United States
         Environmental Protection
         Agency
Office of
Ground-Water Protection
Washington, D.C. 20460
                                                  June 1987
         Water
EPA    Guidelines for
         Delineation of Wellhead
         Protection Areas

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                     AVVBERC LIBRARY  U.S. EPA
GUIDELINES FOR DELINEATION OF
 WELLHEAD PROTECTION AREAS
 Office of Ground-Water Protection
U.S. Environmental Protection Agency
          3une 22, 1987

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                                    FOREWORD

     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 Program is available from the Office of Ground-
Water Protection in Washington, D.C., and from the ten EPA Regions.

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                              ACKNOWLEDGEMENTS

     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 and  Director of the Guidelines Implementation Staff.  The efforts of the
Technical Committee on Hydrogeologic Aspects of the SDWA 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 John   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  out  while balancing the
sometimes conflicting demands of good science and implementable policy.


                                                   Marian Mlay
                                                  Office of Ground-Water Protection

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                               EXECUTIVE SUMMARY

      The Amendments to  the Safe Drinking  Water Act  (SDWA), which were passed in
3une  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 which "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.
                                        ES-1

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HYDROGEOLOGIC AND CONTAMINANT CONTROLS OVER WHPA DELINEATION
     These delineation guidelines provide a  discussion  of the basic concepts of ground-
water  flow and contaminant transport, as they apply to the task 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 lower 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.   Unconfined 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-induced 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.
                                        ES-2

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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 on 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
                                        ES-3

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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  or  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 methods  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.
                                        ES-4

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     Analytical  methods  may  be  used  to define  ground-water flow  boundaries  and
contaminant transport 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.
                                        ES-5

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                                 CONTENTS

FOREWORD
ACKNOWLEDGEMENTS
EXECUTIVE SUMMARY	      ES-1
CONTENTS 	          i
1    INTRODUCTION	        1-1
1.1   LEGISLATIVE AUTHORITY	        1-1
1.2   PURPOSE AND SCOPE OF DOCUMENT	        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	        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	      3-20
   3.3.3    Policy Considerations	      3-22
it    WHPA DELINEATION METHODS	       4-1
4.1   INTRODUCTION TO WHPA DELINEATION METHODS	       4-1
4.2   WHPA DELINEATION METHOD ASSESSMENTS	       4-4
   4.2.1    Arbitrary Fixed Radii	       4-4
   4.2.2    Calculated Fixed Radii	       4-6
   4.2.3    Simplified Variable Shapes	      4-10
   4.2.4    Analytical Methods	      4-14
   4.2.5    Hydrogeologic Mapping	      4-19
   4.2.6    Numerical Flow/Transport Models	      4-29
4.3   WHPA DELINEATION METHOD COSTS	      4-32
4.4   WHPA COMPARATIVE ANALYSIS	      4-35
4.5   METHOD SELECTION CONSIDERATIONS	      4-37
   4.5.1    Technical Considerations	      4-37
   4.5.2    Policy Considerations	      4-40
5    EXAMPLE OF CRITERIA AND METHOD SELECTION	       5-1
5.1   PROBLEM STATEMENT:  THE HYPOTHETICAL STATE	       5-1
5.2   EXAMPLE OF CRITERIA SELECTION	       5-2
   5.2.1    Overall Protection Goals	       5-2
   5.2.2    Technical Considerations	       5-2
   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-l
APPENDIX A-STATE, COUNTY, AND LOCAL
DELINEATION APPROACHES	       A-l
A.I  STATE EXAMPLES	       A-l
                                      u

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                              CONTENTS (cont'd)

   A.I.I    State of Florida	       A-l
   A.1.2    Dade County, Florida	       A-3
   A.I.3    Massachusetts	       A-*
   A.1.4    Vermont	       A-6
A.2  EUROPEAN DELINEATION APPROACHES	       A-7
   A.2.1    The Netherlands	       A-7
   A.2.2    West Germany	       A-9
APPENDIX B—COMPARATIVE ANALYSIS	       B-l
B.I  CAPE COD, MASSACHUSETTS	       B-4
   B.I.I    Hydrogeology of  Study Area	       B-*
   B.I.2    Method Application	       B-*
   B.I.3    Data Requirements	       B-5
   B.1.4    Comparison of Resulting WHPA's	       B-5
B.2  SOUTHERN FLORIDA	       B-13
   B.2.1    Hydrogeology of  Study Area	       B-13
   B.2.2    Method Application	       B-13
   B.2.3    Data Requirements	       B-13
   B.2.*    Comparison of Resulting WHPA's	       B-l*
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.*    Comparison of Resulting WHPA's	       B-19
B.*  SOUTHWESTERN CONNECTICUT	       B-24
   B.4.1    Hydrogeology of  Study Area	       B-2*
   B.4.2    Method Application	       B-24
   B.4.3    Data Requirements	       B-25
   B.4.*    Comparison of Resulting WHPA's	       B-25
B.5  SUMMARY AND CONCLUSION
APPENDIX C—GLOSSARY	       C-l
APPENDIX D-MODEL ASSESSMENT FOR DELINEATING WELLHEAD
PROTECTION AREAS	       D-l
                                      111

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                                      FIGURES
Figure No.                                                                      Page
1-1        General approach to State WHPA delineation ...................        1-4
2-1        Ground-water flow system (stream valley) under
           natural conditions ...........................................        2-2
2-2        Ground-water flow system (stream valley) affected
           by a pumping well ...........................................        2-4
2-3        Confined aquifer with upward leakage .........................        2-7
2-4        Confined aquifer with downward leakage .......................        2-8
2-5        Elimination constant and 99.9% elimination of some
           relevant bacteria and viruses in ground water ...................       2-18
2-6        Terminology for wellhead protection area
           delineation (hypothetical pumping well
           in porous media)  ............................................       2-20
2-7        Terminology for wellhead protection area delineation
           (hypothetical contaminant transport in porous media) ............       2-2 1
2-8        Terminology for wellhead protection area delineation
           (hypothetical ground-water basin in mature karst) ...............       2-23
2-9        Terminology for wellhead protection area delineation
           (hypothetical ground-water basin in fractured rock) ..............       2-24
2-10       Terminology for wellhead protection area delineation
           (hypothetical confined aquifer in porous media) .................       2-25
3-1        Relationship between WHPA delineation criteria
           and physical processes .......................................        3-3
3-2        Aquifer with flat water table and high rainfall
           conditions, where boundaries of ZOI and ZOC
           approximately coincide (conceptual) ...........................        3-5
3-3        Flow velocity ranges ........................................        3-7
3-4        Flow boundaries criteria (conceptual) ..........................        3-9
3-5        Assimilative capacity criteria (conceptual)  .....................       3-10
3-6        Consideration factors that may affect process of
           criteria selection ...........................................       3-18
4-1        Interrelationships of  WHPA methods ...........................        4-3
4-2        WHPA delineation using the arbitrary  fixed radius method ........        4-5
4-3        WHPA delineation using the calculated fixed radius method .......        4-7
4-4        WHPA delineation using FDER volumetric  flow equation
           for well in Florida ...........................................        4-9
                                          IV

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                                 FIGURES (cont'd)


4-5        WHPA delineation using simplified variable shapes method	       4-11

4-6        Examples of standardized forms of WHPA delineation
           using simplified variable shapes	       4-13
4-7        WHPA delineation using the uniform flow analytical model	       4-15

4-8        WHPA delineation using arbitrary fixed radii,
           analytical model, and hydrogeologic mapping
           (example from Massachusetts)	       4-17

4-9        WHPA delineation using analytical models, step 1:
           Determination of downgradient null point using
           pumping test data (example from Cape Cod,
           Massachusetts)	       4-18

4-10       WHPA delineation using analytical models, step 2:
           Identify upgradient null point based on Strahler
           prism model (example from Cape Cod, Massachusetts)	       4-20

4-11       WHPA delineation using analytical models, step 3:
           WHPA delineation using upgradient and downgradient
           null points (example from Cape Cod, Massachusetts) ,	       4-21

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)   	       4-23

4-14       WHPA delineation using hydrogeologic mapping
           (example from Vermont)	       4-25

4-15       WHPA delineation using hydrogeologic mapping:  dye
           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 analysis—What 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 //I,
           Cape Cod, MA, 10-Year TOT	       B-7

B-3        WHPA comparative analysis,  example for well //I,
           Cape Cod, MA, 25-year TOT  	       B-8

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FIGURES (cont'd)
B-4

B-5

B-6

B-7

B-8

B-9

B-10

B-ll

B-12

B-13

B-14

B-15

B-16
WHPA comparative analysis, example for well //I,
Cape Cod, MA, 50-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
Florida, 500-day travel time 	
WHPA comparative analysis, example from Colorado,
1-year TOT 	
WHPA comparative analysis, example from Colorado,
5-year TOT 	
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,
5-year TOT 	
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
        VI

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                                      TABLES

Table No.
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
                                         Vll

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          GUIDELINES FOR WELLHEAD PROTECTION AREA DELINEATION

                                    CHAPTER 1
                                 INTRODUCTION

     Nearly  half the population in  the  United  States  uses wells or springs to  obtain
drinking  water (U.S. Geological  Survey, 1984).  Improper management of contamination
sources resulting from human activities often 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 (SDWA) 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  (SDWA, 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 SDWA 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.
     The  SDWA  incorporates  the  fundamental definition of a WHPA in Subsection
1428(e):
                                        1-1

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     (e)  DEFINITION  OF WELLHEAD  PROTECTION  AREA—As used  in  this
     section, the term 'wellhead protection area' means 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.   The extent  of  a wellhead protection area,
     within a State, necessary to provide protection from contaminants which  may
     have any adverse effect 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 the  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 wellfield
     is located.

     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

     •     Public participation.

