United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
                                 EPA/600/S2-87/035  Sept. 1987
Project  Summary
DRASTIC: A  Standardized
System  for  Evaluating Ground
Water Pollution  Potential  Using
Hydrogeologic  Settings

Linda Aller, Truman Bennett, Jay H. Lehr, Rebecca Petty, and Glen Hackett
  A methodology is described that will
 allow the pollution potential of any
 hydrogeologic setting to be systemat-
 ically 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 form the
 basis of the system and incorporate the'
 major hydrogeologic factors which
 affect and control ground-water move-
 ment including depth to  water, net
 recharge, aquifer media,  soil media,
 topography, impact of the vadose zone
 media and hydraulic conductivity of the
 aquifer. These factors, which form the
 acronym DRASTIC, are incorporated
 into a relative ranking scheme that uses
 a combination  of weights  and ratings
 to produce a numerical value called the
 DRASTIC Index.
  Hydrogeologic settings are combined
 with DRASTIC Indexes to  create units
 which can be graphically displayed on
 a map. The application of the system
 to 10 hydrogeologically variable coun-
 ties resulted in maps with symbols and
 colors which illustrate areas of ground-
 water contamination vulnerability. The
 system optimizes the use of existing
 data to  rank areas with  respect to
 pollution potential to help direct inves-
 tigations and  resource expenditures
 and to prioritize protection, monitoring
 and clean-up efforts.
  The full  report was  submitted  in
partial fulfillment of Contract No. CR-
810715-01 by the National Water Well
Association under sponsorship of the
U.S.   Environmental   Protection
Agency. This report covers a period
from October 1983 to  March 1987,
and work was completed as of April
1987.
  This Project Summary was devel-
oped by EPA's Robert S. Kerr Environ-
mental Research Laboratory, Ada, OK,
to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).

Introduction
  This research project was designed to
create a methodology that will permit the
ground-water pollution potential of any
hydrogeologic setting to be systemati-
cally evaluated anywhere in the United
States. The methodology  has been
incorporated into a standardized system
that can be readily displayed on maps
using existing information. The concepts
inherent to the system were developed
assuming a contaminant with the mobil-
ity of water, introduced  at the surface
and flushed into the ground water  by
precipitation. The methodology  is
designed to  evaluate  ground-water
pollution potential from  a regional
perspective and  should  be applied to
areas 100 acres or larger in size.

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Results
  The system that has been developed
has two  major parts, the designation of
mappable units,  termed hydrogeologic
settings;  and the  superposition  of  a
relative ranking system, called DRASTIC,
which helps the  user evaluate the
relative ground-water pollution potential
of any hydrogeologic setting.
  The standardization system for evalu-
ating ground-water pollution potential
has  been developed within the frame-
work of an existing classification system
of ground-water  regions of the United
States (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

                For the purpose of the present system
              Region  12 (Alluvial Valleys)  has been
              incorporated  into each of  the  other
              regions and Region 15 (Puerto Rico and
              Virgin Islands) has been omitted.
                Because pollution potential cannot be
              determined on a regional scale smaller
              "hydrogeologic settings"  were  deve-
              loped within each region. A  hydrogeo-
              logic  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 mappab
unit with common  hydrogeologic cha
acteristics, and as  a consequenci
common vulnerability to contaminatioi
These hydrogeologic  settings form tti
basis of  the system and permit furth<
delineation  of  the factors  that affei
pollution potential (Figure 2).
  Inherent in each hydrogeologic settin
are  the  physical characteristics th<
affect the pollution potential of grour
water. After evaluating a  number i
factors,  the  most important mappab
factors that control ground-water polli
tion potential were determined to be:
D—Depth to Water Table
R— (Net) Recharge
A—Aquifer Media
S—Soil Media
T—Topography (Slope)
I—Impact of Vadose Zone
C—Conductivity  (Hydraulic)  of  th
    Aquifer
       2. Alluvial Basins
                                                                                                   9. Northeast and
                                                                                                     , Superior Uplands
                                                                                                           7. Glaciated
                                                                                                             Central
                                                                                                             region
                                                                                                       6. Nonglaciated
                                                                                                           Central
                                                                                                           region
                                                           9. Northeast and
                                                             Superior Uplands
                    1. Western Mountain
                             Ranges
                                     16. Nonglaciated
                                       Central regio
                                v	
4. Colorado
  Plateau
  and
  Wyoming
  Basin
  O^^yV
                                                       6. Nonglaciated
                                                         Central .region
                         6.  Nonglaciated
                          Central'region
                                                                      . Coastal Pl^
                                                                  0                  500 Af//es

                                                                  0                  flOO Kilometers
 Figure 1.    Ground-water regions of the United States (After Heath. 1984).

