- 12 -

Currently, all but two States conduct certification and
training programs for both private and commercial applicators.
(EPA operates Federal certification programs in the States
which do not operate their own programs.) State certification
programs must meet standards which were set by EPA through
regulation. In general, State Cooperative Extension Services
are responsible for providing training to pesticide applicators
and State lead pesticide agencies are responsible for certify-
ing the competency of applicators. EPA provides grant funds
to the State lead agencies for administrative costs of main-
taining the certification program; FY 86 funds are approximately
$1.2 million. EPA also provides funds to the U.S. Department
of Agriculture's Extension Service for allocation to State
Extension agencies to provide the training to applicators;

FY 86 funding to the Extension Service is approximately
$1 million.

As a minimum requirement for certification, private
applicators (e.g., farmers) must demonstrate their knowledge of
pest problems and pest control practices; proper storage, use,
handling, and disposal of pesticides and containers; and
knowledge of other subject areas as specified by regulation.
The extent and depth of training provided and the method for
certifying the private applicator is determined by each State.

Commercial applicators, however, are required to demonstrate
their competency by completing written examinations prior to
certification. As specified by regulation, testing must cover
general information on pest control and safe use of pesticides
and more specific information relating to the category (e.g.,
agricultural pest control, forest pest control, etc.) under
which the commercial applicator will be certified. Training
generally precedes the completion of examinations.

An estimated 300,000 commercial and 1.24 million private
applicators have already been certified. While many States
require recertification at specified intervals, the regquire-
ments for recertification vary widely and do not necessarily
include retraining.

Over the years, the number of pesticides classified as
restricted has grown substantially, and precautions for personal
safety and environmental protection have become more complex.

A special task force was established in 1985 by the Assistant
Administrator for Pesticides and Toxic Substances to examine

the applicator certification and training program and make
recommendations for changes that would enhance the program's
effectiveness. In addition to recommendations covering a range
of issues related to the operation and content of the program,
the task force recommended inclusion of ground-water information.
Development of national ground-water educational material is

now underway.


- 32 -

remedial action. Furthermore, areas vulnerable to
ground-water contamination and areas where pesticides
with leaching potential may be in use must be identi-
fied to support decisions on preventive measures.

Concern for the exposures resulting from ground-water
contamination by pesticides will require the above information
as well as an understanding of:

°

Pesticide movement and persistence once they reach
an _ aquifer.

While this information is needed in designing a sampling
scheme for assessing ground-water contamination, it
becomes much more important when attempting to assess

the likelihood of contamination reaching drinking water
taps at levels of concern. To determine this likelihood,
it is necessary to identify the dimensions of a potential
contamination "plume" and the wells which draw water
from it.

Who uses, and how frequently, ground water supplies
that are identified or predicted to be contaminated
at levels of concern.

Only general estimates of the number of people likely
to draw on contaminated ground waters may be required
to support EPA registration decisions. Much more
precise determinations of the extent of exposures may
be required at the local level to support remedial or
prevention decisions.

(While the above information on contamination and expo-
sure information is critical, the reader is reminded

of the importance of toxicity information for assessing
risks and deciding upon regulatory and response actions.
Toxicity considerations are discussed in the next section
of this chapter.)


- 29 -

water protection strategies addressing all sources of
contamination, including pesticides. Many States are reviewing
statutory and regulatory authorities to address pesticides
concerns as part of this effort. Many State plans for ground-
water monitoring also include pesticides. The only grant funds
under FIFRA for State pesticide programs directly are earmarked
for enforcement and certification of pesticide applicators. A
few States are using enforcement funds to help support investi-
gation of ground water contamination incidents; other States
have begun incorporating educational materials on ground water
into certification training programs.

Despite the general need for better coordination among
agencies at the State (and Federal) level, there are several
exceptions. For example, ongoing projects to control nonpoint
sources of water quality problems at the substate level demon-
strate a significant amount of cooperation between Federal,
State, and local agencies. Projects typically include pro-
viding technical and cost-sharing assistance to landowners for
the installation of best management practices, many of which
protect both surface and ground-water quality. In some pro-
jects, participation in Integrated Pest Management programs
is a condition of receiving cost-sharing assistance.


- 37 -

water because they rapidly volatilize from the soil
surface. However, the major ground water problems
caused by the very volatile pesticides EDB, DBCP,

and DCP have dispelled this notion. Contamination

by these volatile pesticides has been blamed on their
mode of application which is direct injection into

the soil. It has also hecome apparent that the actual
volatility of these pesticides when present in water
is critically changed.

This agueous volatility is determined by dividing a
chemical's vapor pressure by its solubility; this value
is termed Henry's Law Constant (H). A compound such

as DBCP has a very high vapor pressure but is also very
water soluble. High water solubility can cause high
vapor pressure chemicals to remain in the soil, par-
ticularly when these pesticides are applied just prior
to irrigation or rainfall.

Soil dissipation: a simplified, general measure of a
pesticide's persistence in soil usually measured as

the length of time required for dissipation of one-half
the concentration of a pesticide and often referred to
as a pesticide's "soil half-life." The soil half-life
of a pesticide can be derived from either laboratory

or field studies, but care must be taken in recording
the conditions of the test including temperature, type
of soil, soil moisture, etc.

Soil dissipation is dependent on a number of environ-
mental processes including vaporization and several
decomposition processes that cause chemical breakdown,
particularly hydrolysis, photolysis and microbial
transformation. Hydrolysis is the reaction of a
chemical with water. Photolysis is the breakdown

of a chemical from exposure to the energy of the sun.
And, microbial transformations result from the meta-
bolic activities of microrganisms within the soil.
When a pesticide resists these decomposition processes
and does not readily evaporate, it will have a long
soil half-life, increasing its potential as a threat
to ground water. This is particularly true if the
same pesticide is highly soluable and does not readily
adsorb to the soil particles. Pesticides with half-
lifes greater than 2 or 3 weeks should be carefully
assessed.



of California and in several municipal drinking water systems
drawing on ground water supplies. The source of contamination
was the widespread and approved use of this chemical in agri-
culture. DBCP ground-water contamination was soon found in
the States of Arizona, Hawaii, Maryland, and South Carolina.

In the same year that DBCP was discovered in California
wells, another pesticide, aldicarb, was found in wells on Long
Island, New York. The Long Island contamination was found to
be a result of normal, approved use of this pesticide on potato
fields to control insects and nematodes. In 1980, aldicarb
was found in 81 wells in the Central Sands region of Wisconsin,
again, as a result of the use of this pesticide on potato fields.
Since then, aldicarb has been found in wells at levels of con-
cern in eleven other States.

Perhaps the most serious case of pesticide contamination
of ground water began with the discovery in 1982 of the pesti-
cide ethylene dibromide (EDB) in two California wells and three
wells in Georgia. By the end of the following year, EDB con-
tamination of ground water had been discovered in 16 different
counties in California, Florida, Georgia, and Hawaii. The EDB
levels reported varied between 0.02 ppb and 300 ppb, but
typically were found between 0.05 and 5 ppb. EDB has been
described by the National Cancer Institute as "the most potent
cancer-causing substance ever found in [their] animal test
program." Finding EDB in numerous wells caused EPA to issue
an immediate emergency suspension of all EDB use as a soil
fumigant in September 1983.

The discovery of pesticide contamination has raised sig-
nificant concern about the threat posed to the nation's ground
water. However, these episodes do not provide a comprehensive
picture of the problem. The design of monitoring efforts to
date has not generally been intended to provide information on
the general relationships between ground~water contamination
and the varied physical/chemical properties of pesticides, the
manner in which they are used (or perhaps, misused), and the
environmental conditions that affect the persistence and move-
ment of these chemicals in the soil. As a result, EPA's efforts
to develop controls to mitigate ground-water contamination by
pesticides has been hampered by a lack of basic information.
EPA's current and planned efforts to gather extensive informa-
tion on pesticides in ground water are described in detail in
Chapter Three.

Table 1 is an EPA-compiled summary of pesticides found in
ground water due to normal application to the land, in various
States where monitoring has occurred. In 1984, a total of 12


- 65 -

currently developing a new strategy for dissemination of health
advisories to better ensure that the information is available

to all interested parties.

Office of Emergency and Remedial Response

The Comprehensive Environmental Response, Compensation and
Liability Act of 1980 (CERCLA) establishes a national program
for responding to releases of hazardous substances into the
environment. In determining the type and level of cleanup to
undertake, the Agency must comply with all applicable or rele-
vant and appropriate Federal public health or environmental
laws, including drinking water standards. The Agency must also
consider other Federal criteria, advisories, guidance, and State
standards such as ODW's health advisories. During this process,
EPA gives primary consideration to the selection of those
response actions that are effective in preventing or, where
prevention is not practicable, minimizing the release of hazard-
ous substances so that they do not migrate to cause substantial
danger to present or future public health, welfare, or the
environment.

As a general rule, the Agency's policy is to attain or
exceed the requirements of applicable or relevant and appropri-
ate Federal public health or environmental laws unless one of
the specifically enumerated situations is present. Where such
a situation is present and a requirement is not followed, the
Agency must document and explain the reasons in the decision
documents. Other Federal criteria, advisories, guidances, and
State standards also will be considered and may be used in
developing remedial alternatives, with adjustments for site-
specific circumstances. If EPA does not use, or uses and
adjusts, any pertinent standards in this category, EPA will
fully document the reasons why in the decision documents.

