with an analytical volumetric equation, a I
concept explained in Section 4 and Appendix B. \
A-l '"
' - ' I
-------
* " " ' - TABLE A-l ,
Y- .. ' : , " ;. . .";: , ! , r : !
t State WHPA Delineation Methodologies and Criteria
* "" " ' ' '; ' ' .'" , i " ' ' ,
,;. ' . '!i , : . I,", : .' .'';' .,".!' Jiiill ,-i V ''" (IS Sill1'* I'1'!:-"I.1 rlf.S. "!'! V,,.,,' ;M*;ii1,1r',. .'>,!'..', ' ;- ''-'] ..'li.iiTij*:.:::1:,1 'ai"1.'* .»!'! K
..!! "" , ' , I1.,'1' ' . ! ! i. \; - ".'V't-kit :S ;iil»;:l«l VI : ' ,.'.:tl( ''':'..*,'i1.1*.1': 7 .:, ,
, < if . , . .. ., .. I' ':: ;,' .';'...,,. ' ;,, (.;: £. i % y Hifiiiffiipi: i1 >,;;; ,-.',;, /;. }>.?- ^; ::;. .; ;>"'. \', ",. "^ Ill W.1K I
»' i ' . ' "''!, i. i» " 'i ' « i' " "'"" ' i ir.1 r,,' 'i.i,,:i',,,' ' "* !.IH> li l/!"«l!l!,:,1 , ,,,tin:.'i ,! , i "« m'f ' ^,1 i»! n M1 V/ , j"1'1" "^n'l"! i"i,,jwii uWt ifi 1';,,,llilil!llPilln!ll,!J I'llP
11 i ' ;«; , ' ' . ; ='.;, , K;,.::: . ^'..>:".'w: i'^Selected
Criteria Locations
Method ReUed on Where Used*
Arbitrary Fixed Radius Distance Nebraska
:_," " :I , '',' ., Fh>rida '^'J_[ ^ ', |
. ; ''.''.,''. ' Edgartown, MA
Duxbury, MA
Calculated Fixed Radius Distance: Florida
Time of Travel [
Simplified Variable Shapes Time of Travel Southern England
Drawdown
Analytical Flow Model
Geologic/Geomorphic
Numerical Flow/Transport
Model
Drawdown
Physical Features
Physical Features
Time of Travel
Drawdown
Cape Cod, MA
Duxbury, MA
Edgartown, MA
West Germany
Holland
Vermont
Connecticut
Duxbury, MA
Dade Co., FL
Broward Co., FL
Palm Beach, FL
or being considered
A-2
!, , 'M:' iiliED !'- I jl'l i.', 'h.
(Ill
milt
i
-------
Within^these concentric zones, discharges into the ground-water from stormwater
systems, underground storage facilities, underground product pipelines, and other sources
«*,'; . ' . . , '
are subject to varying degrees of control depending on their proximity to the wellhead. r
For example, the proposed law prohibits new .discharges and new installations within the
200-foot zone of protection. Within the 5-year zone of protection, new discharges from,
several types of facilities are subject to control and monitoring requirements. New
discharges of industrial wastes that contain hazardous constituents are prohibited and new
discharges of treated domestic waste effluents are allowed, provided a number of
conditions are met. F
A.1.2 Dade County, Florida
Dade County has developed a comprehensive wellhead protection program,
consisting of five elements: water management, water and wastewater treatment, land
use policy, environmental regulations and enforcement, and public awareness and
involvement. The program applies to an array of prohibitions, restrictions, permit .
requirements, land use tools, and management controls designed to protect all of Dade t
County's public water supply wells from contamination by the approximately 900
substances which the County has identified as hazardous. Features of the program
include:
' Delineation of recharge areas around wellfields using numerical computer
models with some in-field verification through monitoring of head F
relationships
Application of land-use restrictions within the recharge areas and the
designated wellfield protection zones
Public education programs
Establishment of water treatment programs 3
Development of water management and pollutant source control regulation.
Where the State of Florida defines two concentric protection zones, Dade County
establishes three. The inner two are delineated as 30- and 210-day TOT's. The outermost
zone is the larger of either a 500-day TOT or a 1-foot drawdown. The largest WHPA,
approximately 7 miles across, is associated with the Northwest Wellfield.
I
A-3
.-'' ' ' - ' ' '.' ''I
-------
Furthermore, Dade County maintains a computerized inventory of contaminant
^sources, and issues approximately 10,000 operating permits; per year to recognized,
nonresidential users within the delineated wellfield protection zones:
A.1.3 Massachusetts
The Commonwealth of Massachusetts does not require extensive WHP (except for
micrpbial threats), but does incorporate the concept as an option, and fosters it through
the Aquifer Land Acquisition Program (ALA). The goals of th« program are to help local
officials define the primary water recharge' areas around public water supply wells, to
work with local officials to properly address land uses within the recharge areas of these *
wells, and to reimburse eligible applicants for land acquired in key segments of recharge
areas for water supply protection purposes. The program encourages a mix of strategic
land acquisition and effective land use controls to achieve water well protection.
As part of the program, the Massachusetts Department of Environmental Quality
Engineering (DEQE) has defined three zones of contribution that compose the total I
recharge areas for a public well. Theoretically these three zones constitute the
geographic area in which land uses may affect the drinking water supply well.
Zone 1, the 400-foot radius or other designated area surrounding a water
supply well, must be in compliance with the DEQE Drinking Water Regulation
(310 CMR 22.00).
Zone II is the area of an aquifer that contributes water to a well under the
most severe recharge and pumping conditions that can be realistically
anticipated. It is bounded by the ground-water divides that result from
pumping the well, and by the edge of the aquifer with jess permeable materials
such as till and bedrock. At some locations, streams and lakes may form
recharge boundaries.
Zone III is that land area beyond the area of Zone II from which surface water
:: , . "' '. ,: [ /',, " " " III I I I i
and ground water drain into Zone II. The surface drainage area as determined
";. ", ' ...' '' i1:. '..'..
by topography is commonly coincident with the ground-water drainage area
i ,' i ' i. -i.". i ',;',, t j
and will be used to delineate Zone HI. In some locations, where surface and
ground-water drainage are not coincident, Zone III shall consist of both the
I. .. , . . > ,,:',! ,v. ,, ,.-' , . !. .i , . i ... , .1 |i' ... , , !.. .-,ii.-,,,i, M>
surface drainage and the ground-water drainage areas. |
V.
!:,! 11 I, ' ,''! ! ! , ',V» i! ' /I-, i?'. "...''li/1 ., J.-.'',,,l,''v. !'" .'.i'!1'11:'':!», !#',! Jui! mill, u '"'!', t!}! i ,:!:i! ft iJI
-------
The delineation and management of these three zones form the basis of an ALA
grant program^through which local governments compete to obtain funds from the State
to purchase land for water well protection purposes.
The Commonwealth has restricted the reimbursement for land purchases to Zone II. ' '
The rationale for this decision was that Zone II areas consist of relatively permeable
surficial deposits and represent the area of the municipality in which land uses have the
greatest potential for adversely impacting the local water wells(s). Zone I was eliminated
from the reimbursement scheme because under Massachusetts law the water supplier is
already required to control land use within the'400-foot radius surrounding the well. It r
should be noted, however, that land purchase is used primarily as an incentive to foster
participation in the program. Even with some of the small glacial aquifers in the State, a
minor portion of the land in the recharge area can be purchased. The key protection is
afforded by the adoption of ordinances, which the State requires for acceptance of ALA *
grants.
The program requires applicants to supply four major categories of information: I
aquifer/water supply information, land use information, resource protection plans, and
land acquisition information. Under the first category, Zones I, II, and III must be
delineated and mapped. Any pump tests or modeling used to delineate zones must be
documented.
Some level of land use information must be supplied for all three zones. All major
land, use activities such as commercial, residential, agricultural, and industrial uses in E
Zone II must be mapped and public transportation corridors identified. For areas in Zone
III, only those land use activities that pose significant threats to ground watersuch as
hazardous waste sites, surface impoundments, landfills, auto junkyards, underground
storage tanks, salt storage sheds, and sand and gravel operationsneed be documented.
11 > , ..'.,'.
Information on a water resources protection strategy that identifies existing and/or 3
proposed land use controls designed to protect the supplies must be included in the
submittal for the suggested land and/or easement .purchase. The State uses this
information to determine whether there is a sound basis for the locality acquiring the land
and whether the town will indeed be able to complete the land acquisition should an award
be granted.
A-5
1
-------
All applications are ranked and prioritized based on two major criteria: the value
and use df'the resource and the degree of resource protection thai can be ^xp^^ |,.om
%ws proposed water protection strategy. .
A.1.4 Vermont " . ^ " .; '. ,s
The State of ..Vermont is developing a Statewide wellhead protection program. As
part of this, the Agency for Environmental Conservation (AEC) is developing regulations
that will be used to map the cones of influence, the primary recharge areas, and the
", i . ,,' ' -if j .: ,. 'i1 .;,;.'';w'.r""<;\ n i i i « i
secondary recharge areas of water wells in Vermont. These maps will be used by AEC and
other regulatory agencies in their permitting activities. f
One set of tools currently available to State regulatory agencies making
management decisions are the existing maps of recharge areas or Aquifer Protection
Areas that were delineated in the Vermont Aquifer Protection Area (APA) Project in the
1970's. The project resulted in 209 individual APA's located in 10* Vermont towns. An
APA is defined as the land surface area that encompasses; the recharge, collection, _
transmission, and storage zones for a town's well or spring. i
Eight categories of APA's were delineated based on hydrogeologic factors:
* Wells in unconfinedand leaky unconsolidatedaquifers with available
, , " J : S l"« , ' ' I' , , ,' | '"', , , , ', i' i 'in1;']:, ., I .!,'!'': i1' 1 ]," \\f 11} ,1'ijr' ii,Sf 'i||n|i I,,,, , i » | i', i; Tiln , ,|;,,, , i'» i ,|,: , m, ,'' . ,i ' ; :;,;! , ,,,., |i, ] ; ', - »,]];-;;»,;,- >,';.;;;;]], ;:;|]
engineering pump tests
Wells in unconfined and leaky unconsolidated ac[uifers without engineering
pump tests ;
Wells in confined unconsolidated aquifers
"'::| 'il ' "l'1 ", ':' ', '.,! '' ' ' ' I . II I I I -I
Bedrock1 wells, using an infiltration model
Bedrock wells, using a leakage model
Springs in unconsolidated material and at the interface between |
unconsolidated material and bedrock, with high relief in the upgradient
'"' i1 ' ,. ' , ' "',''' ii ; ""',.', -I , i » in i| n i i n I i IN fi 11 i in
direction
Springs in unconsolidated material and at the interface between
unconsolidated material and bedrock, with low relief in the upgradient
direction
1
Springs emanating from bedrock.
A-6
1
-------
There are no .regulations associated with mapped APA's, but Vermont's existing regulatory _
programs use WPA's to flag areas needing special consideration during the review process
on development applications. .
A.2 EUROPEAN DELINEATION APPROACHES
At least 11 European countries have developed ground-water protection programs
comparable to the WHPA concept (Figure A-l). The European Community (EC) Directive
, on the Protection of Groundwater Against Pollution Caused by Certain Dangerous
Substances (80/63/EC), issued in December 1979# requires member states to protect (by
law, regulation, and administrative provision) all usable ground waters against direct/and [
indirect discharges of certain listed substances.. However, ground-water protection
programs in Europe significantly predate this directive. Development of policies to
1 ', " ~ ' '* . ' '
prevent movement of contaminants into the subsurface environment began in the last
century, through the most important laws and regulations date to the 1950's, West
Germany and the Netherlands have the mo$t extensive experience in this area, and their
programs are described here. . [
European programs generally involve the delineation of at least three zones of
protection, defined by distance and/or TOT. These are more or less concentric rings,
starting with the area immediately around the wellhead. Typically, an outermost zone is
drawn to the recharge area boundary. Within these zones, restrictions are imposed on a
number of activities including, but not limited to do, waste disposal sites, the transport
and storage of hazardous chemicals, waste water disposal, and the application of
teachable pesticides. The degree of restriction decreases as the distance from the
wellhead increases.
A.2.1 The Netherlands
The Netherlands delineates three or more zones of protection, based on aquifer type
(van Waegeningh, 1985 and 1987). These zones are generally defined using analytical *
models whose applications require some degree of technical expertise. When the effort '
began, simple fixed-radius approaches were used. Analytical methods are now the most
widespread approach. Numerical models for WHPA assessment around key wells are
increasingly common, though analytical methods are still used for the areas closest to the
pumping wells (Heij, 1987). The first protective area lies immediately around the
wellhead, up to 30 meters away, and is purchased by the water authority. The second I
zone is defined by a 60-day TOT, and is designed to protecj the well from microbial
A-7
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contaminants. There is then a >ater protection" area, roughly comparable to the WHPA
boundaries. This is subdivided into areas within 10-year and 25-year TOT, roughly 800 and
1,200 meters from the well in the Netherlands. An outermost zone, the "far recharge
area," is delineated to the outer boundary of the well recharge area.
A^2 West Germany ' ,
The West German wellhead protection strategy, though it was developed first, is
quite comparable to the Dutch approach, and also depends largely on analytical solutions.
Zone I covers the immediate wellhead area, to a radius of 10 to 100 meters. Zone II is
delineated by a 50-day TOT. The "water protection area," Zone III, is subdivided into
inner and outer areas. Zone, m A extends up to 2 kilometers from the well (if the aquifer
boundaries are more distant). Zone HI B extends to the outer boundary of the recharge
area. Since many aquifers are contained within sedimentary basins, hydrogeologic
mapping and numerical simulation procedures are used in a basin-by-basin approach.
I
A-9
-------
I
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APPENDIX B A
' ' V a J ' ' .',.. '
^ . COMPARATIVE ANALYSIS
' *' ' ' . ' ' ' ''.''..
Comparative analyses of WHPA methods were presented in Chapter ft as a valuable I
approach for State wellhead protection. This appendix provides examples of comparative
analyses of method applications for wells in Massachusetts, southern Florida, Colorado,
and Connecticut. Each comparative analysis focused on an existing or proposed well or .
