Untied States
           Environmental Protection
           Agency
           Roberts Kerr Environmental
           Research Laboratory
           Ada OK 74820
EPA/600/2-85/018
May 1985
           Research and Development
vvEPA
DRASTIC: A
Standardized System for
Evaluating Ground Water
Pollution Potential Using
Hydrogeologic Settings

-------
                             EPA/600/2-85/018
                                    May 1985
DRASTIC: A Standardized
   System for Evaluating
  Ground Water Pollution
        Potential Using
  Hydrogeologic Settings
                   by

 Linda Aller, Truman Bennett, Jay H. Lehr, and Rebecca J. Petty
          National Water Well Association
            Worthington, Ohio 43085
            Cooperative Agreement
               CR-810715-01
               Project Officer

               Jerry Thornhill
         Applications and Assistance Branch
     Robert S. Kerr Environmental Research Laboratory
             Ada, Oklahoma 74820
  Robert S. Kerr Environmental Research Laboratory
       Office of Research and Development
      U.S. Environmental Protection Agency
           Ada, Oklahoma 74820
                     U.S. Environmental Protection Agency
                     Region V, Library
                     230 South Dearborn Street
                     Chicago, Illinois  60604

-------
                                      Notice

        The information in this document has been funded wholly or in part by the U.S.
        Environmental Protection Agency under Cooperative Agreement CR-810175-
        01 to the National Water Well Association. It has been subject to the Agency's
        peer and administrative review  and  approved  for publication  as  an EPA
        document.
U,S.  Environmental Protection Agency

-------
                             Foreword

The  U.S. Environmental  Protection  Agency was established to coordinate
administration of the major Federal programs designed to protect the quality of
our environment.

An important part of the Agency's effort involves the search for information
about environmental problems, management techniques and new technologies
through which optimum use of the Nation's land and water resources can be
assured and the threat pollution poses to the welfare of the American people can
be minimized.

EPA's Office of Research and Development conducts this search through  a
nationwide network of research facilities.

As one of the facilities, the Robert S. Kerr Environmental Research Laboratory is
the Agency's center of expertise for investigation of the soil and subsurface
environment. Personnel at the laboratory are responsible for management of
research programs to: (a) determine the fate, transport and transformation rates
of pollutants in the soil, the unsaturated zone and the saturated zones of the
subsurface environment; (b) define the processes to  be used in characterizing
the soil  and subsurface environment as a receptor  of pollutants; (c) develop
techniques for predicting the effect of pollutants on ground water, soil  and
indigenous organisms;  and (d) define and demonstrate the applicability  and
limitations of using  natural processes, indigenous to the soil and subsurface
environment, for the protection of this resource.

This report contributes to that knowledge which is essential in order for EPA to
establish and enforce pollution control standards which are reasonable, cost
effective and provide  adequate environmental  protection  for the American
public.
                                            Clinton W. Hall
                                            Director
                                            Robert S. Kerr Environmental
                                            Research Laboratory

-------
                              Abstract

A  methodology is  described that will allow the pollution potential  of  any
hydrogeologic setting to be systematically evaluated anywhere in the United
States. The system has two major portions: the designation of mappable units,
termed hydrogeologic settings, and the superposition of a relative rating system
called DRASTIC.

Hydrogeologic settings are described for different regions in the United States.
These settings incorporate the major  hydrogeologic factors which affect  and
control ground-water movement including depth to water table, net recharge,
aquifer media, soil media, topography,  impact of the vadose zone and hydraulic
conductivity of the aquifer. These factors, which form the acronym DRASTIC, are
used to infer the potential for contaminants to enter  ground water. These
settings form the basis for the entire system and create units which can be
graphically displayed on a map.

The relative ranking scheme  uses  a  combination  of weights and ratings to
produce a numerical value, called the DRASTIC  INDEX,  which helps prioritize
areas with respect  to ground-water contamination vulnerability. The entire
system optimizes the use of existing data and provides an evaluation which can
be used to direct resources and waste  disposal activities to appropirate areas.

This report was submitted in partial fulfillment of Cooperative Agreement No.
CR-810715-01 by the National Water Well Association under the sponsorship of
the Robert S. Kerr Environmental Research Laboratory, Ada, Oklahoma. This
report covers a period from October  1983 to February 1985, and work  was
completed as of February 1985.
                                   IV

-------
                             Contents

                                                                Page

Disclaimer	 ii
Foreword	iii
Abstract	iv
Figures	  ix
Tables	 xi
Acknowledgements	xiii
Section
 1.   Introduction	 1
      Objectives and scope 	 1
      Project background	 2
      Classificatidn systems 	 2
      Some existing systems which evaluate ground-water
        pollution potential	 3
 2.   Development of the System and Overview	5
      Hydrogeologic settings	 5
      DRASTIC  	 7
      Agricultural DRASTIC	10
      Integration of hydrogeologic settings and DRASTIC	11
 3.   DRASTIC: A Description of the Factors	14
      Ground-water contamination and DRASTIC	14
      Depth to water	15
      Net recharge	16
      Aquifer media	16
      Soil media	17
      Topography	18
      Impact of the vadose zone	19
      Hydraulic conductivity of the aquifer	20
      Interaction between parameters	20
 4.   How to Use Hydrogeologic Settings and DRASTIC	23
      Organization of the document	23
      Where to obtain information on DRASTIC parameters	23
      Steps for use of the system	24
      How to use the range in media ratings	27
      How to evaluate confined aquifers	27
      Single factors overrides	28
      Build-your-own-settings 	29
      How to interpret a DRASTIC INDEX	29
 5.   Impact—Risk Factors	30
 6.   Hydrogeologic Setting of the United States by Ground Water
     Regions	31
     1. Western Mountain Ranges	40
        1 Aa East   Mountain Slopes	41
        1 Ab West  Mountain Slopes	42
        1 Ba East   Alluvial Mountain Valleys	42
        1 Bb West  Alluvial Mountain Valleys	43
        1 Ca East   Mountain Flanks	44

-------
                   Contents (continued)

   1 Cb West   Mountain Flanks	44
   1 D         Glacial Mountain Valleys	45
   1EA East   Wide Alluvial Valleys (External Drainage)	46
   1 Eb West   Wide Alluvial Valleys (External Drainage)	46
   1 F         Coastal Beaches	47
2.  Alluvial Basins  	48
   2A         Mountain Slopes	49
   2B         Alluvial Mountain Valleys	50
   2C         Alluvial Fans 	51
   2D         Alluvial Basins (Internal Drainage)	52
   2E         Playa Lakes	52
3.  Columbia Lava Plateau	54
   3A         Mountain Slopes	56
   3B         Alluvial Mountain Valleys	57
   3C         Hydraulically Connected Lava Flows	57
   3E         Alluvial Fans 	59
4.  Colorado Plateau and Wyoming Basin	60
   4A         Resistant Ridges	*	61
   4B         Consolidated Sedimentary Rocks	62
   4C         River Alluvium	63
   4D         Alluvium and Dune Sand	63
5.  High Plains	65
   5A         Ogallala	67
   5B         Alluvium	67
   5C         Sand Dunes	68
   5D         Playa Lakes	68
   5E         Braided River Deposits 	69
6.  Non-Glaciated Central	71
   6A         Mountain Slopes	73
   6B         Alluvial Mountain Valleys	73
   6C         Mountain Flanks	74
   6Da        Alternating SS, LS, SH-Thin Soil	75
   6Db        Alternating S, LS, SH-Deep Regolith	75
   6E         Solution  Limestone  	76
   6Fa        River Alluvium With Overbank	77
   6Fb        River Alluvium Without Overbank	77
   6G         Braided River Deposits 	78
   6H         Triassic Basins	78
7.  Glaciated Central	80
   7Aa        Glacial Till Over Bedded Sedimentary Rock	82
   7Ab        Glacial Till Over Outwash	82
   7Ac        Glacial Till Over Solution Limestone	83
   7Ad        Glacial Till Over Sandstone	84
   7Ae        Glacial Till Over Shale	84
   7Ba        Outwash	85
   7Bb        Outwash Over Bedded Sedimentary	86
   7Bc        Outwash Over Solution Limestone 	86
   7C         Moraine	87
   7D         Buried Valley	88
   7Ea        River Alluvium With Overbank Deposit	88
   7Eb        River Alluvium Without Overbank Deposit	89
   7F         Glacial Lake Deposits	90
   7G         Thin Till Over Bedded Sedimentary	90
   7H         Beaches, Beach Ridges, and Sand Dunes  	91

-------
                       Contents (continued)

     8. Piedmont and Blue Ridge	92
        8A        Mountain Slopes	93
        8B        Alluvial Mountain Valleys	94
        8C        Mountain Flanks	94
        8D        Thick Regolith	95
        8E        River Alluvium	96
        8F        Mountain Crests	96
     9. Northeast and Superior Uplands 	98
        9A        Mountain Slopes	99
        9B        Alluvial Mountain Valleys	100
        9C        Mountain Flanks	100
        9Da       Glacial Till Over Crystalline Bedrock	101
        9Db       Glacial Till Over Outwash	102
        9E        Outwash	102
        9F        Moraine	103
        9Ga       River Alluvium With Overbank	104
        9Gb       River Alluvium Without Overbank 	104
    10. Atlantic and Gulf Coastal Plain	106
        10Aa      Confined Regional Aquifers	108
        10Ab      Unconsolidated & Semi-Consolidated Shallow
                  Surficial Aquifer	108
        lOBa      River Alluvium With Overbank Deposit	109
        10Bb      River Alluvium Without Overbank Deposit	110
        10C       Swamp  	110
    11. Southeast Coastal Plain	112
        11A       Solution Limestone 	113
        11B       Coastal Deposits	114
        11C       Swamp  	114
        11D       Beaches & Bars	115
    12. Hawaii	116
        12A       Mountain Slopes	117
        12B       Alluvial Mountain Valleys	118
        12C       Volcanic Uplands 	119
        12D       Coastal Beaches	119
    13. Alaska	121
        13A       Alluvium	121
        13B       Glacial and Glaciolacustrine Deposits of the
                  Interior Valleys 	123
        13C       Coastal Lowland Deposits	124
        13D       Bedrock of the Uplands and Mountains  	124
References	127
Appendices
  A. Processes and Properties Affecting Contaminant Fate
       Fate and Transport	131
        Density	131
        Solubility	131
        Sorption	132
        Ion exchange	133
        Oxidation-reduction	133
        Biodegradation	134
        Hydrolysis 	135
        Volatilization	135
        Buffering and neutralization	136
        Dilution	136

                                  vii

-------
                      Contents (continued)

      Dispersion	1 36
      Viscosity	137
      Mechanical filtration	137
B.   Characteristics of Ground-Water Contaminants	140
      Inorganic metals	140
      Inorganic non-metals	142
      Organic compounds 	143
C.   Sources of Ground-Water Contamination	1 56
      Ground-water quality problems that originate on the
        land surface	157
      Ground-water quality problems that originate in the
        ground above the water table	1 59
      Ground-water quality problems that originate in the
        ground water below the water table	161
                                 VIII

-------
                                 Figures

 Number                                                       Page
 1  Ground water regions of the United States	6
 2  Format of hydrogeologic setting	 6
 3  Graph of ranges and ratings for depth to water	9
 4  Graph of ranges and ratings for net recharge	9
 5  Graph of ranges and ratings for aquifer media	10
 6  Graph of ranges and ratings for soil media	11
 7  Graph of ranges and ratings for topography	11
 8  Graph of ranges and ratings for impact of the vadose zone	12
 9  Graph of ranges and rating for hydraulic conductivity	13
10  Travel of contaminant with same density as water in the aquifer	14
11  Travel of contaminant that is denser than water in the aquifer	14
12  Travel of contaminant that is less dense than water
    in the aquifer	15
1 3  Travel of contaminant that is denser than water and sinks
    in the aquifer	15
14  Travel of contaminant that is denser than water in the aquifer in a
    direction opposed to the ground-water flow direction	15
1 5  Depth to water in a confined and unconfined aquifer	16
1 6  Soil textural classification chart	18
17  Description and illustration for setting  7Aa—glacial till over
    bedded sedimentary rocks	25
18  Description and illustration for setting  6Da—alternating
    sandstone,  limestone and shale-thin soil	25
19  Ground-water regions of the United States	31
20  Map Legend	39
A-1 Schematic of pathlines showing longitudinal and transverse
    dispersion	137
A-2 Plume configuration based on contaminant input	138
B-1 Covalent bonding arrangements of carbon atoms	145
                                    IX

-------
                               Tables

Number                                                         Page
  1   Sources of hydrogeologic information	7
  2   Assigned weights for DRASTIC features	8
  3   Assigned weights for agricultural DRASTIC features	8
  4   Ranges and ratings for depth to water	8
  5   Ranges and ratings for net recharge	8
  6   Ranges and ratings for aquifer media	8
  7   Ranges and ratings for soil media	9
  8   Ranges and ratings for topography	9
  9   Ranges and ratings for impact of vadose  zone media	9
10   Ranges and ratings for hydraulic conductivity	9
11   Potential sources of ground-water contamination and
     mode of replacement	14
12   Range of values of hydraulic conductivity and permeability	24
13   Conversion factors for permeability and hydraulic
     conductivity units	25
14   DRASTIC and agricultural DRASTIC charts for setting 7Aa—glacial
     till over bedded sedimentary rocks	26
15   DRASTIC and agricultural DRASTIC charts for setting
     6Da—alternating sandstone, limestone and shale-thin soil	26
16   DRASTIC rating for Maco I	28
17   DRASTIC rating for Maco II	28
18   Hydrogeologic settings and associated DRASTIC INDEX by region	32
19   Hydrogeologic settings and associated DRASTIC INDEX
     sorted by rating	32
20   Hydrogeologic settings and associated DRASTIC INDEX
     sorted by setting title	33
21   Hydrogeologic settings and associated agricultural DRASTIC
     INDEX by region	34
22   Hydrogeologic settings and associated agricultural DRASTIC
     INDEX sorted by rating	34
23   Hydrogeologic settings and associated agricultural DRASTIC
     INDEX sorted by setting title	35
24   Summary of the principal physical and hydrologic characteristics
     of the ground-water regions of the United States	37
25   Common ranges for the hydraulic characteristics of ground-water
     regions of the United States	38
26   Ranges and ratings for depth to water	39
27   Ranges and ratings for net recharge	39
28   Ranges and ratings for aquifer media	39
29   Ranges and ratings for soil media	39
                                 XI

-------
                         Tables (continued)

30  Ranges and ratings for topography	39
31  Ranges and ratings for impact of the vadose zone	39
32  Ranges and ratings for hydraulic conductivity	39
B-1 EPA list of 129 priority pollutants and the relative frequency of
    these materials in industrial waste waters	144
B-2 Substances known to occur in ground water, ranges of detected
    concentrations, exceeded standards, examples of uses and
    quantitative estimates of carcinogenic potency and
    noncarcinogenic toxicity	147
                                 XII

-------
                       A cknowledgements

This document creates a standardized system which can be used to evaluate
ground-water pollution potential. At the inception of the project, the implications
for use of such a system were realized and a technical advisory committee was
assembled. Prominent individuals with ground-water expertise  respresented
federal and state agencies, the Canadian government and private consultants.
Throughout the development of the system, the committee provided guidance
and direction. The document is a resu It of the synthesis of many approaches and
opinions of individual committee members. Although each of the individuals
contributed positively and effectively to the process, this report is a product of the
National Water Well Association and is not endorsed entirely by each of the
committee members. Successful completion of the project is due to the time and
effort which an unusually able advisory committee was willing to devote to this
activity. To the following named persons, grateful acknowledgement of their
contributions is made:

      Michael Apgar, Delaware Department of Natural Resources
      Jim Bachmaier, USEPA,  Office of Solid Waste
      William Back, USGS
      Harvey Banks, Consulting Engineer, Inc.
      Truman Bennett,  Bennett & Williams, Inc.
      Robert E. Bergstrom, Illinois State Geological Survey
      Stephen Born, University of Wisconsin
      Keros Cartwright, Illinois State Geological Survey
      Stuart Cohen, USEPA, Hazard Evaluation Division
      Steve Cordle, USEPA, Office of Research and Development
      George H. Davis, USGS,  retired
      Stan Davis,  University of Arizona
      Art Day, USEPA, Land Disposal Branch—OSW
      Norbert Dee, USEPA, Office of Ground Water Protection
      Donald A. Duncan, South Carolina Department of Health and
        Environmental Control
      Catherine Eiden, USEPA, Hazard Evaluation Division
      Grover Emrich, SMC Martin, Inc.
      Glen Galen, USEPA,  Land Disposal Branch
      Phyllis Garman, Consultant, Tennessee
      Jim Gibb, Illinois State Water Survey
      Todd Giddings, Todd  Giddings & Associates
      Ralph Heath, USGS,  retired
      Ron Hoffer,  USEPA, Office of Ground Water Protection
      George Hughes, Ontario Ministry of the Environment
      Jack Keeley, USEPA, Kerr Environmental Research Laboratory
      Jerry Kotas, USEPA,  Office of Waste Programs Enforcement
      Harry LeGrand, Consultant, North Carolina
      Fred Lindsey, USEPA, Waste Management and Economics Division
      Paula Magnuson, Geraghty & Miller, Inc.
      Martin Mifflin, University of Nevada
      Walter Mulica, IEP, Inc.
      John Osgood, Pennsylvania Bureau of Water Quality
      Wayne Pettyjohn, Oklahoma State University
      Paul Roberts, Stanford University
                                  XIII

-------
      John Robertson, Weston Designers & Consultants
      Dave Severn, USEPA, Hazard Evaluation Division
      Frank Trainer, USGS, retired
      Warren Wood, USGS

The basic conceptual  foundation for this system is modeled after a waste
disposal site evaluation technique developed by Harry LeGrand. The geographic
framework for the presented system is developed within ground-water regions
as defined by Ralph C. Heath. A special note of acknowledgement and gratitude
is made to those  two individuals  for  their  inspiration  and assistance  in
developing this document.
                                   XIV

-------
                                           Section 1
                                          Introduction
Objectives and Scope
The purpose of this project is to create a methodology
that will permit the ground-water pollution potential
of any hydrogeologic setting to be systematically
evaluated with existing information anywhere in the
United States. This document has been prepared to
assist planners,  managers, and administrators in the
task of evaluating the relative vulnerability of areas to
ground-water contamination from various sources of
pollution. Once this evaluation is complete, it can be
used to help direct resources, waste disposal, and
other land-use  activities to the appropriate areas.
This  document will also be useful to industry per-
sonnel who desire to understand the  relationship
between various  practices  and  the  ground-water
pollution potential associated with  them and  to
university personnel who teach the fundamentals of
hydrogeology and ground-water contamination.  It
has been assumed that the reader has only a  basic
knowledge of hydrogeology and the processes which
govern ground-water contamination.  However, the
greater the experience of the user, the more useful
the system  will  become because the  system can
expand to be beneficial at any level of expertise. This
report is not designed or intended to replace on-site
inspections, or specifically to site any type of industrial
facility or practice. Rather, it is intended to provide a
basis for comparative evaluation of areas with respect
to potential for pollution of ground water.

The  scope  of this project  includes  not only the
development of a standardized system for evaluating
pollution potential but also the creation  of a system
which can be readily displayed on maps. For purposes
of mapping,  the United States has been divided into
hydrogeologic settings. These settings  incorporate
the many hydrogeologic factors which will influence
the vulnerability of  that setting  to  ground-water
pollution. The settings have been chosen to represent
areas larger than 100 acres in size, thereby limiting
the system to use as a screening tool and not as a site
assessment  methodology.
The scope of this project does not include producing
pollution potential maps of the entire United States.
Rather, a set of demonstration maps will be prepared
to show howthe system could display the information
on a  map for ease of  use and reference. Inherent in
this demonstration is the idea that the standardized
system cannot be finalized until it has been exten-
sively tested in a wide  variety of representative
settings.  Therefore,  this system  and the  setting
descriptions will be  continually evolving until the
demonstration project is complete.

In the formulation of this document an attempt was
made to try to assimilate the thought processes of
knowledgable  professional  hydrogeologists when
evaluating  the ground-water pollution potential of
any area. From this thought process a simple-to-use
and easy-to-understand methodology has been de-
veloped.  It  is  important  to remember  that this
document is intended to be used as a screening tool
and is not intended to replace the need for profes-
sional expertise and field work in assessing the
pollution potential in  specific areas.

The system has been designed to  use information
which is  available  through  a variety of sources.
Information on the parameters, including the depth to
water in an area, net recharge, aquifer media, soil
media, general topography or slope,  vadose zone
media, and  hydraulic conductivity of the aquifer is
necessary to evaluate  the ground-water pollution
potential of any area using hydrogeologic settings.
Although  much  of this information is available in
existing  reports, some might require estimation. In
choosing parameters for which information is already
available in some form, this system does not include
many parameters and  types of information which
would be available from a more detailed site invest-
igation. Therefore, it  is important to realize that this
document provides only a general, broad assessment
to be used to evaluate sites for potential pollution.

To help illustrate two potential uses of this document,
examples  have been included: (1) When a  profes-
sional hydrogeologist is asked  to recommend the
most hydrogeologically acceptable site for municipal
waste disposal  in  a county area, he  begins  by
reviewing many types of different information. From
the information, he immediately rejects sites which
are obviously unsuitable and continues to narrow his
focus until a number of the most promising areas are
identified. Hewill usually then recommendthat more
detailed information be obtained and/or site invest-
igations be made on the most  promising areas before
any type of further action is taken. This is analogous
to the purpose of this document. It provides the user
with an idea of where to direct resources for further
evaluation. (2) When state or local administrators

-------
have limited resources available to devote to ground-
water protection, they  are forced to focus these
resources in certain areas. The system presented in
this document helps identify areas which are more or
less vulnerable than others to contamination. This
delineation allows administrators to direct  their
resources to those more vulnerable areas most critical
to the management problems, thereby making the
most of the limited resources which are available.

Project Background

With the scope of the project in mind it is necessary to
understand the importance of this document. Ground
water is clearly regarded to be one of our nation's
most  valuable resources.  Americans  have long
depended on ground water for many uses, but the
primary use has been as a source of drinking water.
Over 90 percent of the nation's public water supplies
obtain their source water from ground water (Lap-
penbusch,  1984). Additionally, 97  percent of the
water needs for domestic use in rural areas is served
by ground-water resources (Solley et al., 1983).

National reliance on ground water has  increased
dramatically over the past  20 years. In the last 10
years alone, ground-water use has increased almost
30 percent while surface water withdrawals have
increased only 15 percent (Solley et al.,  1983). It is
anticipated that the nation's reliance on ground water
will  continue  to increase  as  demand  for water
increases in the future.

Concomitant with our reliance on ground water has
come the need to protect our ground-water resources
from contamination. Although contamination due to
man has occurred for centuries, only in the past few
years has the nation become aware of the dangers of
ground-water contamination and of the many ways in
which  ground water can  become  contaminated.
Moreover, in recent decades, the diversity of potential
pollutants produced and used by man has increased
dramatically. Since 1974, the Congress of the United
States has been making an attempt to  protect  the
nation's ground-water resources through legislation.
The Safe Drinking Water Act (SDWA) (Public Law
93-523) mandated  the  establishment of drinking
water standards to protect the public health, estab-
lished the underground injection control (UIC) pro-
gram to protect underground  sources of drinking
water from subsurface injection of wastes through
wells,  and  established the Sole-Source  Aquifer
program. The  Resource Conservation and Recovery
Act (RCRA) (Public Law 94-580), passed in October
1976 and amended in November 1982, is the legisla-
tion which controls the management and disposal of
solid and hazardous waste in such a manner that
ground water will not be contaminated. The amended
Federal Insecticide, Fungicide and Rodenticide  Act
(FIFRA) (Public Law 92-516) as first passed in October
1972 and amended in 1 975 and 1 978, allows EPA to
prohibit or mitigate ground-water contamination by
pesticides by denying registrations, by modifying
application methods, and through cancellations and
suspensions of pesticides registrations. FIFRA also
explicitly requires EPA  to monitor environmental
pollution. The Toxic Substances Control Act (TSCA)
(Public Law 94-469), signed into law in October 1976,
has no direct impact on ground-water protection but
has the potential to  be  used as a mechanism in
ground-water protection  because the  Act  provides
EPA with the power to regulate the use and manu-
facture of specific  chemicals, some of which  may
pose  ground-water contamination potential.  The
Surface  Mining  Control  and  Reclamation  Act
(SMCRA) of  1977 is the  legislation which controls
environmental impacts resulting from all mining
activities: By establishing standards for these facil-
ities, ground water may once  again be protected.
Finally,  the  Comprehensive  Emergency Response
Compensation and Liability Act(CERCLA) also known
as "Superfund" provides a mechanism for the clean-
up of ground water which has been contaminated at
abandoned hazardous waste sites. A more complete
discussion of these acts and their provisions which
relate to ground water is given by Lehr, et al. (1984).
This host of legislative measures has sought to help
prevent the pollution  of ground water in the future
andto help mitigatesomeofthe problems which have
been created in the past.

Because prevention is the key to helping ensure that
future practices do not result in ground-water con-
tamination, it is now more important than ever to use
planning and management tools to help recognize the
places where certain activities pose a higher risk. This
document addresses this need by providing an
approach which can be used to help direct resources
to protect ground water for future generations.

Classification Systems

One of the fundamental needs of any natural science
is the development of an effective system  to group
similar  entities  into  categories. Well-established
systems exist in  the fields of botany,  geology, and
many other  sciences (Joel, 1926). These systems
permit an appropriately trained person to gain certain
insight  about  an  entity simply by knowing the
appropriate category in which it is grouped.

This systematic  and logical way of  imposing an
artificial system  on natural entities has long been
used in the field of geology also. For example, rocks
have been classified according to origin and minerals
grouped according  to crystal systems. However, as a
science expands  and  changes, so must the types of
systems used to describe those characteristics which
need to be studied. The field of hydrogeology is one
area of geology which has only been overtly recog-

-------
nized since the term was coined by Lucas in 1879
(Davis and Dewiest,  1966). Since that time hydro-
geology has expanded, from a discipline devoted to
water  occurrence  and  availability, to include  the
broad aspect of water quality and solute chemistry.
Definition of water quality is fundamental  to  the
protection of the ground-water resource from pollu-
tion.

The  idea of an organized  way to describe ground
water systems is not new. Meinzerf 1923) prepared a
small-scale map of the United States showing general
ground-water provinces. Thomas (1952) and Heath
(1984) prepared similar but more detailed maps and
descriptions which  grouped aquifers mainly on their
water-bearing characteristics within certain geo-
graphic areas. Blank and Schroeder( 1973) attempted
to classify aquifers  based on the properties of rocks
which affect ground water. Of  all these systems,
geographic ones have been more widely accepted as
ways to  describe the quantity  of water  which is
available in various regions.

Some Existing Systems Which Evaluate
Ground-Water Pollution Potential

Within the last 20  years the need to  expand these
systems or to create a new system to address ground-
water quality has become evident. Many different
systems have been developed to address site selection
for waste disposal facilities such  as sanitary landfills
or liquid waste ponds. Among these, the LeGrand
System (LeGrand,  1983) and the modified version
used by the U.S. EPA in the Surface Impoundment
Assessment (SIA) are probably the most well known.
The  LeGrand system uses numerical weighting to
evaluate ground-water pollution potential from  a
given waste disposal site. By  evaluating the site
through a series of four stages, a description of the
hydrogeology of the site, the relative aquifer sensi-
tivity combined with the contaminant severity,  the
natural pollution potential presented at that site, and
the engineering  modifications which might change
that  potential are all evaluated.

The  LeGrand  system presupposes only a  limited
technical  knowledge but encourages the user to
become familiar with the concepts presented in the
manual so that skilled judgements can be made inthe
subjective portion  of the  system. The similarities
between sites are emphasized and the uniqueness of
each site is downplayed.

The U.S. EPA methodology (U.S. EPA, 1983) uses the
basic LeGrand System to define the hydrogeologic
framework, but modifies the system to place empha-
sis  on establishing a monitoring  priority for  the
facility. Once the hydrogeologic characteristics have
been rated, a table  is used to define the monitoring
priority. This priority may be adjusted by the rater
using prescribed techniques.  Once  again  only  a
limited technical knowledge is presupposed.

Other systems have been designed to tailor the
results to more specific purposes. Thornthwaite and
Mather  (1957) and Fenn  et  al.  (1975) developed
water-balance methods to  predict the leachate gen-
eration at solid waste disposal sites. This approach  is
based on the premise that by knowing the amount of
infiltration into the landfill and the design of the cell,
the leachate quantity for the  landfill can be deter-
mined. The system is intended as a tool to be used by
engineers in the early design phase of a  facility.

Gibb et al. (1983) devised a rating scheme to establish
priorities for existing waste disposal sites with respect
to their threat to human health by ground water. Via
ranking the site through four factors, (1) health risk of
the waste and  handling mode, (2) population at risk,
(3) proximity to wells or aquifers, and (4) susceptibility
of aquifers, a number that ranges from 0-100 was
used to display the relative risk. The system was used
in a specific 2-county  assessment  by technically
qualified individuals.

Another rating scheme, developed by the Michigan
Department of Natural Resources (1983), is designed
to rank  large numbers  of  sites in terms of risk of
environmental contamination. By evaluating the five
categories: (1) release potential, (2)  environmental
exposure,  (3) targets, (4) chemical hazard, and (5)
existing exposure, the user obtains a number ranging
from 0 to 2000 points which evaluates  the relative
hazard of that site with respect to other  sites in
Michigan.

Seller and Canter (1980) evaluated seven empirical
methods to determine their usefulness in predicting
the ground-water pollution effects of a waste disposal
facility at a particular site. The methods they reviewed
included rating schemes, a decision tree approach, a
matrix and a criteria-listing  method. They determined
that each method took into  account the  natural
conditions and facility design and construction, but
that each  method was  best applied  to the specific
situation for which it was designed.

This brief review of selected existing systems reveals
that there are a number  of methods that can be
applied to site-specific situations or to evaluation of
the pollution potential of existing sites.  However,  a
planning tool  is needed for  use  before the  site-
specific methods are employed. The system must (1)
function as a management tool, (2)  be  simple and
easy-to-use, (3) utilize available information, and (4)
be  able to be used by  individuals  with  diverse
backgrounds and levels of expertise. This document
contains a system which  attempts to meet these
needs and to provide the  planning tool necessary
before site-specific evaluations.

-------
References

Blank, Horace R. and Melvin C. Schroeder, 1973.
  Geologic classification of aquifers; Ground Water,
  Vol. 11, No. 2, pp. 3-5.

Davis, S. N. and R. J.  DeWiest, 1966. Hydrogeology;
  John Wiley & Sons, 463 pp.

Fenn, Dennis G., Keith J.  Hanley,  and Truett V.
  DeGeare, 1975. Use of the water balance method
  for predicting leachate generation from solid waste
  disposal sites;  U.S. EPA Solid Waste Report No.
  168, Cincinnati, Ohio, 40 pp.

Gibb, James P., Michael J. Barcelona,  Susan C.
  Schock, and Mark W. Hampton, 1983. Hazardous
  waste in Ogle and Winnebago Counties: potential
  risk via ground water due  to past and  present
  activities; Illinois Department of Energy and Natural
  Resources, Document No. 83/26, 66 pp.

Heath, Ralph C., 1984. Ground water regions of the
  United States; United States Geological Survey
  Water Supply Paper 2242, 78 pp.

Joel, A. H., 1926. Changing viewpoints and methods
  in soil classification; reprinted in Soil Classification,
  Charles W. Finkl, Jr., editor (1982), Hutchinson
  Ross Publishing Co.,  Stroudsburg,  Pennsylvania,
  pp. 52-59.

Lappenbusch, W. L, 1984. Health effects of drinking
  water contaminants; Proceedings of theThirty-first
  Ontario Industrial  Waste Conference, Ontario
  Ministry of the Environment, Ontario, Canada, pp
  271-291.

LeGrand, Harry E., 1 983. A standardized system for
  evaluating  waste-disposal sites; National Water
  Well Association, Worthington, Ohio, 49 pp.

Lehr, Jay  H., David M. Nielsen, and John J. Mont-
  gomery, 1984. U.S. federal legislation pertaining to
  ground water protection;  Groundwater Pollution
  Microbiology, Gabriel Bitton and Charles P. Gerba,
  editors, John Wiley & Sons, pp. 353-371.

Meinzer, Oscar E., 1923. Outline of ground-water
  hydrology; United States Geological Survey Water
  Supply Paper 494, 71 pp.

Michigan Department of Natural Resources, 1983.
  Site assessment system (SAS) for the  Michigan
  priority ranking system under the Michigan Envi-
  ronmental Response Act; Michigan Department of
  Natural Resources, 91 pp.

Seller, L. E.  and L. W.  Canter, 1980. Summary of
  selected ground water quality impact assessment
  methods; National Center for Ground Water Re-
  search  Report No.  NCGWR 80-3, Norman, Okla-
  homa, 142  pp.
Solley, Wayne B., Edith B.  Chase,  and William  B.
  Mann, 1983. Estimated use of water in the United
  States in 1980; United States Geological Survey
  Circular 1001, 56 pp.

Thomas, Harold E., 1952. Ground water regions  of
  the United States—their storage facilities; Interior
  and Insular  Affairs Committee,  U.S.  House  of
  Representatives, 76 pp.

Thornthwaite, S. W. and J. R. Mather, 1957. Instruc-
  tions and  tables for computing potential evapo-
  transpiration and the water balance; Drexel  Insti-
  tute of Technology, Laboratory of Climatology,
  Publications in Climatology, Centerton, New Jersey,
  Vol. 10, No. 3, 311  pp.

United States Environmental  Protection Agency,
  1983. Surface impoundment assessment national
  report; U.S. EPA-570/9-84-002, 200 pp.

-------
                                           Sect/on 2
                         Development of the System and Overview
The focus of this project is to create a system which
can be used to evaluate the ground-water pollution
potential of any area in the United States. The system
presented herein has two major portions: the designa-
tion of mappable units, termed hydrogeologic set-
tings; and the application of  a scheme for  relative
ranking of hydrogeologic parameters, called DRAS-
TIC, which  helps  the user  evaluate the  relative
ground-water pollution potential of any hydrogeologic
setting. Although the two parts of the system are
interrelated, they are discussed separately in a logical
progression.

At  the  inception of the project,  the far-reaching
implications of a standardized system for evaluating
ground-water pollution potential were realized, and a
broadly-based,  highly qualified technical advisory
committee was assembled to  help direct this effort.
Through the direction and help of many, and discus-
sion of  opinions and suggestions, this system has
evolved to represent a compromise approach.  Further
reference to the roleofthecommitteewill be made in
the section discussing  the  development  of the
DRASTIC Index. A list of committee members can be
found in the acknowledgement section.


Hydrogeologic Settings

This document has been prepared using the concept
of hydrogeologic settings. A hydrogeologic setting is a
composite description of all the major geologic and
hydrologic factors which affect and control ground-
water movement into, through, and out of an area. It
is defined as a mappable unit with common hydro-
geologic characteristics, and as  a consequence,
common vulnerability to contamination by introduced
pollutants. From these factors it is possible to make
generalizations about both ground-water availability
and ground-water pollution potential.

In order to assist  users  who may have a  limited
knowledge of hydrogeology, the entire standardized
system for evaluating ground-water pollution poten-
tial has been developed within the framework of an
existing classification system of ground-water re-
gions of the United States. Heath (1984) divided the
United States into 15 ground-water regions based on
the features in a ground-water system which affect
the occurrence  and availability of  ground water
(Figure 1). These regions include:
  1.  Western Mountain Ranges
  2.  Alluvial Basins
  3.  Columbia Lava Plateau
  4.  Colorado Plateau and Wyoming Basin
  5.  High Plains
  6.  Nonglaciated Central Region
  7.  Glaciated Central Region
  8.  Piedmont and Blue Ridge
  9.  Northeast and Superior Uplands
10.  Atlantic and Gulf Coastal Plain
11.  Southeast Coastal Plain
12.  Alluvial Valleys
13.  Hawaiian Islands
14.  Alaska
15.  Puerto Rico and Virgin Islands

Region 12, Alluvial Valleys, is "distributed" through-
out the United States.

For the  purposes of the present system. Region 12
(Alluvial Valleys) has been reincorporated into each of
the other  regions and Region  15  (Puerto Rico and
Virgin Islands) has been omitted.  Since the factors
which influence ground-water occurrence and avail-
ability also  influence the pollution potential of an
area, this regional framework is used to help familiar-
ize the user with the basic hydrogeologic features of
the region. An annotated description  of each of the
regions and the significant hydrogeologic factors are
included in Section 9, Hydrogeologic Settings of the
United States by  Ground-Water Regions.

Because pollution potential cannot be determined on
a regional scale,  smaller  "hydrogeologic settings"
were developed within each of the  regions described
by Heath (1984). These hydrogeologic settings create
units which are  mappable and, at the same time,
permit further delineation of the factors which affect
pollution potential.

Each hydrogeologic setting is described in a written
narrative section and illustrated in a block diagram.
Figure 2 shows the format which is used throughout
the document. The  descriptions are used to  help
orient the user to typical geologic and hydrologic
configurations which are found in each region and to
help focus attention on significant parameters which
are important in pollution potential assessment. The
block diagram enables  the  user  to visualize the
described setting by indicating  its  geology, geomor-
phology, and hydrogeology.

-------
Figure 1.    Ground-water regions of the United States (After Heath, 1984).
   2. Alluvial Basins
                                                7.
                                              Glaciated
                                               Central
                                                Region


                                     vo^fr'6. Nonglaciated
                                              Central
                                              Region
                                                    9 Northeast and
                                                      Superior Uplands
                             Nonglaciated Central "
                                       Region
                                         9 Northeast and
                                         Superior Uplands
                                         1. Western Mountain
                                                        6 Nonglaciated
                                                            Central
                                                            Region
                       . Colorado/J1^?
                        Plateau
                        and
                        Wyoming
                        Basin
6. Nonglaciated
 Central Region
                    6. Nonglaciated
                      Central Region
                                                               a coastal Plain
A set of hydrogeologic settings has been developed
for  each region. The document is designed so that
once the broad geographic area is located, the user
does not have to refer to other hydrogeologic settings
in other regions. This means that similar hydrogeo-
logic  settings may appear  more than once  in the
document, but that they have been tailored to reflect
the typical hydrogeologic conditions  within each
individual region.

Hawaii

(12C) Volcanic Uplands

This hydrogeologic setting is characterized by mod-
erately rolling topography, at medium elevations, and
rich, dark, soils developed from the basaltic bedrock.
The soils are permeable, rainfall is high, and recharge
is high. Bedrock is composed primarily of alternating
extrusive basaltic lava flows and interlayered weath-
ered zones formed  between flows. Ground water
occurs at moderate to deep depths, and aquifer yield
is controlled by fracture zones, vesicular zones (both
primarily cooling features), and the inter-flow weath-
                                                                            800 kilometers
    ered zones. Hydraulic conductivity is high. As with
    other settings in Hawaii, heavy  pumping stresses
    often result in salt-water intrusion. This is a reflection

    Figure 2.    Format of hydrogeologic setting.

-------
of the fact  that each island  is surrounded by and
underlain by salt water, with the fresh water occur-
ring in a lenticular body that floats on the salt water.
Ground water yield is therefore limited quite specif-
ically to the amount of water recharged annually.

DRASTIC
Inherent in each  hydrogeologic setting are the
physical characteristics which affect the ground-
water pollution potential. A wide  range of technical
positions was considered regarding the relative
importance  of the many physical characteristics that
affect pollution potential. Factors including aquifer
chemistry,  temperature,  transmissivity,  tortuosity,
gaseous phase transport, and others were evaluated.
The  availability of mappable  data  has  also been
considered.  As a result of this evaluation, the most
important mappable factors that control the ground-
water pollution potential were determined to be:

  D—Depth to water
  R—(Net) Recharge
  A—Aquifer Media
  S—Soil Media
                          T—Topography (Slope)
                          I —Impact of the Vadose Zone
                          C—Conductivity (Hydraulic) of the Aquifer
                       These factors  have  been  arranged to form  the
                       acronym, DRASTIC, for ease of reference. A complete
                       description of the important mechanisms considered
                       within each  factor and  a description of the signif-
                       icance  of the factor are included  in  Section 3,
                       DRASTIC: A Description  of the Factors. While this list
                       is not all  inclusive, these factors, in combination,
                       were determined to include the basic requirements
                       needed to assess the general pollution potential of
                       each hydrogeologic setting. The  DRASTIC factors
                       represent measurable parameters for which data are
                       generally available from a variety of sources without
                       detailed reconnaissance. Sources of this information are
                       listed in Table 1.
                       A numerical  ranking system to assess ground-water
                       pollution potential in hydrogeologic settings has been
                       devised  using the  DRASTIC  factors. The system
                       contains three significant parts: weights, ranges, and
                       ratings.  A description  of the  technique  used for
                       weights and ratings can be found in Dee et at., (1973).
Table 1.    Sources of Hydrogeologic Information
Source
U.S. Geological Survey
State Geological Surveys
Depth
to
Water
Table
X
X
Net
Recharge
X
X
Aquifer
Media
X
X
Soil
Media

Topography
X
Impact
of the
Vadose
Zone
X
X
Hydraulic
Conductivity
of the
Aquifer
X
X
State Department of Natural/
  Water Resources
U.S. Department of Agriculture-
  Soil Conservation Service
State Department of
  Environmental Protection
Clean Water Act "208" and
  other Regional Planning
  Authorities
County and Regional Water
  Supply Agencies and
  Companies (private water
  suppliers)
Private Consulting Firms
  (hydrogeologic, engineering)
Related Industry Studies
  (mining, well drilling,
  quarrying, etc.)
Professional Associations
  (Geological Society of
  America, National Water Well
  Association, American
  Geophysical Union)
Local Colleges and Universities
  (Departments of Geology,
  Earth Sciences, Civil
  Engineering)
Other Federal/State Agencies
  (Army Corps of Engineers,
  National Oceanic and
  Atmospheric Administration)
X

X
           X
           X
X

X
X

X
X

X

-------
(1) Weights—Each DRASTIC factor has been eval-
uated with respect to the other to  determine the
relative importance of each factor. Each  DRASTIC
factor has been assigned  a relative weight ranging
from 1 to 5 (Table 2). The most significant factors have
weights of 5; the least significant, a weight of 1. This
exercise was accomplished by the committee using a
Delphi (consensus) approach. These weights are a
constant and may not be changed. A second weight
has been assigned to reflect the agricultural usage of
herbicides and pesticides (Table 3). These weights are
also constants and cannot  be changed. A description
of the usage of this second system can be found in
Section 2  under the heading, "Agricultural DRAS-
TIC."
Table 2.   Assigned Weights for DRASTIC Features

               Feature                  Weight
    Depth to Water Table
    Net Recharge
    Aquifer Media
    Soil Media
    Topography
    Impact of the Vadose Zone
    Hydraulic Conductivity of the Aquifer
Table 3.
Assigned Weights for Agricultural DRASTIC
Features
               Feature
                           Agricultural
                            Weight
    Depth to Water Table
    Net Recharge
    Aquifer Media
    Soil Media
    Topography
    Impact of the Vadose Zone
    Hydraulic Conductivity of the Aquifer
                               5
                               4
                               3
                               5
                               3
                               4
                               2
(2) Ranges—Each DRASTIC factor has been divided
into either ranges or significant media types which
have an impact on pollution potential (Tables 4-10). A
discussion of the media types is included in Section 3,
Aquifer Media, Soil Media, and Impact of the Vadose
Zone. The ranges and media  types are graphed to
show the  linearity and  non-linearity of the factor
(Figures 3-9).


(3) Ratings—Each range for  each DRASTIC factor
has been  evaluated with  respect to  the others to
determine the relative  significance of each range
with respect to  pollution  potential. Based on  the
graphs, the range for each DRASTIC factor has been
assigned  a rating which varies between 1  and 10
(Tables 4-10). The factors of D, R, S, T, and C have
been assigned one value per range. A and I have been
                                          assigned a "typical" rating and a variable rating. The
                                          variable rating allows the  user to choose either a
                                          typical value or to adjust the value based on more
                                          specific knowledge. The ratings are the same for both
                                          the DRASTIC Index  and the modified Agricultural
                                          DRASTIC Index.

                                          This system allows the user to determine a numerical
                                          value for any  hydrogeologic setting by using an
                                          additive model. The equation for determining the
                                          DRASTIC Index is:
       DRD
                                                   RW
                                                                             + TRT
                                                                               RW
                                                   + !R!W + CRCW = Pollution Potential
                                          where:
                                                      R = rating
                                                      W = weight
                                          Table 4.    Ranges and Ratings for Depth to Water

                                                             Depth to Water
                                                                 (feet)
                                                     Range
                            Rating
0-5
5-10
15-30
30-50
50-75
75-100
100 +
Weight: 5
10
9
7
5
3
2
1
Agricultural Weight:







5
Table 5.   Ranges and Ratings for Net Recharge
Net Recharge
(inches)
Range
0-2
2-4
4-7
7-10
10 +
Weight: 4
Rating
1
3
6
8
9
Agricultural Weight:






4
                                           Table 6.    Ranges and Ratings for Aquifer Media

                                                              Aquifer Media
Range
Massive Shale
Metamorphic/lgneous
Weathered Metamorphic/lgneous
Thin Bedded Sandstone,
Limestone, Shale Sequences
Massive Sandstone
Massive Limestone
Sand and Gravel
Basalt
Karst Limestone
Weight: 3
Rating
1-3
2-5
3-5

5-9
4-9
4-9
6-9
2-10
9-10
Typical Rating
2
3
4

6
6
6
8
9
10
Agricultural Weight: 3
                        8

-------
Table 7.    Ranges and Ratings for Soil Media

                      Soil Media
             Range
      Rating
Thin or Absent
Gravel
Sand
Shrinking and/or Aggregated Clay
Sandy Loam
Loam
Silty Loam
Clay Loam
Nonshrinking and Nonaggregated Clay
Weight: 2
       10
       10
        9
        7
        6
        5
        4
        3
        1
Agricultural Weight: 5
Table 8.    Ranges and Ratings for Topography

                     Topography
                    (percent slope)
Range
0-2
2-6
6-12
12-18
18 +
Weight: 1
Rating
10
9
5
3
1
Agricultural Weight: 3
Table 9.    Ranges and Ratings for Impact of Vadose
           Zone Media

              Impact of Vadose Zone Media
Range
Silt/Clay
Shale
Limestone
Sandstone
Bedded Limestone, Sandstone, Shale
Sand and Gravel with
significant Silt and Clay
Metamorphic/lgneous
Sand and Gravel
Basalt
Karst Limestone
Weight: 5
Rating Typical Rating
1-2
2-5
2-7
4-8
4-8

4-8
2-8
6-9
2-10
8-10
Agricultural
1
3
6
6
6

6
4
8
9
10
Weight: 4
Table 10.    Ranges and Ratings for Hydraulic Conductivity

                 Hydraulic Conductivity
                      (GPD/FT2)
Range
1-100
100-300
300-700
700-1000
1000-2000
2000 +
Weight: 3
Rating
1
2
4
6
8
10
Agricultural Weight:

2
Once a  DRASTIC  Index has  been computed,  it is
possible to identify areas which are more likely to be
susceptible to ground-water contamination  relative
to one another. The higher the DRASTIC Index, the
greater the  ground-water pollution  potential.  The
DRASTIC Index provides only a  relative evaluation
tool and is not designed to provide absolute answers.
Therefore, the numbers generated in the DRASTIC
Index and in the agricultural DRASTIC Index cannot
be equated.

Figure 3   Graph of ranges and ratings for depth to water.
 10-

  Q«


  8-

  7-

  6-
                                                       c

                                                       oc
                                                          6   10  20  30  40  50  60  70  80  90  100
                                                                               Feet
                                                       Figure 4. Graph of ranges and ratings for net recharge.
                                               5    6    7   8   9   10
     0123
                                             Inches

                                             9

-------
Agricultural DRASTIC

Agricultural DRASTIC is designed to be used where
the activity of concern is the application of herbicides
                                            and pesticides to an area. It represents a special case
                                            of  the DRASTIC  Index.  The only way in which
                                            Agricultural DRASTIC differs from DRASTIC is  in the
                                            assignment of relative weights for the seven DRASTIC
Figure 5. Graph of ranges and ratings for aquifer media.
      10-
       9-
       8-
       7-
       6-
   I   5H
   CD
   DC
       4-H
       3-
       2-
        1 —
                                                 Relative ranges of ease of pollution for the
                                                 principal aquifer types.

                                                 Ranges are based upon consideration of:
                                                   a) route length and tortuosity
                                                   b) potential for consumptive sorption
                                                   c) dispersion
                                                   d) reactivity and
                                                   e) degree of fracturing
                                                 Primary factors affecting rating:

                                                 1  Reactivity (solubility and fracturing)
                                                 2. Fracturing
                                                 3. Route  length  and tortuosity,  sorption,
                                                   dispersion. All essentially determined by grain size,
                                                   sorting, and packing
                                                 4 Route length and tortuosity as determined
                                                   by bedding and fracturing
                                                 5. Sorption and dispersion
                                                 6 Fracturing,  route  length  and tortuosity,
                                                   influenced by intergranular relationships
                                                 7. Reactivity (solubility) and fracturing
                                                 8 Fracturing and sorption
CO
-C

CD
>
en
en
CD
o
ffi
c
_O)
^x
u
^
Q.
O


  0)
  O
  C
el) 0)
11B
lo  I
- - j—  v.;
-D C/3  C
0  ^  CD
-O 03  CO
® O  ¥

c«  i
£ i  5
i- _i  S
't    CO
                         01
                         C
                         O
                         (fl
                         0>
O
>
en
en
cs
CO
(5
T3
c
CO    ^

1    8
ro    to
CO
n
                                                       CD
                                                       C
                                                       O
                                                       en
                                                       0)
                                   iu
                                   m
                              Primary Media
                            10

-------
factors. All  other parts  of  the two  indexes are
identical; the ranges, ratings, and instructions for use
are the same.  If the user is concerned with the
ground-water  pollution potential  of  an area  by
herbicides  and  pesticides, then  the  weights for
Agricultural DRASTIC should be  used.

Agricultural DRASTIC was created to address the
important processes which specifically offset the fate
and transport of herbicides and pesticides in the soil.
These processes, however, may not be as significant
when assigning weights to the other DRASTIC factors
for non-agricultural activities. Thus, by  comparing
Tables 2 and 3, it can be seen that for non-agricultural
activities. Soil Media is assigned a weight of 2, while
for the modified Agricultural DRASTIC, the Soil Media
is assigned a weight of 5. Topography, Impact of the
Vadose Zone,  and  Hydraulic Conductivity  of the
Aquifer are also slightly different. By making these
adjustments, the committee addressed the  special
conditions which influence the potential for ground-
water contamination by pesticides and herbicides. It
is  important to note that  the relative relationship
between the  DRASTIC factors was not deemed
Figure 6. Graph of ranges and ratings for soil media.
  10-


   9-


   8-


   "7 _


   6-
03  5 —
IT
  4 -


  3 -


  2-


  1 -
        -o
        c
        C 03
        O CD
        * i
E
co
o
             O
                         -a
                          c
                             O 03
                             E CD
                             ^ 0)
                             E o>
-o
c

                              o
                              c
                              .c
                                      Figure 7. Graph of ranges and ratings for topography.
                                           10-
                                            9-
                                            8-
                                            7-
                                            B-\
                                            4-
                                            3-
                                                         2-
                                                         1 -
                                                     I
                                                     CO
                                       I
                                       03
                                                                          (O
                                                                          CN
                                            I
                                           rsl
                                           6
                       Primary Media
                       Percent Slope

significantly different enough to warrant the devel-
opment of any other modified DRASTIC indexes. The
user should be reminded that weights may  not be
changed  for  any of the DRASTIC  factors.  These
relative weights form the basis for the system and any
changes will make the system invalid.


Integration of Hydrogeologic
Settings and DRASTIC

The mappable hydrogeologic units and the DRASTIC
Index have been combined to provide the user with a
relative pollution potential for all typical hydrogeologic
settings in the United States. A "typical" range for
each DRASTIC factor is assigned to each  hydro-
geologic setting and a DRASTIC Index is determined
for each typical hydrogeologic setting. These settings
are developed as guides and are not designed to be
representative of each and every area. The ranges for
each factor may be adjusted by the user and the rating
adjusted  accordingly when available data indicate
different  conditions. These hydrogeologic settings

-------
Figure 8. Graph of ranges and ratings for impact of the vadose zone
   10-
    9-
    8-
    7-
    6-
 §   5-I
 CD
 oc
    3-
    2 —
     1-
                          Relative impact of the principal Vadose Zone
                          Media types. Range based upon
                            a) Path length and tortuosity
                            b) potential for dispersion and consequent
                              dilution
                            c) reactivity (solubility)
                            d) consumptive sorption
                            e) fracturing
                           Primary factors affecting rating
                             1.  Consumptive sorption and fracturing
                             2.  Fracturing  and reactivity
                             3   Fracturing; path length as influenced by
                                mtergranular relationships
                             4   Fracturing; path length and tortuosity as
                                influenced by bedding planes, sorption,
                                and reactivity
                             5.  Path length and tortuosity as impacted
                                by  bedding  gram  size, sorting  and
                                packing, sorption
                             6.  Path length and tortuosity as influenced
                                by gram size, sorting, and packing
                             7.  Reactivity and fracturing
                                  _cu
                                   CO
                                  .c
                                  in
                                   tn
                                   c
                                   o
                                        CO
            o
                  SI
                  CO




CD
C
O
CO
CD
E
_i




CD
C
0
CO
•a
c
CO
c/j
VJ
CD
C
O
05
CD
E

T3
CD
•a
•a
CD
CO
g
"CD
CD
^
tj

ro O
"O
CO C
t/3 CO
0
CD
C
_O5
\
O
SI
a

o
E
2
S
5
T3
C.
ID
CO
ro
m
            •r-    «-    CM
                               Primary Media
                              12

-------
Figure 9. Graph of ranges and ratings for hydraulic
        conductivity.
   10-
    9-
    8-I
    7-
    6-
    5-
    4-
    3-
    2-
                   I
                  o
                  o
                  co
 I      I
o
o
P"*"     O
8     8
                                    o
                                    CN
                                    6
                                    o
                                    o
            o
            o
            o
                          gpd/ff2
provide units which are mappable and permit the
drafting of pollution potential maps. Thus, the user
can use hydrogeologic settings as  a mappable unit,
define the area of interest by modifying the ranges
within a setting to reflect specific conditions within
an area, choose corresponding ratings, and calculate
a pollution potential DRASTIC Index or a specialized
index for agricultural pesticides and herbicides.


References

Dee, Norbert, Janet Baker, Neil Drobny, Ken Duke, Ira
  Whitman, and Dave Fahringer, 1973. An environ-
  mental  evaluation system for  water resource
  planning; Water Resources Research, Vol. 9, No. 3,
  pp. 523-535.

Heath, Ralph C., 1984. Ground-water regions of the
  United States; U.S. Geological Survey Water Supply
  Paper 2242, 78 pp.
                                                                          13

-------
                                             Section 3
                           DRASTIC: A Description of the Factors
Ground-Water Contamination and
DRASTIC

Ground-water  pollution is caused  by a variety of
substances originating from many different activities.
In general,  man-influenced  contaminants  enter
ground water through three pathways: (1) the placing
or spreading of liquids or water soluble products on
the land surface, (2) the burial of substances in the
ground above the water table, or (3) the emplacement
or injection  of materials  in the ground below the
water  table  (Lehr et al., 1976). Table 11  lists the
activities which cause contamination through one or
more of these pathways. A brief description of each of
these activities is included in Appendix C, Sources of
Ground-Water Contamination.

After release at the land  surface, the  contaminant
may infiltrate  downward  through the soil, vadose
zone, and saturated zone finally reaching the aquifer.
If the volume of contaminant is not great,  the con-
taminant may be flushed toward the water table by
infiltrating precipitation  or additional amounts of
contaminant. Once within the aquifer, the contam-
inant may: (1) travel at the velocity of and in the
direction of ground water (Figure 10), (2) travel slower
than the ground water (Figure 11), (3) float on the
surface  of the water table (Figure 12), (4) "sink"
through  the  aquifer to the bottom (Figure 13) or (5)
under  some  conditions,  may actually move  in  a
direction against the flow of the ground water (Figure
14). Generally, the majority of contaminants travel in
the  direction of ground-water  flow at a velocity
somewhat less than that of the ground water.

As the contaminant travels through  this system,
attenuation of the contaminant may take place. Atten-
                Figure 10.  Travel of contaminant with same density as water
                          in the aquifer.

                              Source
                      Ground Water
                      Flow Direction
                Figure 11. Travel of contaminant that is denser than water in the
                        aquifer.
                             Source
                   Ground Water
                   Flow Direction
                                                     Water Table
                                            	2	
                uation includes those mechanisms which reduce the
                velocity of the contaminant through processes such
                as dilution, dispersion, mechanical filtration, volatil-
                ization, biological assimilation  and decomposition,
                precipitation, sorption,  ion  exchange,  oxidation-
                reduction, and buffering and neutralization (Pye and
Table 11.    Potential Sources of Ground-Water Contamination and Mode of Emplacement (After Lehr et al., 1976)
On the Land Surface
                                      In the Ground Above the Water Table
                                   In the Ground Below the Water Table
1. Land disposal of either solid or liquid
   waste materials
2. Stockpiles
3. Disposal of sewage and water-treatment
   plant sludge
4. Salt spreading on roads, airport runways
   and parking lots
5. Animal feed lots
6. Fertilizers and pesticides
7. Accidental spills of hazardous materials
8. Paniculate matter from airborne sources
1. Leaching tile fields, cesspools and
  privies
2. Holding ponds and lagoons
3. Sanitary landfills
4. Waste disposal in excavations
5. Leakage from underground storage
  tanks
6. Leakage from underground pipelines
7. Artificial recharge
8. Sumps and dry wells
9. Graveyards
1. Waste disposal in wet excavations
2. Drainage wells and canals
3. Abandoned/improperly constructed
  wells
4. Exploratory wells
5. Water supply wells
6. Waste disposal walls
7. Mines
8. Salt water intrusion
                                                   14

-------
Figure  12.  Travel of contaminant that is less dense than
           water in the aquifer.
           Source
                                  Water Table
                              	y	
   Ground Water
   Flow Direction
Figure 13. Travel of contaminant that is denser than water and
         sinks in the aquifer.
            Source
                                Water Table
                        	X	
 Ground Water
 Flow Direction
Figure 14.
Travel of contaminant that is denser than water in
the aquifer in a direction opposed to the water
flow direction.


             Source
      Ground Water
      Flow Direction
Kelley, 1984; Fetter, 1980). Dilution is accomplished
by hydrodynamic dispersion. The degree of attenua-
tion which can occur is a function of (1) the time that
the contaminant  is in  contact  with  the material
through which it  passes,  (2) the grain size and
physical and chemical  characteristics of the material
through which it passes, and (3) the distance which
the contaminant has  traveled.  In general,  for any
given material the longer the time and greater the
distance, the greater the effects of attenuation. In a
similar manner, the greater the surface area of the
material through which the contaminant passes, the
greater the potential for sorption of the contaminant
 and hence for attenuation. The greater the reactivity
 of  the  material  through which the contaminant
 passes, the greater the potential for attenuation.

 Any combination of these processes may be active
 depending on the hydrogeologic conditions and the
 contaminant.  It is therefore necessary  to  have a
 general idea of these processes and whether they are
 active. A discussion of the mechanisms which control
 contaminant movement is included in Appendix A,
 Processes and Properties Affecting Contaminant Fate
 and Transport.

 The effectiveness of dilution and attenuation proc-
 esses is largely determined by (1) the rate and loading
 of the applied contaminant, (2) the characteristics of
 the contaminant, and (3) the physical characteristics
 of the area. Ultimately, it  is these factors which
 control the ground-water pollution potential of any
 area. The rate and loading factor which generally is of
 site-specific character is discussed briefly in Section
 5, IMPACT—Risk Factors. The characteristics of the
 contaminants are discussed in more detail in Ap-
 pendix B,  Characteristics of  Ground-Water Contam-
 inants. However, it is the physical properties char-
 acterized  by the  hydrogeologic setting of the area
 which determine the extent to which the attenuation
 mechanisms may have the potential to be active.

 Because it is neither practical nor feasible to obtain
 quantitative evaluations of these intrinsic mechan-
 isms from a regional perspective, it is necessary to
 look at the  broader  physical parameters which
 incorporatethe many processes. Each of the DRASTIC
 parameters includes various mechanisms which will
 help to evaluate the vulnerability of ground water. A
 description of each DRASTIC feature and the included
 processes is contained in the following sections.
Depth to Water
The water table is the expression of the surface below
the ground level where all the pore spaces are filled
with water. Above the water table, the pore spaces
are partially  filled with water  and air. The water
table may be present in any type of media and may be
either permanent or seasonal. For purposes of this
document, depth to water refers either to the depth to
the water surface in an unconfined aquifer or to the
top of the  aquifer where the  aquifer is confined
(Figure 15). Depth to water does not include saturated
zones which  have  insufficient permeability to yield
significant  enough quantities of water to  be con-
sidered an aquifer.

The depth to water is important primarily because it
determines the depth of material through which a
contaminant must travel before reaching the aquifer,
and it may help to determine the amount of time
during which contact with the surrounding media is
                                                                         15

-------
Figure 15. Depth to water in a confined and unconfined aquifer.
       Depth to Water
                  \
            Water Table
                    Unconfined Aquifer
                    -,—7—7—7—7—r Confining Layer-
                     Confmed Aquifer
maintained. The depth to water is also  important
because  it provides the  maximum  opportunity for
oxidation by atmospheric oxygen. In general, there is
a greater chance for attenuation to occur as the depth
to water increases because deeper water levels infer
longer travel times.  Figure 3 shows the relative
importance of depth to water. The ranges in depth to
water as defined in the DRASTIC system have been
determined  based on what are considered to be
depths where the significance for pollution potential
changes.


Net Recharge

The primary source of ground water is precipitation
which infiltrates through the surface of the ground
and  percolates to the water  table. Net recharge
indicates the amount of water per unit area of land
which penetrates the ground surface and reaches the
water table. This recharge water is thus available to
transport a contaminant vertically to the water table
and horizontally within the aquifer.  In addition, the
quantity of water available for dispersion and dilution
in the vadose zone and in the saturated zone is
controlled by this  parameter. In areas where the
aquifer is unconfined, rechargetotheaquifer usually
occurs more readily  and the pollution potential is
generally greater than in areas with confined aquifers.
Confined aquifers are partially protected from contam-
inants introduced  at the surface by layers  of low
permeability media which retard water movement to
the confined aquifer. In some parts of some confined
aquifers, head distribution is such that movement of
water is through the confining bed from the confined
aquifer into the unconfined  aquifer. In this situation,
there is little opportunity for local contamination of
the confined aquifer. For a  better understanding of
how to deal with this situation, refer to the Section 4,
How to Evaluate Confined Aquifers. The principal
recharge area for the confined aquifer is often many
miles away.  Many confined aquifers  are not truly
confined and are partially recharged by migration of
water through the  confining layers. The more water
that  leaks  through,  the greater  the  potential for
recharge to carry pollution into the aquifer. Recharge
water, then, is a principal vehicle for  leaching and
transporting sol id or liquid contaminants to the water
table. Therefore, the greater the recharge, the greater
the potential for pollution.  This  is true until the
amount of recharge is great enough to cause dilution
of the contaminant andthe pollution potential ceases
to increase and may actually decrease. For purposes
of this document, this phenomena has been acknowl-
edged but the ranges and associated ratings do not
reflect the dilution factor.

One  additional factor which must be considered is
augmentation of natural recharge through artificial
recharge or by  irrigation. When a range  for net
recharge is assigned, these additional  sources  of
water must be considered.


Aquifer Media

Aquifer media refers to  the  consolidated or uncon-
solidated medium which serves as an aquifer (such as
sand and gravel or limestone). An aquifer is defined
as a medium which will yield sufficient quantities of
water for use. Water is held by aquifers in the pore
spaces of granular and clastic rock and  in the frac-
tures and solution  openings  of non-clastic and non-
granular rock. Rocks which yield water from  pore
spaces have primary porosity; rocks where the water
is held  in openings such as fractures and solution
openings  which were  created after the rock was
formed have secondary porosity. The aquifer medium
exerts the major control over the route and  path
length which a contaminant must follow. The  path
length is an important control (along with hydraulic
conductivity and gradient) in determining the  time
available for attenuation processes such as sorption,
reactivity, and dispersion  and also the amount  of
effective surface area of materials contacted in the
aquifer. The route which a contaminant will take can
be strongly influenced by fracturing or by any other
feature such as an interconnected series of solution
openings  which may provide  pathways for easier
flow. In general, the larger the grain size and the more
fractures or openings within the aquifer, the higher
the permeability  and  the  lower the attenuation
capacity;  consequently  the greater the pollution
potential.