(1) Health Effects Assessments (HEAS)

Among the other Federal criteria, advisories, guidances,
and State standards considered, Health Effects Assessment (HEA)
values are given primary consideration. HEA values are developed
by the Office of Research and Development (ORD) for the Office
of Emergency and Remedial Response (OERR). They are subject
to change as new and better information becomes available.
For those hazardous substances for which HEA values have not
been developed, other public health and environmental values
should be considered.


- 47 -

TABLE 4

SUMMARY OF EPA/USGS MONITORING FOR PESTICIDES IN GROUND WATER

PESTICIDES RESPON-
PROGRAM PURPOSE LOCATION MONITORED SIBILITY STATUS REMARKS
OPP-ODW To determine 1500 Approx. 50 ODW/OPP. Survey Report due
Nat'l nature & extent existing + breakdown State & being late 1988.
Survey of pesticides public & products. county designed Focus is
of Pesti- in g-w nation- private govts ag pesti-
cides in wide and human wells in will cides, but
Drinking exposure to agric. probably will include
Water them via areas of partici- chlordane &
Wells drinking H20. U.S. pate. NO3. Random
ODW_use: develop sampling in
MCLs, HAs. high-med-low
OPP _use:Identify pest. usage
reg. needs, e.g. & vulnera-
cancellations, bility areas
restrictions, etc.
Evaluation To determine 14 regions Emphasis USGS Recon- Will take
of G-Water nature and throughout on trace niassance .4 years to
Quality in extent of U.S. metals and completed. complete.
Relation toxics con- organics, 2nd, OPP funding
to Land tamination in including inten- reconnaissance
Use - USGS various regions pesticides sive and testing
Toxic of the U.S., and phase to for Triazines,
Waste- to develop capa- begin for Nematocides,
G-Water bility to predict selected  Alachlor,
Contamin- g-w quality in studies Carbofuran &
ation terms of local FY 86 Organophos~
Program hydrogeology , phades in Kan-
climate & land use. sas, Nebraska
and California.
USGS To study g-w Through~ Variable, USGS Ongoing USGS's major
Fed/State quantity and out USA depending and g-water
Coopera~ quality in on concerns State monitoring
tive specific areas of state program. $100
Program of concern. Some million per
studies focus on year, 50/50
agricultural Fed-State
chemicals.
“DB G-Water Determine extent Seminole Co, EDB USGS, OPP Initial
tudy in of contamination Georgia & County study com-
seminole and source(s); Ag Exten- plete.
lo, GA. support EPA's sion Agent Follow-up
emergency sus- in prepar-
pension decision. ation.


- 45 -

of pesticides in the environment, predictive model develop-
ment, monitoring protocols, assessment of remedial measures,
and impact analysis. USDA will rely on its Soil Conservation
Service and State Cooperative Extension Service to transfer
knowledge gained through its research efforts to rural agri-
cultural community programs in a manner relevant to local
issues.

Fate of Pesticides in Ground Water. Understanding the
movement and fate of pesticides once in the saturated zone or
aquifer is critical to determining if contaminated ground water
will reach a well -- particularly one used for drinking water.
Such information is also needed in any sampling design for
ground-water monitoring.

Soil or rock which transmits relatively large amounts of
water is called an aquifer. Productive (high water-yielding)
aquifers generally Consist of unconsolidated materials (e.g.,
sands and gravels), permeable rock (e.g., Sandstone), or rock
with large fractures or cavities (e.g., limestone). Water
and pollutants are transmitted more slowly and therefore over
shorter distances through clays and other less permeable
materials, which are called aguitards or aquicludes.

Water enters an aquifer through its recharge zone, usually

a relatively flat area where the geological formation which
comprises the aquifer outcrops at the ground surface. Pesti-
cides or other pollutants spread on the ground in a recharge
area will enter the aquifer if they are not adsorbed by the
soil. This contamination of a recharge zone may increase with
increased rainfall or irrigation. Ground-water contamination
is more likely if the depth to the water table is shallow. A
shallow water table is common in humid regions, especially in
the spring.

Once it enters an aquifer, water flows very slowly --
typically feet per day or feet per year -- down a hydraulic
gradient until it discharges into a stream, lake, ocean, or
well. If the aquifer slopes beneath an overlying aquiclude
and water is trapped under pressure in it, then the formation
is called a confined, or artesian, aguifer. Until recently,
"confined" aguifers were thought to be protected from seepage
of contaminants in aquifers above and below by the intervening
impermeable strata. However, there is recent evidence that
organic chemicals can seep through thick clays that do prevent
water penetration.

There has been a proliferation of ground-water fate models.
No "best" model yet exists, and all such models require exten-
sive calibration for any site-specific application.


-51-

-- Model validation, in which models are tested and
refined to predict leaching under a variety of
field conditions, will enhance our ability to
make more accurate predictions on a site-by-site
basis. When the model validation work currently
underway at Dougherty Plains is complete, EPA
should have improved understanding of the factors
which affect leaching and be able to make more
accurate prediations ef aqround-water contamination.

-~ Methods are needed for obtaining accurate, site-
specific soils and hydrogeologic data to enter
into leaching models. Inappropriate input data is
the largest source of error in model predictions.

The effects of different application practices (rate,
timing, method, irrigation and cultivation practices)
on pesticide leaching to ground water have not been
well understood. Since pesticide usage and application
practices interact with environmental conditions to
contaminate ground water, it is important to be able to
evaluate them in the development of national strategies
and individual farm plans. EPA's Integrated Environ-
mental Management Division will complete an evaluation
in 1986 of the influence of farming practices and
environmental conditions on pesticide concentrations

in ground water, surface water, and air. This study
covers 18 pesticides, and looks at the influence of
tillage (conservation) practices and hydrogeologic
factors in three regions of the U.S. However, signi-
ficant uncertainty will remain after this study is
completed.

-~ Further investigation is needed to reduce the
uncertainty in these analyses and to consider
a broader range of chemicals, hydrogeologic
conditions, and application practices. Required
"mechanistic" studies by pesticide munufacturers,
as well as continued EPA research, would help
provide this information.

What conditions other than leaching from land applica-
tion can result in ground water contamination?

A number of these conditions are known. They include
pesticide spills at manufacturing/formulating and
mixing/loading sites, backflushing from chemigation
systems, disposal of pesticide products and containers

in abandoned wells and dry wells, seepage into improperly


- 55 -

II. Assessing Health Risks From Pesticides

A. The Need for Health Significance Information

Understanding the health effects of pesticides in drinking
water is essential to developing an approach for addressing the
problem of pesticides in ground water. Just as modeling and
monitoring are vital tools for assessing the environmental
presence and significance of pesticides in ground water, a
variety of health numbers and health assessment activities
provide the tools needed by EPA to evaluate the health signi-
ficance of pesticides in ground water.

Health significance findings are vital to EPA in supporting
regulatory decisions and response actions for pesticides occur-
ring in ground water. Determining the health significance of
pesticides is also known as risk assessment, and risk assessment
along with several other important considerations forms the basis
for risk management decisions to initiate regulatory and/or
response actions as appropriate. EPA's regulatory and response
actions can be effective and responsive only if they are based
on sound data and assessments of the nature and degree of the
risks posed.

EPA uses a somewhat standardized procedure for assessing
health/environmental risks. However, even though individual
Agency program offices all follow the same basic risk assess-
ment process (which will be described later in this section),
they often arrive at different characterizations of the nature
and degree of the risks posed, and make different decisions
concerning management of pesticide contaminants in ground water.
These differences occur almost invariably because different
statutory mandates, priorities, and management considerations
are brought to bear on the same pesticide chemicals and ground-
water contamination problems. A considerable effort is being
made within EPA to achieve a unified position on the health
significance of pesticide residues in ground water so that
risk management decisions may be consistent, if not identical,
across program lines.

EPA is starting from a relatively advantageous position
in addressing the health significance of pesticides in ground
water. More is known about the toxicity of pesticides than
about many other chemicals, since many pesticides have under-
gone extensive toxicity testing for the purpose of establishing
tolerances for residues in food. Where toxicity data on


- 43 -

D. Efforts to Improve the Information Base

Pesticide Leaching. EPA is improving the information
base on factors affecting pesticide leaching by: (1) gathering
additional information on the use practices of individual
pesticides; (2) developing and validating models that attempt
to simulate pesticide leaching under various conditions, and
(3) supporting ground-water monitoring studies.

For any pesticide that has the physical and chemical char-
acteristics of a potential leacher, EPA requires the pesticide
registrant to submit detailed information on the use history
of the chemical. For existing pesticides, the registrant may
have to provide information on: the crops and geographic areas
where the chemical has been used over the past five years; the
amounts applied; and the types of application methods employed.
The registrant may also be required to submit key factor infor-
mation on the soil and hydrogeology (discussed in next section)
of the area where the pesticide has been or is to be used.

In addition to gaining information on the specific use
practices of individual pesticides, numerous efforts are underway
by EPA and others to improve basic understanding of the processes
that affect the potential for pesticides to contaminate ground
water. These efforts are aimed primarily at furthering the
development and validation of the models used to predict the
movement of pesticides into ground water.