= well field. The sites chosen all had some WHPA delineation already in place or in process.
The State, county, or locality that performed WHPA delineation utilized the method of its
choice. Criteria and criteria thresholds varied, depending on specific program goals. To i
complete these analyses as method comparisons, additional approaches Were applied. The
four basic methods used were: .
Calculated fixed radius (CFR), based on the State of Florida's approach
Analytical methods
Uniform flow model 1
u ' . ,
Strahler prism model
Numerical model.
The comparative analyses present examples of delineation method selections as they
might be encountered in "real world" situations. The analyses compared WHPA's
' ' ' N' ' ' ' ' ' f
delineated by different methods for a single well or well field and one set of *
hydrogeologic parameters. Direct comparison of areas resulting from each of these
methods should be made with a understanding that the areas being compared may
represent different types of zones. For example, as discussed in Chapter 4, the area
resulting from applying the uniform flow model is the zone of contribution of the well,
whereas areas resulting from application of numerical models (particularly as presented in _
this appendix) yield zones of influence or zones of transport. These comparisons are based *
on the assumption that the numerical model yields the most "accurate" delineations of
WHPA's. Therefore, comparisons use the WHPA resulting from the numerical methods as
the standard. ,
In each case study, different delineation methods were used for individual well(s)
using the same or very similar hydrogeologic parameters. The delineation methods used in I
the comparative analysis and the type of data required by each method are shown in
B-l
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B-3
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B.1 CAPE COD, MASSACHUSETTS
B.1.1 Hydrogeology of Study Area ..
"The principal water-bearing formations on Cape Cod, predominantly unconsolidated 1
sands and gravels, are parts of a coastal complex of end moraines and outwash plains. The
study area's major geologic formations include the Mashpee pitted outwash plain deposits,
the Buzzards Bay moraine deposits, and the Buzzards Bay outwash deposits. The majority
of the study area is situated over the Mashpee pitted outwash plain. The surf icial outwash
deposits are composed of fluvially-bedded gravels and gravelly sands deposited following
recession of the Cape Cod Bay and Buzzards Bay lobes. At depth, silty sands and till have F
also been identified. Recharge to the ground-water system is provided primarily through
precipitation during the winter and spring seasons. Typicallyj the study area averages 43
inches of precipitation annually, with reported estimates of annual recharge to the
ground-water system between 12 and 24 inches. Remaining precipitation is lost through
evapotranspirationj a small portion is lost through direct runoff to streams, ponds, and
swamps. I
v MI t - ,. ... . .. .' I . , ... V
B.1.2 Method Application
WHPA delineation methods used in the Cape Cod comparative analysis included (1) a
calculated fixed radius method, (2) two analytical methods (tfie uniform flow model and
the Strahler prism model), and (3) a numerical model. Comparative analyses of delineated
.areas were done for two wells. ' f
Calculated Fixed Radius. The calculated fixed radius (CFR) method used was the Florida
Department of Environmental Resources volumetric flow equation (De Han, 1986).
WHPA's delineated with the CFR equation were delineated based on travel-time criteria
of 10,25, and 50 years.
Analytical Methods. The first analytical method used was the uniform flow model (Tpdd, j»
1980) (see Chapter 4). The model was used to estimate |he downgradient and lateral
extent of the WHPA's. The upgradient boundaries for these examples were determined
using 10-, 25-, and 50-year TOT distances determined from a travel time equation used in v
i i i , ,,,,,,, : , ',, , , , , I,,, ,, t , , I,, i
England (see Chapter 4). The second analytical method applied, the Strahler prism model
(Horsley, 1983) combines analytical and graphical techniques (Chapter 4). With this
method, distances to downgradient and upgradient WHPA boundaries were determined £
using distance-drawdown curves, and a model developed for ground-water flow on Cape
Cod. The WHPA's were then delineated as the areas supplying surface recharge to the
-------
pumping wells, with the calculated downgradient and upgradient bounds being the
delineated area of recharge.
Numerical Method. WHPA's delineated with the numerical model were, obtained from a
1985 study in which time-dependent (10-, 25-, and 50-year) ZOC's were delineated for six '
wells in the area (Camp, Dresser, and McKee, 1986), using a three-dimensional finite
element model for ground-water flow and transport.
B.1.3 Data Requirements
, \ . , '
Data used in the CFR and analytical methods are listed in Table B-l. These
f,
_
at best global approximations to the spatially varying parameters. In contrast, the
numerical model can take into account aquifer heterogeneities and the impact of flow
boundaries (such as lakes and streams) in the area of WHPA delineation. The spatially
changing parameters in the model are described in the original report by CDM (1986).
B.1.4 Comparison of Resulting WHPA's *
Figures B-2 through B-7 show the delineated WHPA's for the two wells on Cape Cod
using the CFR equation, the numerical model, the uniform flow model, and the Strahler
prism model. For well 1 (Figures B-2 through B-*) the uniform flow model provided the
largest area of coverage for TOT's of 10, 25, and 50 years. The Strahler prism model
provided less coverage than the numerical model for a 50-year TOT, although the overlap
with the numerical model was considerable. In several comparisons, the CFR equation F
was found to delineate the smallest area, and is therefore the least accurate of the
methods. In addition, the CFR equation was less accurate as the criteria threshold
increased. These deviations from the standard WHPA can be attributed to the fact that
the CFR equation does not account for conditions of a sloping water table (i.e., gradient is
not one of the parameters in the equation).
' ' ' '' - ' ' ' ' ' -B
In the case of well 2, the uniform flow model provided results comparable to the "
numerical model, as is shown in Figures B-5 through B-7. The relative accuracy of the.
results is apparently due to the smaller effect of flow boundaries (such as surf ace water
bodies) on ground water near the well, the uniform flow model provided the largest area
of coverage, followed by the Strahler method. Both of these methods, provided a larger
area of coverage than the numerical model, with a high degree of commonality. As with .
well 1, the CFR equation was found to provide the least area, although it relatively better
for the smaller TOT's. This probably reflects the regional slope of the water table.
B-5
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Figure B-2
WHPA Comparative Analysis, Example lor
Well # 1 Cape Cod, MA, 10-Year TOT
ANALYTICAL MODEL
CALCULATED FIXED RADIUS
EQUATION
I
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B-7
1
-------
%t
Figure B-3 1
WHPA Comparative Analysis, Example for
Well #1 Cape Cod, MA, 25- Year TOT
V
*"» NUMERICAL MODEL
MiMBMBB ANALVTICAI MnnPt
4,^«/ /**V0.VH'
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Figure B-4
WHPA Comparative Analysis, Example for
Well #1 Cape Cod, MA, 50-Year TOT
NUMERICAL MODEL
ANALYTICAL MODEL
STRAHLER PRISM MODEL
CALCULATED FIXED RADIUS
EQUATION
WILDLIFE ' /~7"
I
B-9
-------
T t
Figure B-5
WHPA Comparative Analysis Example for
Well #2 Cape Cod, MA 10 Year TOT
SCALE
NUMERICAL MODEL
ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
B-10
E
I
-------
Figure B-6
WHPA Comparative Analysis Example for
% Well #2 Cape Cod, MA 25^Year TOT
SCALE
NUMERICAL MODEL
ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
B-ll
-------
Figure B-7
WHPA Comparative Analysis Example for
Well #2 Cape Cod, MA, 50-Year TOT
SCALE
NUMERICAL MODEL
mmm ANALYTICAL MODEL
MI SYRAHLER PRISM MODEL
» CALCULATED FIXED
RADIUS EQUATION
f
f
B-12
-------
SOUTHERN FLORIDA
1 . ' ' V.' . ' ' .- ', ' '' '
B.2.1 Hydrogeology of Study Area
Virtually all of southeast Florida's residential, commercial, and industrial water is I
supplied by hundreds of public and private wells that tap the Biscayne Aquifer. The top of
this aquifer lies just 2 to 5 feet beneath the ground surface, and it is recharged by
rainfall, streams, canals, and lakes. Approximately 80 to 150 feet deep in place, the
aquifer thins along the western boundaries of the study area. The lithology is largely
permeable limestones and sandstones. Ground-water flow in the aquifer is primarily
horizontal and eastward, toward the sea. f
B.2.2 Method Application , .
Delineation methods used in the Southern Florida comparative analysis were the
CFR equation, an analytical model, and a numerical model., The comparison was done for
a well field consisting of three wells. WHPA's were delineated for all methods based on
TOT criteria thresholds of 30, 210, and 500 days (the County's WHPA criteria). .
Calculated Fixed Radius. The CFR equation used was Florida's volumetric equation (see
Chapter 4).
Analytical Method. The analytical technique applied was the uniform flow model (Todd,
1980). For modeling purposes, the well field was analyzed as a single well.
Numerical Model. The numerical model used was a three-dimensional finite difference «
model (McDonald and Harbaugh, 1984) in which WHPA's were delineated based upon
drawdown and TOT criteria thresholds (Dames & Moore, 1986).
B.2.3 Data Requirements , '
Data requirements for each method are listed in Figure B-l. Similar parameters
were used as input in each method; they were obtained from a report on the. numerical
modeling study and are shown in Table B-l. Figure B-l shows that not all hydrogeologic *
parameters were used for each method of delineation. The numerical model required the
most data and was assumed to provide the most accurate results. In addition, this method
was the only method that could take into account the impacts of flow boundaries (such as
canals) in the area of WHPA delineation.
'''. "'.' ' ''. * ' . . .-':' I
B-13
. . "'-'". ..''... '" .: i
-------
Comparison of Resulting WHPA's
t.- ' - ' ' ' ' .' "' ': .;.'-'" ' ":
The*VCFR approach provided a moderate overlap with and less coverage than the
numerical model for TOT's of 30, 210, arid 500 days, as shown In Figures B-8 through B-10.
' " Ml ' ' ll I ' ''l «" ,,M , ' ",. ' |,"h ,. I ' I ',!' " 7 'l ' ' ,I,P 'I ..I ^K : : < . I , ,1 i ,111 **
For this well field, no surface-water flow boundary features are located near the well
field that affect ground-water flow, although many canals that could have such effects
are located in well-field areas in southern Florida. The relatively flat water-table slope
in this area is another factor critical to the closer match among methods than in the
latter Cape Cod example.
I
E
i
-------
V.
Figure B-8
WHPA Comparative Analysis
Example from Florida, 30-Day TOT
LEGEND
FDER VOLUMETRIC EQUATION
^ UNIFORM FLOW MODEL
NUMERICAL MODEL
WELL
0 2000 Feet
SeeEnlarged Area
se and Legend
I .ENLARGED AREA
/ / ////I
,f
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B-15
-------
Figure B-9
WHPA Comparative Analysis
Example from Florida, 210-Day TOT
FOER VOLUMETRIC EQUATION
UNIFORM FLOW MODEL
NUMERICAL MODEL
See Enlarged
and Legend
I ENLARGED AREA
" / / ffin
'
II-
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B-16
-------
Figure B-10
WHPA Comparative Analysis
Example from Florida, 500-Day TOT
ENLARGED AREA
S^R, -31 *
f 7'See Enlarged Area
N ? and Legend
LEGEND
FDER VOLUMETRIC EQUATION
UNIFORM FLOW MODEL
NUMERICAL MODEL
f
I
B-17
-------
CENTRAL COLORADO
: ' ;,.,, ' i;. ' : IJ" ' ( :' ';; ;-"/ ', .;''. " .' '' !,' .: t';"'l>J
Th**e COP^tive a^y*** *>r *« State of Colorado,are based on unpublished
Information obtained from a joint effort by EPA^Region vra, theColoradoDepartment of
Health, and the U.S. G«>lpgical Survey. As part of of this pUot^roJejrt effort, WHPA's
WC1t dlineate!i -^H - -^"^W^Y ^ travel-time criteria and the application of an
analytical method (the uniform flow equations by Todd, 1980)for the purpose of
determining zones of contribution to wells used by the Cherokee Water District.
" i..1 " . ' ; ;vt! ::* '.,'," ".: ).;. - ." ['',-"' -::/.'[ 'i I , j.'i^tV.?.'" *f""
B3.1' Hydrogeology of Study Area ' ' ' , '
Currently, the Cherokee Water District witodraws watec from the Black Squirrel '
Aquifer and exports it to suburbs east of Colorado Springs and to the Falcon Air Fprce
Station. The aquifer is located about 25 miles east of Colorado Springs. The setting is
largely rural, and toe wells are subject to contamination from agricultural sources. The
Black Squirrel basin is drained by Black Squirrel Creek and its tributaries. Streams iq the
area are intermittent, flowing only in response to thunderstorms, snowmelt, and prolonged
rainfall. All streams are ephemeral and do not provide dependable sources of, water. The '
basin is underlain by an alluvial aquifer and the four bedrock aquifers of the Denver Basin.
The Black Squirrel Creek aquifer is approximately 100 square miles in extent (at a
saturated thickness of at least 60 feet) and ..receives surfacer,Scharge from an area of
approximately 350 square miles. Average annual recharge is estimated to be 0.6 to 1.3
inches. Recharge to the alluvial aquifer is about 9,000 aore^i:eet per year, as infiltration [
of precipitation and upward leakage from bedrock aquifers. Natural discharge is
estimated to be equally divided between evapotranspiration from ground water and
ground-water outflow at toe downgradient end of the basin.