For purposes of this  document, aquifer media have
been designated by descriptive names.  Each medium
is listed in the order of increasing pollution potential.
A discussion of each  medium follows:

 (a)  Massive Shale—Thick bedded shales, claystone
     or clays which typically yield only small quanti-
     ties of water  from fractures and which  have a
     low pollution potential. Pollution potential is
     influenced by the degree of fracturing.
                       16

-------
(b)  Metamorphic/lgneous—Consolidated bedrock
     of metamorphic or igneous origin which con-
     tains little or no primary porosity  and which
     yields water only from fractures within the rock.
     Typically well yields are low  and the relative
     pollution potential is a function of the degree of
     fracturing.
(c)  Weathered Metamorphic/lgneous—Unconsoli-
     dated material,  commonly termed  regolith  or
     saprolite, which is derived by weathering of the
     underlying consolidated bedrock,  and  which
     contains primary porosity. The pollution poten-
     tial is largely influenced by the amount  of clay
     material present: the higher the clay content,
     the lower the pollution potential.
(d)  Bedded Sandstone,  Limestone, and  Shale—
    Typically thin bedded sequences of sedimentary
    rocks which contain primary porosity but where
    the controlling factor in determining pollution
    potential is the degree of fracturing.
(e)  Massive Sandstone—Consolidated  sandstone
    bedrock which contains both primary and sec-
    ondary porosity and is typified by thicker deposits
    than  the  Bedded  Sandstone  Limestone and
    Shale sequences. Pollution potential is largely
    controlled by both the degree of fracturing and
    the primary porosity of the sandstone.
(f)  Massive Limestone—Consolidated limestone or
    dolomite bedrock  which  is characterized  by
    thicker deposits than Bedded Sandstone, Lime-
    stone, and Shale sequences.  Pollution potential
    is largely affected by the degree of fracturing
    and the amount of solution of the limestone.
(g)  Sand and Gravel—Unconsolidated mixtures  of
    sand- to gravel-sized particles which contain
    varying amounts of fine materials. Sands and/or
    gravels which have only small  amounts of fine
    material are  termed "clean."  In general, the
    cleaner and more coarse-grained the aquifer,
    the greater the pollution potential.
(h)  Basalt—Consolidated extrusive igneous bedrock
    which contains bedding planes, fractures,  and
    vesicular porosity. The term is  used  herein in a
    generic sense, even though it is actually a rock
    type.  Pollution  potential is  influenced by the
    amount of  interconnected openings which are
    present in the lava flow  materials.
 (i)  Karst Limestone—Consolidated limestone bed-
     rock  which has been  dissolved to the point
     where large, open, interconnected cavities and
     fractures are present. This is a special case of
     Massive Limestone.

     A graphic display of the ratings which have been
     assigned to each media  is contained in Figures.
     This graph also contains a more complete listing
     of the mechanisms which affect the  pollution
     potential of that media. Because this DRASTIC
     parameter is less quantifiable, the user will be
     instructed to choose a rating based on the above
     discussion  and  available  information  on the
     geology of the area (Section 4, How to Use the
     Range in Media Ratings).

Soil Media

Soil media refers to that  uppermost portion of the
vadose zone characterized by significant biological
activity.  For purposes  of this  document,  soil is
commonly considered the upper weathered zone of
the earth which averages three feet or less. Soil has a
significant impact on the amount of recharge which
can infiltrate into the ground and hence on the ability
of a contaminant to move vertically into the vadose
zone. Moreover, where the soil zone is fairly thick, the
attenuation  processes of  filtration,  biodegradation,
sorption, and volatilization may  be quite significant.
Thus, for certain  on-land surface practices  such as
agricultural  applications of pesticides or application
of herbicides, soil can  be a  primary influence  on
pollution potential. In general, the pollution potential
of a soil is largely affected by the type of clay present,
the shrink/swell potential of that clay, and the grain
size of the soil. In general, the less the clay shrinks
and swells and the smaller the grain size, the less the
pollution potential. The quantity of organic material
present in the soil may also be  an important factor.
Soil media are best described by referring to the basic
soil types as  classified  by the Soil  Conservation
Service. A description of the  soil media in order of
increasing pollution potential follows:

 (a)  Nonshrinking  Clay—Illitic or  Kaolinitic  clays
     which  do not expand and contract with the
     addition  of  water and therefore do not  form
     vertical secondary permeability which increases
     the pollution potential.
 (b)  Clay Loam—A soil textural classification which
     is characterized by 15-55 percent silt, 27-40
     percent clay, and 20-45 percent sand (Figure
     16). Because of the  high amounts of clay and
     restrictive permeabilities, it has a low pollution
     potential.
 (c)  Silty Loam—A soil textural classification char-
     acterized by 50-85 percent silt, 12-27 percent
     clay, and 0-50 percent  sand (Figure 16). The
     pollution potential is still low, but higher than a
     clay loam because of typically lower percentages
     of clay.
 (d)  Loam—A soil textural classification  character-
     ized by 25-50 percent silt, 7-27 percent  clay,
     and 0-50 percent sand(Figure 16). The pollution
     potential is still low, but  higher than a silt  loam
     because of lower percentages of clay and silt.
 (e)  Sandy Loam—A soil textural classification char-
     acterized by 0-50 percent silt, 0-20 percent clay,
     and 15-50 percent sand  (Figure 16). The pollu-
                                                                         77

-------
Figure 16. Soil textural classification chart (Soil Conservation Service, 1951).
                                              100
                                 o
                                                 Percent Sand
     tion potential is greater than a loam due to the
     higher percentage of sand.
 (f)  Shrinking Clay—Characterized by montmorillon-
     itic clays or smectites which have an expanding
     lattice that swell and contract with alternating
     wetting and drying. Although the cracks formed
     on drying, swell as the clay hydrates, the ability
     of pollutants to move rapidly upon initial wetting
     is documented. Although usually of low perme-
     ability, this medium can  have a seemingly high
     pollution  potential  based on the  secondary
     vertical permeability created by the cracking of
     the media upon drying.
(g)  Sand—A size-based delineation of angular or
     rounded particles ranging in size from 1 716 mm
     to 2 mm.  Sands are typically free of silts and
     clays  and therefore  have  a high  pollution
     potential.
 (h)  Gravel—A particle-based size classification
     typified by particles larger than 2 mm in size and
     commonly a mixture of sand, silt,  clay, and
     gravel  with  a  preponderance of large-sized
     particles.  Permeability is rapid and  pollution
     potential is high.
 (i)  Thin or Absent—If a soil layer is not present or if
     the layer  is so thin as to be considered  inef-
     fective, the pollution potential is very high and
     this category should be used. Figure 6 contains
     a graphic representation of the pollution poten-
     tial of soil media.

Topography

As used here, "topography" refers to the  slope and
slope variability of the  land surface. Basically, topo-
graphy  helps control the likelihood that a  pollutant
                        18

-------
will run off or remain on the surface in one area long
enough to infiltrate. This is particularly important in
activities  such as  application of pesticides  and
herbicides where the effect of the contaminant tends
to be cumulative. Therefore, the greater the chance of
infiltration, the higher the pollution potential  as-
sociated with the slope. Topography influences soil
development and therefore has an effect on attenua-
tion. Topography is  also significant from the stand-
point that the gradient and direction of flow often can
be inferred for water table conditions from the general
slope of the land. Typically, steeper slopes  signify
higher ground-water velocity.

Figure 7 contains the ranges which were chosen as
significant for pollution potential. These ranges
correspond to the  ranges identified by  the  Soil
Conservation Service for percent slope. The  ranges
are assigned ratings assuming that 0-2 percent slope
provides the greatest opportunity  for a pollutant to
infiltrate  because neither the pollutant nor much
precipitation exits the area as runoff. Conversely, 18+
percent slope affords  a high  runoff capacity and
therefore  a  lesser  probability  of infiltration with
subsequent lower pollution potential. However, steep
slopes are more conducive to rapid  erosion and
contamination of surface water.
Impact of Vadose Zone

The vadose zone is defined as that zone above the
water table which is unsaturated. For purposes of this
document, this strict definition can be applied to all
water  table aquifers. However, when evaluating  a
confined aquifer, the "impact" of the vadose zone is
expanded to include both the vadose zone and any
saturated  zones which overlie  the  aquifer. The
significantly restrictive zone above the aquifer which
forms the confining layer is used as the type of media
which  has the most significant impact.

The type of vadose  zone  media determines the
attenuation characteristics of the material below the
typical soil horizon  and above  the  water table.
Biodegradation, neutralization, mechanical filtration,
chemical reaction, volatilization, and dispersion are
all  processes  which may occur within  the vadose
zone with a general lessening of biodegradation and
volatilization with depth. The media also control the
path length and routing, thus affecting the  time
available for attenuation and the quantity of material
encountered. The routing is strongly influenced by
any fracturing present. The materials at the top of the
vadose zone also exert an influence on soil develop-
ment.

Vadose zone media have been designated by descrip-
tive names. Each medium, listed in order of increasing
pollution potential, is discussed as follows:
(a)  Silt/Clay—A deposit of silt- and clay-sized
    particles which  serves as  a  barrier  to retard
    movement of liquids. The high clay content
    provides a low  pollution potential. Shrinking
    clays and higher silt concentrations increase
    the pollution potential.

(b)  Shale—A consolidated, thick-bedded clay rock
    which may be fractured. Pollution potential  is
    low but increases with the degree of fracturing.

(c)  Limestone—Consolidated massive limestone or
    dolomite which typically contains fewer bedding
    planesthan Bedded Limestone, Sandstone, and
    Shale sequences (see  "e" below).  Pollution
    potential is influenced by the degree of fractur-
    ing, with a high  density of fracturing  increases
    the chance for pollutant migration.

(d)  Sandstone—A consolidated sand  rock which
    contains both primary and secondary porosity
    and is typified by thicker bedding than compared
    to  Bedded Limestone, Sandstone, Shale se-
    quences. Pollution potential is largely controlled
    by  the degree of fracturing  and the primary
    porosity of the sandstone.

(e)  Bedded Limestone, Sandstone, Shale—Typically
    thin-bedded  sequences of sedimentary rocks
    which contain primary porosity but where the
    controlling factor in determining pollution po-
    tential is the  degree of fracturing.

 (f)  Sand and Gravel with Significant Silt and Clay—
    Unconsolidated  mixtures  of  sand and gravel
    which contain an appreciable amount of  fine
    material affect pollution potential  by having a
    high concentration of clay or by reducing the
    permeability  of the deposit. These deposits are
    commonly referred to as "dirty"  and  have a
    lower pollution  potential than "clean" sands
    and  gravels. In general,  finer-grained  and
    "dirtier" sands have a lower pollution potential
    than coarser-grained "dirtier" gravels.

(g)  Metamorphic/lgneous—Consolidated rock  of
    metamorphic or igneous origin which contain
    no significant primary porosity and which permit
    movement of liquids through fractures.  The
    relative pollution potential is a function of the
    degree of fracturing.

(h)  Sand and Gravel—Unconsolidated mixtures  of
    sand- to gravel-sized particles which contain
    only small amounts of fine materials. The range
    in rating reflects principally a grain size distri-
    bution where unsorted smaller grained deposits
    have a  lower  pollution potential and  larger
    grained, well-sorted deposits  have a higher
    pollution potential.
                                                                         19

-------
 (i)  Basalt—Consolidated extrusive igneous bedrock
     which contains bedding planes, fractures, and
     vesicular porosity.  This  is a  special case of
     Metamorphic/lgneous. The term is used herein
     in a generic sense,  even though it is actually a
     rock type. Pollution potential is influenced by the
     number and amount of interconnected openings
     present in the lava flow materials. Pollution
     potential  is typically high because there is little
     chance for attenuation once a pollutant enters
     the fracture system.

 (j)  Karst Limestone—Consolidated limestone bed-
     rock which has  been dissolved  to the point
     where  large open interconnected  cavities and
     fractures are present. This is a special case of
     Limestone, where  pollution potential is high
     based on the amount of open area  in the rock.

A  graphic display of the ratings which have been
assigned to  each medium is contained in Figure 8.
This graph also contains a more complete listing of
the mechanisms which affect the pollution potential
of that media. Because  this DRASTIC  parameter  is
less quantifiable, the user is instructed to choose a
rating based on the above discussion and available
information  on the geology of the area (Section 4,
How to Use the Range in Media Ranges).


Hydraulic  Cbnductivity of the Aquifer

Hydraulic conductivity refers  to  the ability of the
aquifer materials to transmit water, which in turn,
controls the rate at which  ground water will flow
under a given  hydraulic  gradient. The rate at which
the ground water flows also controls the rate at which
a contaminant will be  moved away from the point at
which it enters the aquifer. Hydraulic conductivity is
controlled by the amount and interconnection of void
spaces within the aquifer  which may occur as a
consequence  of intergranular porosity, fracturing,
bedding planes, etc. For  purposes of this document,
hydraulic conductivity is divided into ranges where
high hydraulic conductivities  are  associated with
higher pollution potential. This is because the pol-
lutant hasthe potential for moving quickly awayfrom
the  point in the aquifer where  it is introduced.
Obviously, a wide range of hydraulic conductivities
are present  in all  areas. The  values assigned are
considered to  be typical for the settings described.
Figure 9 shows the relative importance of the ranges.
 Interaction Between Parameters
 From the above discussion and in the application of
 the DRASTIC Index, it will be recognized that there is
 apparent redundance between some of the param-
 eters. The depth to the water, for example, affects the
 quantity of material that will be  encountered by a
pollutant moving downward toward an aquifer. The
thicker the section in a given setting, the greater the
effect may be upon  the degradation, retardation, or
attenuation of the pollutant.

However, in considering the  impact of the vadose
zone, degradation, retardation, and other significant
attenuation processes are all varied according to the
nature of the materials present, and their condition
within  the vadose zone. If, for instance, the vadose
zone is moderately  fractured  granite, the materials
within the vadose zone will have only a slight impact
on most  pollutants  entering the vadose zone. The
protection provided will be a function of depth and the
failure of critical fractures to interconnect.

If, however, the vadose zone is comprised of unfrac-
tured glacial till (silt/clay), it can be anticipated that
consumptive sorption will be moderately high; infil-
tration will be moderately low; retardation will be
significant; and with any substantial thickness of till,
considerable time will be required for most (conserv-
ative) pollutants to penetrate the till. Thus  it can be
seen that the redundant consideration of degradation,
retardation, and attenuation within the context of
both depth to water  and impact of the vadose zone is
useful  in the comparative evaluation of sites.

Net recharge determines, on  an annual basis, the
quantity of water from precipitation that is  available
for vertical transport, dispersion,  and  dilution of a
pollutant  from a  specific point of application. Net
recharge exemplifies how some parameters can have
both positive  and  negative effects.  For  example,
greater recharge typically means more rapid transport
of a pollutant and therefore less time for attenuation.
However, in this  situation, dilution is also greater
thereby exerting  a  positive influence  because the
concentration of an introduced contaminant will be
lessened. It is also evident that a thick unsaturated
zone, with a  layered sequence of a bedded and
fractured shales,  sandstones, and limestones, can
have a profound  impact on all three  of the  same
factors (transport, dispersion, dilution) that are of
primary importance  to net recharge.

Topography  and soil media also  influence net re-
charge. Topography  has site-specific influence which
determines whether the capacity for recharge is high
or low at a given point. The permeability of the surface
soils has a similar impact. However, the nature of the
surface soil materials has an additional impact upon
potential  pollutant  attenuation, consumptive  sorp-
tion, route length anddirection, and time available for
penetration.

In addition to its direct  influence upon recharge,
topography exerts a significant influence upon soil
thickness, drainage characteristics, and profile de-
velopment. These factors, in turn, influence soil
media as well as the previously-mentioned factors. \r\
                        20

-------
addition, topography  usually  bears  a predictable
relationship to  hydraulic gradient,  and direction  of
probable pollutant  movement  under water  table
conditions, with a consequent  impact on dispersion
and dilution.

The upper portion of the vadose zone exerts influence
on the type of soils developed on the surface. The
vulnerability of an aquifer to a given pollution event
varies in responsetothe nature of the materials in the
vadose zone; grain size, sorting, reactivity, bedding,
fracturing, thickness, sorptive character. In general,
finer grain-size materials, i.e. clays and  silt, have
lower hydraulic conductivity, greater capacity for the
temporary and  long-term attenuation of pollutants,
and  greater  sorptive  capacity. If  expandable  clay
minerals are present, the sorptive capacity is further
enhanced. If a material (seven moderately cemented,
then grain  size and sorting may be less significant
than the degree of cementation.

If the material in the vadose zone is reactive to the
pollutant, or soluble in it, then there may be two
different effects. First, the pollutant may be retarded
(a positive effect) or second, the solution of the vadose
zone material may actually increase permeability and
allow subsequent introduction of pollutants to pass
through more quickly with less retardation (a negative
effect). In the case of reactive pollutants, the impor-
tance of secondary by-products must be considered. It
is here that the risks associated with gaseous phase
transport are most likely to have an impact on ground
water.

The thickness of the vadose zone and the degree of
fracturing and frequency of bedding planes in it all
impact upon the tortuosity, route length, dispersion,
and  consequent travel time that  is required  for a
pollutant to move through the vadose zone. This is not
only of time-delay importance but is important as the
control of contact time for reactions to occur.

The vadose zone, including the surf icial soil, is also of
great importance as the zone where most of the
biologic activity occurs. There are natural organisms
found in this zone that break down many polluting
substances into secondary by-products, both harm-
less and harmful. For many chemicals these reactions
are very poorly understood, if at all, but it is known
that  with sufficient time the eventual results are
generally beneficial. Among the best known of these
processes at present are the bacterial fixation of iron
and  the bacterial  breakdown  of  non-chlorinated
hydrocarbons under natural conditions. Both of these
processes occur in the vadose zone and in the aerobic
portion of shallow aquifers.

The  hydraulic conductivity, together with  gradient
and porosity of the aquifer beneath a site, influences
the rate of movement of an introduced pollutant away
from the point of  introduction. In conjunction with
hydraulic  gradient, conductivity also controls the
direction of movement. These are, in turn, affected
with regard to dispersion, by grain  size,  bedding,
fracturing, and tortuosity.

It is evident that all of the DRASTIC parameters are
interacting, dependent variables. Their selection is
based not on available data quantitatively developed
and rigorously applied, but on a subjective under-
standing of "real world" conditions at a given area.
The value of the DRASTIC parameters is in the fact
that they  are based on information that is readily
available for most portions of the United States, and
which can be obtained and meaningfully mapped in a
minimum of time and at minimum cost. The DRASTIC
ranking scheme can then be applied by enlightened
laymen for valid comparative evaluations  with ac-
ceptable results.

If the vulnerability of a site, or sites, to pollution were
to be evaluated with regard to travel time,  flux, and
concentration  associated  with the incidence  of a
pollutant introduced at the site, the DRASTIC param-
eters would be distributed as follows:

 A. Travel Time

    —  Depth to Water
    —  Soil Media
    —  Impact of Vadose Zone
    —  Net Recharge
    —  Conductivity

 B. Flux

    —  Aquifer Media
    —  Conductivity (Existence of  Gradient As-
         sumed)

 C. Concentration

    —  Depth to Water
    —  Net Recharge
    —  Aquifer Media
    —  Soil Media
    —  Topography
    —  Impact of Vadose Zone
    —  Conductivity

It  should be noted that although the DRASTIC
parameter of hydraulic conductivity of the aquifer is
mapped as a function of the ability of a pollutant to be
moved from a point of incidence,  the direction  of
migration is a function of gradient and rate depends
on both conductivity and gradient.


References

Fetter, C. W., 1980. Applied hydrogeology; Charles E.
  Merrill Publishing Company, 448 pp.

Lehr, Jay H., WayneA. Pettyjohn, Truman W. Bennett,
  James R. Hanson, and Laurence E. Sturtz, 1 976. A
                                                                         21

-------
  manual of laws, regulations,  and institutions for
  control ofground water pollution; U.S. EPA-440/9-
  76-006.

Pye, Veronica I. and Jocelyn Kelley, 1984. The extent
  of groundwater contamination in the United States;
  Groundwater  Contamination, National  Academy
  Press, pp. 23-33.

Soil Conservation Service, 1951. Soil survey manual;
  U.S. Department of Agriculture, 503 pp.
                       22

-------
                                          Section 4
                    How to Use Hydrogeologic Settings and DRASTIC
The system described in this document presents a
simple and  easy-to-use  approach to assess the
ground-water pollution potential of any area. Al-
though the final system appears simplistic, the sys-
tem actually includes  many complex concepts and
relationships. Before an attempt is made to make full
use of this system, the user needs to develop an
appreciation for the complexity of evaluating ground-
water pollution  potential. It is not necessary to
understand every concept in detail, but the greater
the depth of understanding, the more useful the
system becomes. DRASTIC provides mappable results
which can be used to provide a quick  reference of
relative pollution potential of different areas. DRAS-
TIC is designed to be used as a planning or screening
tool. DRASTIC and associated maps cannot be used in
site-specific evaluations because of local complex-
ities in geologic conditions.
Organization of the Document

As described  in  Section  2, Development  of the
System and Overview, the entire United States has
been divided into 13 geographic regions and each
region  subdivided into hydrogeologic settings. Sec-
tion 6, Hydrogeologic Settings of the United States by
Ground-Water Regions, contains an annotated des-
cription of each region, a geographic location map for
each region, and an illustration of  the major hydro-
geologic features of the region. Each hydrogeologic
setting contains a written narrative, an illustration,
and two DRASTIC charts. These  charts contain a
listing of the seven DRASTIC features, an example of
typical  ranges for each  feature  which might be
encountered in the region, a listing of  the weight
which has been assigned to the DRASTIC feature, a
rating which corresponds  to the associated range
(from Tables 4-10), a column which  reflects the
weight multiplied by the rating for each factor, and a
total DRASTIC Index. The same  information is con-
tained in the second agricultural DRASTIC chart. The
significant difference between the charts is in the
weights assigned to each DRASTIC feature, thus
yielding a separate specialized agricultural DRASTIC
Index.
Table 18 contains a complete listing of all  hydro-
geologic settings and their associated DRASTIC I ndex.
Table 19  arranges  the  hydrogeologic settings by
increasing DRASTIC Index values. Table 20 arranges
the hydrogeologic  settings alphabetically  so  that
comparison of similar settings in different  regions
can be accomplished. Tables 21 -23 contain the same
information computed for the modified agricultural
DRASTIC Index. These lists have been prepared to
assist the user in evaluating the relative pollution
potential for many hydrogeologic settings. Following
these listings are Tables 24 and 25 which provide a
summary of principal physical and hydrologic charac-
teristics and common ranges of the hydraulic charac-
teristics of the ground-water regions as defined by
Heath (1984). These values may assist the user in
evaluating hydrogeologic settings.


The other important information necessary to  use
DRASTIC is contained in the ranges and rating tables
for each factor. For ease of reference, Tables 4-10
have been reprinted in Section 6 as Tables 26-32.
This set of tables consists of a complete listing of the
DRASTIC factors, the ranges and associated rating for
each factor, and the weights for both the DRASTIC
and modified agricultural DRASTIC system.
Where to Obtain Information on
DRASTIC Parameters

Before an area can be evaluated using the DRASTIC
system, the basic information on each factor must be
found. DRASTIC has been designed to use informa-
tion which is available from a variety of sources. Table
1  contains a listing of possible sources  of hydro-
geologic  information and  the types of information
which may be available from each. The most common
source of information for  each parameter is listed
below:

(1)  Depth to Water—Well  logs or hydrogeologic
     reports;
(2)  Net  Recharge—Water resource reports com-
     bined with data on precipitation  from the
     National Weather Service;
(3)  Aquifer Media—published geologic and hydro-
     geologic reports;
(4)  Soil Media—published soil survey reports  or
     local mapping projects conducted by the Soil
     Conservation Service;
                                               23

-------
(5)  Topography—published U.S. Geological Survey
    topographic maps (various scales);
(6)  Impact of the VadoseZone—published geologic
    reports;
(7)  Hydraulic Conductivity of the  Aquifer—pub-
    lished hydrogeologic reports. (Of all the factors,
    this information may be the most difficult to find.
    Because it  is related  very closely to aquifer
    media, if necessary, hydraulic conductivity may
    be estimated using Table 12). Conversion factors
    for permeability and hydraulic conductivity are
    found in Table 13.

It should be noted that the more accurate the data
used to compute the  index, the more reliably the
pollution potential can be assessed. There may be
many gaps in the data, of course. These gaps can be
filled with careful interpolation if such interpolation is
reasonable.
Steps for Use of the System

In order to use the DRASTIC system, the user must
follow a few simple  steps. The following  example
illustrates how to use the system. A decision-maker
wishes to evaluate the pollution potential of two
areas in a county. The county is located along the
glacial boundary such that part of the county lies in
the Glaciated Central  Region and the other part lies in
the Non-Glaciated Central Region.  Precipitation  in
the area averages 42 inches per year. Area I is typified
by 5 to 20 feet of glacial till deposits, which overlie
fractured  sandstones  and shales  with hydraulic
conductivities ranging from 100 to 300 gpd/ft2. The
terrain is  rolling,  and depth to the water  in the
sandstones  averages 30 feet below land surface.
Typical soils have mixtures of sand, silt, and clay with
predominant clay  fractions. Area  II is typified  by
alternating sequences of sandstone, limestone, and
 Table 12. Range of values of hydraulic conductivity and permeability (Freeze and Cherry, 1979)
Unconsohdated k k k k k
Rocks






;
2 ±j
: «
J CD 1
n -D T3 1
- co c tn
a CD co •*:
<: E « §

CD o
Q- 0) O
c £
ra Q.
i- TJ
-a o c
£ E to „
U CO CD ^ CD
0 CD £ £ £
ro g 2 .0 S
"- 1 $ Q -a
-J t/3


T3
Deposits
























(darcy) (cm2) (cm/s) (m/s) (gal/day/ft2)


0
CD
f
^.
1

TJ
Iw
CD
QJ
"^ CJ
03 J
^ 1
£ \
•\
J









V) 1
(




r/
—
|f
CO
o
CO
>- ^3
T,l 1^
C W ™
^ 0 « « I
" ^ ir "S c
i H = w
"Mi
— J o oi
I

CD
C

i









3 m

\ 1


1






























r105

-104


-103

-102

-10


- 1


-10'1



-10'2


-10'3

-10'4


-10-5

-10'6

-TO'7

-io-3

-io-4


-10-5

-io-6

-io-7


-10-8


-10-9



-10-'°


-10-"

-10-'2


-10-13

-10-'4

-1Q-15

-102

-10


-1

-io-1

^10~2


-10-3


-10-4



-io-5


-10-6

-io-7


-10-8

-10-9

-10-'°

-1
r-106
-io-1


-io-2

-IO-3

— 10'4


-10 5


-io-6



-io-7


-TO'8

-TO-9


-10-10

-10-"

-10'12

l_1Q-8 i-1Q-'6 l-10~11 1— 1Q-13



-105

-10"

-103


-102


-10



- 1


-10-'

-io-2


-TO-3

-10-"


-10-5
-10-"

-io-7

-------
Table 13.   Conversion Factors for Permeability and Hydraulic Conductivity Units (Freeze and Cherry, 1979)

                              Permeability, k*                             Hydraulic conductivity, K

cm2
ft2
darcy
m/s
ft/s
U.S. gal/day/ft2
cm2
1
9.29 x 102
9.87 x 10-"
1.02 x 1CT3
3.11 x 10-
5.42 x 10-10
ft2
1.08 x 10°
1
1.06 x 10-"
1.10 x 10-"
3.35 x 10-'
5.83 x 10-13
darcy
1.01 x 10=
9.42 x 1010
1
1.04 x 10B
3.15 x 10"
5.49 x 10-7
m/s
9.80 x 102
9.11 x 106
9.66 x 10-"
1
3.05 x 10-'
4.72 x 10'7
ft/s
3.22 x 103
2.99 x 10s
3.17 x 10-5
3.28
1
1.55 x 10-6
U.S. gal/day/ft2
1.85 x 10"
1.71 x 1012
1.82 x 10'
2.12 x 10"
6.46 x 105
1
*To obtain k in ft2, multiply k in cm2 by 1.08 x 10~3
shale with moderate fracturing and hydraulic con-
ductivity averaging 300 gpd/ft2. Relief is low and
slopes are commonly 2  percent. Depth to water
averages 40 feet. Soil is thin but significant with soils
reflecting equal mixtures of  sand,  silt,  and clay.
Average net recharge is 8 inches per year.

(1)  Identify the Region in which the area is located.
    Become familiar with the hydrogeology of the
    region. Area I is in the Glaciated Central Region
    and Area  II  is  in the Non-Glaciated Central
    Region.
(2)  Identify which hydrogeologic setting most close-
    ly approximates the conditions of the area. Area
    I  most closely approximates Setting 7Aa—Gla-
    cial Till  Over Bedded Sedimentary Rocks; Area
    II, 6Da—Alternating Sandstone, Limestone and
    Shale—Thin Soil. For ease of reference, these
    setting descriptions are included as Figures 17
    and 18  and Tables 14 and 15.

(3)  Evaluate available area  information for each
    DRASTIC parameter against the ranges chosen
    for each DRASTIC parameter listed in the top
    table (Tables 14 and 15). In Area I (Table 14), the
depth to water averages 30 feet; the assigned
range of 30-50 would seem appropriate. There-
fore, the associated rating of 5 (Table 4) does not
need to be changed. No value for Net Recharge
was available; however, precipitation  in  the
region is 42 inches per year and recharge will
typically be restricted  due to the presence of
clayey till; the assigned range  of 4-7 seems
appropriate. Therefore, the associated rating of
6 (Table 5) does not need to be changed. The
aquifer media  are fractured sandstones and
shales; thin bedded sandstone, limestone, and
shale sequences are present, so this is appro-
priate. Therefore,  the  associated rating of 6
(Table 6)  does  not need to be changed. Soils
have a predominant clay fraction but contain silt
and sand; clay loam is the prevalent soil, so the
chart designation would be appropriate. There-
fore, the associated rating of 3 (Table 7) does not
need to be changed.  Terrain  is rolling;  2-6
percent slopes  are  predominant.  The  listed
range  is acceptable.  Therefore, the associated
rating of 9 (Table 8) does not need to be changed.
The vadose zone is comprised of glacial till; silt
and clay is the most significant portion of the
Figure  17.  Description and illustration for setting 7 Aa—    Figure 18.
           glacial till over bedded sedimentary rocks.
     Description and illustration for setting 6Da—
     alternating sandstone, limestone and shale-thin
     soil.
                                                                          25

-------
Table 14. DRASTIC and Agricultural DRASTIC Charts for
for Setting 7Aa — Glacial Till Over Bedded
Sedimentary Rocks
Setting 7Aa Glacial Till Over
Bedded Sedimentary Rock
Feature
Depth to Water
Table
Net Recharge
Aquifer Media



Soil Media
Topography
Impact
Vadose Zone
Hydraulic
Conductivity

Range
30-50

4-7
Thin
Bedded SS,
LS, SH
Sequences
Clay Loam
2-6%
Silt/Clay

100-300


Weight
5

4
3



2
1
5

3

DRASTIC
General
Rating
5

6
6



3
9
1

2

Index
Table 15. DRASTIC and Agricultural DRASTIC Charts
for Setting 6Da — Alternating Sandstone,
Limestone and Shale-Thin Soil
Setting 6Da Alternating SS,
LS, SH-Thin Soil
Number
25

24
18



6
9
5

6

93
Setting 7Aa Glacial Till Over
Bedded Sedimentary Rock
Feature
Depth to Water
Table
Net Recharge
Aquifer Media



Soil Media
Topography
Impact
Vadose Zone
Hydraulic
Conductivity
Range
30-50

4-7
Thin
Bedded SS,
LS, SH
Sequences
Clay Loam
2-6%
Silt/ Clay

100-300

Agricultural
Weight
5

4
3



5
3
4

2

Rating
5

6
6



3
9
1

2

Number
25

24
18



15
27
4

4

Feature
Depth to Water
Table
Net Recharge
Aquifer Media



Soil Media
Topography
Impact
Vadose Zone
Hydraulic
Conductivity

Range
15-30

4-7
Thin
Bedded SS,
LS, SH
Sequences
Loam
2-6%
Bedded
LS, SS, SH
1-100


Weight
5

4
3



2
1
5

3

DRASTIC
General
Rating
7

6
6



5
9
6

1

Index

Number
35

24
18



10
9
30

3

129
Setting 6Da Alternating SS,
LS, SH-Thin Soil
Feature
Depth to Water
Table
Net Recharge
Aquifer Media



Soil Media
Topography
Impact
Vadose Zone
Hydraulic
Conductivity
Range
15-30

4-7
Thin
Bedded SS,
LS, SH
Sequences
Loam
2-6%
Bedded
LS, SS, SH
1-100

Agricultural


DRASTIC
Index
117


Agricultural
Weight
5

4
3



5
3
4

2

Rating
7

6
6



5
9
6

1

Number
35

24
18



25
27
24

2

Agricultural
DRASTIC
Index
155
    glacial till and is appropriate. Therefore, the
    associated rating of 1 (Table 9) does not need to
    be changed. Hydraulic conductivity values for
    the bedrock range  from 100-300 gpd/ft2 as
    listed on the chart. Therefore, the associated
    rating of  2  (Table  10)  does not need to be
    changed.  Since all  the ranges in the hydro-
    geologic setting are acceptable, no values need
    to be modified for this area. The DRASTIC Index
    has already been computed for  the user by
    multiplying each rating by the assigned weight
    to obtain the  value listed  in the "number"
    column. The  sum  of the  "numbers"  is the
    DRASTIC Index. In this instance, the DRASTIC
    Index of 93 is simply read from  the chart. It
    should  be noted here that weights are never
    changed.  These were determined by the com-
    mittee and are the essence of the system.

In Area II (Table 15), depth to water averages 40 feet.
The range on  the chart  indicates 10-30 feet.  This
range is not acceptable. The user should refer toTable
4 to find the correct  range which  most closely
approximates the area. In this case, 30-50 would be
appropriate. Note the corresponding  rating would
now be 5 instead of 7 and the resultant weight of 5
multiplied by a rating of 5 is 25 instead  of 35.  Net
recharge is 8 inches per year; 4-7 is an acceptable
range and the associated rating of 6 does not need to
be changed. The aquifer is alternating sequences of
shale with moderate fracturing; the media listed on
the chart is accurate and the associated rating of 6
does not need to be changed. Soils are typified by
equal mixtures of  sand, silt,  and clay; this is  the
definition of loam, so the range is adequate and the
associated rating of 5 does not need to be changed.
Topography is low(2 percent slope); the range is listed
as 2-6 percent. The user may, based on observation,
choose 0-2 percent, and change the rating as before,
or  may accept the  range of 2-6 if correct.  For
demonstration purposes, the user can refer to Table
8, choose a 0-2 percent range, change the rating from
                       26

-------
9 to 10, and multiply by the weight of 1 to obtain an
answer of 10 instead of 9. The vadose zone media are
fractured limestones, sandstones, and shales; this is
acceptable. Therefore, the associated rating of 6 does
not  need to be  changed. Hydraulic  conductivity
averages  300 gpd/ft2; the range indicates 1-100
gpd/ft2. Refer to Table 10 to choose the appropriate
range. In this case,  100-300 gpd/ft2 is chosen, the
associated rating of 2 is substituted and multiplied by
3 to obtain 6. The DRASTIC Index cannot be read off
the chart because not all the ranges were appropriate
for the setting. Calculate the correct DRASTIC Index
by adding the numbers 25+ 32 + 18 + 10+10 + 30 + 6 =
131. The decision maker can then compare the two
areas relative to one another.

From the  above discussion,  it is evident that  the
hydrogeologic settings serve as a guide to the user in
evaluating the appropriate range for  each DRASTIC
factor. Each range has an associated rating which can
then be integrated into DRASTIC by combining it with
the weighting factor.  The information to evaluate
each DRASTIC factor and choose the appropriate
range may not always be  expressed in exactly the
sameterms which are used in this document. Section
3,  DRASTIC: A Description of the Factors,  contains a
brief description of what is included in each of the
media terms so that  the  most accurate DRASTIC
range can be chosen.


How to Use the Range in Media Ratings

Because geologic media are  more highly variable
than many of the  quantifiable DRASTIC factors, the
associated rating for each of the ranges is a number
which can vary within the rating indicated  on  the
chart. For example,  Table 6 contains the rating for
aquifer media. Basalt  has a rating which can vary
from 2-8.  By referring to Section 3, Aquifer Media,
Impact of the VadoseZone, which contains a descrip-
tion of the variables which affect the rating, the user
may choose an appropriate rating for the area being
evaluated. For example, the basalts in the Columbia
Lava Plateau are extremely variable in the degree of
interconnection of openings. In one area, the open-
ings may  be highly connected and  be assigned a
rating of 10. If data  indicated a moderate degree of
interconnection, a rating of 7 might be chosen. In this
way the user can more closely approximate the actual
conditions in the  area. For purposes of the hydro-
geologic settings, a typical rating is assigned to each
of  the ranges. The user has the option of  using this
typical rating where applicable.


How to Evaluate Confined Aquifers

Confined aquifers  are treated, in the DRASTIC Index,
by evaluating the  relative importance of  their con-
finement.  Although the confined aquifer  may have
either an upward or downward leakage component,
hydraulic gradients which result in upward flow are
not taken into consideration because (a) the  aquifer
already has a degree of protection and (b) upward
gradients  are easily  reversed by  local pumpage.
Therefore, for purposes of the DRASTIC Index, the
worst case scenario of a gradient into the aquifer is
always  assumed. A judgement must be made in
several of the DRASTIC factors as to the proper way to
evaluate that factor in the specific setting. Factors
that must be varied and the guidance for making the
judgement of variation are as follows:

  Depth to Water—This factor can  be evaluated as
    either the depth  to the  water surface  in  an
    unconfined aquifer, or as the depth to the top of
    the  aquifer where the aquifer is confined.

  Net Recharge—varies with the degree of confine-
    ment.

  Aquifer Media—no change in judgement calls.

  Soil Media—varies with the degree of confinement,
    but  is  less sensitive than Net Recharge. When
    there is significant confinement, this rating is not
    read off the chart but is assigned a value  of 1.

  Topography—similar in  impact  to  Soil  Media,
    except that the relationship  is inverse. When
    there is significant confinement, this rating is not
    read off the chart but is assigned a value of 1.

  Impact of VadoseZone—Since the "impact" of the
    vadose zone  is now, in effect, considered as a
    functional aquitard, this zone  is treated  as a
    Silt/Clay  media, and is assigned the associated
    chart rating of 1.

  Hydraulic Conductivity—no change in judgement.

From this discussion it can be seen that the vulner-
ability of a specific aquifer to pollution varies with its
degree  of confinement, but that the  comparative
vulnerability of two protected aquifers is a function of
their ability to disperse a pollutant from the point of
application. To illustrate this, compare setting 7Ac,
Glacial  Till  Over Solution  Limestone, with  setting
10Aa, Unconsolidated and  Semi-Consolidated Re-
gional Aquifers (Section 6). Setting 7Ac is typified by
conditions in northeastern Indiana, and Setting 10Aa
is typified  by  the Tidewater area in  Virginia.  Both
aquifers are  confined. In the first example (7Ac),
piezometric levels rise above the carbonate aquifer
and saturate the lower portion of the surficial till. The
most important depth is the depth to the top of the
saturated zone. In spite of the confinement, average
recharge over the area is relatively high. Soil media
and topography are  still significant, even though it
could  be argued that their importance should  be
somewhat reduced. This would give  the setting a
lower rating.
                                                                       27

-------
In the second example,  setting 10Aa,  the deep
aquifers are clearly confined by an overlying aquitard
that separates the shallow water table aquifer (setting
10Ab)  from the deeper zone.  While the shallow
aquifer provides recharge  to the deeper, the rate of
leakage is very, very low. U nder this circumstance the
Depth to Water is interpreted to be the depth to the top
of the principal aquifer being considered.  Net re-
charge to the deeper zone is almost negligible. Soil
media has no real significance, nor does topography,
so both ratings are reduced to a minimum value, or 1.
The "impact" of the vadose zone is considered an
effective aquitard, and is therefore rated as a silt/clay,
or 1, regardless of its actual composition.

From a comparison of the  two ratings, 129 (Setting
7Ac) versus 53 (Setting 10Aa), it is apparent that the
deeper, highly confined, coastal aquifer is much more
protectedthan the shallow,  partially-confined aquifer.
The deep coastal aquifers are actually only highly
vulnerable  to injected pollutants and widespread
pollution of the overlying shallow aquifer, from which
recharge is derived over a substantial period of time.
Thus,  in all DRASTIC  settings  the total hydraulic
condition must be considered in order to evaluatethe
degree of protection provided to the aquifer being
considered.


Single Factor Overrides

In some instances, it will be found that the DRASTIC
Index  cannot adquately compensate for a single
parameter  that is so dominant  that it overrides all
other parameters. This may be a consideration that is
glaringly apparent, as in a highly-fractured surficial
karstarea, as is evident in parts of Florida, Indiana, or
Kentucky; or, it may be a much more subtle consid-
eration that involves design decisions and perhaps
policy decisions.

Tables 16 and 17 provide the DRASTIC ratings for two
actual sites, referenced as  Maco I and Maco II. These
sites are both located in the till plains portion of the
Glaciated Central  Region about five miles apart.
Based on the available data, both sites are underlain
by 25 to 40  feet of dense  till containing a few
discontinuous lenses of dirty sand and gravel that
rarely exceed four inches in thickness. In the absence
of fracturing  or stratification,  the horizontal and
vertical permeabilities  of the tills tend to fall in the
10~6 to 10~7gpd/ft2 range.

At site Maco I, the till overlies  fractured limestone
which serves as a regional aquifer and has a hydraulic
conductivity usually in the 300-700 gpd/ft2 range.
Water in the limestone is confined, with the regional
piezometric surface at about 30feet. The overlying till
is saturated only in association with the occasional
discontinuous lense of sand and gravel. These zones
can be considered "perched."
Table 16.   DRASTIC Rating for MACO I
MACO
Feature
Depth to Water
Net Recharge
Aquifer Media

Soil Media
Topography
Impact
Vadose Zone
Hydraulic
Conductivity
I
Range
15-30
4-7
Massive
Limestome
Clay Loam
2-6%
Silt/Clay

300-700


Weight
5
4
3

2
1
5

3

General
Rating
7
6
4

3
9
1

4

DRASTIC Index

Number
35
24
12

6
9
5

12

103
Table 17.   DRASTIC Rating for MACO

        MACO II
General
Feature
Depth to Water
Net Recharge
Aquifer Media

Soil Media
Topography
Impact
Vadose Zone
Hydraulic
Conductivity

Range
5-15
4-7
Massive
Shale
Clay Loam
2-6%
Silt/Clay

1-100


Weight
5
4
3

2
1
5

3

DRASTIC
Rating
9
6
2

3
9
1

1

Index
Number
45
24
6

6
9
5

3

98
At the Maco II site, the till overlies dense, fractured
shale. The hydraulic conductivities of the shale are
less than 1 gpd/ft2. As a consequence of the relative
impermeability of the shale bedrock, the overlying till
is saturated from the depth of about five feet, even
though the elevation,  topography,  and soils are
similar at the two sties.

It can be seen by comparing Tables 16 and 17 that
Maco II has a slightly  more favorable  rating than
Maco I. The principal reason is because there is no
significant aquifer at risk at site Maco II. However, site
Maco II has a "water table," albeit a saturated till at a
depth of five feet. At site Maco I a landfill, for example,
could be properly designed and operated at a max-
imum depth of  15 feet  and be well  within the
unsaturated zone,  with a substantial thickness of
dense, low permeability  material at the base to
protect the regional aquifer. Construction of a landfill
at Maco II (with the more favorable rating) involves
operating a saturation  zone landfill, which  often
requires a serious policy decision from the permitting
agency.

With  regard to the proper application of the DRASTIC
Index to this situation, the question is "Is the shallow,
five-foot depth to saturation of sufficient significance
to 'override' all of the other favorable aspects of the
site." This should be considered  for all  parameters
                        28

-------
that are very highly-rated, i.e., in the rating range of
8-10.
Another single factor override  would be exposed,
highly-fractured or dissolved bedrock which would
provide a direct conduit to an aquifer. Knowledge of
the area being mapped is usually required in order to
know when overrides must be applied.


Build-Your-Own-Settings

From the above discussion it should become obvious
that for any given area  in the United States, the
ground-water pollution potential can be estimated by
choosing appropriate ranges  for each  DRASTIC
parameter without referring to any  hydrogeologic
setting described in Section 6, Hydrogeologic Settings
of the United States by Ground-Water Regions. In
essence this is true. However, for purposes of creating
a mappable unit, the settings create units which are
mappable and  which can be evaluated by super-
imposing DRASTIC. The geographic relationship also
helps the user evaluate more thoroughly the char-
acteristics of an area thereby helping create sound
judgement calls and a more realistic DRASTIC Index.


How to Interpret a DRASTIC Index

The culmination of the  evaluation of any hydro-
geologic setting is a numerical value termed the
DRASTIC Index. The higher the  DRASTIC Index, the
greater the  ground-water pollution potential. DRAS-
TIC is designed to yield a relative  numerical value
which can readily be compared to a value obtained for
another setting either in the same region or in  a
different region.  A numerical value  of 160, for
example, has no intrinsic meaning. That number is of
value only with respect to other numbers generated
by the same DRASTIC Index.

Because this document addresses a DRASTIC Index
and a  modified agricultural DRASTIC Index, the
natural  tendency  is to compare  the two indexes
generated for one  site and try to draw a conclusion.
The numerical values, in and of themselves, have no intrinsic
meaning so comparison between indexes should not
be made; only invalid conclusions will be drawn.


References

Freeze, R. A. and J. A. Cherry, 1979. Groundwater;
  Prentice-Hall, 604 pp.

Heath, Ralph C., 1984. Ground-water regions of the
  United States; U.S. Geological Survey Water Supply
  Paper 2242, 78 pp.
                                                                      29

-------
                                            Section 5
                                     impact—Risk Factors
The DRASTIC Index estimates the vulnerability of any
setting to pollution on  the  basis  of determinable
geologic parameters. It does not, however, indicate a
variety of other parameters that often point out the
significance of the DRASTIC Index under the influ-
ence  of  cultural and physical modifications. For
example, a site with a low DRASTIC Index, indicating
moderate or low vulnerability to contamination, may
be located very near to a large population center. The
proximity to a population that can be exposed greatly
increases the risk, or impact, of  an incidence  of
pollution at the prospective site. Thus it can quickly be
noted that not only the size of the population exposed,
and the human/non-human nature of that popula-
tion, but the time required for the pollutant to travel
from the point of incidence to the population at risk, is
a serious consideration within a given setting.

Travel time is considered only tangentially by the
DRASTIC Index. It is implied by "hydraulic conductiv-
ity," but becomes interpretable, and meaningful, only
when the distance to be traveled from a source of
contamination to a point of concern  is known, and
when the gradient, or inclination of the water table is
considered. Thus, the travel time of a pollutant from
point of introduction until it reaches  a population is
not  given  by the  DRASTIC  Index,  but  must  be
evaluated separately,  by persons with adequate data
and expertise for each specific site.

In a similar manner, the risk to a given population is
dependent on  the toxicity  of the pollutant being
introduced.  Obviously,  if the pollutant being intro-
duced is non-toxic to the population exposed, there is
little or no riskto that population as a consequence of
the exposure. When the pollutant is quite toxic, it is
obvious that minimal exposure of the population may
be very serious, even where travel time as controlled
by gradient, distance, and hydraulic  conductivity is
great.

Essentially, the DRASTIC Index for a given setting is
derived on the basis of the vulnerability of the site to
an invasion of water, hence the  name "hydrogeo-
 logic setting." Actually, the concern is not about the
vulnerability of a setting to water, but rather with the
vulnerability of that setting  to contaminants. Water
forms the common baseline, but the site vulnerability
varies with the specific properties of the contaminant
being applied.  Obviously all settings cannot  be
mapped for all potential contaminants, so in  many
instances critical judgements have to be made about
the risks involved. Where accidental spills are in-
volved, these  judgements  must be made rapidly,
conservatively,  and on the  basis of the best data
available. Where design judgements are to be made,
they should be made on the basis of adequate field
and  laboratory testing. It should always be kept in
mind that some substances are so toxic that there are
no "safe" settings available.

In addition to travel time,  toxicity,  and population
exposed, the risk  is influenced by "loading" factors.
Whether the application rate is a slug application, as
in an accidental spill; an intermittent application, as
with  herbicides,  pesticides, and  fertilizers;  or  a
continuous application, such as a  leaking tank or
lagoon, has an obvious bearing upon the total load of
material  reaching an exposed population. Loading is
also influenced by the concentration of the polluting
substance. If the incident  pollutant is highly con-
centrated, it is apparent that the exposed population
is at much greater risk than would be the case if the
pollutant were less concentrated. All of the  atten-
uating factors, dilution, dispersion, sorption, filtration,
reaction, etc.  are more effective at lesser loading
rates.
In order to assist in the understanding of the basic risk
factors, travel time, population exposed, loading and
toxicity,  and  how these risk  factors  impact the
DRASTIC Index, the following acronym is suggested:
  I   Inclination of the water table (gradient)
         Direction of slope in ft/ft (feet per foot)
  M  Measured  horizontal distance
         Distance to point of exposure infeetor miles
  P   Population exposed
         Human or non-human
  A  Application rate
         Slug, intermittent, or continuous
   C    Concentration
         Concentration of pollutant, often in mg/l
  T   Toxicity
         Degree of toxicity to the population exposed
When the DRASTIC Index of a particular setting is
evaluated with regard to these parameters of impact,
as a consequence of a particular pollutant, a reason-
able judgement can be made with respect to the risk
to the population exposed.
                                                 30

-------
                                               Section 6
         Hydrogeologic Settings of the United States by Ground-Water Regions
Figure 19.  Ground-water regions of the United States (After Heath, 1984).
  2 Alluvial Basins
                                                                                                     7
                                                                                                   Glaciated
                                                                                                   Central
                                                                                                     Region
                                                                                               6. Nonglaciated
                                                                                                   Central
                                                                                                   Region
                              9. Northeast and
                               Superior Uplands
                Region    "
                    V
                Vl. Western Mountain
-  „  Nonglaciated Central ^>
 ? ^V rV       Dnn.nn 	 &''
 
                                                                                             9. Northeast and
                                                                                             Superior Uplands
      3 Columbia
        Lava Plateau
                                  6. Nonglaciated
                              \	^	
                                      Region
         2. Alluvial
           Basins
Plateau
and
Wyoming
Basin
                                                   6. Nonglaciated
                                                    Central Region
                     6  Nonglaciated
                       Central Region
                                                                               500 miles
                                                               i  ' i  i' l  *l  l ' i t
                                                             0                 800 kilometers
                                                    31

-------
Table 18.    Hydrogeologic Settings and Associated DRASTIC
            Index by Region
Number
1Aa East
1Ab West
1Ba East
1Bb West
1Ca East
ICbWest
1D
1Ea East
1Eb West
1F
2A
2B
2C
2D
2E
3A
3B
3C
3D
3E
4A
4B
4C
4D
5A
5B
5C
5D
5E
6A
6B
6C
6Da
6Db
6E
6Fa
6Fb
6G
6H
7Aa
7Ab
7Ac
7Ad
7Ae
7Ba
7Bb
7Bc
7C
7D
7Ea
7Eb
7F
7G
7H
8A
8B
8C
8D
8E
8F
9A
9B
9C
9Da
9Db
9E
9F
Title
Mountain Slopes
Mountain Slopes
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Mountain Flanks
Mountain Flanks
Glaciated Mountain Valleys
Wide Alluvial Valleys (External Drainage)
Wide Alluvial Valleys (External Drainage)
Coastal Beaches
Mountain Slopes
Alluvial Mountain Valleys
Alluvial Fans
Alluvial Basins (Internal Drainage)
Playa Lakes
Mountain Slopes
Alluvial Mountain Valleys
Hydraulically Connected Lava Flows
Lava Flows Not Connected Hydraulically
Alluvial Fans
Resistant Ridges
Consolidated Sedimentary Rocks
River Alluvium
Alluvium and Dune Sand
Ogallala
Alluvium
Sand Dunes
Playa Lakes
Braided River Deposits
Mountain Slopes
Alluvial Mountain Valleys
Mountain Flanks
Alternating SS, LS, SH-Thin Soil
Alternating SS, LS, SH-Deep Regolith
Solution Limestone
River Alluvium with Overbank
River Alluvium without Overbank
Braided River Deposits
Triassic Basins
Glacial Till Over Bedded Sedimentary Rock
Glacial Till Over Outwash
Glacial Till Over Solution Limestone
Glacial Till Over Sandstone
Glacial Till Over Shale
Outwash
Outwash Over Bedded Sedimentary
Outwash Over Solution Limestone
Moraine
Buried Valley
River Alluvium with Overbank Deposit
River Alluvium without Overbank Deposit
Glacial Lake Deposits
Thin Till Over Bedded Sedimentary
Beaches, Beach Ridges and Sand Dunes
Mountain Slopes
Alluvial Mountain Valleys
Mountain Flanks
Thick Regolith
River Alluvium
Mountain Crests
Mountain Slopes
Alluvial Mountain Valleys
Mountain Flanks
Glacial Till Over Crystalline Bedrock
Glacial Till Over Outwash
Outwash
Moraine
Rating
65
70
128
146
83
106
180
158
180
196
74
132
122
122
110
98
168
156
105
105
88
87
162
102
109
107
150
110
185
103
152
105
129
131
196
136
187
190
106
93
127
129
99
78
176
156
186
125
156
124
191
135
111
202
75
162
106
100
176
70
75
180
106
103
129
190
166
Table 18. (Continued)
                                                              Number
                                                                                          Title
                                                                                                                   Rating
                                                               9Ga        River Alluvium with Overbank                  136
                                                               9Gb        River Alluvium without Overbank               191
                                                               lOAa       Confined Regional Aquifers                     53
                                                               10Ab       Unconsolidated & Semi-Consolidated Shallow
                                                                           Surficial Aquifer                            184
                                                               10Ba       River Alluvium with Overbank Deposit           132
                                                               10Bb       River Alluvium without Overbank Deposit        187
                                                               10C        Swamp                                     202
                                                               11A        Solution Limestone                           218
                                                               11B        Coastal Deposits                              191
                                                               11C        Swamp                                     224
                                                               11D        Beaches and Bars                            190
                                                               12A        Mountain Slopes                              164
                                                               12B        Alluvial Mountain Valleys                      184
                                                               12C        Volcanic Uplands                             165
                                                               12D        Coastal Beaches                              201
                                                               13A        Alluvium                                     140
                                                               13B        Glacial & Glaciolacustrine Deposits of the
                                                                           Interior Valleys                              131
                                                               13C        Coastal Lowland Deposits                      140
                                                               13D	Bedrock of the Uplands and Mountains           92
                                                              Table 19.     Hydrogeologic Settings and Associated DRASTIC
                                                                           Index Sorted by Ratings
Number
10Aa
1Aa East
8F
1Ab West
2A
9A
8A
7Ae
1 Ca East
4B
4A
13D
7Aa
3A
7Ad
8D
4D
9Da
6A
3D
3E
6C
ICbWest
6H
8C
9C
5B
5A
2E
5D
7G
2D
2C
7Ea
7C
7Ab
1 Ba East
7Ac
9Db
Title
Confined Regional Aquifers
Mountain Slopes
Mountain Crests
Mountain Slopes
Mountain Slopes
Mountain Slopes
Mountain Slopes
Glacial Till Over Shale
Mountain Flanks
Consolidated Sedimentary Rocks
Resistant Ridges
Bedrock of the Uplands and Mountains
Glacial Till Over Bedded Sedimentary Rock
Mountain Slopes
Glacial Till Over Sandstone
Thick Regolith
Alluvium and Dune Sand
Glacial Till Over Crystalline Bedrock
Mountain Slopes
Lava Flows Not Connected Hydraulically
Alluvial Fans
Mountain Flanks
Mountain Flanks
Triassic Basins
Mountain Flanks
Mountain Flanks
Alluvium
Ogallala
Playa Lakes
Playa Lakes
Thin Till Over Bedded Sedimentary
Alluvial Basins (Internal Drainage)
Alluvial Fans
River Alluvium with Overbank Deposit
Moraine
Glacial Till Over Outwash
Alluvial Mountain Valleys
Glacial Till Over Solution Limestone
Glacial Till Over Outwash
Rating
53
65
70
70
74
75
75
78
83
87
88
92
93
98
99
100
102
103
103
105
105
105
106
106
106
106
107
109
110
110
111
122
122
124
125
127
128
129
129
                            32

-------
Table 19. (Continued)
          Table 20. (Continued)
Number
                             Title
Rating    Number
                                                                                             Title
Rating
6Da        Alternating SS, LS, SH-Thin Soil                129
13B        Glacial & Glaciolacustrine Deposits of the
             Interior Valleys                              131
6Db        Alternating SS, LS, SH-Deep Regolith           131
10Ba       River Alluvium with Overbank Deposit           132
2B         Alluvial Mountain Valleys                       132
7F         Glacial Lake Deposits                          135
9Ga        River Alluvium with Overbank                   136
6Fa        River Alluvium with Overbank                   136
13A        Alluvium                                     140
13C        Coastal Lowland Deposits                       140
IBbWest  Alluvial Mountain Valleys                       146
5C         Sand Dunes                                   150
6B         Alluvial Mountain Valleys                       152
3C         Hydraulically Connected Lava Flows              156
7Bb        Outwash Over Bedded Sedimentary              156
7D         Buried Valley                                  156
1Ea East    Wide Alluvial Valleys (External Drainage)          158
4C         River Alluvium                                162
SB         Alluvial Mountain Valleys                       162
12A        Mountain Slopes                              164
12C        Volcanic Uplands                              165
9F         Moraine                                      166
3B         Alluvial Mountain Valleys                       168
7Ba        Outwash                                     176
8E         River Alluvium                                176
1EbWest  Wide Alluvial Valleys (External Drainage)          180
1D         Glaciated Mountain Valleys                     180
9B         Alluvial Mountain Valleys                       180
10Ab       Unconsolidated & Semi-Consolidated Shallow
              Surficial Aquifer                            184
12B        Alluvial Mountain Valleys                       184
5E         Braided River  Deposits                         185
7Bc        Outwash Over Solution Limestone               186
6Fb        River Alluvium without Overbank                187
10Bb       River Alluvium without Overbank Deposit         187
6G         Braided River  Deposits                         190
11D        Beaches and Bars                              190
9E         Outwash                                     190
11B        Coastal Deposits                               191
9Gb        River Alluvium without Overbank                191
7Eb        River Alluvium without Overbank Deposit         191
6E         Solution Limestone                            196
1F         Coastal Beaches                               196
12D        Coastal Beaches                               201
7H         Beaches, Beach Ridges and Sand  Dunes          202
10C        Swamp                                      202
11A        Solution Limestone                            218
11C        Swamp                                      224
Table 20.     Hydrogeologic Settings and Associated DRASTIC
             Index Sorted by Setting Title
Number
2D
2C
3E
12B
1Ba East
IBbWest
2B
3B
6B
SB
9B
Title
Alluvial Basins (Internal Drainage)
Alluvial Fans
Alluvial Fans
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Rating
122
122
105
184
128
146
132
168
152
162
180
          13A        Alluvium                                      140
          5B         Alluvium                                      107
          4D         Alluvium and Dune Sand                       102
          6Db        Alternating SS,LS,SH-Deep Regolith             131
          6Da        Alternating SS.LS,SH-Thin Soil                 129
          11D        Beaches and Bars                             190
          7H         Beaches,  Beach Ridges and Sand Dunes         202
          13D        Bedrock of the Uplands and Mountains            92
          5E         Braided River Deposits                         185
          6G         Braided River Deposits                         190
          7D         Buried Valley                                  156
          1F         Coastal Beaches                               196
          12D        Coastal Beaches                               201
          11B        Coastal Deposits                               191
          13C        Coastal Lowland  Deposits                      140
          10Aa       Confined  Regional Aquifers                      53
          4B         Consolidated Sedimentary Rocks                 87
          13B        Glacial & Glaciolacustrine Deposits of the
                       Interior Valleys                              131
          7F         Glacial Lake Deposits                          135
          7Aa        Glacial Till Over Bedded Sedimentary  Rock        93
          9Da        Glacial Till Over Crystalline Bedrock              103
          7Ab        Glacial Till Over Outwash                       127
          9Db        Glacial Till Over Outwash                       129
          7Ad        Glacial Till Over Sandstone                      99
          7Ae        Glacial Till Over Shale                           78
          7Ac        Glacial Till Over Solution  Limestone              129
          1D         Glaciated Mountain Valleys                     180
          3C         Hydraulically Connected Lava Flows              156
          3D         Lava Flows  Not Connected Hydraulically         105
          7C         Moraine                                      125
          9F         Moraine                                      166
          8F         Mountain Crests                                70
          1Ca East   Mountain Flanks                                83
          6C         Mountain Flanks                               105
          ICbWest  Mountain Flanks                               106
          8C         Mountain Flanks                               106
          9C         Mountain Flanks                               106
          12A        Mountain Slopes                              164
          1Aa East   Mountain Slopes                               65
          1AbWest  Mountain Slopes                               70
          2A         Mountain Slopes                               74
          3A         Mountain Slopes                               98
          6A         Mountain Slopes                              103
          8A         Mountain Slopes                               75
          9A         Mountain Slopes                               75
          5A         Ogallala                                       109
          7Ba        Outwash                                      176
          9E         Outwash                                      190
          7Bb        Outwash  Over  Bedded Sedimentary              156
          7Bc        Outwash  Over  Solution Limestone               186
          2E         Playa Lakes                                   110
          5D         Playa Lakes                                   110
          4A         Resistant Ridges                                88
          4C         River Alluvium                                 162
          8E         River Alluvium                                 176
          6Fa        River Alluvium  with Overbank                   136
          9Ga        River Alluvium  with Overbank                   136
          10Bb       River Alluvium  with Overbank Deposit           132
          7Ea        River Alluvium  with Overbank Deposit           124
          6Fb        River Alluvium  without Overbank                187
          9Gb        River Alluvium  without Overbank                191
          10Bb       River Alluvium  without Overbank Deposit         187
          7Eb        River Alluvium  without Overbank Deposit         191
          5C         Sand Dunes                                  150
          11A        Solution Limestone                            218
          6E         Solution Limestone                            196

-------
Table 20. (Continued)
                                                               Table 21. (Continued)
Number
10C
11C
8D
7G
6H
10Ab

12C
1Ea East
1Eb West
Title
Swamp
Swamp
Thick Regolith
Thin Till Over Bedded Sedimentary
Triassic Basins
Unconsolidated & Semi-Consolidated Shallow
Surficial Aquifer
Volcanic Uplands
Wide Alluvial Valleys (External Drainage)
Wide Alluvial Valleys (External Drainage)
Rating
202
224
100
111
106