Over the last 14 years, EPA has developed two leaching
models, PESTANS and PRZM, to assess the potential for pesti-
cides to reach ground water. Extensive work to test and vali-
date these models has been underway for a number of years at
EPA's Doughtery Plains Project in Georgia. The major technical
focus of this effort includes: testing model outputs against
varying hydrogeological conditions and soil properties; testing
individual process descriptions for comparison of relative
importance of key factors; determining impacts of spatial
variability; and formulating additional processes including
those needed to link these unsaturated zone models to saturated
zone models. Field testing at Doughtery Plains will be com-
pleted by EPA in 1987.

EPA is also turning to the U.S. Geological Survey (USGS)
to gain field data for the testing of predictive modeling cap-
abilities. USGS is a natural resource research and investiga~
tion agency responsible for developing basic scientific infor-
mation on the ground-water environment. USGS collects basic
data on the quantity and quality of the nation's ground-water


- 16 -

MCLs are enforceable, and EPA requires public systems to monitor
and report findings to assure that the water they provide com-
plies with the MCLs. EPA proposed RMCLs for about a dozen
pesticides in November 1985. Final RMCLs and proposed MCLs

for these pesticides are scheduled to be issued in the Spring

of 1987.

EPA's Office of Drinking Water also sets non~regulatory
health advisories which provide information on health effects,
analytical methodology, and treatment technology on contaminants
not covered by drinking water regulations and on short-term
exposure to contaminants covered by drinking water regulations.
Health advisories describe concentrations of contaminants in
drinking water at which adverse effects would not be anticipated
to occur, with a margin of safety included to protect sensitive
members of the population. Health advisories are not legally
enforceable Federal standards, and are subject to change as new
and better information becomes available. The advisories are
offered as technical guidance to assist Federal, State, and
local officials make decisions regarding use of water that has
become contaminated. Health advisories for several pesticides
have been issued, and the Agency plans to issue several dozen
more by 1987.

If minimum Federal requirements are met, States may assume
primary responsibility for enforcement of the national drinking
water regulations. States are permitted to set standards that
are more stringent than Federal standards and to set standards
for substances not addressed by Federal regulations.

Under other SDWA provisions, EPA sets regulations to
control underground injection (the UIC program). Agricultural
drainage wells, classified as Class V wells, are not now sub-
ject to Federal regulation. They are a potential source of
ground-water contamination if pesticide-laden surface runoff
enters the drainage well. EPA also administers the sole source
aquifer program authorized by the SDWA. States (as well as
cities, companies, and individuals) may petition EPA to desig-
nate a sole source aquifer. Once designated, the States may
petition EPA to review the potential of a Federally funded
project to contaminate the aquifer.

D. Clean Water Act (CWA)

Nonpoint Source Program

The Clean Water Act (CWA) recognizes that achieving
water quality goals will require controlling nonpoint sources
of pollution. Concerted nationwide efforts to understand the


- 33 -

B. Tools to Assess Contamination and Exposures

To meet the information and assessment needs stated above,
EPA relies on two primary tools: monitoring and predictive
modeling.

The Role of Monitoring. Monitoring provides information
on the actual presence and magnitude of pesticides in soil,
in underlying ground water, at drinking water taps, or in any
other media that is accessible and relevant to issues of con-
cern. Monitoring studies can range from small-scale, intensive
field studies that involve only one pesticide to large-scale,
perhaps national, surveys which analyze for a multitude of
pesticide residues.

Small-scale studies take place on fields which are the
size of a research plot, usually less than 25 acres. Both
prospective and retrospective monitoring are conducted in
small-scale studies. A retrospective small-scale monitoring
study is a snapshot in time following the long-term use of a
pesticide on a field. A prospective study consists of continual
monitoring of a pesticide that begins with its application to
a "clean" test site (i.e., no previous use of the pesticide in
question). The prospective study will monitor for the pesticide
as it moves through the unsaturated zone and into the aquifer.
A prospective study may also follow the fate of the pesticide
once it is introduced into the aquifer.

Generally, a retrospective study is conducted to examine
an existing situation and determine if contamination has
resulted from past practices. A prospective study aims more
toward gaining understanding of the basic process of pesticide
leaching and movement in the aquifer. Prospective studies are
used to help validate predictive models and to determine the
conditions under which a specific pesticide will leach.

Large-scale surveys refers to broad retrospective studies
(usually basin, Statewide, or larger) from which conclusions
can be drawn about the number and concentrations of pesticides
in specific types of wells (e.g., public water supply wells)
or in specific geographic areas (e.g., truck farming on the
mid-Atlantic Coastal Plain).

Monitoring to detect detailed variations in ground-water
quality over large areas is not feasible. Contaminants are
usually so localized around their sources that a network of
samp]e wells is unlikely to detect the complete dimensions.


- 64 -

This exposure factor is judgmental and is adjusted when miti-
gating information exists; however, use of a 20 percent con-
tribution is considered to be reasonably conservative and
protective.

(2) Maximum Contaminant Levels (MCLs)

The general approach to setting MCLs is an evaluation of
the availability and performance of technologies, and an assess-—
ment of the costs of the application of technologies to achieve
various levels (that would be as close to the previously set
RMCL as possible or equal to the RMCL). MCLs are determined
based upon an analysis of technologies, costs, and other factors
relative to feasibility.

The RMCLs and MCLs are published in the Federal Register
and go through the full rulemaking process, including public
review and comment.

(3) Health Advisories (HAs)

The Office of Drinking Water's non-regulatory health
advisory program provides information on health effects, analy-
tical methodology, and treatment technology following inadver-
tent contamination of drinking water. Health advisories also
describe concentrations of contaminants in drinking water at
which adverse effects would not be anticipated to occur. A
margin of safety is included to protect sensitive members of
the population.

Health advisories are not legally enforceable Federal
standards. They are subject to change as new and better infor-
mation becomes available. The advisories are offered as tech-
nical guidance to assist Federal, State, and local officials
responsible for protection of the public health.

The health advisory numbers are developed from data
describing non-carcinogenic end-points of toxicity, using the
Reference Dose procedure described earlier for RMCL development.
Relative source distribution (exposure from drinking water,
food, and air) is also factored into the health advisories.

The health advisories are non-regulatory numbers and do
not go through the rulemaking process. Currently, an informal
mechanism of dissemination exists, by which each Regional Office
receives a set of health advisories and distributes them to
States and other interested parties upon request. In addition,
health advisories are available through the National Technical
Information Service (NTIS). The Office of Drinking Water is


TABLE OF CONTENTS (Cont.)

CHAPTER 3: ASSESSING GROUND WATER IMPACTS
AND HEALTH SIGNIFICANCE

I. Assessing Ground Water Impacts
Of PEStiCideS. cece sceeeveccecereresscvsvece

A. Information Requirements for
Contamination and Exposure Assessment.
B. Tools to Assess Contamination
and EXPOSULES.sccececereeeeerereseveene
C. Current Efforts and Understanding.......
TABLE 3: Chemical/Physical Properties
of Pesticides: Vaules Which
Indicate Potential for Ground-
Water Contamination.....eseeee
D. Efforts to Improve the Information Base.
TABLE 4: Summary of EPA/USGS Monitoring
for Pesticides in Ground Water
E. Remaining Information Needs..reeceeeveee
II. Assessing Health Risks from Pesticides......
A. The Need for Health Significance
Information. sccccecccesccccsvesvcveece
B. Health Risk Assessment for Pesticides
in Ground Waterecseeseeeescscccvsceees
C. Reference Dose as Benchmark.-..sseeeeeeee
D. Program-Specific Risk Numbers
and ASSESSMENLS scorers eeeseesereeerees
E. Current Efforts to Improve Health

Significance Knowledge. .eseeseeveeeeee

CONCLUSION. cece eee ccc e rece vccccenrerernrerccccevessseene

SELECTED REFERENCES. cee eee see e cece veer eer ncrrerreerereene

Page

30

31

33
35

42
43

47
50

55

55

56
59

62
68
70

72


- 67 -

Under section 3(c)(2)(B) of FIFRA, EPA has the authority
to "call in" from registrants any needed data on the health
or environmental effects of their registered pesticides.

In addition, OPP has authority under the Federal Food,
Drug, and Cosmetic Act (FFDCA) to set tolerances, or legal
limits, for pesticide residues in raw agricultural commodities,
processed foods, and animal feeds. No pesticide may be regis-
tered by EPA for a food or feed use until a tolerance has been
established or an exemption from the tolerance requirement has
been issued.

(1) Tolerances for Pesticide Residues

Decisions on tolerances for pesticide residues remaining
in or on treated food or feed products are based on reviews
of data submitted by petitioners, who are often the applicants
for registration. Estimated exposures are compared to the Ref-
erence Dose which is established based on the evaluation of
the entire toxicity data base. For pesticides which are deter-
mined to be oncogenic in laboratory animals, EPA carries out
a low dose risk extrapolation to arrive at levels of risk.
Exposure estimates in the past have usually been carried out
by assuming residues of pesticides at the legal tolerance level
and assuming consumption at the level of standard food factors.
This estimate of exposure is referred to as the Theoretical
Maximum Residue Contribution (TMRC).