     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.
                                      1-2

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1.2  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  to  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
specific 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
models.
     Only  a few States have been active in wellhead protection.  However, numerous
European  nations  have been involved  in  such  programs  (Van  Waegeningh,  1985).
Information based on their experiences has been incorporated into this  document.
                                         1-3

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                    Figure  1-1
General  Approach to State WHPA  Delineation
     STAGE
                  WORKING GROUPS
                   OR COMMITTEES
                    ESTABLISHED
                        I
                 TECHNICAL STUDIES
                        AND
                   INSTITUTIONAL
                     ANALYSIS
                        I
                     DETERMINE
                    STATE WHPA
                     CRITERIA
                        I
                     DETERMINE
                    APPROPRIATE
                   WHPA METHODS
                        1
                DELINEATE BOUNDARIES
                 OF PROTECTION AREA
                    FOR SPECIFIC
                 WELLS/WELL FIELDS
                        I
                      CONDUCT
                    ADDITIONAL
                      STUDIES
                        1
                       REFINE
                    DELINEATION
                   OF BOUNDARIES
                   AS APPROPRIATE

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     EPA expects that delineation of WHPA's will be implemented so as to protect wells
from three general categories of threats--the 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 to:
     •    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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     •     Assist 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 WHP~one  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 aspects of WHP  delineation
must consult the relevant technical section of  the "grant guidance" package for insights
into  EPA's  approach for determining program  "adequacy" under  the  SDWA.   These
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
Protection in EPA Headquarters  and the Regions.
IA  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.
                                         1-6

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     Chapter 2  of  this  guidance  provides  basic  information  on  hydrogeologic  and
contaminant  controls over 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 WHPA;  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

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                                    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

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                                  Figure 2-1
                  Ground-water Flow System (Stream
                    Valley)  Under Natural Conditions
             Recharge
                                                      Recharge
                                                  x Ground-water
                                                 i  Divide
                        ,,-.   	   	                            . I -,.--,   Jl  ~-
          *j/\^'\^'/\^'/\2'/\2~,\ ^Vlow permeability rock-^/^/^^/^
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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
                  Ground-water
                  Divide
      Water Table
    a) CROSS SECT/ON
                            Stream
                                                                  Ground-water
                                                                     Divide
             90    80     70    60
                                                          110 120   110  100
    b) PLAN VIEW
            LEGEND:
              %    Pumping Well
            	Equipotential Lines
           	Ground-water Divide
            	*~  Flow Line
SOURCE: Modified from Driscoll, 1986
Az
Drawdown at Well
Zone of Contribution to the Well
Water Table

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     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 well.

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.

      and

                 Recharge that  enters the aquifer  through the area of influence
            of  a well  will not necessarily travel  to 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.
2.2  OTHER AQUIFER CONSIDERATIONS
     Aquifers  in porous, granular  materials  are commonly  divided into two  types,
unconfined 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 may 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
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
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."  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
(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
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).
     Apart from these hydraulic head relationships,  the low permeabilities of confining
units overlying confined aquifers can reduce both the travel times to and contaminant
concentrations in the aquifer, so that the contaminant may pose  a reduced threat to the
                                         2-6

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                                    Figure  2-3

                Confined Aquifer with  Upward  Leakage
                                                       Water Production Well
   o
   <
   oc
  o

  UJ
  o
  N
                                                                         Potentiometric
   cc

   i
   UJ


   O
   N
                       Cased or Cemented Wells
                                                                 \ Confining Unit

                                                                 •fcjjIAquitardl 5
                    Direction of Ground-water Flow
SOURCE: Everett. 1987
                                                                         NOT TO SCALE

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                                      Figure  2-4
              Confined  Aquifer  with Downward  Leakage
o
HI

O
N
Abandoned or Inadequately
Cased or Cemented Well
            \
                                                       Water Production Well
                                                                 jj'Uncontmed >•'*'••'* Table
                                                                        J.P.op.n.iom.tr
                                                                   Confining Unit
                                                                    Uquitardl
             Direction of Ground-water Flow
SOURCE: Everett. 1987
                                                                            NOT TO SCALE
                                           2-X

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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  depression, 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
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 shallow, 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 shallow  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
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
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

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      Where leakage occurs through adjacent strata, recharge is generally greater in the
deepest parts of 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 Witherspoon (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
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
large  pathways.  As a result, flow velocities in karst aquifers having conduit flow can
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  result 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 basin.
     As discussed  in Chapters 3 and 4, 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
     Subsection  1428(a) of  the  SOW A  requires States to adopt programs "to protect
wellhead areas...from contaminants which may have any adverse affects on the health of
persons."    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 WHPA 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 WHPA criteria,  the
subject of Chapter 3.
2.3.1 Inorganic Chemicals
     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 denitrification, adsorption, bacterial decomposition,
precipitation, and  chelation—all 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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metals  moving through clay, whereas there  is only slight retardation of water-soluble
organic constituents exerting a chemical oxygen demand (Griffin and Shimp, 1978; Griffin,
et al., 1976).  The comparative effectiveness of different clay 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.
      Although certain metals may persist for long periods in ground 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).
      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) sulfide 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 activity, 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 the
character of the substrate (Helling, 1971; Iwata, et al.,  1973; Griffin, et al., 1979).
                                        2-14

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      Decomposition is especially enhanced by micro-organisms, which are most active in
soils and in aerobic, 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  enterotoxin-
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

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                                 TABLE 2-1

          Persistence of Organic Substances in Ground Water 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
Trichioroethane
1,1,1 -TrichJoroethane
Dichlorobenzene
          10
          2
          1
          1
Pesticides* (solubility in
water)

Chlordane
DDT
Dieldrin
Heptachlor
Toxaphene
DDVP
Methyl demeton S
Thimet
          2 to ^
          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
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

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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 2-5).  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

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                                  Figure  2-5
             Elimination  Constant and  99.9% Elimination
                     of  Some  Relevant  Bacteria  and
                         Viruses  in  Ground  Water
   99.9% Elimination    III     |     I     |     I     |     |     I     ]    I
   in Water After    2751  70   35   23   16   14   12    10    9    8    7
                     140  t                             t
                         50 Days                        10 Days
                                      Shigella sp                Coliform bacteria
                            Salmonella faecalis
                                   E. coli
                                   t
                                   Mean of Evaluated Investigations


     More Persistent than E. coli -*	1	^  Less Persistent than E. coli



                                               S. typhi
                  Viruses (Polio-, Hepatitis-, Entero-)
                    S. paratyphi

               S. typhimurium


     Elimination       i     i	1
    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: Matthess, etal.. 1985
                                      __

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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 bring concentrations of  specific contaminants
           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 WHPA
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 ZOC 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

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                             Figure 2-6
              Terminology for  Wellhead  Protection
                  Area Delineation (Hypothetical
                 Pumping  Well in Porous  Media)
                                                       i^-GROUNDWATER
                                                       f     DIVIDE
    LAND SURFACE
                                                             PREPUMPING
                                                            WATER LEVEL
                           (A) VERTICAL PROFILE
NOT TO SCALE
                (B) PLAN VIEW
LEGEND:
  V Water table
   » Ground-water Flow Direction
  • Pumping Well
 ZOI Zone of Influence
 ZOC Zone of Contribution


                    2-20

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                   Figure 2-7
    Terminology  for Wellhead  Protection
       Area  Delineation (Hypothetical
 Contaminant Transport in Porous Media)
                                               GROUND-WATER
                                                   DIVIDE
                                                  PREPUMPING
                                                  WATER LEVEL
                (A  VERTICAL PROFILE
LEGEND:            (B) PLAN VIEW

  S   Water Table
 I   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

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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
ZOT's are shown within the area of influence of the well, where contaminant travel times
are significantly accelerated due to the high hydraulic gradients and flow velocities in this
area. The ZOT is part of the ZOC, 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 ZOC 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 ZOC 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 than the unconfined water table  suggests that this  should 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
approach  might focus  on  a portion of  the  contributing area, based upon some TOT
threshold within the  aquifer.
                                        2-22

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                                  Figure  2-8
      Terminology  for Wellhead Protection  Area Delineation
        (Hypothetical  Ground-water  Basin in  Mature  Karst)
  VERTICAL PROFILE
                   i	1.1   . ' i	I   .  i	1.1.1
                                                                    WATER SUPPLY
                                                                       SPRING
                                                            ZOC
          A
  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.
LEGEND:
   O  Sinkhole
   •  Water Supply Spring
 •^**^- Surface Stream
 —— Conduit System
   V  Water Table

       Limestone
SOURCE: Modified from Quinlan and Ewers, 1985
            NOT TO SCALE
                                       2-23

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                             Figure 2-9
            Terminology for Wellhead Protection  Area
             Delineation (Hypothetical Ground-water
                      Basin in Fractured Rock)
            Ground-
            water
            Divide
 VERTICAL PROFILE
                                                       Stream
 PLAN VIEW
SOURCE: Modified from Otton, 1981
                                                                A'
LEGEND:
  2  Water Table

  ^X Fractures
	  	 Ground-water Divide
                                                             NOT TO SCALE

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                                   Figure 2-10

       Terminology for Wellhead  Protection Area  Delineation

          (Hypothetical Confined  Aquifer in  Porous  Media)
                                                       ZOI
 o


 cc
 UJ
 UJ


 O
 N
 O
 tr

 ui

 O
 N
         I                     r
         |    Abandoned or Inadequately
         .    Cased or Cemented Well


§|^^§^|!gi^
zy°$ifc~r""n'''10~ -'-'•"*'**-•"'••'-
                                               -Area of Net Downward Leakage-


                                                     Water Production Well
                       '.ro'.^'-o.'te

                                                           >:j:(V
                                                                          Potentiometric

                                                                            Surface
                                                              3 Confining Unit

                                                              >\vlAquitardl ^
                                          i            ,
                                     .. .-  -•.. -. - -.• ... .--fct .«---
                                    •••?^•^^^^^•''i:-' *'•*"•'• •*.'-w••-• Vvyy."-y• *^.•**.•• *fjj?H^jC•''i'
Pre-pumping

  Level
                                                              f°'*t
   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

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                                     CHAPTER 3
                              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.
      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
using a criterion for WHPA  delineation, a value or  set of values must be selected  to
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 4 will describe how criteria and criteria thresholds can be
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

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     •     Time of travel
     •     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 3-1, 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  WHPA 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, since  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

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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  in  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 to 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.
Reliance on the ZOI may therefore lead to inappropriate protection in many settings.
3.1.3  Time  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

-------
                            Figure 3-2
            Aquifer with  Flat Water Table  and High
            Rainfall Conditions, Where  Boundaries of
             ZOI and  ZOC Approximately Coincide
                            (Conceptual)
                    ZOI  = ZOC
           RECHARGE
                        PUMPING
                         WELL
RECHARGE
DRAWDOWN
CONTOURS
                 (A) VERTICAL PROFILE
                                                         LAND SURFACE
                                                           PREPUMPING
                                                          WATER LEVEL
                                                        .BEDROCKSURFACE
                                                NOTE:
                                                For the case of small hydraulic
                                                gradient, the ZOI =
             LEGEND:
                * Direction of Ground-water Flow
                   (B) PLAN VIEW
                                                  - Water Table
                                                            NOT TO SCALE
                                 3-5

-------
for a contaminant to reach a well would be affected not only by the distance to the well
but also by the 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 well(s).  Relatively high threshold values for a TOT criterion may be selected
in these cases if  possible, though some concerns over implementability 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  transport" 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
on uncontaminated ground-water flow rates) may be problematic.
      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
                                         3-6

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safety for the vast majority of contaminants. The consequence is that arrival times may
be more accurately estimated than contaminant concentrations.
3.1.4  Flow Boundaries
      A WHPA delineation criterion based on flow 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 flow boundaries as a criterion follows from the
approach of protecting the well's ZOC.  This assumes that  a contaminant  entering the
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.
      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
      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 contaminant(s) 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
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