184
165
158
180
                                                               Number
                                                                                            Title
                                                                                                                     Rating
Table 21.
Number
1Aa East
1Ab West
1Ba East
1Bb West
1Ca East
ICbWest
ID
1Ea East
lEbWest
1F
2A
2B
2C
2D
2E
3A
3B
3C
3D
3E
4A
4B
4C
4D
5A
5B
5C
5D
5E
6A
6B
6C
6Da
6Db
6E
6Fa
6Fb
6G
6H
7Aa
7Ab
7Ac
7Ad
7Ae
7Ba
7Bb
7Bc
7C
7D
7Ea
Hydrogeologic Settings and Associated
Agricultural DRASTIC Index by Region
Title
Mountain Slopes
Mountain Slopes
Alluvial Mountain Valleys
Alluvial Mountain Valleys
Mountain Flanks
Mountain Flanks
Glaciated Mountain Valleys
Wide Alluvial Valleys (External Drainage)
Wide Alluvial Valleys (External Drainage)
Coastal Beaches
Mountain Slopes
Alluvial Mountain Valleys
Alluvial Fans
Alluvial Basins (Internal Drainage)
Playa Lakes
Mountain Slopes
Alluvial Mountain Valleys
Hydraulically Connected Lava Flows
Lava Flows Not Connected Hydraulically
Alluvial Fans
Resistant Ridges
Consolidated Sedimentary Rocks
River Alluvium
Alluvium and Dune Sand
Ogallala
Alluvium
Sand Dunes
Playa Lakes
Braided River Deposits
Mountain Slopes
Alluvial Mountain Valleys
Mountain Flanks
Alternating SS, LS, SH-Thin Soil
Alternating SS, LS, SH-Deep Regolith
Solution Limestone
River Alluvium with Overbank
River Alluvium without Overbank
Braided River Deposits
Triassic Basins
Glacial Till Over Bedded Sedimentary Rock
Glacial Till Over Outwash
Glacial Till Over Solution Limestone
Glacial Till Over Sandstone
Glacial Till Over Shale
Outwash
Outwash Over Bedded Sedimentary
Outwash Over Solution Limestone
Moraine
Buried Valley
River Alluvium with Overbank Deposit
Rating
91
97
166
184
99
122
214
192
214
221
105
165
155
157
139
122
202
182
143
123
117
108
186
131
136
135
177
139
216
132
176
126
155
160
216
156
209
221
135
117
145
145
121
103
196
182
206
148
178
149
                                                               7Eb       River Alluvium without Overbank Deposit         224
                                                               7F         Glacial Lake Deposits                          165
                                                               7G         Thin Till Over Bedded Sedimentary              135
                                                               7H         Beaches, Beach Ridges and Sand Dunes         225
                                                               8A         Mountain Slopes                              102
                                                               8B         Alluvial Mountain Valleys                       185
                                                               8C         Mountain Flanks                              123
                                                               8D         Thick Regolith                                117
                                                               8E         River Alluvium                                198
                                                               8F         Mountain Crests                              113
                                                               9A         Mountain Slopes                              102
                                                               9B         Alluvial Mountain Valleys                       202
                                                               9C         Mountain Flanks                              122
                                                               9Da       Glacial Till Over Crystalline Bedrock              134
                                                               9Db       Glacial Till Over Outwash                       153
                                                               9E         Outwash                                     210
                                                               9F         Moraine                                      180
                                                               9Ga       River Alluvium with Overbank                   156
                                                               9Gb       River Alluvium without Overbank                213
                                                               lOAa      Confined Regional Aquifers                      53
                                                               lOAb      Unconsolidated & Semi-Consolidated Shallow
                                                                            Surficial Aquifer                             206
                                                               lOBa      River Alluvium with Overbank Deposit           157
                                                               10Bb      River Alluvium without Overbank Deposit         220
                                                               10C       Swamp                                      233
                                                               11A       Solution Limestone                            243
                                                               11B       Coastal Deposits                              224
                                                               11C       Swamp                                      251
                                                               11D       Beaches and Bars                             225
                                                               12A       Mountain Slopes                              177
                                                               12B       Alluvial Mountain Valleys                       192
                                                               12C       Volcanic Uplands                              174
                                                               12D       Coastal Beaches                              230
                                                               13A       Alluvium                                      164
                                                               13B       Glacial & Glaciolacustrine Deposits of the
                                                                            Interior Valleys                              158
                                                               13C       Coastal Lowland Deposits                       164
                                                               13D       Bedrock of the Uplands and Mountains           118
Table 22.
Number
10Aa
1Aa East
1Ab West
1Ca East
8A
9A
7Ae
2A
4B
8F
7Aa
4A
8D
13D
7Ad
ICbWest
9C
3A
3E
8C
6C
Hydrogeologic Settings and Associated
Agricultural DRASTIC Index Sorted by Ratings
Title Rating
Confined Regional Aquifers
Mountain Slopes
Mountain Slopes
Mountain Flanks
Mountain Slopes
Mountain Slopes
Glacial Till Over Shale
Mountain Slopes
Consolidated Sedimentary Rocks
Mountain Crests
Glacial Till Over Bedded Sedimentary Rock
Resistant Ridges
Thick Regolith
Bedrock of the Uplands and Mountains
Glacial Till Over Sandstone
Mountain Flanks
Mountain Flanks
Mountain Slopes
Alluvial Fans
Mountain Flanks
Mountain Flanks
53
91
97
99
102
102
103
105
108
113
117
117
117
118
121
122
122
122
123
123
126
                             34

-------
Table 22. (Continued)
Number
                             Title
Rating
4D        Alluvium and Dune Sand                       131
6A        Mountain Slopes                              132
9Da       Glacial Till Over Crystalline Bedrock             134
5B        Alluvium                                     135
6H        Tnassic Basins                                135
7G        Thin Till Over Bedded Sedimentary              135
5A        Ogallala                                      136
5D        Playa Lakes                                  139
2E        Playa Lakes                                  139
3D        Lava Flows Not Connected Hydraulically         143
7Ab       Glacial Till Over Outwash                       145
7Ac       Glacial Till Over Solution Limestone             145
7C        Moraine                                      148
7Ea       River Alluvium with Overbank Deposit           149
9Db       Glacial Till Over Outwash                       153
2C        Alluvial Fans                                 155
6Da       Alternating SS,LS,SH-Thm Soil                 155
6Fa       River Alluvium with Overbank                  156
9Ga       River Alluvium with Overbank                  156
2D        Alluvial Basins (Internal Drainage)               157
10Ba      River Alluvium with Overbank Deposit           157
13B       Glacial ft Glaciolacustrine Deposits of the
              Interior Valleys                              158
6Db       Alternating SS,LS,SH-Deep Regolith            160
13A       Alluvium                                     164
13C       Coastal Lowland Deposits                      164
2B        Alluvial Mountain Valleys                       165
7F        Glacial Lake Deposits                          165
1Ba East   Alluvial Mountain Valleys                       166
12C       Volcanic Uplands                             174
6B        Alluvial Mountain Valleys                       176
5C        Sand Dunes                                 177
12A       Mountain Slopes                              177
7D        Buried Valley                                 178
9F        Moraine                                     180
3C        Hydraulically Connected Lava Flows             182
7Bb       Outwash Over Bedded Sedimentary             182
IBbWest  Alluvial Mountain Valleys                       184
8B        Alluvial Mountain Valleys                       185
4C        River Alluvium                                186
12B       Alluvial Mountain Valleys                       192
1Ea East   Wide Alluvial Valleys (External Drainage)         192
7Ba       Outwash                                    196
8E        River Alluvium                                198
3B        Alluvial Mountain Valleys                       202
9B        Alluvial Mountain Valleys                       202
10Ab      Unconsolidated ft Semi-Consolidated Shallow
              Surficial  Aquifer                            206
7Bc       Outwash Over Solution Limestone              206
6Fb       River Alluvium without Overbank               209
9E        Outwash                                    210
9Gb       River Alluvium without Overbank               213
1EbWest  Wide Alluvial Valleys (External Drainage)         214
1D        Glaciated Mountain Valleys                     214
6E        Solution Limestone                           216
5E        Braided  River Deposits                        216
10Bb      River Alluvium without Overbank Deposit        220
1F        Coastal Beaches                              221
6G        Braided  River Deposits                        221
11B       Coastal Deposits                              224
7Eb       River Alluvium without Overbank Deposit        224
7H        Beaches, Beach Ridges and Sand Dunes        225
 11D       Beaches and Bars                            225
 12D       Coastal Beaches                              230
 10C       Swamp                                      233
 11A       Solution Limestone                           243
 11C       Swamp                                      251
                                                                 Table 23.
                                                                 Number
                       Hydrogeologic Settings and Associated
                       Agricultural DRASTIC Index Sorted by Setting
                       Title
                                                                                               Title
                                                                 Rating
          2D         Alluvial Basins (Internal Drainage)                157
          2C         Alluvial Fans                                  155
          3E         Alluvial Fans                                  123
          8B         Alluvial Mountain Valleys                       185
          2B         Alluvial Mountain Valleys                       165
          6B         Alluvial Mountain Valleys                       176
          3B         Alluvial Mountain Valleys                       202
          IBbWest   Alluvial Mountain Valleys                       184
          1Ba East    Alluvial Mountain Valleys                       166
          9B         Alluvial Mountain Valleys                       202
          12B        Alluvial Mountain Valleys                       192
          5B         Alluvium                                      135
          13A        Alluvium                                      164
          4D         Alluvium and Dune Sand                       131
          6Db        Alternating SS,LS,SH-Deep Regolith            160
          6Da        Alternating SS,LS,SH-Thin Soil                 155
           11D        Beaches and Bars                             225
          7H         Beaches, Beach Ridges and Sand Dunes         225
           13D        Bedrock of the Uplands and Mountains          118
          5E         Braided River Deposits                         216
          6G         Braided River Deposits                         221
          7D         Buried Valley                                  178
           1F         Coastal Beaches                               221
           12D        Coastal Beaches                               230
           11B        Coastal Deposits                               224
           13C        Coastal Lowland  Deposits                      164
           10Aa       Confined Regional Aquifers                      53
          4B         Consolidated Sedimentary Rocks                108
           13B        Glacial ft Glaciolacustrine Deposits of the
                        Interior Valleys                              158
           7F         Glacial Lake Deposits                          165
           7Aa        Glacial Till Over Bedded Sedimentary Rock       117
           9Da        Glacial Till Over Crystalline  Bedrock             134
           7Ab        Glacial Till Over Outwash                      145
           9Db        Glacial Till Over Outwash                      153
           7Ad        Glacial Till Over Sandstone                     121
           7Ae        Glacial Till Over Shale                          103
           7Ac        Glacial Till Over Solution Limestone             145
           1D         Glaciated Mountain Valleys                     214
           3C         Hydraulically Connected  Lava Flows             182
           3D         Lava Flows Not Connected Hydraulically         143
           7C         Moraine                                      148
           9F         Moraine                                      180
           8F         Mountain Crests                               113
           1Cb West  Mountain Flanks                              122
           6C         Mountain Flanks                              126
           8C         Mountain Flanks                              123
           9C         Mountain Flanks                              122
           1Ca East   Mountain Flanks                               99
           12A        Mountain Slopes                              177
           9A         Mountain Slopes                              102
           2A         Mountain Slopes                              105
           6A         Mountain Slopes                              132
           1Ab West  Mountain Slopes                               97
           1Aa East   Mountain Slopes                               91
           3A         Mountain Slopes                              122
           8A         Mountain Slopes                              102
           5A         Ogallala                                      136
           7Ba        Outwash                                     196
           9E         Outwash                                     210
           7Bb       Outwash Over Bedded Sedimentary             182
           7Bc        Outwash Over Solution Limestone              206
           5D         Playa Lakes                                  139
           2E         Playa Lakes                                  139
           4A         Resistant Ridges                              117
           8E         River Alluvium                                198

-------
Table 23. (Continued)
Number
                             Title
                                                      Rating
4C         River Alluvium                                186
6Fa        River Alluvium with Overbank                   156
9Ga        River Alluvium with Overbank                   156
10Ba       River Alluvium with Overbank Deposit           157
7Ea        River Alluvium with Overbank Deposit           149
6Fb        River Alluvium without Overbank                209
9Gb        River Alluvium without Overbank                213
10Bb       River Alluvium without Overbank Deposit        220
7Eb        River Alluvium without Overbank Deposit        224
5C         Sand Dunes                                  177
6E         Solution Limestone                            216
11A        Solution Limestone                            243
11C        Swamp                                      251
10C        Swamp                                      233
8D         Thick Regolith                                117
7G         Thin Till Over Bedded Sedimentary              135
6H         Triassic Basins                                135
10Ab       Unconsolidated & Semi-Consolidated Shallow
             Surficial Aquifer                            206
12C        Volcanic Uplands                              174
1EbWest  Wide Alluvial Valleys (External Drainage)         214
1Ea East   Wide Alluvial Valleys (External Drainage)         192
                              36

-------
Table 24.    Summary of the Principal Physical and Hydrologic Characteristics of the Ground-Water Regions of the United States
            (after Heath, 1984)

                                                                           Characteristics of dominant aquifers













Region
No. Name




1 Western
Mountain
Ranges
2 Alluvial Basins
3 Columbia Lava
Plateau
4 Colorado
Plateau and
Wyoming
Basin
5 High Plains
6 Nonglaciated
Central Region
7 Glaciated
Central Region
8 Piedmont and
Blue Ridge
9 Northeast and
Superior
Uplands
10 Atlantic and
Gulf Coastal
Plain
1 1 Southeast
Coastal Plain
12 Hawaii
13 Alaska
Lomponen

Upnc0"- Confining
flnefd beds
aquifer






I
0
D ^
I 1
g e Z > e
£ S | o •£
| I | 3" 1
E 5 | £ § S
f 6 | § | *
o> CT c: g> En Q)
I i i 1 1 1
I 5 Q I £ £
X X


X X
X X

X X



X X
X X

X X

X X

X X


X X


X X

X X
X X
its ot the system Water-bearing Composi- Storage and Recharge and
openings tion transmission properties discharge conditions
Confined Presence and Secon- Degree of _ . Trans- _ u „. .
aquifers aT^ PrmarY darv solubility PorosltV missivity Recharge Discharge
1
3
ffl
-o
1
"c
o
°
» (0
. 1 - 1 i a 1 ! - 1 .

1 I?s|l|'i| ? I 1 r s ? & 1
9 §Sli-§S?S« E I r E - ^ i E£"
lI:|^|"|5lSs| i I 8 V | I §il
illllslllglll 1 «? "e «• 1 | s s •£ £ !
^llHt^jIgiSis » Si5I§S!|v|ig3g|
roQ-OcoOO-o^^t0^^ -Q r«i o o in CM u> — s("^-'Ocra
|^"|l§IiScclS?*| ASVAS^|"Slf™||
•5*.-^ w a>o o g £ £.a",2"o S<3 ?^^ ? "S "* £" -S S"^ ^ ^o
IZS^wlsSflSHt^lScgjSSM^Swji^^^M^I
X XXXX X XXXX


X XX XXX XXX
X XXXXX XX XX

X XXXX X XXXX



X X X XXX XX
X XXXXX XX XXXX

X XXXXXX X X X X

X XXXX X XXX

X XXXX XXXX


X XX XX X X XXXX


X XX X XX X XXX

X X XXXX XXX
X XXXXXX XX
                                                                                         37

-------
Table 25. Common Ranges for the Hydraulic Characteristics of Ground-Water Regions of The United States (after Heath, 1984)

Region
No
1






2





3






4


5



Common ranges in hydraulic characteristics of the dominant aquifers
Transmissivity Hydraulic conductivity Recharge rate
Region Geologic situation m2day~' ft^ay1 m day"1 ft day"1 mm yr1 in yr1
Western Mountains with 100 5 5,000,000 0 0003 15 0 001 50 3 50 0 1 2
Mountain thin soils over
Ranges fractured rocks.
alternating with
narrow alluvial
and, in part,
glaciated valleys
Alluvial Basins Thick1 alluvial 20 20,000 2,000 200,000 30 600 100 2,000 003 X 0 001 1
(locally glacial)
deposits in basins
and valleys
bordered by
mountains
Columbia Lava Thick sequence of 2,000 500,000 20,000 5,000,000 200 3,000 500 10,000 5 300 02 10
Plateau lava flows
interbedded with
unconsolidated
deposits and
overlain by thin
soils
Colorado Thin1 soils over 0.5 100 5 1,000 0003 2 0.01 503 50 0.01 2
Plateau and fractured
Wyoming Basin sedimentary rocks
High Plains Thick alluvial 1,000 10,000 10,000 100,000 30 300 100 1,000 5 80 0.2 3
deposits over
fractured
sedimentary rocks

Well yield
m'min"1 gal min~1
0.04 0.4 10 100






004 20 100 5,000





04 80 100 20,000






0.04 2 10 1,000


0.4 10 100 3,000



Nonglaciated    Thin regoltth over
Central region   fractured
                sedimentary rocks

Glaciated       Thick  glacial
Central region   deposits over
                fractured
                sedimentary rocks

Piedmont and   Thick  regollth over
Blue Ridge      fractured
                crystalline and
                meta morphosed
                sedimentary rocks

Northeast and   Thick  glacial
Superior        deposits over
Uplands         fractured
                crystalline rocks
  300     10,000    3,000   100,000
                                               300   10
  100
           2,000     1,000    20,000
                                                              1,000
                                                              1,000
             200
   50
                     100
                     500
                             2,000    0.001
                             5,000
                                                      0.003
                                                X
                                                                      30
                                                                100    30
                                                                                 50002        2004     20        100    5,000
                                                                                 30002         10     02      2         50     500
                                                                                 300    1           10     02      2         50     500
                                                                                 300    1           10     0.1        1         20     200
10


11



12





13






Atlantic and
Gulf Coastal
Plain
Southeast
Coastal Plain


Hawaiian
Islands




Alaska






Complexly inter- 500 10,000 5,000 100,000 3 100 10 400 50 600 2
bedded sands.
silts, and clays
Thick layers of 1,000 100,000 10,000 1,000,000 30 3,000 100 10,000 30 500 1
sand and clay over
semiconsolidated
carbonate rocks
Lava flows 10,000 100,000 100,000 1,000,000 200 3,000 500 10,000 30 1,000 1
segmented by
dikes, interbedded
with ash deposits.
and partly overiatn
by alluvium
Glacial and alluvial 100 10,000 1,000 100,000 30 600 100 2,000 3 300 0.1
deposits in part
perennially frozen
and overlying
crystalline.
metamorphic, and
sedimentary rocks
20 04 20 100 5,000


20 4 80 1,000 20,000



40 0.4 20 100 5,000





10 0.04 4 10 1,000






38

-------
Table 26. Ranges and Ratings for Depth to Water
Depth to Water
(feet)
Range Rating
0-5 10
5-10 9
15-30 7
30-50 5
50-75 3
75-100 2
100+ 1
Weight: 5 Agricultural Weight: 5
Table 27. Ranges and Ratings for Net Recharge
Net Recharge
(inches)
Range Rating
0-2 1
2-4 3
4-7 6
7-10 8
10+ 9
Weight: 4 Agricultural Weight: 4
Table 28. Ranges and Ratings for Aquifer Media
Aquifer Media
Range Rating Typical Rating
Massive Shale 1-3 2
Metamorphic/ Igneous 2-5 3
Weathered Metamorphic/ Igneous 3-5 4
Thin Bedded Sandstone,
Limestone, Shale Sequences 5-9 6
Massive Sandstone 4-9 6
Massive Limestone 4-9 6
Sand and Gravel 6-9 8
Basalt 2-10 9
Karst Limestone 9-10 10
Weight: 3 Agricultural Weight: 3
Table 29. Ranges and Ratings for Soil Media
Soil Media
Range Rating
Thin or Absent 10
Gravel 10
Sand 9
Shrinking and/or Aggregated Clay 7
Sandy Loam 6
Loam 5
Silty Loam 4
Clay Loam 3
Nonshrinking and Nonaggregated Clay 1
Weight: 2 Agricultural Weight: 5
Table 30. Ranges and Ratings for Topography
Topography
(percent slope)
Range Rating
0-2 10
2-6 9
6-12 5
12-18 3
18+ 1
Weight: 1 Agricultural Weight: 3
Table 31. Ranges and Ratings for Impact of Vadose
Zone Media
Impact of Vadose Zone Media
Range Rating Typical Rating
Silt/Clay 1-2 1
Shale 2-5 3
Limestone 2-7 6
Sandstone 4-8 6
Bedded Limestone, Sandstone, Shale 4-8 6
Sand and Gravel with
significant Silt and Clay 4-8 6
Metamorphic/ Igneous 2-8 4
Sand and Gravel 6-9 8
Basalt 2-10 9
Karst Limestone 8-10 10
Weight: 5 Agricultural Weight: 4
Table 32. Ranges and Ratings for Hydraulic Conductivity
Hydraulic Conductivity
(GPD/FT2)
Range Rating
1-100 1
100-300 2
300-700 4
700-1000 6
1000-2000 8
2000+ 10
Weight: 3 Agricultural Weight: 2
Figure 20. Map legend.
* Sands and Silts
yf/^/r-1?!" Igneous, Metamorphic _; - ; ~__T. Sand and Silt

(V.i'.i'iii
39

-------
                               /.   Western Mountain Ranges

(Mountains with thin soils over fractured rocks, alternating with narrow alluvial and, in part, glaciated valleys)
The  Western Mountain Ranges encompass three
areas totaling 708,000 km2. The largest area extends
in an arc from the Sierra Nevada in California, north
through the Coast Ranges and Cascade Mountains in
Oregon and Washington, and east and south through
the Rocky Mountains in Idaho and Montana into the
Bighorn Mountains in Wyoming and the Wasatch and
Uinta Mountains in Utah. The second area includes
the southern Rocky Mountains, which extend from
the Laramie Range in southeastern Wyoming through
Central Colorado into the Sangre de Cristo Range in
northern New Mexico. The smallest area includes the
part of the  Black Hills in  South Dakota in which
Precambrian rocks  are exposed. Summits in the
Rocky Mountains and Sierra Nevada exceed 3,500 m.
The  general appearance of the Western Mountain
Ranges, with the exception of the Black Hills, is tall,
massive  mountains alternating with relatively  nar-
row, steep-sided valleys. The summits and sides of
the mountains  in much of the region have  been
carved into distinctive shapes by mountain glaciers.
The ranges that comprise the southern Rocky Moun-
tains are separated by major lowlands that  include
North Park, Middle Park, South Park, and the Wet
Mountain Valley. These lowlands occupy downfolded
or down-faulted structural troughs as much as 70 km
wide and 160 km long. The mountains in the  Black
Hills are lower in altitude than most of the mountains
in other parts of the region.

As would be expected in such a large region, both the
origin of the mountains and the rocks that form them
are complex. Most of the mountain ranges are under-
lain by granitic and metamorphic rocks flanked by
consolidated  sedimentary  rocks of Paleozoic to
Cenozoic age. The other ranges, including the San
Juan Mountains in southwestern Colorado  and the
Cascade Mountains in Washington and Oregon, are
underlain by lavas and other igneous rocks.

The summits and slopes of most of the mountains
consist of bedrock exposures or of bedrock covered by
a layer of boulders and other rock fragments produced
by frost action and other weathering processes acting
on the bedrock. This layer is generally only a few
meters thick on the upper slopes but forms a relatively
thick apron along the base of the  mountains. The
narrow valleys are underlain by relatively thin, coarse,
bouldery alluvium washed from the higher slopes.
The  large synclinal valleys and those  that occupy
down-faulted structural troughs are underlain by
moderately thick deposits of coarse-grained alluvium
transported by streams from the adjacent mountains.

The  Western Mountain Ranges and the  mountain
ranges in adjacent regions are the principal  sources
of water supplies developed at lower altitudes  in the
western half of the conterminous United  States. As
McGuinness( 1963) noted, the mountains of the west
are moist "islands" in a sea of desert or semidesert
that covers  the western half of the  Nation. The
mountains force moisture-laden air masses moving
eastward from the Pacific to rise to higher  and cooler
altitudes. As the air cools,  moisture condenses into
clouds and precipitates. The heaviest precipitation
falls on the western slopes; thus, these slopes are the
major source of runoff and are also the most densely
                                               40

-------
vegetated. Much of the precipitation falls as snow
during the winter, and its slow melting, starting at the
lower altitudes in early spring, maintains streamflow
at large  rates until late June or early July. Small
glaciers occur in the higher mountain ranges, especi-
ally in the northern Rocky  Mountains, the Cascades,
and  the  Sierra  Nevada;  locally, as  in  northern
Washington they also provide significant sources of
summer runoff.

Melting snow and rainfall at the higher altitudes in
the region provide abundant water for ground-water
recharge.  However,  the  thin  soils and  bedrock
fractures in areas underlain by crystalline rocks fill
quickly, and the remaining water runs off overland to
streams. Because of their small storage capacity, the
underground openings provide limited base runoff to
the streams, which at the  higher altitudes flow only
during rains or snowmelt periods. Thus, at the higher
altitudes in this region underlain by crystalline rocks,
relatively little opportunity exists for development of
ground-water supplies. The best opportunities exist
in valleys that contain at least moderate thicknesses
of saturated  alluvium  or in areas underlain by
permeable sedimentary or volcanic  rocks. Ground-
water supplies in the valleys are obtained both from
wells drawing from the  alluvium and from wells
drawing from the underlying rocks. The yields of wells
in crystalline bedrock and  wells drawing water from
small, thin deposits of alluvium are generally ade-
quate only for domestic and stock needs. Large yields
can be obtained from the alluvial deposits that overlie
the major lowlands and from wells completed in per-
meable sedimentary or volcanic rocks.
Western Mountain Ranges

(1Aa)  Mountain Slopes—East

This hydrogeologic setting is characterized by steep
slopes on the sides of mountains, a thin soil cover and
highly fractured bedrock. Ground water is obtained
primarily from the fractures in the bedrock which may
be of sedimentary, metamorphic or igneous origin.
The  fractures provide  localized sources of ground
water and well yields are typically limited  even
though  the hydraulic conductivity is  often  high
because of the fractures. Due to the steep slopes, thin
soil and small storage capacity of the fractures, runoff
is significant. Thicker weathered zones (soils) may
develop locally particularly on talus slopes with local
perched zones common. These eastern facing slopes
are located in the rain shadow of the mountains and
only limited rainfall  is derived from the moisture
laden prevailing westerly winds, thus ground-water
recharge rarely exceeds 1  inch/year. Ground-water
levels are extremely  variable but are typically deep.
Most of these areas are water deficient on an annual
basis. The migration  of pollutants introduced at the
surface will be dependent on the current climatic
conditions; pollutants will tend to infiltrate easier and
further during wet periods as opposed to dry periods.
Setting 1 Aa East Mountain Slopes
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

100+
0-2
Metamorphic/
Igneous
Thin or Absent
1 8+%
Metamorphic/
Igneous

1 00-300

Weight

5
4

3
2
1

5

3
General
Rating

1
1

3
10
1

4

2

Number

5
4

9
20
1

20

6
                              DRASTIC Index   65
Setting 1 Aa East Mountain Slopes
    Feature
                  Range
            	Agricultural	
             Weight   Rating  Number
Depth to Water
  Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
  Zone
Hydraulic
  Conductivity
    100+
    0-2
Metamorphic/
   Igneous
Thin or Absent
    18+%
Metamorphic/
   Igneous

   100-300
5
4

3
5
3

4

2
 1
 1

 3
10
 1

 4

 2
 5
 4

 9
50
 3

16

 4
                              Agricultural
                              DRASTIC Index
                                           91
                                                                         41

-------
Western Mountain Ranges

(1A b)  Mountain Slopes— West

This setting is similar to (1 Aa) Mountain Slopes—East
except that ground-water levels are typically more
shallow and precipitation greatly exceeds the amount
which  falls on the  eastern  slopes. Even though
rainfall is more abundant, recharge is still low due to
the steepness of  the slopes and density of the
underlying bedrock and may only exceed 2 inches/
year in places where precipitation is very high and soil
cover is unusually  favorable. Due to increased
precipitation, pollutants may tend to migrate to the
water table more rapidly, but be more diluted, than on
the comparable eastern slopes.
Setting 1 Ab West Mountain Slopes
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

75-100
0-2
Metamorphic/
Igneous
Thin or Absent
1 8+%
Metamorphic/
Igneous

1 00-300


Weight Rating

5 2
4 1

3 3
5 10
3 1

4 4

2 2
Agricultural
DRASTIC Index
Number

10
4

9
50
3

16

4

97
 Setting 1 Ab West Mountain Slopes
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
0-2
Metamorphic/
Igneous
Thin or Absent
18+%
Metamorphic/
Igneous

1 00-300

Weight

5
4

3
2
1

5

3
General
Rating

2
1

3
10
1

4

2

Number

10
4

9
20
1

20

6
                              DRASTIC Index   70
Western Mountain Ranges

(1Ba)  Alluvial Mountain Valleys—East

This hydrogeologic setting of eastward facing interior
valleys  is characterized by thin bouldery alluvium
which overlies fractured  bedrock of sedimentary,
metamorphic or igneous origin. The alluvium, which
is derived from the surrounding steep slopes serves
as a  localized source of water. Where  soil  cover
exists, it typically is  gravel sized and offers  little
protection from pollution. Water levels are typically
moderately deep because of the lack of precipitation
on the  eastern slopes and the low net recharge.
Ground water is obtained from the coarser grained
deposits within the valley, but these deposits also
have  a fraction of finer grained deposits which can
influence water movement. Ground water may also
be obtained  from the fractures in the underlying
bedrock which are typically in direct hydraulic con-
nection with the  overlying alluvium.  Since  these
valleys are usually structurally controlled, there is the
possibility  that  any  pollutants  introduced  at  the
surface may  migrate into the fractures beneath the
alluvium and disperse  rapidly from  the site  of
incidence.
                        42

-------
Setting 1 Ba East Alluvial Mtn. Valleys
                                   General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

Range
30-50
0-2
Sand and Gravel
Gravel
2-6%
Sand and Gravel
1 00-300

Weight Rating
5 5
4 1
3 8
2 10
1 9
5 8
3 2
DRASTIC Index
Number
25
4
24
20
9
40
6
128
Setting 1 Ba East Alluvial Mtn. Valleys
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

Range
30-50
0-2
Sand and Gravel
Gravel
2-6%
Sand and Gravel
100-300

Agricultural
Weight Rating
5 5
4 1
3 8
5 10
3 9
4 8
2 2
Agricultural
DRASTIC Index

Number
25
4
24
50
27
32
4
166
                                                     Setting 1 Bb West Alluvial Mtn. Valleys
                                                                                        General
                                                         Feature
                  Range
Weight   Rating  Number
                                                     Depth to Water
                                                       Table            15-30
                                                     Net Recharge         2-4
                                                     Aquifer Media   Sand and Gravel
                                                     Soil Media          Gravel
                                                     Topography
                                                     Impact Vadose
                                                       Zone
                                                     Hydraulic
                                                       Conductivity
                                                                        2-e
              Sand and Gravel
                 100-300
                              5
                              4
                              3
                              2
                              1
          7
          3
          8
         10
          9
35
12
24
20
 9

40
                                                                                    DRASTIC Index  146
Western Mountain Ranges
(1Bb)  Alluvial Mountain Valleys—West
This setting,  which  includes coastal valleys  and
westward-sloping interior valleys, is similar to (1 Ba)
Narrow Alluvial  Valleys—East.  Water  Levels are
typically shallower due to higher amounts of precipi-
tation  and subsequently greater ground-water re-
charge. Soils tend to be deeper with better developed
soil profiles.  Bedrock weathering is usually deeper,
with increased mass wasting due  to freeze/thaw
cycles that may occur in the higher valleys of some
areas. The migration  of pollutants introduced at the
surface will,  in most cases,  be predictably  down-
gradient in the relatively short, straight, narrow, well-
defined valleys.
Setting 1 Bb West Alluvial Mtn. Valleys
                                  Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
2-4
Sand and Gravel
Gravel
2-6%

Sand and Gravel

1 00-300


Weight Rating

5 7
4 3
3 8
5 10
3 9

4 8

2 2
Agricultural
DRASTIC Index
Number

35
12
24
50
27

32

4

184
                                                                            43

-------
Western Mountain Ranges

(1Ca)  Mountain Flanks—East

This hydrogeologic setting is characterized by moder-
ate to steep topographic relief and dipping fractured
consolidated sedimentary  rocks, which dip toward
and underlie the adjacent wide alluvial valleys. Soil
cover is usually thicker than on the upper mountain
slopes and typically has weathered to a sandy loam.
Alluvium and/or talus deposits are not included in
this setting. These sedimentary rocks,  when  frac-
tured, typically have hydraulic conductivities similar
to the fractured bedrock on the mountain slopes.
Depth to the water table varies, but is typically deep
dueto lack of precipitation and moderate topographic
relief, and net recharge is very low. Pollutants that
may be introduced at the surface will tend to migrate
most  rapidly along dipping  bedding planes,  and
through fractures.
Setting 1 Ca East Mountain Flanks
                                Agricultural
Setting 1 Ca East Mountain Flanks
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
0-2
Thin Bedded SS,
LS.SH Sequences
Sandy Loam
12-18%
Bedded LS, SS,
SH

100-300
Weight

5
4

3
2
1

5

3
Rating

2
1

6
6
3

6

2
Number

10
4

18
12
3

30

6
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

75-100
0-2
Thin Bedded SS,
LS.SH Sequences
Sandy Loam
12-18%
Bedded LS, SS,
SH

1 00-300


Weight Rating

5 2
4 1

3 6
5 6
3 3

4 6

2 2
Agricultural
DRASTIC Index
Number

10
4

18
30
9

24

4

99
                                                  Western Mountain Ranges

                                                  f 1 Cb)  Mountain Flanks— West

                                                  This setting  is similar to (1Ca) Mountain Flanks—
                                                  East. Ground-water levels, however, are typically not
                                                  quite as deep and ground-water recharge is greater
                                                  due to  the greater amount of precipitation on the
                                                  western slopes. Soil depths are often greater, with
                                                  more developed soil profiles. These soils are charac-
                                                  terized  by higher clay and loam content than those
                                                  that occur on the eastern slopes. Analagous to the
                                                  eastern flanks, any pollutants that are introduced will
                                                  tend to  migrate along bedding planes and fractures.
                              DRASTIC Index   83
                        44

-------
Setting 1 Cb West Mountain Flanks
                                   General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
2-4
Thin Bedded SS,
LS.SH Sequences
Sandy Loam
12-18%
Bedded LS, SS,
SH

100-300
Weight

5
4

3
2
1

5

3
Rating

5
3

6
6
3

6

2
Number

25
12

18
12
3

30

6
                              DRASTIC Index   106
Setting 1 Cb West Mountain Flanks
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



Range Weight Rating Number
30-50
2-4
Thin Bedded SS,
LS.SH Sequences
Sandy Loam
12-18%
Bedded LS, SS,
SH

100-300



5 5
4 3

3 6
5 6
3 3

4 6

2 2

Agricultural
DRASTIC Index
25
12

18
30
9

24

4


122
Setting 1 D Glacial Mountain Valleys
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
4-7
Sand and Gravel
Gravel
2-6%

Sand and Gravel

700-1000



Weight

5
4
3
2
1

5

3


GG nsra I

Rating

9
6
8
10
9

8

6


DRASTIC Index


Number

45
24
24
20
9

40

18


180
                                                    Setting 1 D Glacial Mountain Valleys
Western Mountain Ranges

(1D)   Glaciated Mountain Valleys

This hydrogeologic setting is characterized by moder-
ate topographic relief, and  very coarse  grained
deposits associated with the near mountain glacial
features,  such  as  cirques and  paternoster lakes.
These deposits  may  serve as localized sources of
water. Water tables are typically shallow with coarse
grained deposits present at the  surface. Mountain
glaciers  may be present in some areas. Although
precipitation may not be great, recharge is relatively
high when compared to other settings in the region
because of the large volumes of water produced from
the glaciers during the summer melting cycle. These
recent glacial deposits are underlain  by fractured
bedrock of igneous or metamorphic origin all of which
are in direct hydraulic connection with the overlying
deposits. The fractured bedrock may also serve as a
local source of ground water.
                                                                                      Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Range
5-15
4-7
Sand and Gravel
Gravel
2-6%
Weight
5
4
3
5
3
Rating
9
6
8
10
9
Number
45
24
24
50
27
Impact Vadose
 Zone         Sand and Gravel
Hydraulic
 Conductivity     700-1000
                              Agricultural
                              DRASTIC Index
 32
 12
214
                                                                           45

-------
Western Mountain Ranges

(1Ea)  Wide Alluvial Valleys (With External
Drainage)—East

This hydrogeologic setting is characterized by low
relief and moderately thick deposits of coarsegrained
alluvium deposited by water. It is  similar to Narrow
Alluvial Valleys except that the valleys are better
developed  and the  streams which occupy their
channels have a  shallower gradient. Typically the
alluvial deposits are finer grained and thicker than the
Narrow Alluvial Valleys. The alluvium in this setting
serves as the  major source of ground water and is
often capable of supplying large quantities  of water.
Surficial deposits are usually coarse grained and
water  levels are relatively shallow even though
precipitation and net recharge are low. The alluvium
is underlain by layers of permeable sedimentary rock
which  receive their primary source of recharge from
the adjacent  mountain  flanks. The sedimentary
sequence is underlain by fractured bedrock of igneous
or metamorphic origin. Ground water may also be
obtained from the permeable sedimentary rocks.
Setting 1 Ea East Wide Alluvial Valleys (External Drainage)
                                Agricultural
Setting 1 Ea East Wide Alluvial Valleys (External Drainage)
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
2-4
Sand and Gravel
Gravel
2-6%

Sand and Gravel

700-1000
Weight

5
4
3
2
1

5

3
Rating

7
3
8
10
9

8

6
Number

35
12
24
20
9

40

18
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
2-4
Sand and Gravel
Gravel
2-6%

Sand and Gravel

700-1000


Weight Rating

5 7
4 3
3 8
5 10
3 9

4 8

2 6
Agricultural
DRASTIC Index
Number

35
12
24
50
27

32

12

192
Western Mountain Ranges

(1 Eb)   Wide Alluvial Valleys (External
Drainage)—West

This setting is similar to (1 Ea) Wide Alluvial Valleys
(External Drainage)—East except that water  levels
are typically shallow because of higher precipitation
and greater ground-water recharge. Soils tend to be
better developed and thicker  in the areas bordering
the mountain flanks (1Cb),  however, in the  valley
lowlands,  gravelly soils predominate. Pollutants
introduced at the surface in these  wide alluvial
valleys tend to migrate rapidly in the coarser grained
deposits and travel into and along fracture planes.
                              DRASTIC Index  158
                        46

-------
Setting 1 Eb West Wide Alluvial Valleys (External Drainage)
                                   General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
4-7
Sand and Gravel
Gravel
2-6%

Sand and Gravel

700-1000
Weight

5
4
3
2
1

5

3
Rating

9
6
8
10
9

8

6
Number

45
24
24
20
9

40

18
                              DRASTIC Index   180
Setting 1 Eb West Wide Alluvial Valleys (External Drainage)
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
4-7
Sand and Gravel
Gravel
2-6%

Sand and Gravel

700-1000


Weight Rating

5 9
4 6
3 8
5 10
3 9

4 8

2 6
Agricultural
DRASTIC Index
Number

45
24
24
50
27

32

12

214
                                                    Setting 1 F Coastal Beaches
                                                                                       General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

0-5
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

700-1 000
Weight

5
4
3
2
1

5

3
Rating

10
9
8
9
10

8

6
Number

50
36
24
18
10

40

18
                                                                                  DRASTIC Index  196
Western Mountain  Ranges

(IF)  Coastal Beaches

This hydrogeologic setting is characterized by  low
topographic relief, near sea level elevation and sandy
surface soils. These areas have very high  potential
infiltration rates. These areas are commonly ground
water discharge areas, which, when utilized for fresh
water supply, are quickly endangered by salt-water
intrusion. Due to their very permeable nature and thin
vadose zone, they are very vulnerable to pollution.
Under natural  gradients, pollution of this zone is
usually discharged to the sea. However, with inland
pumping, flow  is rapidly reversed to the  pumping
center.
Setting 1 F Coastal Beaches
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

0-5
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

700-1 000


Weight Rating

5 10
4 9
3 8
5 9
3 10

4 8

2 6
Agricultural
DRASTIC Index
Number

50
36
24
45
30

24

12

221
                                                                           47

-------
                                      2.   Alluvial Basins

      (Thick alluvial deposits in basins and valleys bordered by mountains and locally of glacial origin)
The Alluvial Basins region occupies a discontinuous
area of 1,025,000 km2  extending  from  the  Puget
Sound-Willamette Valley area of Washington  and
Oregon to west Texas.  The region consists  of an
irregular alternation of basins or valleys and mountain
ranges. From the standpoint of topography, it is useful
to contrast this region with the Western Mountain
Ranges. In the Western  Mountain Ranges the high
areas,  the mountains, are the dominant feature. In
the Alluvial Basins region the low areas, the basins
and valleys, are the dominant feature. The principal
exception to this generalization is the Coast Ranges of
southern California which,  though included in  this
region, topographically more closely  resemble the
Western Mountain Ranges.

Most of the Nevada and  all of the Utah parts of this
region  are an area of internal drainage referred to as
the Great Basin. No surf ace or subsurface flow leaves
this part of the region, and all water reaching it from
adjacent areas and from precipitation is returned to
the atmosphere by evaporation or by thetranspiration
of plants.

The basins and valleys are diverse in size, shape, and
altitude. They range in  altitude  from about 85 m
below sea level in Death Valley in California to 2,000
m above sea level in the San Luis Valley in Colorado.
The basins range in size from a few hundred meters in
width and a kilometer or two in length to,  for the
Central Valley of California, as much as 80 km in
width and 650  km  in  length.  The  crests  of the
mountains are commonly 1,000 to 1,500 m above the
adjacent valley floors.

The surrounding mountains, and the bedrock beneath
the basins, consist of granite and metamorphic rocks
of Precambrian  to Tertiary age  and consolidated
sedimentary rocks of Paleozoic to Cenozoic age. The
rocks are broken along fractures and faults that  may
serve as water-bearing openings. However, the open-
ings in the granitic and metamorphic rocks  in the
mountainous area have a relatively small capacity to
store and to transmit ground water.

The dominant element in the hydrology of the region
is the thick  (several hundred to several thousand
meters)  layer  of generally unconsolidated alluvial
material that partially fills the basins.  Except for the
part  of the region  in Washington and Oregon, the
material was derived from  erosion of the adjacent
mountains and was transported down steep-gradient
streams into the basins where it was deposited as
alluvial fans. Generally, the coarsest  material in an
alluvial  fan  occurs at  its apex,  adjacent  to  the
mountains; the  material  gets progressively  finer
toward the center  of the basins. In time, the fans
formed by adjacent streams coalesced to  form a
continuous and thick deposit of alluvium that slopes
gently from the mountains toward the center of the
basins. These alluvial-fan deposits are overlain by or
grade into fine-grained  flood plain,  lake, or playa
deposits in the central part of most basins. The fine-
grained deposits are especially suited to large-scale
cultivation.

The Puget Sound and Willamette Valley areas differ
geologically from the remainder of the region.  The
                                               48

-------
Puget  Sound area is underlain  by  thick and very
permeable deposits of gravel and sand laid down by
streams of glacial meltwater derived from icetongues
that invaded the area from the  north during the
Pleistocene. The gravel and sand are interbedded
with clay in parts of the area. The Willamette Valley is
mostly underlain by interbedded  sand, silt and clay
deposited on floodplains by the Willamette River and
other streams.

The Alluvial Basins region is the driest area in the
United States, with large parts of it being classified as
semiarid and arid. Annual precipitation in the valleys
in Nevada and Arizona ranges from about 100 to 400
mm. However, in the mountainous areas throughout
the region, in the northern part of the Central Valley of
California, and  in the  Washington-Oregon  area,
annual precipitation ranges from about 400 mm to
more than 800 mm. The region also  receives runoff
from streams that originate in the mountains of the
Western  Mountain Ranges region.

Because  of  the very thin cover  of  unconsolidated
material  on the mountains in the Alluvial  Basins
region, precipitation runs off rapidly down the valleys
and out onto the fans where it infiltrates into the
alluvium.  The water moves through the  sand and
gravel  layers toward the centers  of the basins. The
centers  of  many  basins consist of flat-floored,
vegetation-free areas onto which "ground water may
discharge and on which overland runoff may collect
during intense storms.  The water that collects in
these areas, which are  called playas, evaporates
relatively quickly, leaving both a thin deposit of clay
and other sediment transported by overland runoff
and a crust consisting of the soluble  salts that were
dissolved in the water.

Studies in the region have shown that the hydrology
of the  Alluvial  Basins  is more complex than that
described in the preceding paragraph, which applies
only to what has been described as "undrained closed
basins." Water may movethrough permeable bedrock
from one basin to another, arriving,  ultimately, at a
large playa referred to as a "sink" into the ground, as
the name might imply, but by evaporating, as in other
playas. In those parts of the Alluvial Basin region
drained by perennial streams, including the  Puget
Sound-Willamette Valley area, the Central Valley of
California, and  some of the valleys  in Arizona and
New Mexico, ground-water discharges to the streams
from the alluvial deposits. However, before entering
the streams, water may  move down some valleys
through the alluvial deposits for tens of kilometers. A
reversal of this situation occurs  along the  lower
Colorado River and at the upstream end of the valleys
of some  of the other perennial streams; in  these
areas,  water moves from  the streams  into the
alluvium to supply the needs of the adjacent vegetated
zones.
Ground water is the major source of water in the
Alluvial Basins region. Many of the valleys in this
region have been developed for agriculture. Because
of the dry climate, agriculture requires intensive
irrigation. In the part  of this region drained by the
Colorado River, ground water used for irrigation in
1975 amounted to about 6 billion cubic  meters
(4,864,000 acre-feet). Most of the  ground water is
obtained from wells drawing from the sand and gravel
deposits in the valley  alluvium. These  deposits are
interbedded with finer grained layers of silt and clay
that  are also saturated with water.  When hydraulic
heads in the sand and gravel layers are lowered by
withdrawals, the water in the silt and clay begins to
move slowly into the sand and gravel. The movement,
which in some areas takes decades to become signif-
icant, is accompanied by compaction of the silt and
clay  and subsidence of the land surface. Subsidence
is most severe in parts of the Central Valley, where it
exceeds 9 m in one area, and in  southern Arizona,
where subsidence of  more than  4 m  has  been
observed.

In both the Alluvial Basins and the Colorado Plateau
regions,  large volumes of water are transpired by
phreatophytes (water-loving plants) of small econom-
ic value that  live along streams and in  other wet
areas. In an effort to increase the amount of water
available for  irrigation and other uses,  numerous
studies have been made to determine the volumes of
water used by phreatophytes and to devise means to
control them.  A few small control efforts  have  been
made, but none have proven economically effective.
Alluvial Basins

(2A)  Mountain Slopes

This hydrogeologic setting is characterized by steep
slopes on the side of mountains, a thin soil cover and
highly fractured bedrock. Ground water is obtained
primarily from the fractures in the bedrock which may
be of sedimentary, metamorphic  or igneous origin.
The fractures provide only localized sources of ground
water and well  yields  are  typically limited  even
though  the hydraulic  conductivity may be  high
because of the fractures. Due to the steep slopes, thin
soil cover and small storage capacity of the fractures,
runoff is significant and  ground-water  recharge is
minimal. Ground-water levels are extremely variable,
but are typically deep.
                                                                        49

-------
Setting 2 A Mountain Slopes
                              DRASTIC Index   74
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
0-2
Metamorphic/
Igneous
Thin or Absent
12-18%
Metamorphic/
Igneous

1-100
Weight

5
4

3
5
3

4

2
Rating

3
1

3
10
3

4

1
Number

15
4

9
50
9

16

2
                                                   Alluvial Basins

                                                   (2B)  Alluvial Mountain Valleys

                                                   This hydrogeologic setting is characterized by thin
                                                   bouldery alluvium which overlies fractured bedrock of
                                                   sedimentary, metamorphic or igneous origin. Slopes
                                                   in the valley typically range from 2-6%. The alluvium,
                                                   which is derived from the surrounding steep slopes
                                                   serves as a localized source of water. Water levels are
                                                   moderate in depth, but because of the low rainfall,
                                                   ground-water recharge is low. Ground water may
                                                   also be obtained from the fractures in the underlying
                                                   bedrock which are typically in  direct hydraulic con-
                                                   nection with the overlying alluvium.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
0-2
Metamorphic/
Igneous
Thin or Absent
12-18%
Metamorphic/
Igneous

1-100

Weight

5
4

3
2
1

5

3
General
Rating

3
1

3
10
3

4

1

Number

15
4

9
.>/-
1
"0

£>
'!-'
r<
»"*/—
20 «i4
3

20

3
                                                    Setting 2 B Alluvial Mountain Valleys
                                                                                       General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
0-2
Sand and Gravel
Sand
2-6%

Sand and Gravel

300-700
Weight

5
4
3
2
1

5

3
Rating

5
1
8
9
9

8

4
Number

25
4
24
18
9

40

12
                                                                                  DRASTIC Index  132
                              Agricultural
                              DRASTIC Index  105
                        50

-------
Setting 2 B Alluvial Mountain Valleys
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

30-50
0-2
Sand and Gravel
Sand
2-6%

Sand and Gravel

300-700


Weight Rating

5 5
4 1
3 8
5 9
3 9

4 8

2 4
Agricultural
DRASTIC Index
Number

25
4
24
45
27

32

8

165
Alluvial Basins

(2C)  Alluvial Fans

This hydrogeologic setting is characterized by gently
sloping alluvial deposits which are coarser near the
apex in the mountains and grade toward finer deposits
in the basins. Within the alluvial deposits are layers of
sand and gravel which extend into the central parts of
the adjacent basins.  The alluvial fans serve as local
sources of water and also as the recharge area for the
deposits in the adjacent basin. The portion of the fan
extending farthest into the basin may function as a
discharge area, especially during seasons when the
upper portion of the fan  is  receiving substantial
recharge. Discharge zones are usually related to flow
along the top of stratified clay layers. Ground water
discharge zones are less vulnerable to pollution than
recharge zones. Where the discharge/recharge rela-
tionship is  reversible the greater vulnerability of the
recharge condition must be evaluated. Ground-water
levels are  extremely variable, and the quantity of
water available is limited because of the low precipi-
tation and low net  recharge. Ground-water depth
varies from over 100 feet near the mountains to zero
in the discharge areas. The alluvial fans are underlain
by fractured bedrock  of sedimentary, metamorphic or
igneous origin which are typically in direct hydraulic
connection with the overlying  deposits. Limited
supplies of ground  water are  available from the
fractures in the bedrock.
Setting 2 C Alluvial Fans
Feature Range
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

50-75
0-2
Sand and Gravel
Sand
2-6%

Sand and Gravel

300-700

Weight

5
4
3
2
1

5

3
General
Rating

3
1
8
9
9

8

4

Number

15
4
24
18
9

40

12
Setting 2 C Alluvial Fans
                              DRASTIC Index  122
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
0-2
Sand and Gravel
Sand
2-6%

Sand and Gravel

300-700
Weight

5
4
3
5
3

4

2
Rating

3
1
8
9
9

8

4
Number

15
4
24
45
27

32

8
Agricultural
DRASTIC Index
155
                                                                          51

-------
Alluvial Basins

(2D)  Alluvial Basins (Internal Drainage)

This hydrogeologic setting is characterized  by  low
topographic relief and thick deposits of unconsoli-
dated alluvial material formed by coalescing alluvial
fans. The sand and gravel deposits within the alluvium
are the major source of water in the region. The sand
and gravel is interbedded with finer grained layers of
saturated clay and silt which serve  as a source of
recharge to the sand  and gravel when head differ-
ences are significant. The alluvium is underlain by
fractured igneous or metamorphic rocks and consoli-
dated sedimentary rocks.  Although  some  of  the
sedimentary rocks are permeable  and water may be
obtained from fractures in the crystalline bedrock, the
abundance of water in the alluvium and the greater
depth of the bedrock serves to minimize use of these
sources. Since these basins have  internal drainage,
natural  gradients  are low  near the  basin centers.
Thus, the primary direction of pollutant  migration,
under normal conditions, would be downward,  and
outward radially from  the point of  incidence.
                       Setting 2 D Alluvial Basins (Internal Drainage)
                                                       Agricultural
 Setting 2 D Alluvial Basins (Internal Drainage)
                                   General
     Feature         Range
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone

Hydraulic
Conductivity

30-50
0-2
Sand and Gravel
Sand
2-6%

S & G w/sig.
Silt and Clay

300-700

5
4
3
2
1


5

3

5
1
8
9
9


6

4

25
4
24
18
9


30

12
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone

Hydraulic
Conductivity


Range

30-50
0-2
Sand and Gravel
Sand
2-6%

S & G w/sig
Silt and Clay

300-700


Weight Rating

5 5
4 1
3 8
5 9
3 9


4 6

2 4
Agricultural
DRASTIC Index
Number

25
4
24
45
27


24

8

157
                       Alluvial Basins
                       (2E)  Playa Lakes
                       This hydrogeologic setting is characterized by very
                       low topographic relief and thin layers of clays and
                       other fine grained sediments which overlie alluvial
                       deposits. The playa areas serve as a catchment for
                       water during periods of significant runoff; when the
                       precipitation event is  over, the water evaporates,
                       leaving a crust of soluble salts on the surface. Ground
                       water is obtained from  the  layers of sand which
                       underly the finer-grained deposits. Water levels are
                       extremely variable but are typically deep. The playa
                       beds  are  significant  recharge  areas due  to the
                       ground-water  "mounding" that occurs seasonally
                       beneath the playas. The rate of recharge, as compared
                       to evaporation, is largely a function of the permeability
                       of the materials forming the bed of the playa, and the
                       distribution, in time, of precipitation.
                               DRASTIC Index  122
                         52

-------
Setting  2 E Playa Lakes
                                        General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone

Hydraulic
Conductivity
Range

75-100
0-2
Sand and Gravel
Shrink/ Agg. Clay
0-2%

S & G w/sig.
Silt and Clay

700-1 000
Weight

5
4
3
2
1


5

3
Rating

2
1
8
7
10


6

6
Number

10
4
24
14
10


30

18
                                  DRASTIC Index   110
Setting  2 E Playa Lakes
    Feature
     Range
                                      Agricultural
Weight   Rating  Number
Depth to Water
  Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
  Zone

Hydraulic
  Conductivity
    75-100
      0-2
Sand and Gravel
Shrink/Agg. Clay
     0-2%

  S & G w/sig.
  Silt and Clay

   700-1000
   5
   4
   3
   5
   3
 2
 1
 8
 7
10
10
 4
24
35
30
                   24
                   12
                                  Agricultural
                                  DRASTIC Index
                                  139
                                                                                      53

-------
                                 3.   Columbia Lava Plateau

(Thick sequence of lava flows irregularly interbedded with  thin unconsolidated deposits and overlain by thin
soils)
 The  Columbia Lava  Plateau occupies an  area  of
 366,000 km2  in  northeastern California,  eastern
 Washington  and  Oregon, southern  Idaho,  and
 northern Nevada. As its name implies, it is basically a
 plateau standing  at an altitude generally between
 500 and 1,800 m above sea level that is underlain by a
 great thickness of lava flows irregularly interbedded
 with silt, sand, and other unconsolidated deposits.
 The plateau is bordered on the west by the Cascade
 Range, on the north by the Okanogan Highlands, and
 on the  east by the Rocky Mountains. On the south it
 grades into the Alluvial Basins regoin, as the  area
 occupied by lava  flows decreases and  the typical
 "basin and range" topography of the Alluvial Basins
region gradually prevails. Most of the plateau in Idaho
is exceptionally flat over large areas, the principal
relief being  low cinder (volcanic) cones  and  lava
domes. This area and much of the area in California,
southeastern Oregon,  and Nevada is underlain by
much of the youngest lava, someof which is less than
1,000 years old. In Washington the flows are older,
some dating back to the Miocene Epoch. Altitudes in a
few of the mountainous areas in the  plateau region
exceed 3,000 m.

The great sequence of lava flows, which ranges in
thickness from less than  50 m adjacent  to the
bordering mountain ranges to more than 1,000 m in
south-central Washington and southern Idaho, is the
principal water-bearing unit in the region. The water-
bearing lava  is underlain by granite, metamorphic
rocks, older lava flows, and sedimentary rocks, none
of which are very permeable. Individual lava flows in
the water-bearing zone range  in thickness from
several meters to more than 50 m and average about
15m. Most of the lava is basalt which reached the
surface both through extensive fissures and through
local eruption centers. Because basaltic lava is very
fluid when molten, it flows considerable distances
down surface depressions and over gently sloping
surfaces and forms, when it solidifies, a relatively flat
surface. Some flows are sheetlike and can be followed
visually for several kilometers along the walls of steep
canyons. Other flows, where the lava  issuing  from
eruption  centers followed surface depressions, are
lobate, or tonguelike.
The volcanic rocks yield water mainly from permeable
zones that occur at or near the contacts between
some flow layers. The origin of these flow-contact or
interflow zones is complex but involves, among other
causes, the relatively rapid cooling of the top of flows,
which results in formation of a crust. As the molten
lava beneath continues to  flow, the crust may  be
broken into a rubble of angular fragments which in
places contain numerous holes where gas bubbles
formed and which give the rock the appearance of a
frozen  froth.  The slower cooling of the central and
lower parts of the thicker flows results in a dense,
flint-like  rock which in the lower part contains rela-
tively widely spaced, irregular fractures and which
grade upward into a zone containing relatively closely
                                                54

-------
spaced vertical fractures that break the rock into a
series of hexagonal columns (Newcomb, 1961).

Periods of time ranging from less than 100 years to
thousands of years elapsed between  extrusion of
successive lava flows. As a result, parts of some flows
are separated by soil zones and, at places, by sand,
silt, and clay deposited by streams or  in lakes that
existed on the land surface before being buried by
subsequent  lava extrusions.  These  sedimentary
layers, where they  occur between  lava flows, are
commonly referred to as "interflow  sediments."
Gravel, sand, silt,  and clay, partly formed by the
present streams and partly of glacial origin, cover the
volcanic rocks and the older exposed bedrock in parts
of the area.

From the standpoint of the hydraulic characteristics
of the volcanic  rocks, it  is useful  to divide the
Columbia Lava Plateau region into two parts: (1) the
area  in southeastern Washington,  northeastern
Oregon, andtheLewiston area of Idaho, part of which
is underlain  by volcanic rocks of the Columbia River
Group; and (2) the remainder of the area, which also
includes the  Snake River Plain. The basalt underlying
the Snake River Plain is referred to as the Snake River
Basalt; that underlying southeastern Oregon and the
remainder of this area has been divided into several
units, to  which  names of local origin are applied
(Hampton, 1964).

The Columbia River Group is of Miocene to Pliocene
age and consists of relatively thick flows that  have
been deformed into a series of broad folds and offset
locally along normal  faults. Movement  of ground
water occurs primarily through the interflow zones
near the top of flows and, to a much smaller extent,
through fault zones and through joints developed in
the dense central and lower parts of the flows. The
axes of sharp folds and the offset of the interflow
zones along  faults form subsurface dams that affect
the movement of ground water. Water reaching the
interflow zones tends to move down the dip of the
flows from fold axes and to collect undip behind faults
that are transverse to the  direction  of movement
(Newcomb, 1961). As a result, the basalt in parts of
the area is divided into a series of barrier-controlled
reservoirs which are only poorly connected hydraul-
ically to adjacent reservoirs.
The water-bearing basalt underlying California,
Nevada, southeastern Oregon, and southern Idaho is
of Pliocene to Holocene age and consists of small,
relatively thin flows that have been affected to a much
smaller extent by folding and faulting than has the
Columbia River Group. The thin flows contain exten-
sive,  highly  permeable  interflow  zones  that  are
relatively effectively interconnected through a dense
network of cooling fractures.  Structural barriers to
ground-water  movement, such as those  of the
Columbia River Group, are of minor importance. This
is demonstrated by conditions  in the 44,000-square-
kilometer area of the Snake River Plain east of Bliss,
Idaho,  which  Nace (1958) thought might  be the
largest unified ground-water reservoir on the North
American continent. (It is probable that this distinction
is held by the Floridan aquifer, which underlies an
area of 212,000 km2 in Alabama, Florida, Georgia,
and South Carolina. See region 11).

The  interflow  zones form a complex sequence of
relatively  horizontal aquifers that are  separated
vertically by the dense central  and lower parts of the
lava  flows and by interlayered clay and silt. Hydrol-
ogists estimate that the interflow zones, which range
in thickness from about 1 m to about 8 m, account for
about 10 percent of the basalt. MacNish and Barker
(1976) have estimated, on the  basis of studies in the
Walla Walla River basin in Washington and Oregon,
that the hydraulic conductivity along the flow-contact
zones may be a billion times largerthan the hydraulic
conductivity across the dense  zones. The  lateral
extent  of individual aquifers  depends on the area
covered by the different lava flows, on the presence of
dikes and other igneous intrusions, and on faults and
folds that terminate the porous zones, especially in
the Columbia River Group.


The  large  differences in hydraulic conductivity be-
tween aquifers and the intervening "confining zones"
result in significant differences in hydraulic heads
between different aquifers. These differences reflect
the head losses that occur as water moves vertically
through the system. As a result, heads decrease with
increasing depth in recharge areas and increase with
increasing depth near the streams that serve as major
lines of ground-water discharge. The difference in
heads between different aquifers can result in the
movement of large volumes of water  between
aquifers through the open-hole (uncased) sections of
wells.

Much of the Columbia Lava Plateau region is in the
"rain shadow" east of the Cascades and, as a result,
receives  only 200  to  1,200 mm  of  precipitation
annually. The  areas that receive the least precipita-
tion  include the plateau area immediately east of the
Cascades and the Snake River Plain. The areas that
receive the largest amounts of precipitation  include
the east flank of the Cascades and the areas adjacent
to the Okanogan Highlands and the Rocky Mountains.
Recharge  to the ground-water system depends on
several factors, including the  amount and seasonal
distribution of precipitation and the permeability of
the surficial materials. Most precipitation occurs in
                                                                        55

-------
the winter and thus coincides with the cooler, non-
growing season when conditions are most favorable
for recharge.  Mundorff (Columbia-North  Pacific
Technical Staff, 1970) estimates that recharge may
amount to  600 mm in  areas underlain by highly
permeable young lavas that receive abundant precipi-
tation. Considerable recharge also occurs by infiltra-
tion of water from streams that flow onto the plateau
from the adjoining mountains. These  sources of
natural recharge are supplemented in agricultural
areas by the infiltration of irrigation water.
Discharge from the ground-water system occurs as
seepage to streams, as spring flow, and by evapo-
transpiration in areas where the water table is at or
near the land surface. The famous Thousand Springs
and other springs along the Snake River canyon in
southern Idaho are, in fact, among the most spec-
tacular displays of ground-water  discharge in the
world.
The  Columbia Lava Plateau region is mantled by
mostly thin soils developed on alluvial and wind-laid
deposits that are well suited for agriculture. Because
of the arid and semiarid climate in most of the region,
many crops require intensive irrigation. In 1970, for
example, more than 15,000 km2 (3.75 million acres)
were being irrigated on the Snake River Plain. Water
for  irrigation  is obtained both  by  diversions  from
streams  and  by wells that tap the lava interflow
zones. Much  of  the  water applied for irrigation
percolates  downward  into the lava  and then moves
through the ground-water system to the Columbia
and  Snake Rivers and to other streams that  have
deeply entrenched channels. The effect of this "return
flow" is graphically indicated by a long-term increase
in the flow of the  Thousand Springs and other  large
springs along the  Snake River gorge between Milner
and King Hill—from about 110m3 sec"1 in 1902, prior
to significant  irrigation, to more than 225 m3 sec"1 by
1 942,  after decades of  irrigation on adjacent and
upstream parts of the plateau.  Prior to the start of
irrigation, the water represented by this increased
flow reached the Snake River below King Hill through
tributary streams and natural ground-water dis-
charge.
The large withdrawal of water in the Columbia Lava
Plateau for irrigation, industrial, and other uses has
resulted in  declines in ground-water levels of as
muchas30to60 m in several areas. In most of these
areas, the  declines have  been slowed or stopped
through regulatory restrictions or other changes that
have  reduced withdrawals. Declines are still occur-
ring, at rates as much as a few meters per year, in a
few areas.
Columbia Lava Plateau

(3A)  Mountain Slopes

This hydrogeologic setting is characterized by steep
slopes on the side of mountains bordering the plateau,
a thin soil cover and fractured bedrock. Steep slopes
also occur on cinder cones within the plateau. Ground
water is obtained primarily from the fractures in the
bedrock which may be sedimentary, metamorphic or
igneous origin. The  fractures  provide  localized
sources of ground water and well  yields are typically
limited. Due to the thin soil cover, topography, and
small storage capacity of the fractures,  runoff is
significant. Ground-water levels are extremely vari-
able but are typically deep. Due to  lack of rainfall, low
hydraulic conductivity,  and steep topography, net
recharge is very low.
Setting 3 A Mountain Slopes
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
2-4
Metamorphic/
Igneous
Thin or Absent
12-18%
Metamorphic/
Igneous

1000-2000
Weight

5
4

3
2
1

5

3
Rating

2
3

3
10
3

4

8
Number

10
12

9
20
3

20

24
                             DRASTIC Index   98
                       56

-------
Setting 3 A Mountain Slopes
                                 Agricultural
Setting 3 B Alluvial Mountain Valleys
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
2-4
Metamorphic/
Igneous
Thin or Absent
12-18%
Metamorphic/
Igneous

1 000-2000
Weight

5
4

3
5
3

4

2
Rating

2
3

3
10
3

4

8
Number

10
12

9
50
9

16

16
                             Agricultural
                             DRASTIC Index   122
Columbia Lava Plateau

(3B)  Alluvial Mountain Valleys
This hydrogeologic setting is characterized by thin
bouldery alluvium which overlies fractured bedrock of
sedimentary, metamorphic or igneous origin. The
alluvium,  which  is derived from the surrounding
steep slopes serves as a localized source of water.
Water levels are typically moderate and recharge to
the ground  water may  be of significance.  Ground
water may also be obtained from the fractures in the
underlying  bedrock  which  are typically in  direct
hydraulic connection with the overlying alluvium.
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
2-4
Sand and Gravel
Gravel
2-6%

Sand and Gravel

700-1 000
Weight

5
4
3
2
1

5

3
Rating

9
3
8
10
9

8

6
Number

45
12
24
20
9

40

18
                             DRASTIC Index   168
                                                   Setting 3 B Alluvial Mountain Valleys
                                                                                    Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
2-4
Sand and Gravel
Gravel
2-6%

Sand and Gravel

700-1000


Weight Rating

5 9
4 3
3 8
5 10
3 9

4 8

2 6
Agricultural
DRASTIC Index
Number

45
12
24
50
27

32

12

202
                                                   Columbia Lava Plateau

                                                   I3C)  Hydraulically Connected Lava Flows

                                                   This hydrogeologic setting is characterized by  low
                                                   topographic relief, a thin sandy soil cover and a thick
                                                   sequence of successive lava flows which is irregularly
                                                   interbedded with thin unconsolidated deposits. The
                                                   lava beds are underlain by poorly-permeable bedrock
                                                   of igneous, sedimentary or metamorphic origin.
                                                   Ground water is obtained primarily from the interflow
                                                   zones comprised of sequential,  thin, lava flows and
                                                   related sedimentary deposits, cooling fractures, lava
                                                   tubes, and minor structural features. Water levels are
                                                   extremely variable but are typically deep. Well yields
                                                   may vary from low to extremely high depending on
                                                   the characteristics of the underlying lava flows at  a
                                                   particular site. Ground-water recharge may be  ap-
                                                   preciable because the layers of lava are intercon-
                                                   nected hydraulically. This setting is characterized by
                                                   the deposits that occur in southwestern Idaho (Snake
                                                   River area), northern  Nevada, southeastern Oregon,
                                                   and extreme northeastern California, which are of
                                                   Pliocene  to Holocene  age.
                                                                         57

-------
Setting 3 C Hydraulically Connected Lava Flows
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
2-4
Basalt
Sand
2-6%

Basalt

2000+
Weight

5
4
3
2
1

5

3
Rating

3
3
9
9
9

9

10
Number

15
12
27
18
9

45

30
                             DRASTIC Index  156
Setting 3 C Hydraulically Connected Lava Flows
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
2-4
Basalt
Sand
2-6%

Basalt

2000+
Weight

5
4
3
5
3

4

2
Rating

3
3
9
9
9

9

10
Number

15
12
27
45
27

36

20
Agricultural
DRASTIC Index
182
Columbia Lava Plateau
(3D)  Lava Flows Not Connected Hydraulically
This hydrogeologic setting is characterized by  low
topographic relief, a thin cover of gravel, sand, silt,
and clay of stream and glacial origin and a sequence
of thick lava  flows irregularly  interbedded with
                                                   unconsolidated deposits, which have been deformed
                                                   into a series of folds and normal faults. The lava
                                                   sequence is underlain by poorly-permeable bedrock
                                                   of  igneous, sedimentary, or metamorphic origin.
                                                   Ground water is obtained primarily from the interflow
                                                   zones of sedimentary deposits and cooling fractures
                                                   which occur between successive layers of  lava.
                                                   Water levels are extremely variable, but are typically
                                                   deep. The presence of thick impermeable zones may
                                                   produce perched water-table conditions or disrupt
                                                   the hydraulic continuity of water bearing zones. The
                                                   flow of ground water is controlled by locally offset
                                                   normal faults which form a series of hydraulically
                                                   poorly-connected reservoirs. This setting is charac-
                                                   terized by deposits that occur in the Columbia  River
                                                   area in southern Washington, northern Oregon, and
                                                   northern Idaho which are Miocene to Pliocene (?) in
                                                   age.
                                                   Setting 3 D Lava Flows Not Connected Hydraulically
                                                                                     General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone

Hydraulic
Conductivity
Range

50-75
2-4
Thin Bedded SS,
LS, SH Sequences
Sand
2-6%

Bedded LS, SS,
SH

1-100
Weight

5
4

3
2
1


5

3
Rating

3
3

6
9
9


6

1
Number

15
12

18
18
9


30

3
DRASTIC Index  105
                        58

-------
Setting 3 D Lava Flows Not Connected Hydraulically
                           	 Agricultural
    Feature
                         Setting 3 E Alluvial Fans
                  Range
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography

50-75
2-4
Thin Bedded SS,
LS.SH Sequences
Sand
2-6%

5
4

3
5
3

3
3

6
9
9

15
12

18
45
27
Impact Vadose
  Zone         Bedded LS, SS,
SH
Hydraulic
Conductivity 1-100


4 6

2 1
Agricultural
DRASTIC Index
24

2

143
Columbia Lava Plateau

(3E)  Alluvial Fans

This hydrogeologic setting is characterized by alluvial
sediments which  are thickest near the mountain
slopes and thin toward the interior basin. Topography
is steep to moderate.  Fan sediments range  from
coarse,  unsorted debris on the upper slopes grading
to well-sorted and stratified gravels, sands, and clays.
Recharge is a function of precipitation and evapora-
tion, sincethe permeability ofthesurface materials is
usually  high. Ground-water movement is generally
unidirectional from the  adjacent highlands toward
the basin.  Depth  to ground water is generally
moderate to deep.  These fans may serve as  local
sources of water and also as the recharge area for the
deposits in the adjacent basin  and the lower extrem-
ities may serve as discharge areas to local streams.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
2-4
Sand and Gravel
Sandy Loam
6-12%
S & G w/sig
Silt and Clay

300-700

Weight

5
4
3
2
1

5

3
General
Rating

2
3
8
6
5

6

4

Number

10
12
24
12
5

30

12
                                                     Setting 3 E Alluvial Fans
                                                         Feature
                                                                       Range
                                                                                   DRASTIC Index   105
                                                    	Agricultural	
                                                     Weight   Rating  Number
                         Depth to Water
                          Table
                         Net Recharge
                         Aquifer Media
                         Soil Media
                         Topography
                         Impact Vadose
                          Zone
                         Hydraulic
                          Conductivity
    75-100
     2-4
Sand and Gravel
  Sandy Loam
    6-12%
 S & G w/sig
  Silt and Clay

   300-700
5
4
3
5
3
10
12
24
30
15

24
                                                       Agricultural
                                                       DRASTIC Index
                              123
                                                                           59

-------
                        4.   Colorado Plateau and Wyoming Basin

                          (Thin soils over consolidated sedimentary rocks)
The Colorado Plateau and Wyoming Basin region
occupies an area of 414,000 km2 in Arizona, Colorado,
New Mexico, Utah,  and Wyoming. It is a region of
canyons and cliffs; of thin, patchy, rocky soils; and of
sparse vegetation adapted to the arid and semiarid
climate. The large-scale structure of the region is that
of a broad plateau standing at an altitude of 2,500 to
3,500 m and underlain by essentially  horizontal to
gently  dipping layers  of consolidated  sedimentary
rocks. The plateau structure has been modified by an
irregular alternation of basins and domes, in some of
which major faults have caused significant offset of
the rock layers.