, ' i
1 !,i,: 'i, ' .. in " , i ^ i " t ,i 'i , , i. , !T , | » . »...,; ,'!! ", : ji ii',.!i.i i1 in i "Jim i", i>i|i i!iii,;;'|i ; ,, i,|,, ,,:[» ,i;,; i,, I,:,|HM, i1-: vj", ,,i; ,'.'.,' ., f " ':,"( r A iiiK^W1 *.'iWhilim'VMi.jiii.ii
The source of water to the wells tapping toe alluvial aquifer is primarily from
aquifer storage. Therefore, ground-water withdrawals have lowered toe water table and
reduced toe discharge to evapotranspiration. Changes in ground-water outflow due to §
pumping have been small. Changes in leakage from bedrock aquifers are not known, but
are assumed to be smalL Withdrawals from ground water have been about 11,000 acre-
feet per year, 8,000 for agricultural consumption and 3,000 for municipal use. The source
of this water has been storage in the alluvial aquifer^andi. salvage of ground water that
would have been los| to evapotranspiration. Obtaining accurate Jnowledge of sources and ,
losses, affecting toe^ aquifer is complied by wells'^''^t/'^ ^used".',,
seasonally for agricultural irrigation. " "'"''" "'" ' '" ""' "' "'
::iiin""!k':i;irii I'llpUnii i
?, \ r'ii!.i 'I,1:
"''.i:1!'!11". "fi.;,11'1! i1""!
\ ' .,.',' " '," y-" * ;n..i. ,1'K1*1'- ,l If1".. .'""','.';;, " --.A ." K:'|I :', '[^r.'^.iff.j1 ^ ft'i; Ti'vK
B-18
-------
B.3.2 Method Application
'.--' '\-i- ' " " ' '-.'' '. ''-.
WHPA ^delineation methods used in the Colorado comparative analysis included
V ' ' ' ' ' i - * '
calculated fixed radius and analytical methods. A comparative analysis was done for one
well. I
Calculated Fixed Radius. The calculated fixed radius (CFR) method used was the Florida
volumetric equation (see Chapter 4). WHPA's were delineated for travel times of 1 and 5
years.
Analytical Method. The analytical method applied, the uniform flow model (Todd, 1980),
was used to estimate the downgradient and lateral envelope of the WHPA. The upgradient f
boundaries were determined using 1-, 5-, and 20-year TOT distances determined by the
regional ground-water flow velocity, determined from non-pumping water-level maps for
the area.
Two approaches were used tp apply the uniform flow model. The first approach was
described in Chapter 4. In the second approach, the uniform model was applied by the I
USGS in a slightly different way. The ZOC to the pumping well was assumed to reach its *
maximum calculated width at the well rather than at some distance upgradient from the
well, as assumed with the first approach. Also, a buffer zone was added beyond the
calculated ZOC for the well. The buffer zone was computed by doubling the distance
from the well to the downgradient null point 2 (X^) and from the well tp the ZOC
boundary 2 (YL> (Figure 4-7). The buffer zone was extended outward from the calculated .
ZOC boundary at the well by 50 feet for every 100 feet of distance upgradient from the
well.
') , , I '
B.3.3 Data Requirements
Data used in the CFR and analytical methods for the Colorado comparative analysis
are listed in Table B-l. The parameters shown in Table B-l were obtained from,USGS
studies in the area and parameters reflect conditions around the wells.
B.3.4 Comparison of Resulting WHPA's
Figures B-ll through B-13 show the delineated WHPA's for the well in Colorado
using the CFR and the two approaches using the uniform flow model. For the 1-year TOT
threshold, the WHPA's delineated using the different methods were relatively similar. For
the 5-year TOT, however, there is less similarity among WHPA's delineated using the I
B-19
-------
various methods- Differences ^"e JB«!y. due to the fact that the CFR does not
Incorporate the regional slope of the water table, as the analytical methods do.
> ,, :.,. . . ... . '.-..: : (. , . ...
4 For the 20-year TOT distances,, only the two approaches used in the analytical
methods are compared. The WHPA's delineated with the two methods are relatively
similar, though the USGS-delineated WHPA is wider near the well. With the addition of
the buffer 7»ne in |he USGS approach, however, the: resulting WHPA's are substantially
larger. Since the effects of the irrigation wells and irrigation flow returns have not been
included in this comparative analysis, the addition of a buffer zone to the analytically
determined WHPA's appears to be a reasonably conservative approach.
I
B-20
-------
Figure B-ll
WHPA Comparative Analysis, Example from
Colorado, 1-Year TOT
> V
UNIFORM FLOW MODEL
UNIFORM FLOW MODEL
(DELINEATED BY U.S.G.S.)
FDER VOLUMETRIC EQUATION
WELL
-------
Figure B-12
WHPA Comparative Analysis, Example from
Colorado, 5-Year TOT
2000 Feet
UNIFORM FLOW MODEL
UNIFORM FLOW MODEL
(DELINEATED BY U.S.G.S.)
FDE-R VOLUMETRIC EQUATION
WELL
«; /'v.MiS^&nljittL&issSsiM.i'li'J
-il
-------
Figure B-13
WHPA Comparative Analysis, Example from
Colorado, 20-Year TOT and Buffer Zone
2000 Feet
SCALE
_ UNIFORM FLOW MODEL
... UNIFORM FLOW MODEL
(DELINEATED BY U.S.G.S.)
^~ BUFFER ZONE
(DELINEATED BY U.S.G.S.)
WELL _j
E
B-23
I
-------
I
B.* SOUTHWESTERN CONNECTICUT
^ In 11985, the Connecticut Department of Environmental Protection, in cooperation
with the U.S. Geological Survey, conducted a comprehensive study of the ground-water \
resources of the Cannondale Aquifer in southwestern Connecticut (Meade and Knowlton, ,
1985). That study served as the basis and major source: of information for the
comparative analysis presented in this section. The Cannondalle Aquifer is located in the «
town of Wilton, which is approximately 6 miles north of the city* of Norwalk.
B.t.1 Hydrogeology of the Study Area ,<
The Norwalk River basin is very similar, both geologically and hydrologically, to
most of the river basins in southwestern Connecticut. The basin is underlain by
crystalline bedrock, discontinuously covered by unconsolidated sand and gravel stratified
drift deposits. These deposits exhibit a capacity to store and transmit water greater than
does the underlying crystalline bedrock. This capacity of the deposits to transmit water,
along with their hydraulic connection to the streams flowing through valleys containing
the stratified drift deposits, make such stream-valley systems the most prolific type of
aquifer for public water supplies in southwestern Connecticut.
The Cannondale Aquifer consists of stratified drift deposits covering a land surface
area of approximately 0.32 square mile, with a maximum thickness of 140 feet.
Approximately 30 percent (0.15 square mile) of the aquifer has a saturated thickness of
less than 10 feet. The Norwalk River runs north-south through the aquifer for a length of
about 7,000 feet and a width ranging from 5 to 50 feet.
Precipitation, falling on both the stratified drift deposits and the surrounding till-
bedrock uplands, is the major source of water that recharges the stratified drift aquifers.
Water derived from both rainfall and snow melt directly on the stratified drift deposits
seeps into the ground and percolates through the unsaturaited zone where losses to
evapotranspiration and soil moisture occur. The remainder of the water reaches the
water table and is incorporated into the ground-water flow system. Very little water is
lost from the stratified drift deposits as a result of overland runoff.
B.4.2 Method Application
Delineation methods used in the Connecticut comparative analysis were a calculated
fixed radius equation, an analytical model, and a numerical model, the comparison was
done for a well field consisting of two wells.
: f'h ,:., '"""iiijW'i!,",, "ft,
-------
Calculated Fixed Radius. The calculated fixed radius method used was the Florida
volumetric equation (see Chapter 4). WHPA's were delineated for TOT's of 1 and 5 years. .
f - - , - . . . - - - ,
Analytical Method. The analytical model used to estimate the downgradient and lateral [
extents of the WHPA was the uniform flow model (Todd, 1980). The upgradient
boundaries were determined from a travel-time equation used in England (see Chapter 4).
WHPA's were delineated for TOPs of 1 and 5 years. The two wells were treated as a
'.. ' ' ' '
single well in the uniform flow model application.
Numerical Model. The numerical model used was a two-dimensional finite-difference
ground-water flow model (Trescott, et al.y 1976) applied by the USGS (Meade and i
Knowlton, 1985). WHPA's were delineated based upon flow boundaries defining the ZOC
to a pumping well and drawdown criteria defining the ZOI.
B.4.3 Data Requirements ~
Parameters used in the Connecticut comparative analysis are shown in Table B-l.
The parameters used were obtained from a report on the numerical modeling study (Meade |
and Knowlton, 1985). In this study, extensive data collection was done to characterize
hydrogeologic parameters. Parameters were found to vary throughout the study area and
the parameters used in the comparative analysis were those closest to the wells for which
the WHPA's were delineated.
B.4.4 Comparison of Resulting WHPA's
. '-.' ... E
Figures B-14 and B-15 show the resulting WHPA's for the two wells in Connecticut
delineated with the CFR method, analytical model, and numerical model. For a TOT of 1
year (Figure B-l4) results of the CFR and analytical model are relatively similar.
However, WHPA's delineated with these methods are smaller than those delineated with
the numerical model using flow boundaries and drawdown as criteria.
For the 5-year TOT's, the CFR and analytical model provide greater variation in k
results. The larger difference is likely due to the effects of regional ground-water
gradients. The CFR and analytical model also provide results geometrically different
from the numerical model. This is probably because the CFR and analytical models do not
account for flow boundaries, such as streams and geologic contacts, that significantly
affect ground water flowing to this well field. .
i
B-25
-------
Figure B-14
WHPA Comparative Analysis, Example from
Connecticut, 1-Year TOT
2000 Fttt
I
SCALE
M^^MBMI NUMERICAL MODEL,
HYDROGEOLOGIC
MAPPING (ZOI AND ZOO
i > ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
B-26
1
-------
Figure B-15
WHPA Comparative Analysis, Example from
% Connecticut, 5-Year TOT
2000 Feet
SCALE
mmm NUMERICAL MODEL,
HYDROGEOLOGIC
MAPPING (ZOI AND ZOO
' ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
i
B-27
e
-------
B.5 SUMMARY AND CONCLUSION
1 * V. ' " " J" ' ' '
Different methods can provide significantly different levels of accuracy for WHPA
^delineation around a well field. This is'particularly true if surf ace. water affects ground-
water flow or heterogeneous hydrogeologic conditions exist. The process of deciding on a
method for delineating WHPA*s in an area should include consideration of the validity of
the method under existing hydrogeologic conditions in the area (including flow boundaries
and gradients), the desired accuracy, and the cost/implementation tradeoffs in moving
,, ,, ,
from relatively simple to more comprehensive methodologies. Comparative analyses have
: i , ' ., j " v ,, i i " ,*..,;- -;nj i,"1:«!";,"' i1,,;'!"" -,i« IR :;; W;iiV::'i :r .;: ,'! ; t.fv .;, ',";, - :,?;'::,, «":, \ i ',.,,v;,:'..'.
also been shown useful for evaluating criteria and criteria thresholds for consideration in
State WHP programs.
The methodology and nomenclature used to evaluate the comparative analyses are
shown in. Figure B-16. Table B-2 is a summary of the comparative analyses for the four
different localities. The table shows the results of each method and considers the percent
of mutual coverage, under-protection relative to the largest area, and erroneous coverage
' . ' 'Hi ' ' " '' !' "" '! , - " ii !', '',"«" "":",','. v DM!1 '' I1!' ',, I" " j
relative to the method considered to be the most accurate. Results are shown for a 5-
year TOT for the Connecticut example, a 500-day TOT for the''Florida "example'," and a 50-
year TOT for the Cape Cod example. Because WHPA's delineated by numerical modeling
were not available as a standard for comparison for the Colorado example, its results are
not shown in Table B-2.
For the Connecticut comparative analysis, the CFR model covered the entire
numerically delineated WHPA and did not under-protect. However, this method provided
considerable erroneous coverage when compared with the numerically delineated WHPA.
For this example, the low accuracy was due to the effects of flow boundaries and
significant regional ground-water gradients not incorporated in the CFR model.
For the analytical model in the Connecticut example, the method covered nearly all
of the numerically delineated WHPA and provided relatively little under-protection.
However, as with the CFR model, significant erroneous coverage was due to the effects
of flow boundaries.
For the Florida comparative analysis, the WHPA delineated with the CFR model was
about half the size of the numerically generated WHPA and ho erroneous coverage was
provided. The analytically generated WHPA, however, covered all of the numerically
generated WHPA and provided only a slight amount of erroneous protection. For tills
"1
B-28
-------
V
Figure B-16
Comparative Analysis Nomenclature
Percent mutual coverage = (Am/Altd) X 100%
Percent under protection = (Au/A,td) X 100%
Percent erroneous coverage = ( 7 *" )X 100%
V "ltd /
WHERE:
A«d = Area given by the method used as the standard for comparisons.
Ae - Area given by method to be evaluated.
An, = Area mutually covered by both methods.
Au = Area not covered by method being evaluated.
B-29
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B-30
-------
comparative analysis, the CFR and analytical models provided more accurate protection
than in the%£onnecticut example because Water table gradients are lower and flow
boundaries are generally absent.
For the Massachusetts comparative analysis, the CFR equation provided a relatively
high degree of both under-protection and erroneous coverage. The analytical model, in
contrast, provided a high degree of mutual coverage and a small amount of under-
protection. However, this method provided a relatively large area of erroneous coverage.
The differences in the delineated WHPA's for this comparison were due to the presence of
significant regional ground-water gradients and' the presence of hydrologic boundaries,
including ponds and streams.
I
I
B-31
-------
Ill Hill illlilllllllllllilll
In 1 hi i '
in IK ' in
-------
APPENDIX C
H- GLOSSARY
»*.''' ' ' ; . '-._..''-
*",'"' . - ' m
The purpose of this Glossary is to provide a list of terms commonly used by I
hydrogeologists, as well as some specific terms used in ground-water contamination
assessments and wellhead protection. The definitions provided in this glossary are not
* necessarily endorsed by EPA nor are they to be viewed as suggested language for
regulatory purposes. Not all of these terms appear in this document. Numbers in
parentheses indicate the reference sources for most of the hydrogeologic terms; the major
source was (1). Some adaptations of the definitions in these published references is t
included.
GLOSSARY REFERENCES
(1) Subsurface-Water Glossary Working Group. 1987. Subsurface-water flow and
solute transportglossary of selected terms. Ground-Water Subcommittee, m
Interagency Advisory Committee on Water Data. (Unpublished review draft). .,'*
(2) Driscoll, F. G. 1986. Groundwater and Wells. Second Edition, 3ohnson
Division, St. Paul, Minnesota. ;
(3) Fetter, C. W., 1980. Applied Hydrogeology. Charles E. Merill Publishing
Company, Columbus, Ohio.