-------
                                      Figure  3-4
                            Flow  Boundaries Criteria
                                     (Conceptual)
                                                        River Discharging to Ground-water
(a)
                                                     1. PUMPING WELL_—^
                                                               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) ].
                     S  Water Table
                     •—f Direction of Ground-water Flow
                                            3-9
                                                                                 NOT TO SCALE

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     There are no known examples of the use of an assimilative capacity criterion to
delineate a WHPA  for a  wide range of contamination threats.   The existence and the
kinetics of attenuation processes are closely  tied to 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  factor 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:
     •     TOT—5 to 50 years (within the aquifer); less than 5 years in high-flow settings
     •     Distance--!,000 feet to more than 2 miles
     •     Drawdown—0.1 to 1.0 foot
     •     Flow Boundaries—Physical and hydrologic
                                        3-11

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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 goal(s)
      •     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
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                        POLICY ISSUES
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(Hydrogeologic Setting,
Technical Capabilities,
Sources of Contamination,
Other Technical
Considerations)
                      3-18

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-------
3.3.2 Technical Considerations
      This  subsection identifies the  technical factors that can  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 that 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
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 the 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
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
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 TOT's 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
specific site are incorporated by the criterion.
3.3.3 Policy Considerations
      Because a  parallel effort  by EPA is addressing policy/management  issues, this
subsection  will  describe only  a few  basic  policy  considerations for illustration.   The
discussion is not intended to be comprehensive.
      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  understood 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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base, or are labor intensive to apply will be expensive. This may 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.
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.
                                         3-24

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                                    CHAPTER 4
                           WHPA 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
surface in the next few years.
4.1   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 sophistication—from
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

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                                TABLE *-l

             WHPA Delineation Methods and Example Applications
             Method
Example Locations Where Used
Arbitrary Fixed Radii
     Nebraska
     Florida
     Cape Cod, Massachusetts
Calculated Fixed Radii
     Florida
     Vermont
Simplified Variable Shapes
     Southern  England
Analytical Methods
     Cape Cod, Massachusetts
     West Germany
     Holland
Hydrogeologic Mapping
     Vermont
     Connecticut
     Cape Cod, Massachusetts
Numerical Flow/Transport Models
     Southern  Florida
     Cape Cod, Massachusetts

-------
                         Figure 4-1
            Interrelationships of WHPA Methods
                     QUANTITATIVE
                    ANALYTICAL, NUMERICAL
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 ARBITRARY
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  RADIUS
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                                 MAPPING
ARBITRARY
     FIXED RADIUS
   WITH EXTENSION TO
     BOUNDARIES
(PHYSICAL OR HYDROLOGIC)
PHYSICAL
FEATURES

-------
geologic or  geornorphic  controls  on  ground-water  flow.   Intermediate  methods  lie
somewhere between these three "corners."
      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 the 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
      Various  aspects  and specific  examples  of  the  WHPA delineation  methods  are
discussed  in the  following  subsections.   Brief  indications of  the costs involved in
implementation  and  application of  each  method are  presented  here,  though more
quantitative cost estimates are provided in Section 4.3.
4.2.1  Arbitrary Fixed Radii
      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  technique for applying a distance
criterion, can  be  very inexpensive, and  requires relatively little  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.

-------
         Figure 4-2
 WHPA Delineation Using the
Arbitrary Fixed Radius Method
                          WHPA BOUNDARY
                                     NOT TO SCALE

-------
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 areas of heterogeneous and non-
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 aren't 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.
4.2.2 Calculated Fixed Radii
      Delineation of a WHPA using the calculated fixed radii 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  hydrogeology  or  where significant
hydrologic boundaries are present.

-------
                 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 hydrogeologic 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

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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 II 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 an 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)
             _ A/  u4Tt '
            r — \i   F

Where         T =   aquifer transmissivity
               t =    time to reach steady state
               S =    storativity  or specific yield of aquifer
and u is a dimensionless parameter related to the well  function
            W(u) =    ^p

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  =  200 ft2/day
               t   =   1 day
               S  =  0.02
               Q  =  25gpm
               s   =  0.05 feet
                                         4-8

-------
                       Figure 4-4
WHPA Delineation  Using FDER Volumetric  Flow
            Equation for Well  in Florida
    PUMPING
     WELL
                               r =
= 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.)
      .Qt= n-TrH r2
             \
  VOLUME  VOLUME OF
  PUMPED   CYLINDER

-------
and the radius of the  primary protection zone is 315 feet.  To provide a more accurate
WHPA, this  calculated  radius  is then  skewed  in  the  direction of  ground-water  flow
patterns.
4.2.3 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 extents  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.
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
requires a  relatively small amount  of field  data.  In addition, relatively little technical
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
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
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
may be moderate, although  the  costs of implementation (i.e., selecting the appropriate
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
hydrogeologic parameters needed to calculate the shapes of the standardized forms and to
determine  the overall ground-water  flow directions in the vicinity  of specific wells.
                                        4-10

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                                Figure  4-5

               WHPA  Delineation Using Simplified
                     Variable  Shapes  Method
     STEP 7: DELINEATE STANDARD/ZED FORMS FOR CERTAIN AQUIFER TYPE
 Pumping Rate =
Q2
0-3
                      -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: APPL Y 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

-------
Example:  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 ZOC.  Therefore, another technique  is necessary to
close 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
            t  =  -
In  (Z ±
                                           ±  rx)
where
            Z  =
                  2n Kbi
where

     v      =  ground-water flow velocity

     tx     =  travel time from point x to pumping well

     S      =  specific yield or storativity
     K     =  hydraulic conductivity

     b      =  saturated thickness

     i      =  gradient

     rw    =  well radius

     rx     =  distance from point x to pumping well
     +      =  whether point x is  upgradient (+) or downgradient (-) from pumping well.

     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.
                                        4-12

-------
                             Figure 4-6

    Examples of Standardized Forms of WHPA  Delineation

                Using  Simplified Variable Shapes

      (Example from Southern  England for Chalk Aquifers)
          £
          J£
          in
           0.5
     Natural Springs
Pumping Rate <5MI/d
Pumping Rate 5 to 15 Ml/d
  LEGEND:


   • Pumping Well
                                 £
                                 .*
                                 in
                                     -1.5km-
                         Pumping Rate :>15MI/d
          DIRECTION OF GROUND WATER FLOW


           t
SOURCE: Southern Water Authority, 1985
                                4-13

-------
4.2.4  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 (Todd,
1980) shown in Figure 4-7 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
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.
      The uniform flow model can be used to  calculate distances that define the ZOC of a
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
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.
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
                                        4-14

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                                Figure 4-7
                     WHPA Delineation Using the
                    Uniform  Flow  Analytical Model
                                 GROUND
                              Q /SURFACE
              ORIGINAL
             PIEZOMETRIC
              SURFACED
          DRAWDOWN CURVE
                                      CONFINED
                                      AQUIFER
                                  , ,
                                  (a)
                                     IMPERMEABLE
                                                            LU
                                 EQUIPOTENTIAL LINES
                                    GROUNDWATER
                                        DIVIDE

             UNIFORM-FLOW
               EQUATION
                                   x =	Q_
                                    L   2?rKbi
                            Q
                           2Kb!
  DISTANCE TO
DOWN-GRADIENT
  NULL POINT
BOUNDARY
  LIMIT
    LEGEND:

       • Pumping Well




SOURCE: Todd, 1980
       Where:
       Q= Well Pumping Rate
       K = Hydraulic Conductivity
       b = Saturated Thickness
       i = Hydraulic Gradient
       n= 3.1416
                                NOT TO SCALE

-------
for each WHPA.  The data may be derived from pertinent local 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 1:  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 <5c Co.,  1985). The distance to  the downgradient divide (X),
or stagnation point at the well, was calculated using the equation

            X  =  2 9p.  = 1,167 feet


where

      Q     =  pumping rate of the well = 134,760 ft3/day

      i      =  hydraulic gradient of the water table = 0.00125
      T     =  aquifer transmissivity =  14,700 ft^/day.

      The maximum width of the influx zone (Y) is calculated  using the equation

      Y     =  -jT = 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 2:  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.

Example 3:  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
the top 75  feet of the  aquifer, which  is 225 feet thick.   Because the ratio of the well
depth to aquifer thickness is 1:3, the distance to the  upgradient null point is assumed to
                                        4-16

-------
                             Figure  4-8
       WHPA Delineation Using Arbitrary Fixed Radii,
        Analytical Model,  and Hydrogeologic Mapping
                  (Example from Massachusetts)
                       WELL
                                            APPROXIMATE DOWN-
                                            GRADIENT NULL POINT
                                                   f = 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
NOT TO SCALE

-------
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                            4-18

-------
equal one-third the distance to the  regional ground water divide, which is 10,500 feet in
the example (Figure 4-10).
      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  lithology 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

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                               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    Up-Gradient
          /DIVIDE          Null Point
     10
                                                DOWN GRADIENT
                                                NULL POINT
                                                            WELL DEPTH
  LU
  LLJ
  z
  o
  LU
-100
    -200
    -300
    -400
         (EXAGGERATED PROFILE)
                                               Z = Well Depth = 50 FEET
                                               b = Saturated Thickness = 225 FEET
                                               RATIO '•
                                                          = 0.33
                                          LEGEND:
                                                ZONE OF CONTRIBUTION
                                                AQUIFER SATURATED THICKNESS
                                                DIRECTION OF GROUND-WATER
                                                FLOW
                                            V   WATER TABLE
                                            Z = WELL DEPTH
SOURCE: Horsley, 1983
                                                              NOT TO SCALE
                                   4-20

-------
                  Figure 4-11
 WHPA Delineation  Using Analytical Models
Step 3:  WHPA Delineation  Using Upgradient
        and Downgradient Null Point
   (Example from Cape Cod, Massachusetts)
                         •DP-GRADIENT NULL POINT
       -60'
                      DOWN-GRADIENT NULL POINT
       ZONE OF CONTRIBUTION = WHPA
                                         2000 Feet
SOURCE: Horsley, 1983
                                  LEGEND:
                                       Contour Line
                                       Pumping Well
                      4-21

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                          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.
                               