The region is bordered on the east, north, and west by
mountain ranges that tend to obscure its plateau
structure. The northern part of the region—the part
occupied by the Wyoming Basin—borders the  Non-
glaciated Central  region at the break in the Rocky
Mountains between the Laramie  Range  and the
Bighorn  Mountains. The region contains  small,
isolated mountain ranges, the most prominent being
the Henry Mountains and the La Sal Mountains in
southeastern Utah.  It  also contains,  rather widely
scattered over the region, extinct volcanoes and lava
fields, the most prominent example being the San
Francisco Mountains in north-central Arizona.

The rocks that underlie the region consist principally
of sandstone, shale, and limestone of Paleozoic to
Cenozoic age. In parts of the region  these rock units
include  significant  amounts of  gypsum  (calcium
sulfate). In the Paradox Basin in western Coloradothe
rock units  include thick deposits of sodium- and
potassium-bearing minerals, principally halite (so-
dium chloride). The sandstones and shales are most
prevalent  and most extensive in occurrence. The
sandstones are the principal sources of ground water
in the region and contain water in fractures developed
both along bedding planes and across the beds and in
interconnected pores. The most productive sand-
stones are those in which calcium carbonate or other
cementing material has been deposited only around
the point of contact of the sand grains. Thus, many of
the sandstones are only partially cemented and retain
significant primary porosity.

Unconsolidated deposits  are  of relatively  minor
importance in this region. Thin deposits of alluvium
capable of yielding  small  to moderate supplies of
ground water occur along parts of the valleys of major
streams, especially adjacent to the mountain ranges
in the northern and eastern parts of the region. These
deposits are partly of glacial origin. In  most of the
remainder of the region there are large expanses of
exposed bedrock,  and the soils, where present, are
thin and rocky.

Erosion has produced  extensive lines of prominent
cliffs in the  region. The  tops of these cliffs are
generally underlain and protected by resistant sand-
stones. Erosion of the domes has produced a series of
concentric, steeply dipping ridges, also developed on
the more resistant sandstones.

Recharge of the sandstone aquifers occurs where
they are exposed  above the cliffs and in the ridges.
                                               60

-------
Average precipitation ranges from about 150 mm in
the lower areas to about 1,000  mm  in the higher
mountains.  The  heaviest  rainfall occurs  in  the
summer in isolated, intense thunderstorms during
which some recharge occurs where intermittent
streams flow across sandstone outcrops. However,
most recharge occurs in the winter during snowmelt
periods. Water moves down the dip of the beds away
from  the  recharge  areas to discharge  along  the
channels of major streams through seeps and springs
and along the walls of  canyons cut by the streams.

The condition described in the preceding paragraph,
whereby intermittent  streams serve as sources of
ground-water recharge and perennial streams serve
as lines of  ground-water  discharge,  is relatively
common in  this region and in the Alluvial Basins
region to the south and west. Streams into which
ground water discharges are referred to as gaining
streams. Conversely, streams that recharge ground-
water systems are referred to as losing streams. The
gaining streams and  the losing streams  may be
different streams. However, in many areas the same
stream may be a gaining  stream  in its headwaters,
especially where these drain the wetter mountainous
areas, become a losing stream as it flows onto the
adjoining  lower areas, and, ultimately,  become a
gaining stream again in its lowermost reaches where
it serves as a regional drain.

The quantity of water available for recharge is small,
but so are the porosity and the transmissivity of most
of the sandstone aquifers. Because of the general
absence of a thick cover of unconsolidated rock in the
recharge areas, there is relatively I ittle opportunity for
such materials to serve as a storage reservoir for the
underlying bedrock. The water  in the sandstone
aquifers is unconfined in the recharge areas and is
confined down-dip. Because most of the sandstones
are consolidated, the storage  coefficient  in  the
confined parts of the aquifers is very small. This small
storage coefficient together with the  small trans-
missivities, results in  even smaller rates of with-
drawal causing extensive cones of  depression around
pumping wells.

Springs exist at places near the base of the sandstone
aquifers where they crop out along  the sides of
canyons.  Discharge from the springs results  in
dewatering the upper parts of the aquifers for some
distance back from the canyon walls.

The Colorado Plateau and Wyoming Basin is a dry,
sparsely populated  region  in which  most water
supplies are obtained from the perennial streams that
flow  across  it from the bordering mountains. Less
than 5 percent of the  water needs are supplied by
ground water, and the development of even  small
ground-water supplies requires the application of
considerable knowledge  of the occurrence of both
rock units and their structure, and of the chemical
quality of the water. Also,  because of the large
surface relief and the dip of the aquifers, wells even
for domestic or small livestock supplies must pene-
trate to depths of a few hundred meters in much of the
area. Thus, the development of ground-water supplies
is far more expensive than in most other parts of the
country. These negative  aspects  notwithstanding,
ground water in the region can support a substantial
increase over the present  withdrawals.
As in most other areas of the country underlain by
consolidated sedimentary rocks, mineralized (saline)
water—that is, water  containing more than 1,000
mg/l of dissolved solids—is widespread in  occur-
rence. Most of the shales  and siltstones contain
mineralized water throughout the region and below
altitudes of about  2,000  m.  Freshwater—water
containing less than 1,000 mg/l of dissolved solids—
occurs only in the most permeable sandstones and
limestones. Much of the mineralized water is due to
the solution of gypsum and halite by water circulating
through beds that contain these minerals. Although
the  aquifers  that  contain  mineralized water  are
commonly overlain by aquifers containing freshwater,
this  situation is  reversed in  a  few places  where
aquifers containing mineralized water are underlain
by more permeable aquifers  containing freshwater.
Colorado Plateau and Wyoming Basin

(4A)  Resistant Ridges

This hydrogeologic setting is characterized by moder-
ate to steep slopes, and a very thin soil cover which
overlies dipping fractured consolidated sedimentary
rocks. The resistant sandstones cap the cliffs and
ridges and form hogbacks. These  same sandstone
units comprise  the aquifers  that are the principal
sources of ground water.  The aquifers receive
recharge in the areas where the sandstone is exposed
at the surface. Recharge is low because  of the
topography and the lack of precipitation in the area.
Water levels are extremely variable, but are typically
deep.
                                                                       61

-------
Setting 4 A Resistant Ridges
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
0-2
Thin Bedded SS,
LS, SH Sequences
Thin or Absent
12-18%
Bedded LS, SS,
SH

1-100
Weight

5
4

3
2
1

5

3
Rating

2
1

6
10
3

6

1
Number

10
4

18
20
3

30

3
                                                   layer which commonly weathers to a sandy loam. The
                                                   sandstones serve as the principal source of ground
                                                   water. The water is obtained from fractures developed
                                                   along bedding planes  and  from within the  pore
                                                   spaces. Water levels are typically deep and recharge
                                                   is low because of the lack of precipitation. Intermittent
                                                   streams often serve as sources of recharge, however,
                                                   the major source of recharge occurs in the resistant
                                                   ridges where the bedrock is exposed. The sandstones
                                                   may be  also confined, with small storage values and
                                                   low yield wells.
                             DRASTIC Index   88
Setting 4 A Resistant Ridges
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

75-100
0-2
Thin Bedded SS,
LS, SH Sequences
Thin or Absent
12-18%
Bedded LS, SS,
SH

1-100


Weight Rating

5 2
4 1

3 6
5 10
3 3

4 6

2 1
Agricultural
DRASTIC Index
Number

10
4

18
50
9

24

2

117
Setting 4 B Consolidated Sedimentary Rocks
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
0-2
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
6-12%
Bedded LS, SS,
SH

1-100
Weight

5
4

3
2
1

5

3
Rating

3
1

6
6
5

6

1
Number

15
4

18
12
5

30

3
                                                                                DRASTIC Index  87
Colorado Plateau and Wyoming Basin

(4B)  Consolidated Sedimentary Rocks

This hydrogeologic setting is characterized by alter-
nating layers of moderately-dipping, fractured, con-
solidated, sedimentary rocks covered by a sandy soil
                       62

-------
Setting 4 B Consolidated Sedimentary Rocks
                          	Agricultural
    Feature
                        Setting 4 C River Alluvium
                 Range
Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



50-75
0-2
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
6-12%
Bedded LS, SS,
SH

1-100



5 3
4 1

3 6
5 6
3 5

4 6

2 1
Agricultural
DRASTIC Index

15
4

18
30
15

24

2

108
Colorado Plateau and Wyoming Basin

(4 C)  River A lluvium

This hydrogeologic setting  is characterized by low
topography and deposits of alluvium along parts of
valleys of perennial and intermittent streams.  The
alluvium yields small to moderate supplies of ground
water. Water is obtained from sand and gravel layers
which are interbedded with finer-grained  alluvial
deposits; these are usually in direct hydraulic contact
with the  perennial  or intermittent  stream.  Water
levels  are extremely  variable but  are  commonly
moderately shallow. Although precipitation is  low,
recharge is significant due to the low topography and
sandy loam soil cover. The alluvium is underlain by
consolidated sedimentary rocks which are often in
direct hydraulic connection  with the overlying de-
posits.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig
Silt and Clay

700-1000

Weight

5
4
3
2
1

5

3
General
Rating

9
6
8
6
9

6

6

Number

45
24
24
12
9

30

18
                                                                                DRASTIC Index  162
                                                  Setting 4 C River Alluvium


                                                      Feature         Range
                                                        Agricultural
                                                  Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



15-30
4-7
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig
Silt and Clay

700-1000



5 9
4 6
3 8
5 6
3 9

4 6

2 6
Agricultural
DRASTIC Index

45
24
24
30
27

24

12

186
                        Colorado Plateau and Wyoming Basin

                        (4D)  Alluvium and Dune Sand

                        This hydrogeologic setting is characterized by moder-
                        ate topography derived from unconsolidated alluvial
                        sediments that have formed under various deposi-
                        tional environments. These alluvial  deposits vary
                        from lacustrine deposits in the Wyoming  Basin area
                        to dune sands in the Navajo area of northern Arizona
                        and northwestern New Mexico. Much of the entire
                        region  is covered by thin alluvium. The hydraulic
                        conductivity of the alluvium is  high throughout the
                        area, including the sand dunes portion. Recharge is
                        limited by low precipitation and evaporation. The
                        alluvium serves as moderate water supplies in some
                        areas; provides some discharge to streams, and acts
                        as storage for recharge to deeper aquifers.
                                                                        63

-------
Setting 4 D Alluvium and Dune Sand
                                       General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
0-2
Sand and Gravel
Sand
6-12%
S & G w/sig.
Silt and Clay

100-300
Weight

5
4
3
2
1

5

3
Rating

3
1
8
9
5

6

2
Number

15
4
24
18
5

30

6
                                  DRASTIC Index   102
Setting 4 O Alluvium and Dune Sand
                                     Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
0-2
Sand and Gravel
Sand
6-12%
S & G w/sig.
Silt and Clay

1 00-300
Weight

5
4
3
5
3

4

2
Rating

3
1
8
9
5

6

2
Number

15
4
24
45
15

24

4
• Agricultural
DRASTIC Index
131
                           64

-------
                                        5.   High Plains

                       (Thick alluvial deposits over fractured sedimentary rocks)
The High Plains region occupies an area of 450,000
km2 extending from South Dakota to Texas. The plains
are a remnant of a great alluvial plain built in Miocene
time by streams that flowed east from the Rocky
Mountains. The  plain originally extended from the
foot of the mountains to a terminous some hundreds
of kilometers east of its present  edge. Erosion by
streams  has removed  a  large part of  the  once
extensive plain, including all of the part adjacent to
the mountains, except in a small area in southeastern
Wyoming.
The original depositional surface of the alluvial plain
is still almost unmodified in large areas, especially in
Texas and New Mexico, and forms a flat, imperceptibly
eastward-sloping  tableland  that  ranges  in altitude
from about 2,000 m near the Rocky Mountains to
about 500 m along its eastern edge. The surface of
the southern High Plains contains numerous shallow
circular depressions, called playas, that intermittently
contain water following heavy rains. Some geologists
believe these  depressions  are due to solution of
soluble materials by percolating  water and accom-
panying compaction of the alluvium. Other significant
topographic features include sand dunes, which are
especially prevalent in central and northern Nebraska,
and  wide,  downcut valleys of streams that flow
eastward across the area from the Rocky Mountains.

The High Plains region is underlain by one of the most
productive and most intensively developed aquifers in
the United States. The alluvial materials derived from
the Rocky Mountains, which are referred to as the
Ogallala Formation, are the dominant geologic unit of
the High  Plains  aquifer. The Ogallala  ranges in
thickness from a few meters to more than 200 m and
consists of poorly sorted and generally unconsolidated
clay, silt, sand, and gravel.

Younger alluvial materials of Quaternary age overlie
the Ogallala Formation of late Tertiary age in most
parts of the High Plains.  Where these deposits are
saturated, they form a part of the High Plains aquifer;
in parts of south-central Nebraska and central Kansas,
where the Ogallala  is absent, they comprise the
entire aquifer. The Quaternary deposits are composed
largely of material  derived from the  Ogallala and
consist of alluvial deposits of gravel, sand, silt, and
clay  and  extensive areas of sand dunes. The most
extensive area of dune sand occurs in the Sand Hills
area north of the Platte River in Nebraska.

Other, older geologic units  that are hydrologically
connected to the Ogallala thus form a part of the High
Plains aquifer, includetheArikaree Group of Miocene
age and a small part of the underlying  Brule Forma-
tion. The Arikaree Group underlies  the Ogallala in
parts of  western Nebraska, southwestern  South
Dakota, southeastern Wyoming, and  northeastern
                                                65

-------
Colorado. It is predominantly a massive, very fine to
fine-grained sandstone that locally contains beds of
volcanic ash, siIty sand, and sandy clay. The maximum
thickness of the Arikaree is about 300 m, in western
Nebraska. The  Brule  Formation of  Oligocene age
underliesthe Arikaree. In most of the area in which it
occurs, the Brule forms the base of the High Plains
aquifer. However,  in  the southeastern corner of
Wyoming  and the  adjacent  parts of Colorado and
Nebraska, the Brule contains fractured sandstones
hydrauhcally interconnected to the overlying Arikaree
Group; in this area the Brule is considered to be a part
of the High Plains aquifer.

In the remainder of the region, the High Plains aquifer
is underlain by several formations,  ranging in age
from Cretaceous to Permian and composed principally
of shale, limestone, and  sandstone. The oldest of
these, of Permian age, underlies parts of northeastern
Texas,  western Oklahoma, and  central Kansas and
contains layers of relatively soluble minerals includ-
ing gypsum, anhydrite, and halite  (common  salt)
which  are dissolved  by circulating  ground water.
Thus, water from the rocks of Permian age is relatively
highly mineralized  and not usable for irrigation and
other purposes that require freshwater. The  older
formations in the  remainder of the  area contain
fractured sandstones and  limestones interconnected
in parts of the area with the High  Plains aquifer.
Although these formations yield freshwater, they are
not widely used as  water sources.

Prior to the erosion that removed most of the western
part of  the Ogallala,  the High  Plains aquifer was
recharged by the streams that flowed onto the plain
from the mountains to the west as well as by  local
precipitation. The only source of recharge now is local
precipitation, which ranges from about 400 mm along
the western boundary of the  region to about 600 mm
along  the  eastern  boundary.  Precipitation and
ground-water recharge on the High Plains vary in an
east-west direction, but recharge to the High Plains
also varies in a north-south direction. The average
annual rate of recharge has been determined to range
from about 5 mm in Texas and New Mexico to about
100 mm in the Sand Hills in Nebraska. This large
difference is explained by differences in evaporation
and transpiration and by differences in the permeabil-
ity of the surficial materials.

In some parts  of the  High Plains, especially in the
southern part, the near-surface layers of the Ogallala
have been cemented with lime (calcium carbonate) to
form a material of relatively low permeability  called
caliche. Precipitation  on areas underlain by caliche
soaks slowly into the ground. Much of this precipita-
tion collects in playas that are underlain by silt and
clay, which hamper infiltration, with the result that
most of the water is lost to evaporation. During years
of  average or  below  average  precipitation,  all or
nearly all of the precipitation  is returned to the
atmosphere  by evapotranspiration. Thus, it is only
during years of excessive precipitation that significant
recharge occurs and this, as noted above, averages
only about 5 mm per year in the southern part of the
High Plains.

In the Sand Hills area, the lower evaporation and
transpiration and the permeable sandy soil results in
about 20 percent of the precipitation (or about 100
mm annually) reaching the water table as recharge.

The water table of the High Plains  aquifer has a
general slope toward the east of about 2 to 3 m per km
(10 to 15 ft per mile). Gutentag and Weeks (1980)
estimate, on  the  basis  of the  average hydraulic
gradient and aquifer characteristics, that water moves
through the aquifer at a rate of about 0.3 m (1 ft)  per
day.

Natural discharge from the aquifer occurs to streams,
to springs and seeps along  the eastern boundary of
the plains, and by evaporation and transpiration in
areas where the water table is within a few meters of
the land surface.  However, at  present the largest
discharge is probably through wells. The widespread
occurrence of permeable layers of sand and gravel,
which permit the construction  of large-yield wells
almost any place  in the  region, has  led to  the
development of an extensive agricultural economy
largely dependent on irrigation. Gutentag and Weeks
(1980)  estimate that  in 1977 about 3.7  x  1010 m3
(30,000,000 acre-ft) of water was pumped from more
than  168,000  wells to irrigate  about 65,600 km2
(16,210,000 acres). Most of this water is derived from
ground-water storage, resulting in a long-term con-
tinuing decline in ground-water levels in parts of the
region of as much as 1 m per year. The lowering of the
water table has resulted  in a  10 to 50  percent
reduction in the  saturated thickness of the High
Plains aquifer in an area of 130,000 km2 (12,000 mi2).
The largest reductions  have occurred in the Texas
panhandle and in parts of Kansas and New Mexico.

The depletion of ground-water storage  in the High
Plains, as reflected in the decline in the water table
and the reduction  in the saturated thickness, is a
 matter of increasing concern in the region. However,
from the standpoint of the  region as a whole,  the
depletion does not yet represent a large part  of the
storage that is available for use. Weeks and Gutentag
(1981) estimate, on the basis of a specific yield of 1 5
 percent of the total volume of saturated material, that
the available (usable) storage in 1980 was about 4 x
 1012  m3 (3.3 billion acre-ft). Luckey, Gutentag,  and
Weeks (1981) estimate that this is only  about 5
 percent less than the storage that was available at the
 start of withdrawals. However, in areas where intense
 irrigation has long  been  practiced, depletion of
 storage is severe.
                        66

-------
High Plains

(5A)  Ogallala

This hydrogeologic setting is characterized by moder-
ately flat topography and thick deposits of poorly-
sorted, semi-consolidated, clay, silt, sand and gravel
that may be underlain by fractured sedimentary rock
which  are  in  hydraulic connection with overlying
deposits. In some parts of the High Plains, especially
in the southern part, shallow zones of the unconsoli-
dated deposits have been cemented  with  calcium
carbonate.  The  permeability of  this  caliche layer
varies with  the degree of cementation, fracturing, and
clay mineral content. Precipitation averages less than
20 inches per year and recharge is very low through-
out most of this water deficient area. The bedrock and
the overlying semi-consolidated deposits both serve
as extensive sources of ground water. Water  levels
are typically  deep,  but extremely  variable. The
Ogallala is underlain  by bedded, unconsolidated
deposits of fractured sandstone, volcanic ash, silty
sand, sandy clay, and shales. These formations are
hydraulically connected  to  the  Ogallala, and  the
overlying alluvium, from  which they derive their
recharge.

Setting 5 A Ogallala
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
0-2
Sand and Gravel
Shrink/Agg. Clay
2-6%
S & G w/sig.
Silt and Clay

700-1 000

Weight

5
4
3
2
1

5

3
General
Rating

2
1
8
7
9

6

6

Number

10
4
24
14
9

30

18
Setting 5 A Ogallala


    Feature        Range
      Agricultural
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



75-100
0-2
Sand and Gravel
Shrink/ Agg. Clay
2-6%
S & G w/sig.
Silt and Clay

700-1000



5 2
4 1
3 8
5 7
3 9

4 6

2 6
Agricultural
DRASTIC Index

10
4
24
35
27

24

12

136
High Plains
(SB)  Alluvium
This hydrogeologic setting is characterized by low to
moderate relief, and is comprised of gravel, sand, silt,
and clay alluvial  sediments. These deposits are
variable in thickness. They form, where saturated, a
portion of the High Plains aquifer, and locally all of it
where the Ogallala is missing. Water  levels are
variable, but  typically  deep.  Recharge  is  limited
throughout most of the area by low precipitation. The
shallow caliche layer of cemented, unconsolidated
deposits also  develops  in  the  alluvium in some
localities. Similar to the Ogallala, recharge  to the
deeper sandstones is through the alluvial deposits.
                              DRASTIC Index  109
                                                                          67

-------
Setting 5 B Alluvium
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

50-75
0-2
Sand and Gravel
Sandy Loam
0-2%
S & G w/sig.
Silt and Clay

300-700

Weight

5
4
3
2
1

5

3
General
Rating

3
1
8
6
10

6

4

Number

15
4
24
12
10

30

12
Setting 5 B Alluvium
                              DRASTIC Index  107
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

50-75
0-2
Sand and Gravel
Sandy Loam
0-2%
S & G w/sig.
Silt and Clay

300-700


Weight Rating

5 3
4 1
3 8
5 6
3 10

4 6

2 4
Agricultural
DRASTIC Index
Number

15
4
24
30
30

24

8

135
                                                    Setting 5 C Sand Dunes
                                                                                      General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
0-2
Sand and Gravel
Sand
2-6%

Sand and Gravel

2000+
Weight

5
4
3
2
1

5

3
Rating

5
1
8
9
9

8

10
Number

25
4
24
18
9

40

30
                                                                                 DRASTIC Index  150
High Plains

(5C)  Sand Dunes

This hydrogeologic setting is characterized by hilly
topography comprised of sand dunes which overlie
thick poorly-sorted sand and gravel deposits. The
sand dunes are in direct hydraulic connection with
the underlying deposits.  Because of their relatively
low water table, these dunes do not serve as sources
of ground water, but serve as local recharge areas. In
contrast to other areas of the High Plains, recharge
rates  are  higher  due to  lower evaporation and
permeable sandy soils, but are limited by available
precipitation.
                                                    Setting 5 C Sand Dunes
Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

30-50
0-2
Sand and Gravel
Sand
2-6%

Sand and Gravel

2000+


Weight Rating

5 5
4 1
3 8
5 9
3 9

4 8

2 10
Agricultural
DRASTIC Index
Number

25
4
24
45
27

32

20

177
                                                    High Plains
                                                    (5D)  Play a Lakes

                                                    This hydrogeologic  setting is  characterized by low
                                                    topographic relief and thin layers of clays and other
                                                    fine grained  sediments which overlie the  alluvial
                        68

-------
deposits. The playa areas serve as a catchment for
water during periods of  significant runoff. Ground
water is obtained from  the  layers of sand which
underlie the finer-grained deposits. Water levels are
extremely variable, but are typically deep. The playa
beds are significant recharge areas due to the rainfall
that collects in  them. The  rate  of recharge, as
compared to evaporation, is largely a function of the
permeability of the materials forming the bed of the
playa, and the distribution, in time, of precipitation.
Setting 5 D Playa Lakes
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
0-2
Sand and Gravel
Shrmk/Agg. Clay
0-2%
S & G w/sig
Silt and Clay

700-1 000

Weight

5
4
3
2
1

5

3
General
Rating

2
1
8
7
10

6

6

Number

10
4
24
14
10

30

18
Setting S D Playa Lakes

    Feature         Range
                              DRASTIC Index  110
      Agricultural
Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



75-100
0-2
Sand and Gravel
Shrink/ Agg. Clay
0-2%
S & G w/sig.
Silt and Clay

700-1000



5 2
4 1
3 8
5 7
3 10

4 6

2 6
Agricultural
DRASTIC Index

10
4
24
35
30

24

12

139
                        High Plains

                        (5E)  Braided River Deposits
                        This hydrogeologic setting is characterized by deposits
                        of alluvium  which occur within the flood plain of
                        streams and rivers. The stream is characterized by a
                        low gradient, wide channel and a series of inter-
                        connected shallow channels which form  a braided
                        pattern. Water levels are typically shallow,  and some
                        streams  may  be intermittent. The  river  alluvium
                        sometimes serves as a significant  source of ground
                        water but is most important as a source of recharge
                        since it overlies more productive semi-consolidated
                        deposits. The  underlying  deposits are  in  direct
                        hydraulic connection with the overlying alluvium, so
                        the potential for pollution  of the aquifer is high.
                        Although precipitation, which averages less than 20
                        inches per year is a limiting factor, recharge may be
                        very high due to seasonal or perennial stream flow on
                        these very permeable deposits.
                        Setting 5 E Braided River Deposits

                            Feature        Range
                                                                                      General
                                                                               Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

5-15
4-7
Sand and Gravel
Sand
0-2%

Sand and Gravel

1 000-2000

5
4
3
2
1

5

3

9
6
8
9
10

8

8

45
24
24
18
10

40

24
                                                                                  DRASTIC Index  185
                                                                          69

-------
Setting 5 E Braided River Deposits
                                       Agricultural
     Feature	Range	Weight   Rating   Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
5-15
4-7
Sand and Gravel
Sand
0-2%
Sand and Gravel
1 000-2000
5
4
3
5
3
4
2
9
6
8
9
10
8
8
Agricultural
DRASTIC Index
45
24
24
45
30
32
16
216
                             70

-------
                              6.  Nonglaciated Central Region

                           (Thin regolith over fractured sedimentary rocks)
                                                 west. The part of the region in eastern Colorado and
                                                 northeastern New Mexico is separated from the
                                                 remainder of the region by the High Plains region. The
                                                 Nonglaciated Central region also includes theTriassic
                                                 Basins  in Virginia and  North  Carolina  and the
                                                 "driftless" area in Wisconsin, Minnesota, Iowa, and
                                                 Illinois where glacial deposits, if present, are thin and
                                                 of no hydrologic importance. The region is a topo-
                                                 graphically complex area that ranges from the Valley
                                                 and Ridge section of the Appalachian Mountains on
                                                 the east westward across the Great Plains to the foot
                                                 of the Rocky Mountains. It includes, among other hilly
                                                 and mountainous areas,  the Ozark  Plateaus  in
                                                 Missouri and Arkansas. Altitudes range from 150 m
                                                 above sea level in central Tennessee and Kentucky to
                                                 1,500 m along the western boundary of the region.
                                                 The region is also geologically complex. Most of it is
                                                 underlain by consolidated sedimentary rocks that
                                                 range in age from Paleozoic to Tertiary and consist
                                                 largely of sandstone, shale, carbonate rocks (lime-
                                                 stone and dolomite), and conglomerate. A small area
                                                 in Texas  and  western Oklahoma is  underlain by
                                                 gypsum. Throughout most of the region  the rock
                                                 layers  are horizontal  or  gently dipping.  Principal
                                                 exceptions are the Valley and Ridge section of the
                                                 Wichita and Arbuckle Mountains in Oklahoma, and
                                                 the Ouachita Mountains in Oklahoma and Arkansas,
                                                 in all of which  the rocks have been folded and
                                                 extensively faulted. Around the Black Hills and along
                                                 the eastern  side of the Rocky Mountains  the rock
                                                 layers have been bent up sharply toward the moun-
                                                 tains and truncated by erosion. The Triassic Basins in
                                                 Virginia and North Carolina are underlain by moderate.
                                                 to gently dipping beds of shale and sandstone that
                                                 have been extensively faulted and invaded by narrow
                                                 bodies of igneous rock. These basins were formed in
                                                 Triassic time when major faults in the crystalline
                                                 rocks of the Piedmont resulted in the formation of
                                                 structural depressions up to several thousand meters
                                                 deep and more than 25 km wide and 140 km long.
The nonglaciated Central region is an area of about
1,737,000  km2 extending from  the  Appalachian
Mountains on the east to the Rocky Mountains on the
The land surface in most of the region is underlain by
regolith formed by chemical and mechanical break-
down of the bedrock. In the western part of the Great
                                               71

-------
Plains the residual soils are overlain by or intermixed
with eolian (wind-laid) deposits. The  thickness and
composition of the regolith depend on the composi-
tion and structure of the parent  rock  and on the
climate, land cover, and topography. In areas under-
lain by relatively pure limestone, the regolith consists
mostly of clay and is generally only a few meters thick.
Where the limestones contain chert  and in areas
underlain  by shale and sandstone, the regolith is
thicker, up to 30 m or more in some areas. The chert
and sand form moderately permeable soils, whereas
the soils developed on shale are finer grained and less
permeable.
Recharge of the ground-water system in this region
occurs primarily in the outcrop areas of the bedrock
aquifers in the uplands between streams. Precipita-
tion inthe region ranges from about 400 mm per year
in the western part to more  than 1,200 mm in the
eastern part. This wide difference in precipitation is
reflected in recharge rates, which range from about 5
mm per year  in west Texas and New Mexico to as
much as 500 mm  per  year in Pennsylvania  and
eastern Tennessee. Discharge from the ground-water
system is by springs and seepage into streams and by
evaporation and  transpiration  in areas where the
water table is within a few meters of land surface.
The principal water-bearing openings in the bedrock
are fractures along which the rocks have been broken
by stresses imposed on the Earth's crust at different
times since the rocks were consolidated. The fractures
generally occur in three sets. The first set, andtheone
that  is probably of greatest importance from  the
standpoint of ground water and well yields, consists
of fractures developed along the contact between
different  rock layers, in other words, along bedding
planes. Where the sedimentary  layers making up the
bedrock are essentially horizontal, the bedding-plane
fractures are more or less parallel to the land surface.
The two remaining sets of fractures are essentially
vertical and thus cross the bedding planes at a steep
angle. The primary difference between the sets of
vertical fractures is in the orientation of the fractures
in each set. For example, in parts of the region one set
of vertical fractures is  oriented in a northwest-
southeast direction and the other  set in a northeast-
southwest direction. The vertical  fractures facilitate
movement of water across the  rock layers and thus
serve as the principal hydraulic connection between
the bedding-plane fractures.
In parts of the region in which the bedrock has been
folded or  bent, the occurrence and orientation of
fractures are more complex. In these areas the dip of
the rock layers and the  associated bedding-plane
fractures range from horizontal to vertical. Fractures
parallel to the land surface,  where  present, are
probably less numerous and of more limited  extent
than in areas of flat-lying rocks.
The openings developed along most fractures are less
than a millimeter wide. The principal exception occurs
in limestones and dolomites, which are more soluble
in water than most other rocks. Water moving through
these rocks gradually enlarges the fractures to form,
in time, extensive cavernous  openings  or  cave
systems. Many large springs  emerge from  these
openings; one in this region is Big Spring, in Missouri,
which has an average discharge of 36.8 m3 sec"1.
The yield of wells depends on (1) the number and size
of fractures  that are penetrated and the extent to
which they have been enlarged by solution, (2) the
rate of recharge, and (3) the storage capacity of the
bedrock and regolith. Yields of wells in most of the
region are small, in the range of 0.01 to 1 m3 min~1
(about 2.5 to about 250 gallons per minute), making
the Nonglaciated Central  region  one of  the  least
favorable ground-water regions in the country. Even
in parts of the areas underlain  by cavernous  lime-
stone, yields are moderately low because of both the
absence of a thick regolith and  the  large water-
transmitting  capacity  of the  cavernous  openings
which quickly discharge the water that reaches them
during periods of recharge.
The  exceptions  to the  small  well  yields are the
cavernous limestones of the Edwards Plateau, the
Ozark Plateaus, and the Ridge and Valley section. The
Edwards Plateau in Texas is bounded on the south by
the Balcones Fault Zone, in which limestone and
dolomite up to 1  50 m in thickness has been exten-
sively faulted. The faulting has facilitated the devel-
opment of solution openings which makes this zone
one of the most  productive aquifers in the country.
Wells of the City of San Antonio are located in thrs
zone; individually, they have yields of more than 60
m3
Another  feature that makes much of this region
unfavorable for  ground-water development is the
occurrence of salty water at relatively shallow depths.
In most of the Nonglaciated Central region, except the
Ozark Plateaus, the Ouachita and Arbuckle Moun-
tains, and the Ridge and Valley section, the water in
the bedrock contains more than 1,000 mg/l of dis-
solved solids at depths less than 1 50 m. Most of the
salty water is believed to be connate— that is, it was
trapped in the rocks when they emerged from the sea
in which they were deposited. Other possible sources
include: (1 ) seawater that entered the rocks during a
later time when the land again was beneath the sea;
and (2) salty water derived  from solution of salt beds
that underlie parts of the region.
                       72

-------
The presence of connate water at relatively shallow
depths is doubtless due to several factors, including,
in the western part of the area,  a semiarid climate
and, consequently, a  small rate  of recharge. Other
factors probably include an extremely slow rate of
ground-water circulation at depths greater than a few
hundred meters.
Setting 6 A Mountain Slopes
                                  General
Non-Glaciated Central

(6A)  Mountain Slopes

This hydrogeologic setting is characterized by rela-
tively steep slopes on the side of mountains or hills, a
thin soil cover and fractured bedrock. Ground water is
obtained primarily from the fractures in the bedrock
which  may be  of  sedimentary,  metamorphic or
igneous origin but which are commonly alternating
sedimentary layers, and  also from bedding planes
between the sedimentary layers. The fractures pro-
vide only localized sources of ground water and well
yields are typically  limited. Although  precipitation
may be  significant in some areas, due to the steep
slopes, thin soil cover, and small storage capacity of
the fractures, runoff is significant and ground-water
recharge is low. Water levels are extremely variable
but are commonly moderately deep. Perched ground-
water zones are  common. These sedimentary  rocks
may range in attitude from nearly horizontal,  as in
parts of  the western Appalachian Plateau, to steeply
dipping, as seen in the Valley and Ridge province, the
Wichita, Arbuckle,  and Ouachita  Mountains, the
Black Hills, and on the eastern slopes of the Rockies.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
0-2
Thin Bedded SS,
LS, SH Sequences
Thin or Absent
12-18%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
2
1

5

3
Rating

5
1

6
10
3

6

1
Number

25
4

18
20
3

30

3
                             DRASTIC Index  103
Setting 6 A Mountain Slopes

    Feature        Range
     Agricultural
Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



30-50
0-2
Thin Bedded SS,
LS, SH Sequences
Thin or Absent
12-18%
Bedded LS,
SS, SH

1-100



5 5
4 1

3 6
5 10
3 3

4 6

2 1
Agricultural
DRASTIC Index

25
4

18
50
9

24

2

132
                                                   Non-Glaciated Central
                                                   (6B)  Alluvial Mountain Valleys
                                                   This hydrogeologic setting is characterized by thin
                                                   bouldery alluvium which overlies fractured bedrock of
                                                   sedimentary,  metamorphic or  igneous origin  but
                                                   which is commonly comprised of alternating sedi-
                                                   mentary layers. The alluvium, which is derived from
                                                   the surrounding slopes, serves as a localized source
                                                   of water. Water is obtained from sand and gravel
                                                   layers which are interspersed between finer-grained
                                                   deposits. Surficial deposits have typically weathered
                                                   to a sandy loam. Water levels are relatively shallow
                                                   but may be extremely variable. Ground water may
                                                   also be obtained from the fractures in the underlying
                                                   bedrock which are typically in direct hydraulic con-
                                                   nection with the overlying alluvium.
                                                                        73

-------
                                                   Non-Glaciated Central
                                                   (6C)  Mountain Flanks

                                                   This hydrogeologic setting is characterized by moder-
                                                   ate topographic relief and moderately-dipping, frac-
                                                   tured, consolidated, sedimentary rocks. Soil cover is
                                                   usually  thicker than on the  mountain slopes and
                                                   typically has weathered to a sandy loam. Although
                                                   precipitation can be significant, ground-water re-
                                                   charge is only moderate due to the slope. Water levels
                                                   are typically  moderately deep although they  are
                                                   extremely variable. The mountain flanks serve as the
                                                   recharge area for aquifers which are confined in
                                                   adjacent areas. Ground water is obtained from the
                                                   permeable sedimentary rocks or from fractures in the
                                                   sedimentary rocks.  The sedimentary rocks may be
                                                   underlain  by fractured bedrock of igneous, meta-
                                                   morphic or sedimentary origin which yield little water.
                                                   Sedimentary beds may be either horizontal or dipping,
                                                   as indicated for the higher mountain slopes (6A), and
                                                   have a similar geographic distribution.
Setting 6 B Alluvial Mountain Valleys
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig.
Silt and Clay

700-1 000

Weight

5
4
3
2
1

5

3
General
Rating

7
6
8
6
9

6

6

Number

35
24
24
12
9

30

18
                              DRASTIC Index  152
Setting 6 B Alluvial Mountain Valleys
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig.
Silt and Clay

700-1 000
Weight

5
4
3
5
3

4

2
Rating

7
6
8
6
9

6

6
Number

35
24
24
30
27

24

12
Agricultural
DRASTIC Index
176
                                                   Setting 6 C Mountain Flanks
                                                                                      General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
2-4
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
6-12%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
2
1

5

3
Rating

5
3

6
6
5

6

1
Number

25
12

18
12
5

30

3
                                                                                 DRASTIC Index  105
                        74

-------
Setting 6 C Mountain Flanks
                                 Agricultural
Setting 6 Da Alternating SS, LS, SH—Thin Soil
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
2-4
Thin Bedded SS,
IS, SH Sequences
Sandy Loam
6-12%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
5
3

4

2
Rating

5
3

6
6
5

6

1
Number

25
12

18
30
15

24

2
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Thin Bedded SS,
LS, SH Sequences
Loam
2-6%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
2
1

5

3
Rating

7
6

6
5
9

6

1
Number

35
24

18
10
9

30

3
Agricultural
DRASTIC Index
126
DRASTIC Index
129
Non-Glaciated Central

(6Da)  Alternating SS, LS, and SH—Thin Soil
                                          \
This hydrogeologic setting is characterized by low to
moderate topographic  relief, relatively thin loamy
soils overlying  horizontal  or slightly dipping alter-
nating layers of fractured consolidated sedimentary
rocks.  Ground  water  is  obtained  primarily from
fractures along bedding planes or intersecting vertical
fractures. Precipitation varies widely in the  region,
but recharge  is moderate where precipitation is
adequate. Water levels are extremely variable but on
the average  moderately  shallow. Shale  or clayey
layers often form  aquitards, and where sufficient
relief is present, perched ground-water zones of local
domestic importance are often developed.
                                                   Setting 6 Da Alternating SS, LS, SH—Thin Soil
                                                                                   Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Thin Bedded SS,
LS.SH Sequences
Loam
2-6%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
5
3

4

2
Rating

7
6

6
5
9

6

1
Number

35
24

18
25
27

24

2
Agricultural
DRASTIC Index
155
                                                   Non-Glaciated Central

                                                   (6Db)  Alternating SS, LS, and SH—Deep Regolith

                                                   This hydrogeologic setting is identical to 6Da Alter-
                                                   nating SS, LS, and SH—Thin Soil except that the
                                                   surficial deposits typically have been  weathered to
                                                   form clay loams which grade into weathered bedrock
                                                   which help retard the movement of pollutants through
                                                   the ground to the water  table. These  thick  soil
                                                   deposits are usually in direct,  hydraulic connection
                                                   with the underlying fractured sedimentary deposits.
                                                                         75

-------
Setting 6 Db Alternating SS, LS, SH— Deep
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
2-6%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
2
1

5

3
Regolith
General
Rating

7
6

6
6
9

6

1

Number

35
24

18
12
9

30

3
                             DRASTIC Index  131
Setting 6 Db Alternating SS, LS, SH-
-Deep Regolith
    Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
4-7
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
2-6%
Bedded LS,
SS, SH

1-100


Weight Rating

5 7
4 6

3 6
5 6
3 9

4 6

2 1
Agricultural
DRASTIC Index
Number

35
24

18
30
27

24

2

160
                                                   Non-Glaciated Central

                                                   (6E)  Solution Limestone
                                                   This hydrogeologic setting is characterized by moder-
                                                   ate, but variable, topographic relief and deposits of
                                                   limestone which have been partially dissolved along
                                                   bedding and fracture planes to form a network of
                                                   solution cavities and caves.  Soil is usually thin or
                                                   absent,  but where present is commonly  a  clayey
                                                   loam. Recharge  is usually greater than 10 inches per
                                                   year because the region receives significant amounts
                                                   of  rainfall  which  is easily recharged through  the
                                                   solution channels. Runoff return  through solution
                                                   channels into surface watercourses  is sometimes
                                                   very high. Water levels are typically moderately deep.
                                                   The limestone  serves  as a significant source of
                                                   ground water because of the high hydraulic conduc-
                                                   tivity of the solution channels. Caves  related to this
                                                   setting are widespread, but their greatest concentra-
                                                   tion occurs in a  band 200-400 miles wide extending
                                                   from central Missouri through western Virginia.
                                                   Setting 6 E Solution Limestone
                                                                                     General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
10+
Karst Limestone
Thin or Absent
6-12%

Karst Limestone

2000+
Weight

5
4
3
2
1

5

3
Rating

5
9
10
10
5

10

10
Number

25
36
30
20
5

50

30
                                                                                 DRASTIC Index   196
                        76

-------
Setting 6 E Solution Limestone

    Feature        Range
      Agricultural
                        Setting 6 Fa River Alluvium With Overbank
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



30-50
10+
Karst Limestone
Thin or Absent
6-12%

Karst Limestone

2000+



5 5
4 9
3 10
5 10
3 5

4 10

2 10
Agricultural
DRASTIC Index

25
36
30
50
15

40

20

216
Non-Glaciated Central

(6Fa)  River Alluvium With Overbank

This hydrogeologic  setting is characterized  by  low
topography and deposits of alluvium along parts of
stream valleys. Water is obtained  from sand and
gravel layers which are interbedded with finer grained
alluvial deposits. The floodplain is covered by varying
thicknesses of fine grained silt and  clay called
overbank deposits. The overbank thickness is usually
thicker along major streams (commonly  as much as
40 feet), and thinner along minor streams. Precipita-
tion varies widely over the region,  but  recharge is
somewhat  reduced  because of the  impermeable
nature of the overbank  deposits and subsequent
clayey loam soils  which typically cover the surface.
There is usually substantial recharge, however, due
to infiltration  from the  associated  stream.  Water
levels are typically moderately shallow. The alluvium
is commonly in direct hydraulic connection with the
underlying sedimentary rocks.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Sand and Gravel
Clay Loam
0-2%

Silt/Clay

1000-2000

Weight

5
4
3
2
1

5

3
General
Rating

7
8
8
3
10

1

8

Number

35
32
24
6
10

5

24
                                                                                 DRASTIC Index  136
                                                    Setting 6 Fa River Alluvium With Overbank
                                                                                    Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Sand and Gravel
Clay Loam
0-2%

Silt/Clay

1 000-2000
Weight

5
4
3
5
3

4

2
Rating

7
8
8
3
10

1

8
Number

35
32
24
15
30

4

16
Agricultural
DRASTIC Index
156
                         Non-Glaciated Central
                         (6Fb)  River Alluvium Without Overbank
                         This setting is identical to 6Fa River Alluvium with
                         Overbank  except  that no significant  fine grained
                         floodplain  deposits occupy the  stream valley. This
                         results in significantly higher recharge where precipi-
                         tation  is  adequate and sandy loam soils occur at the
                         surface.  Water levels are typically closer to the
                         surface because the fine-grained overbank deposits
                         are not present.
                                                                         77

-------
Setting 6 Fb River Alluvium Without Overbank
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
7-10
Sand and Gravel
Sandy Loam
0-2%

Sand and Gravel

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

9
8
8
6
10

8

8
Number

45
32
24
12
10

40

24
                              DRASTIC Index  187
Setting 6 Fb River Alluvium Without Overbank
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
7-10
Sand and Gravel
Sandy Loam
0-2%

Sand and Gravel
1 6*00-2000


Weight Rating

5 9
4 8
3 8
5 6
3 10

4 8
2 8
Agricultural
DRASTIC Index
Number

45
32
24
30
30

32
16

209
                                                    Setting 6 G Braided River Deposits
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

0-5
4-7
Sand and Gravel
Sand
0-2%

Sand and Gravel

1000-2000

Weight

5
4
3
2
1

5

3
General
Rating

10
6
8
9
10

8

8

Number

50
24
24
18
10

40

24
                                                                                  DRASTIC Index  190
Non-Glaciated Central

(6G)  Braided River Deposits

This hydrogeologic setting is characterized by deposits
of alluvium which occur within the  floodplain  of
streams and rivers. The stream is characterized by a
low gradient, wide channel and series of intercon-
nected shallow  channels which  form a  braided
pattern. Water levels  are typically shallow.  This
setting is found only in the western portion of this
ground-water region. The river alluvium does not
serve as a significant source of ground water where it
overlies more productive semi-consolidated deposits.
However, recharge from the river is substantial and
the  underlying deposits are in direct hydraulic con-
nection with the overlying alluvium; therefore, the
potential for pollution of the aquifer  is high. Although
precipitation commonly averages less than 20 inches
per  year,  recharge is relatively high due to the flat
topography and sandy surficial deposits.
                                                    Setting 6 G Braided River Deposits
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

0-5
4-7
Sand and Gravel
Sand
0-2%

Sand and Gravel

1000-2000


Weight Rating

5 10
4 6
3 8
5 9
3 10

4 8

2 8
Agricultural
DRASTIC Index
Number

50
24
24
45
30

32

16

221
Non-Glaciated Central
(6H)  Triassic Basins
This hydrogeologic setting is characterized by moder-
ately dipping, highly faulted beds of sandstone, shale,
and silty limestone. Conglomeritic deposits occur in
                         78

-------
some areas. These basins tend to be bounded by high
angle faults, with the basins being elongate in the
NE-SW directions. The sedimentary beds may be cut
by narrow (dikes, etc.) igneous intrusions, and are
sometimes indurated by the intrusive activity. The
Triassic formations are often red in color due to high
iron concentrations,  but green colors are also com-
mon. These deposits may serve as a localized source
of water and water levels are variable.
Setting 6 H Triassic Basins
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
4-7
Massive
Sandstone
Sandy Loam
2-6%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
5
3

4

2
Rating

2
6

6
6
9

6.

1
Number

10
24

18
30
27

24

2
Agricultural
DRASTIC Index
135
Setting 6 H Triassic Basins
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
4-7
Massive
Sandstone
Sandy Loam
2-6%
Bedded LS,
SS, SH

1-100
Weight

5
4

3
2
1

5

3
Rating

2
6

6
6
9

6

1
Number

10
24

18
12
9

30

3
                              DRASTIC Index  106
                                                                          79

-------
                                7.   Glaciated Central Region

                          (Glacial deposits over fractured sedimentary rocks)
The Glaciated Central  region occupies an area of
1,297,000 km2 extending from the Triassic Basin in
Connecticut and  Massachusetts  and the Catskill
Mountains  in New York on the east to the northern
part of the Great Plains in Montana on the west. The
part of the region in New York and Pennsylvania is
characterized  by rolling hills  and low,  rounded
mountains that reach altitudes of 1,500 m. Westward
across Ohio to the western boundary  of the region
along the Missouri River, the region is flat to gently
rolling.  Among the  more  prominent topographic
features in this part of the region are low, relatively
continuous ridges (moraines) which were formetl at
the margins of ice sheets  that moved southward
across the  area  one  or more times during the
Pleistocene age.
The Glaciated Central region is underlain by relatively
flat-lying consolidated sedimentary rocks that range
in age  from Paleozoic to Tertiary. They  consist
primarily of sandstone, shale, limestone, and dolo-
mite.  The  bedrock  is overlain  by glacfal deposits
which, in most of the area, consist chiefly of till, an
unsorted mixture of rock particles deposited directly
by the ice  sheets. The till is interbedded with and
overlain by sand and gravel deposited by meltwater
streams, by silt and clay deposited in glacial lakes,
and, in  large parts of the  North-Central States, by
loess,  a well-sorted  silt  believed to  have  been
deposited primarily by the wind.

On the Catskill Mountains and other  uplands in the
eastern part of the  region, the glacial deposits are
typically only a  few to several  meters thick, but
localized deposits as much as 30 m thick are common
on southerly slopes. In much  of the  central and
western  parts of the region, the glacial deposits
exceed 100 m in thickness. The principal exception is
the "driftless" area  in Wisconsin, Minnesota,  Iowa,
and Illinois, where the ice,  if it invaded the area, was
too thin to erode preexisting soils or to deposit a
significant thickness of till. Thus, the bedrock in this
area is overlain by thin soils derived  primarily from
weathering of the rock. This area, both  geologically
and  hydrologically,  resembles  the Nonglaciated
Central  region and is, therefore,  included as part of
that region.

The glacial  deposits are thickest in  valleys in the
bedrock surface; thicknesses of 100 to 300 m occur in
the valleys of the Finger Lakes in New York. In most of
the region  westward from Ohio to the Dakotas, the
thickness of the glacial deposits exceeds the relief on
the preglacial  surface, with the result that the
locations of valleys and  stream channels in the
preglacial surface are no longer discernible from the
land surface. The glacial deposits in valleys  include,
in addition to till and lacustrine silts and clays,
substantial thicknesses of highly permeable sand and
gravel.

Ground water occurs both in the glacial deposits and
in the bedrock. Water occurs in the glacial deposits in
pores between the rock particles and in the  bedrock
primarily  along  fractures. The  dominant water-
                                                80

-------
bearing fractures in the bedrock are along bedding
planes. Water also occurs in the bedrock in steeply
dipping fractures that cut across the  beds and,  in
some  sandstones and conglomerates,  in primary
pores  that were not  destroyed  in the  process  of
cementation and consolidation.

Large parts of the region are underlain by limestones
and  dolomites  in which  the fractures  have  been
enlarged by solution. Caves are relatively common in
the limestones where the ice sheets were relatively
thin, as near the southern boundary of the region and
in the "driftless" area. A few caves occur in other
parts of  the region,  notably in the Mohawk River
valley in  central  New York, where they were appar-
ently protected from glacial erosion by the configura-
tion of the bedrock surface over which the ice moved.
However, on the whole, caves and other large solution
openings, from  which large springs  emerge  and
which yield large quantities of water to wells in parts
of the Nonglaciated Central region,  are much  less
numerous and hydrologically much less important in
the Glaciated Central region.

The glacial deposits are recharged by precipitation on
the interstream areas and serve both as a source of
water to shallow wells and as a reservoir for recharge
to the underlying bedrock.  Precipitation ranges from
about 400 mm per year in the western part of the
region to about  1,000 mm  in  the  eastern  part.
Recharge also depends on the permeability of the
glacial deposits exposed at the land surface and on
the slope of the surface. On sloping hillsides underlain
by clay-rich till, the annual rate of recharge, even in
the humid eastern part of the region, probably does
not exceed 50 mm. In contrast, relatively flat areas
underlain by sand and gravel may receive as much as
300  mm of recharge annually in the eastern part of
the region. Recharge of the ground-water system in
the Glaciated Central region occurs primarily in the
fall, after plant growth has stopped and cool tempera-
tures have reduced evaporation, and again during the
spring thaw before plant  growth  begins. Of these
recharge periods, the spring thaw is usually dominant
except when fall rains are unusually heavy. Minor
amounts of rechargealso may occur during midwinter
thaws and during unusually wet summers.

Ground water in small to moderate amounts can be
obtained anyplace in the region, both from the glacial
deposits  and from the bedrock. Large to very large
amounts  are obtained from the  sand and gravel
deposits and from some of the limestones, dolomites,
and  sandstones in the North-Central States.  The
shales are the least productive bedrock formations in
the region.

As is the case in the Nonglaciated Central region,
mineralized water occurs at relatively shallow depth
in the bedrock in large parts of this region. Because
the principal constituent in the mineralized water is
sodium chloride (common salt), the water is com-
monly referred to as saline or salty. The thickness of
the freshwater zone  in the bedrock depends  on the
vertical hydraulic conductivity of both the bedrock and
the glacial deposits and on the effectiveness of the
hydraulic connection  between them. Both the fresh-
water and the underlying saline water move toward
the valleys of perennial streams to discharge. As a
result, the depth to saline water is less under valleys
than under uplands, both because of lower altitudes
and because of the upward movement of the saline
water  to  discharge.  In those parts  of  the  region
underlain by saline water, the  concentration of
dissolved solids  increases with depth. At depths of
500 to 1,000 m  in much of the region, the mineral
content of the water approaches that of seawater
(about 35,000 mg/l). At greater depths, the mineral
content may reach concentrations several times that
of seawater.

Because the Glaciated  Central region resembles in
certain aspects both the Nonglaciated Central region
(region 6) to  the south  and the Northeast and
Superior Uplands region (region 9) to the north, it may
be useful  to comment  on  the principal differences
among these three regions.  First,  and as is already
apparent,  the bedrock in the Glaciated Central and
the Nonglaciated Central regions is similar in compo-
sition and structure. The difference in  these two
regions is in the composition and other characteristics
of the overlying unconsolidated  material.  In the
Nonglaciated Central  region this material consists of
a relatively thin layer that is derived from weathering
of the underlying bedrock and that  in any particular
area is of relatively uniform composition.   In the
Glaciated  Central  region,  on the  other hand, the
unconsolidated  material consists of a layer, ranging
in thickness from a few meters to  several hundred
meters, of diverse composition  deposited  either
directly from glacial ice  (till) or by meltwater streams
(glaciofluvial deposits). From a hydrologic standpoint,
the unconsolidated  material in  the Nonglaciated
Central region  is  of  minor  importance  both as a
source of water and as a reservoir for storage of water
for the bedrock. In contrast, the glacial deposits in the
Glaciated  Central region serve both as a source of
ground water and as  an important storage reservoir
for the bedrock.

The Glaciated Central region and the Northeast and
Superior Uplands  region  are similar in that the
unconsolidated  material in both consists of  glacial
deposits. However, the  bedrock in the two regions is
different. The bedrock in the Glaciated Central region,
as we have already seen, consists of consolidated
sedimentary rocks  that  contain both steeply dipping
fractures and fractures along bedding planes. In the
Northeast and Superior Uplands, on the other hand.
                                                                        81

-------
the bedrock is composed  of intrusive igneous and
metamorphic rocks (nonbedded) in which most
water-bearing openings are steeply-dipping fractures.
Asa result of the differences in fractures, the bedrock
in the Glaciated Central region is, in general,  a more
productive  and more important source of ground
water than the bedrock in the Northeast and Superior
Uplands region.

