United States
Environmental Protection
Agency
Research and Development
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
EPA/600/S2-91/043 Oct. 1991
EPA Project Summary
Regional Assessment of Aquifer
Vulnerability and Sensitivity in
the Conterminous United States
Wayne A. Pettyjohn, Mark Savoca, and Dale Self
The full report provides, In a gener-
alized, largely graphic format, a repre-
sentation of ground-water vulnerability,
precipitation distribution, population
density, potential well yield, and aquifer
sensitivity for each of the 48 contermi-
nous states. A classification scheme is
developed based on an assessment of
the vulnerability of surficial and rela-
tively shallow aquifers. Aquifer sensi-
tivity is related to the potential for
contamination. That is, aquifers that
have a high degree of vulnerability and
are in areas of high population density
are considered to be the most sensi-
tive. About 46 percent of the land area
of the conterminous United States con-
sists of vulnerable Class I aquifers. Of
this amount, 26.4 percent is Class la,
10.4 percent is Class Ib and Ib-v, 8.1
percent is Class Ic, and Class Id ac-
counts for an additional 1.4 percent.
The moderately vulnerable Class II aqui-
fers cover about 1 percent of the United
States, while the least vulnerable, Class
III, makes up about 19 percent. The un-
defined systems, Class U, account for
an additional 19 percent.
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 documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Introduction
In 1974 Congress enacted the Safe
Drinking Water Act (PL93-523) to protect
public health and welfare, as well as exist-
ing and future underground sources of
drinking water. To achieve this end, the
U.S. Environmental Protection Agency
(EPA), through the Underground Injection
Control (UIC) program, has and is devel-
oping regulations for the protection of Un-
derground Sources of Drinking Water
(USDWs) from contamination by the sub-
surface emplacement of fluids through
wells.
UIC regulations defined and established
5 classes of injection wells.
Class I—used to inject hazardous
and non-hazardous waste beneath
the lowermost formation containing a
USDW.
Class II—used to inject brine from oil
and gas production, enhanced oil re-
covery and for storage of hydrocar-
bons.
Class III—used in conjunction with
solution mining of minerals.
Class IV—used to inject hazardous
or radioactive wastes into or above a
USDW (banned nationally).
Class V—wells not included in Class
I, II, III or IV which typically inject
non-hazardous waste into or above
a USDW. Also known as shallow
injection wells.
Class V wells involve the disposal of
waste such as agricultural drainage, storm
water/industrial drainage, raw sewage and
some industrial process water. According
to the most recent inventory reported by
EPA, there are approximately 170,000
Class V injection wells in the United States,
but this estimate is probably far too low. An
Printed on Recycled Paper
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assessment is provided in the Report to
Congress, Class V Injection Wells.
The greatest number of shallow injec-
tion wells occurs in areas of high popula-
tion density. The types most likely to be
present in industrial/urban/suburban areas
include storm water and industrial drain-
age wells, improved sinkholes, domestic
waste water disposal wells, industrial pro-
cess water and waste wells, auto service
station waste disposal wells, and aban-
doned water supply wells used for waste
disposal.
As a group, abandoned wells are the
most pervasive and potentially dangerous
of all the shallow injection wells; they are
found in both rural and urban areas.
An evaluation of the potential for ground-
water contamination caused by shallow
injection wells is a major undertaking be-
cause of the vast number of wells and their
wide distribution throughout an extensive
array of diverse hydrogeologic settings. To
limit the potential impact of shallow injec-
tion weHs on the Nation's ground water, a
scheme is needed to prioritize regions so
that, initially, the most sensitive and pro-
ductive or potentially productive ground-
water areas receive maximum attention.
Although this investigation was de-
signed specifically to answer a need in the
Underground Injection Control program, the
products are equally valuable to assess
the potential for ground-water contamina-
tion from other surface or near surface
sources.
Purpose and Scope
The purpose of this report is not to
classify ground water or ground-water re-
gions, but rather to provide, in a general-
ized, largely graphical format, a manual
that displays, for each of the 48 contermi-
nous states, a representation of ground-
water vulnerability, precipitation distribution,
population density, potential well yields,
and aquifer sensitivity. This manual can be
used by local, state, or federal regulatory
agencies to rapidly assess and, in a gen-
eral manner, prioritize ground-water pro-
tection activities relative to shallow injection
wells and other surface or near surface
sources of contamination.
In addition, the maps can be used to
delineate areas that provide or potentially
provide the greatest amount of ground
water to the largest number of people.