-------
                       Figure 4-13
 WHPA  Delineation  Using  Hydrogeologic Mapping
            (Use of Ground-water Divides)
                                           LAND SURFACE
              WHPA
STREAM
VALLEY
   STREAM
                      \
WHPA      DRAWDOWN    GROUND-WATER
          CONTOURS /   DIVIDE

                                                        A'
LEGEND:
  V  Water Table
  •  Pumping Well
———Ground-water Divide
 ^—*~  Direction of Ground-water Flow
 E%*%l WHPA
                            1-23

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Costs.   Costs  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 will 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
the assumption that shallow local ground-water flow mirrors topography.
      Hydrogeologic 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
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
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 contaminants to  a  well is known,
the information can be used to better understand  ground-water flow in the area, and the
specific sources of water in the well.
      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  to  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.
Geophysics.  Surface  geophysical  techniques have also  been applied in aquifer mapping
investigations.  These  techniques measure  the surface response of subsurface elastic,
                                        4-24

-------
                           Figure 4-14
                    WHPA Delineation Using
                     Hydrogeoiogic Mapping
                     (Example from Vermont)
                Primary Area
               , Secondary Area
                Topographic Divide
              PRIMARY AREA (STRATIFIED DRIFT)
              SECONDARY AREA (TILL AND BEDROCK)
SOURCE: Vermont Dept. of Water Resources, 1985
                               4-25

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                                    Figure 4-15
        WHPA Delineation  Using  Hydrogeologic  Mapping:
                 Dye  Tracing  (Example  From  Kentucky)
              -600-^ Potentiometric surface
              „  f  Traced flow route
                •   Sinking spring
              	-O Spring-fed stream
              	Intermittent stream
^-— Sinking stream
   B . • Inferred 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.
Modified from Quinlan and Ewers, 1985
                                                                           NOT TO SCALE
                                          4-26

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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 determines 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.
     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

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determined and the extent of WHPA's could thus be modified according to the locations of
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
14 dating) may be present also.
     Trichlorofluoromethane (CC^F) 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.   CC13F 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.
     Numerical Flow/Transport Models
     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
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
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

-------
     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 numerical solute transport model
that uses the generated head field as input calculates the WHPA 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 is included as Appendix  D to this report (van  der
Heijde and Beljin, 1987).  An additional, useful guide for  model selection is 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 in the  report  "Model Assessment  for
WHPA Delineation" by IGWMC (Beljin and van  der Heijde, 1987).
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  hydrogeology. 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

-------
                       Figure 4-16
        Simulation Procedure Used in WHPA
        Delineation  with Numerical  Modeling
                               CHOOSE MODEL
                               DEPENDING ON:
                           - PROPERTIES OF SYSTEM
                           -AVAILABLE DATA
                           -AVAILABLE RESOURCES
  INPUT PARAMETER/
BOUNDARY CONDITIONS
 FOR A GIVEN PERIOD
        1
     RUN HEAD
    SIMULATION
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     CONDITION
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     HEAD FIELD
NO
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                        RUN TRAVEL
                           TIME
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             .CALIBRATION,
   MEASURED
  WATER LEVEL
FOR SAME PERIOD
                          DO THEY
                         COMPARE?

-------
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 TOT's (based on the multiple WHPA
zone approach) for a well field in the Biscayne aquifer.
4.3  WHPA DELINEATION METHOD COSTS
     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, although dollar figures  have
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" 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,
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
                                              I      I

     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.
W  WHPA COMPARATIVE ANALYSIS
     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
      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 left 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.
Defensibility. 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.
                                         4-40

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                                    CHAPTER 5
                 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.
      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 unconsolidated sands or  sands and gravels.
                                        5-1

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     •     Certain industries wili be affected by  the WHPA program, and the threat of
           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's  in  an expedient
           manner.
     •     Degree of protection considerations have established that the goal of WHPA
           delineation will be  to  provide  management  of the  well-field area.   It  is
           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 III, respectively.
     •     Approximately 900 wellheads will be in  the first phase for delineation relative
           to chemical threats (i.e., Zone III).
     •     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.
5.2.2  Technical Considerations
     As noted in the problem statement (subsection 5.3.2), most of the aquifers requiring
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
                                         5-2

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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
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
thresholds for the TOT criteria can be established and  applied.  These will  focus on the
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 II).   A 15-year TOT  was seen  as  an
appropriate  threshold to protect the well  against  the threat of chemical contamination
(Zone III).  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.
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.
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.

-------
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 TOT's 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.
                                         5-5

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Relevance to Protection  Goal.   Given the hydrogeologic settings in the State, and the
other assumptions outlined above, most criteria were acceptabie.  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 the 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 for
methods that could map a TOT criterion (Table 4-3).
      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 4.5.1.  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 standpoint of policy considerations, and in  particular relevance to  the
protection goal, analytical models were clearly preferred  over numerical procedures.  The
latter, if  used  for all wells, would be prohibitively expensive  and would prevent the State
from meeting its statutory responsibilities.
                                          5-10

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                                       R-l

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Desaulniers, D.E., J.A. Cherry, and P. Fritz.  1981.  Origin, Age and Movement of Pore
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                                        R-2

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                                        R-3

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Theis, C.V.  1935.  The Relation Between the Lowering of the Pieziometric Surface and
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     Hydrogeologists,   International  Contributions  in  Hydrogeology, Vol.  6.    Heise
     (publisher), Hannover, West Germany.
Van Waegeningh, H.G.  1985.  Protection of Ground-Water Quality, pp. 111-121 and 159-
     166.  in Matthess, et al., 1985 (above).
Van Waegeningh, H.G.  1986. Borderlands of Ground-Water Protection Zones.  Proceedings
     of the  19th Congress of the International Association of Hydrogeologists, Karlovy
     Vary, Czechoslovakia.  Stavebni Geologic,  Prague.
Van Waegeningh, H.G., 1987.   Personal communication.   National Institute of  Public
     Health  and Environmental Hygiene, Bilthoven, The Netherlands.
Vermont  Department  of  Water Resources.   1985.   Vermont Aquifer  Protection Area
     Reference Document.
                                        R-6

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Vorhees,  M.L.  1985.  User's Reference Guide for an Interactive Solute Transport Model.
     Lake Wales, Florida.
Walton, W.C.  1970.  Groundwater Resource Evaluation.  McGraw-Hill Book Co., New
     York.
Walton, W.C.  1984.  Practical Aspects of Ground Water Modeling.  National Water Well
     Association.  Worthington, Ohio.
Yates,  M.V., C.P. Gerba, and L.M.  Kelley.  1985.  Virus Persistence in Groundwater.
     Applied and Envirommental Microbiology. Vol. 49. No. 4.
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.
                                       R-7

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                                    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
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
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.g., 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
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
concept explained in Section 4 and Appendix B.
                                        A-l

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                                   TABLE A-l

                 State WHPA Delineation Methodologies and Criteria
Method
Arbitrary Fixed Radius
Calculated Fixed Radius
Simplified Variable Shapes
Analytical Flow Model
Geologic/Geomorphic
Numerical Flow/Transport
Model
Criteria
Relied on

Distance
Distance
Time of Travel

Time of Travel
Drawdown

Drawdown
Physical Features
Physical Features
Time of Travel
Drawdown
Selected
Locations
Where Used*

Nebraska
Florida
Edgartown, MA
Duxbury, MA

Florida
Southern England
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

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     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.
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.
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
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
           relationships
     •     Application  of  land-use  restrictions  within  the  recharge areas  and  the
           designated wellfield protection zones
     •     Public education programs
     •     Establishment of water treatment programs
     •     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.
                                        A-3

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     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 wellf ield protection zones.
A. 1.3 Massachusetts
     The Commonwealth of Massachusetts does not require extensive WHP (except for
microbial threats), but does incorporate the concept as an option, and fosters  it through
the Aquifer Land Acquisition Program (ALA).  The goals of the 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
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 less 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
           and ground water drain into  Zone II.  The surface drainage area as determined
           by topography is commonly coincident with the  ground-water drainage area
           and will be used to delineate Zone III. In some locations, where surface  and
           ground-water  drainage are  not coincident,  Zone  III shall consist of both the
           surface drainage and the ground-water drainage areas.

-------
      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
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:
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
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 water—such as
hazardous  waste  sites,  surface  impoundments,  landfills,  auto  junkyards,  underground
storage tanks, salt storage sheds,  and  sand and gravel operations—need be documented.
      Information on a water resources protection strategy that identifies existing and/or
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

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      All applications are ranked and prioritized based on two major criteria:  the value
and use of the resource and the degree of resource protection that can be expected from
the proposed water protection strategy.
A. 1.4 Vermont
      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
secondary recharge areas of water wells in Vermont.  These maps will be used by AEC and
other regulatory agencies in their permitting activities.
      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 104 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.
      Eight categories of APA's were delineated based on hydrogeologic factors:
      •     Wells  in  unconfined  and  leaky  unconsolidated aquifers   with  available
           engineering pump tests
      •     Wells in  unconfined and  leaky unconsolidated  aquifers without engineering
           pump tests
      •     Wells in confined unconsolidated aquifers
      •     Bedrock 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
           direction
      •     Springs  in   unconsolidated   material  and   at  the   interface   between
           unconsolidated  material and  bedrock, with  low  relief  in  the upgradient
           direction
      •     Springs emanating from bedrock.
                                         A-6

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There are no regulations associated with mapped APA's, but Vermont's existing regulatory
programs use APA'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
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  most 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
leachable 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
zone is defined by  a 60-day TOT, and is designed to protect the well from  microbial
                                        A-7

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contaminants. There is then a "water 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.2.2 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 III A extends up to 2 kilometers from the well (if the aquifer
boundaries are more distant). Zone III 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.
                                        A-9

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                                    APPENDIX B
                             COMPARATIVE ANALYSIS

     Comparative analyses of WHPA methods were presented in Chapter 4 as a valuable
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
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
                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
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
the comparative  analysis  and the type of data required  by each method are shown in
                                        B-l

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Figure B-l.  Given  the varying criteria thresholds chosen  by the various government
bodies, it was not possible in this assessment to consider the same criteria and methods
for all cases.
      Methods and criteria thresholds used in these comparative analyses have not been
endorsed  or  approved  by EPA.  The  analyses  presented  here  are  intended only  to
demonstrate  a  valuable  procedure,  rather  than  to  endorse or critique any specific
delineation method.  In addition, these analyses are not meant to support or critique the
WHPA delineation criteria or  methods  chosen by the State or  locality.   Furthermore,
numerous assumptions were made that may affect the  accuracy of the WHPA boundaries
shown. The results should therefore not be used to judge WHP in these specific areas.
                                         B-2

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B.1 CAPE COD, MASSACHUSETTS
B.I.I  Hydrogeology of Study Area
     The principal water-bearing formations on Cape Cod, predominantly unconsolidated
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 surficial 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
also been identified.   Recharge to the ground-water system is  provided primarily through
precipitation during the winter and spring seasons.  Typically,  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
evapotranspiration; a small portion is  lost through  direct runoff to streams, ponds, and
swamps.
B.I.2 Method Application
     WHPA delineation methods used in the Cape Cod comparative  analysis included (1) a
calculated fixed radius method, (2) two analytical methods (the uniform  flow  model and
the Strahler prism model), and (3) a numerical model.  Comparative analyses of delineated
areas were done for two wells.
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 (Todd,
1980) (see Chapter 4).   The  model  was  used to estimate the 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
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
                                         B-4