The largest fresh-water supply in North America, the
Great Lakes, is located in this region. Bordering the
Great  Lakes, there  are abandoned  beach  ridges,
present-day beaches and sand dunes, all of which are
very sensitive environmental areas.
Setting 7 Aa Glacial Till Over Bedded Sedimentary Rock
                          	General	
    Feature
                 Range
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

30-50
4-7
Thin Bedded SS,
LS, SH Sequences
Clay Loam
2-6%

Silt/Clay

100-300

5
4

3
2
1

5

3

5
6

6
3
9

1

2

25
24

18
6
9

5

6
                                                                                DRASTIC Index   93
Glaciated Central

(7A a) Glacial Till Over Bedded Sedimentary Rocks

This  hydrogeologic setting is characterized by low
topography and relatively flat-lying, fractured sedi-
mentary  rocks consisting of sandstone, shale and
limestone which are covered by varying thicknesses
of glacial till. The till is chiefly  unsorted deposits
which  may  be interbedded with loess or  localized
deposits of sand and  gravel. Although ground water
occurs in both the glacial deposits and in the inter-
secting bedrock fractures, the bedrock is the principal
aquifer. The glacial till serves as a source of recharge
to the underlying bedrock. Although precipitation is
abundant in most of the region, recharge is moderate
because of the glacial till and soils which are typically
clay  loams. Depth to water  is extremely variable
depending in part on  the thickness of the glacial till,
but tends to average around 30 feet.
Setting 7 Aa Glacial Till Over Bedded Sedimentary Rock
                          	Agricultural
    Feature
                 Range
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



30-50
4-7
Thin Bedded SS,
LS, SH Sequences
Clay Loam
2-6%

Silt/Clay

1 00-300



5 5
4 6

3 6
5 3
3 9

4 1

2 2
Agricultural
DRASTIC Index

25
24

18
15
27

4

4

117
                                                   Glaciated Central
                                                   (7Ab) Glacial Till Over Outwash
                                                   This hydrogeologic setting is characterized by low
                                                   topography and outwash materials which are covered
                                                   by varying thicknesses of glacial till. The till is chiefly
                                                   unsorted deposits which  may be  interbedded with
                                                   loess or localized deposits of sand and gravel. Surf icial
                                                   deposits  have usually  weathered  to a  clay loam.
                                                   Although ground water occurs in  both  the glacial
                                                   deposits and in the underlying outwash, the outwash
                                                   serves as the principal aquifer because the fine-
                                                   grained deposits have been  removed  by glacial
                                                   meltwater. The  outwash is in direct hydraulic con-
                                                   nection with the glacial till and glacial till  serves as a
                                                   source of recharge for the underlying outwash. This
                                                   setting is similar to (7Aa) Glacial Till Over Bedded
                                                   Sedimentary Rock and (7Ac) Glacial Till Over Solution
                                                   Limestone in that although precipitation is abundant
                                                   in most of the region, recharge is moderate because
                        82

-------
of the relatively  low permeability of the overlying
glacial till. Depth to water table is extremely variable
depending in part on the thickness of the glacial till,
but averages around 30 feet.
                                   Glaciated Central

                                   (7Ac)  Glacial Till Over Solution Limestone

                                   This  hydrogeologic setting is characterized by low
                                   topography and solution limestone which are covered
                                   by varying thicknesses of glacial till. The till is chiefly
                                   unsorted deposits which may be interbedded with
                                   loess or localized deposits of sand and gravel. Surficial
                                   deposits  have usually  weathered to a clay loam.
                                   Although ground water occurs in both the glacial
                                   deposits and in the underlying limestone, the  lime-
                                   stone, which  typically  contains  solution  cavities,
                                   serves as the principal aquifer. The limestone is in
                                   direct hydraulic connection with the glacial till and
                                   the glacial till serves  as a source of recharge for the
                                   underlying limestone. This setting is similar to (7Aa)
                                   Glacial Till Over Bedded Sedimentary Rock and (7Ab)
                                   Glacial Till Over Outwash in that although precipita-
                                   tion is abundant in most of the region, recharge  is
                                   moderate because of the relatively low permeability
                                   of the overlying glacial till. Depth to water  table  is
                                   extremely variable depending in part on the thickness
                                   of the glacial till, but is typically moderately deep.
Setting 7 Ab Glacial Till Over Outwash
                                   General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Sand and Gravel
Clay Loam
2-6%

Silt/Clay

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

7
6
8
3
9

1

8
Number

35
24
24
6
9

5

24
                              DRASTIC Index   127
Setting 7 Ab Qlacial Till Over Outwash

    Feature
               Agricultural
Range
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



15-30
4-7
Sand and Gravel
Clay Loam
2-6%

Silt/Clay

1000-2000



5 7
4 6
3 8
5 3
3 9

4 1

2 8
Agricultural
DRASTIC Index

35
24
24
15
27

4

16

145
Setting 7 Ac Glacial Till Over Solution Limestone
                           	 General
    Feature
                                                                      Range
                                                              Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

30-50
4-7
Karst Limestone
Clay Loam
2-6%

Silt/Clay

2000+

5
4
3
2
1

5

3

5
6
10
3
9

1

10

25
24
30
6
9

5

30
                                                                                  DRASTIC Index   129
                                                                           83

-------
Setting 7 Ac Glacial Till Over Solution Limestone
                           	Agricultural

    Feature
                        Setting 7 Ad Glacial Till Over Sandstone
                  Range
We i g htR ating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

30-50
4-7
Karst Limestone
Clay Loam
2-6%

Silt/Clay

2000+

5
4
3
5
3

4

2

5
6
10
3
9

1

10

25
24
30
15
27

4

20
Agricultural
DRASTIC Index
145
                                                           General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
4-7
Massive
Sandstone
Clay Loam
2-6%

Silt/Clay

300-700
Weight

5
4

3
2
1

5

3
Rating

5
6

6
3
9

1

4
Number

25
24

18
6
9

5

12
                                                                                  DRASTIC Index
                                                                                                99
                                                    Setting 7 Ad Glacial Till Over Sandstone
                                                                                     Agricultural
Glaciated Central

(7A d)   Glacial Till O ver Sandstone

This  hydrogeologic setting is  characterized by low
topography and relatively flat-lying fractured sand-
stones which are covered by varying thicknesses of
glacial till. The till is chiefly unsorted deposits which
maybeinterbeddedwith loess or localized deposits of
sand and gravel. Although ground water occurs in
both the  glacial deposits  and in the intersecting
bedrock fractures, the bedrock is the principal aquifer.
The glacial till serves as a source of recharge to the
underlying bedrock. Although  precipitation is abun-
dant in most  of the region, recharge is moderate
because of the glacial tills which typically weather to
clay loam. Depth to water table is extremely variable,
depending in part on the thickness of the glacial till,
but tends to average around 40 feet.
. Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
4-7
Massive
Sandstone
Clay Loam
2-6%

Silt/Clay

300-700
Weight

5
4

3
5
3

4

2
Rating

5
6

6
3
9

1

4
Number

25
24

18
15
27

4

8
Agricultural
DRASTIC Index
121
                                                    Glaciated Central

                                                    (7A e)   Glacial Till O ver Shale
                                                    This hydrogeologic setting is similar to (7Ad) Glacial
                                                    Till Over Sandstone except that varying thickness of
                                                    till overlie fractured flat-lying shales. The till is chiefly
                                                    unsorted deposits with interbedded lenses  of loess
                                                    and sand and gravel. Ground water is derived from
                                                    either localized sources in the overlying till or from
                                                    deeper,  more permeable formations.  The shale is
                                                    relatively impermeable and does not serve as  a
                                                    source of ground water. Although precipitation is
                                                    abundant, recharge is minimal from the till to deeper
                                                    formations  and occurs only  by  leakage of  water
                                                    through the fractures.
                         84

-------
Setting 7 Ae Glacial Till Over Shale


    Feature
                 General
                 Range
          Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

30-50
4-7
Massive Shale
Clay Loam
2-6%

Silt/Clay

1-100

5
4
3
2
1

5

3

5
6
2
3
9

1

1

25
24
6
6
9

5

3
Setting 7 Ae Glacial Till Over Shale


    Feature
                             DRASTIC Index   78
               Agricultural
Range
Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



30-50
4-7
Massive Shale
Clay Loam
2-6%

Silt/Clay

1-100



5 5
4 6
3 2
5 3
3 9

4 1

2 1
Agricultural
DRASTIC Index

25
24
6
15
27

4

2

103
Glaciated Central
(7Ba)  Outwash
This hydrogeologic setting is characterized by moder-
ate to  low topography and varying thicknesses  of
outwash which overlie sequences of fractured sedi-
                        mentary  rocks. The outwash consists of water-
                        washed deposits of sand and gravel which serve as
                        the principal aquifer in the area. The outwash also
                        serves as a source of recharge to the underlying
                        bedrock. Precipitation is abundant throughout most
                        of the area  and  recharge is  moderate  to  high.
                        Recharge is somewhat restricted by the sandy loam
                        soil which typically develops in this setting. Water
                        levels are extremely variable but relatively shallow.
                        Outwash generally refers to water washed or ice
                        contact deposits, and can include a variety of morpho-
                        genic forms. Outwash plains are thick sequences of
                        sands and gravels that are laid down in sheet-like
                        deposits from  sediment laden  waters draining off,
                        and from within a glacier. These deposits are well
                        sorted and have relatively high permeabilities. Kames
                        and eskers are ice-contact deposits.  A kame is an
                        isolated hill or mound of stratified sediments depos-
                        ited in an opening within or between ice blocks, or
                        between  ice blocks and valley  walls. An esker is a
                        sinuous or meandering ridge of well sorted sands and
                        gravels that are remnants of streams  that existed
                        beneath and within the glaciers. These deposits may
                        be in direct hydraulic  connection  with underlying
                        fractured bedrock.
                                                   Setting 7 Ba Outwash
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Sand and Gravel
Sandy Loam
2-6%

Sand and Gravel

1000-2000

Weight

5
4
3
2
1

5

3
General
Rating

7
8
8
6
9

8

8

Number

35
32
24
12
9

40

24
                                                               DRASTIC Index  176
                                                                         85

-------
Setting 7 Ba Outwash
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range
15-30
7-10
Sand and Gravel
Sandy Loam
2-6%
Sand and Gravel
1 000-2000
Weight
5
4
3
5
3
4
2
Rating
7
8
8
6
9
8
8
Agricultural
DRASTIC Index
Number
35
32
24
30
27
32
16
196
Setting 7 Bb Outwash Over Bedded Sedimentary
                                 General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
10+
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
2-6%

Sand and Gravel

100-300
Weight

5
4

3
2
1

5

3
Rating

7
9

6
6
9

8

2
Number

35
36

18
12
9

40

6
                                                                               DRASTIC Index   156
Glaciated Central

(7Bb)  Outwash Over Bedded Sedimentary

This hydrogeologic setting is characterized by moder-
ate to low topography and relatively flat-lying, frac-
tured sedimentary rocks consisting of sandstones,
shales, and limestone which are covered by varying
thicknesses of glacial outwash. The outwash consists
of a variety of water-washed deposits of sand and
gravel which serve as the principal aquifer in the
areas.  The outwash  also  serves  as  a source of
recharge to the underlying bedrock. Precipitation is
abundant throughout most of the area and recharge
is moderate  to  high. Water levels are extremely
variable, but typically shallow.
                                                  Setting 7 Bb Outwash Over Bedded Sedimentary
                                                                                   Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
10+
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
2-6%

Sand and Gravel

100-300
Weight

5
4

3
5
3

4

2
Rating

7
9

6
6
9

8

2
Number

35
36

18
30
27

32

4
Agricultural
DRASTIC Index
182
                                                   Glaciated Central

                                                   (7Be)   Outwash Over Solution Limestone

                                                   This hydrogeologic setting is characterized by low
                                                   topography and solution limestone which is covered
                                                   by  varying thicknesses of glacial outwash. The
                                                   outwash consists of varying types of water-washed
                                                   deposits that typically weather to sandy loam soils.
                                                   Both the outwash and the solution limestone serve as
                                                   principal aquifers in the area. The solution limestone
                                                   is in direct hydraulic  connection with the  glacial
                                                   outwash  and the outwash serves  as a source of
                                                   recharge for the underlying limestone. Water levels
                                                   are extremely variable and in part dependent on the
                                                   thickness of the overlying outwash.
                        86

-------
Setting 7 Be Outwash Over Solution Limestone
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
10+
Karst Limestone
Sandy Loam
2-6%

Sand and Gravel

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

7
g
10
6
9

8

8
Number

35
36
30
12
9

40

24
                              DRASTIC Index  186
Setting 7 Be Outwash Over Solution Limestone
                           	Agricultural
    Feature         Range
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



15-30
10+
Karst Limestone
Sandy Loam
2-6%

Sand and Gravel

1000-2000



5 7
4 9
3 10
5 6
3 9

4 8

2 8
Agricultural
DRASTIC Index

35
36
30
30
27

32

16

206
Glaciated Central
(7C)  Moraine
This hydrogeologic setting is characterized by moder-
ate to  moderately steep topography and  varying
thicknesses of mixed glacial deposits which overlie
sequences of relatively flat-lying fractured sedimen-
                                                   tary rocks. This setting is similar to (7Ba) Outwash in
                                                   that the sand and gravel within the morainal deposits
                                                   may be well-sorted and serve as the principal aquifer
                                                   in the area. These deposits also serve as a source of
                                                   recharge for the underlying bedrock. Moraines also
                                                   contain  sediments that  are  typically unsorted and
                                                   unstratified; these deposits contain more fines than
                                                   outwash deposits, are less permeable and character-
                                                   istic of glacial till. Moraines are typically mounds or
                                                   ridges of till which were deposited along the margin
                                                   of a stagnant or retreating glacier. Surficial deposits
                                                   often weather  to  a sandy  loam. Precipitation is
                                                   abundant throughout the region and ground-water
                                                   recharge is  moderate.  Water  levels are extremely
                                                   variable, based in part on the thickness of the glacial
                                                   till, but are typically fairly shallow.
                                                    Setting 7 C Moraine
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Sand and Gravel
Sandy Loam
6-12%

Silt/Clay

300-700

Weight

5
4
3
2
1

5

3
General
Rating

7
8
8
6
5

1

4

Number

35
32
24
12
5

5

12
                                                                                  DRASTIC Index   125
                                                                          87

-------
Setting 7 C Moraine

    Feature        Range
     Agricultural
                        Setting 7 D Buried Valley
Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



15-30
7-10
Sand and Gravel
Sandy Loam
6-12%

Silt/Clay

300-700



5 7
4 8
3 8
5 6
3 5

4 1

2 4
Agricultural
DRASTIC Index

35
32
24
30
15

4

8

148
Glaciated Central

<7D)  Buried Valley

This hydrogeologic setting is characterized by thick
deposits of sand and gravel that have been deposited
in a former topographic low (usually a pre-glacial river
valley) by glacial meltwaters. These deposits  are
capable of yielding large quantities of ground water.
The deposits may or may not underlie a present-day
river and may  or may  not  be in direct hydraulic
connection  with  a stream. Glacial  till  or  recent
alluvium  often overlies the buried valley. Usually the
deposits are several times more permeable than the
surrounding bedrock, with finer  grained alluvium
covering  the underlying sand and gravel. Soils are
typically  a sandy loam.  Recharge to the sand and
gravel  is  moderate and water levels  are commonly
relatively shallow, although  they  may be quite
variable.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
7-10
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig
Silt and Clay

1 000-2000

Weight

5
4
3
2
1

5

3
General
Rating

5
8
8
6
9

6

8

Number

25
32
24
12
9

30

24
                                                   Setting 7 D Buried Valley
                                                                                 DRASTIC Index   156
                                                                                    Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
7-10
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig.
Silt and Clay

1 000-2000
Weight

5
4
3
5
3

4

2
Rating

5
8
8
6
9

6

8
Number

25
32
24
30
27

24

16
Agricultural
DRASTIC Index
178
                        Glaciated Central

                        (7Ea)  River Alluvium With Overbank Deposits

                        This hydrogeologic setting is characterized by  low
                        topography and thin to moderately thick deposits of
                        flood deposited alluvium along portions of the river
                        valley. The alluvium is underlain by fractured bedrock
                        of sedimentary, metamorphic, or igneous  origin.
                        Water is obtained from sand and gravel layers which
                        are interbedded with finer-grained alluvial deposits.
                        The floodplain is covered by varying thicknesses of
                        fine-grained silt and clay called overbank deposits.
                        The overbank thickness is usually greater along major
                        streams(as much as40feet) andthinner along minor
                        streams.  Precipitation  in  the region varies,  but
                        recharge is somewhat reduced because of the silty
                        and clayey overbank soils which typically cover the
                        surface. Water levels are moderately shallow. Ground
                        water is in direct hydraulic contact with the surface
                        stream. The alluvium  may serve as a significant
                        source of  water and  may also be in direct hydraulic
                        contact with the underlying sedimentary rocks.
                        88

-------
Setting 7 Ea River Alluvium With Overbank Deposit
                                   General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
4-7
Sand and Gravel
Silty Loam
0-2%

Silt/Clay

700-1000
Weight

5
4
3
2
1

5

3
Rating

7
6
8
4
10

1

6
Number

35
24
24
8
10

5

18
                               DRASTIC Index   124
Setting 7 Ea River Alluvium With Overbank Deposit
                                  Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
4-7
Sand and Gravel
Silty Loam
0-2%

Silt/Clay

700-1000


Weight Rating

5 7
4 6
3 8
5 4
3 10

4 1

2 6
Agricultural
DRASTIC Index
Number

35
24
24
20
30

4

12

149
Glaciated Central
(7Eb)  River Alluvium Without Overbank
This setting is identical to (6Fa) River Alluvium with
Overbank  except that no  significant fine-grained
floodplain  deposits occupy the stream valley. This
                                                     results in significantly higher recharge where precipi-
                                                     tation is adequate and  sandy  soils occur  at  the
                                                     surface. Water levels  are  moderate to  shallow in
                                                     depth. Hydraulic contact with the surface stream is
                                                     usually excellent, with alternating recharge/discharge
                                                     relationships varying  with stream  stage.  These
                                                     deposits also serve as a good source of recharge to
                                                     the underlying fractured bedrock.
                                                     Setting 7 Eb River Alluvium Without Overbank Deposit
                                                                                         General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

700-1000
Weight

5
4
3
2
1

5

3
Rating

9
9
8
9
10

8

6
Number

45
36
24
18
10

40

18
                                                                                    DRASTIC Index   191
                                                     Setting 7 Eb River Alluvium Without Overbank Deposit
                                                                                       Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

700-1000


Weight Rating

5 9
4 9
3 8
5 9
3 10

4 8

2 6
Agricultural
DRASTIC Index
Number

45
36
24
45
30

32

12

224
                                                                            89

-------
Glaciated Central

(7F)  Glacial Lake Deposits

This hydrogeologic  setting is characterized by flat
topography and varying thicknesses of fine-grained
sediments that overlie sequences of fractured sedi-
mentary rocks. The deposits are composed of fine-
grained silts and clays  interlayered with fine sand
that settled out in glacial lakes and exhibit alternating
layers relating to seasonal fluctuations. As a conse-
quence of  the thin alternating layers there  is  a
substantial difference between the vertical and
horizontal permeability with the horizontal commonly
two or more orders of magnitude greater than the
vertical. Due  to their fine-grained  nature, these
deposits typically weather to  organic-rich sandy
loams with a range in permeabilities  reflecting
variations in sand content. Underlying glacial deposits
or bedrock serve as the major source of ground water
in the region. Although precipitation is  abundant,
recharge is controlled  by  the  permeability of the
surface clays,  however, in all instances recharge  is
moderately  high because of the impact of the  low
topography. Water levels are variable, depending on
the thickness of the lake sediments and the underlying
materials.
Setting 7 F Glacial Lake Deposits


    Feature         Range     Weight   Rating  Number
General
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

15-30
4-7
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
0-2%
S & G w/sig.
Silt and Clay

100-300

5
4

3
2
1

5

3

7
6

6
6
10

6

2

35
24

18
12
10

30

6
                 Setting 7 F Glacial Lake Deposits


                     Feature        Range     Weight   Rating  Number
Agricultural
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



15-30
4-7
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
0-2%
S & G w/sig.
Silt and Clay

100-300



5 7
4 6

3 6
5 6
3 10

4 6

2 2
Agricultural
DRASTIC Index

35
24

18
30
30

24

4

165
                 Glaciated Central

                 (7G)  Thin Till Over Bedded Sedimentary

                 This hydrogeologic setting is characterized by moder-
                 ate to low topography and deposits of thin, patchy,
                 glacial till overlying  alternating layers of fractured
                 consolidated sedimentary  rocks.  The  till,  where
                 present, is primarily unsorted deposits of clay, sand,
                 and gravel. Although ground water occurs in both the
                 till and in the intersecting fractures of the bedrock,
                 the bedrock is the principal  aquifer. The glacial till
                 serves as a source of recharge to the underlying
                 bedrock. Although precipitation is abundant in most
                 of the region, recharge is moderate because  of the
                 glacial tills and  clayey soils. Water levels are ex-
                 tremely variable, but usually  moderate.
                              DRASTIC Index  135
                        90

-------
Setting 7 G Thin Till Over Bedded Sedimentary
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Thin Bedded SS,
LS, SH Sequences
Clay Loam
2-6%

Silt/Clay

1 00-300
Weight

5
4

3
2
1

5

3
Rating

7
8

6
3
9

1

2
Number

35
32

18
6
9

5

6
                              DRASTIC Index  111
Setting 7 G Thin Till Over Bedded Sedimentary
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
7-10
Thin Bedded SS,
LS, SH Sequences
Clay Loam
2-6%

Silt/Clay

100-300


Weight Rating

5 7
4 8

3 6
5 3
3 9

4 1

2 2
Agricultural
DRASTIC Index
Number

35
32

18
15
27

4

4

135
                                                    Setting 7 H Beaches, Beach Ridges and Sand Dunes
                                                                                       General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

0-5
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

10
9
8
9
10

8

8
Number

50
36
24
18
10

40

24
                                                                                  DRASTIC Index  202
Glaciated Central

(7H)   Beaches, Beach Ridges, and Sand Dunes

This hydrogeologic setting is characterized by low
relief,  sandy surface soil that is predominantly silica
sand, extremely high infiltration rates and low sorp-
tive capacity in the thin vadose zone. The water table
is very shallow  beneath the  beaches bordering the
Great  Lakes. These beaches  are commonly ground-
water  discharge areas. The  water table is slightly
deeper beneath  the rolling dune topography and the
vestigial inland beach ridges.  All of these areas serve
as recharge sources for the underlying sedimentary
bedrock  aquifers, and they often serve  as local
sources of water supply.
Setting 7 H Beaches. Beach Ridges and Sand Dunes
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

0-5
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

1 000-2000


Weight Rating

5 10
4 9
3 8
5 9
3 10

4 8

2 8
Agricultural
DRASTIC Index
Number

50
36
24
45
30

24

16

225
                                                                           91

-------
                             8.   Piedmont Blue Ridge Region

            (Thick regolith over fractured crystalline and metamorphosed sedimentary rocks)
The Piedmont and Blue Ridge region is an area of
about 247,000 km2 extending from Alabama on the,
south to Pennsylvania on the north. The Piedmont
part of the region consists of low, rounded hills and
long,  rolling,  northeast-southwest  trending ridges
whose summits range from about a 100 meters above
sea level along its eastern boundary with the Coastal
Plain to 500 to 600 m along its boundary with the Blue
Ridge area to the west. The Blue Ridge is mountainous
and includes the highest peaks east of the Mississippi.
The mountains, some of which reach altitudes of
more  than 2,000 m, have smooth-rounded outlines
and are bordered by well-graded streams flowing in
relatively narrow valleys.

The Piedmont and Blue Ridge region is underlain by
bedrock of Precambrian and Paleozoic age consisting
of igneous and metamorphosed igneous and sedi-
mentary rocks. These include granite, gneiss, schist,
quartzite, slate, marble, and phyllite. The land surface
in the Piedmont and Blue Ridge is underlain by clay-
rich, unconsolidated material  derived from  in situ
weathering of the underlying bedrock. This material,
which averages about 10 to 20 m in thickness and
may be as much as 100 m thick on some ridges, is
referred to as  saprolite. In many valleys, especially
those of larger streams, flood plains are underlain by
thin, moderately well-sorted alluvium deposited by
the streams. When the distinction between saprolite
and alluvium  is not important, the term regolith is
used to refer to the layer of unconsolidated deposits.

The regolith contains water in  pore spaces between
rock particles. The bedrock, on the other hand, does
not have any  significant intergranular  porosity. It
contains water, instead, in sheetlike openings formed
along fractures (that  is,  breaks  in  the otherwise
"solid"  rock).  The hydraulic conductivities of  the
regolith and the bedrock are similar and range from
aboutO.001 to 1 m day"1. The major difference in their
water-bearing characteristics is their porosities, that
of regolith being about 20 to 30 percent and that of
the bedrock aboutO.01 to 2 percent. Small supplies of
water adequate for domestic needs can be obtained
from the regolith through large-diameter bored or dug
wells. However, most wells, especially those where
moderate supplies of water are needed, are relatively
small in diameter and are cased through the regolith
and finished with open holes in the bedrock. Although,
as noted, the hydraulic conductivity of the bedrock is
similar to that of the regolith, bedrock wells generally
have much larger yields than regolith wells because,
being deeper, they have a much larger available
drawdown.

All ground-water systems function both as reservoirs
that store water and as pipelines (or conduits) that
transmit water from recharge areas to discharge
areas. The yield of bedrock wells in the Piedmont and
Blue Ridge region depends on the number and size of
fractures penetrated by the open hole  and on the
replenishment of the fractures by seepage into them
from the overlying regolith. Thus, the ground-water
system in this region can be viewed, from the stand-
point of ground-water development, as a terrane in
                                               92

-------
which the reservoir and pipeline functions are effec-
tively separated. Because of its larger porosity, the
regolith functions as a reservoir which slowly feeds
water downward into the fractures in the bedrock.
The fractures serve as an intricate interconnected
network of pipelines that transmit water either to
springs or streams or to wells.

Recharge of the ground-water system occurs on the
areas above the flood plains of streams, and natural
discharge occurs as seepage springs that are common
near the bases of slopes and as seepage into streams.
With respect to recharge conditions, it is important to
note that forested areas, which include most of the
Blue Ridge and much of the Piedmont, have thick and
very permeable soils overlain by a thick layer of forest
litter. In these areas, even on steep slopes, most of the
precipitation seeps into the soil zone, and most of this
moves  laterally through the soil in a thin, temporary,
saturated zone to surface depressions or streams to
discharge. The  remainder seeps  into the  regolith
below the soil zone, and much of this ultimately seeps
into the underlying bedrock.

Because the yield of bedrock wells depends on the
number of fractures penetrated by the well, the key
element in selecting well sites is recognizing the
relation between the present surface topography and
the location of fractures in the bedrock. Most of the
valleys, draws, and other surface depressions indicate
the presence of more intensely fractured zones in the
bedrock which are more susceptible to weathering
and erosion than are the intervening areas. Because
fractures in the  bedrock are the  principal avenues
along which ground water moves, the best well sites
appear to be in draws on the sides of the valleys of
perennial streams where the bordering  ridges are
underlain  by substantial  thicknesses of regolith.
Wells located at such sites seem to be  most effective
in penetrating open water-bearing fractures and in
intercepting ground water draining from the regolith.
Chances of success seem  to be somewhat less  for
wells on the  flood plains of perennial streams,
possibly because the alluvium obscures the topo-
graphic expression of bedrock fractures. The poorest
sites for wells are on the tops of ridges and mountains
where  the regolith cover  is thin or absent and the
bedrock is sparsely fractured.

As a general rule, fractures near the bedrock surface
are most numerous and have the largest openings, so
that the yield of most wells is not i ncreased by drilling
to depths greater than about 100 m. Exceptions to this
occur in Georgia, South Carolina, and North Carolina
and  some other areas where water-bearing, low-
angle faults or fractured zones are present at depths
as great as 200 to 300 m.

The Piedmont and Blue Ridge region has long been
known as an area generally unfavorable for ground-
water development. This reputation seems to have
resulted both from the small reported yields of the
numerous domestic wells in use in the region that
were, generally, sited as a matter of convenience and
from a failure to apply existing technology to the
careful selection of well sites where moderate yields
are needed. As water  needs in the region increase
and as reservoir sites on streams become increasingly
more difficult to obtain, it will be necessary to make
more intensive use of ground water.
Piedmont and Blue Ridge

(8A)  Mountain Slopes

This hydrogeologic setting is characterized by steep
slopes on the side of mountains, a thin soil cover and
fractured bedrock. Ground water is obtained primarily
from the fractures  in the bedrock which may be of
sedimentary, metamorphic,  or igneous origin but
which is commonly metamorphic or igneous. The
fractures provide localized sources of ground water
and well yields are typically limited. Although precipi-
tation is abundant,  due to the steep slopes, thin soil
cover and small storage  capacity of the fractures,
runoff is significant and  ground-water  recharge is
only moderate. Water levels are extremely variable
but are commonly deep.
                                                                       93

-------
Setting 8 A Mountain Slopes
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
2-4
Metamorphic/
Igneous
Thin or Absent
18+
Metamorphic/
Igneous

1-100
Weight

5
4

3
2
1

5

3
Rating

2
3

3
10
1

4

1
Number

10
12

9
20
1

20

3
DRASTir Indnx 75
Setting 8 A Mountain Slopes
                                 Agricultural
Feature

Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



Range


75-100
2-4
Metamorphic/
Igneous
Thin or Absent
18+
Metamorphic/
Igneous

1-100



Weight Rating Number


5 2
4 T
^ o
3 3
5 10
3 1
4 4

2 1

Agricultural
DRASTIC Index


10
1 ")
\ f.
9
50
3
16

2


102
Setting 8 B Alluvial Mountain Valleys

Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



Range

5-15
7-10
Sand and Gravel
Loam
2-6%
S & G w/sig.
Silt and Clay

300-700



Weight

5
4
3
2
1

5

3

DRAG
General
Rating

9
8
8
5
9

6

4

!TIP InHav

Number

45
32
24
10
9

30

12

1RO
Piedmont and Blue Ridge

(8B)  Alluvial Mountain Valleys

This hydrogeologic setting is characterized by thin
bouldery alluvium which overlies fractured bedrock of
sedimentary, metamorphic,  or igneous origin. The
alluvium,  which  includes both mass-wastage and
water-sorted debris, is derived from the surrounding
slopes, and serves as a localized  source of water.
Water is obtained from sand and gravel layers which
are interspersed between  finer-grained  deposits.
Surficial deposits have typically weathered to a loam.
Water levels are usually relatively shallow but are
extremely variable. Ground water is  also obtained
from the fractures in the underlying bedrock, which"
are typically in direct  hydraulic connection with the
overlying alluvium.
                                                    Setting 8 B Alluvial Mountain Valleys
Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
7-10
Sand and Gravel
Loam
2-6%
S & G w/sig.
Silt and Clay

300-700


Weight Rating

5 9
4 8
3 8
5 5
3 9

4 6

2 4
Agricultural
DRASTIC Index
Number

45
32
24
25
27

24

8

185
                                                   Piedmont and Blue Ridge
                                                   <8C)  Mountain Flanks
                                                   This hydrogeologic setting is characterized by moder-
                                                   ate topographic relief and moderately-dipping, frac-
                        94

-------
tured, consolidated sedimentary rocks. Soil cover is
usually  thicker than on the  mountain slopes and
typically has weathered to a sandy  loam or loam.
Although  precipitation is  abundant, ground-water
recharge is moderate due to the soil cover and slope.
Water levels are typically moderately-deep although
they are extremely variable. The mountain flanks
serve as the recharge area for aquifers  which are
typically confined in adjacent valley areas.
Setting 8 C Mountain Flanks
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
2-4
Thin Bedded SS,
LS, SH Sequences
Loam
6-12%
Bedded LS,
SS, SH

100-300
Weight

5
4

3
2
1

5

3
Rating

5
3

6
5
5

6

2
Number

25
12

18
10
5

30

6
Setting 8 C Mountain Flanks
                              DRASTIC Index  106
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
2-4
Thin Bedded SS,
LS, SH Sequences
Loam
6-12%
Bedded LS,
SS, SH

100-300
Weight

5
4

3
5
3

4

2
Rating

5
3

6
5
5

6

2
Number

25
12

18
25
15

24

4
Piedmont and Blue Ridge

(8D)  Thick Regolith

This hydrogeologic setting is characterized by moder-
ate to low  slopes covered by  thick regolith  and
underlain by fractured bedrock of igneous, sedimen-
tary, or metamorphic origin. The regolith is typically
clay-rich but may also serve as  a source of  ground
water for low-yield wells. This regolith functions as a
reservoir for ground-water recharge to the bedrock
which  is in direct hydraulic  connection with the
overlying regolith. The bedrock typically yields larger
amounts of ground water than the regolith when the
well intersects fractures in the bedrock.
                                                   Setting 8 D Thick Regolith
                                                                                     General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
4-7
Weathered
Meta./lg.
Clay Loam
6-12%

Silt/Clay

1-100
Weight

5
4

3
2
1

5

3
Rating

9
6

4
3
5

1

1
Number

45
24

12
6
5

5

3
                                                                                 DRASTIC Index  100
                              Agricultural
                              DRASTIC Index  123
                                                                         35

-------
Setting 8 D Thick Regolith
                                 Agricultural
 Setting 8 E River Alluvium
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
4-7
Weathered
Meta./lg.
Clay Loam
6-12%

Silt/Clay

1-100
Weight

5
4

3
5
3

4

2
Rating

9
6

4
3
5

1

1
Number

45
24

12
15
15

4

2
Agricultural
DRASTIC Index
117
Piedmont and Blue Ridge

(8E)  River A lluvium

This hydrogeologic setting is characterized by low
topography  and deposits of varying  thickness  of
alluvium along parts of stream valleys. The alluvium
is  underlain by fractured igneous, metamorphic,  or
consolidated  sedimentary rocks. Water is obtained
from sand and gravel which is overlain and inter-
bedded with finer-grained alluvial deposits. Surficial
deposits usually weather to a sandy loam. The sand
and gravel within the alluvium serves as the principal
aquifer, but the alluvium also serves as the source of
ground-water recharge for the underlying aquifer.
Precipitation is abundant and recharge is moderately
high,  limited only by the loamy surficial deposits.
Water levels are extremely variable, but are typically
moderately shallow.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
7-10
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig.
Silt and Clay

1000-2000

Weight

5
4
3
2
1

5

3
General
Rating

9
8
8
6
9

6

8

Number

45
32
24
12
9

30

24
                                                   Setting 8 E River Alluvium
                                                                                 DRASTIC Index  176
                                                                                    Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
7-10
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig.
Silt and Clay

1000-2000
Weight

5
4
3
5
3

4

2
Rating

9
8
8
6
9

6

8
Number

45
32
24
30
27

24

16
Agricultural
DRASTIC Index
198
Piedmont and Blue Ridge

(8F)  Mountain Crests

This hydrogeologic setting is characterized by moder-
ate to steep topography on the crests of mountains
with thin soil cover and exposed fractured bedrock.
Ground water is obtained primarily from the fractures
in the bedrock which may  be of sedimentary, meta-
morphic, or igneous origin but which is commonly
metamorphic  or igneous. The  fractures  provide
localized sources of ground water and well yields are
typically limited. Although  precipitation is abundant,
due to the slopes, thin soil cover, and small storage
capacity of the fractures,  runoff is significant and
ground-water  recharge  is low.  Water  levels  are
extremely variable but commonly deep.

-------
Setting 8 F Mountain Crests
                                        General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

Range

100+
0-2
Metamorphic/
Igneous
Thin or Absent
2-6%
Metamorphic/
Igneous

1-100

Weight Rating

5 1
4 1

3 3
2 10
1 9

5 4

3 1
DRASTIC Index
Number

5
4

9
20
9

20

3
70
Setting 8 F Mountain Crests

Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



Range

100+
0-2
Metamorphic/
Igneous
Thin or Absent
2-6%
Metamorphic/
Igneous

1-100


Agricultural

Weight Rating Number

5 1
4 1

3 3
5 10
3 9

4 4

2 1
Agricultural
DRASTIC Index

5
4

9
50
27

16

2

113
                                                                                     97

-------
                           3    Northeast and Superior Uplands

                          (Glacial deposits over fractured crystalline rocks)
The Northeast and Superior Uplands region is made
up of two separate areas totaling about 415,000 km2.
The Northeast Upland encompasses the Adirondack
Mountains, the Lake Champlain valley, and nearly all
of New England. The parts of  New England not
included are the Cape Cod area and nearby islands,
which are included in the Atlantic and Gulf Coastal
Plain  region, and the Triassic lowland along the
Connecticut River in Connecticut and Massachusetts,
which is included in the Glaciated Central region. The
Superior Upland encompasses most of the northern
parts of Minnesota and Wisconsin adjacent to the
western end of Lake Superior. The Northeast and
Superior Uplands are characterized by rolling hills
and low mountains. Land-surface altitudes in the
Northeast Upland range from sea level to more than
1,500 m on some of the peaks in the Adirondacks and
White Mountains. In contrast to the  mountainous
areas in the Northeast, the Superior Upland is in an
area of rolling hills whose summits reach altitudes of
only 300 to 600 m.

Bedrock in the region ranges in age from Precambrian
to Paleozoic and consists mostly of granite, syenite,
anorthosite, and other intrusive igneous  rocks and
metamorphosed sedimentary  rocks consisting  of
gneiss, schist, quartzite, slate, and marble. Most of
the igneous and metamorphosed sedimentary rocks
have been intensely folded and cut by numerous
faults.

The bedrock is overlain by unconsolidated deposits
laid down by ice sheets that covered the areas one or
more times during the Pleistocene and by gravel,
sand, silt,  and clay laid down by meltwater streams
and in lakes that formed during the melting of the ice.
The thickness of the glacial deposits ranges from a
few meters on the higher mountains, which also have
large expanses of barren rock, to more than 100 m in
some valleys. The most extensive glacial  deposit is
till, which was laid down as  a nearly continuous
blanket by the ice, both in valleys and on the uplands.
In most of the valleys and other low areas, the till is
covered by glacial outwash consisting of interlayered
sand and  gravel, ranging in thickness from a few
meters to more than 20 m, that was deposited  by
streams supplied by glacial meltwater. In  several
areas, including parts of the Champlain valley and the
lowlands adjacent to Lake Superior, the unconsoli-
dated deposits consist of clay and silt deposited in
lakes that formed during the melting of the ice sheets.

Ground-water supplies are obtained  in the  region
from both the glacial deposits and the underlying
bedrock. The largest yields come from the sand and
gravel deposits, which in parts of the valleys of large
streams are as much as 60 m thick. Other sand and
gravel deposits, not thick or productive enough to be
included in the Alluvial Valleys region, occur locally in
most valley and lowland areas in the Northeast and
Superior Uplands region and  serve* as  important
sources of water.

Water occurs in the bedrock in fractures similar in
origin, occurrence, and hydraulic characteristics to
those in the Piedmont and Blue Ridge region. In fact.
                                              98

-------
the primary difference  in ground-water conditions
between the Piedmont and Blue Ridge region and the
Northeast and Superior Uplands region is related to
the materials that overlie the bedrock. In the Piedmont
and  Blue  Ridge, these consist of unconsolidated
material derived from weathering of the underlying
bedrock. In the Northeast and Superior Uplands the
overlying materials consist of glacial deposits which,
having been transported either by ice or by streams,
do not have a composition and structure controlled by
that of the underlying bedrock. These differences in
origin  of the regolith between the Northeast  and
Superior Uplands and the Piedmont and Blue Ridge
are an  important consideration in the development of
water  supplies,  as is  discussed  in the following
paragraphs.

Recharge from precipitation generally begins in the
fall after plant growth  stops. It continues intermit-
tently over  the winter during thaws and culminates
during the  period between the spring thaw and the
start of the growing season.  Precipitation  on the
Northeast Upland, about 1,200 mm per year, is twice
that  on the Superior Upland,  with the result that
recharge,  both  to  the  glacial  deposits and  to the
underlying  bedrock, is largest in the Northeast. The
glacial deposits in the  region  serve  as a storage
reservoir for the fractures in the underlying bedrock,
in the  same way the  saprolite functions  in the
Piedmont and Blue Ridge region. The major difference
is that the glacial deposits on hills and other upland
areas are much thinner than the saprolite in similar
areas in the Piedmont and Blue Ridge and, therefore,
have a much smaller ground-water storage capacity.

Water supplies in the Northeast and Superior Uplands
region are  obtained from open-hole drilled wells in
bedrock, from drilled and screened or open-end wells
in sand and gravel, and from large-diameter bored or
dug wells in till. The development of water supplies
from bedrock, especially in the Superior Upland, is
more uncertain than from the fractured rocks in the
Piedmont and  Blue Ridge region because  the ice
sheets that advanced across  the region removed the
upper, more fractured part of the rock and also tended
to obscure many of the fracture-caused depressions
in the  rock surface with the layer of glacial till. Thus,
use  of surface  depressions  in this region to select
sites of bedrock wells is not as satisfactory as in the
Piedmont and Blue Ridge.

Most of the rocks  that underlie the Northeast and
Superior Uplands are relatively insoluble, and, con-
sequently,  the  ground water  in both the  glacial
deposits and the bedrock generally contains less than
500 mg/l of dissolved  solids. Two  of the most
significant water-quality problems confronting the
region, especially the Northeast Upland section, are
acid precipitation and pollution caused by salts used
to de-ice highways. Much of the precipitation  now
falling on the Northeast (in 1982) has a pH  in the
range of 4 to 6  units. Because of the low buffering
capacity of the soils derived from the rocks underlying
the area, there is relatively little opportunity for the pH
to be increased. One of  the results  of this  is the
gradual  elimination of living organisms from many
lakes and  streams. The effect on  ground-water
quality, which will develop much more slowly, has not
yet been determined. The second problem—that of
de-icing salts—affects ground-water quality adjacent
to streets and roads maintained for winter travel.
Northeast and Superior Uplands

(9A)  Mountain Slopes

This hydrogeologic setting is characterized by steep
slopes on the side of mountains, a thin soil cover and
fractured bedrock. Ground water is obtained primarily
from the fractures in the bedrock which may be of
sedimentary, metamorphic,  or igneous origin  but
which is commonly  metamorphic  or igneous.  The
fractures provide localized sources of ground water,
and well yields are typically limited. Although precipi-
tation is abundant, due to the steep slopes, thin soil
cover and small storage capacity of the fractures,
runoff is significant and ground-water recharge is
moderate. Water levels are extremely variable but are
commonly deep.
                                                                        99

-------
Setting 9 A Mountain Slopes
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
2-4
Metamorphic/
Igneous
Thin or Absent
18+
Metamorphic/
Igneous

1-100
Weight

5
4

3
2
1

5

3
Rating

2
3

3
10
1

4

1
Number

10
12

9
20
1

20

3
Setting 9 A Mountain Slopes
                             DRASTIC Index   75
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range
Weight Rating Number
Setting 9 B Alluvial Mountain Valleys
75-100
2-4
Metamorphic/
Igneous
Thin or Absent
18+
Metamorphic/
Igneous

1-100


5 2
4 3

3 3
5 10
3 1

4 4

2 1
Agricultural
DRASTIC Index
10
12

9
50
3

16

2

102

Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



Range

5-15
7-10
Sand and Gravel
Sandy Loam
2-6%

Sand and Gravel
700-1 000



Weight

5
4
3
2
1

5
3


General
Rating

9
8
8
6
9

8
6



Number

45
32
24
12
9

40
18


                                                                                DRASTIC Index  180
Northeast and Superior Uplands

(9B)  Alluvial Mountain Valleys

This hydrogeologic setting is characterized by thin,
bouldery alluvium which overlies fractured bedrock of
sedimentary, metamorphic, or  igneous origin but
which are commonly alternating sedimentary layers.
The alluvium, which is derived from the surrounding
slopes serves as a localized source of water. Water is
obtained from  sand and gravel layers  which are
interspersed between fine-grained deposits. Surficial
deposits have typically weathered to  a sandy loam.
Water  levels are  relatively shallow  but  may  be
extremely variable.  Ground  water  may  also  be
obtained from the fractures in the underlying bedrock
which are usually in direct hydraulic connection with
the overlying alluvium.
Setting 9 B Alluvial Mountain Valleys
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
7-10
Sand and Gravel
Sandy Loam
2-6%

Sand and Gravel

700-1 000


Weight Rating

5 9
4 8
3 8
5 6
3 9

4 8

2 6
Agricultural
DRASTIC Index
Number

45
32
24
30
27

32

12

202
                                                   Northeast and Superior Uplands

                                                   (9C)  Mountain Flanks

                                                   This hydrogeologic setting is characterized by moder-
                                                   ate topographic relief and moderately dipping, frac-
                       100

-------
tured, consolidated sedimentary rocks. Soil cover is
usually  thicker than on the mountain slopes and
typically has weathered to a sandy loam. Although
precipitation can be significant, ground-water  re-
charge is moderate due to the slope. Water levels are
typically moderately deep, although they are extreme-
ly variable. The mountain flanks serve as the recharge
area for aquifers which are  confined  in adjacent
lowland areas. Ground water is obtained from the
permeable sedimentary rocks or from fractures and
bedding planes in the sedimentary rocks. The sedi-
mentary rocks  may be underlain by fractured bedrock
of igneous, metamorphic, or sedimentary origin
which yield little water.
Setting 9 C Mountain Flanks
                                Agricultural
Setting 9 C Mountain Flanks
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
2-4
Thin Bedded SS,
LS, SH Sequences
Sandy Loam
12-18%
Bedded LS,
SS, SH

1 00-300
Weight

5
4

3
2
1

5

3
Rating

5
3

6
6
3

6

2
Number

25
12

18
12
3

30

6
                              DRASTIC Index   106
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

30-50
2-4
Thin Bedded SS,
US, SH Sequences
Sandy Loam
12-18%
Bedded LS,
SS, SH

1 00-300
Weight

5
4

3
5
3

4

2
Rating

5
3

6
6
3

6

2
Number

25
12

18
30
9

24

4
Agricultural
DRASTIC Index
122
Northeast and Superior Uplands

(9Da)  Glacial Till Over Crystalline Bedrock

This hydrogeologic setting is characterized by moder-
ately low topographic relief and varying thicknesses
of glacial till overlying severely fractured, folded, and
faulted bedrock of igneous and metamorphic origin
with minor occurrences of bedded sedimentary rocks.
The till is chiefly unsorted deposits which  may be
interbedded with localized deposits  of sand and
gravel. Although  ground water occurs in both the
glacial deposits and fractured bedrock, the bedrock is
the principal aquifer. The  glacial  till serves as a
recharge source. Although precipitation is abundant,
recharge is only moderately high because of the low
permeability of the glacial till  and  the surficial
deposits  which typically weather to loam. Depth to
water is extremely variable depending  in  part on the
thickness of the glacial till, but is typically moderately
shallow.
                                                                        101

-------
Setting 9 Da Glacial Till Over Crystalline Bedrock
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Metamorphic/
Igneous
Loam
2-6%

Silt/Clay

1-100
Weight

5
4

3
2
1

5

3
Rating

7
8

3
5
9

1

1
Number

35
32

9
10
9

5

3
                              DRASTIC Index  103
Setting 9 Da Glacial Till Over Crystalline Bedrock
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Range

15-30
7-10
Metamorphic/
Igneous
Loam
2-6%
Weight

5
4

3
5
3
Rating

7
8

3
5
9
Number

35
32

9
25
27
Impact Vadose
  Zone            Silt/Clay
Hydraulic
  Conductivity       1-100
4

2
                              Agricultural
                              DRASTIC Index
  4

  2


134
                      Setting 9 Db Glacial Till Over Outwash

                          Feature
                                                                                      General
                                                                     Range
                                    Weight  Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

30-50
7-10
Sand and Gravel
Loam
2-6%

Silt/Clay

1 000-2000

5
4
3
2
1

5

3

5
8
8
5
9

1

8

25
32
24
10
9

5

24
                                                    DRASTIC Index  129
                                                    Setting 9 Db Glacial Till Over Outwash
                                                                                     Agricultural
 Northeast and Superior Uplands

 (9Db)  Glacial Till Over Outwash
 This  hydrogeologic setting  is characterized by low
 topography and outwash materials which are covered
 by varying thicknesses of glacial till. The till is chiefly
 unsorted deposits which  may  be interbedded with
 localized  deposits of  sand and gravel.  Surficial
 deposits have usually weathered to a loam. Although
 ground water occurs in both the glacial till and in the
 underlying outwash,  the  outwash serves as the
 principal aquifer because the fine-grained deposits
 have been removed by glacial meltwater.  The out-
 wash is in direct hydraulic connection with the glacial
 till and the glacial till serves as a source of recharge
 for the underlying outwash. Precipitation is abundant
 in the region but recharge is moderate because of the
 relatively low permeability of the overlying glacial till.
 Depth to water table is extremely variable depending
 in part on the thickness of the glacial till, but averages
 around 30 feet.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

30-50
7-10
Sand and Gravel
Loam
2-6%

Silt/Clay

1000-2000


Weight Rating

5 5
4 8
3 8
5 5
3 9

4 1

2 8
Agricultural
DRASTIC Index
Number

25
32
24
25
27

4

16

153
                       Northeast and Superior Uplands

                       (9E)   Outwash
                       This hydrogeologic setting is characterized by moder-
                       ate topographic relief and varying thickness of out-
                       wash which overlie fractured bedrock of sedimentary.
                        102

-------
metamorphic, or igneous origin. The outwash consists
of water-washed deposits of sand and gravel which
often serve as the principal aquifers in the area, and
which typically have a sandy loam surficial layer. The
outwash also serves as a source of recharge to the
underlying bedrock.  Recharge is abundant  and
ground-water recharge is  high. Water levels are
extremely variable, but are relatively shallow.
Setting 9 E Outwash
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sandy Loam
2-6%

Sand and Gravel

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

9
9
8
6
9

8

8
Number

45
36
24
12
9

40

24
Northeast and Superior Uplands

(9F)  Moraine

This hydrogeologic setting is characterized by moder-
ate topography and  varying thicknesses of mixed
glacial deposits which overlie  fractured bedrock of
sedimentary, igneous, or metamorphic origin.  This
setting issimilarto(9E)Outwash in that the sand and
gravel within the morainal deposits is well-sorted and
serves as the principal aquifer in the area. These
deposits also serve as a source of rec'harge for the
underlying bedrock. Moraines also contain sediments
that are typically unsorted and  unstratified; these
deposits contain more fines than outwash deposits,
are less permeable and characteristically more like
glacial till. Moraines are typically mounds or ridges of
till  which were deposited along the margin  of  a
stagnant or retreating glacier. Surf icial deposits often
weather to a sandy loam.  Precipitation is abundant
throughout the region and ground-water recharge is
moderately high. Water levels are extremely variable,
based in part on the thickness of the glacial till, but are
typically fairly shallow.
                             DRASTIC Index   190
Setting 9 E Outwash
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

5-15
10+
Sand and Gravel
Sandy Loam
2-6%

Sand and Gravel

1 000-2000


Weight Rating

5 9
4 9
3 8
5 6
3 9

4 8

2 8
Agricultural
DRASTIC Index
Number

45
36
24
30
27

32

16

210
                                                   Setting 9 F Moraine
                                                                                     General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Sand and Gravel
Sandy Loam
6-12%

Sand and Gravel

700-1000
Weight

5
4
3
2
1

5

3
Rating

7
8
8
6
5

8

6
Number

35
32
24
12
5

40

18
                                                                                 DRASTIC Index  166
                                                                         103

-------
Setting 9 F Moraine
                                Agricultural
Setting 9 Ga River Alluvium With Overbank
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
7-10
Sand and Gravel
Sandy Loam
6-12%

Sand and Gravel

700-1000


Weight Rating

5 7
4 8
3 8
5 6
3 5

4 8

2 6
Agricultural
DRASTIC Index
Number

35
32
24
30
15

32

12

180
Northeast and Superior Uplands

(9Ga)  River Alluvium With Overbank

This hydrogeologic setting  is characterized by low
topography and thin to moderately thick deposits of
alluvium along parts of river valleys. The alluvium is
underlain by fractured  bedrock of sedimentary,
metamorphic, or igneous origin. Water is obtained
from sand and gravel  layers which are interbedded
with finer-grained alluvial deposits. The flood plain is
covered by varying thicknesses of fine-grained silt
and  clay, called overbank  deposits.  The overbank
thickness is usually greater along major streams (as
much as 40 feet) and  thinner along minor streams.
Precipitation is abundant, but recharge is somewhat
reduced because of the silty overbank deposits and
subsequent clayey loam soils which  typically cover
the surface. Water levels are typically moderately
shallow and may be hydraulically connected to the
stream or river. The alluvium may serve as a signifi-
cant source of  water  and is also usually in  direct
hydraulic connection with the underlying bedrock.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Sand and Gravel
Clay Loam
0-2%

Silt/Clay

1 000-2000

Weight

5
4
3
2
1

5

3
General
Rating

7
8
8
3
10

1

8

Number

35
32
24
6
10

5

24
                                                                                DRASTIC Index  136
                                                   Setting 9 Ga River Alluvium With Overbank
                                                                                   Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
7-10
Sand and Gravel
Clay Loam
0-2%

Silt/Clay

1 000-2000


Weight Rating

5 7
4 8
3 8
5 3
3 10

4 1

2 8
Agricultural
DRASTIC Index
Number

35
32
24
15
30

4

16

156
Northeast and Superior Uplands

(9Gb)  River Alluvium Without Overbank

This hydrogeologic setting is identical to (9Ga) River
Alluvium With Overbank except that no significant
fine-grained flood plain deposits occupy the stream
valley. This results  in significantly higher recharge
where precipitation is adequate and sandy soils occur
at the surface. Water levels are moderate to shallow
in depth. Hydraulic contact with the surface stream is
usually excellent, with alternating recharge/discharge
relationships varying  with stream stage.  These
deposits serve as a good source of recharge to the
underlying fractured bedrock.
                        104

-------
Setting 9 Gb River Alluvium Without Overbank
                                       General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadosa
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sandy Loam
0-2%

Sand and Gravel

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

9
9
8
6
10

8

8
Number

45
36
24
12
10

40

24
                                  DRASTIC Index  191
Setting 9 Gb River Alluvium Without Overbank
                                      Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

Range
5-15
10+
Sand and Gravel
Sandy Loam
0-2%
Sand and Gravel
1 000-2000

Weight Rating
5 9
4 9
3 8
5 6
3 10
4 8
2 8
Agricultural
DRASTIC Index
Number
45
36
24
30
30
32
16
213
                                                                                    705

-------
                            10.  A tlantic and Gulf Coastal Plain

                            (Complexly interbedded sand, silt, and clay)
The Atlantic and Gulf Coastal Plain region is an area
of about 844,000 km2 extending from  Cape Cod,
Massachusetts, on the north to the Rio Grande in
Texas on the south. This region  does not include
Florida and parts of the adjacent States; although
those areas are a part of the Atlantic and Gulf Coastal
Plain physiographic  province, they together form a
separate ground-water region.  (See region 11,
"Southeast Coastal Plain.")

The Atlantic and Gulf Coastal Plain region ranges in
width from a few kilometers near its northern end to
nearly a thousand kilometers in the vicinity of the
Mississippi River. The  great  width near the Missis-
sippi reflects the effect of a major downwarped zone
in the Earth's crust that extends from the Gulf of
Mexico to about the confluence of the Mississippi and
Ohio Rivers. This area is referred to as the Mississippi
embayment.
The topography of the region ranges from extensive,
flat,  coastal swamps and marshes 1 to 2 m above
sea level to rolling uplands, 100 to 250 m above sea
level, along the inner margin ofthe region.

The region is underlain by unconsolidated sediments
that  consist principally of sand, silt, and clay trans-
ported by streams from the adjoining uplands. These
sediments, which range in age from Jurassic to the
present, range in thickness from less than a meter
near the inner edge of the region to more than 12,000
m in southern Louisiana. The greatest thicknesses
are along the seaward edge of the region and along
the axis of the Mississippi embayment. The sediments
were deposited on floodplains and as deltas where
streams  reached the  coast  and,  during  different
invasions of the region by the sea, were reworked by
waves and ocean currents. Thus, the sediments are
complexly interbedded to the extent that most of the
named geologic  units into which  they  have been
divided  contain  layers  of the  different types of
sediment  that underlie  the region.  These named
geologic units (or formations) dip toward the coast or
toward the axis of the Mississippi embayment, with
the result that those that crop out at the surface form
a series of bands roughly parallel to the coast or to the
axis  of the embayment. The oldest formations crop
out along the  inner margin of the region, and the
youngest crop out in the coastal area.

Within any formation the coarsest grained materials
(sand, at places interbedded with thin gravel layers)
tendtobe most abundant near source areas. Clay and
silt  layers become  thicker  and  more numerous
downdip.

Although sand, silt, and clay, as noted above, are the
principal types of material underlying the Atlantic and
Gulf Coastal Plain, there are also a small amount of
gravel interbedded with the sand,  a few beds com-
posed  of  mollusk shells, and  a small  amount of
limestone present in the region. The most important
limestone  is the semi-consolidated  Castle  Hayne
Limestone of Eocene age which underlies an area of
about 26,000 km2 in eastern North  Carolina, is more
than 200 m thick in much of the area, and is the most
productive aquifer in North Carolina. A soft, clayey
limestone (the chalk of the Selma Group) of Late
                                              106

-------
 Cretaceous age underlies parts of eastern Mississippi
 and western Alabama, but instead of being an aquifer
 it is an important confining bed.

 From the standpoint of well yields and ground-water
 use, the Atlantic and Gulf Coastal Plain is one of the
 most important regions in the country. Recharge to
 the ground-water system occurs in the  interstream
 areas,  both where sand layers crop out  and  by
 percolation downward across the interbedded clay
 and silt layers. Discharge from the system occurs by
 seepage  to streams, estuaries,  and  the  ocean.
 Movement of water from recharge areas to discharge
 areas is controlled, as in all ground-water systems, by
 hydraulic gradients, but in this region the pattern of
 movement is complicated by down-dip thickening of
 clay which hampers upward discharge.  As a result,
 movement down  the dip of the permeable layers
 becomes increasingly slow with  increasing distance
 from the outcrop areas. This causes many flow lines
 to converge on the discharge areas located on major
 streams  near  the downdip part of  outcrop areas.
 These areas of concentrated ground-water discharge
 are referred to as "artesian-water gaps" by LeGrand
 and Pettyjohn (1981).

 Wells that yield moderate to large quantities of water
 can be constructed almost anywhere in the  region.
 Because  most of the aquifers consist of unconsoli-
 dated sand, wells require screens; wh'ere the sand is
 fine-grained and well sorted, the common practice is
 to surround the screens with a coarse sand or gravel
 envelope.

 Withdrawals near the outcrop areas of aquifers are
 rather quickly balanced by increases in recharge and
 (or) reductions  in  natural discharge. Withdrawals at
 significant distances downdip  do  not  appreciably
 affect conditions in the outcrop area and thus  must be
 partly or largely supplied from  water in storage in the
 aquifers and confining beds.

 The reduction of storage in an aquifer in the vicinity of
 a pumping well is reflected in a decline in ground-
 water levels and is necessary  in  order to establish a
 hydraulic gradient toward the well. If withdrawals are
 continued for long periods in areas underlain by thick
 sequences of unconsolidated  deposits, such as the
 Atlantic and Gulf Coastal Plain, the lowered ground-
 water levels in the aquifer may result in  drainage of
 water from layers of silt and clay. The depletion of
 storage in fine-grained beds results in subsidence of
 the land surface. Subsidence in parts of the Houston
 area totaled about 9 m as of 1978. Subsidence near
 pumping centers in the Atlantic Coastal Plain  has not
 yet  been  confirmed but is believed to be occurring,
 though at a slower rate than  along the Texas Gulf
 Coast.

The depletion of storage in confining beds is  perma-
 nent, and subsidence of the land  surface that results
from such depletion is also permanent. On the other
hand, depletion of storage in aquifers may not be fully
permanent, depending on the availability of recharge.
In arid  and semiarid regions, recharge  rates  are
extremely small, and depletion of aquifer storage is,
for  practical purposes,  permanent.  Depletion of
storage in aquifers in these regions is referred to as
mining. In humid regions, recharge is sufficient to
replace aquifer storage rather quickly, once with-
drawals are stopped, so that depletion of  aquifer
storage in these areas is not considered to be mining.
The important point is that depletion of storage in the
confining layers of silt and clay in both arid and humid
regions is permanent but is not normally considered
to be ground-water mining. The term "mining" is
applied by most ground-water hydrologists  only to
areas in which aquifer storage is being permanently
depleted.

Depletion of storage in the aquifers underlying large
areasoftheAtlanticandGulf Coastal Plain is reflected
in long-term declines in ground-water levels. These
declines suggest that withdrawals in these areas are
exceeding the long-term yield of the aquifers.

This  is a water-management  problem  that  will
become more important as rates of withdrawal  and
the lowering of water levels increase. Solutions to
this problem include (1) concentrating withdrawals
as close as possible to outcrop (recharge)  areas, (2)
dispersing withdrawals in regions remote from the
outcrop areas over the widest possible area, and (3)
increasing withdrawals from surficial aquifers to the
maximum possible extent.

Another problem that affects ground-water develop-
ment in the region concerns the presence of saline
water in the deeper parts of most  aquifers.  The
occurrence  of  saline water  is controlled  by  the
circulation of freshwater which, as noted previously,
becomes increasingly  slow down the dip of  the
aquifers. Thus, in some of the deeper  aquifers, the
interface between freshwater and saltwater is in-
shore, but in parts of the region, including parts of
Long  Island, New Jersey, and Mississippi,  the inter-
face in the most intensively developed aquifers  is a
significant distance offshore. Pumping  near  the
interfaces has  resulted  in problems  of  saltwater
encroachment locally.

Another  significant  feature of the ground-water
system  in  this  region  is the presence  of "geo-
pressured" zones at depths of 1,800 to 6,100 m in
Texas  and  Louisiana  which contain water at  a
temperature of 80°C to more than 273°C. Water in
these zones contains significant concentrations of
natural gas, and the water in some zones is under
pressures sufficient to support a  column of water
more than 4,000 m above land surface. Because the
elevated temperature, natural gas, and high pres-
                                                                       107

-------
sures are all potential energy sources, these zones
are under intensive investigation.
Atlantic and Gulf Coastal Plain

(10A a)   Confined Regional A quifers

This hydrogeologic setting is characterized by moder-
ately  low topographic relief and  gently  dipping,
complexly interbedded unconsolidated  and  semi-
consolidated deposits  which consist  primarily of
sand, silt, and clay. Outcrops of these deposits form a
series of bands roughly parallel to the coast or to the
axis of the Mississippi Embayment. The outcrop areas
and overlying semi-permeable beds are the principal
sources of recharge to the formations which serve as
regional aquifers. Precipitation is abundant and
recharge is moderately  high in the outcrop areas but
low regionally to deep zones. Surficial deposits
typically weather to a sandy loam. Large quantities of
water are obtained from the sand and gravel and sand
deposits within the aquifer. Water levels are ex-
tremely variable and typically are shallower toward
the shoreline. When ground water is heavily pumped
near the shoreline, these aquifers are very susceptible
to salt-water intrusion. Since the shallow  aquifers
are very vulnerable to pollution due to their permeable
nature,  and the deeper aquifers are recharged from
the shallow ones, the  entire system is  somewhat
susceptible to ground-water pollution. The degree of
vulnerability varies according to the nature of the
deposits and the amount of recharge.
Setting 10 Aa Confined Regional Aquifers
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

100+
0-2
Sand and Gravel
*
«

Silt and Clay

300-700
Weight

5
4
3
2
1

5

3
Rating

1
1
8
1
1

1

4
Number

5
4
24
2
1

5

12
                             DRASTIC Index   53
Setting 10 Aa Confined Regional Aquifers
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

100+
0-2
Sand and Gravel
#
•*

Silt and Clay

300-700
Weight

5
4
3
5
3

4

2
Rating

1
1
8
1
1

1

4
Number

5
4
24
5
3

4

8
Agricultural
DRASTIC Index
53
                                                  Atlantic and Gulf Coastal Plain
                                                  (WAb)  Unconsolidated & Semi-Consolidated
                                                           Shallow Surficial Aquifer

                                                  This setting  is  very similar to  (10Aa) Confined
                                                  Regional Aquifers except that the principal aquifer is
                                                  the shallow surficial deposits which serve as a local
                                                  source of water and typically provide recharge for the
                                                  regional aquifer. Water is obtained from the surficial
                                                  sand and gravel which  may be separated from the
                                                  underlying regional aquifer by a confining layer. This
                                                  confining layer typically leaks providing recharge to
                                                  the deeper zones. Surficial  deposits are sandy loams.
                                                  Water levels tend to be quite shallow, especially near
                                                  the coast. Precipitation is abundant and recharge to
                                                  the ground water  is high. These  deposits are very
                                                  vulnerable to ground-water pollution due to their
                                                  permeable nature.
                       705

-------
Setting 10 Ab Unconsolidated & Semi-Consolidated Shallow
            Surficial Aquifer
                                  General
    Feature
                  Range
Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

5-15
1O
Sand and Gravel
Sandy Loam
2-6%

Sand and Gravel

700-1 000

5
4
3
2
1

5

3

9
9
8
6
9

8

6

45
36
24
12
9

40

18
                              DRASTIC Index  184
Setting 10 Ab Unconsolidated & Semi-Consolidated Shallow
            Surficial Aquifer
                          	Agricultural	
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sandy Loam
2-6%

Sand and Gravel

700-1000
Weight

5
4
3
5
3

4

2
Rating

9
9
8
6
9

8

6
Number

45
36
24
30
27

32

12
Agricultural
DRASTIC Index
206
Atlantic and Gulf Coastal Plain

(10B a)  River A lluvium With O verbank

This hydrogeologic setting is characterized by low
topography and thin to moderately thick deposits of
alluvium along parts of river valleys. The alluvium is
underlain  by  consolidated  and  semi-consolidated
sedimentary rocks. Water is obtained from sand and
gravel layers  which are interbedded  with finer-
grained alluvial deposits. The floodplain is covered by
varying  thicknesses of  fine-grained,  silty  deposits
called overbank deposits. The overbank thickness is
usually greater along major streams (as much as 40
feet) and thinner along minor streams. Precipitation
in the region is abundant, but recharge is somewhat
reduced because of the silty overbank deposits and
subsequent silty soils  which typically cover the
surface. Water levels are typically moderately shal-
low. The alluvium may serve as a significant source of
water and may be in direct hydraulic connection with
the underlying sedimentary rocks. The alluvium may
also serve as a source of recharge to the underlying
bedrock. Many streams in this setting provide only
fine-grained deposits (silts and clays) and as such do
not form good  aquifers. They still,  however, provide a
good source of recharge.
                                                    Setting  10 Ba River Alluvium With Overbank Deposit
                                                                                      General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
7-10
Sand and Gravel
Silty Loam
0-2%

Silt/Clay

700-1000
Weight

5
4
3
2
1

5

3
Rating

7
8
8
4
10

1

6
Number

35
32
24
8
10

5

18
                                                                                  DRASTIC Index  132
                                                                         109

-------
Setting 10 Ba River Alluvium With Overbank Deposit
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
7-10
Sand and Gravel
Silty Loam
0-2%

Silt/Clay

700-1000


Weight Rating

5 7
4 8
3 8
5 4
3 10

4 1

2 6
Agricultural
DRASTIC Index
Number

35
32
24
20
30

4

12

157
Atlantic and Gulf Coastal Plain

(lOBb)   River Alluvium Without Overbank

This setting is identical to (10Ba) River Alluvium With
Overbank except that  no  significant  fine-grained
floodplain deposits  occupy the stream valley. This
results in significantly  higher recharge and  sandy
soils at the surface. Water levels are typically closer to
the surface because banks of fine-grained deposits
are not present. Throughout much of this region there
is an abundance of coarse-grained material, which
limits this setting for water supply. These materials,
however, provide a  good source of recharge to the
underlying consolidated and semi-consolidated bed-
rock.
Setting  10 Bb River Alluvium Without Overbank Deposit
                          	General	
    Feature
                                                                     Range
                           Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

5-15
10+
Sand and Gravel
Sand
0-2%
S & G w/sig.
Silt and Clay

1000-2000

5
4
3
2
1

5

3

9
9
8
9
10

6

8

45
36
24
18
10

30

24
                                                                                 DRASTIC Index  187
                                                   Setting 10 Bb River Alluvium Without Overbank Deposit
                                                                              	Agricultural
                                                       Feature
                                                                     Range
                           Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



5-15
10+
Sand and Gravel
Sand
0-2%
S & G w/sig.
Silt and Clay

1 000-2000



5 9
4 9
3 8
5 9
3 10

4 6

2 8
Agricultural
DRASTIC Index

45
36
24
45
30

24

16

220
Atlantic and Gulf Coastal Plain
                                                   (IOC)  Swamp

                                                   This hydrogeologic setting is characterized by low
                                                   topographic relief and deposits of sand, and sand and
                                                   gravel, which overlie consolidated and semi-consoli-
                                                   dated  sedimentary  rocks.  Surficial deposits are
                                                   typically sand mixed with organic material. The
                                                   surficial sands are usually in hydraulic connection
                                                   with the underlying aquifers and serve as a source of
                                                   recharge. Precipitation is  abundant and potential
                                                   recharge is high. Water levels are typically at or near
                                                   the surface during the majority of the year. While a
                                                   swamp is frequently a ground water discharge zone,
                                                   and as such not especially vulnerable to pollution, it is
                                                   surficially  an  environmentally sensitive area.  It
                                                   should also be noted that a slight reversal in gradient
                                                   would easily convert the swamp into a ground water
                                                   recharge zone. Thus, it is potentially highly vulnerable
                                                   to ground-water pollution.
                       110

-------
Setting 10 C Swamp
    Feature	Range
                                       General
                               Weight  Rating  Number
Depth to Water
  Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
  Zone
Hydraulic
  Conductivity
                     0-5
                     10+
               Sand and Gravel
                    Sand
                    0-2%

               Sand and Gravel

                  1000-2000
10
 9
 8
 9
10
50
36
24
18
10

40

24
                                  DRASTIC Index   202
Setting IOC Swamp

    Feature          Range
                                     Agricultural
                               Weight   Rating  Number
Depth to Water
  Table
Net Recharge
Aquifer Media
Soil Media
                     0-5
                     10+
               Sand and Gravel
                    Sand
                    0-2%
Topography
Impact Vadose
  Zone          Sand and Gravel
Hydraulic
  Conductivity      1000-2000
10
 9
 8
 9
10
50
36
24
45
30

32

16
                                 Agricultural
                                 DRASTIC Index   233

-------
                                7 7.   Southeast Coastal Plain

                 (Thick layers of sand and clay over semi-consolidated carbonate rocks)
The Southeast  Coastal Plain is an  area  of about
212,000 km2 in Alabama, Florida, Georgia, and South
Carolina. It is a relatively flat, low-lying area in which
altitudes range  from sea level at the coast to about
100 m down the center of the Florida peninsula and
as much as 200  m on hills in Georgia near the interior
boundary of the region. Much of the area, including
the Everglades  in southern  Florida, is a nearly flat
plain less than 10m above sea level.