: (4) Bates, R. L. and 3. A. 3ackson. Glossary of Geology. American Geological
Institute, Falls Church, Virginia.
(5) Laney, R. L., and C. B. Davidson. 1986. Aquifer Nomenclature Guidelines.
U.S. Geological Survey Open File Report 86-534.
(6) American Society of Civil Engineers. 1985. Ground Water Management.
Manual 40. *
GLOSSARY
* Absorption. The process by which substances in gaseous, liquid, or solid form dissolve or
mix with other substances (6).
/"Adsorption. Adherence of ions or molecules in solution to the surface of solids (1). The I
assimilation of gas, vapor, or dissolved matter by the surface of a solid (2). The
C-l
-------
attraction and adhesion of a layer of ions from an aqueous solution to the solid mineral
surfaces; with which it is in contact (3).
tAdvection. The process whereby solutes are transported by the .bulk mass of flowing
fluid (1). The process by which solutes are transported by the bulk motion of the flowing
ground water (2).
i !!,|'' / »',.!,<, I", ii1,'1 " I" ill if,!
Alluvial. Pertaining to or composed of alluvium or deposited by a stream or running
water (2).
. > ''!,, I 1
Alluvium. A general term for clay, silt,, and sand, gravel, or similar, unconsolidated
material deposited during comparatively recent geologic time by a stream or other body
of running water as a sorted or semisorted sediment in the bed of the stream or oo Us,
floodplain or delta, or as a cone or fan at the base of a mountain slope (2).
, HI, »' " i |i , , i I,. , i' ,'!, , '', ,' ',1 !»'''ii' l,i|!l'il"ii|:''' , 'I '! "f ' ' 'i i, ! ' V ' \\ \ ', ,"' ,'!' I , ' ."I'I.1:1
Analytical model. A model that provides approximate or exact solutions to simplified
, , ' i ,ir . ' '. .''I : ,; '. ! !,;":' ! ::;': *,! v";;; ' m- i(j'M^;.,,L/:. i-nrv, V"i*;v:.'.." ::"<...".." -,... ,.. ,-
forms of the differential equations for water movement and solute transport. Analytical
" '. '"ill ' ' ''','!, V..' !' ' '' ' " .':'.','' f.f "'ii "' .,(,' "' H'.'&'.'liTJ1!'1^ '' ,' . , . ', . !-"ll " ', Vj ( ;, ,..,;. r
models can generally be solved with calculations or computers.
Anisotropy. The condition of having different properties in different directions (1).' The
condition under which one or more of the hydraulic properties of an aquifer vary
according to the direction of flow (3).
Anthropogenic. Involving the impact of man on nature; induced or altered by the presence
and activities of man.
" , ,':' i .-;' . " ', ','.','',!.'.',' :' ":('';'!,;'/.«:'['-.'. ' i.'..i.',r;1'.1 '. ''.' ,:,( I f
Aquifer. A formation, group of formations, or part of a formation that contains sufficient K
, i ' " .. i M'1'!. f' '.' ,".." ',.' '-"!,' ", ,i" :. iirlM* I'l:,,'! :'i I'i'-1;1.11 ".';,'!:/:'!'!'.' t, '!"i";, '""ir'I'S1''1;
saturated permeable material to yield sufficient, economical quantities of water to wells
and springs (1,2). 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 and springs (3). '
Aquifer system. A body of permeable and relatively imj>ermeable materials that |
functions regionally as a water-yielding unit. It comprises two or more permeable units
1 ' " ' ' I ' '' '"'- '' ": ''>' '" ' !| ''' !i 1|'1'1 ' "''' i*1*"''"'1! """- -"'"I ""^ '* '' '!" "I'./'.11 .1: f - ,. '*" i-.1 "-' i'i,:v,!,"
separated at least locally by confining units that impede ground-water movement but do
not greatly affect the regional hydraulic continuity of the system. The permeable
materials can include both saturated and unsaturated sections (1). *
Aquifer test. A test to determine hydrologic properties of an aquifer, involving the
withdrawal of measured quantities of water from, or addition of water to, a well and the i
C-2
-------
measurement of resulting changes in head in the aquifer both during and after the period
of discharge ^addition (1,2).
, Area of influence. Area surrounding a pumping or recharging well within which the water i
table or potentiometric surface has been changed due to the well's pumping or recharge
(1).
4 Artesian. Commonly used expression, generally synonymous with (but less favored term
than) "confined."
Artesian aquifer. Commonly used expression, generally synonymous with (but less favored
term than) "confined aquifer." - F
Artesian well. A well deriving its water from a confined aquifer (2). ,
Attenuation. The process of diminishing contaminant concentrations in ground water, due
to filtration, biodegradation, dilution, sorption, volatilization, and other processes.
Base flow. That part of stream discharge not attributable to direct runoff from f
precipitation or snowmelt, usually sustained by ground-water discharge (1). That part of a I
stream discharge derived from ground water seeping into the stream (3),
/ ~ ' .
Bedrock. A general term for the rock, usually solid, that underlies soil or other
unconsolidated material (2).
Bernoulli's Equation. Under conditions of steady flow of water, the sum of the velocity
head, the pressure head, and the head due to elevation at any given point is equal to the |
sum .of these heads at any other point plus or minus the head losses between the points due
to friction or other causes (*).
. Breakthrough curve. A plot of relative concentration versus time, where relative
concentration is defined as C/CQJ the concentration at a point in the ground-water flow
domain divided by the source concentration.
.'-.' ' ' ...- 3
Calibration. Adjustment of the input data until computed heads match the field values.
CAPA. See Critical Aquifer Protection Area.
^ Capillary action. The movement of water within the interstices of a porous medium due
to the forces of adhesion, cohesion, and surface tension acting in a liquid that is in
^ contact with a solid. Synonymous with capillarity, capillary flow, and capillary a
migration (1). i
C-3
-------
Capillary fringe. The zone at the bottom of the vadose zone where ground water is drawn
upward by capillary force (2). The zone immediately above the water table, where water
*is drawn upward by capillary action (3).
Capillary rise. The height above a free water surface to which water will rise by capillary
action (1).
I! , i ^ 'H,!,,I' 'i" ,i " II I , |J I
Capillary water.. Water held in the soil above the phreatic surface by capillary forces; or
soil water above hydroscopic moisture and below the field capacityTl).
Carbonate. A sediment formed by the organic or inorganic precipitation from aqueous
solution of carbonates of calcium, magnesium, or iron (2).
Carbonate rocks. A rock consisting chiefly of carbonate minerals, such as limestone and
dolomite (2).
1 'J ' * ' >;ii! " f 111 |ii i i i
Clastic. Pertaining to a rock or sediment composed principally of broken fragments that
'"'j i , f ''ii ' hiiwi; .,,";, I I |
are derived from pre-existing rocks or minerals and that naive been transported some
distance from their places of origin (2).
Coefficient of storage. The volume of water an aquifer releases from or takes into
11 ' ' ' ' - : I
storage per unit surface area of the aquifer per unit change in head (2).
Coefficient of transmissivity. See transmissivity (2).
'! !' ,|i " , :.'i' ," ' i ;' ; I'i'i::. -, ; ,",] ;"i "' !,, ",;', , I'li.jfjlir T", M"!!' i,! illlliiii''!!''!11..!;!1 ilk."'"i"' '!;«ii!:(', «' :". /! jLi'i'J1! '!" ' 'i!,, i*! 'i',,, . i,:"vK1!' !'' II
Colloid. Extremely small solid particles, 0.0001 to 1 micron insize^ which will not settle
out of a solution; intermediate between a true dissolved particle and a suspended solid,
which will settle out of solution (2).
Cone of depression (COD). A depression in the ground-water table or potentiometric
surface that has the shape of an inverted cone and develops around a well from which
water is being withdrawn. It defines (in cross-section) the area of influence of a well.
Also called pumping cone and cone of drawdown (COD) (1,2).
Confined aquifer. An aquifer bounded above and below by confining units of distinctly
lower permeability than the aquifer media; or one containing confined ground water (1).
An aquifer in which ground water is under pressure significantly greater than atmospheric
and its upper limit is the bottom of a bed of distinctly lower hyraulic conductivity than
that of the aquifer itself.
I
Confining unit. A hydrogeologic unit of relatively impermeable material, bounding one or
more aquifers. This is a general term that has replaced aquitard, aquifuge, and aquiclude
I
I
-------
and is synonymous with confining bed (1). A body of material of low hydraulic
conductivity that is stratigraphically adjacent to one or more aquifers. It may lie above
or below the aquifer (3). . .
Connate water. Ground water entrapped in the interstices of a sedimentary or extrusive
igneous rock at the time of its deposition (1).
Consolidated aquifer. An aquifer made up of consolidated rock that has undergone
solidification or lithification.
Contaminant. An undesirable substance not* normally present, or an usually high
concentration of a naturally occurring substance, in water, soil, or other environmental I
medium (1).
Contamination. The degradation of natural water quality as a result of man's activities.
There is no implication of any specific limits, since the degree of permissible
contamination depends upon the intended end use, or uses, of the water (2).
/ , - ' - '
Convective transport. The component of movement of heat or mass induced by thermal I
gradients in ground water (see advection).
Criteria, WHPA. Conceptual standards that form the basis for WHPA delineation. WHPA
criteria can include distance, drawdown, time of travel, assimilative capacity, and flow
boundaries.
Critical Aquifer Protection Area (CAPA). As defined in the Safe Drinking Water Act, is V
(1) all or part of an area located within an area for which an application of designation as
a sole or principal source aquifer (pursuant to Section U2
-------
i" *«" I '« 111" I J|1
Density. Matter measured as mass per unit volume expressed In pounds per gallon (Ib/gal),
pounds per cubic foot Ob/ft3), and kilograms per cubic meter (kg/n»3) (2). The mass of
j , ,;' ,i Tilt,, 11! *' ii ' j ,:: « , ." , : .,,;" i , '! , , x,; t' \.i t,,."- i;; \a\ ',»/i o< ii i,;!' ii*|' n; iiftii'iiji1 T : v, liniii11 iilcinwiiii'i r, wi! ,,,:;|.. 11» 11" ,,:i A " ,'.' i "in - r j ;,; ,1,1,1 i,' i;i« ir n t \ ,1:11,1* fp\ (, "iim t i 'Mi * i»
^quantity of a substance per unit volume. Units are kilpgramis p^r.cubic meter or grams
per cubic centimeter (3). "'""" """ ! ' f
' '''":" , , ' ,» ,111;, i .nigi-jiiii! , ' , , " i , , " ",.',!,'..''",, ''i1 ,! ! :n< ,\ ii"1!"1!, V1 '^^i.'^H.V^Ii^i'.l'iii!!!1!:1!11!.1',1"!'!1 ^IIRH'^iiW^ 'i'1'1, '",;.'.:'" ''i'l'limi ', '"''J,!1,, ""Si It1 (/im I;1,!,:'!'':!':,',":: In/."ill,.:1 A' h'SB* .lllilllilil'yirli Sin
Desorption. See sprption, which is the reverse process.
Diffusion coefficient. See molecular diffusion.
'"i,1' ,, ' '', 'i ii! ' i ' 'i ,,',,, I, ' ''! I1 ji, j',! ., ' I,.?,, 1,1", ' : , ' "'ll'".'i|;!' i! ,:' 'ii!!!ii'iii!|i! '..iNili'illrll'lilW,,'iifh,, illiiiri""" i 'I,,'! I'vihiiiil'iiill'..!1'!. i"1!.' l:!r;:i."ii,, .i''i|f!'.. i!in, ':.,', n'!i> M.' '! '"ill ,.,. 'iiln. nji1
i.ilr i, , , ..,, , , ,,,,., i , ,, ... . M,, ii,,,,iii :,, ,, :,,, ,, , '' ',,', ;,,
Diffusivity, soil water. The hydraulic conductivity divided by the differential water
capacity, or the flux of water per unit gradient of moisture content in the absence of
other force fields (1). f
Direct precipitation. Water that falls directly into a lake or stream without passing
through any land phase of the runoff cycle (3).
Discharge area. An area in which ground water is discharged ito the land surface, surface
1111 " , . ' ' , " ; : i : i - . .- ,
watCT» or atmosPne,re ^V. ^ arca j" ^h*cn t!lere are MPW^ coniponents of hydraulic
head in the aquifer. Ground water is f towing toward the surface in a discharge area and I
may"escape as a spring, seep, or base flow, or by" evapora'tion"ainid franspiration" (3). :" '
Discharge velocity. An apparent velocity, calculated by Darcy's law, which represents the
flow rate at which water would move through an aquifer if the aquifer were an open
conduit.. Also called specific discharge (3).
Dispersion. The spreading and mixing of chemical constituents in ground water caused by
« i ,..,,,,.. , , ii,,,..,. , , , ., .,,... ., ,«».., 1*f , , , , j.,,,,, ,
diffusion and "^^S d"« to microscopic variations in velocities within and between
pores (2).
Dispersion coefficient. A measure of the spreading of a flowing substance due to the
nature of the porous medium (and specific substance or fluid properties), with
interconnected channels distributed at random in all directions. Also the sum of the
coefficients of mechanical dispersion and molecular diffusion in a porous medium (1).
'i' ! '! i .'vr'lt , " ' "i "'"'i' " I II I I II II I I II III I I I
,', ,' ' I1" '''i,1!!11 . " i', ' , ' j" ' I I I I I 111 III 11 I I " I
Dispersivity. A property of a porous medium (and the specific substance or fluid) that
determines the dispersion characteristics of the contaminant in that medium by relating
i ,.. , I'.piHi . , , .,'. '',l'( iv'; i"" e.« ; '. ;';( i: ". ,'.<:" f ' i-i :f, ,::*'li : n iiBi r; wn.'::.,;i i r,' '(,1 * "ii ?, ?r,, *..,7*^7 " P
the components of pore velocity to the dispersion coefficient (1).