-------
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.I.3 Data Requirements
     Data used  in the  CFR and analytical  methods  are  listed in  Table B-l.  These
parameters reflect only hydrogeologic properties of the aquifer near the wells.  These are
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.I.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-4) 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
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).
     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 surface 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 for

 Well  # 1  Cape Cod, MA, 10-Year TOT
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                    B-7

-------
                Figure B-3
WHPA Comparative Analysis, Example for
  Well #1   Cape  Cod, MA, 25-Year  TOT
   NUMERICAL MODEL
   ANALYTICAL MODEL
   CALCULATED FIXED RADIUS
   EQUATION
                                   WILDLIFE
                             MANAGEMENT AREA
                     B-8

-------
                               Figure  B-4
          WHPA Comparative  Analysis, Example for
             Well #1   Cape Cod, MA,   50-Year TOT
        —• NUMERICAL MODEL
         —i ANALYTICAL MODEL

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-------
                      Figure  B-5
     WHPA  Comparative Analysis Example for
      Well #2   Cape  Cod, MA  10  Year  TOT
                                              -'.Waqiioit Village
                                             •••
      2000 Feet
SCALE
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ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
                           B-10

-------
                      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
0
I
2000 Feet
   SCALE
                                    NUMERICAL MODEL
                                    ANALYTICAL MODEL
                                   I I M I I
                                  ii STRAHLER PRISM MODEL
                                  • CALCULATED FIXED
                                    RADIUS EQUATION
                              B-12

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B.2 SOUTHERN FLORIDA
B.2.1  Hydrogeology of Study Area
     Virtually all  of southeast Florida's residential, commercial, and industrial water  is
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.
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.
                                       B-13

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B.2.4 Comparison of Resulting WHPA's
     The CFR approach provided a moderate overlap with and less coverage  than  the
numerical model for TOT's of 30, 210, and 500 days, as shown in Figures B-8 through B-10.
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.

-------
                          Figure  B-8
                WHPA Comparative  Analysis
            Example  from  Florida, 30-Day  TOT
             LEGEND

• ••	FDER VOLUMETRIC EQUATION

— — — UNIFORM FLOW MODEL

          NUMERICAL MODEL
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                              B-15

-------
              Figure B-9

      WHPA Comparative Analysis

    Example from Florida, 210-Day TOT

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                 B-16

-------
                  Figure  B-10
        WHPA Comparative  Analysis
   Example from  Florida, 500-Day  TOT
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  UNIFORM FLOW MODEL

  NUMERICAL MODEL
                      B-17

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B.3 CENTRAL COLORADO
     These comparative  analyses for the State  of  Colorado are based on  unpublished
information obtained from a joint effort by EPA Region VIII, the Colorado Department of
Health, and the U.S.  Geological Survey.  As part  of of this pilot-project effort, WHPA's
were delineated based on flow-boundary and 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.
B.3.1  Hydrogeology of Study Area
     Currently, the Cherokee Water  District withdraws water from the Black Squirrel
Aquifer and exports it to suburbs east of Colorado Springs and to the  Falcon Air Force
Station.  The aquifer is located about 25 miles east of Colorado Springs.  The  setting is
largely rural, and the wells are subject to contamination  from agricultural  sources.  The
Black Squirrel basin is drained by Black Squirrel Creek and its tributaries.  Streams in 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 surface  recharge 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 acre-feet 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 the downgradient end of the basin.
     The source of water to the  wells  tapping  the  alluvial  aquifer is primarily  from
aquifer storage.  Therefore, ground-water withdrawals have lowered the  water table and
reduced the  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 and  salvage of ground water  that
would  have been lost  to evapotranspiration.  Obtaining accurate knowledge of sources and
losses  affecting  the  aquifer  is  complicated  by   wells  that  are unmetered  and  used
seasonally  for agricultural irrigation.
                                        B-18

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B.3.2 Method Application
      WHPA  delineation  methods  used  in  the  Colorado comparative  analysis included
calculated fixed radius and analytical methods.  A comparative analysis was done for one
well.
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
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 to apply the uniform flow model.  The first approach was
described in Chapter 4.  In the second approach, the uniform model was applied  by the
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  (Xj_) and  from the well to 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.
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-l3 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
                                       B-19

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various  methods.   Differences  are likely  due to  the fact that  the  CFR  does  not
incorporate the regional slope of the water table, as the analytical methods do.
     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 zone in the 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.
                                        B-20

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                          Figure  B-ll
        WHPA Comparative  Analysis, Example from
                    Colorado, 1-Year TOT
0        2000 Feet
|	|
   SCALE
UNIFORM FLOW MODEL
UNIFORM FLOW MODEL
(DELINEATED BY U.S.G.S.)
FDER VOLUMETRIC EQUATION
WELL
                              B-21

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                      Figure  B-12
    WHPA Comparative Analysis, Example from
                Colorado, 5-Year  TOT
      2000 Feet
SCALE
•— UNIFORM FLOW MODEL
— UNIFORM FLOW MODEL
   (DELINEATED BY U.S.G.S.)
• • FDER VOLUMETRIC EQUATION
 • WELL
                          B-22

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                      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
                          B-23

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B.4 SOUTHWESTERN CONNECTICUT
     In 1985, 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 Cannondale Aquifer is located in the
town of Wilton, which is approximately 6 miles north of the city of Norwalk.
B.4.1  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  unsaturated  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.

-------
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.
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  TOT's 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., 1976)  applied by the USGS  (Meade and
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
     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
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.
                                       B-25

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                       Figure B-14
    WHPA Comparative  Analysis, Example from
                Connecticut, 1-Year TOT
SCALE
NUMERICAL MODEL,
HYDRO-GEOLOGIC
MAPPING (ZOI AND ZOC)
ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
                           B-26

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                      Figure B-15
    WHPA Comparative Analysis,  Example from
               Connecticut,  5-Year  TOT
SCALE
NUMERICAL MODEL,
HYDROGEOLOGIC
MAPPING (ZOI AND ZOO

ANALYTICAL MODEL
CALCULATED FIXED
RADIUS EQUATION
                          B-27

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B.5 SUMMARY AND CONCLUSION
     Different methods can provide significantly different levels of accuracy for WHPA
delineation around a well field. This is particularly true if surface 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
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
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 no 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 this
                                        B-28

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                        Figure  B-16
     Comparative Analysis Nomenclature
                            Astd
          Percent mutual coverage = (Am/Astc|) X 100%

          Percent under protection = (Au/Astcj) X 100%

          Percent erroneous coverage = (—£_——JX100%

WHERE:
   Astd =  Area given by the method used as the standard for comparisons.

   Ae  =  Area given by method to be evaluated.

   Am =  Area mutually covered by both methods.

   Au  =  Area not covered by method being evaluated.
                           B-29

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Table B-2
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CFR = Calculated Fixed Radius
AM= Analytical Model
NM = Numerical Model
N/A - Not Applicable
1. Numerical modelling results not available as a standard for comparison
2. Comparison done for 5-Year TOT
3. Comparison done for 500-Day TOT
4. Comparison done for 50-Year TOT for Well No. 1
B-30

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comparative analysis, the CFR and analytical models provided more accurate protection
than in the Connecticut 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.
                                        B-31

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                                    APPENDIX C
                                     GLOSSARY

      The purpose of  this Glossary is to provide a  list  of terms  commonly used  by
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
included.

                              GLOSSARY REFERENCES
      (1)   Subsurface-Water Glossary  Working Group.  1987.  Subsurface-water flow and
           solute transport—glossary of selected terms.   Ground-Water  Subcommittee,
           Interagency Advisory Committee on Water Data. (Unpublished review draft).
      (2)   Driscoll,  F. G.   1986.   Groundwater and  Wells,  Second Edition, Johnson
           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. Jackson.  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
assimilation of gas, vapor,  or  dissolved  matter by the  surface  of a solid (2).   The
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attraction and  adhesion of a layer of ions from an aqueous solution to the solid  mineral
surfaces with which it is in contact (3).
Advection.  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).
Alluvial.  Pertaining to or composed of alluvium or deposited by a stream or  running
water (2).
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 on its
floodplain or delta, or as a cone or fan at the base of a mountain slope (2).
Analytical  model.  A  model that  provides approximate  or  exact solutions to simplified
forms of the differential equations for water movement and solute transport.  Analytical
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.
Aquifer. A formation, group of formations, or part of a formation that contains sufficient
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  impermeable  materials  that
functions regionally as a  water-yielding unit.  It comprises two  or  more permeable units
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
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measurement of resulting changes in head in the aquifer both during and after the period
of discharge or addition (1,2).
Area of influence.  Area  surrounding a pumping or recharging well within which the water
table or potentiometric surface has been changed due to the well's pumping or recharge
(1).
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."
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
precipitation or snowmelt, usually sustained  by ground-water discharge (1).  That part of a
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 (4).
Breakthrough curve.   A plot of relative  concentration  versus time,  where  relative
concentration is defined as C/Cg; the concentration at a point in the  ground-water flow
domain divided by the source concentration.
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
migration (1).
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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).
Capillary water.  Water held in  the soil above the phreatic surface by capillary forces; or
soil water above hydroscopic moisture and below the field capacity (1).
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).
Clastic.  Pertaining  to a rock or sediment composed principally of broken fragments that
are derived from pre-existing rocks or minerals and that have  been transported some
distance from their places of origin (2).
Coefficient  of storage.   The volume  of  water an aquifer releases from or takes into
storage per unit surface area of  the aquifer per unit change in head (2).
Coefficient of transmissivity. See transmissivity (2).
Colloid.  Extremely small solid particles, 0.0001 to 1 micron in size,  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.
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
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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
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
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
(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  1424(e)) has been submitted and
approved by the Administrator not  later than  24 months after the date of enactment and
which satisfies the criteria established by the  Administrator; and (2) all or part of an  area
that is  within  an  aquifer designated as a  sole source aquifer  (SSA), as of the date  of
enactment of  the  Safe Drinking  Water  Act  Amendments of  1986, and  for  which  an
areawide ground-water protection plan has been approved under Section 208 of the Clean
Water Act prior to such enactment.
Darcy's law.  An empirically derived equation  for the flow of fluids through porous media.
It is based on the assumptions that flow  is laminar and inertia can be neglected, and states
that velocity of flow is directly proportional to hydraulic gradient (see specific discharge).
Delay time. Duration of time for contaminant or water to move from point of concern to
the well; analogous to time-of-travel.
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Density. Matter measured as mass per unit volume expressed in pounds per gallon (Ib/gal),
pounds per cubic foot (lb/ft^), and kilograms per cubic meter (kg/m^) (2). The mass of
quantity of a substance per unit volume.  Units are kilograms per cubic  meter or grams
per cubic centimeter (3).
Desorption. See sorption, which is the reverse process.
Diffusion coefficient. See molecular diffusion.
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).
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 to the land  surface, surface
water, or atmosphere (1).   An area in which there are upward components of hydraulic
head in the aquifer.  Ground water is flowing toward the surface  in a discharge area and
may escape as a spring, seep, or base flow, or by evaporation and transpiration (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
diffusion  and mixing due 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).
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
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).
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Drawdown.   The vertical distance  ground-water elevation is  lowered,  or the amount
pressure head  is reduced, due to 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
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
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
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).
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Fissure.   A  surface  of  a fracture or crack  in a  rock along which there  is a distinct
separation Ct).
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
modeling  domain  using numerical  methods  to arrive at an approximate solution  to the
differential equation of ground-water flow.
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).
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.
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 breakin a rock, which includes  cracks, joints and faults (4).
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).
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GPD. Gallons per day, a measure of the withdrawal rate of a well.
Gravitational head.  Component of  total hydraulic head related to the position of a given
mass of 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
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
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.
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.
Ground-water flow.  The movement of  water through  openings in sediment and rock that
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.
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Ground-water mound.  Raised  area in a water table or other potentiometric surface,
created by ground-water recharge.
Ground-water recharge.  Process of water addition to the saturated zone, or the volume
of water added by this process (1).
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
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
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
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 (1).  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 m^/day/m^  or  m/day (2). A coefficient
of proportionality describing the rate at which water can  move  through a permeable
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
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
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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 f lowpath.
      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).
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).
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).
Hydrostatic pressure. Pressure exerted by the weight of water at any given point  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
the presence of an excess of water; expressed in units of velocity (1).
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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
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 neighboring 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, or
other fluid; synonymous with void or pore (1).
Intrinsic permeability.  Pertaining to  the relative ease with which a porous medium can
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
for contaminants to move through  the saturated zone and reach a well.
Isoconcentration.   Graphic  plot of points  having  the same  contaminant concentration
levels.
Isotropy.  The condition in which the properties of interest (generally hydraulic properties
of the aquifer) are the same in all directions (1).
Karst topography.   A type of terrain that is formed on limestone, 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).
Laminar flow.  Fluid flow in which the head loss is  proportional to the first power of the
velocity; synonymous with streamline flow and viscous flow.  The stream  lines remain
distinct  and the  flow directions at  every  point  remain  unchanged  with  time.   It  is
characteristic of  the  movement of ground water (1).  Type  of flow  in which the fluid
particles follow paths that are smooth, straight, and parallel to the channel walls.  In
laminar  flow, the  viscosity of the fluid damps out  turbulent motion.   Compare  with
turbulent flow (2).
                                        C-12