The land surface of the Southeast Coastal Plain is
underlain by unconsolidated deposits of Pleistocene
age consisting of sand, gravel, clay, and shell beds
and, in southeastern Florida,  by semi-consolidated
limestone. From the coast up to altitudes of nearly
100 m,  the  surficial deposits  are  associated with
marine terraces formed when the Coastal Plain was
inundated at different times by the sea. In most of the
region the  surficial  deposits  rest on formations,
primarily of middle to late Miocene age, composed of
interbedded  clay, sand, and  limestone.  The  most
extensive Miocene deposit is the Hawthorn Forma-
tion. The formations of middle to late Miocene age,
and where those formations are absent, the surficial
deposits  overlie  semi-consolidated limestones and
dolomites that are as much as 1,500 m thick. These
carbonate rocks range in age from early Miocene to
Paleocene and are generally referred to collectively
as Tertiary limestones.

The Tertiary  limestone that underlies the Southeast
Coastal Plain constitutes one of the most productive
aquifers in the United States and is the feature that
justifies treatment of the region separately from the
remainder of the Atlantic and Gulf Coastal Plain. The
aquifer,  which  is known  as the  Floridan aquifer,
underlies all of Florida and southeast Georgia and
small areas  in  Alabama  and  South Carolina. The
Floridan  aquifer consists of layers several meters
thick composed largely of loose aggregations of shells
of foraminifers and fragments of echinoids and other
marine organisms  interbedded with much thinner
layers of cemented  and cherty  limestone. The
Floridan, one of the most productive aquifers  in the
world, is the principal source of ground-water sup-
plies in the southeast Coastal Plain region.

In southern Florida, south of Lake Okeechobee,  and in
a belt about 30 km wide  northward along the east
coast of Florida to the vicinity of St. Augustine, the
water in the Floridan aquifer contains more than 100
mg/l of chloride. In this area, most water supplies are
obtained from surficial aquifers, the most notable of
which underlies the southeastern part of Florida and
which in the Miami area consists of 30 to 100 m of
cavernous limestone and sand referred to as the
Biscayne aquifer. The  Biscayne  is  an unconfined
aquifer which is recharged by local precipitation and
by infiltration of water from canals that drain  water
from impoundments (conservation areas) developed
                                               112

-------
in the Everglades. It is the principal source of water
for municipal, industrial, and irrigation uses and can
yield as much as 5 m3 min~1 (1,300 gal min~1) to
small-diameter wells less than 25 m deep finished
with open holes only 1 to 2 m in length.

The surficial aquifers in the remainder of the region
are composed primarily of sand, except in the coastal
zones of Florida where the sand is interbedded with
shells and thin limestones.  These surficial aquifers
serve as sources of small ground-water supplies
throughout the region and are the primary sources of
ground water where the water intheFloridan aquifer
contains more than about 259 mg/l of chloride.

The Floridan aquifer, as noted above, is the principal
source of ground water in the region. Ground water in
the upper part of the aquifer is unconfined  in the
principal  recharge areas in Georgia and in  west-
central Florida. In the remainder of the region, water
in the aquifer is confined by clay in the Hawthorn
Formation and in other beds that overlie the aquifer.
Recharge occurs where the potentiometric surface of
the Floridan aquifer is lower than the water table in
the overlying surficial aquifer. The principal recharge
areas include a broad area along the west side of
Florida extending from the central part of the penin-
sula to south-central Georgia and an area extending
from west-central Florida through southeast Alabama
into  southwest Georgia. In these areas, recharge
rates are estimated to exceed 120 mm yr~1 (5 in. yr~1).
Recharge occurs by infiltration of precipitation directly
into the limestone, where it is exposed at the land
surface, and by seepage through the permeable soils
that partly mantle the limestone in the outcrop  areas.
Considerable recharge also occurs in the  higher parts
of the recharge areas through permeable openings in
the confining beds, where these beds have been
breached by the collapse of caverns in the limestone
during the process of sinkhole formation. Thus, the
land surface in  most  of  Florida north of Lake
Okeechobee  is marked  by thousands of closed
depressions ranging in diameter from a few meters to
several kilometers.  The larger depressions, which
represent a more  advanced stage of solution  of the
limestone and collapse of the overlying material, are
occupied by lakes generally referred to  as sinkhole
lakes.

Discharge from the  Floridan aquifer occurs through
springs and by seepage to streams. Considerable
discharge also occurs by diffuse seepage across the
overlying confining beds in areas where  the potenti-
ometric surface of the aquifer  stands  at a higher
altitude than the water table. In most of these areas,
which  include the  southern third  of  the Florida
peninsula, the east coast area and major stream
valleys of  Florida, and the coastal zone and  major
stream vaMeys of Georgia and South Carolina, wells
open to the aquifer will flow at the land surface. Such
wells are called "flowing artesian wells." The most
spectacular discharge from the Floridan aquifer is
through sinkholes  exposed along streams  and off-
shore. Florida has 27 springs of the first magnitude at
which the average  discharge exceeds 2.83  m3 sec"1
(100 ft3 sec'1). The largest is  Silver Springs,  which
has  an  average discharge of 23.2  m3 sec~1 (530
million gallons per day) and  reached a maximum
discharge of 36.5 m3 sec~1 on September 28, 1960.
Heath and Conover(1 981 (estimate that the combined
discharge from Florida's springs  is 357 m3 sec~1 (8
billion gallons per day).

The  marked difference in  ground-water conditions
between the Southeast Coastal Plain and the Atlantic
and  Gulf Coastal Plain regions is apparent  in the
response of ground-water  levels  to withdrawals. In
the Atlantic and Gulf Coastal Plain region most large
withdrawals  are accompanied  by  a pronounced
continuing decline in ground-water  levels.  In the
Southeast Coastal  Plain, on the  other  hand, large
withdrawals have significantly lowered ground-water
levels in only  a few areas.
Southeast Coastal Plain

(11 A)  Solution Limestone

This hydrogeologic setting is characterized by low to
moderate topographic relief and deposits of limestone
which have been partiallydissolvedtoform a network
of solution cavities  and caves.  Surficial  deposits
typically consist of sands. Precipitation is abundant
and recharge is high. Water levels are variable but are
usually moderate in the limestone and shallow in the
overlying surficial  sands. These sands serve as an
important source of recharge for the limestones. Due
to the presence of a shallow water table and direct
recharge to the limestone these surficial sands are
very vulnerable to pollution.  Near the coast, these
aquifers are very susceptible to salt-water intrusion.
                                                                       113

-------
Setting  11 A Solution Limestone
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Karst Limestone
Sand
2-6%

Karst Limestone

2000+
Weight

5
4
3
7
1

5

3
Rating

9
9
10
9
9

10

10
Number

45
36
30
18
9

50

30
                              DRASTIC Index  218
Setting  11 A Solution Limestone

    Feature         Range     Weight  Rating  Number
Agricultural
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity



5-15
10+
Karst Limestone
Sand
2-6%

Karst Limestone

2000+



5 9
4 9
3 10
5 9
3 9

4 10

2 10
Agricultural
DRASTIC Index

45
36
30
45
27

40

20

243
                   Setting 11 B Coastal Deposits
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

700-1000

Weight

5
4
3
2
1

5

3
General
Rating

9
9
8
9
10

8

6

Number

45
36
24
18
10

40

18
                                                                                 DRASTIC Index   191
Southeast Coastal Plain

(11 B)   Coastal Deposits

This hydrogeologic setting is  characterized by flat
topography and unconsolidated deposits of carbonate,
sand, gravel, clay, and shell beds which overlie semi-
consolidated carbonate rocks.  The surficial deposits
serve as direct use sources of ground water and also
serve as recharge for the  underlying carbonate rocks
where the gradient is downward toward the car-
bonates. The carbonates serve as a source of ground
water but may contain saline  water in some areas.
Precipitation is abundant  and recharge is high. Water
levels may vary, but are typically close to the surface.
                                                    Setting 11 B Coastal Deposits

                                                       Feature        Range
                                                    Agricultural
                                              Weight   Rating  Number
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

5-15
10+
Sand and Gravel
Sand
0-2%

Sand and Gravel

700-1 000

5
4
3
5
3

4

2

9
9
8
9
10

8

6

45
36
24
45
30

32

12
Agricultural
DRASTIC Index
224
                                                    Southeast Coastal Plain
                                                    (11C)   Swamp
                                                    This hydrogeologic setting is  characterized by flat
                                                    topographic relief, very high water levels, and deposits
                                                    of limestone which have partially been dissolved to
                        114

-------
form a network of solution cavities and caves. Soils
are typically sand and recharge is high due to the
abundant precipitation. The limestone typically serves
as the  major regional aquifer. Water levels  are
typically at or above the surface during the majority of
the year. These swamps are typically discharge areas,
but due to their environmental vulnerability, and
possible gradient reversal, they should be regarded as
areas of maximum (potential) recharge.
Southeast Coastal Plain
(1 ID)   Beaches and Bars
This hydrogeologic setting is characterized by moder-
ate to flat topographic  relief and unconsolidated
deposits of water-washed  sands. These sands are
well-sorted and very permeable, and  may serve as
localized sources of ground water. These deposits
also serve as a source of recharge to the underlying
unconsolidated coastal  deposits.  Precipitation  is
abundant and  recharge  is  high. Water levels may
vary, but are typically shallow. These arears are highly
susceptible to pollution due to their high permeabil-
ities.
Setting 11 C Swamp
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

0-5
10+
Karst Limestone
Sand
0-2%

Karst Limestone

2000+

Weight

5
4
3
2
1

5

3
General
Rating

10
9
10
9
10

10

10

Number

50
36
30
18
10

50

30
                                                   Setting  11 D Beaches and Bars
Setting 11 C Swamp
                             DRASTIC Index   224
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sand
2-6%

Sand and Gravel

700-1000

Weight

5
4
3
2
1

5

3
General
Rating

9
9
8
9
9

8

6

Number

45
36
24
18
9

40

18
Setting 11 D Beaches and Bars
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

Range
0-5
10+
Karst Limestone
Sand
0-2%
Karst Limestone
2000+

Weight Rating
5 10
4 9
3 10
5 9
3 10
4 10
2 10
Agricultural
DRASTIC Index
Number
50
36
30
45
30
40
20
251
                                                                                 DRASTIC Index  190
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sand
2-6%

Sand and Gravel

700-1000
Weight

5
4
3
5
3

4

2
Rating

9
9
8
9
9

8

6
Number

45
36
24
45
27

36

12
Agricultural
DRASTIC Index
225
                                                                        115

-------
                                    12.   Hawaiian Islands

   (Lava flows segmented in part by dikes, interbedded with ash deposits, and partly overlain by alluvium)
  I Off
40*
40°
                                      'Off
                       VI
                         HAWAIIAN
                         --. ISLAND

                     / F I C
O C E A F<
 The Hawaiian Islands region encompasses the State
 of Hawaii and consists of eight major islands occu-
 pying  an area of 16,707 km2  in the Pacific Ocean
 3,700 km southeast of California. The islands are the
 tops of volcanoes that rise from the ocean floor and
 stand  at altitudes ranging from a few meters to more
 than 4,000  m above sea  level.  Each island  was
 formed by lava that issued from one or more eruption
 centers. The islands have a  hilly to mountainous
appearance resulting from erosion that has carved
valleys into the volcanoes and built relatively narrow
plains along parts of the coastal areas.

Each of the Hawaiian Islands is underlain by hundreds
of distinct and separate lava flows, most of which are
composed of  basalt. The lavas issued in repeated
outpourings  from narrow zones of fissures,  first
below sea level, then above it. The lavas that extruded
below the sea  are  relatively  impermeable. Those
formed above sea level tend to be highly permeable,
with interconnected openings that formed as the lava
cooled, cavities and openings that were not filled by
the overlying flow,  and lava  tubes  (tunnels).  The
central parts  of the  thicker flows tend to be more
massive and  less permeable; the  most  common
water-bearing openings are joints and faults  that
formed after the lava solidified. Thin layers of ash and
weathered volcanic  rock occur irregularly between
some of the flows that formed above sea level. The
lava flows in valleys and parts of the coastal plains are
covered by a thin layer of alluvium consisting of coral
(limestone) fragments, sand-size fragments of basalt,
and clay.

The fissures through which the lava erupted tend to
cluster near eruption centers. Flows from the fissures
moved down depressions on the adjacent slopes to
form layers of lavathatdipat angles of4to 10degrees
toward the margins of the volcanoes. The result, prior
to modification by erosion, is a broad, roughly circular,
gently convex mountain similar in shape to a warrior's
shield. Thus,  volcanoes of the Hawaiian type are
referred to as shield volcanoes. When eruption along
a fissure ceases, the lava  remaining in the fissure
solidifies to form a dike.

All  of the  islands have sunk,  to some extent, as a
result of a downward flexing of the Earth's crust
caused by the weight of the volcanoes.  This has
resulted in flows that formed above sea level being
depressed below sea level. The upper parts of these
flows contain freshwater that serves as an important
source of water.

In mineral composition  and  nature  of the water-
bearing openings, the lavas that form the Hawaiian
Islands are very similar to those in the Columbia
Plateau region. Thus, from these two standpoints,
                                               116

-------
these regions could be combined into one. There is,
however, one important difference that justifies their
treatment as separate regions. This difference relates
to the presence of seawater around and beneath the
islands, which  significantly affects the occurrence
and development of water supplies.

From the standpoint both of description and  of
development, it is useful to divide the ground-water
system of the Hawaiian Islands into three parts. The
first part consists of the higher areas of the islands in
the vicinity of the eruption centers. The rocks in these
areas are formed into a complex series of vertical
compartments surrounded by dikes developed along
eruption fissures. The ground water in these com-
partments is  referred to as dike-impounded water.
The second, and by far the more important, part of the
system  consists of the  lava  flows that flank the
eruption centers and that contain fresh ground water
floating on saline ground water. These flank flows are
partially  isolated hydraulically from  the  vertical
compartments developed by the dikes that surround
the eruption centers. The fresh ground water in these
flows is referred to as basal ground water. In parts of
the coastal areas the basal water is confined by the
overlying  alluvium.  The third  part  of the system
consists of fresh water  perched, primarily in lava
flows, on soils, ash, or thick impermeable lava flows
above basal ground water.

The ground-water system is recharged by precipita-
tion which ranges annually from about 160 mm to
more than 11,000 mm. This wide range in precipita-
tion reflects the effect of the islands on the moist
northeast trade  winds. As the moisture-laden winds
are deflected upward by the mountains, precipitation
falls on the higher elevations. Precipitation is heaviest
on  mountains below 1,000 m and  lightest in the
coastal areas on the leeward side of the islands and at
elevations above 1,000 m on the islands of Maui and
Hawaii. The  average annual  precipitation on the
islands is estimated to be about 1,800 mm. Because
of the highly permeable nature of the volcanic soils, it
is estimated that about 30 percent of the precipitation
recharges the ground-water system.

Some discharge of  dike-impounded ground water
doubtless  occurs through fractures in the dikes into
the flanking lava flows. This movement must be
small, however, because water stands in the com-
partments at levels hundreds of meters above sea
level and the principal discharge occurs as springs on
the sides and at the  heads of valleys where erosion
has removed parts of the dikes. Both the basal ground
water and the perched ground water in the lava flows
surrounding the  dike-bounded compartments  is
recharged by precipitation and by streams leaving the
dike-bounded area. Discharge is to  streams and  to
springs and seeps along the coast.
 The basal water  is the principal source of ground
 water on the islands. Because the  freshwater  is
 lighter (less dense) than seawater, it floats as a lens-
 shaped body on the underlying seawater. The thick-
 ness of the freshwater zone below sea level essenti-
 ally depends  on the height of the freshwater head
 above sea level. Near the coast the zone is thin, but
 several kilometers inland from the coast on the larger
 islands it reaches  thicknesses of at least  a few
 hundred meters.  In parts of the coastal zone, and
 especially on the leeward side of the  islands, the
 basal ground water is brackish.

 Forty-six percent of the water used in Hawaii in 1 975,
 or 3.1 x 106 m3 day"1, was ground water. It is obtained
 through horizontal tunnels and through both vertical
 and inclined wells. Tunnels  are  used  to  obtain
 supplies of basal water near the coast where the
 freshwater zone is thin. Tunnels are also used to tap
 dike-impounded  water. These  tunnels encounter
 large flows of water when the principal  impounding
 dike is penetrated and it is necessary to drain most of
 the water in  the  saturated zone above the tunnel
 before construction can be completed. Thereafter, the
 yield of the tunnel reflects the rate of recharge to the
 compartment tapped by the tunnel. To avoid a large
 initial waste of water and to preserve as much storage
 as possible, the Honolulu Board of Water Supply has
 begun to construct inclined wells to obtain  dike-
 impounded water. Vertical wells are used to obtain
 basal water and perched ground water in inland areas
 where the thickness of the freshwater zone permits
 the use of such wells.
Hawaii
(12A)  Mountain Slopes
This hydrogeologic setting is characterized by steep
slopes composed of volcanic lava flows, breccia, and
related extrusive magmatic rocks. Soils are thin, but
highly  permeable  where present.  Rubble alluvial
deposits are common. Because of the steep topog-
raphy and elevation the water table tends to be deep.
Water occurs in the fractures and vesicular zones of
the basaltic  lava  flows, and along the relatively
horizontal inter-flow zones. Overall, hydraulic conduc-
tivity is moderately high, due to the density of fracture
zones. Perched water table zones are common, where
water in an inter-flow zone between successive lava
flows is delayed from moving downward by a dense
layer of clayey material, or  basalt. The dense layer
acts as an aquitard. Rainfall is high, and with perme-
able surface material recharge is also high.
                                                                      117

-------
                                                   Hawaii

                                                   (12B)  Alluvial Mountain Valleys
                                                   This hydrogeologic setting is characterized by narrow,
                                                   steep-walled valleys, with moderate to steep seaward
                                                   slope. The valleys contain alluvial material varying
                                                   typically from zero to a few tens of feet in thickness.
                                                   Waterfalls and related features are common near the
                                                   ocean. The alluvium consists of basaltic debris and
                                                   the weathered products thereof. Soils are moderately
                                                   developed, thin, and quite permeable. Rainfall is high,
                                                   infiltration, or recharge,  is  high, and vegetation is
                                                   lush. The alluvium below stream grade is generally
                                                   saturated  at  a shallow level,  and  is sometimes
                                                   hydraulically  connected  to  the  permanent  water
                                                   table, sometimes to perched zones, and sometimes,
                                                   particularly in the  upper reaches,  leaks  into the
                                                   vadose  zone.  Hydraulic conductivity of both the
                                                   alluvium and underlying aquifers is high.
Setting 12 A Mountain Slopes
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

100+
10+
Basalt
Thin or Absent
18+%

Basalt

2000+
Weight

5
4
3
2
1

5

3
Rating

1
g
9
10
1

g

10
Number

5
36
27 ,
20
1

45

30

Setting 12 A Mountain Slopes
                              DRASTIC Index  1 64
                                 Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

Range Weight
Rating Number
Setting 12 B Alluvial Mountain Valleys
100+
10+
Basalt
Thin or Absent
18+%

Basalt

2000+

5
4
3
5
3

4

2

1
g
g
10
1

g

10

Agricultural
DRASTIC Index
5
36
27
50
3

36

20

177

Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose

Hydraulic
Conductivity

Range
5-15
10+
Sand and Gravel
Sandy Loam
12-18%


1000-2000

Weight
5
4
3
2
1

5
3

General
Rating
g
g
8
6
3

8
8


Number
45
36
24
12
3

40
24
                                                                                 DRASTIC Index  184
                        118

-------
Setting 12 B Alluvial Mountain Valleys
                                 Agricultural
                                                   Setting 12 C Volcanic Uplands
                                                                                      General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
10+
Sand and Gravel
Sandy Loam
12-18%

Sand and Gravel

1000-2000
Weight

5
4
3
5
3

4

2
Rating

9
9
8
6
3

8

8
Number

45
36
24
30
9

32

16
Agricultural
DRASTIC Index
192
Hawaii

(12C)  Volcanic Uplands

This hydrogeologic setting is characterized by moder-
ately rolling topography, at medium elevations, and
rich, dark, soils developed from the basaltic bedrock.
The soils are permeable, rainfall is high, and recharge
is high. Bedrock is composed primarily of alternating
extrusive basaltic lava flows and interlayered weath-
ered zones  formed between flows.  Ground water
occurs at moderate to deep depths, and aquifer yield
is controlled by fracture zones, vesicular zones (both
primarily cooling features) and the inter-flow weath-
ered zones.  Hydraulic conductivity is high.  As with
other settings in Hawaii, heavy pumping stresses
often result in salt-water intrusion. This is a reflection
of the fact that  each island  is surrounded by and
underlain by salt water, with the fresh water occur-
ring in a lenticular body that floats on the salt water.
Ground-water yield is therefore limited quite specifi-
cally to the amount of water recharged annually.
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
10+
Basalt
Sandy Loam
6-12%

Basalt

2000+
Weight

5
4
3
2
1

5

3
Rating

2
9
9
6
5

9

10
Number

10
36
27
12
5

45

30
                                                   Setting 12 C Volcanic Uplands
                                                                                 DRASTIC Index  165
                                                                                    Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

75-100
10+
Basalt
Sandy Loam
6-1 2%

Basalt

2000+
Weight

5
4
3
5
3

4

2
Rating

2
9
9
6
5

9

10
Number

10
36
27
30
15

36

20
                              Agricultural
                              DRASTIC Index  174
Hawaii

(12D)  Coastal Beaches

This hydrogeologic setting is characterized by low to
moderate topography, near sea  level, with sandy
materials at the surface. The sandy soils are very
permeable, and direct recharge from rainfall is high
where ground-water levels permit. Because of their
location  these  settings are often discharge areas
where ground water is lost into the ocean. Manage-
ment of this  area is essential  to  the  maximum
utilization of the  ground-water  resources of the
islands. It should be noted that all discharge areas are
potential recharge areas, and as such  potentially
vulnerable to pollution.
                                                                         119

-------
Setting 12 D Coastal Beaches
                                       General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

0-5
10+
Sand and Gravel
Sand
2-6%

Sand and Gravel

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

10
9
8
9
9

8

8
Number

50
36
24
18
9

40

24
                                  DRASTIC Index   201
Setting 12 D Coastal Beaches
                                     Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

0-5
10+
Sand and Gravel
Sand
2-6%

Sand and Gravel

1000-2000


Weight Rating

5 10
4 9
3 8
5 9
3 9

4 8

2 8
Agricultural
DRASTIC Index
Number

50
36
24
45
27

32

16

230
                           720

-------
                                         13.   Alaska

         (Glacial and alluvial deposits, occupied in part by permafrost, and overlying crystalline,
                               metamorphic, and sedimentary rocks)
The Alaska region encompasses the State of Alaska,
which occupies an area of 1,519,000 km2  at the
northwest corner of North America. Physiographical-
ly, Alaska can be divided  into four divisions—from
south to north, the Pacific Mountain System, the
Intermontane Plateaus, the Rocky Mountain System,
and the Arctic Coastal Plain. The Pacific Mountain
System is the Alaskan equivalent of the Coast Range,
Puget Sound Lowland, and Cascade provinces of the
Washington-Oregon area. The Intermontane Plateaus
is a lowland  area of plains, plateaus,  and  low
mountains comparable  to  the  area  between  the
Cascades-Sierra Nevada and the Rocky Mountains.
The Rocky Mountain System is a continuation of the
Rocky Mountains of the  United States  and Canada,
andthe Arctic Coastal Plain is the geologic equivalent
of the Great Plains of the United States and Canada.
The coastal areas and lowlands range in altitude from
sea level to about 300  m, and the higher mountains
reach altitudes of 1,500 to 3,000 m. Mt. McKinley in
the Pacific Mountain System is the highest peak in
North America, with an altitude of about 6,300 m.

As would be expected  of any area its size,  Alaska is
underlain by a diverse  assemblage of rocks. The
principal  mountain ranges have cores of igneous and
metamorphic rocks ranging in age from  Precambrian
to Mesozoic. These are overlain  and flanked by
younger  sedimentary and volcanic rocks. The sedi-
mentary  rocks include  carbonates,  sandstones, and
shales. In much of the region the bedrock is overlain
by unconsolidated deposits of gravel, sand, silt, clay,
and glacial till.

Climate has a dominant  effect on hydrologic condi-
tions in Alaska. Mean annual air temperatures range
from -12°C in the Rocky Mountain System and  the
Arctic Coastal Plain to about 5°C in the coastal zone
adjacent  to the Gulf of Alaska. The present climate
and the colder climates that  existed intermittently in
the past have resulted in the formation of permafrost,
or perennially frozen ground. Permafrost is present
throughout the State except in a narrow strip along
the southern and southeastern coasts. In the northern
part of the Seward Peninsula, in the western and
northern  parts of the Rocky Mountain System, and in
the Arctic Coastal  Plain, the permafrost extends to
depths as great as 600 m and is continuous except
beneath deep lakes and in the alluvium beneath the
deeper parts of the channels of streams. South of this
area and  north of the coastal strip, the permafrost is
discontinuous  and depends on exposure,  slope.
                                              121

-------
vegetation, and  other  factors.  The permafrost is
highly  variable in thickness  in this zone but is
generally less than 100 m thick.

Much of the water in Alaska is frozen for at least a part
of each year: that on the surf ace as ice in streams and
lakes or as snow or glacier ice  and that below the
surface as winter frost and permafrost. Approximately
half  of Alaska, including the mountain  ranges and
adjacent  parts  of  the  lowlands,  was  covered  by
glaciers during the Pleistocene  age. About 73,000
km2, or one-twentieth of the region, is still occupied
by glaciers, most of which are in the mountain ranges
that  border the Gulf of  Alaska. Precipitation, which
ranges from about 130 mm yr~1 in the Rocky Mountain
System and the Arctic Coastal Plain to about 7,600
mm yr~1 along the southeast coast, falls as snow for 6
to 9  months of the year and even year-round in the
high mountain regions. The snow remains on the
surface until  thawing conditions  begin, in May in
southern and central Alaska and  in June in the arctic
zone. During the period  of subfreezing temperatures,
there is no overland runoff, and many streams and
shallow lakes not receiving substantial ground-water
discharge are frozen solid.

From the standpoint of ground-water availability and
well yields, Alaska is divided into three zones. In the
zone of continuous permafrost, ground water occurs
beneath the permafrost and also in small,  isolated,
thawed zones that penetrate the  permafrost beneath
large lakes and deep holes in the channels of streams.
In the zone of discontinuous permafrost, ground
water occurs  below the permafrost and  in sand and
gravel deposits that underlie the  channels and flood-
plains of major streams. In the zone of discontinuous
permafrost, water contained in silt, clay, glacial till,
and  other fine-grained deposits usually is frozen.
Thus, in this zone the occurrence of ground water is
largely controlled by hydraulic  conductivity. In the
zone not affected by permafrost, which includes the
Aleutian Islands, the western  part of the Alaska
Peninsula, and the southern and southeastern coastal
areas, ground water occurs both  in the bedrock and in
the  relatively  continuous  layer of unconsolidated
deposits that mantle the bedrock.

Relatively little is known about  the occurrence and
availability of ground water in the bedrock. Perma-
frost extends into the bedrock in  both the zones of
continuous and discontinuous permafrost, but springs
that issue from carbonate rocks in the Rocky Mountain
System indicate the  presence of  productive water-
bearing openings. Small supplies of ground water
have also  been developed from  sandstones, from
volcanic rocks, and from faults  and fractures in the
igneous and metamorphic rocks.

Recharge of the aquifers in the Alaska region occurs
when the ground is thawed in the areas not underlain
by permafrost. This period generally lasts only from
June through September. Because the ground, even
in nonpermafrost areas,  is still frozen when  most
snowmelt runoff occurs,  relatively little recharge
occurs in interstream areas by infiltration of water
across the unsaturated zone. Instead, most recharge
occurs through the channels of streams where they
flow across the alluvial fans that fringe  the moun-
tainous  areas and  in alluvial  deposits for some
distance downstream. Because of the large hydraulic
conductivity of the sand and gravel in these areas, the
rate of infiltration is large. Seepage investigations
along Ship Creek near Anchorage indicate channel
losses of 0.07  m3  sec"1  km  ,  which  gives  an
infiltration rate through the wetted perimeter of about
0.4 m day"1
Discharge from aquifers occurs in the downstream
reaches of streams and through seeps and  springs
along the coast. The winter flow of most Alaskan
streams is sustained by ground-water discharge. In
the interior and  northern regions, this discharge is
evidenced by the buildup of ice (referred to locally as
"icings") in the channels of streams and  on the
adjacent floodplains.
Unlikethe 12 regions which comprise the contiguous
United States, both Alaska and Hawaii are political
subdivisions,  not discrete ground-water  regions.
Hawaii can betreated as a single region because of its
smaller size and relative geologic simplicity. Alaska,
however,  due to its size and complexity includes
several major ground-water regions. For purposes of
this document, these regions are considered hydro-
geologic settings.
 Alaska
 (13A)  Alluvium
 This hydrogeologic setting includes floodplains, ter-
 races, and alluvial fans of both major valleys and
 upland and mountain valleys. Braided streams are
 present in the major valley floodplains. Heavy silt/
 rock flour loading in streams results in subtantial silt
 and clay deposition along with the alluvial sands and
 gravels.  Ground-water levels are  usually shallow
 near  the streams,  into which the  ground water
 discharges, and considerably deeper along the higher
 terraces. Recharge to the ground water is seasonal,
 following snowmelt and thawing of frozen areas.
 Except for the south coastal area, precipitation is light
 to  moderate and usually in the form of  snow.
 Topography is moderate, with a unidirectional down-
 stream ground-water movement. Hydraulic conduc-
 tivities are moderate to very high  in the  cleaner
 portions of the sand and gravel aquifers.
                       122

-------
Setting 13 A Alluvium
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
2-4
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig.
Silt and Clay

700-1 000

Weight

5
4
3
2
1

5

3
General
Rating

7
3
8
6
9

6

6

Number

35
12
24
12
9

30

18
Setting 13 A Alluvium
                              DRASTIC Index  140
                                  Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity

Range
15-30
2-4
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig.
Silt and Clay
700-1 000

Weight Rating
5 7
4 3
3 8
5 6
1 9
4 6
2 6
Agricultural
DRASTIC Index
Number
35
12
24
30
27
24
12
164
Alaska
(13B)  Glacial and Glaciolacustrine Deposits of
        the Interior Valleys
This hydrogeologic setting is characterized by tills and
associated  outwash deposits,  as well  as  glacier-
                                                     related lake deposits of interbedded sand, silt, and
                                                     clay.  Ground-water  levels are  relatively  shallow.
                                                     Surface soils are typically organic sandy loams with
                                                     moderate conductivity. Recharge is moderate to low,
                                                     primarily  limited by the period of thaw and annual
                                                     precipitation. Topography is moderate,  and the hy-
                                                     draulic conductivity of  the  outwash  aquifers is
                                                     generally high.
                                                     Setting 138 Glacial & Glaciolacustraine Deposits:  Interior
                                                                Valleys
                                                                                         General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
2-4
Sand and Gravel
Sandy Loam
2-6%

Silt/Clay

1 000-2000
Weight

5
4
3
2
1

5

3
Rating

9
3
8
6
9

1

8
Number

45
12
24
12
9

5

24
                                                                                    DRASTIC Index   131


                                                     Setting 13 B Glacial & Glaciolacustraine Deposits:  Interior
                                                                Valleys
                                                                                       Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

5-15
2-4
Sand and Gravel
Sandy Loam
2-6%

Silt/Clay

1 000-2000
Weight

5
4
3
5
3

4

2
Rating

9
3
8
6
9

1

8
Number

45
12
24
30
27

4

16
Agricultural
DRASTIC Index
158
                                                                           123

-------
Alaska

(13C)  Coastal-Lowland Deposits
This hydrogeologic setting includes coastal plains,
deltaic deposits of major streams, beaches and near-
shore bars and spits, and deposits of deep alluvial
coastal  basins and valleys.  Permafrost severely
affects the northernmost portions of this setting,
which  is within the permanent permafrost zone.
Where not permanently frozen, recharge rates are
high seasonally, particularly along streams which are
hydraulically connected to the ground water. Ground-
water depths  are at or near the elevation  of the
surface streams, and topographic slopes are  low to
moderate. The primary aquifers in this setting are the
alluvial sands and gravels that are interbedded with
silts and  clays.  Thick sequences  of  all types of
materials are common.
Setting 13 C Coastal Lowland Deposits
                                Agricultural
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity


Range

15-30
2-4
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig
Silt and Clay

700-1000


Weight Rating

5 7
4 3
3 8
5 6
3 9

4 6

2 6
Agricultural
DRASTIC Index
Number

35
12
24
30
27

24

12

164
                                                  Alaska

                                                  (13D)  Bedrock of the Uplands and Mountains

                                                  This hydrogeologic setting is characterized by deposits
                                                  of carbonate rocks, limestone, sandstone, volcanics,
                                                  and other igneous  and metamorphic rocks. These
                                                  formations underlie a thin veneer of alluvium beneath
                                                  a large portion of the state. Water levels within this
                                                  setting are variable,  but generally deep. Exceptions to
                                                  this are discharge zones along the flanks of many
                                                  mountains.  The most  notable example of this are
                                                  springs discharging from carbonate rocks along the
                                                  flanks of mountains. Recharge is limited by precipita-
                                                  tion, topography, and predominant permafrost. Soils
                                                  are  generally thin  and poorly developed.  Aquifer
                                                  conductivities vary from low in some of the fractured
                                                  metamorphics to very high in the solution-dissolved
                                                  carbonates.
Setting 13 C Coastal Lowland Deposits
                                  General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media
Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

15-30
2-4
Sand and Gravel
Sandy Loam
2-6%
S & G w/sig
Silt and Clay

700-1 000
Weight

5
4
3
2
1

5

3
Rating

7
3
8
6
9

6

6
Number

35
12
24
12
9

30

18
                             DRASTIC Index  140
                        124

-------
Setting 13 D Bedrock of the Uplands and Mountains
                                       General
Feature
Depth to Water
Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
Zone
Hydraulic
Conductivity
Range

100+
0-2
Thin Bedded SS,
LS, SH Sequences
Thin or Absent
12-18%
Bedded LS,
SS, SH

300-700
Weight

5
4

3
2
1

5

3
Rating

1
1

6
10
3

6

4
Number

5
4

18
20
3

30

12
                                  DRASTIC Index   92
Setting  13 D Bedrock of the Uplands and Mountains
                              	Agricultural
    Feature
     Range
                               Weight   Rating  Number
Depth to Water
  Table
Net Recharge
Aquifer Media

Soil Media
Topography
Impact Vadose
  Zone
Hydraulic
  Conductivity
      100+
      0-2
 Thin Bedded SS,
LS, SH Sequences
 Thin or Absent
    12-18%
   Bedded LS,
    SS, SH

    300-700
 1
 1

 6
10
 3

 6

 4
 5
 4

18
50
 9

24

 8
                                  Agricultural
                                  DRASTIC Index
                                  118
                                                                                   125

-------
References
Gutentag, E. D. andJ. B. Weeks, 1980. Watertable in
  the High Plains Aquifer in 1978 in parts of Colorado,
  Kansas, Nebraska, New Mexico, Oklahoma, South
  Dakota, Texas and Wyoming; U.S. Geological
  Survey Hydrologic Investigations Atlas 642.

Hampton, E. R., 1964. Geologic factors that control
  the occurrence and availability of ground water in
  the Fort Rock Basin, Lake County, Oregon; U.S.
  Geological Survey Professional Paper  383-B,  29
  pp.

Heath, Ralph C., 1984. Ground water regions of the
  United States; U.S. Geological Survey Water Supply
  Paper 2242, 78 pp.

LeGrand, H. E. and W. A. Pettyjohn, 1 981. Regional
  hydrogeologic concepts  of  homoclinal flanks;
  Ground Water, Vol. 19, No. 3, pp. 303-310.

Luckey, R. R. and E. D. Gutentag, 1981. Water-level
  and saturated-thickness changes, predevelopment
  to 1980,  in the  High Plains Aquifer  in  parts of
  Colorado, Kansas, Nebraska, New Mexico, Okla-
  homa, South  Dakota, Texas  and  Wyoming; U.S.
  Geological Survey Hydrologic Atlas 652.

MacNish, R.  D. and  R. A.  Barker, 1976.  Digital
  simulation of a basalt aquifer system, Walla Walla
  River Basin, Washington and Oregon; Washington
  Department of Ecology, Water Supply Bulletin 44.

McGuiness, C. L., 1963. The role of ground water in
  the national water situation; U.S. Geological Survey
  Water Supply Paper 1800, 1121 pp.

Nace,  R. L., 1958. Hydrology  of the Snake River
  basalt; Washington Academy of Science Journal,
  Vol.48, No. 4, pp. 136-138.
Newcomb,  R.  C.  1961. Storage of ground water
  behind subsurface dams  in  the Columbia River
  basalt, Washington, Oregon and Idaho; U.S. Geo-
  logical Survey Professional Paper 383-A,  15 pp.
Weeks, J.  B. and  E. D. Gutentag, 1981. Bedrock
  geology,  altitude of base and  1980 saturated
  thickness of the High Plains Aquifer  in parts of
  Colorado, Kansas,  Nebraska, New Mexico, Okla-
  homa, South Dakota, Texas and Wyoming; U.S.
  Geological Survey Hydrologic Investigations Atlas
  648.
                       726

-------
                                        References
 1.  Abrams,  E. F., D. Derkics, C. V. Fong, D. K.
    Guinan, and K. M. Slimak, 1975. Identification
    of organic compounds in effluents from indus-
    trial sources; NTIS PB-241641, 211  pp.

 2.  Anderson, M. P., 1984.  Movement  of contam-
    inants in groundwater: groundwater transport-
    advection and dispersion; Groundwater  Con-
    tamination, National Academy Press, pp. 37-45.

 3.  Blank, Horace R. and  Melvin  C.  Schroeder,
    1973. Geologic classification of aquifers;
    Ground Water, Vol. 11, No. 2, pp. 3-5.

 4.  Bouwer, E. J., B. E. Rittmann, and P.  L. McCarty,
    1981. Anaerobic degradation of halogenated 1 -
    and 2-carbon organic compounds; Environmen-
    tal Science & Technology, Vol. 15, No. 5,  pp.
    596-599.

 5.  Bouwer,  Herman, 1978. Groundwater hydrol-
    ogy; McGraw-Hill, 480 pp.

 6.  Brown,  K. W., G. B.  Evans, Jr.,  and B. D.
    Frentrop eds., 1983. Hazardous  waste land
    treatment; Butterworth Publishers,  692 pp.

 7.  Callahan, M., M. Slimak, N. Gabel, I. May, F.
    Fowler, R. Freed, P.  Jennings, R. Duffee, F.
    Whitmore, B. Maestri, W. Mabey, B. Hold, and
    C. Gould, 1979.  Water related fate of  129
    priority pollutants. Vol. I—introduction  and
    technical  background, metals and  inorganics,
    pesticides and PCBs; U.S. EPA-440/4-79-029a,
    pp. 2-1 through 2-14.

 8.  Cherry, J. A., R. W. Gillham, and J. F. Barker,
    1984. Contaminants in groundwater: chemical
    processes; Groundwater  Contamination, Na-
    tional Academy Press, pp. 46-66.

 9.  Claus, D. and N. Walker, 1964. The decomposi-
    tion of toluene by soil bacteria; Journal General
    Microbiology, Vol. 36, pp. 107-122.

10.  Cohen, S. Z., S. M. Creeger, R. F. Carsel, and C.
    G. Enfield, 1984. Potential for pesticide contam-
    ination  of ground water resulting from agri-
    cultural  uses;  American  Chemical  Society
    Symposium Series #259, Treatment Disposal of
    Pesticide  Wastes, Krueger  and Seiber,  eds.,
    Washington, D.C.
11.   Davis, S. N. and R. J. DeWiest, 1966. Hydro-
     geology; John Wiley & Sons, 463 pp.

12.   Dee,  Norbert, Janet  Baker, Neil Drobny, Ken
     Duke, Ira Whitman, and Dave Fahringer, 1973.
     An environmental evaluation system for water
     resource planning; Water Resources Research,
     Vol. 9, No. 3, pp. 523-535.

13.   Dohnalek, D. A. and J. A. Fitzpatrick, 1983. The
     chemistry of reduced sulfur species and their
     removal from ground water supplies; Journal
     AWWA, Vol. 75, No. 6, pp. 298-308.

14.   Erlich, G. G., D.  F. Goerlitz, E. M. Godsy, and M.
     F. Hult, 1 982. Degradation of phenolic contam-
     inants in ground water by  anaerobic bacteria:
     St. Louis, Minnesota; Ground Water, Vol.  20,
     No. 6, pp. 703-710.

15.   Farb, D. 1978. Upgrading hazardous  waste
     disposal sites: remedial approaches;  U.S. EPA
     #SW-677, Cincinnati, Ohio, 40 pp.

16.   Fenn, DennisG., Keith J. Hanley, andTruettV.
     DeGeare,  1975. Use of the water balance
     method for predicting leachate generation from
     solid waste disposal sites; U.S. EPASolidWaste
     Report No.  168, Cincinnati, Ohio, 40 pp.

17.   Fetter, C. W.,  1980. Applied Hydrogeology;
     Charles E. Merrill Publishing Company, 448 pp.
18.   FMC Corporation, 1 983. Industrial waste treat-
     ment with hydrogen peroxide; Industrial Chem-
     ical Group, Philadelphia, Pennsylvania, 23 pp.

19.   Freeze, R. A. and J. A. Cherry, 1979. Ground-
     water; Prentice-Hall, 604 pp.
20.   Fuller, W.  H.  and  J. Artiola, 1978. Use of
     limestone to limit contaminant movement from
     landfills; Proceedings Fourth Annual Research
     Symposium, Land  Disposal  of  Hazardous
     Wastes, U.S. EPA-600/9-78-01 6, pp. 282-298.

21.   Gibb, James P., Michael J. Barcelona, Susan C.
     Schock, and Mark W. Hampton, 1983. Hazard-
     ous waste in Ogle and Winnebago Counties:
     potential risk via ground water due to past  and
     present activities; Illinois Department of Energy
     and Natural Resources, Document No. 83/26,
     66 pp.
                                              727

-------
22.  Gibson, D. T., 1978. Microbial transformation of
     aromatic pollutants; Aquatic Pollutants, Perga-
     mon Press.

23.  Griffen, R., R. Clark, M. Lee, and E. Chian, 1978.
     Disposal  and removal of polychlorinated  bi-
     phenyls  in  soil;  Proceedings  Fourth Annual
     Research Symposium, Land Disposal of Haz-
     ardous Wastes, U.S. EPA-600/9-78-016, pp.
     169-181.

24.  Gutentag,  E.  D., and J. B.  Weeks,  1980.
     Watertable inthe High Plains Aquifer in 1978 in
     parts  of  Colorado, Kansas,  Nebraska, New
     Mexico,  Oklahoma, South Dakota, Texas and
     Wyoming; U.S. Geological Survey Hydrologic
     Investigations Atlas 642.

25.  Hampton, E. R.,  1964. Geologic  factors that
     control the occurrence and availability of ground
     water in  the Fort Rock  Basin, Lake County,
     Oregon;  U.S. Geological  Survey Professional
     Paper 383-B, 29 pp.

26.  Haque, R., D. W. Schmedding, and V. H. Freed,
     1 974. Aqueous solubility, adsorption and vapor
     behaviour of polychlorinated biphenyl Arochlor
     1254; Environmental Science &  Technology,
     Vol. 8, pp. 139-142.

27.  Harsh, K., 1975. In situ  neutralization of  an
     acrylonitnle spill; Ohio Environmental Protec-
     tion Agency, Dayton, Ohio, pp. 187-189.

28.  Heath, Ralph C., 1984. Ground-water regions of
     the United States;  U.S. Geological Survey
     Water Supply Paper 2242, 78 pp.

29.  Jhaveri,  V.  and A.  J. Mazzaua,  1983. Bio-
     reclamation of ground and groundwater—case
     history; Proceedings of the National Conference
     on Management of Uncontrolled  Hazardous
     Waste Sites, Washington, D.C., pp. 242-247.

30.  Joel,  A.  H.,  1926.  Changing viewpoints and
     methods in soil classification; reprinted  in Soil
     Classification, Charles W. Finkl, Jr.,  editor
     (1982), Hutchinson Ross Publishing Co., Strouds-
     burg, Pennsylvania, pp. 52-59.

31.  Karickhoff, S. W., D. S. Brown, and T. A. Scott,
     1979. Sorption of hydrophobic pollutants  on
     natural sediments;  Water Research, Vol. 13,
     No. 3, pp. 241-248.

32.  Keenan, C. W.  and J. H. Wood, 1971. General
     college chemistry; Harper & Row, 717 pp.

33.  Keith, L A. and W. A. Telliard, 1979. Priority
     pollutants, I-A perspective view; Environmental
     Science  &  Technology,  Vol.  13,  No.  4, pp.
     416-423.
34.  Kobayashi, H. and B. E. Rittmann, 1 982. Micro-
     bial removal of hazardous organic compounds;
     Environmental  Science & Technology, Vol. 1 6,
     No. 3, pp. 170A-183A.

35.  Lappenbusch, W. L.,  1984.  Health  effects of
     drinking water contaminants;  Proceedings of
     the Thirty-first Ontario Industrial Waste Con-
     ference, Ontario Ministry of the Environment,
     Ontario, Canada, pp. 271 -291.

36.  LeGrand, Harry E., 1983. A standardized system
     for evaluating  waste-disposal  sites; National
     Water Well Association, Worthington, Ohio, 49
     pp.

37.  LeGrand, H. E. and  W.  A.  Pettyjohn,  1981.
     Regional hydrogeologic concepts of homoclinal
     flanks;  Ground Water, Vol.  19, No. 3, pp.
     303-310.

38.  Lehr, Jay H., David M. Nielsen, and John J.
     Montgomery, 1984.  U.S. federal  legislation
     pertaining to ground water protection; Ground-
     water Pollution Microbiology,  Gabriel  Bitton
     and Charles P. Gerba, editors, John Wiley &
     Sons, pp. 353-371.
39.  Lehr, Jay  H.,  Wayne A.  Pettyjohn, Truman
     Bennett, James R.  Hanson, and Laurence E.
     Sturtz, 1 976. A manual of laws, regulations and
     institutions  for control of ground water pollu-
     tion, U.S. EPA-440/9-76-006.

40.  Leppencott, W. T.,  A. B. Garrett,  and  F. H.
     Verhoek, 1978. Chemistry; John Wiley & Sons,
     pp. 646-697.

41.  Liu,  D., W.  Stra'chan,  K. Thomson, and K.
     Kwasniewska, 1981. Determination of the
     biodegradability of organic compounds; Environ-
     mental Science & Technology, Vol.  15, No. 7,
     pp. 788-793.
42.  Luckey, R. R. and E. D. Gutentag, 1981. Water-
     level and saturated-thickness changes, prede-
     velopmentto 1 980, in  the High Plains Aquifer in
     parts of Colorado, Kansas, Nebraska, New
     Mexico, Oklahoma, South Dakota, Texas and
     Wyoming;  U.S. Geological Survey Hydrologic
     Atlas 652.

43.  Matthess, G., 1981. In situ treatment of arsenic
     contaminated ground  water; The Science of the
     Total Environment, No. 21, pp.  99-104.

44.  Matthess, G. and J.C.Harvey, 1982. Properties
     of groundwater; John Wiley & Sons, pp. 73-114.

45.  MacNish, R. D. and R. A. Barker, 1976. Digital
     simulation of a basalt aquifer system. Walla
     Walla River Basin, Washington and Oregon;
                       128

-------
     Washington Department of  Ecology, Water
     Supply Bulletin 44.

46.  McGuiness, C. L, 1963. The role of ground
     water in the  national water situation;  U.S.
     Geological Survey Water Supply Paper 1800,
     1121 pp.

47.  Meinzer, Oscar E., 1923. Outline of ground-
     water hydrology; United States Geological
     Survey Water Supply Paper 494, 71 pp.

48.  Michigan Department  of Natural Resources,
     1983. Site assessment system  (SAS) for the
     Michigan priority ranking system  under the
     Michigan Environmental Response Act; Mich-
     igan Department of Natural Resources, 91 pp.

49.  Nace, R. L., 1958. Hydrology of the Snake River
     basalt; Washington Academy of  Science Jour-
     nal, Vol. 48, No. 4, pp. 136-138.

50.  Newcomb, R. C., 1 961. Storageof ground water
     behind subsurface dams in the Columbia River
     basalt,  Washington, Oregon  and Idaho;  U.S.
     Geological Survey Professional  Paper 383-A,
     15pp.

51.  Office of Technology Assessment, 1984.  Pro-
     tecting the nation's groundwater from contam-
     ination,  Vol. I, II;  U.S. Congress, Washington,
     D.C.,  503 pp.

52.  Page, A. L., 1974. Fate  and  effects of trace
     elements in sewage sludge when applied to
     agricultural lands; U.S. EPA 670/2-74-005.

53.  Pye,  V.  I., R. Patrick, and J.  Quarles, 1983.
     Groundwater contamination in the United
     States;  University of Pennsylvania Press, 314
     PP.
54.  Pye, Veronica I. and Jocelyn Kelley, 1 984. The
     extent of groundwater contamination in the
     United  States;  Groundwater  Contamination,
     National Academy Press, pp. 23-33.

55.  Rott,  U., 1981. Protection and  improvement of
     ground water quality by oxidation processes in
     the aquifer; Quality of Ground Water, Proceed-
     ings of an International Symposium, The Nether-
     lands, Elsevier Scientific Publication Company,
     pp. 1073-1076.

56.  Roberts, P. U., 1981. Nature of  organic contam-
     inants in ground water  and approaches  to
     treatment; AWWA Seminar Proceedings, Or-
     ganicChemical Contaminants in Ground Water:
     Transport and Removal, pp. 47-66.

57.  Sawyer, C. N. and P. L. McCarty, 1978. Chem-
     istry for environmental engineering; McGraw-
     Hill, pp. 94-163.
58.  Seller, I.E. and L.W. Canter, 1980. Summary of
     selected ground water quality impact assess-
     ment  methods;  National Center for Ground
     Water  Research Report No.  NCGWR  80-3,
     Norman, Oklahoma, 142 pp.

59.  Soil Conservation Service,  1951. Soil survey
     manual; U.S. Department of Agriculture, 503
     pp.

60.  Solley, Wayne B., Edith B. Chase, and William B.
     Mann,  1983.  Estimated  use  of water in the
     United States in 1980. United States Geological
     Survey Circular 1001, 56  pp.

61.  Solomons, T.  W., 1980. Organic chemistry;
     John Wiley & Sons, pp. 634-639.

62.  Snoeyink, V. L.  and  D. Jenkins,  1980. Water
     chemistry; John  Wiley & Sons, 463 pp.

63.  Stover,  E. L. and D. F. Kineannon, 1983.
     Contaminated ground water treatability—a case
     study; Journal  AWWA,  Vol.  75, No. 6, pp.
     292-298.

64.  Tabak, H. H., S. A. Quave, C. I. Mashm, and E. F.
     Barth,  1980.  Biodegradability studies  with
     priority pollutant organic compounds; Staff
     Report, Wastewater  Research Division, U.S.
     EPA Research Center, Cincinnati, Ohio.

65.  Thomas, Harold E., 1 952. Ground water regions
     of the United  States—their storage  facilities;
     Interior and Insular  Affairs  Committee, U.S.
     House of Representatives, 76 pp.

66.  Thornthwaite, S. W.  and  Mather, J.  R.,  1957.
     Instructions and tables for computing potential
     evapotranspiration and  the  water  balance;
     Drexel Institute  of Technology, Laboratory of
     Climatology, Publications  in Climatology,  Cen-
     terton, New Jersey, Vol. 10, No. 3,311 pp.

67.  Todd,  D.  K., 1980.  Groundwater hydrology;
     John Wiley & Sons, 535 pp.

68.  Tolman, A., A.  Ballestero,  W. Beck, and G.
     Emrich, 1978. Guidance manual for minimizing
     pollution from waste disposal  sites; U.S. EPA-
     600/2-78-142, pp. 328-331.

69.  United States Environmental Protection Agency,
     1983. Surface Impoundment Assessment Na-
     tional Report, U.S. EPA 570/9-84-002, 200 pp.

70.  Weast,  R.  C., ed.,  1983. CRC handbook  of
     chemistry and physics; CRC Press, Inc.

71.  Weeks, J. B. and E. D. Gutentag, 1 981. Bedrock
     geology, altitude of base  and  1980 saturated
     thickness of the High Plains Aquifer in parts of
     Colorado, Kansas,  Nebraska, New Mexico,
     Oklahoma, South Dakota, Texas and Wyoming;
                                                                     729

-------
     U.S. Geological Survey  Hydrologic Investiga-
     tions Atlas 648.

72.  Weldon, R.  A., 1979. Biodisposal farming of
     refinery oily wastes; reprinted from API Oil Spill
     Conference  Proceedings, March 19-22, 1979.

73.  Wetherold,  R. G., D.  D. Rosebrook, and E. W.
     Cunningham, 1981. Assessment of hydro-
     carbon emissions from land treatment of  oily
     sludges; Proceedings of the Seventh Annual
     Research Symposium, Land Disposal: Hazard-
     ous Waste, U.S. EPA-600/9-81-002b.

74.  Wilson, J. L, R. L Lenton, and J. Porras eds.,
     1 976.  Groundwater pollution: technology, eco-
     nomics and mangement; Department of Civil
     Engineering, Massachusetts Institute of Tech-
     nology, Report No. TR 208, pp. 17-21.
                       130

-------
                                         Appendix A

          Processes and Properties Affecting Contaminant Fate and Transport
Most potential ground-water contaminants are re-
leased at or slightly above the water table as a result
of various industrial, agricultural, and other human
activities.
The attenuation of contaminants as they travel
through the unsaturated zone  and ground-water
system is affected by a variety of naturally occurring
physical processes and chemical reactions that often
cause the contaminant to change its physical state or
chemical form. This change may result in removal of
the contaminant from the ground-water system. The
extent of these reactions is dependent on hydrogeo-
chemical conditions present in the ground water such
as pH, redox-potential and solid surface area.  How-
ever, the chemical processes within dynamic ground-
water systems are complex, and are highly dependent
on site-specific aquifer and soil  characteristics as
well as the effects of individual contaminants in the
system (Cherry et al., 1984). Therefore, although the
importance of these chemical reactions in attenuation
of contaminants is  widely recognized, prediction of
the amount of attenuation of a contaminant in any
environment is still  very difficult.
Attenuation includes those mechanisms that lessen
the severity or amounts of contaminants. The com-
ponents which affect attenuation arethephysical and
chemical processes and properties including density,
solubility, sorption,  biodegradation, oxidation-reduc-
tion, dilution,  hydrolysis,  dispersion,  viscosity,
mechanical filtration,  ion exchange,  volatilization,
and buffering or neutralization. The degree of attenu-
ation that occurs is dependent on: (1 ) the time that the
contaminant is in contact with the material through
which it passes; (2) the grain size, and physical and
chemical characteristics of the  material through
which  it passes; and (3) the distance which the
contaminant has traveled. For most materials, the
longer the time, the greater the surface area and the
greater the distance of travel, the greater the degree
of attenuation. Movement of ground water is slower
in rocks with high surface areas, such as found in a
fine-grained porous medium, than in rocks where
water  movement is  primarily through  fault and
fracture channels or solution openings. Additionally,
flow velocity decreases  with lower gradients and
increasing depth; subsequently,  ground water is in
prolonged contact with rock materials (Matthess and
Harvey,  1982).
Another factor affecting attenuation includes surface
area in the aquifer media. The greater the surface
area of the material through which the contaminant
passes, the greater the potential for sorption of the
contaminant. Likewise, the greater the reactivity of
the material through which the contaminant passes,
the greater the potential for attenuation.
The many physical processes and chemical reactions
present in a ground-water system may work individu-
ally or in combination to provide varying degrees of
attenuation  depending on  the hydrogeochemical
conditions  and the  particular  contaminant.  The
following discussion  addresses each physical and
chemical process and describes the respective impact
on contaminants.

Density

The density of any substance is defined as mass per
unit volume. The movement of a contaminant in an
aquifer is directly affected by the density of the fluid
with respect to the density of the ground water. Low
density contaminants tend to float on top of the water
table; high density contaminants tend to sink to the
bottom of the aquifer.
Once a contaminant has entered an aquifer, it will be
transported as a function of density in the direction of
ground-water flow at a rate between a fraction of an
inch a  day to a few feet per day. Under the  ideal
condition  of  a  homogeneous  aquifer media, the
contaminant  will begin  to  disperse forming an
elliptical plume (Pye et al., 1983; Todd, 1980). Move-
ment and dispersion of the plume is affected by the
density  of the  contaminant, the character  of the
geologic formation through which the contaminant
passes andthe reactive nature of the contaminant. In
a uniform geologic formation, the more  dense the
contaminant, the greater will  be  the downward
migration of that  contaminant  and the slower the
contaminant will travel in relation to the velocity of
ground-water flow.

Solubility

As a contaminant is introduced into an aquifer, the
contaminant is generally partially dissolved in water,
forming either miscible or immiscible solutions. A
potential contaminant may also remain  insoluble,
                                               131

-------
depending on the chemical characteristics of the
contaminant. The solubility of a substance is defined
as the mass of a substance that will dissolve in a unit
volume of solute under specified chemical conditions
(Freeze and Cherry, 1979). The solubility of a consti-
tuent in water is dependent on variations in tempera-
ture, pressure, pH, redox  potential (Eh),  and the
relative concentrations of other substances in  solu-
tion. The interactions of these chemical parameters
make  it  difficult to predict the solubilities  of many
substances  in ground  water (Davis and DeWiest,
1 966; Snoeyink and Jenkins, 1980).

Substances are dissolved in water, or become soluble,
because the water molecule exhibits a charge which
tends to attract other molecules in solution. When the
attractive forces that hold a substance together are
less than or equal to the attractive force of the water
molecule, the substance will dissolve. Conversely,
those substances that are held together by attractive
forces  stronger  than the  attraction  of the  water
molecule do not dissolve to any appreciable degree in
water,  thus  forming immiscible liquids or solids. A
good example is oil and water; the two substances do
not mix because  the oil  is only  slightly soluble  in
water. Substances that have been dissolved may be
reprecipitated as  a consequence of equilibria shifts
and deposited in  the void spaces of the aquifer.  In
addition,  immiscible  fluids may be  transformed
through similar changes in solubility.

The chemical reaction which transforms a dissolved
substance  to a  solid form  is  precipitation.  The
precipitation of a dissolved substance may be initiated
by changes in pressure, temperature, pH, concentra-
tion, or oxidation-reduction. In addition, the introduc-
tion of another substance that changes the equilibrium
concentrations in the solution, or  which  reacts
chemically with the dissolved substance may cause
precipitation. The resultant solid is deposited in the
void spaces of the aquifer, thereby reducing the space
available for transport of the ground water.

Several types of contaminants  can  be effectively
removed from the ground water through precipitation.
Calcium salt solutions have been shown to effectively
precipitate free fluorides (Tolman et al., 1978). Alkalis
and/or sulfides may precipitate heavy metals. Stover
and Kincannon (1983) have conducted successful
experiments with regulated pH conditions, demon-
strating the precipitation of metals using lime. Since
oxidation-reduction reactions may change the chem-
 ical state of a substance by rendering it insoluble, this
reaction  has proven effective in changing dissolved
chromium to a less soluble  state thereby removing it
from the ground  water (Tolman et al., 1978; Fuller
and Artiola, 1 978). The FMC Corporation (1983) has
conducted extensive studies using hydrogen peroxide
to  oxidize various sulfide  compounds and initiate
 precipitation. Vapors escaping from a contaminated
site may cause heavy metals to be transported and
re-deposited.  Each  of these  chemical  reactions
provides a  method of changing the solubility of a
substance,  thereby removing the contaminant from
the ground water and precipitating  it in  the void
spaces of the aquifer. Even though the contaminant
has changed form, the precipitate may be re-dissolved
and the process repeated. When a precipitate re-
dissolves, the contaminant may not be in its original
form and may form a different  solute which may or
may not be harmless.

Sorption

Sorption is  a combination of  two processes, adsorp-
tion and absorption. Adsorption occurs when mole-
cules or ions are attached to the surface of charged
particles by weak Van der Waals or covalent bonds.
Adsorption  differs from absorption in that the latter
involves penetration by  the  absorbed  substance
(Keenan and Wood,  1971;  Matthess and Harvey,
1982). Sorption occurs on  all surfaces where bonding
conditions  are present. Sorption  increases with in-
creasing surface area, which is usually a function of
decreasing grain size. Colloidal  particles  range in
diameter size from 10"3 to 10~6 mm. These particles
tend to  have a large  charge relative to their surface
area (Freeze and Cherry, 1979). Porous geologic
materials  that are  composed of an  appreciable
amount of  colloidal-sized  particles exhibit a higher
capability  to sorb constituents  onto the particle
surfaces.

The subsurface materials  that exhibit sorptive
properties include clay minerals, hydrous iron, man-
ganese, aluminum oxides, organic substances (par-
ticularly humus), glauconites and the rock-forming
minerals mica, feldspar, aluminous augite and horn-
blende  (Matthess and Harvey,  1982; Freeze  and
Cherry, 1979;  Davis and DeWiest,  1966). These
minerals are commonly present in colloidal form and
contain especially large surface areas available for
sorption.
The surface charge on a mineral in the saturated or
unsaturated zone creates an  attractive force. This
charge  may be due to (1) imperfections or substitu-
tions  in the  crystal lattice of the  particle  or (2)
chemical  reactions  at the  surface of the particle
involving weak hydrogen bonding, due to the presence
of water. The pH of the water  and the crystal structure
of the mineral have a direct affect on the charge of the
particle surface; waters with a high pH and  highly
crystalline materials typically  produce net negative
charges on the particle  surface  thus favoring the
sorption of positive constituents or cations (Matthess
and Harvey, 1982).  There  is  a  direct relationship
between the quantity of a  substance sorbed on  a
particle surface and the quantity of the substance
suspended in solution. In general, an increase in the
                        132

-------
concentration of the substance in solution  will
increase the quantity sorbed.

The presence of organic materials in porous materials
appears to be an important factor in the sorption of
non-ionic  organic substances. Those organic sub-
stances that are nonpolar (not attracted to water) and
relatively insoluble tend to be readily sorbed by soils
and sediments containing clays and organic carbon.
The sorption of nonpolar aromatic and chlorinated
hydrocarbons has been  shown to increase with
decreasing particle size and subsequently increasing
organic carbon content (Karickhoff et al.,  1979).
Sorption of polar organics primarily occurs through
weak hydrogen bonds to mineral particles (Cherry et
al., 1 984; Brown et al., 1983). Studies by Haque et al.
(1974) and Griffen et al. (1978) indicate that sorption
of PCBs was enhanced in materials with  greater
surface area and higher organic content. The sorptive
capabilities of clays and soils appear promising for
attentuation of some contaminants, however, further
experimentation is necessary due to the complexity of
chemical reactions that occur in the sorption process.
Ion Exchange

The process of ion exchange is similar to sorption,
however, stronger ionic bonding occurs on the particle
surfaces. Ion-exchange processes are virtually limited
to colloidal size particles because these particles have
large electrical charges with respect to their surface
areas. Colloidal particles range in diameter size from
1CTJto 10~emm.

Ion exchange occurs when there is a surface charge
imbalance. These surface charges are a result of (1)
imperfections or ionic substitutions within the crystal
or particle, or (2) chemical dissociation reactions at
the particle surface. Upon exposure to water the
charged molecules attract hydroxyl groups (OH") to
the surface. When these hydroxyl groups break down,
the resulting charge imbalance attracts oppositely
charged particles (Freeze and Cherry, 1979). Ionic
substitutions within particle surfaces also cause a
charge imbalance that attracts oppositely charged
ions. These ions comprise an adsorbed layer that is
interchangeable; thus the process is reversible.  An
example of ionic substitutions occurs within silicate
minerals. Aluminum ions tend to substitute for the
silica  ions, forming an unbalanced charge on the
mineral surface. The nature of the  surface charge
that develops is dependent on pH; positively charged
surfaces develop at low pH and a negatively charged
surface prevails with a high pH. Clay minerals are the
primary geologic materials of colloidal size that exhibit
surface charges as  a result of ionic substitutions.
Organic materials such as humus and plant roots in
soils and  recent sediments also  exhibit  high ion-
exchange capacities  (Davis  and  DeWeist, 1966;
Matthess and Harvey, 1982).