The TMRC assumes that 100% of each crop for which the
pesticide is registered is actually treated and that all crops
contain residues at the tolerance level. When the TMRC exceeds
the Reference Dose, the Office of Pesticide Programs attempts
to more realistically estimate exposure to determine the actual
extent of risk. If essential data are not available, registrants
are required to submit the data under FIFRA section 3(c)(2)(B).
If after this evaluation the TMRC is still exceeded, OPP can
reduce or revoke tolerances for various commodities.

Over the course of the last few years, the Office of
Pesticide Programs has developed the capability to be more
precise and detailed in its description of exposure. The new
"tolerance assessment system" (TAS), developed by the Office
of Pesticide Programs allows the calculation of the mean dietary
exposure for the U.S. population and for 22 subgroups. It
will also calculate distributions of exposure, individual
commodity contributions, crop group distributions, exposure
to a pesticide on the days that a commodity is eaten (single


- 66 -

The HEA values represent two types of route-specific
exposure levels that have been estimated for systemic toxicants.
The first, the maximum dose tolerated for subchronic exposure,
is an estimate of an exposure level which would not be expected
to cause adverse effects when exposure occurs during a limited
time interval, i.e., for an interval which does not constitute
a significant portion of the lifespan. This type of exposure
estimate has not been extensively used, or rigorously defined,
as previous risk assessment efforts have been primarily directed
toward exposures from toxicants in ambient air or water where
lifetime exposure is assumed.

The maximum dose tolerated for chronic exposure is similar
in concept to the Reference Dose. It is an estimate of an expo-
sure level which would not be expected to cause adverse effects,
when exposure occurs for a significant portion of the lifespan.
This estimate is route-specific and estimates acceptable expo-
sure for a given route with the implicit assumption that expo-
sure via other routes is insignificant.

The HEA values are non-regulatory numbers and do not go
through the rulemaking process. Currently, an informal mechanism
of dissemination exists, in which each Regional Office receives
a set of HEAs and the HEAs are distributed to States and other
interested parties upon request. In the future, HEAsS will be
available through both the Center for Environmental Research
Information (CERI) of ORD, and the National Technical Informa-
tion Service (NTIS).

Office of Pesticide Programs

The Federal Insecticide, Fungicide, and Rodenticide
Act (FIFRA) authorizes a pre-market licensing or registration
process for all pesticides marketed and used in the United
States. Registration decisions are based on the evaluation
of test data submitted by registrants in accordance with Part
158 of Title 40 of the Code of Federal Regulations (U.S. EPA,
1982).

Toxicity data requirements for food use pesticides typically
include the following studies: a battery of acute tests, two
chronic studies (including one in a non-rodent), two oncogenicity
studies (in two species), two teratology tests (in two species),
a multigeneration reproduction study, and other tests, such as
a delayed neurotoxicity test, depending on the chemical struc-
ture. Environmental fate studies are also required for all
terrestrial outdoor use pesticides. These are the studies
upon which OPP bases its determination of a pesticide's
leaching potential.


- 69 -

human exposure, the Agency has in recent years initiated several
efforts to assure that risk assessments themselves are consis-
tent across the Agency.

The Agency is developing guidelines to be used by all EPA
programs in evaluating toxicity studies for a variety of health
effects. Because of the continuing evolution in risk assessment
methodology, a standing Risk Assessment Forum has been estab-
lished that will convene technical panels as needed to revise
the guidelines and help resolve new or unusual problems not
addressed by the guidelines. A committee of senior scientists
has also been set up to achieve consensus on conflicting
“Reference Doses" (formerly known as Acceptable Daily Intake,
or ADI) which now exist and to assure use of one Reference Dose
for each chemical throughout the Agency. The Agency anticipates
establishing a comparable committee to assure consistency in the
way the Agency expresses cancer risks.

Coordination between the Office of Pesticide Programs and
the Office of Drinking Water is particularly important, for each
has a need to determine risks presented by pesticides in the
diet and in drinking water. The two offices are now implementing
a Memorandum of Understanding outlining how they will share and
use information in developing health guidances for pesticides.
The offices plan to develop jointly, on an accelerated basis,
more than 50 health guidances on those pesticides that will
be included in the National Survey of Pesticides in Drinking
Water Wells.


- 27 -

III. State Programs Addressing Pesticides in Ground Water

While the Federal government sets national policy as well
as standards and regulations, the States are generally respon-
sible for implementing them. Federal efforts to address pesti-
cides in ground water must consider existing State programs
available for implementation, the effect of Federal actions on
State organizations and programs, and what support States will
need to carry out their implementation responsibilities.

Because of the variety of State agencies involved and the
limited degree of coordination among them in many States, it is
difficult to obtain a definitive picture of past and existing
State efforts to address pesticides in ground water at this
time. During the summer of 1985, EPA conducted a limited review
of written reports on the subject, grant activities under several
EPA programs, and other materials to compile a summary of known
State programs. EPA Regional office staff reviewed the material
in the draft summaries with key officials in each State.

While this compilation of information from a variety of
sources is recognized as being incomplete for some individual
State programs, when analyzed together, some general conclusions
can be drawn. Following is a preliminary analysis of the status
of State programs for pesticides in ground water. Individual
State summaries are being published in a separate document.

Perhaps the most important conclusion to be drawn is that
. while the majority of States recognize the potential signifi-
cance of the pesticides in ground water problem, efforts to
address the problem have been fragmented. Often, the agency
responsible for pesticides control is housed in the State
agriculture department while primary responsibility for water
quality and waste disposal programs is located in a State
environmental protection agency. Responsibility for assuring
safe drinking water often rests in still another agency, such
as a public health department. Each agency may have performed
tasks related to pesticides in ground water, but there has
been limited coordination among them. This situation mirrors
in many respects the need for coordination between EPA programs
and other Federal agencies at the national level.

Most of the monitoring States have performed thus far for
pesticides in ground water has been in response to a known or
suspected problem. Of the 24 States which reported specific


-13-

FIFRA Compliance and Enforcement

Historically, primary responsibility for enforcing FIFRA
rested with the Federal government. In 1972, Congress amended
FIFRA to allow EPA to set up cooperative programs with the States
to share the responsibilities for enforcing the Act and for
training and certifying applicators. The 1978 amendments
strengthened the State role, giving qualified States responsi-
bility for enforcing the requirements governing pesticide use.
All but two States (Nebraska, Wyoming) have assumed this
responsibility.

Before the 1972 amendments, the Federal program was limited
to enforcing such product-related violations as mislabeling,
inefficacy, chemical deficiencies, and failure to register.

Only criminal sanctions were available to address violations.

The 1972 amendments authorized EPA to enforce the requirements
governing pesticide use and provided for administrative civil

penalties as well as criminal sanctions.

Pesticide users must comply with label directions specifying
the crops and pests the product can be used on; approved rates
and methods for application; and the precautions that must be
taken before, during, and after application. Along with the
shift in primary responsibility for use enforcement to the
States, the focus of the program has shifted gradually away
from emphasizing productrelated enforcement to paying greater
attention to the health and environmental problems that arise
from using pesticides.

Under FIFRA cooperative enforcement grants, each State
sets priorities for annual compliance efforts by identifying
and ranking specific pesticide use and product-related prob-
lems the State is experiencing. Each State must also evaluate
whether certain national problems are problems the State needs
to address. For the first time in FY 85, ground water was
identified as a national problem for such consideration. Many
States have ground water initiatives as part of their overall
compliance programs.

In addition to directly administering compliance programs
in Nebraska and Wyoming, EPA conducts national direct compliance
monitoring programs. In cooperation with the Food and Drug
Administration, EPA audits laboratories performing tests in
support of pesticide registrations to ensure that the quality
of the data submitted is satisfactory. The environmental
fate data and monitoring studies now being required to help
the Agency determine a pesticide's leaching potential are
subject to such audits. EPA also inspects pesticide imports
to ensure that they comply with FIFRA requirements.


- 19 -

E. Resource Conservation and Recovery Act (RCRA)

Hazardous Waste Program (Subtitle C)

In 1976, the U.S. Congress passed the Resource Conservation
and Recovery Act (RCRA) which amended the Solid Waste Disposal
Act (SWDA). This legislation regulates disposal of waste, in-
cluding pesticides which may create a hazard, to assure minimum
effects on human health and the environment. RCRA places the
burden of protecting the environment on all users and handlers
of hazardous materials, and such material may include the active
and/or inert ingredients of pesticide products.

The marketing and use of pesticides is regulated by EPA
under FIFRA and by the States under applicable laws and regu-
lations. However, once pesticide applications are completed,
any excess pesticide concentrate, unapplied diluted pesticide,
or discarded pesticide containers may also be regulated as
waste (and some as hazardous wastes) under RCRA.

While most of the pesticide products sold in the U.S.
are not regulated as hazardous waste, some are considered
toxic waste ("toxic commercial products") or acutely toxic
waste ("acutely hazardous commercial-chemical products") by
virtue of their chemical and toxicity characteristics. Such
pesticides are included on the RCRA F and E lists respectively.
Pesticide-containing wastes that are considered hazardous
wastes under RCRA are subject to extensive regulatory require-
ments governing storage, transportation, treatment, and disposal,
and severe penalties may be imposed in the event of violation.