Distribution coefficient. The quantity of a solute sorbed per unit weight of a solid divided
by the quantity dissolved in water per unit volume of water (1).
Drainage basin. The land area from which surface runoff drains into a stream system (3).
C-6
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, . ' . 1 '
Drawdown. The vertical distance ground-water elevation is lowered, or the amount
pressure head is reduced, due Jo the removal of ground water. Also the decline in
potentiometric surface caused by the withdrawal of water from a hydrogeologic unit (1). "
The Distance between the static water level and the surface of the cone .of depression (2).
A lowering of the water table of an unconfined aquifer or the potentiometric surface of a I
confined aquifer caused by pumping of ground water from wells (3).
Dynamic equilibrium. A condition of which the amount of recharge to an aquifer equals
the amount of natural discharge (3).
Effective porosity. The amount of interconnected pore space through which fluids can
pass, expressed as a percent of bulk volume. Part of the total porosity will be occupied by v f
static fluid being held to the mineral surface by surface tension, so effective porosity will
be less than total porosity (3).
Effluent stream. See gaining stream.
Equipotential line. Surface (or line) along which the potential is constant (1). A contour
line on the water table or potentiometric surface; a line along which the pressure head of I
ground water in an aquifer is the same. Fluid flow is normal to these lines in the direction
of decreasing fluid potential (2). A line in a two-dimensional ground-water flow field such
that the total hydraulic head is the same for all points along the line (3).
Equipotential surface (line). A surface (or line) in a three-dimensional ground-water flow
field such that the total hydraulic head is the same everywhere on the surface (3).
'-.'. , . . ^ , , ^ , -.
Evapotranspiration. Combined loss of water from a land area, during a specified period of
time, through evaporation from the soil and transpiration of plants (2). The sum of
evaporation plus transpiration (3).
Evapotranspiration, actual. The evaporation that actually occurs under given climatic and
soil-moisture conditions (3).
Evapotranspiration, potential. The evapotranspiration that would occur under given
climatic conditions if there were unlimited soil moisture (3).
Exchange capacity. Amount of exchangeable ions, measured in milliequivalents per 100
grams of solid material at a given pH. The total ionic charge of the adsorption complex
active in the adsorption of ions (see cation exchange) (1).
" ' '. -'.' ' -'- ' ' ' I
C-7
-------
Fissure. A surface of a fracture or crack in a rock along which there is a distinct
> 14). ' ' . "' ! "'
Flow line. The general path that a particle of water follows under laminar flow
conditions (1). Line indicating the direction followed by ground water toward points of »
discharge. Flow lines are perpendicular to equipotential lines (2).
Flow model. A digital computer model that calculates a hydraulic head field for the
11 ,'» i" , , ' . .. ' ' .' ifl! '! _ 1 I I II I I I . i ft
modeling domain using numerical methods to arrive at an approximate solution to the
differential equation of ground-water flow.
>" ' , >.'i: Ml , ' . ,, ', 'i, « mi ..in,!,. : - nun , ,i ,,| ,
< . . ]..',.
Flow net. A graphical representation of flow lines and equipotential lines for two- [
dimensional, steady-state ground-water flow (1).
Flow path. Subsurface course a water molecule or solute would follow in a given ground-
water velocity field (1).
Flow, steady. A characteristic of a flow system, where the magnitude and direction of
specific discharge are constant in time at any point (1). f
"< " '" 'i ' >' ' . :" '' - ' ; " .", " i '"! : i '"> ' ""t1 E
_i" : - _; ; ; ; -, :; -m _'; ; ,;; ;;;;', "__ i;"; ; 'r ;; ";;";;;;;;;;;~ ;"'" ;; ;; ,;;r:;,,;;,' .,",;;;; ;.; ;,;;,, j, , B
Flow, uniform. A characteristic of a flow system where specific discharge has the same
magnitude and direction at any point (1).
Flow, unsteady (nonsteady). A characteristic of a flow system where the magnitude
and/or direction of the specific discharge changes with time (1).
Flow velocity. See specific discharge. r
Fluid potential. Mechanical energy per unit mass of a fluid at any given point in space
and time, with regard to an arbitrary state and datum (1).
Flux. See specific discharge.
Formation. A body of rock of considerable thickness that has characteristics making it
distinguishable from adjacent rock unit.
Fracture. A general term for any breaWn a rock, which includes cracks, joints and faults'(4)."
. ; , , ' I1:. : ' I'11
Gaining stream. A stream or reach of a stream, the flow of which is being increased by
inflow of ground water. Also known as an effluent stream (3).
Glacial drift. A general term for unconsolidated sediment transported by glaciers and
deposited directly on land or in the sea (2).
C
C-8
B
-------
GPO. Gallons per day, a measure of the withdrawal rate of a well. .
Gravitational fiead. Component of total hydraulic head related to the position of a given
'.*-.. ' ,
masvof water relative to an arbitrary datum (1).
Gravitational water. Water that moves into, through, or out of a soil or rock mass under (
the influence of gravity (1).
Ground water, that part of the subsurface water that is in the saturated zone (1). The
water contained in interconnected pores located below the water table in an unconfined
aquifer or located in a confined aquifer (3).
* ' >' :' .-'.'-
Ground-water barrier. Rock or artificial material with a relatively low permeability that [
occurs (or is placed) below ground surface, where it impedes the movement of ground
water and thus causes a pronounced difference in the heads on opposite sides of the v
barrier (1).
Ground-water basin. General term used to define a ground-water flow system that has
defined boundaries and may include more than one aquifer underlain by permeable .
materials that are capable of storing or furnishing a significant water supply. The basin I
includes both the surface area and the permeable materials beneath it (1). A rather vague
designation pertaining to a ground-water reservoir that is more or less separate from
neighboring ground-water reservoirs. A ground-water basin could be separated from
adjacent basins by geologic boundaries or by hydrologic boundaries (3).
Ground water, confined. Ground water within an aquifer that underlies a confining unit. r
Ground-water discharge. Flow of water released from the zone of saturation (1).
Ground-water divide. Ridge in the water table, or potentiometric surface, from which
» . . .''-'."
ground water moves away at right angles in both directions (1). Line of highest hydraulic
head in the water table or potentiometric surface.
\ ' . | . - f
Ground-water flow. The movement of water through openings in sediment and rock that g
occurs in the zone of saturation (1).
Ground-water model. A simplified conceptual or mathematical image of a ground-water
system, describing the feature essential to the purpose for which the model was developed
and including various assumptions pertinent to the system. Mathematical ground-water
models can include numerical and analytical models.
I
C-9
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I
Ill
111
Ground-water mound. Raised area in a water table or other potentiometric surface,
created ^y ground-water recharge. .............
'
i
%Groij-water recharge. Process of water addition to the saturated zone, or the volume
of water added by this process (1). [
............. *" " . . i ........ ', ................ "' ......... "
Head, static. The height above a standard datum of the surface of a column of water (or
other liquid) that can be supported by the static pressure at a given point. The static head
is the sum of the elevation head and the pressure head (1).
Head, total. The sum of the elevation head (distance of a point above datum), the
pressure head (the height of a column of liquid that can be supported by static pressure at f
the point), and the velocity head (the height to which the liquid can be raised by its
kinetic energy) (1). See also hydraulic head.
'* , . / ' , ' '
Heterogeneity. Characteristic of a medium in which material properties vary from point
to point (1).
Homegeneity. Characteristic of a medium in which material properties are identical m
throughout (1). " , ^ - *
Hydraulic barrier. Modifications to a ground-water flow system that restrict or impede
movement of contaminants (1).
Hydraulic conductivity (K). Proportionality constant relating hydraulic gradient to
specific discharge, which for an isotropic medium and homogeneous fluid, equals the K
' ' "'' " '"li'ii" ... ...: 'I » '. ',.. ' . ~i..Ji'. "'"' "i"'.. ' i1'.:,,, "i."1 > ** * ^ ,j |^
volume of water at the existing kinematic viscosity that will move in unit time under a *
unit hydraulic gradient through a unit area measured at right angles to the direction of
flow(l). The rate of flow of water in gallons per day through a cross section of one
square foot under a unit hydraulic gradient, at the prevailing temperature (gpd/ft^ in
the Standard International System, the units are -m3/day/m2 or m/day (2). A coefficient
of proportionality describing the rate at which water can move through a permeable _
'!, j g
medium. The density and kinematic viscosity of the water must be considered in
determining hydraulic conductivity (2).
Hydraulic conductivity, effective. Rate of water flow through a porous medium that
contains more than one fluid (such as water and air in the unsaturated zone), which should h
be specified in terms of both the fluid type and content and the existing pressure (1).
Hydraulic gradient (i). Slope of a water table or potentiometric surface. More |
specifically, change in static head per unit of distance in a given direction, generally the
C-10
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direction of the maximum rate of decrease in head (1). The rate of change in total head
per unit of Distance of flow in a given direction (2). The change in total head with a
change in distance in a given direction. The direction is that which yields a maximum
rate of decrease in head (3). The difference in hydraulic heads (hi - h2>, divided by the {
distance (L) along the flowpath. ''
i= (hi-h2)/L
Hydraulic head. Height above a datum plane (such as mean sea level) of the column of
, water that can be supported by the-hydraulic pressure at a given point in a ground-water
system. Equal to the distance between the water level in a well and the datum plane (1). F
Hydrodynamic dispersion. Spreading (at the macroscopic level) of the solute front during
transport resulting from both mechanical dispersion and molecular diffusion (1). The
process by which ground water containing a solute is diluted with uncontaminated ground
water as it moves through an aquifer (see dispersion coefficient) (3).
Hydrogeologic. Those factors that deal with subsurface waters and related geologic »
aspects of surface waters (2). I
Hydrogeologic parameters. Numerical parameters that describe the hydrogeologic
characteristics of an aquifer such as porosity, permeability, and transmissivity.
Hydrogeologic unit. Any soil or rock unit or zone that because of its hydraulic properties
has a distinct influence on the storage or movement of ground water (1).
f, . . .
--_- r. .. _._.., j. . w,^6,.,. WA woi-ci 01 oiij Bivcu jiutiii in a
body of water at rest (1).
Immiscible. The chemical property where two or more liquids or phases do not readily
dissolve in one another, such as oil and water (1).
Impermeability. Characteristic of geologic materials that limit their ability to transmit
significant quantities of water under the pressure differences normally found in the »
subsurface environment (1).
Infiltration. The downward entry of water into soil or rock (1).
Infiltration rate. Rate at which soil or rock under specified conditions absorbs falling
rain, melting snow, or surface water; expressed in depth of water per unit time. Also, the
maximum rate at which water can enter soil or rock under specified conditions, including I
the presence of an excess of water; expressed in units of velocity (1).
C-ll
-------
or
Influent stream. See losing stream.
interference. The;result of two or more, pumping wells, the drawdown cones of which
"intercept. At a given location, the total well interference is the sum of the drawdowns
» ',,,'',,' r ,,,i ,, ,',;, r , i, .i'wi, !!!!!;::; Kivvi ,,'!!'i ,ij ,1 , . ; inn: ii IB, ,' ' I" " /Hi , '',Ih,"'T''',i'i 'Tft'Trt r*^,*"*,,,
due to each individual well (3). The condition occurring when the area of influence of a
water well comes into contact with or overlaps that of a neighlwing well, as when two
wells are pumping from the same aquifer or are located near each other (2).
Interstice. An opening or space in rock or soil that may be occupied by air, water,
other fluid; synonymous with void or pore (lj».
'Intrinsic permeability. Pertaining to the relative ease with which a porous medium can f
transmit a liquid under a hydraulic or potential gradient. It is a property of the porous
medium and is independent of the nature of the liquid or the potential field (3).
Ion. Any element or compound that has gained or lost an electron, so that it is no longer
neutral electrically, but carries a charge (2).
Isochrone. Plotted line graphically connecting all points having the same time of travel f
for contaminants to move through the saturated zone and reach a well.
Isocoocentration. Graphic plot of points having the same contaminant concentration
levels. " ' '- " '
botropy. The condition in which the properties of interest (generally hydraulic properties
of the aquifer) are the same in all directions (1).
. .', . . : ' -." I " .".,:''. ' ' . ' ' ,::;>';.;!liiV :j""?:; 1;\,:> :;!-;.:>-::i, !'' i:'.: 'i ':its
Karst topography. A type of terrain that is formed on limestonie, gypsum, and other rocks
by dissolution, and is characterized by sinkholes, caves, and underground drainage (1).
Kinematic viscosity. The ratio of dynamic viscosity to mass density. It is obtained by
dividing dynamic viscosity by the fluid density. Units of kinematic viscosity are square
meters per second (2).
1 . ' "" ;-.'i.J/ '.. ' ' v ':'.; :; HlfT^iKV! .:
-------
Leaching. Removal of materials in solution from rock, soil, or waste; separation or '
dissolving out of soluble constituents from a porous medium by percolation of water (1).
Leakage. Flow of water from one hydrogeologic unit to another. This may be natural, as
through a somewhat permeable confining layer, or anthropogenic, as through an uncased I
well. It may also be the natural loss of water from artificial structures, as a result of
hydrostatic pressure (1).
Leaky aquifer. An artesian or water table aquifer that loses or gains water through
adjacent semipermeable confining units (1).
Limestone. A sedimentary rock consisting chiefly of calcium carbonate, primarily in the F
form of the mineral calcite (1).
Losing stream. A stream or reach of a stream that is losing water by seepage into the
ground. Also known as an influent stream (3).
Matrix. Solid framework of a porous material or system (1).
Maximum Contaminant Level (MCL). Maximum permissible level of a contaminant in §
water that is delivered to the users of a public water system. MCL is defined more
explicitly in SDWA regulations (*0 CFR Section 141.2).
MCL. See Maximum Contaminant Level.
1 ~ '
Mechanical dispersion. Process whereby solutes are mechanically mixed during advective
transport, caused by the velocity variations at the microscopic level; synonymous with p
hydraulic dispersion (1). The coefficient of mechanical dispersion is the component of
mass transport flux of solutes caused by velocity variations at the microscopic level (1).