The most common ion exchange involves the transfer
of cations  on charged  surfaces. Cation exchange
capacity is the capability of a charged surface layer to
attract positive ions in the zone  adjacent to that
charged  surface  (Freeze  and Cherry, 1979). The
affinity for  attraction  of  cations  varies with  the
valence, or charge, of the ion andthe ionic size. Other
things being equal, the affinity for ion exchange is
greater when the ion has a higher valence. For ions of
the same valence, the affinity for exchange increases
with atomic number and decreases with  increasing
hydrate radius (Matthess and Harvey, 1982).

Other  colloidal particles that exhibit  ion-exchange
capacities include hydrated oxides of iron and man-
ganese. Hydrated oxides of iron selectively sorb zinc,
copper,  lead, mercury,  chromium,  molybdenum,
tungsten, and  vanadium through ion  exchange.
Similarly, hydrated oxides of manganese will bond to
copper, nickel, cobalt, chromium, molybdenum, and
tungsten (Matthess and Harvey, 1  982). Clay minerals
tend to preferentially bond zinc, copper, lead, mercury,
and radioactive elements such as rubidium, cesium,
arid strontium. Certain organic dyes are firmly bonded
to clays by strong electrostatic bonds (Matthess and
Harvey,  1982).  For cationic organic  substances,
increasing valence will tend to increase the  capacity
for bonding to clay surfaces, and vice versa for anionic
organic constitutents (Brown et al., 1983).

Ion exchange can provide a means for attenuation of
heavy  metals and certain organic substances if the
bonding  is sufficiently strong to  prevent reversal of
the chemical reaction and release of the contaminant
back into the ground-water system.


Oxidation-Reduction

Oxidation and reduction (redox)  are geochemically
important processes because together with pH, they
control the solubility, and thus the presence of many
substances  in water. These reactions involve the
transfer  of electrons between dissolved, gaseous,
and solid substances in the water. As a result of this
electron transfer, there is a change in  the oxidation
state of the substance. A redox reaction consists of
two parts or  half reactions. In the  oxidation reaction,
the substance loses,  or donates electrons; in the
reduction reaction, the substance accepts, or gains
electrons. Oxidation and  reduction  reactions are
always coupled; no free electrons can exist in solution
and electrons must be conserved (Snoeyink and
Jenkins,  1980).

Deposits above the water table contain voids which
are usually filled with atmospheric gases containing
oxygen. Percolating water carries dissolved atmos-
                                                                       733

-------
pheric oxygen to the water table where the processes
of diffusion and dispersion can carry  it to deeper
water  levels  (Matthess and  Harvey,  1982).  The
presence or absence of dissolved oxygen  in the
ground water is one factor which controls whether
oxidizing or reducing conditions will predominate.
Oxidation may be initiated in  ground water by the
presence or introduction of an oxidizing agent, such
as potassium permanganate, or a change in valence
state of ions  such as Fe+3 and Mn+3.  In general,
oxidation processes are increased in warm climates,
and are more complete  in humid  and humid/arid
climates than  in arid climates.

Microorganisms are responsible for a large proportion
of redox reactions which  occur in ground water. The
principal microorganisms involved in redox processes
are bacteria which contain enzymes. Bacteria and
their enzymes  utilize redox processes to provide
energy for cell synthesis and  maintenance (Freeze
and Cherry, 1979). Bacteria that require oxygen are
known as aerobic bacteria, while anaerobic bacteria
cannot tolerate dissolved oxygen in the water.

In many contaminated ground-water systems, dis-
persion exerts a strong influence on the redox state of
the ground water. Dispersion causes a continuous
mixing  of waters that  are  different  in  chemical
composition and redox potential. The mixing of these
waters by dispersion affect the redox and pH condi-
tions  and may instigate other chemical reactions
within the system.

The  use of oxidation-reduction reactions for the
attenuation of contaminants has proven effective for
both inorganic and organic substances. The introduc-
tion of oxidizing agents into ground water is the most
important mechanism of oxidation after microorga-
nisms. Detoxification through oxidation of cyanides
(Farb, 1978) and organic cyanides (Harsh, 1975) has
been accomplished through the application of sodium
hypochloride  in conjunction with pH adjustments to
produce substances that are insoluble. Dohnalek and
Fitzpatrick (1983) documented removal of hydrogen
sulf ide from ground water in laboratory studies using
oxidants. The FMC Corporation (1983) has conducted
extensive experimentation using hydrogen peroxide
to oxidize  various  sulfides and  organic  sulfides
thereby rendering them insoluble. Certain organic
compounds such as phenols, aldehydes, hydroqui-
nine, as well as chlorine compounds and cyanides
can  also be  ozidized by hydrogen peroxide (FMC,
1983).  Matthess (1981) achieved  treatment  of
arsenic-contaminated ground water by accelerating
the natural precipitation process through the injection
of theoxidant potassium permanganate. The soluble
arsenic species was oxidized to  the less  soluble
arsenate state and precipitated as iron and manga-
nese arsenates and hydroxides, thus removing the
arsenic from  the ground water and eliminating the
contamination  problem.  Injection of oxygenated
water into an aquifer has also been shown to improve
water quality by stimulating iron  and manganese
bacteria. The bacteria then provided the adsorption-
oxidation mechanism that precipitated the iron and
manganese hydroxides (Rott  et al.,  1981). Other
chemicals susceptible to oxidation include phenols,
aromatic amines, and dienes (Cherry et al.,  1984).
The application  of a strong reducing agent has also
proven effective in changing the oxidation state of
chromium causing  the formation of an  insoluble
chromium product.

The mechanisms of oxidation and reduction provide a
means for reducing the solubility and causing subse-
quent precipitation through several reactions. Those
most effective reactions for reducing solubility include
a change in oxidation state, the formation of new
compounds, and the  enhancement  of  naturally
occurring bacterial processes.
Biodegradation

Biodegradation  results from the enzyme-catalyzed
transformation of organic compounds by microbes,
principally bacteria, fungi, actinomycetes, algae, and
yeasts. Biological treatment can eliminate hazardous
organic wastes by transforming them into innocuous
forms, degrading  them by mineralization to carbon
dioxide and water, or by anaerobically decomposing
them to carbon dioxide and methane (Kobayashi and
Rittmann, 1982). Bacteria and other microbes require
nutrients to produce the necessary enzymes that use
or attack the organic  compounds. Most microbes
require oxygen, water, and nutrients such as carbon,
nitrogen, phosphorus,  and trace  metals. Aerobic
bacteria require the presence of free oxygen; anaer-
obic bacteria require the absence of dissolved oxygen.
The  metabolic processes of both types of bacteria are
energy efficient and tend to enhance certain critical
reactions. Reactions such as reductive dehalogena-
tion, nitroreduction and reduction of sulfoxides are
catalyzed by anaerobic  bacteria  (Kobayashi and
Rittmann, 1982).

Biodegradation of a broad  range of organic  com-
pounds particularly those that  are man-made, have
been demonstrated in laboratory studies. It is difficult
to predict the exact transformations that may occur,
due  to the complexity of chemical reactions present in
natural systems  of mixed microbes  and  organic
compounds  (Cherry et al.,  1984; Kobayashi and
Rittmann, 1982). Biodegradation is dependent  on
interactions in a natural environment such as  redox
potential, dissolved oxygen, pH, temperature, pre-
sence of other compounds, salinity, other competing
organisms, and the concentrations of compounds and
organisms. Organic compounds need  to  be  fairly
soluble in water in order to be utilized by microbes.
                       134

-------
Biodegradation can be limited if there are antagonistic
interactions between two types of microbes, such as
bacteria and fungi (Kobayashi and Rittmann, 1982).
In addition, very low compound concentrations in a
substrate  may pose problems;  certain  organisms
require minimal threshold values for survival and/or
production of necessary enzymes.

Certain man-made organic compounds are refractory
or  resistant to biodegradation.  This resistance  is
generally due to the presence of chemical substitu-
ents such as nitrogroups, chlorines, and amines, that
are attached to the parent compound.  Generally,
larger molecules are less degradable than smaller
ones (Kobayashi and Rittmann, 1982). Other impor-
tant refractory compounds are halogenated organics
which are very resistant to biodegradation (Brown et
al.,  1983). These halogenated organics include pesti-
cides, plasticizers,  solvents,  and trihalomethanes.
Chlorinated  compounds such  as  DDT  and other
pesticides have been  the most frequently studied
compounds. The first  step in degradation of halo-
genated organics involves dehalogenation by several
biological mechanisms. Anaerobic reductive dehalo-
genation is an important mechanism in degradation
of pesticides and certain halogenated aliphatic com-
pounds.
Kobayashi  and  Rittmann (1982) and Tabak et al.
(1980), indicate that most man-made organic com-
pounds will undergo biodegradation to some extent.
Actinomycetes and fungi are known to attack a wide
variety of complex organic compounds. These mi-
crobes can grow under low nutrient conditions, wide
temperature ranges and wide pH ranges. Actinomy-
cetes break compounds down into groups that can be
utilized by other organisms. Certain types of fungi are
able to degrade complex hydrocarbons including the
degradation of DDT. Fungi are believed to be capable
of degrading PCBs more efficiently than bacteria
(Gibson, 1978).  Fungal metabolism is  generally
incomplete and requires other microbes for complete
degradation. Bacteria have been found to degrade a
wide variety of compounds under aerobic conditions.
Bacteria are the major agents in the degradation of
hydrocarbons and heterocyclic compounds (Kobayashi
and Rittmann, 1982; Jhaveri and  Mazzacca, 1983;
Weldon,  1979; Tabak  et al., 1980; Liu et al., 1981;
Claus and Walker, 1964; Cherry  et  al., 1984).

Anaerobic bacteria degrade organic compounds to
carbon dioxide and methane under oxygen-deficient
conditions. Although  little  is known about these
bacteria, four groups that utilize each of the metabolic
products are responsible for degradation of the other
groups. These bacteria are capable of dehalogenation,
nitrosamine degradation, reduction of epoxide groups,
reduction of nitro groups and  the breakdown  of
aromatic structures (Kobayashi and Rittmann, 1982;
Tabak et al., 1980). In a study conducted by Ehrlich et
al. (1982) an aquifer contaminated by phenols and
polynuclear aromatic hydrocarbons such as naph-
thelene showed  significant  reductions in these
contaminants within 1000 m  of the contamination
source. Contaminant attenuation has been attributed
to anaerobic  degradation of the  hydrocarbons  by
bacteria. Laboratory studies indicate that anaerobic
bacteria are capable of degrading certain halogenated
1 - and 2-carbon organic compounds such as trihalo-
methanes, chloroform, and trichloroethylenes (Bouwer
etal., 1981).


Hydrolysis

The breakdown of substances under the influence of
H+ and OH" ions in the water is known as hydrolysis.
The  breakdown  of  minerals  by  hydrolysis is an
important reaction that occurs in the ground water,
causing relatively insoluble minerals  to form  new
minerals while releasing  ions  into solution.  The
hydrolysis process is dependent on pH, which controls
the amounts of hT and OH" ions in solution,  in
addition to the oxidation-reduction potential (Matthess
and Harvey, 1982).  Hydrolysis is  most effective at
high temperatures, low pH, and low redox potential.
Hydrolysis is the  basic reaction in the weathering
processes which  acts upon rocks and aids in the
production of clays and soils.

Hydrolysis  of  an  organic  compound involves the
introduction of a hydroxyl group (-OH) into the
chemical structure, usually with the loss of a chemical
group (X). The rate of hydrolysis of organic compounds
is dependent on pH conditions and the presence of
metal ions. A common hydrolysis  reaction involves
the replacement of halogens (X)  by a hydroxyl group
(Cherry et al.,  1984). The occurrence of hydrolysis
may aid in contamination attenuation. Certain organic
compounds may be broken down by hydrolysis into
simpler compounds  that may then be easily assimi-
lated through other processes. An example would be
the hydrolysis of esters into a simple alcohol and acid
that would comprise less harmful constituents in the
ground water.
Hydrolysis is an important process in the attenuation
of pesticides. It may be used to help predict the rate of
decay of pesticides  in the soil. (Cohen et al., 1984;
Cherry et al., 1984). Hydrolysis of atrazine and other
pesticide derivatives has been  shown to  operate
faster when humic material is  present. Hydrolysis
rates for breakdown of pesticides  have been deter-
mined for certain organic groups  (Cherry et al., 1984;
Callahan et al., 1979; Cohen, 1984).
Volatilization
Volatilization is defined as the loss of a compound to
the atmosphere. This process provides an attenuation
                                                                      735

-------
mechanism for those compounds that are resistant to
degradation  and/or weakly absorbed, and to those
that exhibit low solubilities and high vapor pressures
(Callahan et  al., 1979; Brown et al., 1983). Organic
constituents with high vapor pressures  are more
easily volatilized from the soil. Compounds that are
not soluble  tend to be available for volatilization
longer because  they are  not readily removed by
water. Persistent organic constituents that are not
easily  removed  by  other  processes may tend to
volatilize after a period of time. Organic compounds
tend to volatilize more easily if they are less strongly
sorbed by the soil.

Factors that  affect volatilization include vapor pres-
sure, water solubility, soil moisture, adsorption, wind
speed, turbulence, temperature,  depth below land
surface and time (Brown et al., 1983; Callahan et al.,
1 979). Studies indicate that the highest volatilization
of organics occurs within minutes of application and
decreases substantially within one hour (Wetherold
etal., 1981).

Volatilization of organics is generally restricted to the
purgable or volatile organic compounds. These com-
pounds include hydrocarbons, compounds with sim-
ple function groups such as alcohols, halides,  and
sulfur-containing compounds, and compounds con-
taining unsaturated functional groups such as alde-
hydes, ketones, and esters. Increasing air humidity,
soil temperature, and soil moisture have been shown
to increase  volatilization rates (Wetherhold  et al.,
1981).
A buffer solution is comprised of a weak acid or base
plus a salt of that acid or base. A solution of this type
will maintain a relatively constant pH even though a
strong acid or base is added. A common example of
this is the acetic acid-sodium acetate solution which
will maintain a relatively constant  pH when HCI is
added, due to the H+ions from the HCI combining with
the acetate ions, as follows:
Cl'+
      HCI
Therefore,  no change occurs  in the hydrogen  ion
concentration.

Carbonate  systems provide very effective buffering
systems in natural waters and waste waters (Snoeyink
and Jenkins, 1 980). The system is essentially based
on a weak acid, carbonic, and sodium bicarbonate. As
a consequence of the natural equilibria established
between these parameters a relatively constant, near
neutral pH is maintained for most  ground waters,
making many important biological processes possible.

The precipitation of chromium from water is directly
controlled by variable pH values by providing suitable
electron  donors to change the chromium to a less
soluble oxidation  state (Tolman et al., 1978; Fuller
and Artiola, 1978). The  use  of  variable pH levels
enables the detoxification of cyanide through oxida-
tion and subsequent precipitation of insoluble cyanide
compounds (Farb, 1978).
Buffering and Neutralization

Buffering and neutralization are chemical reactions
which are similar. Neutralization is  achieved by
balancing the pH  or  activity of the hydrogen ion
concentration so that a neutral solution is produced.
Buffering refers to the ability  of a substance to
maintain a constant pH over a wide range of concen-
trations. The neutralization of an  acid  or  base
produces water and neutral salts. Lime is effective in
neutralization of acidic wastes.

Many biological processes rely on maintaining neutral
pH levels  to  enhance  biodegradation  of organic
constituents (Brown et al., 1983). Neutral pH levels
are maintained  in soils by  their natural buffering
capacity. Aluminum ions in the surface of clay colloids
maintain an equilibrium of hydroxide ions in the soil
solution. The actual pH range  of a soil may  vary
according to the predominant clay constituent present
(Brown et al., 1 983). Neutralization of contaminants
through pH adjustment is generally achieved by the
addition of an acid or base, precipitation, and oxidation
reduction.
Dilution

The dilution of ground-water contaminants occurs
through the addition of water by precipitation or other
sources, introduced into the ground-water system.
Dilution  is an integral mechanism  of dispersion
occurring on  a microscopic and  macroscopic  scale
(Todd,  1980).  These mixing mechanisms produce
longitudinal and transverse dispersion of the con-
taminant such that the concentration decreases with
the distance from the point of introduction. According
to Todd (1980), dilution may be the most important
mechanism for attenuation after the pollutant enters
the ground-water system.


Dispersion

A porous medium is composed of  particles of varying
sizes,  shapes, and orientations.  As water  flows
through a porous  medium, the velocity varies across
pore space and around particles. As a result, when a
contaminant  is  introduced into  a  ground-water
system,  it tends  to spread, or disperse,  so  as  to
gradually occupy  an increasing volume of that flow
system. Thus, dispersion constitutes a non-steady,
                        136

-------
irreversible mixing process by which the contaminant
disperses within the surrounding ground water (Todd,
1980).

Dispersion has two components, longitudinal and
transverse. Longitudinal  dispersion occurs in the
direction of flow and is  caused by differences  in
macroscopic velocities as the water moves across
pore spaces and around particles winding a tortuous
path through the  media in the  direction of  flow.
Transverse dispersion occurs in two  dimensions
normal  to ground-water flow  and  results  from
repeated division and deflection of the water flow by
the particles (Todd, 1980;  Bouwer, 1978). Figure A-1
illustrates transverse and longitudinal dispersion in a
saturated porous medium.

Figure A-1  Schematic of pathlines showing longitudinal and
           transverse dispersion (Bouwer, 1978).
                         Longitudmal dispersion occurs
                         when a contaminant enters
                         at A or B.

                         Longitudinal and transverse
                         dispersion occurs when a
                          contaminant enters at C
Dispersion is a  phenomenon  that is caused by a
combination of two processes, molecular diffusion
and mechanical dispersion that occurs with laminar
flow in a porous medium (Todd, 1 980; Wilson et al.,
1976). The  result of  these processes produces a
contaminant plume with distinctly different character-
istics dependent on the way the contaminant is
introduced into the system. Figure A-2(a) illustrates
the configuration of a plume  that forms from  the
continuous input of contaminant, whereas Figure A-
2(b) represents input of a contaminant in pulses. The
contaminant plume developes an expanding elliptical
shape with declining concentration per unit mass of
aquifer because  of the process of dispersion (Freeze
and Cherry, 1979).

The relative rates of dispersion and the subsequent
configuration of the  contaminant plume are depend-
ent on the homogeneity of the aquifer. Most laboratory
testing of dispersion has been restricted to homoge-
neous, sandy mediums. Heterogeneous aquifer media
present a complex dispersion pattern related to the
respective hydraulic conductivities of the individual
stratigraphic units. High conductivity units dominate
the flow of contaminants in the ground-water system
as well as provide zones of migration where contam-
inants would move  more  quickly than  through
adjacent units of low conductivity (Freeze and Cherry,
1979). The predomination of heterogenous geologic
units  that serve as aquifers has necessitated the
quantification of contaminant transport  through
mathematical  models  (Freeze and Cherry, 1979;
Bouwer, 1978;  Roberts, 1981;  Anderson,  1984).
These models have been extended to include mole-
cular diffusion, the adsorption of solutes by the media
and the decay of radioactive materials. The primary
emphasis of these models is to provide an  effective
means  of predicting the  extent  of  contaminant
dispersion, contaminant flow velocities, and concen-
trations at various points within the  plume. Most
modeling  efforts are constrained by the  lack  of
adequate control data.


Viscosity

The viscosity of a fluid is the property of resistance to
relative motion and shear deformation during flow.
The more viscous the fluid, the greater the shear
stress, and thus, the resistance to flow. Viscosity is
affected by temperature; the higher the temperature,
the lower the viscosity, and the easier it will be for a
fluid to move through the pores in a media. Viscosity
of water has a direct affect on hydraulic conductivity
that can bequantifiedasan inverse linear relationship
(Bouwer, 1978). Reducing the viscosity by half will
double the hydraulic conductivity.

Thus, the viscosity  of a  contaminant will partially
control the rate of migration. More viscous contam-
inants will not move as easily through porous media.
Consideration of contaminant viscosity if  it differs
significantly from water viscosity, in conjunction with
other applicable chemical reactions, may be neces-
sary for prediction of contaminant migration.

Mechanical Filtration
Mechanical  filtration removes contaminants which
are larger than the pore spaces of the host  medium.
This process is most effective in finer-grained mate-
rials such as clay or soil, but can  occur in coarse-
grained media depending on the  paniculate sizes
being filtered. The effects  of  mechanical  filtration
increase with decreasing pore and/or channel size
within the media. Retention of larger particles may
effectively reduce  the permeability of the  media.
Chemical reactions such as precipitation may form
larger, insoluble particles that are retained by the
media, thereby affecting porosity and permeability.
The effectiveness of mechanical filtration for removal
of contaminants is thus dependent on grain size and
sorting of the media, and hydraulic conditions within
the media, andtheparticulatesizeofthecontaminant
being transported through the medium.
                                                                       137

-------
Figure A-2  Plume configuration based on contaminant input (Freeze and Cherry, 1979).
         Continuous
         Point Source
          Of Tracer
                                                (a)
       -»• Uniform Flow
  Instantaneous
   Point Source
                        3<7ti
                                         3o>
                                                (b)
References

Anderson, M. P., 1984. Movement of contaminants in
  groundwater:  groundwater transport—advection
  and  dispersion;  Groundwater  Contamination,
  National Academy Press, pp. 37-45.

Bouwer, E. J., B. E. Rittmann,  and P. L. McCarty,
  1981. Anaerobic degradation of halogenated 1-
  and 2-carbon organic compounds; Environmental
  Science & Technology, Vol. 15, No. 5, pp. 596-599.

Bouwer, H., 1978. Groundwater hydrology; McGraw-
  Hill, pp. 342-402.

Brown, K.  W., G. B. Evans, Jr.,  and B. D. Frentrop,
  eds., 1983.  Hazardous waste  land  treatment;
  Butterworth Publishers, 692 pp.

Callahan,  M. A., M.  Slimak, N. Gabel,  I.  May, F.
  Fowler,  R. Freed,  P. Jennings, R. Duffee, F.
  Whitmore, B. Maestri, W.  Mabey, B. Holt, and C.
  Gould, 1979. Water related fate of 129  priority
  pollutants, Vol. I—introduction and technical back-
  ground,  metals  and  inorganics, pesticides  and
  PCBs; U.S. EPA-440/4-79-029a, pp. 2-1  through
  2-14.

Cherry, J. A., R. W.  Gillham,  and J. F. Barker, 1984.
  Contaminants in groundwater: chemical processes;
  Groundwater Contamination,  National Academy
  Press, pp. 46-66.
Claus, D. and N. Walker, 1964. The decomposition of
  toluene by soil bacteria; Journal General Micro-
  biology, Vol. 36, pp. 107-122.

Cohen, S. Z., S. M. Creeger, R. F. Carsel, and C. G.
  Enfield, 1984. Potential for pesticide contamination
  of ground water resulting from agricultural  uses;
  American  Chemical Society  Symposium Series
  #259, Treatment  Disposal  of  Pesticide Wastes,
  Krueger and Seiber, eds., Washington, DC.

Davis, S. N. and R. J. DeWiest, 1966. Hydrogeology;
  John Wiley & Sons, 463 pp.

Dohnalek,  D. A. and J. A.  Fitzpatrick.  1983. The
  chemistry of reduced sulfur  species and  their
  removal from  ground water  supplies; Journal
  AWWA, Vol. 75, No. 6, pp. 298-308.

Ehrlich, G. G., D. F. Goerlitz, E. M. Godsy, and M. F.
  Hult, 1982. Degradation of phenolic contaminants
  in ground water by anaerobic bacteria: St. Louis,
  Minnesota; Ground Water, Vol. 20, No. 6, pp. 703-
  710.

Farb, D., 1978. Upgrading hazardous waste disposal
  sites: remedial approaches; U.S. EPA #SW-677,
  Cincinnati, Ohio, 40 pp.

FMC Corporation, 1983. Industrial waste treatment
  with hydrogen peroxide; Industrial Chemical Group,
  Philadelphia, Pennsylvania,  23 pp.
                      138

-------
Freeze, R. A. and J. A. Cherry, 1979. Groundwater;
  Prentice-Hall, 604 pp.
Fuller, W. H. and J. Artiola, 1978. Use of limestone to
  limit contaminant movement from landfills; Pro-
  ceedings of the 4th Annual Research Symposium,
  Land Disposal  of Hazardous Wastes, U.S. EPA-
  600/9-78-016, pp. 282-298.

Gibson,  D.  T., 1978. Microbial  transformation  of
  aromatic pollutants; Aquatic Pollutant, Pergamon
  Press.
Griffen,  R.,  R. Clark, M.  Lee, and E. Chian,  1978.
  Disposal and removal of polychlorinated biphenyls
  in soil; Proceedings of  the 4th Annual Research
  Symposium, Land Disposal of Hazardous Wastes,
  U.S. EPA-600/9-78-016, pp. 169-181.

Hague, R., D. W. Schmedding, and V. H.  Freed, 1974.
  Aqueoussolubility, adsorption and vapor behaviour
  of polychlorinated biphenyl Arochlor 1254; Envi-
  ronmental Science & Technology, Vol. 8, pp. 1 39-
  142.

Harsh,  K., 1975. In situ neutralization  of an acrylo-
  nitrile spill; Ohio Environmental Protection Agency,
  Dayton, Ohio, pp.  187-189.

Jhaveri, V. andA. J. Mazzacca, 1983. Bio-reclamation
  of ground and groundwater—case history; Proceed-
  ings of the National Conference on Management of
  Uncontrolled Hazardous Waste  Sites, Washington,
  DC, pp. 242-247.

Karickhoff, S. W., D. S. Brown, and T. A. Scott, 1979.
  Sorption  of  hydrophobic  pollutants on  natural
  sediments; Water Research, Vol. 13, pp. 241 -248.

Keenan, C. W. and J. H. Wood, 1971. General college
  chemistry; Harper & Row, 717 pp.

Kobayashi,  H. and B. E. Rittmann, 1982. Microbial
  removal of hazardous organic  compounds; Envi-
  ronmental Science & Technology, Vol. 16, No. 3, pp.
  170A-183A.

Liu,  D., W. Strachan,  K. Thomson, and K. Kwas-
  niewska, 1981. Determination of the biodegradabil-
  ity of organic compounds; Environmental Science
  & Technology, Vol. 15, No. 7, pp. 788-793.
Matthess, G.,  1981.  In  situ  treatment of  arsenic
  contaminated ground water; The  Science of the
  Total Environmental.  No. 21, pp. 99-104.

Matthess, G. and J. C. Harvey, 1982.  Properties of
  ground water; John Wiley & Sons, pp. 73-114.

Pye, V. I., R. Patrick, and J. Quarles, 1983. Ground-
  water contamination in the United States;  Univer-
  sity of Pennsylvania Press, 314 pp.

Rott, U., 1981. Protection and improvement of ground
  water quality by oxidation processes in the aquifer;
  Quality of Ground Water; Proceedings of an Inter-
  national  Symposium, The Netherlands;  Elsevier
  Scientific Publication Company, pp. 1073-1076.

Roberts, P. U., 1981. Nature of organic contaminants
  in ground  water and approaches  to treatment;
  AWWA Seminar Proceedings, Organic Chemical
  Contaminants in Ground Water: Transport  and
  Removal, pp. 47-66.

Snoeyink, V. L. and D.  Jenkins, 1980. Water chem-
  istry; John Wiley & Sons, 463 pp.

Stover, E. L. and D. F. Kineannon, 1 983. Contaminated
  ground water treatability—a case study; Journal
  AWWA, Vol. 75, No. 6, pp. 292-298.

Tabak, H. H., S. A. Quave, C. I. Mashni, and E. F. Barth,
  1980.  Biodegradability studies with priority pollu-
  tant organic compounds; Staff Report, Wastewater
  Research  Division, U.S. EPA Research Center,
  Cincinnati, Ohio.

Todd,  D. K.,  1980.  Groundwater  hydrology; John
  Wiley  & Sons, pp. 31  6-352.
Tolman, A., A. Ballestero, W. Beck, and G. Emrich,
  1978.  Guidance manual for minimizing pollution
  from waste disposal sites; U.S. EPA-600/2-78-
  142, pp. 328-331.
Weldon, R. A., 1979. Biodisposal farming of refinery
  oily wastes; reprinted from API Oil Spill Conference
  Proceedings, March 19-22, 1979.

Wetherhold, R. G.,  D. D. Rosebrook, and E. W.
  Cunningham, 1981.  Assessment of hydrocarbon
  emissions from land treatment of  oily  sludges;
  Proceedings of the 7th Annual  Research Sympo-
  sium,  Land Disposal: Hazardous Waste, U.S. EPA-
  600/9-81-002b.

Wilson,  J. L., R. L. Lenton, and J. Porras, eds., 1 976.
  Groundwater pollution: technology, economics and
  management; Department of Civil  Engineering,
  Massachusetts Institute of Technology, Report No.
  TR208,  pp. 17-21.
                                                                     139

-------
                                         Appendix B

                      Characteristics of Ground-Water Contaminants
Contaminants have  been divided into  inorganic
compounds and organic compounds. For purposes of
this discussion, inorganic compounds are subdivided
into metals and nonmetals, while organic compounds
are separated into groups bearing similar molecular
structures which influence those processes affect ing
the fate and transport of ground-water contaminants.


Inorganic Metals

The  mobility  and  attenuation of  metals  in any
hydrogeologic  setting  is of function of  the  hydro-
chemical ground-water environment. Metals of pri-
mary importance include cadmium, chromium, cop-
per, lead, mercury, manganese, silver, zinc, and iron
for which maximum Federal Drinking Water Stand-
ards have been established. With the exception  of
iron, metals typically occur naturally in the environ-
ment in concentrations below 1  mg/l. Concentrations
are low due to the processes of adsorption, hydrolysis,
precipitation, and oxidation-reduction.

Metals tend to be hydrolized by water and exist as one
or more ionic species. These metals combine readily
with ligands  to form ionic  or  neutral aqueous
complexes. These ligands may be inorganic ions such
as HCOa, CDs,2 SO;,2 Cf, F",  and NOi (Freeze and
Cherry et al., 1979). Any dissolved organic constit-
uents that are  present may also cause complexation
orchelation. Increases in the concentrations of these
anions increase the concentrations of the complexes
that  are formed. The occurrence of a  complexed
species is dependent on the pH and the equilibrium of
a particular complex in the aqueous solution.

The oxidation-reduction potential of the ground water
directly  affects the oxidation state of the metal and
may also affect the nonmetallic anions with which it
forms complexes. Changes in the oxidation state of a
metal may control the relative solubility or insolubility
in water. The mechanism of sorption of trace  metals
is dependent on redox potential and pH.

Sorption of trace metals is an important process
which may maintain metal  concentrations far  below
that provided through solubility constraints.  Trace-
metal sorption occurs due to the presence of colloidal
size  clay particles,  organic matter,  and iron and
manganese hydroxides. In most  oxidizing environ-
ments,  the iron  and  manganese oxides occur  as
surface coatings on grains thereby increasing their
ability to sorbtrace metals(Freeze and Cherry, 1979).
This is particularly effective for Co, Ni, Cn, and Zn in
soils and freshwater sediments.

The hydrochemical environment of a ground-water
system exhibits many effects on trace metals making
the prediction of transport and migration difficult and
complex. In general, the processes of sorption and
precipitation cause the trace metals to migrate very
slowly with respect to ground water flow velocities.
Thus,  the occurrence  of generally localized contam-
ination by trace metals is common.

Cadmium (Cd)

Cadmium-contaminated  wastes are generated  as
byproducts  of cadmium-nickel battery production,
pigments for plastics, enamels and paints, fumicides,
and in electroplating  and metal coatings. The solu-
bility and sorption of cadmium are controlled by pH.
Under acidic or low pH conditions, cadmium solubility
increases while sorption by colloids decreases (Brown
et  al., 1983). Precipitation of cadmium  carbonates
and cadmium phosphates may  reduce cadmium
concentrations at low pH  values. Precipitation  of
cadmium sulfides occurs in reducing environments.
The primary mechanism for cadmium attenuation is
through sorption to organic  matter in soils as organic-
metallic complexes. The contaminant level as estab-
lished in the Federal  Primary Drinking  Water
Standards is 0.01 mg/l.

Chromium (Cr)

Chromium  is present in waste streams as  a con-
sequence of its use as a corrosion inhibitor, produc-
tion of refractory bricks to line metallurgical furnaces,
plating operations, topical antiseptics and  astrin-
gents, and the tanning and dye industries (Brown et
al., 1983). The oxidation-state of the chromium ion
directly affects its toxicity; chromium is the most toxic
and mobile at an oxidation state of +6. This is the most
common form of chromium in industrial wastes, thus
making chromium  a  concern. The soluble salts of
chromium, such assulfateand nitrate, are more toxic
than the insoluble salts of oxides and phosphates.
Under acid conditions, the presence of either oxygen
or an oxidizing agent can change the oxidation state
of chromium from +6to+3(Tolman et al., 1978; Fuller
and Artiola, 1978). The +3 chromium is less toxic and
                                               140

-------
generally immobile in ground water because it will
readily precipitate with carbonates, hydroxides, and
sulfides to form insoluble compounds. The maximum
contaminant  level as  established in  the Federal
Primary Drinking Water Standards is 0.05 mg/l.

Copper (Cu)

Industrial wastes from textile mills, cosmetics manu-
facturing, and hardboard production contain signif-
icant amounts of copper. The sorption of copper onto
colloids is a function of pH; sorption  increases at
higher pH values. Organic  matter present in soils
forms very stable complexes with copper (Brown et
al., 1983). These include complexation with carboxyl
and phenolic groups where sorption is high when iron
and manganese oxide concentrations are low. Exper-
iments indicate that copper  is sorbed appreciably by
quartz and even more strongly by clays. Copper is also
beneficial because low concentrations are necessary
for the metabolic processes  of  decomposition  by
bacteria. The maximum contaminant level as estab-
lished  in the Federal Secondary Drinking Water
Standards is 1.0  mg/l.

Lead(Pb)

Lead  is found in wastes from the manufacture of
lead-acidic  storage batteries, gasoline additives,
ammunition, pigments, paints, herbicides, and insec-
ticides. Lead may precipitate as sulfates, hydroxides,
and carbonates. The presence  of free lead ions
depends on the stability of the lead complex at varying
pH values. At high pH levels, lead is less soluble and
preferentially  sorbed onto clay  surfaces. Under
reduced conditions,  lead becomes mobile and may
form insoluble complexes with organic compounds
(Brown et al., 1 983). The maximum contaminant level
as established in the Federal Primary Drinking Water
Standards is 0.05 mg/l.

Mercury (Hg)
Mercury is present in a wide variety of  industrial
wastes such as electrical apparatus manufacturing,
production  of chlorine and caustic soda, pharma-
ceuticals, paints, plastics, paper products, and mer-
cury batteries. Many pesticides have metals as part of
their  composition.  Of these  pesticides, over  40
percent use mercury as the major metal component
(Brown et al., 1 983). Mercury in the +2 oxidation state
is rapidly and strongly complexed by covalent bonding
to sulfur-containing  organic compounds  and inor-
ganic  soils.  Colloidal  particles  of clay,  iron and
manganese  oxides,  fine sands, and organic matter
readily absorb mercury. Sorption by clay particles is
most  effective at high pH  values. The solubility of
various mercury ionic complexes can be affected by
changes in pH and/or oxidation-reduction. Insoluble
precipitates  of mercury, sulfates, hydroxides, and
nitrates form at  high pH conditions. Insoluble mer-
cury sulfide occurs in reducing conditions, whereas,
insoluble mercury chlorides favor  oxidizing condi-
tions.

Organic mercury compounds such  as phenyl, alkyl,
and methoxyethyl mercury used as fungicides may be
degraded by certain bacteria. However, other bacter-
ial forms tend to produce toxic mercury compounds
with organic  matter (Brown et al.,  1983). The most
toxic form of mercury occurs as methyl mercury and
poses a contamination problem for  the aquatic food
chain.  The  maximum contaminant level  as estab-
lished in the Federal Primary Drinking Water Stand-
ards is 0.002  mg/l.

Manganese (Mn)

The major source of manganese-contaminated waste
waters are from the iron and steel industries and from
the manufacture of paints, disinfectants, and fertil-
izers. The manganese ion commonly occurs as Mn +2,
which  is soluble and mobile,  and Mn +4, which is
insoluble and  thus non-mobile. Under reduced condi-
tions, Mn +2 is strongly sorbed to clay minerals  and
organic matter,  but  becomes less soluble as pH
increases. Under oxidizing conditions several stable
manganese compounds will form (Brown et al., 1983).
Manganese is considered a secondary constituent
under Federal Drinking Water Standards; maximum
contaminant levels are set at 0.05 mg/l.
Silver (Ag)

Silver is found in the waste streams of a variety of
industrial  processes including photographic, mirror,
and  electroplating  manufacturing  (Brown et  al.,
1983). Silver tends to be sorbed through  ion  ex-
change by colloidal particles and precipitated with
common inorganic anions such as carbonate sulfates
and chlorides. The maximum contaminant level as
established in the Federal Primary Drinking Water
Standards is 0.05 mg/l.
Zinc (Zn)

Industrial wastes containing zinc are a byproduct of
brass and bronze alloy production, galvanized metals
for pipes, utensils, insecticides, glues, rubber, inks,
and  glass  (Page,  1974). Zinc  can be attenuated
through precipitation, absorption, and ionic substitu-
tion  (Brown  et  al., 1983). Zinc may be  ionically
substituted for aluminum,  iron, or magnesium in
many clay  minerals. Zinc is primarily sorbed onto
organic colloids which are very soluble and mobile.
Zinc may be sorbed onto the particle surfaces of alloys
and  is generally immobile. The solubility of zinc
precipitates is dependent  on  the  stability of the
complexthat forms under variablepH conditions.The
only insoluble zinc precipitate is zinc sulfate. All other
                                                                       141

-------
precipitates of  zinc are soluble. Zinc is rendered
insoluble in soils and water with a pH greater than
6.5. The maximum contaminant level as established
in the Federal Secondary Drinking Water Standards is
5.0 mg/l.


Iron (Fe)

Iron, under oxidizing conditions  in  ground water,
forms hydrous oxides which provide a major attenua-
tion mechanism for the sorption of trace metals such
as cobalt,  nickel,  copper,  and zinc in  soils and
freshwater sediments.  When this oxide  occurs  as
coatings on grains of a media, it can greatly increase
the sorptive capacity of that medium. Iron  compound
stabilities are dependent on pH and oxidation-reduc-
tion potential. Iron  in reduced form  is soluble and
remains in solution. However, either very small-scale
variations  in the pH/Eh relationship or in bacterial
activity  can result  in precipitation of iron in the
hydrous oxide form. The maximum contaminant level
as established  in the Federal  Secondary Drinking
Water Standards is 0.3  mg/l.  Unlike most other
limits, the  level for iron was  not set because  of
associated  health risks, but rather for water quality
problems associated with staining  and  color. Iron
oxides  precipitate and  stain due to  their relative
insolubility.


Inorganic Nonmetals

The chemical behavior of non-metallic substances in
water has a  significant  effect  on  ground-water
quality. Most non-metals tend to be fairly mobile in
the ground-water system as  ionic species. The type
and amount of each species present is a function of
temperature, pressure, pH, redox potential, dissolved
concentrations, reactivity, and microbial activity.

The following discussion focuses on the major non-
metallic chemicals occurring in ground  water. For
each chemical,  information is presented on the
source(s) of the chemical  and its water chemistry
characteristics. These  nonmetallic chemicals can
occur either naturally in  ground water or as a result of
human activities.


Nitrogen

The most common inorganic contaminant is dissolved
nitrogen in the form of nitrate  (NOa-).  Dissolved
nitrogen also occurs in the form of ammonium (NH4+),
ammonia  (NH3-),  nitrite (N02-), nitrogen (N2), and
nitrous oxide (N20). Common sources of nitrate in
ground water are from the  burial of nitrogen-rich
wastes,  application of  fertilizers, and disposal  of
sewage. When nitrogen-rich compounds are added to
the environment, nitrogen is converted to different
forms. The processes of nitrification (conversion of
NH4+  to NOa-  by oxidation) and  ammonification
(conversion of organic N to NH4->  generally occur
above the water  table where oxygen and organic
matter are abundant (Freeze and Cherry, 1979).

Concentrations of NOa- are not limited by solubility.
Thus, this anionic form is very mobile and  stable
under oxidizing conditions. N03- is not easily retarded
or transformed by chemical processes. The presence
of reducing conditions may initiate denitrification, a
process where NOa- is converted to N2 or N20. These
resulting forms are of less concern from a ground-
water pollution standpoint because  they pose  no
health risk. A maximum contaminant level of 10 mg/l
N has been established for nitrates because of health
concerns in infants when this level is exceeded.
Phosphorous

Phosphorous is not generally considered to be an
intrinsically harmful constituent in ground water in
normal concentrations, but its presence can cause
significant  environmental  problems by decreasing
available oxygen through  accelerated  algae  and
aquatic vegetative growth. The most common source
of phosphorous contamination  is by  agricultural
activity and decomposition  of organic wastes.  Dis-
solved phosphorous can occur  in many forms de-
pending on the pH of the water. Hydrolysis  and
mineralization can convert insoluble forms of phos-
phates to the soluble phosphate ion for use by plants
and organisms (Brown et al., 1983). Degradation and
mobilization of phosphorous by microbes accounts
for a portion of its attenuation. Under certain condi-
tions, phosphorouswill precipitate as iron, aluminum,
or calcium  phosphate or  be sorbed by iron  and
aluminum oxides and hydroxides.

Boron

Boron is released during the decomposition of organic
materials. Partial sorption of boron may occur on iron
and aluminum hydroxyl compounds and clays. The
sorption of boron to these materials is pH dependent;
sorption will not occur at high pH levels.  The amount
of boron that will be sorbed is  dependent on surface
area  and appears to  be  irreversible  due  to the
formation of covalent bonds.  No drinking  water
standards for  human consumption of  boron have
been  set.
Sulfur
Sulfur is moderately abundant in the earth's soils and
is an important plant nutrient. Sulfur, in some form, is
widespread in industrial waste from processes such
as Kraft mills, sugar refining, petroleum refining, and
copper and coal extraction (Brown et al., 1983). Sulfur
is commonly found in two forms; as sulfate (SCu 2) in
                       142

-------
oxidizing conditions, and as sulfide (HS )  or  (H2S)
under  reducing conditions. Sulfides  are toxic and
produce  an odor in water. The FMC Corporation
(1983) has conducted extensive laboratory testing
using hydrogen peroxide to oxidize sulfides to sulfur
and water. Hydrogen peroxide has been shown to be
effective in neutralizing other sulfur compounds that
are common industrial waste effluents. These include
polysulfides,  sulfites, thiosulfates, polythionates,
dithionites, and dithionates. Siulfates are relatively
mobile in the ground-water system as anions. Some
clays have the capability to sorb sulfate onto their
particle surfaces (Brown et al., 1983). Sulfates also
tend to form inorganic  ligands and  complex with
metal ions increasing their solubility. A maximum
contaminant level for sulfates  is established in the
Federal Secondary Drinking Water Standards at 250
mg/l.


Fluoride

The  mobility of fluoride depends on the types and
quantities of cations present in the water that have
formed salts with the fluoride  ion.  Sodium salts of
fluoride (NaF) have  high  solubilities as opposed to
calcium  salts (CaF2) which  have  low  solubilities.
Fluoride may be a natural constituent of ground water
produced from  the  dissolution of  fluoride-bearing
rocks or from industrial wastes such as the production
of phosphatic fertilizers, hydrogen  fluoride,  and
fluorinated hydrocarbons (Brown et al., 1983).  Fluo-
ride may also tend to complex with metallic ions. Soils
with high cation exchange capacities are capable of
retaining fluoride. The  limit  for concentration of
fluoride has been established at 1.4 to 2.4 mg/l in the
Federal Primary Drinking Water Standards.

Chloride

Chloride is very soluble and thus highly mobile in
ground water. Chloride in ground water results from
the dissolution of chloride-bearing rocks  such as
halite, and is a common  product or byproduct (e.g.
chlorinated hydrocarbon wastes) in most industrial
wastes. Another source of chloride is from spillage or
leakage of  brines that are produced in  oil and gas
drilling operations. The maximum contaminant level
as established  in the Federal  Secondary  Drinking
Water Standards is 250 mg/l.


Arsenic

Arsenic is contained in wastes from the production of
herbicides, pesticides, pigments, and wood preserv-
atives (Freeze and Cherry, 1979; Brown et al., 1983).
Arsenic  in natural  ground  water occurs  in four
oxidation states which exist as many different species
under variable conditions. In general, most forms of
arsenic tend to become soluble  under oxidizing
conditions. Solubility is controlled by pH and redox
potential.

The  movement of arsenic in the environment  is
affected by sorption to soils and volatilization. Sorp-
tion  and/or  precipitation  by soil  colloids is  an
important attenuation  mechanism.  These  colloids
include iron  and  aluminum  hydroxides or clays.
Sorption  increases with  increasing pH,  clay,  and
hydroxide content. Levels of  arsenic as low as 10
mg/l have been shown  to be toxic (Brown et al.,
1983). The maximum contaminant  level as estab-
lished in the Federal Primary Drinking Water Stand-
ards is 0.05 mg/l.


Selenium

Sources of selenium which can cause ground-water
contamination include glass, electronics, steel, rub-
ber,  and  photographic  industries.  Selenium  has
properties which are similar to sulfur. Selenium has
three oxidation states. These typically form selenities
and  selanates of sodium and calcium,  and soluble
selenium salts. Selenium anions form selanates with
mercury,  copper,  and cadmium which are very
insoluble (Brown et al., 1983). Selenium  in ground
water is least soluble under acid conditions. Mechan-
isms for selenium attenuation include sorption onto
hydrous iron oxides and precipitation to the insoluble
ferric oxide selenite. The maximum contaminant level
as   established  in the  Primary Federal  Drinking
Water Standard is 0.01 mg/l.


Organic Compounds

The  contamination of  ground-water resources by
organic compounds has resulted in the initiation of
studies on their occurrence  and behavior in the
ground-water system. Many organic compounds of
environmental concern are at trace levels, parts per
billion  or  parts per million. However,  even these
minute levels may exhibit toxic effects on aquatic and
mammalian life forms. The United States Environ-
mental Protection Agency (EPA) has developed a list
of what  are considered to  be  the  129  priority
pollutants and the relative frequency of these mater-
ials  in industrial waste waters  (Keith and Telliard,
1979) (Table B-1).

There are several chemical and biochemical reactions
that  are recognized as having a  potential to signif-
icantly control contamination  migration or attenua-
tion  in ground-water systems. These mechanisms
include sorption, hydrolysis, oxidation-reduction, and
biodegradation. A discussion  of these processes  is
contained in  Section  6,  Processes  and Properties
Affecting Contaminant Fate and Transport.

The solubility of organic compounds may be divided
into  two broad groups; polar and nonpolar. Polar
                                                                       143

-------
Table B-1.    EPA List of 129 Priority Pollutants and the Relative Frequency of These Materials in Industrial Wastewaters
             (Keith and Telliard, 1979)
Percent
of
samples8
Number of
Industrial
categories'"
Percent Number of
of Industrial
samples8 categories'"
31 are purgeable organics
1.2
2.7
29.1
29.3
16.7
7.7
5.0
6.5
10.2
1.4
7.7
1.9
4.2
0.4
1.5
40.2
5
10
25
28
24
14
10
16
25
8
17
12
13
2
1
28
Acrolein
Acrylonitrile
Benzene
Toluene
Ethylbenzene
Carbon Tetrachloride
Chlorobenzene
1,2-Dichloroethane
1,1,1 -Trichloroethane
1,1-Dichloroethane
1,1-Dichloroethylene
1 , 1 ,2-Trichloroethane
1 , 1 ,2-Tetrachloroethane
Chloroethane
2-Chloroethyl vinyl ether
Chloroform
2.1
1.0
34.2
1.9
0.1
1.9
4.3
6.8
0.3
2.5
10.2
10.5
0.2
7.7
0.1

5
5
25
6
1
12
17
11
4
15
19
21
2
18
2

1,2-Dichloropropane
1,3-Dichloropropane
Methylene chloride
Methyl chloride
Methyl bromide
Bromoform
Dichlorobromomethane
Trichlorofluoromethane
Dichlorodifluoromethane
Chlorodibromomethane
Tetrachloroethylene
Trichloroethylene
Vinyl chloride
1 ,2-trans-Dichloroethylene
bis(Chloromethyl) ether

46 are base/neutral extractable organic compounds

6.0

0.5
0.2
1.1
1.0
0.4
10.6
0.9
1.5
1.8
1.1
1.5
0.04
41.9
6.4
5.8
7.6
18.9
4.5
4.2
8.5

9

5
1
7
6
3
18
9
13
9
3
9
1
29
12
15
20
23
12
14
13
!1 ,2-Dichlorobenzene
1 ,3-Dichlorobenzene
1 ,4-Dichlorobenzene
Hexachloroethane
Hexachlorobutadiene
Hexachlorobenzene
1 ,2,4-Tnchlorobenzene
bis(2-Chloroethoxy) methane
Naphthalene
2-Chloronaphthalene
Isophorone
Nitrobenzene
2,4-Dinitrotoluene
2,6-Dinitrotoluene
4-Bromophenyl phenyl ether
bis(2-Ethylhexyl) phthalate
Di-n-octyl phthalate
Dimethyl phthalate
Diethyl phthalate
Di-n-butyl phthalate
Acenaphthylene
Acenaphthene
Buty benzyl phthalate
5.7
7.2
5.1
7.8
m R
1 U.U
2.3
1.6
1.8
3.2
0.8
0.2
0.6
0.1
0
0.2
1.1
0.8
0.1
1.2
0.1
0.1
1.4
11
12
9
14
16

6
6
6
8
4
4
7
2
0
4
4
7
1
5
1
2
6
Fluorene
Fluoranthene
Chrysene
Pyrene
( Phenanthrene
I Anthracene
Benzola (anthracene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzolalpyrene
lndeno(1,2,3-c,d)pyrene
Dibenzo(a,h)anthracene
Benzo(g,h,i)perylene
4-Chlorophenyl phenyl ether
3,3'-Dichlorobenzidine
Benzidine
bis(2-Chloroethyl) ether
1 ,2-Diphenylhydrazine
Hexachlorocyclopentadiene
N-Nitrosodiphenylamine
N-Nitrosodimethylamine
N-Nitrosodi-n-propylamine
bis(2-Chloroisopropyl) ether
1 1 are acid extractable organic compounds
26.1
2.3
2.2
1.6
1.1
6.9
25
11
9
6
6
18
Phenol
2-Nitrophenol
4-Nitrophenol
2,4-Dinitrophenol
4,6-Dinitro-o-cresol
Pentachlorophenol
1.9
2.3
3.3
4.6
5.2

8
10
12
12
15

p-Chloro-m-cresol
2-Chloropenol
2,4-Dichlorophenol
2,4,6-Trichlorophenol
2,4-Dimethylphenol

26 are pesticides/ PCB's
0.3
0.4
0.2
0.6
0.8
0.2
0.5
0.5
0.1
0.04
0.1
0.2
0.2
0.2
3
4
2
4
6
4
3
5
3
1
2
2
3
2
a-Endosulfan
0-Endosulfan
Endosulfan sulfate
a-BHC
/3-BHC
5-BHC
7-BHC
Aldrin
Dieldrin
4,4'-DDE
4,4'-DDD
4,4'-DDT
Endrin
Endrin aldehyde
0.3
0.1
0.2
0.2
0.6
0.5
0.9
0.8
0.6
0.6
0.5
—


3
1
4
2
2
1
2
3
2
3
1
—


Heptachlor
Heptachlor epoxide
Chlordane
Toxaphene
Aroclor 1016
Aroclor 1221
Aroclor 1232
Aroclor 1242
Aroclor 1248
Aroclor 1254
Aroclor 1260
2,3,7,8-Tetrachlorodibenzo-p-dioxin
(TCDD)

                              144

-------
Table B-1. (Continued)
Percent
of
samples8
18.1
19.9
14.1
30.7
53.7
55.5
43.8
Number of
Industrial
categories'1
20
19
18
25
28
28
27

Antimony
Arsenic
Beryllium
Cadmium
Chromium
Copper
Lead
Percent
of
samples3
13 are metals
16.5
34.7
18.9
22.9
19.2
54.6
Number of
Industrial
categories'"
20
27
21
25
19
28

Mercury
Nickel
Selenium
Silver
Thallium
Zinc
  33.4
                                            Miscellaneous
19
Total cyanides
Not available
Not available
Asbestos (fibrous)
Total phenols
aThe percent of samples represents the times this compound was found in all samples in which it was analyzed for divided by the total as of 31
 August 1978. Numbers of samples ranged from 2,532 to 2,998 with the average being 2,617.
bA total of 32 industrial categories and subcategories were analyzed for organics and 28 for metals as of 31 August 1978.
organics exhibit an affinity for water; and therefore do
not bond  or  sorb to  particle  surfaces.  Non-polar
organics are not attracted to water and therefore tend
to be easily  sorbed. The solubility of an organic
substance  also affects  its ability  to  be oxidized,
hydrolyzed, and biodegraded. These properties differ
between the organic groups and those interactions
are often strongly dependent on the hydrogeochem-
ical environmental factors including the pH, redox
potential, and other constituent concentrations in the
water.

The study of organic compounds, known  as organic
chemistry,  deals  with the compounds  of  carbon
(Sawyer and McCarty, 1978). All organic compounds
contain carbon in combination with one or more
elements, most commonly, hydrogen, oxygen, nitro-
gen, phosphorous, and sulfur.  Organic compounds
generally exhibit several properties  that make them
different from inorganic substances. Organic com-
pounds  are generally  combustible, less  soluble in
water, and have lower boiling  and melting points.
Reactions of organic compounds are generally molec-
ular so they  tend to  be slower than most other
chemical reactions. All organic compounds are either
natural, synthetic, or fermentative in origin. Organic
wastes are often  produced from the processing of
                                    natural and synthetic organic materials and fermenta-
                                    tion at industrial facilities.

                                    The basis of an organic compound  is the element
                                    carbon. Carbon is diverse because it maintains four
                                    covalent bonds in addition to the ability of the carbon
                                    atoms to  link together by covalent bonding in a wide
                                    variety of ways (Sawyer and McCarty, 1978). These
                                    bonds may occur as a continuous chain, a branched
                                    chain, a cyclic  ring, or as chains or rings containing
                                    other  elements (Figure  B-1). These structures serve
                                    as the basis for classification of organic compounds.
                                    For example, aliphatic compounds contain chains or
                                    branched  chains  of  carbon  atoms and aromatic
                                    compounds have carbon atoms linked in a six-mem-
                                    ber carbon ring which contains three double bonds
                                    that give them stability. Each of these compounds can
                                    be subdivided  into groupings or homologous series
                                    where each member  in  the series differs from other
                                    members by the addition of an extra carbon group.

                                    The naming  of organic  compounds is complex. The
                                    details of nomenclature may be found in a standard
                                    chemistry text  or the  CRC Handbook of Physics and
                                    Chemistry (Weast, 1983). The Office of Technology
                                    Assessment (1984) provides a comprehensive list of
                                    organic compounds that are known to occur in ground
                                    water, their ranges  of detected concentrations,
Figure B-1 Covalent bonding arrangements of carbon atoms (Lippencott et al., 1978).
     I    I     I     I     I
    c—c—c—c—c-
     I    I     I     I     I
         Straight Chain
                        I    I     I     I
                       •c-c—c-c
                        I    I     I     I
                              —c-
                          Branched Chain
       c-c:
           c:
       X
        Ring
                                                             ^
                                                           Aromatic Ring
                                                                       145

-------
examples  of  uses and  quantitative  estimates of
carcinogenic potency, and  noncarcinogenic toxicity
(Table B-2). This list has been subdivided according to
characteristic organic  classes; aromatic hydrocar-
bons, oxygenated hydrocarbons, hydrocarbons with
specific elements (N,S,P,CI,l,F,Br) and "others." The
"others" group generally corresponds to the aliphatic
hydrocarbons which includes many petroleum prod-
ucts. The following discussions use this classification
for simplicity, but expands upon the groups found
within these classes.
Aliphatic Compound..

A hydrocarbon is a basic organic compound of carbon
and hydrogen that may be of two types; saturated and
unsaturated. A saturated hydrocarbon has adjacent
carbon atoms joined by singlecovalent bonds with all
other bonds to hydrogen atoms. Unsaturated hydro-
carbons have at least two carbon atoms joined by
more than  one  covalent bond with all other bonds
satisfied by hydrogen (Sawyer and McCarty, 1978;
Lippencott et al., 1978).

Saturated compounds range from a compound with
one  carbon atom, to those with  each  successive
compound  containing an additional carbon atom.
These compounds are known as the alkanes or the
methane series and are  relatively inactive.  The
principal source of alkanes is petroleum. Mixtures of
these compounds  comprise gasoline and diesel fuel.
Some other alkanes  include ethane and propane.
Methane is the  simplest hydrocarbon (CH4) and is a
major end product of anaerobic treatment processes
as well as a constituent of natural gas.

In the  alkane series, butane has two isomers.  An
isomer is a compound that has the same molecular
formula, but different structural formulas (Lippencott
et al., 1973).  Many organic compounds exhibit this
property. Compounds containing rings of saturated
carbon atoms are known  as cycloalkanes; they  are
more reactive due to the strained structure of  the
small  ring.  These are commonly known as  the
napthenes and have cyclo-prefixes.

The unsaturated hydrocarbons can lose hydrogen to
bond with other elements or compounds. The alkene
or ethylene series of compounds all have one double
bond between  two  adjacent carbon  atoms.  The
compounds are commonly  called olefins and  are
formed in large quantities during the processing of
petroleum products. The most important reaction of
thealkenes is polymerization, where small molecules
unite to form giant molecules or polymers. The most
common reaction is the polymerization of ethylene to
form polyethylenes. The alkadienes or alkapolyenes
contain more than two carbon-carbon double bonds.
Those hydrocarbons containing triple bonds between
carbon atoms are known as the alkyne or acetylene
series. These compounds  represent starting sub-
stances for many synthetic fibers.


Oxygenated Hydrocarbons

Oxygenated hydrocarbons refer to any organic com-
pound that contains an (OH) group, an oxygen group,
or responds as an acid in a  solution. These may
include both aromatic and aliphatic hydrocarbon
groups.

Alcohols or hydroxy alkyl compounds are considered
to be a step in  the  primary  oxidation  product  of
hydrocarbons. The alcohols are classified into three
groups: primary, secondary, and tertiary, depending
on the location  of the (OH)  group. The  common
alcohols are methyl,  ethyl,  isopropyl, and n-butyl.
Methyl alcohol is used in the synthesis of organic
compounds and in antifreeze. Ethyl alcohol is used in
the production of beverages,  synthesis of organic
compounds,  and in medicines. Isopropyl  alcohol is
used extensively in organic synthesis as is n-butyl
alcohol. Short chain alcohols are soluble in water and
may be volatized and  biodegraded (Brown et  al.,
1983). Polyhydroxyl alcohols contain two hydroxyl
groups per molecule and are known as glycols. These
are commonly used  as radiator anti-freeze com-
pounds and  are very  toxic. Glycerol is a trihydroxy
alcohol used extensively in soaps, foods, cosmetics,
and medicines. Most  alcohols  are easily oxidized by
oxidizing  agents and many microorganisms.  The
aromatic alcohols compose a homologous series with
the pre-word phenyl, for example phenyl methyl.
These alcohols are also  subject to chemical and
biological  oxidation.

Primary alcohols are oxidized  to aldehydes, while
secondary alcohols  oxidize to ketones.  Common
aldehydes include formaldehyde and acetaldehyde.
Formaldehyde is used  extensively  in organic syn-
thesis and  is toxic  to microorganisms,  however,
under dilute concentrations it can be used as food by
microorganisms and  oxidized to carbon dioxide and
water. The chemical  names of all aldehydes end in
-al. Many  of the aromatic aldehydes exhibit fragrant
odors, such  as coumarin and vanillan. The ketones
are used as industrial  solvents and in the synthesis of
organic products.  The most  common  ketone is
acetone. Both aromatic aliphatic ketones are easily
oxidized by microorganisms.