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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
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
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 (40 CFR Section 141.2).
MCL.  See Maximum Contaminant Level.
Mechanical dispersion.  Process whereby solutes are mechanically mixed during advective
transport, caused by  the velocity variations at the microscopic level;  synonymous  with
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).
MGD.  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).
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).
                                        C-13

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Nonpoint source. A source discharging pollutants into the environment that is not a single
point (1).
Observation well.   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.
Partial penetration. When the  intake  portion of the well is less than the full thickness of
the aquifer (2).   A well constructed  in such a way that it draws water directly  from a
fractional part of the total thickness  of the aquifer.  The fractional part may be located
at the top, the bottom, or anywhere else in the aquifer (3).
Paniculate 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).
Permeability.   Ability of a porous medium to transmit fluids under a hydraulic gradient
(1).  The property or capacity of a  porous rock, sediment, or soil 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).

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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
(1).
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).
Phreatic water.  See saturated zone.
Piezometric surface. See potentiometric  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
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
(1).
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.
Potable water. Suitable for human consumption as drinking water (1).
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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).
Potential drop. Difference in total head between two equipotential 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 unconfined 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
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
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).
Radial flow. The flow of  water in an aquifer toward a vertically oriented well (3).
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 (i.e., in/yr) or a volume (2).
Recharge area.  Area in which water reaches the zone of saturation  by surface infiltration
(1).  An  area in which  there are downward components of hydraulic head  in the aquifer.
Infiltration  moves downward into the deeper parts of an aquifer in a  recharge area (3).
                                         C-16

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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.
SDWA.  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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Spring.  Discrete place where ground water flows naturally from rock or soil onto the land
surface or into a surface-water body (1).
SSA.  See Sole Source Aquifer.
Stagnation point.  A place in a ground-water 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).
Static head.  See head, static.
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 1428(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).
Storage, specific.  The  amount of  water released  from or  taken  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
unconfined aquifer, the storativity is equivalent to the specific yield.  Also called storage
coefficient (3).
Time of travel (TOT). The time required for a contaminant to move in the saturated zone
from  a specific point  to a well.
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
                                         C-18

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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
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.
Unconfined.   Conditions  in which the  upper surface of the zone of saturation forms a
water table  under atmospheric pressure (1).
Unconsolidated aquifer.   An aquifer made  up of  loose  material, such as sand or gravel,
that has not undergone lithification.
Underground Injection Control (UIC).   The regulations  for injection wells.  The program
provides grants to States under Section lH3(b) of SDWA.
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
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
effective velocity (1).
                                        C-19

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Water budget.  An evaluation of all the sources of supply and the corresponding discharges
with respect to an aquifer or a drainage basin (3).
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).
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 atmosphere (2).  The
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
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.
Wellfield.  Synonymous with well field.
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).
Wellhead.  The physical structure,  facility,  or device at the land surface from or through
which ground water flows or is pumped from subsurface, water-bearing formations.
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.
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.
ZOC.  See  zone of contribution.
ZOI. 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 (ZOI).  The area surrounding a pumping well within  which  the water
table or potentiometric surfaces have been changed due to ground-water withdrawal.
                                        C-20

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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
well.
ZOT.  See zone of transport.
                                       C-21

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                                   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.
                                       D-l

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                              EXECUTIVE SUMMARY
     One element of the 1986 Amendments  to the Safe Drinking Water Act (SOWA)  of
     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:
     •    Zone of influence around a well or well field
     •    Presence of interfering neighboring wells or well fields
     •    Water table drawdown by the wells or well fields under consideration
     •    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 hydrologic conditions.
     To  determine a site-specific WHPA,  a systematic, analytic approach is necessary;
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
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  movement, concentrations, and mass
balance components  of water-soluble constituents.
                                        D-2

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      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
documentation, and its usability, portability, and modifiability.   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
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

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R.S. Kerr  Environmental  Research  Laboratory in Ada,  Oklahoma.   This  search  was
followed 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
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
descriptions and detailed information on each model, and a comparison of usability and
reliability characteristics.
     A major  limitation of this 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,
inadequate quantity or low quality of data often  restricts model utility.

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                                  ATTACHMENT
                   DESCRIPTION OF MODEL CHARACTERISTICS

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).
     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
           water may percolate to the aquifer and eventually reach the well).
     T     Travel times (isochrones).
     V     Velocities (ground-water velocities).
                                       D-5

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No.
i.





2.







3.







4,










5.




6.





7.







8.





Author(s)
S.P. Neuman
P. A. Wither-
spoon



S.P. Neuman







T.N. Narasimhan







T.A. Prickett
C.G. Lonnquist









G.F. Pinder
E.O. Frind



G.F. Pinder
C.I. Voss




P.S. Huyakorn







P.S. Huyakorn





Contact Address
Dept. of Hydrology and
Water Resources
University of Arizona
Tucson, A2 85721


Dept. of Hydrology and
Water Resources
University of Arizona
Tucson, A2 85721




Battel le Pacific NW Lab
Water and Land Resources
Division
P.O. Box 999
Richland, WA 99352



Consulting Water
Resources Engineers
6 G.H. Baker Drive
Urbana, IL 61801







Dept. of Civil
Engineering
Princeton University
Princeton, NJ 08540

U.S. Geological Survey
Water Resources Division
National Center, M.S. 431
Reston, VA 22092


Geotrans, Inc.
209 El den St., *301
Herndon, VA 22070





Geotrans, Inc.
209 El den St., #301
Herndon, VA 22070



Model Name
( last update)
FREESURF 1
(1979)




UNSAT2
(1979)






TRUST
(1981)






PLASM
(1986)









1 SOQUAD
(1982)



AQU I FEM
(1979)




GREASE 2
(1982)






SATURN 2
(1982)




Model
Description
Simulation of two-dimen-
sional vertical or axi-
symmetric, steady-state
flow in an anisotropic,
heterogeneous, confined
or watei — table aquifer.
A two-dimensional finite
element model for hori-
zontal, vertical or axi-
symmetric simulation of
transient flow in a var-
iably saturated, nonuni-
form, anisotropic porous
med i urn .
To compute steady and
nonsteady pressure head
distributions in multi-
dimensional, heteroge-
neous, variably saturat-
ed, deformable porous
media with complex geom-
etry.
A flexible two-dimen-
sional or quasi -three-
dimensional, transient,
saturated flow model for
single layer or multi-
layered confined, leaky
confined, or water-table
aquifer systems with
optional evapotranspi ra-
tion and recharge from
streams.
Finite element model to
simulate three-dimen-
sional groundwater flow
in confined and uncon-
fined aquifers.
To simulate transient.
areal ground water flow
in an isotropic, hetero-
geneous, confined,
leaky-confined or water
table aqui fer.
To study transient, mul-
tidimensional, saturated
groundwater flow, solute
and/or energy transport
in fractured and unfrac-
tured, anisotropic, het-
erogeneous , mu 1 1 i I ayered
porous media.
To study transient, two-
dimensional variable
saturated flow and sol-
ute transport in aniso-
tropic, heterogeneous
porous media.
Model
Output
AI,CD,RA,F





AI,CD,RA,F







AI,CD,RA,F







AI.CD.RA.F










AI,CD,RA,F




Al .CD.RA.F





AI,CD,RA,F,C,
V






AI,CD,RA,F,C,
V




IGWMC
Key
0020





0021







0120







0322










0510




0514





0582







0583





D-6

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No.
9.








10.









11.






12.






13.







14.








15.