1 ' p - ' . ' , /
MGO. Million gallons per day, a measure of the withdrawal rate of a well.
Miscible. Chemical characteristic of two or more liquids or phases, making them able to
mix and dissolve in each other, or form one phase (1). Ff
Miscible displacement. Mutual mixing and movement of two fluids that are soluble in
each other; synonymous with miscible-phase displacement (1).
Molecular diffusion. Process in which solutes are transported at the microscopic level due
to variations in the solute concentrations within the fluid phases (1). Dispersion of a
chemical caused by the kinetic activity of the ionic or molecular constituents (2).
'. - . .' ' '. ' ... ' " I
C-13
'. " "'. " ' .'. a
-------
Npnpoint source. A source discharging pollutants into the environment that is not a single
point (1).;
A well drilled in a selected location for the purpose of observing
parameters such as water levels and pressure changes (2). A nonpumping well used to
observe the elevation of the water table or the potentiometric surface. An observation
well is generally of larger diameter than a piezometer and typically is screened or slotted
throughout the thickness of the aquifer (3).
Parameter. See hydrogeologic parameter.
the intake portion of the well is less thanthe full thickness of
Permeabmty- ^ity of a porous medium to transmi* fluids under a hydraulic gradient
(1). The property or capacity of a porous rock, sediment, or sp|l for transmitting a fluid;
it is a measure of the relative ease of fluid flow under unequal pressure (2).
Permeability coefficient. Rate of flow of water through a unit cross-sectional area under
a unit hydraulic gradient at the prevailing temperature (field permeability coefficient), or
adjusted to 15 degrees C (1).
C-14
the aquifer (2). A well constructed in such a way that it draws water directly from a
fractional part of the total thickness of,:thsi aquifer. The fractional part may be located
at the top, the bottom, or anywhere else in the aquifer (3).
Partfculate transport. Movement of undissolved particles in subsurface water (1).
Peclet number. Relationship between the advective and diffusive components of. solute |
transport; expressed as the ratio of the product of the average interstitial velocity and
the characteristic length, divided by the coefficient of molecular diffusion. Small values
indicate diffusion dominates; large values indicate advection dominates (1).
Perched water. Unconfined ground water separated from an underlying main body of
ground water by an unsaturated zone (2).
Percolation. Downward movement of water through the unsaturated zone; also defined as
the downward flow of water in saturated or nearly saturated porous media at hydraulic
gradients of 1.0 or less (1). The act of water seeping or filtering through the soil without
a definite channel (2).
I
-------
Permeability, effective. Observed permeability of a porous medium to one fluid phase,
under conditions of physical interaction between the phase and other fluid phases present
"V.. , ' ; . :'-.. .. .- ' j
Permeability, intrinsic. Relative ease with which porous medium can transmit a fluid
under a potential gradient, as a property of the medium itself. Property of a medium
expressing the relative ease with which fluids can pass through it (1).
pH. A measure of the acidity or alkalinity of a solution, numerically equal to 7 for
neutral solutions, increasing with increasing alkalinity and decreasing with increasing
acidity. Originally stood for "potential of hydrogen" (2). f
Phreatic water. See saturated zone,
Piezometric surface. See potentibmetric surface.
Point source. Any discernible, confined, or discrete conveyance from which pollutants are
or may be discharged, including (but not limited to) pipes, ditches, channels, tunnels,
conduits, wells, containers, rolling stock, concentrated animal feeding operations, or f
vessels (1).
Pollutant. Any solute or cause of change in physical properties that renders water unfit
for a given use (3).
Pollution. When the contamination concentration levels restrict the potential use of
ground water (2). £
Pore. See interstice.
Pore space. Total space in an aquifer medium not occupied by solid soil or rock particles
a). , ' .-'.'; .
Porosity (n). Ratio of the total volume of voids available for fluid transmission to the
total volume of a porous medium. Also the ratio of the volume of the voids of a soil or , ^
rock mass that can be drained by gravity to the total volume of the mass (1). The
percentage of the bulk volume of a rock or soil that is occupied by interstices, whether
isolated or connected (2). The ratio of the volume of void spaces in a rock or sediment to
the total volume of the rock or sediment (3). Porosity may be primary, formed during
deposition or cementation of the material, or secondary, formed after deposition or
cementation, such as fractures. f
Potable water. Suitable for human consumption as drinking water (1).
C-15
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Potential. Any of several scalar variables, each involving energy as a function of position
or condition} of relevance here is the fluid potential of ground water (1).
* ' '"' "'; ' .'. " ' ..... ' " ; ..... '] " ' ' ' " j '[' /"'V^'
Potential drop. Difference in total head between two equipoteintial lines (1).
Potentiometric surface. A surface that represents the level to which water will rise in
tightly cased wells. If the head varies significantly with depth in the aquifer, then there
may be more than one potentiometric surface. The water table is a particular
potentiometric surface for an unconf ined aquifer (3).
Pressure head. Hydrostatic pressure expressed as the height (above a measurement point)
of a column of water that the pressure can support (1).
Pressure, static. Pressure exerted by a fluid at rest (1).
Public water supply system. System for provision to the public of piped water for human
:, ."f ;i , .' . " M' ' ,'",;':' .,,..'. ' ",>J>», |;'.> : :; *WW{.v\\, """ i.'rv-f. *,:'. v",v P.. -i>i;l;f\ ''.><*
consumption, if such system has at least 15 service connections or regularly serves at
least 25 individuals daily or at least 60 days out of the year. The term includes any
collection, treatment, storage, and distribution facilities under control of the operator of
such system and used primarily in connection with the system, and any collection or
; , ,:, . . ' . : : ; vl , -,,,, ; , , :,:; ....... fi ...... n '" i ' ' i |
pretreatment storage facilities not under such control that are used primarily in
connection with the system.
:': '"' ,' , . "' '.!..'' ' ' "-:-, - '
Pumping test. A test that is conducted to determine aquifer or well characteristics (1).
A test made by pumping a well for a period of time and observing the change in hydraulic
head in the aquifer. A pump test may be used to determine the capacity of the well and
the hydraulic characteristics of the aquifer. Also called aquifer test (3).
» i , n " . " ' , ,i I i ' ', " i" . ,'":',' ...... ', ,: i ' ir ,i iifj'l1 , ...... | ii | H1" '» ', j1, , "l,,!.,"!,'1, ..I .||i'i"| , i":,: .',"',,
1 " ", ...... " '* ......... l"
Radial flow. The flow of water in an aquifer toward a vertically oriented well (3).
' , , i, ' . ' T ............ f
! , ' ',,. I Ml III II
Radius of influence. The radial distance from the center of a well bore to the point where
there is no lowering of the water table or potentiometric surface (the edge of its cone of
depression) (2).
Recharge (r). The addition of water to the zone of saturation; also, the amount of water
added. Can be expressed as a rate (Le., in/yr) or a volume (2).
Recharge area. Area in which water reaches the zone of saturation by surface infiltration
. . .. " « -I - > ............................. in .......... i ...... i
(1). An area in which there are downward components of hydraulic head in the aquifer.
1 , '''!' ' ' ,, ' ' . ' ' I ''""i'1 ',,M* '
Infiltration moves downward into the deeper parts of an aquifer in a recharge area (3).
C-16
I;] If,1.- "IE;
i
-------
Recharge basin. A basin or pit excavated to provide a means of allowing water to soak
into the ground at rates exceeding those that would occur naturally (2).
«*'' , . . . , ''' .'''"''-
Recharge boundary. An aquifer system boundary that adds water to the aquifer. Streams
and lakes are typical recharge boundaries (2).
Runoff. That part of precipitation flowing to surface streams (1). The total amount of
water flowing in a stream. It includes overland flow, return flow, interflow, and
baseflow (2).
Saturated zone. Portion of the subsurface environment in which all voids are ideally filled
with water under pressure greater than atmospheric (1). The zone in which the voids in
the rock or soil are filled with water at a pressure greater than atmospheric. The water
table is the top of the saturated zone in an unconfined aquifer (3). Also called the
phreatic zone.
SOW A. Safe Drinking Water Act.
Semiconfined. An aquifer that has a "leaky" confining unit and displays characteristics of
both confined and unconfined aquifers (see leaky aquifer) (1).
Sole Source Aquifer (SSA). An aquifer that is the sole or principal source of drinking
water, as established under Section 1424(e) of the SDWA.
Solute transport. Net flux of solute through a hydrogeologic unit, controlled by the flow
of subsurface water and transport mechanisms (1).
Solute transport model. Mathematical model used to predict the movement of solutes
(generally contaminants) in an aquifer through time. ,
Solution channel. Tubular or planar channel formed by solution in carbonate-rock
terrains, usually along joints and bedding planes (4).
* ' ' ' ". >,''""
Sorption. Processes that remove solutes from the fluid phase and concentrate them on
the solid phase of a medium; used to encompass absorption and adsorption (1).
Specific discharge. The volume of water flowing through a unit cross-sectional area of an
aquifer (1).
Specific yield. The ratio of the volume of water that a given mass of saturated rock or
soil will yield by gravity to the volume of that mass. This ratio is stated as a
percentage (1).
C-17
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Sprfng* *frete;P^» **«:« ground water flows naturally from rock or soil onto the land
surface or anto a surface-water body (1). .
i n , , , , , .,*,,,,,,'! , , ,"
SSA. See Sole Source Aquifer. ' ' -
Stagnation point. A place in a ground-wafer flow field at which the ground water is not
moving. The magnitude of vectors of hydraulic head at the point are equal but opposite in
direction (3).
; '. ,: ' _ , _ ,.,'' " ' -:. - ',;, 4\ *K^^,fl'^l»i;- ,!' : <}-.>.,.-.. i.i't:
Static head. See head, static.
, !l!v " ; . !' .' 'i'1*'1 :'' i I l i ' * i
State. Includes, in addition to the several States, only the District of Columbia, Guam,
the Commonwealth of Puerto Rico, the Northern Mariana Islands, the Virgin Islands,
American Samoa, and the Trust Territory of the Pacific Islands.
State Wellhead Protection Program. Program to protect wellhead protection areas within
a State's jurisdiction from contaminants that may have any adverse effects on the health
of persons (SDWA, subsection l«8(a)).
Static water level. The level of water in a well that is not being affected by withdrawal
of ground water (2).
Storage coefficient. Volume of water an aquifer releases from or takes into storage per
unit surface (or subsurface) area per unit change in head (1).
, ;'i - ' ' ,, , ''-, :'i|'' ' ";.. -«",' - \,-(;':ji '; <'jtff;v;!i,'.'.;'! ''. /'..i,/'1: .'';;,v. ;*; ';:\.,;;
Storage, specific. The amount of water released from or ta!Sen into storage per unit
volume of a porous medium per unit change in head (3).
Storativity (s). A dimensionless term representing the volume of water an aquifer
releases from or takes into storage per unit surface area of the aquifer per unit change in
head. It is equal to the product of specific storage and aquifer thickness. In an
unconf ined aquifer, the Storativity is equivalent to the specific yield. Also called storage
coefficient (3).
i " ' ,;'. . ' ' '' , " .'" .',' ' .'if.. ' ,' '.'. ( i ' "
Time of travel (TOT). The time required for a contaminant to move in the saturated zqne
from a specific point to a well.
> ' "-' ' ' ' {' ':';: ' '.;. ' ;"'''. ;.;.>;,r.-1Sif V''RJ ''} '''^,^':- '^]t :
TOT. See time of travel.
Transmissivity (t). Rate at which water of the prevailing; kinematic viscosity is
transmitted through a unit width of the aquifer under a unit hydraulic gradient. It is equal
to an integration of the hydraulic conductivities across the saturated part of the aquifer
perpendicular to the flow paths (1). The rate at which water is transmitted through a unit
" i, ',.'' i . .
C-18
Mr*1,1 '
I
', l! 'll'i'i "i'n i 'l.'u.lt*
<,,:., <« ;1 ii'l y'Sfi ^ "M. l< ;, /J6 "liiillli; i! ' "*: Iklv
-------
width of an aquifer under a unit hydraulic gradient. Transmissivity values are given in
gallons per minute through a vertical section of an aquifer 1 foot wide and extending the
full'saturated height of an aquifer under a hydraulic gradient of one in the English
Engineering system; in the Standard International System, transmissivity is given in cubic [
meters per day through a vertical section of an aquifer 1 meter wide and extending the
full saturated height of an aquifer under a hydraulic gradient of one (2). It is a function of
properties of the liquid, the porous media, and the thickness of the porous media (3).
' " ' ';,''"'- "* - '
Transport. Conveyance of solutes and particles in flow systems (1).
'.'...'.'' . ; '',- . ,
Turbulent flow. Water flow in which the flow lines are confused and heterogeneously F
mixed. It is typical of flow in surface water bodies (2). That type of flow in which the
fluid particles move along very irregular paths. Momentum can be exchanged between
one portion of the fluid and another. Compare with laminar flow (3).
UIC. See Underground Injection Control.
4 _ ' . - ". / ...-('
Unconfined. Conditions in which the upper surface of the zone of saturation forms a ,
water table under atmospheric pressure (1). t
Unconsolidated aquifer. An aquifer made up of loose material, such as sand or gravel,
that has not undergone lithification.
I _.''. ' '
Underground Injection Control (UIC). The regulations for injection wells. The program
provides grants to States under Section 1^3(b) of SOW A.
Unsaturated flow. Movement of water in a porous medium in which the pore spaces are
not filled with water (1).
Unsaturated zone. The zone between the land surface and the deepest or regional water
table. It includes the root zone, intermediate zone, and capillary fringe. The pore spaces
contain water, as well as air and other gases at less than atmospheric pressure. Saturated
bodies, such as perched ground water, may exist in the Unsaturated zone, and water ft
pressure within these may be greater than atmospheric (1). Same as vadose zone.
Vadose zone. See Unsaturated zone.
Velocity, average interstitial (v). Average rate of ground-water flow in interstices,
expressed as the product of hydraulic conductivity and hydraulic gradient divided by the
effective porosity. It is synonymous with average linear ground-water velocity or P
effective velocity (1).