Organic acids represent the highest oxidation state
possible in an organic compound;  further oxidation
produces  carbon dioxide and water (Sawyer and
McCarty, 1978). All organic acids contain a carboxyl
group. Thus, acids with one carboxyl group are known
as monocarboxylic acids and so on. A wide variety of
saturated  and unsaturated acids occur in nature as
constituents of waxes, fats, and oils. These are known
as  fatty acids which  are typically straight chain
                       146

-------
 Table B 2.
 Contaminant
               Substances Known to Occur in Ground Water, Ranges of Detected Concentrations, Exceeded Standards, Examples
               of Uses, and Quantitative Estimates of Carcinogenic Potency and Noncarcinogenic Toxicity (Ota, 1984)
                            Concentration    Standard
                                                                          Examples of uses
                                                                                    Carcino-
                                                                                     genic
                                                                                    potency
                                                                  Noncar-
                                                                  cinogenic
                                                                  toxicity
 Aromatic hydrocarbons
 Acetanilide
 Alkyl benzene sulfonates
 Aniline
 Anthracene
 Benzene
 Benzidine

 Benzyl alcohol

 Butoxymethylbenzene
 Chrysene
 Creosote mixture
 Dibenzla.h.lanthra-
   cene
 Di-butyl-p-benzoquinone
 Dihydrotrimethylquinoline
 4,4-Dinitrosodiphenyl-
   amine
 Ethylbenzene
 Fluoranthene
 Fluorene
 Fluorescein
 Isopropyl benzene
 4,4'-Methylene-bis-2-
   chloroaniline (MOCA)
 Methylthiobenzothiazole
 Napthalene

 o-Nitroaniline

 Nitrobenzene
 4-Nitrophenol
 n-Nitrosodiphenylamine
 Phenanthrene

 n-Propylbenzene
 Pyrene
 Styrene (vinyl benzene)
 Toluene
1,2,4-Trimethylbenzene

Xylenes (m,o,p)


Oxygenated hydrocarbons
Acetic acid

Acetone

Benzophenone

Butyl acetate
N-Butyl-benzylphthalate
Di-n-butyl phthalate

Diethyl ether

Diethyl phthalate
Diisopropyl ether
2,4-Dimethyl-3-hexanol
(parts per billion)
       18
   0.6-20,230
       10
   0.9-4,000
      31
      290
     6.7-82
     18-471


      48

   0.1-6,400




   0.07-300





   10-3,000
     10-38
      470
     20-34
Intermediate manufacturing, Pharmaceuticals, dyestuffs
Detergents
Dyestuffs, intermediate, photographic chemicals,
   Pharmaceuticals, herbicides, fungicides, petroleum
   refining, explosives
Dyestuffs, intermediate, semiconductor research
Detergents,  intermediate, solvents, antiknock gasoline
Dyestuffs, reagent, stiffening agent in rubber
   compounding
Solvent, perfumes and flavors, photographic developer
   inks,  dyestuffs, intermediate
NA
Organic synthesis
Wood preservatives, disinfectants
NA

NA
Rubber  antioxidant
NA

Intermediate, solvent
NA
Resinous  products, dyestuffs, insecticides
Dyestuffs
Solvent, chemical manufacturing
Curing agent for polyurethanes and epoxy resins
Solvent, lubricant, explosives,  preservatives,
  intermediate, fungicide, moth repellant
Dyestuffs, intermediate, interior paint pigments,
  chemical manufacturing
Solvent, polishes, chemical manufacturing
Chemical manufacturing
Pesticides, retarder of vulcanization of rubber
Dyestuffs, explosives, synthesis of drugs, biochemical
  research
Dyestuffs, solvent
Biochemical research
Plastics, resins, protective coatings, intermediate
Adhesive solvent in plastics, solvent, aviation and high
  octane blending stock, dilutent and thinner,
  chemicals, explosives, detergents
Manufacture of dyestuffs, Pharmaceuticals, chemical
  manufacturing
Aviation gasoline, protective coatings, solvent,
  synthesis of organic chemicals
Food additives, plastics, dyestuffs, Pharmaceuticals,
  photographic chemicals, insecticides
Dyestuffs, solvent, chemical manufacturing, cleaning
  and drying of precision equipment
Organic synthesis, odor fixative, flavoring,
  Pharmaceuticals
Solvent
Plastics, intermediate
Plasticizer, solvent, adhesives,  insecticides, safety
  glass, inks, paper coatings
Chemical manufacturing, solvent,  analytical
  chemistry, anesthetic, perfumes
Plastics, explosives, solvent, insecticides, perfumes
Solvent, rubber cements, paint and varnish removers
Intermediate, solvent,  lubricant
Low
High
           Low
                                                                                     Low
                                                                                                 Low
                                                                                              Moderate
           Low
           Low
           Low



           Low

           Low

           Low



           Low
                                                                                               147

-------
Table B-2. (Continued)
Contaminant
Concentration    Standard
                                                                          Examples of uses
                                                       Carcino-    Noncar-
                                                        genic     cinogenic
                                                       potency     toxicity
2,4-Dimethyl phenol
Di-n-octyl phthalate               23
1,4-Dioxane                     2,100
Ethyl acrylate                     —
Formic acid                       —

Methanol (methyl                  —
  alcohol)
Methylcyclohexanone              —
Methyl ethyl ketone               —

Methylphenyl acetamide            —
Phenols (e.g., p-Tert-          10-234,000
  butylphenol)
Phthalic acid                      —
2-Propanol                        —
2-Propyl-1-heptanol                —
Tetrahydrofuran                   —
Varsol                            —

Hydrocarbons with specific elements
(e.g., with N,P,S,CI,Br,l,F)
Acetyl chloride                    —
Alachlor (Lasso)               190-1,700
Aldicarb (sulfoxide and          36-405
  sulfone; Temik)
Aldrin                            -
Atrazine                          —
Benzoyl chloride                   —
Bromacil                       72-110
Bromobenzene                 1.9-5.8
Bromochloromethane              —
Bromodichloromethane         1.4-110

Bromoform                    2.4-110
Carbofuran                     4-160
Carbon tetrachloride           0.3-18,700

Chlordane                        —
Chlorobenzene                  2.7-41
Chloroform                   1.4-1,890

Chlorohexane                     —
Chloromethane (methyl            44
   chloride)
Chloromethyl sulfide               —
2-Chloronaphthalene               83
 Chlorpyrifos                      —
 Chlorthal-methyl (DCPA,           —
   or Dacthal)
 o-Chlorotoluene                  2.4
 p-Chlorotoluene                   —
 Dibromochloromethane          2.1-55
 Dibromochloropropane          1.-137
   (DBCP)
 Dibromodichloroethylene           —
                  Solvent
                     *
                     *
                     *
                     *
                    NA
Pharmaceuticals, plastics, disinfectants, solvent,
  dyestuffs, insecticides, fungicides, additives to
  lubricants and gasolines
Plasticizer for polyvinyl chloride and other vinyls
Solvent,  lacquers, paints, varnishes,  cleaning and
  detergent preparations, fumigants, paint and varnish
  removers, wetting agent, cosmetics
Polymers, acrylic paints,  intermediate
Dyeing and finishing, chemicals, manufacture of
  fumigants, insecticides, solvents, plastics, refrigerants
Chemical manufacturing, solvents, automotive
  antifreeze, fuels
Solvent,  lacquers
Solvent,  paint removers,  cements and adhesives,
  cleaning fluids, printing, acrylic coatings
NA
Resins, solvent, Pharmaceuticals, reagent,
  dyestuffs and indicators, germicidal paints
Dyestuffs, medicine, perfumes, reagent
Chemical manufacturing, solvent, deicing agent,
  Pharmaceuticals,  perfumes, lacquers, dehydrating
  agent,  preservatives
Solvent

Paint and varnish thinner
Dyestuffs, Pharmaceuticals, organic preparations
Herbicides
Insecticide, nematocide

Insecticides
Herbicides, plant growth regulator, weed control agent
Medicine, intermediate
Herbicides
Solvent, motor oils, organic synthesis
Fire extinguishers,  organic synthesis
Solvent, fire extinguisher fluid, mineral and salt
  separations
Solvent, intermediate
Insecticide, nematocide
Degreasers,  refrigerants and propellents, fumigants,
  chemical manufacturing
Insecticides, oil emulsions
Solvent, pesticides, chemical manufacturing
Plastics, fumigants, insecticides, refrigerants and
  propel lants
NA
Refrigerants, medicine,  propellants, herbicide,
  organic synthesis

Oil: plasticizer, solvent for dyestuffs, varnish gums and
  resins, waxes
  Wax: moisture-, flame-, acid-, and insect-proofing of
  fibrous materials; moisture- and flame-proofing of
  electrical cable; solvent (see oil)
NA
Herbicide

Solvent, intermediate
Solvent, intermediate
Organic synthesis
Fumigant, nematocide
                             NA
                                                                                                High
                                                                                     High
Moderate
           Moderate
             High
                                                                                              Moderate

                                                                                              Moderate
                                                                                              Moderate

                                                                                                Low

                                                                                              Moderate
                                                                                              Moderate
                                                                                              Moderate
                                                                                                 Low
                                148

-------
Table B-2. (Continued)
Contaminant
Dibromoethane (ethylene
dibromide, EDB)
Dibromomethane
Dichlofenthion (DCFT)
o-Dichlorobenzene

p-Dichlorobenzene

Dichlorobenzidine
Dichlorocyclooctadiene
Dichlorodiphenyldichloro-
ethane (ODD, TDE)
Dichlorodiphenyldichloro-
ethylene (DDE)
Dichlorodiphenyltrichloro-
ethane (DDT)
1,1-Dichloroethane
1 ,2-Dichloroethane


1 , 1 - Dichloroethy lene
(vinylidiene chloride)
1 ,2-Dichloroethylene
(cis and trans)
Dichloroethyl ether

Dichloroiodomethane
Dichloroisopropylether
( = bis-2-
chloroisopropylether)
Dichloromethane
(methylene chloride)
Dichloropentadiene
2,4-Dichlorophenol
2,4-Dichlorophenoxy-
acetic acid (2,4-D)
1 ,2-Dichloropropane
Concentration
35-300

44.9
—
2.7

0.6-0.7

—
—
—

0.01-0.8

0.05-0.22

0.5-11,330
250-847


1.2-4,000

0.2-323

1,100

2.8-4.1
—


4-8,400

0.36
—
1-85,000

46-60
Standard Examples of uses
•* Fumigant, nematocide, solvent, waterproofing
preparations, organic synthesis
Organic synthesis, solvent
Pesticides
• Solvent, fumigants, dyestuffs, insecticides, degreasers.
polishes, industrial odor control
it Insecticides, moth repellent, germicide, space
odorant, intermediate, fumigants
Intermediate, curing agent for resins
Pesticides
Insecticides

Degradation product of DDT, found as an impurity
in DDT residues
• Pesticides

Solvent, fumigants, medicine
* Solvent, degreasers, soaps and scouring compounds,
organic synthesis, additive in antiknock gasoline,
paint and finish removers
* Saran (used in screens, upholstery, fabrics, carpets,
etc.), adhesives, synthetic fibers
* Solvent, perfumes, lacquers, thermoplastics, dye
extraction, organic synthesis, medicine
Solvent, organic synthesis, paints, varnishes, lacquers,
finish removers, drycleaning, fumigants
NA
Solvent, paint and varnish removers, cleaning solutions


it Solvent, plastics, paint removers, propellants.
blowing agent in foams
NA
• Organic synthesis
it Herbicides

* Solvent, intermediate, scouring compounds, fumigant,
Carcino- Noncar-
genic cinogenic
potency toxicity




Moderate

Moderate

Moderate

Low



High

Low
Low


Moderate













Moderate


Dieldrin                          —
Diiodomethane                   2.0
Diisopropylmethyl                 —
  phosphonate (DIMP)
Dimethyl disulfide                 —
Dimethylformamide               —
2,4-Dinotrophenol (Dino-        124-400
  seb, DNBP)
Dioxins (e.g., TCDD)              —
Dodecyl mercaptan               —
  (lauryl mercaptan)
Endosulfan                       0.8
Endrin                           —
Ethyl chloride                     —

Bis-2-ethylhexylphthalate        12-170
Di-2-ethylhexylphthalate           —
Fluorobenzene                    67
Fluoroform                       3.5
Heptachlor                       —
Heptachlorepoxide                —

Hexachlorobicyclohepta-           2.2
  diene
Hexachlorobutadiene             2.53

a-Hexachlorocyclohexane         6
  (=  Benzenehexachlor-
  ide, or
  a-BHC)
  nematocide, additive for antiknock fluids
Insecticides                                              High
Organic synthesis
NA

NA
Solvent, organic synthesis
Herbicides

Impurity in the herbicide, 2, 4, 5-T                         High
Manufacture of synthetic rubber and plastics,
  Pharmaceuticals, insecticides, fungicides
Insecticides
Insecticides
Chemical manufacturing, anesthetic, solvent,
  refrigerants, insecticides
Plastics                                                  Low
Plasticizers
Insecticide  and larvicide intermediate
Refrigerants, intermediate, blowing agent for foams
Insecticides                                           Moderate
Degradation product of heptachtor, also acts as
  an insecticide
NA

Solvent transformer and hydraulic fluid,  heat-transfer
  liquid
Insecticides
                                                                                               149
Moderate
  High
  High

-------
Table B-2. (Continued)
Contaminant
                            Concentration    Standard
                                                                          Examples of uses
Carcino-     Noncar-
 genic     cinogenic
potency     toxicity
/3-Hexachlorocyclo-               3.8
  hexane (/3-BHC)
  0-BHC)
7-Hexachlorocyclohexane        0.5-43
(7-BHC, or Lindane)
Hexachlorocyclopenta-            —
  diene
Hexachloroethane                4.6

Hexachloronorbomadiene          —
Kepone                          —
Malathion                        —
Methoxychlor                     —
Methyl bromide                   7.4
Methyl parathion                  4.6
Parathion                         —
Pentachlorophenol (PCP)          —

Phorate (Disulfoton)              —
Polybrominated biphenyls          —
  (PBBs)
Polychlorinated biphenyls         8-40
  (PCBs)
Prometon                        —
RDX (Cyclonite)                 3,400
Simazine                         —
Tetrachlorobenzene              5,000
Tetrachloroethanes               4
  (1,1,1,2 e 1,1,2,2)

Tetrachloroethylene (or         717-2,405
  perchloroethylene,
  PCE)
Toxaphene                      1-570
Triazine                          2
1,2,4-Trichlorobenzene            37

Trichloroethanes (1,1,1         0.2-26,000
  and 1,1,2)
1,1,2-Trichloroethylene         210-37,000
  (TCE)

Trichlorofluoromethane            26
  (Freon 11)
2,4,6-Trichlorophenol             —
2,4,5-Trichlorophenoxy-           —
  acetic acid (2,4,5-T)
2,4,5-Trichlorophenoxy-           —
  propionic acid
  (2,4,5-TP or Silvex)
Trichlorotrifluoro-               35-135
  ethane
Trinitrotoluene (TNT)          620-12,600

Tris-(2,3-dibromopropyl)           —
  phosphate
Vinyl chloride                   50-740
Other hydrocarbons
Alkyl sulfonates                   —
Cyclonexane                     540
1,3,5,7-Cyclooctatetraene          —
Dicyclopentadiene                 —
   (DCPD)
2,3-Dimethylhexane                —
                                                        Insecticides
                                                *      Insecticides                                                       Moderate

                                                        Intermediate for resins, dyestuffs, pesticides, fungi-
                                                          cides, Pharmaceuticals
                                                        Solvent, pyrotechnics and smoke devices.                  Low
                                                          explosives, organic synthesis
                                                        NA
                                                •      Pesticides                                                           High
                                                •      Insecticides
                                                •      Insecticides                                                       Moderate
                                                        Fumigants, pesticides, organic synthesis
                                                *      Insecticides
                                                •      Insecticides                                                          High
                                                •      Insecticides, fungicides, bactericides, algicides,                      Moderate
                                                          herbicides, wood preservative
                                                •      Insecticides
                                                        Flame retardant for plastics, paper, and textiles                         Low

                                                *      Heat-exchange and insulating fluids in closed             Moderate
                                                          systems
                                                        Herbicides
                                                *      Explosives
                                                •      Herbicides                                             Moderate
                                                *      NA
                                                *      Degreasers,  paint removers, varnishes, lacquers.          Moderate
                                                          photographic film, organic synthesis, solvent,
                                                          insecticides, fumigants, weed killer
                                                *      Degreasers,  do/cleaning, solvent, drying agent,              Low
                                                          chemical manufacturing, heat-transfer medium,
                                                          vermifuge
                                                *      Insecticides                                            Moderate
                                                        Herbicides
                                                        Solvent, dyestuffs,  insecticides, lubricants,
                                                          heat-transfer medium (e.g., coolant)
                                                *      Pesticides, degreasers, solvent                             Low

                                                *      Degreasers,  paints, drycleaning,  dyestuffs, textiles.          Low
                                                          solvent, refrigerant and heat exchange liquid,
                                                          fumigant,  intermediate, aerospace operations
                                                         Solvent, refrigerants, fire extinguishers, intermediate               Moderate

                                                         Fungicides, herbicides, defoliant                                     Low
                                                •       Herbicides, defoliant                                             Moderate

                                                •       Herbicides and plant growth regulator                                High
                                                         Drycleaning, fire extinguishers, refrigerants,
                                                           intermediate drying agent
                                                         Explosives, intermediate in dyestuffs and
                                                           photographic chemicals
                                                         Flame retardant

                                                         Organic synthesis, polyvinyl chloride and copolymers,
                                                           adhesives                                             Low
                                                         Detergents
                                                         Organic synthesis, solvent, oil extraction
                                                         Organic research
                                                         Intermediate for insecticides, paints and varnishes,
                                                           flame retardants
                                                         NA
                                150

-------
Table B-2. (Continued)
Contaminant
                            Concentration     Standard
                                                Examples of uses
Carcino-    Noncar-
 genic     cinogenic
potency    toxicity
Fuel oil
Gasoline
Jet fuels
Kerosene
Lignin

Methylene blue activated
_
2,000-9,000
—
243,000
7,500i

11
Fuel, heating
* Fuel
Fuel
Fuel, heating, solvent, insecticides
Newsprint, ceramic binder, dyestuffs, drilling fuel
additive, plastics
• Dyestuffs, analytical chemistry
  substances (MBAs)
Propane

Tannin
4,6,8-Trimethyl-1 -nonene
Undecane

Metals and cations
Aluminum
Antimony
Arsenic

Barium
Beryllium
Cadmium

Calcium
Chromium

Cobalt

Copper


Iron
Lead

Lithium

Magnesium

Manganese
Mercury
Molybdenum
Nickel
Palladium

Potassium
Selenium
Silver
Sodium

Thallium
Titanium
Vanadium

Zinc
       —                      Fuel, solvent, refrigerants, propellents, organic
                                 synthesis
     7,500i                    Chemical manufacturing, tanning, textiles,
                                 electroplating, inks, Pharmaceuticals, photography,
                                 paper
                               NA
       —                      Petroleum research, organic synthesis

(parts per million)
    0.1-1,200          *       Alloys, foundry, paints, protective coatings, electrical                  High
                                 industry, packaging, building and construction,
                                 machinery and equipment
       —                      Hardening alloys, solders, sheet and pipe, pyrotechnics              Moderate
   0.01-2,100         *       Alloys, dyestuffs, medicine, solders, electronic devices,     High
                                 insecticides, rodenticides, herbicides, preservative
     2.8-3.8           *       Alloys, lubricant                                                    High
  less than 0.01        it       Structural material  in space technology, inertial          Moderate
                                 guidance systems, additive to rocket fuels,
                                 moderator and reflector of neutrons in
                                 nuclear reactors

    0.01-180          *       Alloys, coatings, batteries, electrical equipment, fire        High
                                 protection systems, paints, fungicides, photography
     0.5-225                    Alloys, fertilizers, reducing agent
   0.06-2,740         *       Alloys, protective coatings, paints, nuclear and             High
                                 high-temperature research
    0.01-0.18          *       Alloys, ceramics, drugs, paints, glass, printing.                        High
                                 catalyst, electroplating, lamp filaments
    0.01-2.8          *       Alloys, paints, electrical wiring, machinery,                         Moderate
                                 construction materials, electroplating, piping,
                                 insecticides
   0.04-6,200         *       Alloys, machinery, magnets
    0.01-5.6          *       Alloys, batteries, gasoline additive, sheet and pipe.                    High
                                 paints, radiation shielding
       —             •       Alloys, Pharmaceuticals, coolant,  batteries, solders,                   Low
                                 propellents
     0.2-70                    Alloys, batteries, pyrotechnics, precision instruments,
                                 optical mirrors
     0.1-110           *       Alloys, purifying agent                                              High
   0.003-0.01          *       Alloys, electrical apparatus, instruments, fungicides,                  High
                                 bactericides, mildew-proofing, paper,
                                 Pharmaceuticals
     0.4-40           *       Alloys, pigments, lubricant
     0.05-0.5          *       Alloys, ceramics, batteries, electroplating, catalyst       Moderate     High
       —                      Alloys, catalyst, jewelry, protective coatings, electrical                 Low
                                 equipment
     0.5-2.4                    Alloys, catalyst
     0.6-20           *       Alloys, electronics, ceramics, catalyst                                High
      9-330           *       Alloys, photography, chemical manufacturing, mirrors,                High
                                 electronic equipment, jewelry, equipment, catalyst,
                                 Pharmaceuticals
     3.1-211           *       Chemical manufacturing, catalyst, coolant, non-glare
                                 lighting for highways, laboratory reagent
       —                      Alloys, glass pesticides, photoelectric applications                    High
       —                      Alloys, structural materials, abrasives, coatings                          Low
       243            *       Alloys, catalysts, target material for x-rays                             High,
                                                                                                 moderate
     0.1-240           *       Alloys, electronics,  automotive parts,  fungicides,                     Moderate
                                 roofing, cable wrappings, nutrition
                                                                                                151

-------
Table B-2. (Continued)
Contaminant
                         Concentration    Standard
                                                                  Examples of uses
                                                                           Carcino-   Noncar-
                                                                            genic     cinogenic
                                                                           potency   toxicity
Nonmetals and anions
Ammonia

Boron

Chlorides

Cyanides

Fluorides

Nitrates
Nitrites
Phosphates
Sulfates
Sulfites

Micro-organisms
Bacteria (coliform)
Viruses

Radionuclides

Cesium 137
Chromium 51

Cobalt 60

Iodine 131
 Iron 59
 Lead 210
 Phosphorous 32

 Plutonium 238,243
 Radium 226
 Radium 228
 Radon 222

 Ruthenium 106
 Scandium 46
 Strontium 90

 Thorium 270
 Tritium
 Uranium 238
 Zinc 65
 Zirconium 95
     1-900



   1.0-49,500

    1.05-14

    0.1-250

    1.4-433

    0.4-33
   0.2-32,318


(parts per billion)
   (picocuries
  per milliliter)
      6.4
*

*

*
    0.8-25
     12.5
     0.817
    150-353
    10-500
Fertilizers, chemical manufacturing, refrigerants,
  synthetic fibers, fuels, dyestuffs
Alloys, fibers and filaments, semi-conductors,
  propellents
Chemical manufacturing, water purification,
  shrink-proofing, flame-retardants, food processing
Polymer production (heavy duty tires), coatings,
  metallurgy, pesticides
Toothpastes and other dentrifices, additive to drinking
  water
Fertilizers, food preservatives
Fertilizers, food perservatives
Detergents, fertilizers, food additives
Fertilizers, pesticides
Pulp production and processing food  preservatives
  High

Moderate
       Gamma radiation source for certain foods
       Diagnosis of blood volume, blood cell life, cardiac
         output, etc.
       Radiation therapy,  irradiation, radiographic testing,
         research
       Medical diagnosis,  therapy, leak detection, tracers
         (e.g., to study efficiency of mixing pulp fibers,
         chemical  reactions, and thermal stability of additives
         to food products), measuring film thicknesses
       Medicine, tracer
       NA
       Tracer, medical treatment, industrial measurements
         (e.g., tire tread wear and thickness  of films and ink)
       Energy source, weaponry
       Medical treatment, radiography
       NA
       Medicine, leak detection, radiography, flow rate
         measurement
       Catalyst
       Tracer studies, leak detection,  semi-conductors
       Medicine, industrial applications (e.g., measuring
         thicknesses, density control)
       NA
       Tracer, luminous instrument dials
       Nuclear reactors
       Industrial tracer (e.g., to study wear in alloys,
         galvanizing, body metabolism,  function of oil
         additives in lubricating oils)
       NA
structures. The lower members of the saturated acid
series are liquids, ranging in order from the sharp
odors of  formic  and  acetic acid  to the  unpleasant
odors of butyric and valeric acids. Butyric acid gives
rancid butter its disagreeable odor. Industrial wastes
from the dairy industry must be treated to prevent
formation of these acids.  These  acids range from
being  completely  soluble  in  water  to  relatively
insoluble. The saturated  acids include  acrylic, oleic,
and linoleic acids which are the general constituents
                                     of the glycerides of most fats and oils (Sawyer and
                                     McCarty,  1978;  Lippencott et  al., 1978).  Organic
                                     acids are utilized by microorganisms through oxida-
                                     tion processes  and are converted to carbon dioxide
                                     and water.  Biodegradation of higher acids may  be
                                     limited by their solubility in water. A wide variety of
                                     aromatic carboxylic acids are known such as benzole
                                     acid, a preservative, salycilic  acid, a constituent of
                                     aspirin, and phthalic acid, an important constituent in
                                     the manufacture of organic compounds. These acids
                            752

-------
are also subject to biodegradation by microorganisms
to carbon dioxide and water.

The phenols are an important aromatic hydrocarbon.
They consist of a basic ring hydrocarbon or benzene
with an attached (OH) group. Phenols are generally
known as carbolic acid which  is widely used as a
disinfectant, and in concentrated solutions is toxic to
bacteria. Phenols occur as  natural constituents of
industrial wastes from coal and petroleum process-
ing. Until recently, phenol was thought to be toxic to
bacteria for biodegradation applications. However,
current studies suggest that bacteria may be able to
degrade low concentrations (Erlich et al., 1982; Tabak
et al., 1980). Studies by the FMC Corporation (1 983)
indicate that hydrogen peroxide is capable of oxidizing
phenols in the presence of a  catalyst  to  produce
carbon dioxide and water.

The next higher group of phenols are creosols. They
are found  in coal tar  and exhibit even higher
germicidal propertiesthan phenols, but are lesstoxic.
Creosols are commonly found in spray disinfectants
such as lysol and in creosote, used in wood preser-
vation. Phenols with more than one (OH) group are
termed polyhydric. Three  industrially important iso-
mers  of polyhydric phenols  include  the catechols,
resorcinals, and hydroquinone. These isomers are
readily oxidized  by microorganisms  (Sawyer and
McCarty, 1978).

The degradation of aliphatic hydrocarbons by micro-
organisms  depends  on  molecular weight,  water
solubility, number of double bonds, degree of branch-
ing, and whether the compound is an open chain or
cyclic compound. Thus, the simplest compounds such
as a straight chain hydrocarbon will be the  most
easily degraded as opposed to a more complex cyclic
compound (Brown et al., 1 983). The degradation rate
decreases with either a decreasing number of double
bonds or with the number and size of alkyl groups.
Sediments  containing  aliphatic hydrocarbons are
generally deficient in nitrogen and phosphorous.
Addition of these fertilizers  greatly  enhances bio-
degradation rates (Brown  et al., 1 983). Volatilization
of low molecular weight hydrocarbons is a mechan-
ism that occurs with increasing temperature and soil
moisture content.
Aromatic Compounds

The aromatic compounds contain stable ring struc-
tures, or cyclic groups, with special alternating single
and double  covalent bonds. These bonds  are  not
normal. Thus, aromatic compounds do not  bond to
substances by addition, but rather by substitution of a
hydrogen atom  for an element or compound. The
simplest aromatic ring  is made up of a six-ringed
carbon atoms bonded to six hydrogen atoms and is
known as benzene or the benzene ring. Substitutions
may occur at one or more hydrogen atom sites. The
benzene series constitutes a single  ring with alkyl
substitutions; these include toluene and xylene and
their respective isomers. These products are found in
coal tar and crude petroleum and are used primarily
as solvents.

A polyring aromatic hydrocarbon consists of one or
more cyclic rings that  are bonded through  shared
carbon  atoms;  these carbon atoms do  not have
attached hydrogen atoms. The polyring aromatic
compounds include  naphthelene  and  anthracene
used in the manufacture  of dyes,  and phenanthra-
cene, an important constituent of  alkaloids such as
morphine and  vitamin D. Halogenated  and nitro-
genous aromatics  will be discussed in the  next
section.

Aromatic compounds are  usually present in  wastes
generated by petroleum refineries,  organic chemical
plants, rubber industries,  and waste streams asso-
ciated with combustion  processes  (Brown  et  al.,
1 983). Most aromatic hydrocarbons are toxic  and/or
carcinogenic and fairly resistant to degradation. The
decomposition  rate  of aromatic  hydrocarbons is
basically substance  dependent,  however,  simple
compounds typically degrade more easily. In addition,
the  more soluble  compounds are more easily  de-
graded by microorganisms (Tabak et al., 1980).
Hydrocarbons with Specific Elements

The  final  group of hydrocarbons  may  be either
aliphatic or aromatic, but has one or more additional
groups with specific elements as substituents, name-
ly nitrogen, sulfur, and phosphorous and the halo-
gens, chlorine, fluorine, iodine  and bromine. The
halogenated organics have received the most atten-
tion  as  ground-water contaminants. These  com-
pounds  are refractory, or very resistant to degrada-
tion. This is thought to be due to the presence of a
halogen; its location and type determine the relative
persistence of the compound (Kobayashi and Ritt-
mann, 1982). These compounds range from simple
alkyl halides to polyhalogen compounds to complex
halogenated hydrocarbons such as DDT. Common
halogenated compounds  include methyl chloride,
ethyl chloride, ethylene bromide, chloroform, carbon
tetrachloride, chlorobenzene, freon (dichlorodif luoro-
methane)  and trihalomethanes. Methyl  and ethyl
chloride were  once  used  as  refrigerants;  ethyl
chloride is used in the manufacture oftetraethyl lead,
an antiknock gasoline additive. Chloroform has been
found in drinking water due to the reaction of chlorine
with natural organic substances in water. Freon is an
extensively used refrigerant due to its non-toxic and
non-flammable properties (Sawyer  and McCarty,
1978).
                                                                      753

-------
Chlorinated hydrocarbons were formerly used ex-
tensively as pesticides and herbicides, many of which
are very resistant to degradation. These include
dioxin, DDT, DDE, Aldrin, Dieldrin, Endrin, Lindane,
Chlordane, Toxaphene, 2,4-D and  2,4,5 TP Silvex
which have  been banned from usage  or  greatly
restricted because of their toxicity and carcinogenic
potentials (Solomons, 1978;  Brown  et  al., 1983;
Abrams  et al., 1975). These products were  used
extensively for agricultural and  defoliant purposes.
Other pesticides and herbicides have been studied to
determine  their potential for attenuation through
hydrolysis, reductive dehalogenation, and biodegrada-
tion.

Hydrolysis involves the introduction of an (OH) group
that commonly replaces the halide. Hydrolysis  rates
are dependent on pH, the presence of humic mater-
ials, and individual compounds (Cherry et al., 1984;
Cohen et al.,  1984). Reductive  dehalogenation in-
volves the removal of the halogen through oxidation-
reduction reactions in low redox state ground water
(Cherry et al.,  1984) and by certain microorganisms
(Kobayashi and Rittmann, 1982). Biodegradation of
halogenated  hydrocarbons has been documented
under both aerobic and anaerobic conditions (Koba-
yashi and  Rittmann, 1982; Cherry  et  al., 1984;
Bouwer et al., 1981; Tabak et al., 1980; Brown et al.,
1983).

Other types of pesticides  include organic phosphor-
ous and carbomate pesticides. Organic phosphorous
pesticides include parathion, which is very toxic, and
malathion  which has low toxicity for  mammals.
Phosphorous pesticides tend to hydrolyze quickly at
or above a  neutral pH, thus  losing  their  toxic
properties.  The carbamates  have generally low
toxicities to mammals. These include IPC, a herbicide,
captan, a fungicide, and ferbam and sevin as insect-
icides. These  pesticides  are highly susceptible  to
degradation (Sawyer and McCarty, 1978).

As a rule, chlorinated aromatics are less degradable
and less soluble than their aliphatic  counterparts.
This has proven true for  the chlorinated benzenes
including hexachlorobenzene (HCB) and its deriv-
atives. These are found as by-products of industrial
processes, and in chlorinated solvents and pesticides.
The rates of  degradation of these compounds are
slow; they may persist in the soil and water for several
years without significant degradation. Certain plants
such as lettuce, carrots, grasses, and potatoes tend to
absorb HCBs from the soil  (Brown et al., 1983). Rates
of degradation are variable depending  on the degree
of chlorination; the less  chlorinated,  the more de-
gradabale (Tabak et al., 1980).

Another  widely  publicized group of  halogenated
organics are  the polychlorinated biphenyls (PCBs).
These are biphenyl molecules with the presence of
one or more chlorine atoms at several locations on
the phenyl structures.  These  mixtures have been
commercially produced since 1 929 with a total of 210
possible compounds. PCBs are classified according to
chlorine content with most industrial mixtures con-
taining 40 to 60 percent chlorine (Solomons, 1980).

PCBs had many uses including heat exchangers in
transformers, in capacitors and thermostats, plasti-
cizers in food bags and polystyrene cups, in printing
inks, and  in waxes. Because the PCBs are highly
persistent and fat  soluble, they tend to collect in the
tissues  of  many  animals and humans. The EPA
bannedthe manufacture, processing, and distribution
of PCBs in 1 979 (Solomons, 1980).

Degradation of PCBs has been found to be affected by
the nature of  the chlorine (Brown et al., 1983).
Degradation tends to increase as the amount of
chlorine substitution decreases; the relative position
of the chlorine also affects rates  of degradation. In
general,  the  lower chlorinated  compounds were
found to be degradable in mixed microbial populations
(Kobayashi and Rittmann,  1982).

Other hydrocarbons with specific elements have the
nitrogen group  as substituents. These include the
amines, amides, anilines, and  nitriles. The amines
are alkyl derivatives of ammonia and may be primary,
secondary, or tertiary depending  on the number of
hydrogen  ammonia atoms that are replaced. The
amines are found  in industrial wastes from fish and
beet-sugar industries, and little is known about their
susceptibility to  biodegradation. The  amides  are
derived  from organic acids  and  ammonia  under
special conditions. The nitriles are organic cyanides
that  are  extensively used in  the manufacture of
synthetic fibers (Sawyer  and  McCarty, 1978). The
most commonly used nitriles include acrylonitrile and
acetonitrile. Attenuation  of nitriles occur  through
oxidation reactions  at specified pH values (Harsh,
1975). The primary form  of amines are known as
analines and are  important compounds for organic
synthesis  and in dyes. The amines were shown to
range in ease of biodegradability depending on the
individual  compound (Tabak et  al., 1980; Kobayashi
and Rittmann, 1982).

Mercaptans or thiols are  aliphatic compounds that
contain sulfur and they have a structure similar to
alcohols. Mercaptans are known  to have disagree-
able  odors and are typically  byproducts  of  kraft
pulping and petroleum processing. The FMC Corpor-
ation (1983) has shown that thiols are readily oxidized
under acid conditions to insoluble products.

References
Abrams, E. F., D. Derkics, C. V. Fong, D. K. Guinan,
  and K. M. Slimak, 1975. Identification of organic
                       154

-------
  compounds in effluents from industrial sources;
  NTISPB-241641,211  pp.
Bouwer, E. J., B.  E. Rittmann, and P. L. McCarty,
  1 981. Anaerobic degradation of halogenated 1 -and
  2-carbon organic compounds; Environmental Sci-
  ence & Technology, Vol. 15, No. 5, pp. 596-599.

Brown, K.  W., G. B. Evans, Jr., and B. D. Frentrop,
  eds., 1983.  Hazardous  waste  land treatment;
  Butterworth Publishers, 692 pp.

Cherry, J. A., R. W. Gillham, and J. F. Barker, 1984.
  Contaminants in groundwater: chemical processes;
  Groundwater Contamination, National  Academy
  Press,  pp. 46-66.

Cohen, S.  Z., S. M. Creeger, R. F.  Carsel, and C. G.
  Enfield, 1984. Potential for pesticide contamination
  of ground water resulting from agricultural uses;
  American Chemical  Society Symposium Series
  #259,  Treatment  Disposal of Pesticide  Wastes,
  Krueger  and Seiber, eds., Washington, D.C.

Erlich, G. G., D. F. Goerlitz, E. M.  Godsy, and M. F.
  Hult, 1982. Degradation of phenolic contaminants
  in ground water by anaerobic bacteria: St. Louis,
  Minnesota;  Ground Water,  Vol. 20, No.  6, pp.
  703-710.

FMC Corporation,  1983.  Industrial waste treatment
  with hydrogen peroxide; Industrial Chemical Group,
  Philadelphia, Pennsylvania, 23 pp.

Freeze, R.  A. and J. A. Cherry, 1979. Groundwater;
  Prentice-Hall, 604 pp.

Fuller, W. H. and J. Artiola, 1978. Use of limestone to
  limit contaminant movement from landfills; Pro-
  ceedings of the 4th Annual Research Symposium
  on Land  Disposal of Hazardous Wastes, U. S. EPA-
  600/9-78-016, pp. 282-298.

Harsh, K.,  1975. In situ  neutralization of an acrylo-
  nitrile spill; Ohio Environmental Protection Agency,
  Dayton, Ohio, pp. 187-189.
Keith, L.  A.  and W.  A.  Telliard,  1979.  Priority
  pollutants, I-A  perspective view; Environmental
  Science & Technology, Vol. 13, No. 4, pp. 416-423.

Kobayashi, H. and B. E.  Rittmann, 1982.  Microbial
  removal of hazardous organic compounds; Environ-
  mental Science & Technology, Vol. 16, No. 3, pp.
  170A-183A.

Lippencott, W. T., A. B. Garrett, and F. H. Verhoek,
  1978. Chemistry; John Wiley & Sons, pp. 646-697.

Office of Technology Assessment, 1984. Protecting
  the nation's groundwater from contamination. Vol.
  I, II; U.S. Congress, Washington,  D.C., 503 pp.
Page, A. L., 1974. Fate and effects of trace elements
  in  sewage sludge when applied to agricultural
  lands; U.S. EPA-670/2-74-005.

Sawyer, C. N. and P. L. McCarty, 1978. Chemistry for
  environmental engineering; McGraw-Hill, pp. 94-
  163.

Solomons,  T. W., 1980. Organic chemistry;  John
  Wiley & Sons, pp. 634-639.

Tabak, H. H., S. A. Quave, C. I. Mashni, and E. F. Barth,
  1980. Biodegradability studies  with  priority pol-
  lutant organic compounds; Staff  Report, Waste-
  water  Research Division, U.S.  EPA Research
  Center, Cincinnati, Ohio.

Tolman, A., A.  Ballestero, W. Beck,  and G. Emrich,
  1978. Guidance manual for minimizing pollution
  from  waste disposal  sites; U.S. EPA-600/2-78-
  142, pp. 328-331.
Weast, R. C., ed., 1983. CRC handbook of chemistry
  and physics; CRC Press, Inc.
                                                                      755

-------
                                          Appendix C
                         Sources of Ground-Water Contamination
The quality of the ground water may be altered by a
wide variety of human activities and naturally occur-
ring phenomena. The innumerable waste materials
and byproducts of man's activities provide potential
for ground-water contamination through a variety of
mechanisms.

Ground water quality problems that are attributed to
man's influence are commonly related to: (1) water-
soluble products that are placed on the land surface
and in  streams or surface impoundments, (2) sub-
stances that are deposited in the ground above the
water table, and (3) disposal, storage, or extraction of
materials below the water table (Lehr et al., 1976).
Sources of ground-water  pollution  are associated
with a  broad range  of industrial, agricultural, com-
mercial, and domestic act ivites. Many of the problems
that arise from wastes as a result of  these activities
are not well  understood,  due to  their complexity.
Technical  solutions  are available  for many  ground
water quality problems through planning, manage-
ment, and/or prevention practices.

The  application of  a rating  system  designed to
estimate potential for ground-water contamination is
of concern with regard to individual contamination
situations.  Because ground-water  contamination
may  occur from  a  variety of  sources,  it may be
necessary to consider and possibly  reevaluate the
importance of a rating factor as the scale of the area
being evaluated changes.

Soil  attenuation  characteristics  such as  sorptive
capabilities, microorganisms, degradation capacities,
and textures are of major importance when consider-
ing the placement of wastes on the land's surface
(e.g.  stockpiles, sludge, wastewaters) and the sub-
sequent potential  for ground-water pollution. How-
ever, the effect of soil is  relatively unimportant for
situations where the soil has been removed, such as
at a landfill,  or  where contaminants are buried
beneath the soil surface (e.g.  storage tanks). Thus,
engineering and other practical considerations of an
area can obviate the application of DRASTIC param-
eters.

Dry contamination sources that are emplaced on the
land  surface,  such   as stockpiles,  fertilizers, and
pesticides  are dissolved and disseminated by rainfall
resulting in the generation of ground-water pollution.
Evaluation of the DRASTIC parameters suggests that
the most important parameters with regard to this
category of  activities are: Depth  to Water, which
controls  contact  time of the  pollutant  with the
unsaturated zone; Net Recharge,  which limits the
quantity of leachate generated; Soil Media, which
affects both organic and inorganic attenuation mech-
anisms; and the Vadose Zone,  which also directly
affects attenuation properties. Parameters of lesser
impact for this category of activities include: Aquifer
Media and Hydraulic  Conductivity, since these are
impacted less by surface-applied  pollutants. Topo-
graphy may be important for surface storage facilities,
but  most agricultural activities  are  confined to
relatively flat terrain.

Wet contamination sources emplaced on the land
surface include waste waters, irrigation waters, and
spills. In this situation, the most  important param-
eters are Depth to Water, Soil Media, Impact of the
Vadose Zone, and Topography which will  affect the
attenuation and infiltration rates of the liquid contam-
inants. Again, because the source is on the surface.
Hydraulic Conductivity and Aquifer  Media are less
important. Net  recharge has a  less negative effect
since the contaminant  is already liquid. High net
recharge may result in dilution.

This type of rationale can also be applied to either
liquid or dry sources emplaced below the surface
which may or may not intersect the water table. The
potential for liquid sources below the water table to
cause contamination, such as leaking underground
storage tanks or drainage wells, is  affected primarily
by the Depth to Water, the Impact of the VadoSeZone,
Hydraulic Conductivity, and the Aquifer Media. These
factors are directly related to attenuation and migra-
tion rates of the contaminant. Surface characteristics
such as Topography, Net Recharge, and Soil Media
would subsequently  be  of  lesser importance for
potential pollution evaluations.

Lastly, for dry contaminant sources emplaced below
the surface (e.g. landfills, quarries) it is necessary to
consider Net  Recharge  in  terms  of volumes of
leachate generated; the Hydraulic Conductivity in
relation to migration  rates; and Aquifer Media for
                                               156

-------
 possible attenuation  of  contaminants,  dispersion,
 dilution, and routing. Again, surface characteristics
 are of lesser importance; Topography, Soil Media, and
 Impact of Vadose Zone.
 Thus, man's activities and the intensity  of these
 activities present  many  potential contamination
 problems. The impact of these activities is discussed
 in Section 5, Impact—Risk Factors. Activities are not
 directly involved in the determination of the DRASTIC
 Index, but their impact is always of serious concern.
 These activities may be categorized according to their
 relative position with respect to the ground water;
 Table 11 represents a comprehensive list of activities
 that are potential sources of contamination and their
 respective  modes of emplacement. Each  of these
 sources will be discussed individually in relation to
 their effects and potential for ground-water contam-
 ination.


 Ground Water Quality Problems that Orig-
 inate on the Land Surface
Land Disposal

One of the major causes of ground-water pollution is
the disposal of solid or liquid waste materials directly
onto the land surface in either individual deposits or
spread over the land. Any soluble products present in
the waste can be transported into the ground water
either with the liquid  portion of the wastes or as a
consequence of precipitation. Land disposal practices
include the application of sewage sludge,  manure,
garbage, industrial wastes, waste tailings, and spoil
piles. These activities are capable of producing a wide
variety of contaminants, including organic chemicals,
inorganic chemicals, and reactive ions.


Stockpiles and Mine Tailings
The presence of material stockpiles, and mine tailings
and spoils, pose  a potential source of ground-water
contamination. An estimated  20 percent of total
production materials  are stored in stockpiles of
varying sizes (OTA, 1984). Materials that are  com-
monly stockpiled that may affect ground-water quality
include salt, coal, various metallic ores (e.g. copper,
uranium,  titanium, vanadium, silver,  lead, zinc),
phosphates, and gypsum. These stockpiles are usual-
ly exposed to precipitation such  that the precipitation
will  dissolve or  react with  other constituents to
produce leachate that can percolate into the ground-
water system. The stockpiling  of salt in snow-belt
states provides a prime example of how stockpiling
can have a dramatic impact on ground-water quality.
The salt, if uncovered, is easily dissolved by precipita-
tion and either infiltrates to the subsurface or runs off
into streams (Lehr,  et al., 1976).
The stockpiling of coal and associated mining proc-
esses can  also degrade  the quality of the ground
water. Most  coal that is mined is associated with
pyrite, an iron sulfide. Contact with water tends to
break the pyrite down into iron hydroxide and sulfuric
acid. These constituents increase the iron and sulfate
levels if they reach the ground water (Bouwer, 1 978).

Spoil piles  are generally disturbed soils and over-
burden from  surface  mining, or  waste rock from
underground  mining. Tailings are the  solid wastes
from the on-site operations of cleaning and extracting
the ores. Both types of waste are usually stored on the
land surface.  Water moving through the waste piles
will mobilize many hazardous constituents, depend-
ing on the materials. Because of  their quantity,
distribution, and nature of their contents, spoil piles
and tailings are major potential  sources of ground-
water contamination.  Hazardous constituents from
this source can include lead, zinc, copper, and other
heavy metals, arsenic, sulfuric acid, and radioactive
elements such  as  uranium and thorium (Bouwer,
1978; Todd,  1980). The  impact of spoil piles and
tailings  is  dependent  on the  location, size, and
composition of the tailings and spoils, the  climate
(amounts of  precipitation), the  hydrogeologic set-
ting, and type of control and containment of the
wastes.
Disposal of Sewage and Water Treatment Plant
Sludge

The  land application of treated waste  waters and
sewage sludge from municipal and industrial sources
is  often used as an  alternative to more expensive
disposal processes. The waste waters are typically
applied as spray irrigation by various land treatment
systems (Bouwer, 1 978; Todd, 1980). Land treatment
of  waste waters is generally capable of removing
nitrogen, phosphorous, organic waste matter, bacter-
ia, and viruses. Sludge wastes may be applied as
compost to agricultural and forested land, disposed of
in  landfills or  applied in land reclamation projects
(OTA,  1984).  Municipal sludges typically contain
nitrogen, phosphorous,  organic  material,  bacteria,
viruses, and metals.  The  presence of  undesirable
constituents may limit the land application of sludges
and waste waters. Some hazardous materials may be
preferentially  sorbed by  plants or  infiltrate  into
ground-water  resources.  However,  studies  have
shown that high-rate land treatment systems are
capable of removing  infectious  bacteria and viruses
through the mechanisms  of sorption,  mechanical
filtration, or die-off (Freeze and Cherry, 1979; Bouwer,
1978). The rate and  duration of sludge and  waste
water application is dependent on the soil and waste
characteristics, the length of the  application, the
nutrient uptake of the cover crop, and the climate.
                                                                       757

-------
Salt Spreading

The increased usage of de-icing  salts rather than
sand and other abrasives in snow belt states provides
an actual and a potential source of ground-water
contamination. The salts consist of commercial rock
and marine salt, with ferric ferrocyanide and sodium
ferrocyanide added to reduce caking (Bouwer, 1 978).
The sodium ferrocyanide is soluble and can increase
the concentrations of cyanide present in ground
water above safe drinking water levels. In addition,
chromate and phosphate may be added to decrease
the corrosiveness of the  salt; these also affect
ground-water quality. Many cases of ground-water
contamination have been cited from road  salt appli-
cations (Bouwer,  1978).  Contamination may  be
minimized  by  designing  roads to reduce de-icing
requirements,  better collection and disposal of salty
run-off, protective salt storage, and use of alternate
de-icing materials.


Animal Feed Lots

Accumulations of  animal  wastes at feed lots can
contaminate ground water by infiltration of leachate
or surface runoff. The primary contaminant of the
leachate is organic, or ammonium, nitrogen which is
converted to nitrate  in the vadose zone. Additional
hazardous constituents include bacteria, viruses, and
phosphates  (Bouwer, 1978; OTA,  1984).  Animal
feedlots are most concentrated in  the corn belt and
High Plains regions.  Ground-water contamination
tends to be more severe at feed  lots underlain by
coarse-textured soils with shallow water tables than
by fine-textured soils with deeper water tables. These
wastes may be controlled by applying animal waste
slurries intermittently to maintain aerobic conditions
in the upper soil. The nitrogen will be converted to
nitrate in the upper soil layer and then be denitrified,
or converted to nitrogen gas and water in the deeper
anaerobic soil layers.


Fertilizers and Pesticides

Modern agricultural practices employ the extensive
use of fertilizers and pesticides to obtain  high crop
yields. The  primary fertilizers are  compounds of
nitrogen, phosphorous, and potassium. Excess potas-
sium and phosphorous are readily sorbed onto soil
particles and  seldom  constitute  a contamination
problem. Crop uptake of fertilizer nitrogen varies from
about  40 to 80 percent  of the amount  applied
(Bouwer, 1980). The remainder is either volatized and
returned to the atmosphere through denitrification,
or percolates downward as  nitrate to contaminate
ground water.  Efficient application of fertilizer, par-
ticularly at peak requirements during growth cycles,
minimizes nitrate contamination (OTA, 1984). Unfor-
tunately, most farmers apply enough fertilizer for the
entire  growing season  prior to planting,  thus in-
creasing the potential for nitrate contamination.

Pesticides  are  chemicals used  for the control  of
insects, fungi, or other  undesirable organisms and
weeds. Agricultural activities account for between 69
and 72 percent of pesticide use; government agencies
and industries use 21 percent; home and garden uses
constitutethe remainder. Agricultural applications of
pesticides have resulted  in ground-water contamina-
tion  in  at  least  18 states  involving  a variety  of
pesticides (OTA, 1984; Cohen et al.,  1984). Contam-
ination can occur from common-use practices, spills,
disposal of excess  pesticides,  and leakage from
storage containers.  Applications of pesticides by
airplanes pose a significant problem  due to the large
quantities applied and indiscriminant application.

The movement and attenuation of pesticides in the
soil  and ground water is  dependent on several
parameters including water solubility, vapor pressure,
speciation, hydrolysis half-life, photolysis half-life,
soil and water sorption properties, and climate (OTA,
1984; Cohen, et al., 1984). The primary parameters
that  account  for pesticide attenuation  are  sorption,
volatilization, biodegradation, and solubility. Those
pesticides that are relatively refractory tend to be the
least soluble and most  resistant to biodegradation
and hydrolysis (Tabak et al., 1984; Cohen et al., 1984).
The  most toxic and refractory  pesticides are the
chlorinated  hydrocarbons such as DDT,  lindane,
endrin,  DDE,  and chlordane. The organic phosphate
pesticides such as malathion and parathion are less
toxic than the chlorinated hydrocarbons and more
easily attenuated. The least toxic pesticides are the
carbamates such as sevin  and captan; these are
easily biodegraded by common soil organisms.


Accidental Spills of Hazardous Materials

A wide variety of hazardous materials are transported
throughout the country by truck, rail,  and aircraft and
transferred at handling facilities such as airports and
loading docks. Accidental spills of hazardous mater-
ials provide  a  definite  potential  for ground-water
contamination.  The National Academy of  Sciences
(NAS)  estimated  that approximately 16,000 spills
occur annually, involving a variety of materials such
as hydrocarbons (i.e. gasoline, jet fuel), pain products,
flammable compounds, various acids, and anhydrous
ammonia (OTA, 1984).

There are presently few  methods available to quickly
and  adequately clean up an accidental hazardous
waste  spill.  To make  matters worse, a  common
practice is to spray the spill area with water in order to
flush the compounds from the road. The hazardous
materials are then washed into drainage ditches  or
streams from  which they  have the  potential  to
infiltrate and  contaminate the ground water.
                        158

-------
The attenuation of hazardous materials is dependent
on the site-specific hydrogeochemical characteristics,
the chemical(s) spilled,  and any remedial actions
performed by authorities on the surface materials at
the time of the spill. An example  of a successful
hazardous material spill  clean-up is given by Harsh
(1975).  An  acrylonitrile spill (cyanide  compound)
resulting from a train derailment was quickly remed-
iated by the Ohio Environmental Protection Agency
through the application of oxidants  that neutralized
the hazardous substance.


Particulate Matter from Airborne Sources

A relatively minor, but potential source of ground-
water  contamination  arises from the  fallout  of
paniculate  matter  from the atmosphere. These
materials fall to the surface of the earth and are
carried as soluble or insoluble products by water to
the subsurface. The primary source of atmospheric
pollution is automobile emissions and various indus-
trial processes. The  major contaminants from these
emissions include sulfur and nitrogen compounds,
asbestos, and heavy metals (OTA, 1984). The distrib-
ution of particulates in the atmosphere and on the
surface depends on their size when released, weather
patterns, and  climate.  The attenuation  of  these
pollutants is dependent  on the site-specific hydro-
geochemical characteristics, the location of pollutant
fallout, and the chemical nature of the pollutant itself.

The infiltration of airborne contaminants tends to be
higher in heavily  industrialized areas (Lehr et al.,
1976).  Perhaps the major environmental concern
today related to airborne contaminants is the effect of
acid rain on the surface and subsurface water quality.
Several contamination  occurrences from airborne
pollutants  have been  cited by  EPA,  particularly
increases in heavy metal concentrations in drinking
water due to industrial emissions.
Ground Water Quality Problems that
Originate in the Ground Above the
Water Table

Leaching Tile Fields, Cesspools, and Privies
A widely distributed source of ground-water pollution
is  septic  tanks  and cesspools. These sources dis-
charge large volumes  of  waste water  into the
subsurface. A septic tank system consists of a buried
tank and leaching tile field designed to collect water
suspended  wastes,  remove settleable solids from
liquids by gravity separation, and permit infiltration of
the effluent into the soil for general  degradation by
soil microorganisms. According to OTA (1984), in the
mid-1970's there were  an estimated 19.5 million
domestic on-site  disposal systems  present in the
United States and unknown numbers of commercial
and industrial systems.

Septic tank systems are the most frequently reported
source of contamination on a local and regional basis
(OTA, 1984). The contaminants are primarily derived
from human wastes and household cleaners; these
include nitrates, chloride, coliform bacteria, viruses,
and a variety of organic and inorganic chemicals. The
major factors that affect the potential for contam-
ination of ground water by septic systems are the
density  of systems  per area,  the hydrogeologic
conditions, and the attenuation  capacity  of the soil
through which the effluent percolates. Problems tend
to arise from systems that are old and deteriorated
and from those systems that are poorly constructed.

Several parameters must be considered in the design
and  installation of a septic system; these include
ground water flow velocity and direction, the storage
and  carrying capacities of the  receiving soil, the
sorptive qualities of  the soil, the  resident  micro-
organism  community and the depth to  the  water
table.
Holding Ponds and Lagoons

Holding ponds and lagoons, because of their relative
numbers and size, present a significant potential for
ground-water contamination. Surface impoundments
are used by  industries and  municipalities for the
treatment, retention, and/or disposal of non-hazard-
ous and  hazardous liquid wastes.  These ponds or
lagoons vary  in size from two to three feet deep, to
more than 30 feet deep, with areas covering from a
fraction of an  acre to thousands of acres (OTA, 1984).
Agricultural,  municipal, industrial,  and  oil and gas
production lagoons are typically less than five acres in
size. However, industrial impoundments are generally
1000 acres or larger. The size of a mining impound-
ment depends on the ore and type of mining. The
wastewater in industrial surface impoundments may
consist of suspended and dissolved solids, pathogenic
organisms, oil and grease, detergents, heavy metals,
and toxic organic chemicals (Pye et al., 1983).

Holding ponds are supposedly "liquid tight," however,
the majority leak large quantities of material, thereby
contributing to ground-water pollution. The installa-
tion of a double-liner system of plastic and clay has
recently become a requirement for these  facilities
under new RCRA regulations. The presence of a liner
combined with a leachate collection drain system will
lower the potential of contamination by constituents
in the holding pond.

The potential  for contamination by a holding pond is
dependent  on head conditions in the pond,  soil
permeability,  depth to the  water  table,  rates of
evaporation and precipitation, geochemical charac-
                                                                       159

-------
teristics of the soil (ion exchange and sorption), the
chemical composition and amounts of waste, andthe
capacity for degradation by soil organisms (Pye et al.,
1983).


Sanitary Landfills

Sanitary  landfills are  constructed excavations that
are filled with hazardous and non-hazardous waste
materials and covered daily by soils. Daily coverage by
soils preventsthe production of odors, smoke, andthe
presence  of vermin and insects. Precipitation  and
surface runoff can  infiltrate  into  these  landfills
producing leachate that can contain soluble hazard-
ous materials. Some hazardous constituents may be
attenuated as the  leachate filters through the soil
zone. However, leachate may still reach the ground
water. Landfills are  commonly covered with clay
and/or soil combinations to minimize the infiltration
of water and production of leachate. However, these
coverings are not totally impermeable and some
moisture penetrates the protective covers.

Approximately 40  percent of the solid hazardous
industrial wastes are disposed  of in some type of
landfill in addition to the large quantities of non-
hazardous wastes  that are also deposited  in these
facilities  (OTA, 1984). Problems arise with older
landfills that are improperly constructed, have  failing
liners, have accepted unknown types and quantities
of wastes, are deteriorating, or have been abandoned.
These older and abandoned landfills pose a definite
threat to  ground water because geologic and  hydro-
geologic characteristics were not considered  in the
initial site selection or design.

Ground-water contamination from landfills may be
minimized by proper design, construction, operation,
and maintenance of a facility (Wilson et al.,  1976).
Provisions must  be  made for controlling traffic,
unloading and  handling different types of wastes,
placement of cover materials, testing of wastes for
acceptance, and adequate ground-water monitoring
to prevent contamination problems.
Waste Disposal in Excavations

The removal of materials such as clay, limestone, and
sand and gravels commonly produces pits or excava-
tions that may have been eventually abandoned and
used as  unregulated waste disposal  sites. A wide
variety of materials have been emplaced in excava-
tions in unknown quantities. These include garbage,
junk automobiles, and liquid wastes such as oil-field
brines and spent acids from steel mills. Disposal of
unregulated waste poses the threat of ground-water
contamination. Often these pits contain some amount
of water, evidence that they are hydraulically con-
nected to the water table and  possibly  deeper
aquifers. Leachate from these wastes may therefore
have direct access to the ground-water system. This
contamination may be avoided through preventative
regulations  and  correct  disposal  of wastes at a
properly designed sanitary landfill or other facility.
Leakage from Underground Storage Tanks

Underground storage tanks are used by industries,
commercial establishments, and individuals for stor-
age  and treatment of products or raw materials
(Wilson et al., 1976). The primary storage materials
are hydrocarbon fuels, but many other substances
are commonly stored in underground tanks, such as
acids,  metals, industrial solvents,  chemicals,  and
chemical wastes. The  most numerous  underground
storage tanks are those used for gasoline and fuel oil.
Gasoline leakage from  leaking  tanks has caused
severe pollution problems throughout the nation.
Because gasoline is less dense than water, it floats on
the surface of the ground water and may leak into
basements, sewers, wells, and springs. In confined
areas,  vapors from these  leaks, disseminated by
ground water, can cause a serious explosion hazard.

Most tanks are composed of either steel or fiberglas.
Unprotected steel is subject to rusting or corrosion by
various materials. Fiberglas may crack or be slowly
dissolved by alcohol blends. Tank age  is a principal
factor in ground-water contamination; studies have
shown that  older tanks exhibit a tendency to  leak
through  deterioration  of the tank (OTA, 1984).
Ground-water pollution is minimized by proper tank
design and emplacement, properly placed monitoring
wells, frequent inspections, and fluid level monitoring.

Leakage from Underground Pipelines

Pipelines  are used to  transport,  collect,  and/or
distribute waste and non-waste products. Leaks that
occur  in pipelines are often difficult to detect and
locate.  Pipeline leakage occurs due to ruptures,
external and internal corrosion, incorrect operation,
and defective welds or pipes (Todd, 1980). Wastes
transported  in pipelines include  municipal sewage,
petroleum products,  brines, ammonia, sulfur, and
coal. Interstate pipelines and all spills are regulated
by the Department of Transportation. Other collection
and distribution pipelines are not regulated other
than during initial installation and are not required to
report  leaks  and spills.
Artificial Recharge

Artificial recharge includes a variety of techniques
used to increase the amount of water infiltrating into
an aquifer. This is achieved through the construction
of pits, ponds or wells, or direct land application so
that the water will seep into the ground or flow or be
                       160

-------
pumped directly into the aquifer. Water that is used
for artificial recharge  commonly consists of  storm
runoff, irrigation return flows, stream water, cooling
water, and treated sewage effluent. The infiltration of
this water may directly affect ground-water quality,
resulting in subsequent contamination. Recharge is
becoming increasingly popular due to the growing
demands for water and the need for recycling.


Sumps and Dry Wells

Sumps and dry wells are typically installed to provide
drainage in problem  areas by collecting runoff or
spilled liquids. These liquids are usually channeled
into the subsurface where they are transmitted to the
ground water. These facilities are especially prone to
cause problems  if they  are located near streams,
lakes or  ponds,  or estuaries  where  ground-water
levels are naturally high.


Graveyards

Leachate from graveyards may cause ground-water
pollution, especially if non leak-proof or no caskets
were used. The potential for ground-water contam-
ination by graveyards is dependent on several factors,
including the characteristics of the soil and depth to
the water table (Lehr et al., 1976). Areas that receive
high amounts of precipitation and have high  water
tables may  be  especially  prone to contamination
problems. Graveyards  also pose a potential contam-
ination problem in areas of hard rock and limestone
terrain where soil covers are thin, and in glaciated
areas where the glacial sand and gravel lenses are
hydraulically interconnected. Few actual cases have
been documented and any contamination problems
would be highly localized.
Ground  Water Quality Problems that Orig-
inate in the Ground Below the Water Table

Waste Disposal in Wet Excavations

The removal and  mining of various materials often
produces  excavations and pits that are  commonly
abandoned after activities cease.  These pits often
extend below the water table and thereby contain
quantities of water. These excavations were used in
the past as repositories for both solid  and  liquid
wastes and presently have the potential to produce
large quantities of leachate. The leachate produced is
in direct  hydraulic  connection with the shallow
ground water and possibly with other deeper aquifers.
drainage wells and canals may be constructed. A
drainage well is a vertical cased hole in the ground or
the bottom of a pond, for example, that allows water
to drain  into  deeper, more permeable  materials.
Pollution of the recharged surface water may thus
contaminate the aquifer.

The construction of extensive channels and channel
deepening may have the potential to affect ground-
water quality. Deepened  channels may  affect the
ground-water gradient and allow infiltration of sur-
face water or the intrusion of salt or brackish water,
thereby causing contamination. Extensive channels
in coastal areas have allowed tidal ocean waters to
flow inland and affect ground-water quality.


Abandoned or Improperly Constructed Wells

The presence of abandoned wells provides a signif-
icant means for ground-water contamination. Wells
that have been abandoned commonly  provide con-
duits for the migration of contaminated water. The
water may be runoff or surface  water that enters
through the open conduit, or may be the migration of
fluid between an aquifer and a zone of undesirable
water quality. When a well is abandoned, the casing
is often pulled or is  allowed to deteriorate so that
casing leaks develop. This readily permits  fluids
under pressure to migrate, upward or downward, and
contaminate the aquifers. Another problem is the
migration of saline water into freshwater aquifers. In
areas where the hydraulic gradient is toward the
freshwater aquifer,  abandoned or  improperly  con-
structed wells  provide  a  conduit resulting in  salt
water contamination and intrusion. The migration of
contaminated fluids may also occur in areas of deep
well disposal  injection  operations. Contaminated
liquids under pressure are able to migrate into other
aquifers via uncased wells and deteriorated casings
in wells.


Exploratory Wells

Exploratory wells and test holes are frequently drilled
to determine the presence of  underground mineral
resources such as coal, salt, oil, or gas, and as seismic
shot holes where an  explosive is discharged to
produce shock waves for seismic sensors. Where
these open holes penetrate more than one aquifer,
they permit  interaquifer  leakage.  Thus,  brackish
water from a saline aquifer could migrate upward or
downward to  contaminate a  fresh water aquifer.
These open holes also allow surface waters to enter
the hole and migrate into other aquifers.
Drainage Wells and Canals

In areas that consist of surficial clays and flat-lying
land with ponds and marshes that are poorly drained,
Water Supply Wells

Improperly constructed water supply wells have the
potential to contaminate ground water and produce

                     161

-------
polluted water. Large diameter dug wells are partic-
ularly prone to contamination from surface runoff if
not properly protected during and following construc-
tion. Improper grouting of the annular space around
the casing may allow surface contaminants to enter
the aquifer. Drainage from  animal feedlots, barn-
yards, septic  tanks, or cesspool  effluent may also
contaminate  improperly constructed  wells. Proper
training and licensing of well drillers and the imple-
mentation  of water well construction  standards
minimizes pollution problems of this nature.
Waste Disposal Wells

Wells are used to inject or discharge either hazardous
or non-hazardous waste into a permeable geologic
unit beneath the surface. Industrial injection wells
may range in depth from a few tens of feet to several
thousand feet. The EPA estimates that at least 21,000
wells in the United States require some  type of
corrective action (OTA,  1984). Contamination from
injection wells  can occur  in a  number of ways,
including: (1) faulty well construction, (2) the migra-
tion of  pressurized fluids  into  nearby  wells  and
aquifers, (3) the forcing upward of pressurized fluids
into faults or fractures in confining beds, (4) injection
into or above usable aquifers, (5) the  migration of
contaminated fluids into other hydraulically connect-
ed aquifers used as drinking water supplies, and (6)
faulty well sealing that allows the entrance of surface
runoff into the well. Since the implementation of the
Federal  Underground Injection Control Act (UIC), the
installation and operation of underground injection
wells is  regulated.


Mines

Excavation and operation of both surface and under-
ground  mines can  disrupt the natural continuity of
aquifers and introduce fractures and pressure chang-
es which affect the ground-water flow. This allows
water to migrate through the fractured  overburden
into other aquifers and/or to mix with mine spoils and
tailings. Often mines will intersect the water table, or
various  aquifers, necessitating dewatering of the
mine by pumping large quantities of water to the
surface. This water may be contaminated and pollute
aquifers, streams,  or surface bodies of water  into
which it infiltrates or drains. Dewatering of mines
may also cause salt water intrusion by lowering the
fresh water table. Underground mining tends to
introduce water and  oxygen into the  subsurface
which results in the oxidation  of  pyrite  and the
subsequent formation of acidic mine drainage (Pyeet
al., 1983). Acid mine drainage is a  mixture of  iron
salts, other  salts, and sulfuric acid, and may sub-
stantially contribute to ground-water contamination.
In order to  protect the  surface  and ground-water
resources,  mining activities must be carefully de-
signed, operated,  and regulated from their planning
phase to final reclamation of the land.


Salt Water Intrusion

Withdrawals of ground water in excess of recharge
capabilities often  results  in  contamination of an
aquifer  by salt water  intrusion.  This  problem  is
especially prevalent in  densely  populated  coastal
areas where large quantities of fresh water are
pumped  daily.  Overdrafting  disrupts  the  natural
hydrologic processes and affects subsequent impacts
on  aquifers and  ground-water quality. Increased
pumpage of fresh water will tend to lower the water
table in the vicinity of the well, causing changes in the
hydraulic gradient. This allows intrusion  of saltwater
along the hydraulic slope into a pumping well (Freeze
and Cherry, 1979). Land subsidence may also occur
with increased pumping and reduction of the water
table. In some coastal areas, injection of freshwater
into aquifers is used to prevent salt-water intrusion.
References

Bouwer,  Herman,  1978. Groundwater  hydrology;
  McGraw-Hill, 480 pp.

Cohen, S. Z., S. M. Creeger, R. F. Carsel, and C. G.
  Enf ield, 1984. Potential for pesticide contamination
  of ground  water resulting from agricultural uses;
  American  Chemical  Society Symposium Series
  #259, Treatment  Disposal  of Pesticide  Wastes,
  Krueger and Seiber, eds., Washington, D.C.

Freeze, R. A. and J. A. Cherry, 1979. Groundwater;
  Prentice-Hall, 604 pp.

Harsh, K., 1975. In situ neutralization  of an acrylo-
  nitrile spiN; Ohio Environmental Protection Agency,
  Dayton, Ohio, pp. 187-189.

Lehr, Jay H., Wayne A. Pettyjohn, Truman Bennett,
  James R. Hanson, and Laurence E. Sturtz, 1976. A
  manual of laws,  regulations and  institutions for
  control of ground water pollution; U.S. EPA-440/9-
  76-006.

Office of Technology Assessment, 1984. Protecting
  the nation's groundwater from contamination. Vol.
  I, II; U.S. Congress, Washington, D.C., 503 pp.

Pye, V. I., R.  Patrick, and J. Quarles, 1983. Ground-
  water Contamination in the United  States; Uni-
  versity of Pennsylvania Press, 314 pp.

Tabak, H. H.,  S. A. Quave, C. I. Mashni, and E. F. Barth,
  1980. Biodegradability  studies with priority  pol-
  lutant organic  compounds; Staff  Report,  Waste-
  water  Research  Division,  U.S.   EPA Research
  Center, Cincinnati, Ohio.
                       162

-------
Todd, D. K.,  1980. Groundwater hydrology; John
  Wiley & Sons, 535 pp.
Wilson, J.  L, R.  L. Lenton, and J. Porras,  1976.
  Groundwater pollution: technology, economics and
  management; Department of Civil  Engineering,
  Massachusetts Institute of Technology, Report No.
  TR208, pp. 17-21.
    USOOVERNMENT PRINTING OFFICE 1985 - 559-111/10838                                          1 63

-------