Author(s)
P. Huyakorn








P. Huyakorn









J.E. Reed
M.S. Bedinger
J.E. Terry




T.R. Knowles






INTERA
Env i ronmenta 1
Consultants,
Inc. and
1 NTERCOMP
Resource
Development 4
Eng., Inc.
C.R. Faust
T. Chan
B.S. Ramada
B.M. Thompson





L.F. Konikow
J.D. Bredehoeft




Contact Address
Geotrans, Inc.
209 El den St., #301
Herndon, VA 22070






IGWMC
Hoi comb Research
Institute
Butler University
4600 Sunset Avenue
Indianapolis, IN 46208




U.S. Geological Survey
Room 2301
Federal Bui 1 ding
700 W. Capitol Ave.
Little Rock, AR 72201


Texas Water
Development Board
P.O. Box 13231
Austin, TX 7871 1



U.S. Geological Survey
Box 25046 Mai 1 Stop 411
Denver Federal Center
Lakewood, CO 80225




Performance Assessment
Dept.
Office of Nuclear Waste
Isolation
Battelle Project Mngmt.
Di v.
505 King Avenue
Columbus, OH 43201

U.S. Geological Survey
431 National Center
Reston, VA 22092



Model Name
( last update)
SEFTRAN
(1983)







TRAFRAP
(1986)








SUPERMOCK
(1975)





GWSIM-I 1
(1981)





SWIP/
SWIPR/
SWENT
(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 con-
figuration of saturated,
heterogeneous aquifers.
A finite element model
to study transient, two
dimensional, saturated
ground water flow and
chemical or radionuclide
transport in fractured
and unfractured, aniso-
tropic, heterogeneous,
multi-layered porous
media.
To simulate transient
stress and response in a
saturated-unsaturated
ground water flow system
including a water-table
aquifer overlying a con-
f i ned aqu i f er .
A transient, two-dimen-
sional, horizontal model
for prediction of water
levels and water quality
in an anisotropic heter-
.ogeneous confined and
unconfined 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 ax i symmet-
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 ,CO,RA,F,C,
V,P







Al ,CD,RA,F,C,
V,P








Al ,CD,RA






Al ,CD,F,C,RA






Al ,CD,RA,F,C,
V






Al ,CD,RA,F








Al ,CD,RA,F,C,
V




IGWMC
Key
0588








0589









0611






0680






0692







0694








0740





D-7

-------
No.
16.










17.










18.





19.






20.









21.






22.





23.




Author (s)
S.P. Garabedian
L.F. Konikow









W.E. Sanford
L.F. Konikow









P.C. Trescott
S.P. Larson




P.C. Trescott
G.F. Pinder
S.P. Larson




Miller, 1 .
J. Marlon-
Lambert







G. Segol
E.O. Frind





K.R. Rushton
L.M. Tom! inson




H.M. Haitjema
O.D.L. Strack



Contact Address
U.S. Geological Survey
431 National Center
Reston, VA 22092








U.S. Geological Survey
431 National Center
Reston, VA 22092








U.S. Geological Survey
Branch of Groundwater
M.S. 411 National Center
Reston, VA 22092


U.S. Geological Survey
Branch of Ground Water
M.S. 41 1 National Center
Reston, VA 22092



Golder Associates
2950 Northup Way
Bel levue, WA 98004







Dept. of Earth Sciences
University of Waterloo
Waterloo, Ontario
Canada N2L 3G1



Dept. of Civi 1
Engineering
Univ. of Birmingham
P.O. Box 363
Birmingham, B15 2TT
United Kingdom
School of Publ ic 4
Environmental Affairs
10th Street
Indiana University
Bloomington, IN 47405
Model Name
( last update)
FRONTRACK
(1983)









MOCDENSE
(1986)









USGS-3D-
FLOW
(1982)



USGS-2D-
FLOW
(1976)




GGWP
(1983)








3-D
SATURATED-
UNSATURATED
TRANSPORT
MODEL
(1976)

AQU-1
(1979)




SYLENS
(1985)



Model
Description
A f in i te di f ference
model for simulation of
convective transport of
a conservative tracer
dissolved in groundwater
under steady or tran-
sient flow conditions.
The model calculates
heads, velocities and
tracer particle
positions.
A model to simulate
transport and dispersion
of either one or two
constituents in ground-
water where there is
two-dimensional, density
dependent flow, it uses
finite-difference and
method of characteris-
tics to solve the flow
and transport equations.
To simulate transient.
three-dimensional and
quasi three-dimensional,
saturated flow in an i 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
ax i symmetric and quasi -
three dimensional flow
and transport of reac-
tive solutes in aniso-
tropic, heterogeneous.
multi-layered aquifer
systems.
Determination of concen-
tration of conservative
or nonconservat i ve sol-
ute in transient, three-
dimensional saturated-
unsaturated flow sys-
tems.
Basic transient model
for single layered two-
dimensional horizontal
ground water f low.


Modeling of steady-state
groundwater flow in re-
gional double aquifer
systems with local in-
terconnect ions.
Model
Output
Al ,CD,RA,F,C,
V,P,T









AI,CD,RA,F,C,
V









Al ,CD,RA,F





Al ,CD,RA,F






Al ,CD,RA,F,C,
V,P,T








AI.CD.F.C






AI.CD.F





Al ,CD,RA,F




IGWMC
Key
0741










0742










0770





0771






1010









1070






1230





1791




D-8

-------
No.
24.







25.









26.





27.




28.






29.








30.








31.







Author(s)
C. Van Den
Akker






P. Van der Veer









S.K. Gupta
C.T. Kincaid
P.R. Meyer
C.A. Newbi I 1
C.R. Cole

S.K. Gupta
C.R. Cole
F.W. Bond


A.E. Reisenauer
C.R. Cole





R.W. Nelson








R.D. Schmidt








L.R. Town ley
J.L. Wilson
A.S. Costa





Contact Address
National Institute for
Water Supply
P.O. Box 150
2260 Ad Leidschendam
The Netherlands



Ri jkswaterstaat
Data Processing Division
P.O. Box 5809
2280 HV Rijswijk (2.H.)
The Netherlands





Battel le Pacific NW Labs
P.O. Box 999
Richland, WA 99352



Battel le Pacific NW Labs
Water and Land Resources
Division
P.O. Box 999
Richland, WA 99352
Water and Land Resources
D i v i s i on
Battel le Paci f ic NW Labs
P.O. Box 999
Richland, WA 99352


Battel le Paci f ic NW Labs
Sigma 5 Bui I ding
P.O. Box 999
Richland, WA 99352





U.S. Dept. of the
Interior
Bureau of Mines
P.O. Box 1660
Twin Cities, MN 551 1 1




Ralph M. Parsons
Laboratory for Water
Resources and
Hydrodynamics
Room 48-21 1
Massachusetts Inst. of
Technology
Cambridge, MA 02139
Model Name
( last update)
FLOP-2
(1975)






MOTGRO
(1981)








CFEST
(1985)




FE3DGW
(1985)



VTT
(1979)





PATHS
(1983)







ISL-50
(1979)







AQUIFEM-1
(1979)






Model
Description
To generate path lines
for steady-state, flow
in a semi -con f i ned, i 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
simul at ion of f low in a
large multi-layered
groundwater basin.
A transient model to
calculate hydraulic head
in conf i ned-unconf i ned
mul t i -1 ayered aquifer
systems, and to generate
streamlines and travel-
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 pathline equations.
A three-dimensional
model to describe tran-
sient flow behaviour of
leachants and ground-
water in an anisotropic,
homogeneous aquifer in-
volving an arbitrary
pattern of injection and
recovery wel Is.
A two-dimensional, fi-
nite-element model for
transient, horizontal
groundwater f low.




Model
Output
C,V,P,T







AI.CD.F.V.P.T









Al ,CD,F,RA,C,
V




Al ,CD.RA,F,V




AI.CO.V.P.T






F,V,C,P,T








V.P.T








Al ,CD,RA,F







IGWMC
Key
1821







1830









2070





2072




2092






2120








2560








2630







D-9

-------
No.
32.







33.







34.







35.






36.







37.







38.






Author(s)
T.A. Prickett
T.G. Naymik
C.G. Lonnquist





D.R. Posson
G.A. Hearne
J.V. Tracy
P.P. Frenzei




J. Boonstra







0. Berney






J.W. Wessel ing







S. Haji-Djafari
T.C. Wei Is






B.Sagar






Contact Address
Consulting Water
Resources Engineers
6 G.H. Baker Drive
Urbana, IL 61801




U.S. Geological Survey
P.O. Box 26659
Albuquerque, NM 87125





1 .L.R.I
P.O. Box 45
Wagen ingen
The Netherlands




Land and Water
Development Division
Food and Agriculture
Organization Un
Via Del le Terme Di
Caracal I a
00100-Rome, Italy
Del ft Hydraul ics
Laboratory
P.O. Box 152
8300 Ad Emmeloord
The Netherlands



D'Appolonia Waste Mgmnt.
Services, Inc.
10 Duff Road
Pittsburgh, PA 15235




Analytic and Computa-
tional Research, Inc.
3106 IngleMOOd Blvd.
Los Angeles, CA 90066



Model Name
( last update)
RANDOM
WALK
(1981)





N.M.F.D.3D
(1980)






S.G.M.P.
(1981)






DlSIFLAQ
(1980)





GROWKWA
(1982)






GEOFLOW
(1982)






AQUIFER
(1982)





Model
Description
To simulate one- or two-
dimensional steady or
unsteady flow and tran-
sport problems in heter-
ogeneous aquifers under
water table and/or arte-
sian or leaky artesian
condition.
Simulation of unsteady
two-dimensional horizon-
tal ground water flow in
multi-layered heterogen-
eous anisotropic aquifer
systems or unsteady
three-dimensional satur-
ated ground water flow.
Simulating steady-state
or transient, two-dimen-
sional, horizontal flow
in a saturated, aniso-
tropic and heteroge-
neous, conf ined/semi-
conf ined/phreat ic aqui-
fer.
Steady-state or tran-
sient simulation of two-
dimensional, horizontal
groundwater f low in a
two- layered, isotropic,
heterogeneous aquifer
system.
Transient simulation of
two-dimensional horizon-
tal groundwater movement
and non-conservative
solute transport in a
multi-layered, anisotro-
pic, heterogeneous aqui-
fer system.
To simulate steady or
nonsteady, two-dimen-
sional areal flow and
mass transport in aniso-
tropic and heterogeneous
aquifers under confined,
leaky confined, or water
table conditions.
Analysis of steady and
non-steady state, two-
dimensional real or
cross-sectional, radial
flow in heterogeneous,
anisotropic multiaquifer
systems.
Model
Output
AI,CD,RA,F,C,
V






Al ,CD,RA,F







Al ,CD,RA,F







Al ,CD,RA,F






Al ,CD,RA,F,C,
V






Al ,CD,RA,F,C,
V






AI,CD,RA,F,V,
P





IGWMC
Key
2690







2740







2800







2870






2982







3220







3230






D-10

-------
No.
39.











40.










41.








42.








43.





44.






45.