The matter of appropriate disposal of all pesticide pro-
ducts is addressed through product labeling. Under FIFRA,
all pesticide products must bear specific label instructions
covering storage and disposal. Such instructions are tailored
to reflect the pesticide's waste classification under RCRA.

Not all pesticide uses or users are subject to the exten-
sive RCRA waste control requirements. Household wastes, for
example, are specifically excluded from RCRA jurisdication.

Most farmers also are exempt from the hazardous waste "generator"
requirements of RCRA, provided that they triple-rinse empty
pesticide containers and dispose of any pesticide residues on
their own property and in a manner consistent with the disposal
instructions on the pesticide label. Commercial applicators

are not automatically exempted, but are under RCRA's jurisdic-
tion only if they generate more than 100 kilograms of regulated
wastes per month. Otherwise, they are considered "Small Quantity
Generators," and need only dispose of hazardous wastes ina
responsible manner as reflected by the product labeling.


-15 -

specific efforts to control pesticides in ground water. In

FY 85, nine States used their grants to help assess the problem,
develop monitoring strategies, and develop management alterna-
tives for pesticides in ground water.

In addition to the State grant program, EPA has initiated
several other actions to improve ground water protection efforts.
The development of an Agricultural Chemicals in Ground Water
Strategy represents a major step toward addressing a source
of contamination which was identified in the EPA Ground-Water
Protection Strategy as needing further attention. It also
represents furtherance of another goal of the Strategy: to
enhance coordination and cooperation between EPA programs
which affect ground water.

A report on ground-water research prepared by a special
EPA Science Advisory Panel includes recommendations for needed
Agency research that can assist in addressing pesticide con-
tamination problems. The Ground-Water Monitoring Strategy
developed in 1985 includes actions to improve the quality,
accessibility, and utility of all ground-water monitoring
data, including data collected on pesticides.

Cc. Safe Drinking Water Act _(SDWA)

The Safe Drinking Water Act (SDWA) is designed to assure
that public water systems (serving over 25 persons or with 15
connections) provide water meeting minimum standards for the
protection of public health. As required by the Act, EPA pub-
lishes drinking water regulations for contaminants which may
have adverse effects on the health of persons. These regula-
tions specify either (1) "maximum contaminant levels" (MCLs)
which specify the maximum contamination level of chemicals
which may be present in the water served to the public, or (2)
treatment techniques that must be used to remove contaminants
which are either technically or economically infeasible to
detect. Its authorities do not extend to private wells.

EPA is required to establish "recommended maximum contami-
nant levels" (RMCLs) before establishing MCLs. RMCLs are non-
enforceable health goals which are set at a level at which, in
the Administrator's judgement, "no known or anticipated adverse
effects on the health of persons occur and which allows an
adequate margin of safety." The maximum contaminant levels
(MCLs) must be set as close to RMCLs as is feasible. Under
the SDWA, feasible means "with the use of the best technology,
treatment techniques, and other means, which the Administrator
finds are generally available (taking costs into consideration)."


- 28 -

findings, the most frequently identified pesticides were aldicard,
EDB, and atrazine. The increased concern about ground water
contamination generally and the recognition of pesticides as a
potential contaminant have led several States to initiate more
comprehensive monitoring programs. These efforts, still largely
in the planning stage, focus monitoring in areas of pesticide
usage where the ground water is considered to be most vulnerable
to contamination.

Many States have initiated user awareness programs to
address at least some aspects of the problem. Most notable
are "Amnesty Day" programs, in which State and local organizers
arrange for the collection and safe disposal of unwanted pesti-
cide products from households and farms. States have also begun
educational programs to increase understanding of ground water
and how it may become contaminated by agricultural practices.

While many States have at least some activities addressing
pesticide contamination, only a few have begun efforts that
could be defined as prevention or control programs. Several
States have established or are developing regulatory programs
to require anti-backsiphoning devices and other safety measures
on chemigation systems which, if not properly equipped and
calibrated, can result in ground water contamination. [Note:
EPA is also proposing requirements for chemigation systems.]

A handful of States are preparing for implementation of
new laws either governing ground-water protection generally,
including pesticide problems, or laws dealing with pesticide
contamination specifically. Since these programs are in the
formative stage, the exact nature of the controls or manage-
ment schemes that will be used are still undetermined. Some
anticipate more vigorous State registration of pesticides to
keep those which threaten ground water from being used in the
State. At least one State law suggests more extensive research
and implementation of Integrated Pest Management as part of
the protection program. Other controls being considered or
implemented include requiring buffer zones around wells, requir-
ing prior approval for the use of certain pesticides, allowing
use only under severe restrictions, and banning the use of
pesticides in areas where monitoring reveals that levels of
health concern are being approached. In developing these pro-
grams, one of the first steps States are taking is identifying
areas where pesticide contamination of ground water is most
likely to be a problem.

For many years, States did a limited amount of ground
water protection plannning using funds under Sections 208, 106
and 205(j) of the Clean Water Act. With the additional impetus
in 1985 and 1986 of special Section 106 qrants for ground water,
virtually all States are now developing and implementing ground-


- 10 -

I. EPA Authorities and Programs

A. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)

Pesticide Registration

The Federal Insecticide, Fungicide, and Rodenticide Act
(FIFRA) gives EPA broad authority to register and reregister
pesticide products, and otherwise regulate pesticide marketing
and use in the U.S. In recognition of the fact that most
pesticides afford our society important pest control benefits
while also inherently posing a degree of hazard to nontarget
species, the statute mandates a balancing of the risks and
benefits associated with any pesticide use. Those uses that
do not cause "unreasonable adverse effects" to man or the
environment, taking into account both their risks and benefits,
may be or may remain registered. Uses that pose unreasonable
adverse effects may be denied registration or removed from
the market after their initial registration. EPA may place
restrictions on the use of pesticides that are registered to
reduce the risk they present.

In addition to registering or placing restrictions on
the use of individual pesticides, EPA has other mechanisms
which may be employed to regulate or establish policy for all
or a group of pesticides. These mechanisms include the rule-
making process (including negotiated rulemaking), Pesticide
Registration (PR) notices, and other special policy statements.

In evaluating a pesticide's risks, EPA takes into consid-
eration both its inherent toxicity and the potential routes
of human exposure to the compound. Since recent data indicates
that people may be exposed to pesticide residues in ground water
if it is used as drinking water, EPA is now considering this
additional potential source of human exposure to pesticide
residues. The Agency is using the full range of PIFRA authori-
ties to gather and evaluate pertinent data and regulate pesti-
cides that pose a risk to ground water, up to and including
cancellation of products that pose an unreasonable risk due
to their occurrence in ground water.

New Chemicals. EPA requires a full complement of data on
human health and environmental effects for registration of a
new pesticide today. Among the environmental fate data currently


- 68 -

serving sizes), as well as an averaged exposure over a period
of time. This new computerized system has the capability of
estimating consumption of a pesticide in drinking water as well
as through food.

Traditionally, exposure to pesticides in drinking water
has not been combined routinely with dietary exposure but has
been compared separately to the Reference Dose. However, the
estimaced «.nosure that is comsared to the Reference Dose can
now be extremeiy accurate, given the limitations specific to
each compound. Consistent with this approach is the combi-
ning of dietary and drinking water exposure as appropriate.

In those cases where drinking water exposure can be quantified,
the Office of Pesticide Programs proposes to assess drinking
water and dietary exposure to pesticides by combining the
drinking water contribution with that resulting from dietary
sources, and characterizing as accurately as possible the
population for which this exposure and its associated risk are
relevant. OPP will also estimate the exposure and percentage
of Reference Dose utilized for the general population (and the
population subgroups that are a part of the new Tolerance
Assessment System) for dietary exposure that does not include
drinking water.

Tolerances established by EPA are regulations and are
published first as proposed and later as final rules in the
Federal Register. Ultimately, they are codified in Parts 21
and 40 of the Code of Federal Regulations. The food and feed
tolerance regulations promulgated by EPA are enforced by the
U.S. Department of Agriculture (for meat, poultry, and eggs)
and the Food and Drug Administration (for other food and feed
conmodities). Both domestic and imported food and feed moving
through the channels of U.S. commerce must comply with the
pesticide tolerance regulations established by EPA. Commodi-
ties found to be in violation of tolerance regulations are
subject to seizure and destruction.

E. Current Efforts to Improve Health Significance Knowledge

Health risk assessment is a relatively new procedure, and
it is often described as both art and science because of the
inherent difficulties involved in determining potential human
health risks based on toxicity data that is often incomplete or
inconclusive. Despite these difficulties, health risk assess-—
ment is a fundamental tool used by all EPA programs to charac-
terize the potential for harm to human health by chemical
substances in the environment. These assessments form a key
part of the basis upon which policy makers determine whether,
and to what extent, measures to reduce risks are warranted.
While decisions regarding risk management for the same chemical
may vary because each EPA program has unique statutory require-
ments and addresses a somewhat different aspect of potential


- 53 -

How do pesticides move and persist once they have
reached an aquifer?

Understanding of the fate and transport of pesticides
in ground water is limited, yet they are important
considerations in determining the extent of a contami-
nation plume and its expected duration. Unfortunately,
ground water movement is difficult to predict in many
types of aquifers and in any case requires substantial
knowledge about the hydrogeologic conditions at the
site of concern. Whether and how the pesticide breaks
down in ground water is also an important consideration
in estimating potential human exposures to the parent
compound and its breakdown products, which may be more
or less toxic.