                                     2

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Hawaii

(12C) Volcanic Uplands

This hydrogeologic setting is characterized by moderately 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 weathered 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 weathered 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 occurring  in a lenticular body that floats on the salt water.
Ground water yield is therefore limited quite specifically to the amount of water recharged
annually
Figure 2.    Format of hydrogeological setting.
  The DRASTIC factors represent meas-
urable parameters for which  data are
generally available  from a variety of
sources  without detailed  reconnais-
sance. Sources of this information are
listed in Table 1.
  Each DRASTIC factor has been  eval-
uated with  respect  to each  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), with the  most
significant factors having a weight of 5
and the least significant  a weight  of 1.
These weights are constant and may not
be changed.
  A special case for the DRASTIC Index
was  developed  for  agricultural areas
where the application of pesticides are
a concern.  Pesticide DRASTIC  was
created  to  address the important pro-
cesses which affect the fate and trans-
port  of pesticides into the subsurface.
The  weights assigned for  each factor
have been modified to reflect the poten-
tial impacts of pesticide application on
ground water (Table 3).
  Each DRASTIC factor has been divided
into either ranges  or significant  media
types which have an impact on pollution
potential. Each range or media has then
been  evaluated with  respect to  each
other to  determine the relative signifi-
cance of each range  or media  with
respect  to  pollution potential. These
ranges and  media  have been assigned
a rating  of from 1 to 10, with the most
significant range or media having a rating
of 10,  and the  least significant a rating
of 1 (Tables 4-10).
  Once  the 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. A  DRASTIC  Index
calculated for  one setting may then be
compared to values  obtained  in  other
settings m  the same  region  or in a
different region.
  Hydrogeologic settings  are combined
with DRASTIC Indexes to create mappa-
ble units which present a "picture" of
the geologic and  hydrogeologic condi-
tions of an area. To fully demonstrate and
test the system, DRASTIC was applied
to 10 counties across the  United States
representing a diversity of  hydrogeologic
conditions including:

  1.  Cumberland County, Maine;
  2.  Finney County, Kansas;
  3.  Gillespie County, Texas;
  4.  Greenville County, South Carolina;
  5.  Lake County, Florida;
  6.  Minidoka County, Idaho;
  7.  New Castle County, Delaware;
  8.  Pierce County, Washington;
  9.  Portage County, Wisconsin; and
10.  Yolo County,  California.

  These counties were chosen to repre-
sent both rural and urban areas and to
exemplify both an  abundance and scar-
city of  available  hydrogeologic  data.
Pollution potential maps showing hydro-
geologic settings and DRASTIC Indexes
were manually drawn for each  county.
To assist in  map readability, each  dem-
onstration map was color-coded using
the DRASTIC Index. A national color code
scheme was  developed  based  on a
simplified statistical evaluation of fre-
quency  of Index occurrence. The colors
of the  spectrum were chosen  to  show
the levels  of  relative  vulnerability to
pollution. The warm colors indicate areas
with potentially greater problems and
cool colors  indicate  areas  with  lower
susceptibility to ground-water pollution.
Figure 3 illustrates the superposition of
the national color  code on a portion of
the pollution  potential  map for Yolo
County, California. Various screens have
been  chosen  to  simulate  the  color
variations on the map.

Conclusion
  The  system  presents a simple and
easy-to-use approach to assess the
ground-water pollution  potential of any
area. Although the final system appears
simplistic, the system actually  includes
many complex concepts  and  relation-
ships. Before an attempt is made to make
full use of this system, the user must
develop an appreciation for the complex-
ity of evaluating ground-water pollution
potential. It  is not necessary to under-
stand every concept  in detail,  but the

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Table 1. Sources of Hydrogeologic Information
Depth to
Source Water
U.S. Geological Survey X
State Geological Surveys X
State Department of Natural/ Water
Resources X
U.S. Department of Agriculture-Soil
Conservation Service
State Department of Environmental
Protection X
Clean Water Act "208" and other
Regional Planning A uthorities X
County and Regional Water Supply
Agencies and Companies (private
water suppliers) X
Private Consulting Firms
Ihydrogeologic, engineering) X
Related Industry Studies (mining, well
drilling, quarrying, etc.) X
Professional Associations
(Geological Society of America,
National Water Well Association.
American Geophysical Union) X
Local Colleges and Universities
(Departments of Geology. Earth
Sciences, Civil Engineering) X
Other Federal/ State Agencies
(Army Corps of Engineers. National
Oceanic and Atmospheric
Administration X
greater the depth of understanding, the
more useful the system becomes.
DRASTIC produces mappable results
that provide a basis for the comparative
ownli la t inn nf aroflQ with rfl*»nflPt to thfi
c vdi ua LIUI i ui a i GOO win i i c9|joL>i \.\j n iw
potential for ground-water pollution.
DRASTIC should not be used for site
specific investigations, but is best applied
on a regional basis to areas greater than
100 acres in size. DRASTIC is designed
to assist individuals with resource
allocation and prioritization of many
types of ground-water related activities
as well as to provide a practical educa-
tional tool.
Net Aquifer Soil
Recharge Media Media
X X
X X