Author (s)
B. Sagar











A.K. Runchal










B. Sagar








J.A. Liggett








G.T. Yeh
D.S. Ward




G.T. Yeh
C.W. Francis





G.T. Yeh
D.D. Huff




Contact Address
Analytic 4 Computational
Research, Inc.
3106 Inglewood Blvd.
Los Angeles, CA 90066








Analytic 4 Computational
Research, Inc.
3106 Inglewood Blvd.
Los Angeles, CA 9006







Analytic 4 Computational
Research, Inc.
3106 Inglewood Blvd.
Los Angeles, CA 90066





School of Civi 1 and
Environmental Eng.
Hoi 1 ister Hal 1
Cornel 1 University
Ithaca, NY 14853




Environmental Sciences
Division
Oak Ridge National Lab
Oak Ridge, TN 37830


Oak Ridge National Lab
Environmental Sciences
Division
Oak Ridge, TN 37830



Environmental
Sciences Division
Oak Ridge National Lab
Oak Ridge, TN 37830


Model Name
( last update)
FRACFLOW
(1981)










PORFLOW-
1 1 and 1 1 I

(1987)







FLOTRA
(1982)







GM5
(1982)







FEMWATER/
FECWATER
( 1 98 1 )



AQUIFLOW
(1984)





FEWA
(1983)




Model
Description
Steady and unsteady
state analysis of densi-
ty-dependent flow, heat
and mass transport in
fractured confined aqui-
fers simulating two-di-
mensionally the process-
es in the porous medium
and one-dimensional 1 y in
the fractures, including
time-dependency of pro-
perties.
Steady or transient, 2-D
horizontal, vertical or
radial and 3-D simula-
tion of density depen-
dent flow heat and mass
transport in anisotro-
pic, heterogeneous, non-
deformable saturated
porous media with time
dependent aquifer and
fluid properties.
Steady or transient,
two-dimensional, areal,
cross-sectional or radi-
al simulation of densi-
ty-dependent flow, heat
4 mass transport in var-
iable saturated, an i so-
tropic, heterogeneous
deformable porous media.
Steady state groundwater
calculations in a com-
plex basin. Steady
state simulation of
three dimensional satur-
ated groundwater flow in
an anisotropic, hetero-
geneous mul ti-aqui fer
system.
A two-dimensional model
to simulate transient,
cross-sectional flow in
saturated-unsaturated
anisotropic, heteroge-
neous porous media.
A two-dimensional finite
element model to simu-
late transient flow in
horizontal, anisotropic,
heterogeneous aquifers
under confined, leaky or
unconfined conditions.
A two-dimensional finite
element model to simu-
late transient vertical-
ly averaged flow in con-
f ined, leaky conf ined,
or water table aquifers.
Model
Output
Al ,CD,RA,F,C,
V.P










Al ,CD,RA,F,C,
V









Al ,CD,RA,F,C,
V.P







Al ,CD,RA,F,V








Al ,CD,RA,F,V





Al .CD.RA.F






AI,CD,RA,F,V





IGWMC
Key
3232











3233










3235








3240








3370





3372






3373





D-ll

-------
No.
46.











47.










48.









49.



50.












51.









Author(s)
G.T. Yeh
D.D. Huff










C. 1 . Voss










R.T. Di 1 Ion
R.M. Cranwel I
R.B. Lantz
S.B. Panwa
M. Reeves





C.S. Desai



D.G. Jorgensen
H. Grubb
C.H. Baker, Jr.
G.E, Hi lines
E.D. Jenkins








J.V. Tracy









Contact Address
Environmental Sciences
Division
Oak Ridge National Lab
Oak Ridge, TN 37830








U.S. Geological Survey
431 National Center
Reston, VA 22092








Sandia National Labs
Albequerque, NM 87185








Dept. of Civil Eng. and
Eng. Mech.
University of Arizona
Tuscon, A2 85721
U.S. Geological Survey
Water Research Dept.
1950 Avenue A-Campus
West
University of Kansas
Lawrence, KS 66044-3897







U.S. Geological Survey
Water Resource Dept.
National Center
Reston, VA 22092






Model Name
(last update)
FEMA
(1984)










SUTRA
(1984)









SWIFT
(1981)








MAST-2D



GWMD3
(1982)











GALERKIN
F 1 N 1 TE
ELEMENT FLOW
MODEL
(1979)





Model
Description
A two-dimensional, fi-
nite element model to
simulate solute trans-
port including radioac-
tive decay, sorption,
and biological and chem-
ical degradation. This
model solves only solute
transport equation and
velocity field has to be
generated by a f low
model .
A finite element simula-
tion model for two-di-
mensional, transient or
unsteady-state, satur-
ated-unsaturated, fluid
density dependent ground
water flow with trans-
port of energy or chemi-
cally reactive single
species solute
transport.
A three-dimensional fi-
nite-difference model
for simulation of cou-
pled, transient, density
dependent flow and tran-
sport of heat, brine,
tracers or radionuc 1 i des
in anisotropic,
heterogeneous confined
aqu i fers.
Coupled transient seep-
age and mass transport
in saturated porous me-
dia.
An ax i symmetric finite
difference model to cal-
culate drawdown due to a
proposed wel 1 , at all
existing wel 1 s in the
section of the proposed
well and in the adjacent
8 sections and to com-
pare drawdowns with al-
lowable 1 imi ts;
includes, an optional
program to evaluate a-
1 lowable dep let ion .
A finite element model
for simulation of two-
dimensional, transient
flow in a isotropic,
heterogeneous, confined
or watertable aquifer in
contact with a stream.
The model includes the
calculation of the sur-
face water bal ance.
Model
Output
F.C











AI,CD,RA,F,C,
V









Al ,CD,RA,F,C,
V.P.T








Al ,CD,F,C,V



Al ,CD,RA,F












Al ,CD,RA,F









IGWMC
Key
3376











3830










3840









3868



3870












3881









D-12

-------
No.
52.










53.






54.








55.






56.





57.





58.






59.








Author(s)
1 . Javandel
C. Doughty
C.F. Tsang








M.G. McDonald
A.W. Harbaugh





C.R. Kolterman








B.J. Travis






P.K.M. van der
Heijde




K.R. Rushton





G.T. Yeh






M.Th. van
Genuchten
W.J. Alves






Contact Address
Lawrence Berkeley Lab
Earth Sciences Division
University of California
Berkeley, CA 94720







Ground Water Branch, WRD
U.S. Geological Survey
WGS - Ma i 1 Stop 433
Reston, VA 22092



Water Resources Center
Desert Research
Institute
University of Nevada
System
Reno, NV



Los Alamos National Lab
Earth and Space Sciences
D i v i s i on
Los Alamos, NM 87545



IGWMC
Hoi comb Research
Institute
Butler University
4600 Sunset Avenue
Indianapol is, IN 46208
Dept. of Civil
Engi neer i ng
Univ. Of Birmingham
P.O. Box 363
Birmingham, B15 2TT
United Kingdom
Environmental Sciences
Division
Oak Ridge National Lab
Oak Ridge, TN 37830



U.S. Sal inity Lab
4500 Glenwood Drive
Riverside, CA 92501






Model Name
( last update)
RESSQ
(1983)









MODFLOW
(1983)





GWUSER/
CONJUN
(1983)






TRACR3D
(1984)





THWELLS
(1987)




RADIAL
(1979)




AT123D
(1981)





ONE-D
(1982)







Model
Description
A semi -analytical model
to calculate two-dimen-
sional contaminant tran-
sport by advection and
adsorption in a homo-
geneous, isotropic con-
fined aquifer of uniform
thickness when regional
flow, sources and sinks
create a steady state
f low field.
A modular three-dimen-
sional finite-difference
ground-water model to
simulate transient flow-
ing in an isotropic, het-
erogeneous, layered aq-
uifer systems.
A combined simulation-
optimization model to
determine optimal pump-
ing locations and rates
for confined aquifer
with or without artifi-
cial recharge or for
conjunctive use of aqui-
fer-stream system.
A three-dimensional fi-
nite-difference model of
transient two-phase flow
and mu 1 ticomponent tran-
sport in deformable,
heterogeneous, reactive
porous/fractured media.
To calculate head draw-
down or buildup caused
by mul t i p le wel 1 s in an
isotropic, heterogen-
eous, nonleady, confined
aqui fer.
Determination of heads
due to radial flow to-
wards a well and simula-
tion of flow in vicinity
of wel 1 .

An analytical 1 , 2, or
3-D simulation of solute
transport in a homogen-
eous, an isotropic aqui-
fer, with decay and re-
tardation from a variety
of sources.
Analytical simulation of
one-dimensional convec-
tive-dispersi ve trans-
port of a solute with
linear adsorption in a
steady-state flow field
in a semi-inf i n i te iso-
tropic, homogeneous aqu-
ifer.
Model
Output
C.V.P.T










Al ,CD,RA,F






Al ,CD,F








Al ,CD,RA,F,C,
V





Al ,CD





Al ,CD,F





C.T






C,T








IGWMC
Key
3940










3980






4070








4270






6022





6062





6120






6220








D-13

-------
No.
60.





61.








62.







63.







64.





Author (s)
D. Koch





INTERA
Environmental
Consultants






W.C. Walton







M.S. Beljin







T. Steenhuis
S. Pacenka




Contact Address
Koch & Associates
1660 S. Fillmore St.
Denver, CO 80210



Battel le Project
Management Division
Performance
Assessment Dept.
Office of Nuclear Waste
Isolation
505 King Avenue
Columbus, OH 43201

IGWMC
Hoi comb Research
Institute
Butler University
4600 Sunset Avenue
Indianapolis, IN 46208


IGWMC
Hoi comb Research
Institute
Butler University
4600 Sunset Avenue
Indianapolis, IN 46208


Northeast Regional
Agricultural
Engineering Service
Ri ley-Robb Hal I
Cornel 1 University
Ithaca, NY 14853
Model Name
(last update)
AQUIFER4
(1984)




VERTPAK-1
(1982)







35
MICRO-
COMPUTER
PROGRAMS
(1984)



SOLUTE
(1985)






MOUSE
(1987)




Model
Description
A radial finite differ-
ence model to simulate
transient three-dimen-
sional groundwater flow
in a leaky-confined aqu-
i f er .
A package of analytical
solutions assembled to
assist in verification
of numerical codes used
to simulate fluid flow,
rock deformation, and
solute transport in
fractured and unfractui —
ed porous media.
A series of analytical
and simple numerical
programs to analyze flow
and transport of solutes
and heat in confined,
leaky or water table
aquifers with simple
geometry.
A package of 8 analyti-
cal models for solute
transport simulation in
groundwater. The pack-
age also includes pro-
grams for unit conver-
sion and error function
calcul at ion.
A set of four 1 inked
models for tracking the
movement and fate of a
soluble chemical in sat-
urated and unsaturated
zones.
Model
Output
AI.CO.F





C.V.T








AI,CD,C,V,T







C,T







•C.T





IGWMC
Key
6305





6340








6350







6380







6390






-------