Increased understanding is needed in several areas:

-- Pesticide behavior in the saturated zone,
including pesticide degradation in aerobic
and anaerobic ground-water environments.

-- Ground-water flow mapping and other hydrogeologic
data in areas where pesticide contamination is
a concern,

~- Estimates of pesticide accumulation in ground
water, including models to predict accumulations
from multi-year applications.

-- Interactive or synergistic effects on ground
water of applying different chemicals.

Who uses, and how freguently, drinking water that
is found or predicted to be contaminated?

Exposure to pesticides in drinking water is poorly under-
stood. There has been very little monitoring for these
chemicals. Private wells are especially threatened
because they are frequently shallow and close to where
crops are grown, but they are seldom if ever tested.
The planned National Survey of Pesticides in Drinking
Water Wells is a statistically designed sampling pro-
gram for pesticides in public and private wells. The
results should enable us to draw conclusions about the
extent of well contamination nationwide and the prob-
ability of contamination in specific locales.


-3-

II. Sources of Pesticide Contamination

Ground water may become contaminated by pesticides at any
point in the life cycle of a pesticide: its manufacture, distri-
bution in commerce, storage, use on the land or in industrial
settings, and disposal. The sources can be grouped into two
general categories based on the characteristics of the contami-
nation which may occur and the type of actions that can be taken
to prevent it.

The first category includes accidental spills and leaks
of pesticides at manufacturing facilities and at other estab-
lishments where bulk pesticides are stored and handled, such
as agricultural chemical dealerships and commercial applicator
facilities. Also included in this category are places, including
hazardous and municipal waste landfills and other waste handling
or treatment facilities, where bulk pesticide wastes are disposed
of. A variety of Federal and State environmental laws and regu-
lations contain provisions to prevent contamination from these
"point" sources. Should contamination occur, it can be charac-
terized as concentrated plumes that are relatively localized
and thus able to be at least partially cleaned up using the
techniques typically available for other ground-water contami-
nation. In addition, the parties who are responsible for the
incident can often be identified and required to pay for the
cleanup.

By far, pesticides are most commonly used to control insect
and weed pests on agricultural and forest land as well as on
homes and gardens and on highway and utility rights of way.

When pesticides are applied to the land, they are carried above,
over, and through the ground by rainfall, runoff, infiltration,
and snowmelt. Pesticides dissolved in runoff water are carried
to surface water or may enter ground water through a variety of
potential routes (such as uncapped wells or sinkholes). Pesti-
cides may also leach into ground water through infiltration at
either the site of application or in runoff retention areas.
Also associated with land application of pesticides is contami-
nation from irrigation systems used to apply pesticides ("chemi-
gation") which may siphon pesticides back into the ground-water
well if not equipped with proper safety devices.

Contamination may also result from small but frequent
spills at mixing and loading areas on the farm field, and from
improper disposal of small quantities of leftover pesticides


- 25 -

result in long-term public benefits, but that the farmer or
rancher is unable to undertake without financial and technical
assistance.

Controlling pollution from nonpoint sources is currently
recognized as one of the primary purposes eligible for cost-
sharing assistance. ASCS is working with SCS and EPA to develop
quantifiable data that can be collected in the Conservation
Reporting and Evaluation System to provide a better tool for
monitoring and evaluating efforts to control nonpoint sources.
ASCS encourages local, State, and national conservation review
groups to identify and rank known nonpoint source problem areas,
including ground-water problems; develop any special practices
needed; and to propose projects for special funding considera-
tion. ASCS also uses data from the Rural Clean Water Program,
including several projects with ground-water quality components,
to aid in evaluating the effectiveness of best management
practices.

De USDA Agricultural Research Service

The Agricultural Research Service (ARS) devotes a major
portion of its efforts toward control of chemical sources of
pollution. The principal thrusts of these efforts are toward
improved chemical use efficiency and development of alternatives
to the use of ‘chemical pesticides, including breeding of disease
resistant crops and biological control of insects. ARS is also
investigating nitrate and pesticide movement through soils.

Research on pesticides and ground water is a relatively
new but rapidly expanding field. To facilitate sharing of
information among researchers and users of research results,
the ARS established a new computer information bank con-
taining brief descriptions of pesticides and ground water
projects. All Federal agencies have already placed projects
into the system and efforts are now underway to obtain and
include projects from such other research institutions as
the land grant universities.

E. U.S. Geological Survey

The U.S. Geological Survey (USGS) of the U.S. Department
of the Interior is the principal Federal agency conducting
ground-water resources investigations, which it performs through
a variety of Water Resources Division programs. A Federal-State
cooperative program was developed to support hydrologic data
collection activities and water resource investigations, with


- 60 -

Standard Uncertainty Factors for Toxicological Effects
Note: An uncertainty factor of 10 is included for each
condition
Condition Uncertainty Factor
o Species extrapolation required 10
o Short term or subchronic data 10
used for estimating chronic
levels
o Data on normal individuals used 10
to estimate levels for sensitive
subgroupings

Reference Doses generally are already available for those
pesticides used on raw agricultural commodities. In addition,
for those pesticides which are determined to be oncogenic in
laboratory animals or in epidemiological studies, EPA extrapo-
lates from various doses to arrive at doses corresponding to
various levels of increased cancer risk. Adjustments for
species differences and for partial lifetime exposure are made
as required using procedures described in EPA's Guidelines for
Carcinogenic Risk Assessment. These risks are presented in
tabular form to help the appropriate regulatory program deter-
mine the risk level which can be tolerated after consideration
of scientific and other factors.

There are several ways in which EPA can use the Reference
Dose and can factor in human exposure to arrive at risk assess-
ments for pesticides in ground water. Different program offices
within EPA use the Reference Dose in different ways, each con-
sidering multi-media exposure to pesticides in a different
fashion. One approach is to factor all sources of exposure
(air, food, and water) into the Reference Dose and, if data are
not available on the relative contribution of the contaminant,
develop an arbitrary apportionment. An alternative approach
is not to apportion the Reference Dose according to sources of
exposure, but instead to consider pesticide uses on a case-by-
case basis, combining dietary and drinking water exposure as
appropriate. The activities of the Office of Drinking Water
(ODW) and Office of Pesticide Programs (OPP) exemplify these
two approaches.



- 62 -

Reference Dose, an ODW-established health advisory
level in drinking water, and for which drinking water
exposure can be quantified), OPP will consider adding
the drinking water contribution to the dietary
contribution resulting from established tolerances,
and characterize as accurately as possible the popula-
tion for which this exposure and its associated risk
are relevant (i.e., the population likely to drink
contaminated water). If the population cannot be
characterized, the uncertainties in the exposure
assessment are clearly expressed. A separate exposure
assessment is made for the general population.

These varying approaches result in different "health
numbers" being used within the Agency even though the starting
point -- the Reference Dose -- is identical. Efforts are on-
going to integrate the two approaches described above so that
consistent risk assessments and health numbers are generated
for pesticides that may contaminate ground water. Options for
addressing this issue are also being developed as part of the
Agricultural Chemicals in Ground-Water Strategy.

D. Program-Specific Risk Numbers and Assessments

Office of Drinking Water

Under the Safe Drinking Water Act, EPA is required to
establish drinking water regulations to assure the safety
of the water served by public water systems. For contaminants
which the Administrator judges may have an adverse effect on
the health of persons, EPA specifies the maximum contaminant
level (MCL) that can be allowed in public water supplies, or
for contaminants that cannot be readily detected, treatment
techniques that must be employed to remove them. EPA is also
required to first specify Recommended Maximium Contaminant
Levels (RMCLs), which are non-enforceable health goals. The
MCLs, which take into account the feasibility and cost of
removing the contaminant, must then be set as close to the
RMCL as feasible and are enforceable. Non-regulatory health
advisories are developed by EPA to provide information following
inadvertant contamination of drinking water. (See discussion
of the Safe Drinking Water Act in Chapter II for a more detailed
discussion.)

(1) Recommended Maximum Contaminants Level (RMCLs)

RMCLs are set based upon a three-category approach in which
chemicals are classified based upon the strength of evidence of
their carcinogenicity as follows:


- 63-

o Category I - Strong evidence of carcinogenicity.
o Category II - Equivocal evidence of carcinogenicity.

o Category III - Inadequate or no evidence of carcin-
ogenicity in animals.

Category I includes those chemicals which, in the judgment
of EPA, have sufficient human or animal evidence of carcinogen-
icity to warrant their regulation as known or probable human
carcinogens. RMCLs for these compounds are set at zero. These
compounds are potential human carcinogens and they have not been
demonstrated to exhibit a threshold; thus it is assumed for the
purpose of regulation that any exposure could contribute some
finite level of risk.

Category II includes those chemicals for which some
limited but insufficient evidence of carcinogenicity exists
from animal data. These are not regulated as known or prob-
able human carcinogens. However, RMCLs reflect the fact that
some experimental evidence of carcinogenicity in animals has
been reported.