Likewise, they also can be used to evalu-
ate the more remote areas. The maps can
provide the investigator with a quick, inex-
pensive means to review the potential for
ground-water contamination and thus de-
velop rapid but generalized evaluations of
large areas. This, in turn, would permit
agencies to develop a protocol for shallow
injection well permitting or impact evalua-
tions.
Methodology
This manual is based entirely on pub-
lished information. State and federal agency
publications catalogs were examined to
obtain information that appeared to fill the
needs of the project. Several workers were
assigned states in which they had actual
experience to increase the accuracy of the
products.
In most cases, aquifer vulnerability
maps were prepared by outlining geologic
units on a 1:500,000 scale base map. Each
unit was assigned a classification that re-
flected published geologic and hydrogeo-
logic descriptions. The geologic units were
transferred to a page size map of the state,
and the area of each unit was measured
by planimeter.
Maps showing the distribution of pre-
cipitation were prepared by means of na-
tional climatological data that are stored
on compact disks and the software pack-
age, MapMaker II. Climate data were
stripped from the compact disks, and ma-
nipulated to obtain combined files of pre-
cipitation and latitude and longitude of each
station. Rather than using a predetermined
time interval, the entire period of record
was used for each station. This data set
and state/county boundary files were used
as input to the MapMaker II program.
Population density maps were prepared
by means of MapMaker II files. The popu-
lation data are based on 1986 estimates.
Aquifer sensitivity maps represent com-
posite illustrations in that they show the
location of population centers that overlie
vulnerable or Class I aquifers. Maps of this
type indicate that even though the aquifer
may be exceptionally vulnerable, only a
small part of the system is highly suscep-
tible to contamination, and these sites are
represented by the location of municipali-
ties, both large and small. Aquifer sensitiv-
ity maps were prepared by overlaying
scanned maps of aquifer vulnerability and
the latitude and longitude of cities. All popu-
lation centers that fell outside of Class I
aquifers were deleted.
JJ.S. Geological Survey reports and
maps proved to be the major sources of
information on potential well yield. The
generalized maps were prepared by trans-
ferring published information to a map of
appropriate scale. These data were then
incorporated into a computer generated
map.
Aquifer classification units do not nec-
essarily match at state borders. This is the
result of compiling geologic and hydrotogic
information that was obtained for each
state. Consequently, a geologic unit in one
state may have been described in such a
manner that it appeared to ba largely, for
example, unconsolidated Class la mate-
rial. The same earth materials in an adja-
cent state may have been described in
such a broad sense that it only could be
classified as '^differentiated" or Class U.
Conclusions
Table 1 in the full report lists details
concerning population, area, and water use
in each of the conterminous states. These
data indicate that about 42.4 percent of the
population served by public water-supply
systems use ground water as a source.
Clearly, these subsurface reservoirs need
to be protected against contamination.
About 46 percent of the land area of
the conterminous United States consists
of vulnerable Class I aquifers. Of this
amount, 26.4 percent is Class la, 10.4
percent is Class Ib and Ib-v, 8.1 percent is
Class Ic, and Class Id accounts for an
additional 1.4 percent. The moderately vul-
nerable Class II aquifers cover about 14
percent of the United States, while the
least vulnerable, Class III, makes up about
19 percent. The undefined systems, Class
U. account for an additional 19 percent.
The percentage of each class of aquifer
present in each state is listed in Table 2 of
the full report.
Although large areas of several states
consist of vulnerable Class I aquifers, aqui-
fer sensitivity is not necessarily high. Aqui-
fer sensitivity is related both to vulnerability
and population density. In aquifer sensitiv-
ity investigations, the potential effect of
population density is best viewed by means
of population centers, which generally are
concentrated along water courses, shore-
lines, and transportation routes. Conse-
quently, the areas where ground water is
most likely to become contaminated by
means of shallow injection wells are in and
adjacent to towns, regardless of size. For
example, all of the population centers in a
county may amount to only a small per-
centage of the total area of the county.
Therefore, the areal extent of an investiga-
tion of aquifer sensitivity could be much
smaller than originally anticipated.
Specific examples of ground-water con-
tamination are not described in this report.
A review of example, however, would show
that no state is free from contamination.
Moreover, no example is unique to any
one state.
•U.S. Government Printing Office: 1992— 648-080/60039
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Wayne A. Pettyjohn, Mark Savoca, and Dale Self are with the Oklahoma State University,
Stiltwater, OK 74078.
Jerry Thomhlll is the EPA Project Officer, (see below).
The complete report, entitled "Regional Assessment of Aquifer Vulnerability and Sensitivity
in the Conterminous United States," (Order No. PB92-100148/AS; Cost: $43.00, 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:
Roberts. 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
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