C-19
\ ' -
'. , I
-------
Water budget. An evaluation of all the sources of supply and 'the corresponding discharges
with respect to an aquifer or a drainage basin (3).
1 Water table. Upper surface of a zone of saturation, where that surface is not formed by a
confining unit; water pressure in the porous medium is equal to atmospheric pressure (1).
stk\ *u\\afKMwmm fc
The surface between the vadose zone and the ground water; that surface of a body of
unconfined ground" water at which the'pressure "is equal to that of the'atnTOsphere (2).' The
,1 " i. ' ' ' '". « mi1 ,: .i,,, ' "i ijiiiu i i', "", < 'T " " '!!,' . » u " <" ' '"ll 'I I-, "i' . i; >'; ' ii ii ' ' >' i ,,'"t'' #3 i :.,:'"' i'' iiWJ'iii11 "'"'ii! I'SlililS!!!! aiiiiwaiiiiiai1 iii«', il III III III II III I 11 "», iilil/i l'l:', "liii^SSSi'f! iliiaSJt!!1!; !*, I'iulU:''!"'!, .a!!1; iiiii'i!"];;*!'1 u\ hi^iJIJ1"
surface in an unconfined aquifer or confining bed at which the pore water pressure is
atmospheric. It 'can be measured by installing shallow wells' extending a few feet into the'
.( i , i > . .""ti ,! i ' ' .' it .' " ;i. «i('., vV'l*''.":' >; "i!.* ii":'Jt)i''Si!'iHif*iwiJS*f JSSSwflKi?! hMSLiiiM!i;'!LTw«'ir«'i.i(iKi».! "ssni"i-'if :s"fA:a isi
zone of saturation and then measuring the water level in those wells (3).
Well field. An area containing two or more wells supplying a public water supply system.
Wellfjeld. Synonymous with well field.
t , ' ' , iT'iill < , ' ,i ,,i ir . , " :, I III ill I I || I
Well, fully penetrating. A well drilled to the bottom of an aquifer, constructed in such a
way that it withdraws water from the entire thickness of the aquifer (3).
: £ -v .'si t." ''^^..v;-v^:::^i i(,!;.^::?3»ffiK^ i in iff"' m'tfffift m
Wellhead. The physical structure, facility, or device at the land surface from or through I
which ground water" flows or is pumped from subsurface,1 water-bearing formation's.
Wellhead Protection Area (WHPA). The surface and subsurface area surrounding a water
well or well field, supplying a public water system, through which contaminants are
reasonably likely to move toward and reach such water well or well field.
Well interference. See interference. i . . ^ _. ^..^ ^ . ^ .....,.;.., : _;,,, (i _ .
' ,: ' . . i :-;;?" , ' -;" ':;,,' ':«;'.;,: ..'.n.^ri!"'- ;r ;r;";; ;v'v.> 'k v,fiiii;';»:i!':;ls^
Well screen. A filtering device used to keep sediment from entering a water well (2).
Well yield. The volume of water discharged from a well in gallons per minute or cubic
meters per day (2).
WHPA. See Wellhead Protection Area.
ZQC. See zone of contribution.
2X31. See zone of influence.
Zone of Contribution (ZOC). The area surrounding a pumping well that encompasses all
areas or features that supply ground-water recharge to the well.
Zone of Influence (ZOD. The area surrounding a pumping well within which the water
table or potentiometric surfaces have been changed due to ground-water withdrawal.
C-20
-------
Zone of Transport (ZOT). The area surrounding a pumping well, bounded by an isochrone
and/or isoconcentration contour, through which a contaminant may travel and reach the
wtll. .-. ' 'f
ZOT. See zone of transport.
F
u
I
C-21
' ', .. . ,- ' : .'' a
-------
m
!,i u i1'' , i, i!
.)') .i1 .".-{ii i,' 'it I; litESBlii'i,;; Ci*1 :'i . ts^;
-------
.--''' ' . ' : \ - ' ': . .
APPENDIX D
'&,*";" " . -
MODEL'ASSESSMENT FOR DELINEATING WELL HEAD PROTECTION AREAS
** ' .
Excerpt From'Draft Report -
Included in this appendix are an edited version of the Executive Summary and a list
of models from this draft report, prepared by Paul K.M. van der Heijde and Milovan S.
Beljin of the International Ground Water Modeling Center at the Holcomb Research
Institute, at Butler Unviersity, Indianapolis, Indiana. This report was prepared at the
request of the Office of Ground-Water Protection through a Cooperative Agreement
between Holcomb Research Institute and the Office of Research and Development at
EPA. Management of this effort was provided by the Robert S. Kerr Environmental
Research Laboratory, Ada, Oklahoma. The final report will be available soon.
f
b-i
i
-------
I'll I III
HIII |i II i i ill ii*
EXECUTIVE SUMMARY
" :V\; ' ,'": ' ' ' , ."' .' . ]
One'element 6f the 1986 Amendments to the Safe Drinking Water Act (SDWA) of
1974 is the protection of wellhead areas from contaminants that 'may have an adverse (
effect on public health. In establishing wellhead protection areas (WHPA's), many factors
need to be considered, including:
;:|i: : ,i " > ) ill'.!.,''.';':":; r ''': i,' :" ,i :. i.! ft. <;:v .!'";";;.i' ' ?;;i;i^Sfejfti^lte^^Hfr!,'ii ;ii";i ffii'i&:.MM'^m ^.iii&iii
Zone of Influence around a well or well field
. : '., -: I 'If ill! !'.. . , , "i s , < . '.'./HV'i:, '"(;< ,iii '"SW'L'fl JWSi'ilkilH'J'iBPlPWifr,1 S'.E'iiJi-'.Mi'raj.'.H.iJ 'Jl'^Wtf
Presence of interfering neighboring wells or well fields
Water table drawdown by the wells or well fields under consideration f
if ' ' , , ii'VII'i,: '"; ; "" , ji'i,, '. , .",,,; ',,4 I II I I I II IIIIII I I Illlll II I l[l ' I
Various sources of contamination in the well recharge area (not necessarily the
same as its zone of influence)
Flow paths, transport velocities, and travel times for various contaminants
under various hydroiogic conditions.
: ' ., ( ' .i'J i ' . '-' ';'. 'i ;. '" -i'-ii-i ,;.;, "' ; :.'.}«(:.: ;>iv,viir*i«H ' :,!';u,,f wi&H.iXtftMuAtiliti/'a*" 's<«^^
- ; i , 'i;;i;i!iji , "', i \; , . -r;, ' ,'. ,';':»;,/"r" :VnV,MvV 1&'!'l.''BlLfriWtlr,lit>'f,i.f i' :|li'iS'iiitin;.w:ii"'B'"':r4iw,*!.(. f its;, (ft Risw^rBewasi
To determine a site-specific WHPA, a systematic, analytic approach is necessary; I
mathematical simulation models provide a viable and often the only method to determine
the WHPA when quantitative criteria are used. Such models are useful instruments in
understanding the mechanisms of ground-water systems and the processes that influence
their quality. Through their predictive capabilities, models provide a means to analyze
the response of the site-specific system to various management alternatives and potential
public health threats. §
This report is aimed at providing information on existing ground-water flow and
contaminant transport and fate models that might be considered for use in a WHPA
delineation study. Although physical ground-water models can be useful for studying
certain problems, the present focus is on mathematical flow and contaminant transport
models in which the causal relationships among various components of the system and its
environment are expressed in terms of mathematics and translated into a computer code. *
Flow models are used to calculate changes in the distribution of hydraulic head of
fluid pressure, drawdowns, rate and direction of flow, travel times, and the position of
interfaces between immiscible fluids. Two types of models can be used to evaluate the
, ' ' " "" ' "' '"' " "' ;''""'' '' 'i ' ' i J| /' .'"" | " ' I
chemical quality of ground water: hydrochemical models describing equilibrium reactions
or reaction kinetics, and models that simulate solute transport and fate. Solute transport
and fate models are",' used .for 'the" prediction' of"' m'ovemerit^ cohcentration&^an'd "mass
,' " | ' ,, ' ['"a, i'ijl ; ' ',,:, , ""!»',,;"'"; ': " '! i. 1,(J11V";;",'"'!h ,, 'I,:| ,:"" *'"''"ij1'' 1.1''«»'<' ''.'"J11: :|;!' »|.i!'i" |.|j!!!":.;E V ' SKf,ffXf§v!i!|1'''i'''"',!"''"''i1 '''''.V'!","'j;i!l':"ll!!JKi!":/i1!11:1 n:1'!''11'!'1'!, '''';i1''?,;',/S, l':; "!ll!.;lf,,:,'!'
balance components of water-soluble constituents. ,
D-2
-------
The major criteria in selecting a model for a particular site-specific WHPA
delineation are the model's suitability for the intended use, reliability, and efficient .
application. A model's efficiency is determined by the availability of its code and i
documentation, and its usability, portability, and modiflability. A perfect match rarely
exists between desired characteristics and those of available models. Reassessment of
the selection criteria and their relative weight is often necessary. -
A major issue in model use is credibility, which is based on its proven reliability and
the extent of its use. It is often assumed that most program errors originally present in a
widely used program have been detected and corrected. Successful prior applications of a [
program in situations comparable to that for which it has been selected increase
confidence in its applicability to the new situation.
A model's credibility can be evaluated in terms of the level of review and testing
applied to it and by evaluating the success rate of its use. Testing a code involves two
phases: .
Verification to check accuracy and assure that the code is fully operational,
Field validation to determine how well the model's theoretical foundation
describes the actual system behavior that the model has been designed to
simulate.
Many of the available models have not been subjected to an extensive review and -
test procedure. Reviews have often been limited to peer review of theory and project
reporting. Though most models have undergone some verification, the results of this are
rarely reported, especially for the more complex models. Only a few models are reported
to have undergone extensive field validation.
With respect to availability of ground-water software, a distinction can be made
between public domain and proprietary software. Models that are available without Ji
restrictions in their use and distribution are considered, to be in the public domain.
Available proprietary software can be obtained or accessed under certain restrictions for
use, duplication, and distribution. '
SELECTED MODELS
Sixty-four models were selected a computerized search of the model annotation |
data bases of the International Ground Water Modeling Center (IGWMC). These data
bases have been developed and maintained over the years with major support of EPA's
D-3
-------
R.S. Kerr Environmental Research Laboratory in Ada. Oklahoma. This search was
,i? ='" %. * * . .
folio wed "by an evaluation of the maintenance and update history of each model's code.
Models were chosen because of their availability, level of. documentation, and
applicability to the wellhead protection zone delineation problem. Of the 64 models, 27
;;/ '," , ' ,;;;w »' -, ,; -,; . ~ , ^J :
are flow and 37 are solute transport models. Fifty-one of the models are numerical and
13 are analytical and semi-analytical. The attachment below contains summary
"' "' I. ' . I"11*! '" "" '' ' ' I 'I "i» «i '..i "I1 'I! 'IP, : ill',"!!'1, ','":"",P P II I III »
descriptions and detailed information on each model, and a comparison of usability and
reliability characteristics.
A major limitation of tills study is the lack of available data on model usability,
reliability, and portability. Many models have not been subjected to the extensive
evaluation required to rate them according to the criteria presented in this report.
Additional activities to fill in the information gaps in this report are desirable.
' Though adequate models are available for analysis of most flow-related problems,
this is not the case for modeling contaminant transport. Accurate modeling of ground-
water pollution is limited by some fundamental problems. Available numerical techniques
are not always adequate for the most complex transport mechanisms. In addition,
; . . , ,,, i jit!! ' ; ; - , -, 'is. ]
inadequate quantity or low quality of data often restricts model utility.
','', i , |lll i, "Illl : :",iiL'I!'!,
',':' , ", i> , i :,'",' 'i|, PI! '!!:' "liif ',1 'I1','""''",, ,1 '' i11'1 |i'ii,,!i''i ifl 'in I", ", h' ,, ""'"' ,, ' !,' 'i'
,i;«'»' ;'3"f (M ii!,;: .,\, illntl' I;;"'*,,!«i! t ' v \-.? ",';)i < '^ h111 ' \^wl ij'I, .i,"' : Jl !. i,/,,i, w i'
',, ,,'i',;,,, ...I'iiwir'f '.,;,!'i^B, i" .nil", IM , ,. | ...,? .:.!?,»J.M>L. ,' !,,i,, A '*' , /"li'l1
, , ";;,i;,, "i:i.;i'1i:'1' .n,,.!1!!!,1!}! "t ^i'1 ]"' ' "l", i1!!;,1 , 'XI'1 r11,!1"^ "V v-,' " "'i1 i;1',,.,"!
I';,:;;?
" ', ;;",, '," ill Jin, Illi'll, 'fill ii'i-iiinil'llllllilil llrlll!1!1!,!1!!!!!!!1'''!!,,
,, "'uHi;:!'!'! viihiiiiiiiiiN"!'^:;*!!!!!:!1,''1' I'liiiiFtiiiiiiiiiii;
i;'(i;',fe'ijii:,ii]JlftaKf
1 L , ,',",' "'!' V',": ;iis' ''i'1 hji ipiiiinil i,' T f ii niil i iiiPii"''", ii, ingniii iiiifiimaii
'iilH'!1" ' ii'l'!'!'1''!1!11' il!"1!?!'1,, L'tiWiW"1!!1:"1 'I'llS'Ii11:,!1 ii Uri!1!1"1!"11!"!!!!!!
JiiJ'v IV,S ".ll'liKJniilliilll!,
I'iiniiiBlj'iii
i
-------
ATTACHMENT
%; DESCRIPTION OF MODEL CHARACTERISTICS
* ; ' ' . '. v " . ' - ' ' .
The "Model Output" column in the tabulation presented below contains the type of
information available from the model output that could be required in WHPA delineation.
The following abbreviations are used:
AI Area of Influence (the area surrounding a pumping or recharging well within
which the potentiometric surface has been changed).
/ , ' t '',',' - .
C Concentration (concentration map of contaminant throughout the simulated
domain).