EPA uses one of two options for setting the RMCLs for
these types of chemicals. The first option consists of setting
the RMCL based upon non-carcinogenic endpoints (the Reference
Dose, with an additional uncertainty factor) if adequate data
exist. The second option consists of setting the RMCL based
upon an estimate of increased lifetime risk. EPA uses the
first option if valid non-carcinogenic data are available upon
which to base a Reference Dose. If valid non-carcinogenic data
are not available and risk levels have been calculated, then
risk calculations are used.

EPA believes that both of these approaches reflect the
primary consideration concerning Category II chemicals: RMCLS
should be less conservative than those for Category I chemicals
and more conservative than those for Category III chemicals.

Category III includes those substances with inadequate
or no evidence of carcinogenicity. RMCLs are calculated based
upon chronic toxicity data using Reference Doses.

The percentage of exposure from drinking water often used
in determining the RMCLs is a 20 percent contribution for organic
chemicals and a 10 percent contribution for inorganic chemicals.
The National Interim Primary Drinking Water Regulations used
20 percent as the drinking water exposure factor for pesticides.


- 22 -

II. Programs of Other Federal Agencies

A variety of Federal agencies support programs that can
help address the problem of pesticides in ground water. Such
Federal agencies as the U.S. Forest Service, Bureau of Land
Management, Fish and Wildlife Service, and National Park Service
manage vast areas of public land. Their use of pesticides to
control insects and weeds on these landholdings may affect
ground-water quality. In addition, these and other Federal
agencies, such as the Tennessee Valley Authority and U.S. Geo-
logical Survey, often perform studies and projects which can
support efforts to address pesticides in ground water. These
agencies participate in the EPA-sponsored Interagency Committee
on Ground-Water Protection, and are increasingly emphasizing
ground-water protection needs in their own operations.

This discussion focuses on the programs of the U.S.
Department of Agriculture (USDA), since USDA provides technical
assistance to individual landowners and a range of incentives
that affect the way landowners choose to manage their land.
Ultimately, landowners make choices regarding pesticide use
and land management practices at a site-specific level. The
agencies advising them play a significant role in ensuring
that landowners make environmentally sound decisions.

Recognizing the potential for ground-water contamination
from agricultural activities, the USDA, under the direction
of the USDA Natural Resources and Environment Commitee, has
begun a departmental analysis of the seriousness of ground-
water problems related to agriculture and of the programs
that deal with those problems. USDA officials anticipate
that program priorities and targeting, as well as eligibility
requirements for some assistance programs, may be adjusted to
help address ground-water protection needs.

A. USDA Extension Service

The USDA Extension Service (USDA-FS) is part of a three-way
partnership (Federal, State, and county) known as the Cooperative
Extension Service (CES). The basic mission of CES is to improve
American agriculture and strengthen American families and com-
munities through the dissemination and application of research-
generated knowledge and leadership techniques. The Federal
partner -- the USDA Extension Service -- provides support for
the State Cooperative Extension organizations by overseeing
the distribution of Federal funds, reviewing CES programs, and
informing States about Federal priorities and programs.


CHAPTER ONE

THE PESTICIDES IN GROUND WATER CHALLENGE



INTRODUCTION

For many years, our society has enjoyed the benefits
of using pesticides to control weed and insect pests. An
assumption behind much of this use has been that pesticides
will either degrade quickly or bind to soil particles until
they eventually break down into more innocuous substances.
Only within the last decade have scientists learned that
pesticides applied to the land can leach through layers of
the earth's surface to enter the ground water below. Leaks
and spills, as well as disposal practices, can also result
in pesticide contamination of ground water.

Increasing national awareness of the need to protect our
ground water resources has led to a recognition that widespread
distribution and use of pesticides is a potentially significant
source of ground-water contamination. Efforts are being initi-
ated at all levels of government to understand the nature of
this problem and devise appropriate solutions.

The U.S. Environmental Protection Agency (EPA) has respon-
sibility under a variety of statutes to protect the quality
of the nation's ground water as well as direct responsibility
for regulating the availability and use of pesticide products.
Since the early 1970's, EPA's Office of Pesticide Programs
has been evaluating the leaching potential of new and existing
chemicals and has taken regulatory actions, including cancella-
tion, on several chemicals found to have the potential to con-
taminate ground water. During this period, EPA has also under-
taken monitoring studies and research efforts designed to help
characterize the risks pesticides pose to ground water.

Shortly after EPA's Ground-Water Protection Strategy
was issued in August, 1984, the Agency initiated an intensive
review of existing information and scientific knowledge about
the extent of pesticide contamination, its causes, its poten~
tial health impacts, and the statutory authorities and programs
available to help address the problem. This report presents
the findings of the Agencywide review. It is intended as a
background document to help inform Federal and State policy
makers and the interested public as they grapple with the
complexities of the pesticides in ground water problem. This
report will also provide background for the Agency's Agricultural
Chemicals in Ground-Water Strategy now under development and
soon to be released for public comment.


-ill-

required are a variety of studies needed to evaluate the
leaching potential of the pesticide. Monitoring studies may
also be required. EPA's intent is to assure that any pesticides
registered for the first time today or in the future will not
pose an unreasonable risk to human health due to contamination
of ground water.

Existing Chemicals. Many of the pesticides currently
registered and on the market were first registered years ago,
before EPA's current data requirements were developed or promul-
gated as regulations. The toxicity and environmental fate data
bases for these old chemicals are often inadequate by today's
standards. The initial decisions to register these pesticides
are being reevaluated on the basis of updated data bases.

The pesticide registration and reregistration programs
under FIFRA enable the Agency to screen both old and new chemi-
cals carefully for potential unreasonable adverse effects, in-
cluding any risks posed by the chemicals' ability to leach to
ground water. Suspected leachers are subjected to further
testing by their producers. Demonstrated leachers that pose
hazards by virture of their toxicity and use patterns may be
the subjects of regulatory actions ranging from label direction
changes and use restrictions to suspension and cancellation of
product registrations.

While much of the chemical-specific data on pesticide
leaching potential is being required of pesticide registrants,
FIFRA research and monitoring authorities and the Agency's
pesticide modeling capabilities enable EPA to produce data
needed to predict, detect, and evaluate pesticide occurrences
in ground water. FIFRA product classification and applicator
certification and training authorities provide a useful vehicle
for assuring proper use of pesticides that are actual or poten-
tial leachers, and for conveying information on prevention of
ground-water contamination to pesticide users. FIFRA industry
and user compliance programs implemented in cooperation with
the States make the Agency's prevention decisions enforceable.

Applicator Certification and Training Program

The primary vehicle available to EPA for educating pesti-
cide applicators in the safe and proper use of pesticides is
the certification program authorized by the 1972 amendments to
FIFRA. Pesticides that are highly toxic or that have serious
environmental hazards associated with their use may be classified
as "restricted use" pesticides. They may only be used by, or
under the direct supervision of, applicators who have been
certified as competent to use these pesticides.


Discharge to Surface Water

Even though ground water moves slowly through the ground,
it usually eventually discharges to surface waters. In some
areas of the country, springs and aquifers contribute large
quantitites of water to the flow of streams. In the coastal
states, aquifers discharge into the seas and wetlands and
supplement fresh-water flows. In other areas, ground waters
discharge into lakes, ponds, and inland wetlands.

If ground water becomes contaminated, the contamination
may eventually appear in surface water. Depending on the
geologic and hydrologic characteristics of the aquifers
involved, contaminated ground water may discharge to surface
areas as quickly as within one day or take as long as a thou-
sand years or more.

Characteristics of Recharge Areas and Unsaturated Zones

The potential for contamination also depends on the charac-
teristics of recharge areas, that is, areas where water enters
the aquifers through geologic formations. In many parts of the
country, the recharge areas are close to the land surface and
may be affected signficantly by land management practices such
as pesticide application.

The depth and types of soils above the aquifer, the depth
from the earth's surface to ground water, and many other factors
affect the potential for contamination. In some areas, the
water table is within 20 feet or less of the land surface, and
the unsaturated zone (the layer between the surface and the
water table) consists of highly permeable sand and gravel beds.
Ground water in these areas may become contaminated relatively
quickly by pesticides. In other areas, the unsaturated zones
are deep, and their beds consist of layers of highly impermeable
materials. Contaminants in such areas may not reach ground
waters, or will do so only after a very long time. Finally,
certain aquifers are buried deep beneath other aquifers. They
become contaminated either through leakage from other aquifers,
through poorly cased wells, or through pollutants entering their
recharge zones.


~17-

nature of and solutions to nonpoint source pollution were first
required in 1972 under Section 208 of the CWA. States and area-
wide agencies were called upon to develop and implement plans for
managing water quality. Among the nonpoint pollutant sources
listed were agriculture and silvicluture; pesticides used in
these activities may contaminate both surface and ground water.

During the mid and late 1970's, EPA funded States to
develop initial plans to assess both point and nonpoint source
problems and control needs. While the principal focus was on
surface water, some States also used Section 208 funds for
development of ground-water management programs.

With elimination of funding under Section 208 after fiscal
year 1981, States and local governments are increasingly using
their own funds, supplemented by other CWA funding sources,
to fund nonpoint source control efforts and related continuing
water quality management efforts. Many States are updating
their original plans and developing information useful for
ground-water management programs.