X X

X X

X X

X X


X

X

X



X X


X X



X X
Impact of the Hydraulic
Conductivi
Topography Vadose Media of the Aquifer
X X
X

X

X

X

X


X

X

X



X


X



X
X
X

X



X

X


X

X





X


X




Table2. Assigned Weights for DRASTIC Table 3. Assigned Weights for Pesticide
Features
Feature Weight
Depth to Water 5
Net Recharge 4
Aquifer Media 3
Soil Media 2

Topography 1
Impact of the Vadose Zone
A4~w:« K
DRASTIC Features
Feature
Depth to Water
Net Recharge
Aquifer Media
Soil Media

Topography
Impact of the Vadose Zone
A4<*w;».

Pesticide
Weight
5
4
3
5

3
A
Hydraulic Conductivity of the
  Aquifer
Hydraulic Conductivity of the
  Aquifer

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Table 4. Ranges and Ratings for Depth
to Water

Depth to Water
{reel/
Range Rating
0-5 10
5-15 9
15-30 7
30-50 5

50-75 3

75-100 2

700+ 7

Weight: 5 Pesticide Weight: 5


Table 5. Ranges and Ratings for Net
Recharge
Net Recharge
(Inches)
Range Rating
0-2 1
2-4 3

4-7 6

7-10 8

70+ 9
Weight: 4 Pesticide Weight: 4









Table 6. Ranges and Ratings for Aquifer Media

Aquifer Media
Range
Massive Shale
Metamorphic/ Igneous
Weathered Metamorphic/ Igneous
Glacial Till
Bedded Sandstone, Limestone and Shale
Sequences

Massive Sandstone

Massive Limestone

Sand and Gravel

Basalt
Karst Limestone
Weight: 3


Table 7. Ranges and Ratings for Soil Table
Media
Soil Media
Range Rating
Thin P" Absent in

Gravel 10

Sand 9
Peat 8
Shrinking and/or
Aggregated Clay 7
Sandy Loam 6
Loam 5
Silty Loam 4
Clay Loam 3
Muck 2
Nonshrinking and
Nonaggregated Clay 1



Rating Typical Rating
1-3 2
2-5 3
3-5 4
4-6 5

5-9 6

4-9 6

4-9 6

4-9 8

2-10 9
9-10 10
Pesticide Weight: 3


8. 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 Pesticide Weight: 3






Weight: 2
Pesticide Weight: 5

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Table 9. Ranges and Ratings for Impact of the Vadose Zone Media
Impact of the Vadose Zone Media
Range
Confining Layer
Silt/Clay
Shale
Limestone
Sandstone
Bedded Limestone. Sandstone. Shale
Sand and Gravel with Significant Silt and Clay
Metamorphic/ Igneous
Sand and Gravel
Basalt
Karst Limestone
Weight: 5
Rating
1
2-6
2-5
2-7
4-8
4-8
4-8
2-8
6-9
2-10
8-10
Pesticide Weight: 4
Table 10. Ranges and Ratings for
Hydraulic Conductivity
T . . _ . Hydraulic Conductivity
Typical Rating W«2'
Range Rating
3 1-100 1
3 100-300 2
6 300-700 4
6 700-1000 6
6 1 000-2000 8
6 20OO+ 10
4 Weight: 3 Pesticide Weight: 2
8
9
10


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           Sea/e //i
I f/gure 3.    Pollution potential map for a portion of Yolo County. California, showing the superposition of the national color code.

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    Linda Alter, Truman Bennett. Jay H.  Lehr. Rebecca Petty, and Glen Hackett
      are with National Water Well Association. Dublin, OH 43017.
    Jerry Thornhill is the EPA Project Officer (see below)
    The complete report, entitled "DRASTIC: A Standardized System for Evaluating
      Ground Water Pollution Potential Using Hydrogeologic Settings," (Order No.
      PB 87-213 914/AS; Cost: $48.95, subject to change) will be available only
      from:
            National Technical Information Service
            5285 Port Royal Road
            Springfield, VA 22161
            Telephone: 703-487-4650
     The EPA Project Officer can be contacted at:
            Robert S. Kerr Environmental Research Laboratory
            U.S. Environmental Protection Agency
            Ada, OK 74820
United States
Environmental Protection
Agency
                                   Center for Environmental Research
                                   Information
                                   Cincinnati OH 45268
Official Business
Penalty for Private Use $300

EPA/600/S2-87/035

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