CD Cone of Depression (the shape of the area of influence, in cross section).
F Fluxes.
P Pathways (path of a contaminant particle in the system).
RA Recharge Area (the permeable layer through which precipitation and surface I
water may percolate to the aquifer and eventually reach the well).
T Travel times (isochrones).
V Velocities (ground-water velocities).
I
D-5
''.'"' ' .-'- ' ' a
-------
ndiii^ ' ijr'ii;^
t ">
HO.
f.
2.
3.
4.
5.
6.
7.
e.
!!. 1 IJ, , *
Auttor(s)
V
S.P. Newman
P.A. NltiMr-
aoon
S.P. NeuMn
T.N. Narasimhan
T.A. PrlcKett
C.&. Lonnqulst
S.F. Pindar
E.O. Frind
C.F. Finder
C.I.. Voas
P.S. Huyakorn
P.S. Hgy«Horn
, iiii*!* : »i i,, i '»,' :'', "1,1. i "
Contact Address
0*pt. of Hydrology and
Nat«r Resources
University of Arizona
Tucson. AZ 85721
Oept. of Hydrology and
Hater Resources
University of Arizona
Tucson, AZ 85721
Sattelle Pacific NW Lab
-Hater and Land Resources
Division
P.O. Box 999
Rich land. HA 99352
Consulting Hater
Resources Engineers
6 6.H. Baker Drive
Urbana, IL 61801
Dept. of Civil
Engineering
Princeton University
Princeton, NJ 08540
U.S. Geological Survey
Hater Resources Division
National Center .M.S. 431
Reston. VA 22092
Geotrans, Inc.
209 Elden St., #301
Herndon, VA 22070
Geotrans, Inc.
209 Elden St., J301
Herndon. VA 22070
Model Nue
(last update)
' FREESURF 1
(1979)
,.
UNSAT2
(1979)
,«
TRUST
(1981)
PLASH
(1986)
ISOOUAD
(1982)
AOUIFEM
(1979)
GREASE 2
(1982)
SATURN 2
(1982)
Model
Description
Simulation of tKO-dlaen-
sional verticil! or axi-
syeoetric, stuady-state
flow in an anlsotropic.
heterogeneous,, confined
or ater-tabUi aquifer.
A two-diMnsi
-------
NO.
9.
10.
11.
12.
13.
14.
15.
Author(s)
JU
«*
P. Huyakorn
P. Huyakorn
J.E. Reed
M.S. Bedinger
J.E. Terry
T.R. Knowles
INTERA
Environmental
Consultants,
Inc. and
INTERCOM?
Resource
Development ft
Eng., Inc.
C.R. Faust
T. Chan
B.S. Ramada
8.M. Thompson
L.F. Konikow
J.D. Bredehoeft
Contact Address
Geotrans, Inc.
209 Elden St., 4301
Herndon, VA 22070
IGHMC
Hoi comb Research
Institute
Butler University
4600 Sunset Avenue
Indianapolis, IN 46208
U.S. Geological Survey
Room 2301
Federal Building
700 H. Capitol Ave.
Little Rock, AR 72201
Texas Water
Deve I opment Board
P.O. Box 13231
Austin, TX 78711
U.S. Geological Survey
Box 25046 Mail Stop 411
Denver Federal Center
Lakewood. CO 80225
Performance Assessment
Dept.
Office of Nuclear Waste
Isolation
Battelle Project Mngnt.
Oiv.
505 King Avenue
Columbus, OH 43201
-
U.S. Geological Survey
431 National Center
Reston, VA 22092
Model Name
(last update)
t"'
SEFTRAN
(1983)
.
TRAFRAP
(1986) ,
f
SUPERMOCK
(1975)
GWSIM-II
(1981)
SNIP/
SWIPR/
SHENT
(1985)
STFLO
(1982)
-
MOC
(1987)
Model
Description
To provide simple and
cost-effective analyses
of two-dimensional fluid
flow and contaminant or
heat transport problems
in areal , cross-section-
al or ax i symmetric eon-
figuration of saturated.
heterogeneous aquifers.
A finite element model
to study transient, two
dimensional, saturated
ground water flow and
chemical or radionucl ide
transport in fractured
and unfractured, an i so-
tropic, heterogeneous.
multi-layered porous
media.
To simulate transient
stress and response in a
saturated-unsaturated
ground water fio» system
including a water-table
aquifer overlying a con-
fined aquifer.
A transient, two-dimen-
sional , horizontal model
for prediction of water
levels and water quality
in an anisotropic heter-
ogeneous confined and
uncon fined aquifer.
To simulate unsteady,
three-dimensional
groundwater flow, heat
, and contaminant trans-
port in an anisotropic.
heterogeneous aquifer.
A linear finite element
code for simulation of
steady-state, two-dimen-
sional (areal or verti-
cal) plane or axisymmet-
ric ground-water flow In
anisotropic, hetero-
geneous, confined, leaky
or water-table aquifers.
To simulate transient.
two-dimensional, hori-
zontal groundwater flow
and solute transport in
confined, semi con fined
or water table aquifers.
Model
Output
' Al ,CD,RA.F,C.
'
Al ,CD,RA,F,C.
AI.CD.RA
AI.CO.F.C.RA
AI.CD.RA.F.C,
V
AI,CO,RA,F
AI,CD,RA,F,C.
V
ifcwMC
Key
0588
0589
0611
,0680
0692
0694
0740
I
D-7
-------
iiin n inn nn|i n
Ho. j Authpr(s)
16.
S.P. Caraoedlan
L.F. Konlkow
17.
18.
19.
W.E. Sanford
UF. Koniko*
20.
P.O. Trescott
5.P. Larson
P.O. Trescott
G.F. Pind*r
S.P. Larson
Miller, I.
J. Marlon-
Lambert
21.
22.
23.
C. Segol
E.O. Frind
K,R. Rushton
L.H. Tomlinson
H.H. Haitjema
O.D.L. Stride
Contact Address
U.S. Geological Survey
431 National Center
Reston, VA 22092
Model Hue
(last update)
FRONTRACK
11983)
U.S. Geological Survey
431 National Center
Reston, VA 22092
MOCDENSE
(1986)
U.S. Geological Survey
Branch of Groundwater
M.S. 411 National Center
Reston, VA 22092
U.S. Geological Survey
Branch of Ground Mater
M.S. 411 National Center
Reston, VA 22092
Colder Associates
2950 Northup Hay
Bellevue, HA 98004
Oept. of Earth Sciences
University of Waterloo
HaterIoo. Ontario
Canada N2L 361
Dept. of Civil
Engineering
Univ. of Birmingham
P.O. Box 363
Birmingham, B15 2TT
United Kingdom
School of Public I
Environmental Affairs
10th Street
Indiana University
Bloomington, IN 47405
USGS-3D-
FLOW
(1982)
USGS-2D-
FLOW
(1976)
GGHP
(1983)
3-0
SATURATEO-
UKSATURATED
TRANSPORT
MODEL
(1976)
AQU-1
(1979)
SYLENS
(1989)
Model
Description
A finite difference
model for simulation of
convective transport of
a conservative tracer
dissolved in groundwater
under steady or tran-
sient flow conditions.
The model calculate*
heads, velocities and
tracer particiit
positions.
A model to simulate
transport and dispersion
of either one or two
constituents in ground-
water where thore i s
two-dimensional, density
dependent flow, it uses
f i n i te-d i f ference and
method of characteris-
tics to solve the flow
and transport equations.
To simulate transient,
three-dimensional and
quasi three-dimnsienal,
saturated flow in an!so-
tropic, heterogeneous
ground water systems.
To simulate transient,
two-dimensional hori-
zontal or vertical flow
in an anisotropic and
hetrogeneous, confined,
leaky-confined or water-
table aquifer.
Steady-state or tran-
sient simulation of two-
dimensional, vertical or
axisymmetric and quasi -
three dimensional flow
and transport of reac-
tive solutes in aniso-
tropic. heterogeneous,
multi-layered aquifer
systems.
Determination of concen-
tration of consorvative
or nonconservatiive sol-
ute in transient, three-
dimensional saturated-
unsaturated floii sys-
tems.
Basic transient model
for single layered two-
dimensional horizontal
ground water flow.
Model ing of steady-state
groundwater flow in re-
gional double aquifer
systems with local in-
terconnections.
Model
Output
TSffiC
Key
AI.CD,RA.F.C.
V,P,T
AI.CO.RA.F.C.
AI,CD,RA,F
AI.CD.RA.F
AI.CO.RA.F.C.
V.P.T
AI.CO.F.C
AI.CD.F
AI.CO.RA.F
0741
I
0742
0770
0771
1010
1070
1230
1791
I
D-S
'I :"'f!
II
-------
No.
" 24.
25.
26.
27.
26.
29.
30.
3'.
Author^.
C. Van Den
Akker
P. Van der Veer
S.K. Gupta
C.T. Kincaid
P.R. Meyer
C.A. Newbill
CD Onl >
» vOlv
S.K. Gupta
C.R. Cole
F.H. Bond
A.E. Reisenauer
C.R. Cole
R.H. Nelson
R.D. Schmidt
L.R. Townley '
J.L. Hi (son
A.S. Costa
Contact Address
National Institute for
Hater Supply
P.O. Box 150
2260 Ad Leidschendam
The Netherlands
Rijkswaterstaat
Data Processing Division
P.O. Box 5809
2280 HV Ri jswijk (2.H.)
The Netherlands
Batteile Pacific NH Labs
P.O. Box 999
Richland, HA 99332
Batteile Pacific NH Labs
Hater and Land Resources
Division
P.O. Box 999
Richland, HA 99352
Hater and Land Resources
Division
Batteile Pacific NH Labs
P.O. Box 999
Richland, HA 993S2
Batteile Pacific NH Labs
Sigma 5 Building
P.O. Box 999
Richland. HA 99352
U;S. Dept. of the
Interior
Bureau of Mines
P.O. Box 1660
Twin Cities. MN 55111
Ralph M. Parsons
Laboratory for Hater
Resources and
Hydrodynamics
Room 48-211
Massachusetts Inst. of
Technology
Cambridge. MA 02139
Model Naaw
(last update
FLOP-2
(1975)
MOTGRO
(1981)
<<
CFEST
(1985)
FE3D8H
(1983)
VTT
(1979)
PATHS
(1983)
ISLtSO
(1979)
AOUIFEM-1
(1979)
"Model ;;
Description
To generate path lines
for steady-state, flow
In a semi-confined, 1 so-
tropic, homogeneous
aquifer without storage
and to calculate resi-
dence times for a number
of water particles.
Prediction of ground-
water head and stream
function for two-dimen-
sional, vertical, steady
and unsteady, single or
multiple fluid flow in
inhoMogeneous, an i so-
tropic, confined or un-
confined aquifers of
arbitrary shapes.
A three-dimensional fi-
nite element Model to
simulate coupled transi-
ent flow, solute- and
heat-transport in satur-
ated porous media.
Transient or steady
state, three-dimensional
Simulation of flow in a '.
large Multi-layered
groundwater basin.
A transient model to
ca 1 cu 1 ate hy drau 1 i c head
in con fined-uncon fined
Multi -layered aquifer
systems, and to generate
streamlines and travei-
times.
To evaluate contamina-
tion problems in tran-
sient, two-dimensional ,
horizontal, groundwater
flow systems using an
analytical solution for
the flow equation and a
numerical solution for
the path line equations.
A three-dimensional
Model to describe tran-
sient flow behaviour of
leachants and ground-
cater in an anisotropic,
homogeneous aquifer in-
volving an arbitrary
pattern of injection and
recovery Mils.
A two-dimensional, fi-
nite-element Model for
transient, horizontal
groundwater flow.
Model
Output
C.V.PJ
AI.CD.F,V,P,T
AI,CD,F,RA.C.
AI,CD.RA,F,V
AI,CD,V,P,T
F.V.C.P.T
,
V.P.T
AI.CD.RA.F
IGHM5
Key
1821
1830
2070
2072
2092
2120
2560
2630
D-9
-------
No.
60}
61.
62.
63.
64.
Author(s)
0. Koch t
IHTERA
Environmental
Consultants
W.C. Wilton
Contact Address
fc.S. Betjin
T. Steenhuis
5. Paeenka
Koch t Associates
1660 S. Fillmore St.
Denver. CO 80210
BatT* 11* Project
Management Division
Performance
Assessment Dept.
Office of Nuclear Hut*
Isolation
505 King Avenue
Columaus, OH 43201
IGWMC
Holcosb Rasaareh
institute
Butler University
4600 Sunset Avenue
Indianapolis. IN 46208
IGWMC
HoIcomb Research
Institute
Butler University
4600 Sunset Avenue
Indianapolis, IN 46208
Northeast Regional
Agricultural
Engineering Service
Riley-Robb Hall
Cornell University
Ithaca, NY 14853
Model Hue
(last update)
AQUIFER4
(1984)
VERTPAK-1
(1982)
"Model
Description
35
MICRO-
COMPUTER
PROGRAMS
(1984)
SOLUTE
(1985)
MOUSE
(1987)
Model
Output
A radial finite differ-
ence Model to simulate.
transient three-dimen-
sional groundwalrer flow
in a leaky-confined aqu-
ifer.
A package of analytical
solutions assent)led to
assist in verification
of numerical coites used
to simulate fluid fio«.
rock deformation, and
solute transport in
fractured and uinfractur-
ed porous Mdia.
A series of analytical
and sinple numerical
programs to analyze flo*
and transport of solutes
and heat in confined,
leaky or water table
aquifers with simple
geometry.
A package of 6analyti-
cal models for solute
transport simulation in
ground«ater. The pack-
age also includes pro-
grams for unit conver-
sion' and error function
calculation.
A set of four I inked
models for tracking the
movement and filte of a
soluble chemicnl in sat-
urated and unsnturated
zones.
Al.CD.F
C.V.T
Key
6305
6340
AI,CD,C,V,T
C.T
6350
6380
C.T
6390
D-14
*O.S. GoYornaint Printing Offic* : 1918 -516-002/B0049
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