Currently, EPA provides grant funds under Section 106 and
Section 205 (j) of the CWA to support a full range of water
quality management activities, including the development and
implementation of nonpoint source and ground-water management
programs. Nonpoint problems are also addressed through funding
provided by the CWA Clean Lakes Program, Great Lakes Demonstra-
tion Projects, and Great Lakes and Estuarine Management Programs.

In general, EPA's nonpoint program focuses on providing
guidance and information transfer between and among States and
localities and in coordinating the nonpoint source-related
activities of other Federal agencies. In addition, EPA provides
financial assistance to States and other agencies under a variety
of programs for nonpoint source monitoring/assessments, planning,
program development, and demonstration projects.

National Nonpoint Source Policy. During 1984, EPA con-
vened an interagency Nonpoint Source Task Force which led to the
development of a National Nonpoint Source Policy and individual
agency strategies to carry out the Policy. The Policy's objec-
tive is to accelerate the development and implementation of non-
point source management programs for both surface and ground
water. The Policy emphasizes that site-specific and source-
specific decision making is the key to effective implementation.

The Policy defines the roles and responsibilities of the
various levels of government and the private sector. States
have the lead for implementing nonpoint source programs for State


itates » Office of Ground-Water May 1986
EPA/440/6-86/002 rental Protection Protection (WH-550G)

Washington DC 20460

SEPA _—St_— Pesticides in
Ground Water:
Background Document

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-~ 39 -

Soil structure: refers to the way soil grains are
grouped together into larger pieces or aggregates --
platy, prismatic, blocky, or granular. Structure is
affected by texture and percent organic matter. Pesti-
cides and water can seep, unimpeded, through seams
between the aggregates.

Porosity: is a function of total pore space, pore size,
and pore size distribution and is determined by soil
texture, structure, and particle shape. Pesticide
transport is more rapid through porous soils.

Soil moisture: refers to the presence of water in soil.
The water in soil ultimately transports pesticides that
are not adsorbed into the water table below. Upward
movement may also occur through capillary action and

by a process termed evapotranspiration in which water
in the soil is lost to the air.

Depth to ground water: the distance a pesticide must
travel through the soil or underlying foundation
material to reach ground water is, of course, a key
determinant in whether contamination will occur at

a particular site.

Application Factors Affecting Leaching. The other category

of factors determining pesticide leaching involves the methods
and conditions of pesticide application. These factors include:

°

°

Local climatic conditions: the degree of pesticide
leaching at a particular site can be directly dependent
on the amount of local rainfall. The temperature of
the soil and surrounding air at a site can also greatly
affect the processes that result in a pesticide's move-
ment and degradation in the environment.

Rate of application: how much and how often a pesticide
is applied to the soil can be the critical determinant
in ground-water contamination.

Timing of application: when a pesticide is applied can
be a major factor depending on local environmental
conditions and temperature and rainfall.

Method of application: a pesticide can be applied to
crops by aerial spraying, topsoil application (granu-
lar, dust, or liguid formulations), soil injection, soil
incorporation, or through irrigation. Soil injection
and incorporation are generally considered to pose the
greatest likelihood for ground-water contamination
problems.



Table 1: Potential Sources of Pesticide Contamination
of Ground Water

Manufacturers/ Industrial Land
Formulators Dealer User Application
SPILLS AND LEAKS
Storage Areas x x x x
Storage Tanks/

Pipelines x x x
Loading/Unloading x x x x
Transport Accidents xX xX x x

‘DISPOSAL
Process Waste x x

Off-specification

material x

Cancelled products x xX xX xX
Containers x x x x
Rinsate x

LAND APPLICATION

Leaching* x
Backflow to irrigation well x
Run-~in to wells, sinkholes x
Mixing/loading areas xX

*Leaching potential affected by chemical-physical properties of
pesticide, hydrogeologic setting, and application and culti-
vation practices



and their containers. Generally, contamination from land
application extends over a wide area (a whole farm or farming
region) at very low concentrations which may build up over

the years of pesticide use. Contamination from leaching may
also mix with contamination from chemigation or small spills
at the same site, making it difficult to determine the precise
cause of the problem.

At the present time, there are no techniques available
for cleaning up contamination that involves a large geographical
area, and it is virtually impossible to identify the party or
parties who are responsible since pesticide use is a common
practice. For these "nonpoint" or diffuse sources, prevention
is the key. Prevention efforts will necessarily involve both
regulation of individual pesticides as well as changes in pest
control and land management practices. In most cases, when
there is widespread low levels of contamination, the only
effective means of providing clean water is to either treat
the ground water before use or find an alternate supply.

The table on page 5 summarizes potential sources of con-
tamination at each stage in the production/use cycle.


- 52 -

sealed wells, and pesticide wastes leaking from landfills
and dumps. However, the location and extent of these
problems is not well known (see below).

Where has pesticide contamination occurred and where
is it a potential threat?

While the first three questions seek better understanding
¢ » pesticides reach grounc water, this one seeks

to answer the extent to which it has, or is likely to,
occur. Of course, it is necessary to understand how
contamination occurs in order to know where to look

for it, so these questions are all interrelated.
Exposures to pesticides in ground water are, by their
very nature, localized problems. There may be numerous
sites across the country where these exposures are

occurring. However, the situation at each of these
sites will be the result of a particular combination

of local causative factors. National assessment of
leaching potential must reflect these local factors.

-- A basic need is thus a national pesticides in
ground water information system that will esti-
mate contamination potential based on pesticide
use, farming practices, location and use of
ground water, and hydrogeologic factors that
determine vulnerability to contamination. The
National Survey of Pesticides in Ground Water,
by conducting monitoring and correlating results
with information on local conditions such as his-
torical pesticide use, is designed to perform
this assessment.

-- Up-to-date and accurate pesticide use data is
needed in sufficient detail to pinpoint loadings
in areas of concern. Historical pesticide usage
information is essential for screening potential
"hot spots" and for generating model inputs, but
the data are usually not available.

-- Field data on pesticides in ground water is scarce.
More actual monitoring is needed to help identify
problem chemicals and affected areas.

-- Comprehensive monitoring of "point" sources of
pesticide contamination (spills, leaks, etc.) is
not feasible because the sources are typically
small and detection is difficult. Because such
sources may result in locally severe contamina-
tion, improved detection efforts are needed.


- 35 -

fate model. Link-ups between unsaturated and saturated
zone models attempt to provide a complete picture of
the distance a pesticide will move from its application
point and the alterations it will undergo as it moves
through the soil and into and through ground water.
Saturated zone models can be useful for making com-
parisons among pesticides and different hydrogeologic
settings.

Interaction of Modeling and Monitoring. Monitoring shares
with modeling a common underlying purpose of providing quantita-
tive information on pesticide contamination of ground water.
While modeling is a mathematical approach aimed at predicting
the fate of pesticides in soil and ground water, monitoring
attempts to measure the actual presence and magnitude of pesti-
cides in these media. Monitoring and modeling complement one
another. Modeling can be used to optimize the design of moni-
toring efforts, helping to limit what needs to be monitored
and where. It is also helpful in organizing and interpreting
the results of a monitoring effort. In turn, monitoring pro-
vides the information necessary to develop, improve, and
validate models.

Together, monitoring and modeling provide the basis for
identifying existing ground-water contamination and resulting
exposures and support decisions on remedial actions. These
tools can also be used to predict the likelihood of further
risks and provide the basis for preventative measures, both
at the national and local levels.

Cc. Current Efforts and Understanding

Although ground-water contamination by pesticides is a
relatively recent public concern, there has been a significant
history of research about the environmental fate of pesticides
that has either directly or indirectly provided some under-
standing of the problem. In particular, there has been a great
deal of work on the fate of pesticides in soil. As a result,
we generally know what types of pesticides have the potential
to leach to ground water and what conditions (i.e., type of
soil, hydrology, application method, etc.) determine or influ-
ence the likelihood of a pesticide to leach. We also know of
certain "abnormal situations" (i.e., spills or disposal) or
uses (e.g-, biocides in wells) that can result in serious point
sources of pesticide contamination of ground water. On the
other hand, as a result of limited monitoring and ground-water
fate modeling, we have a basic information gap as to where
pesticide contamination has or could occur and the extent of
subsequent exposures. —


- 24 -

The traditional focus of SCS activities has been on
protecting topsoil. More recently, SCS has turned its atten-~
tion to protecting surface and ground water quality as well.
Several SCS activities will directly or indirectly support
efforts to deal with pesticides in ground water.

SCS soil surveys, completed for most counties, provide
detailed information on soils as well as other information
important for assessing vulnerability to ground-water contami-
nation from the application of agricultural chemicals. SCS
is initiating field studies on pesticides in ground water,
creating a position for a technical specialist on interactions
between pesticides and ground water, and developing a training
program on this subject. Other activities include formulating
an SCS Geographical Information System; developing data on
both the cost-effectiveness of various measures for managing
nonpoint sources and on the quantification of problems and
impacts; ongoing water quality training for Federal, State
and local officials; and reassessment and review of SCS program
targeting, resource, and incentives issues in light of water
quality concerns.

Several other SCS-supported projects also address issues
pertaining to pesticides in ground water. SCS is cooperating
with the University of Rhode Island in a study of the trans-
port of agricultural chemicals into ground water under various
crops and land treatment practices. In South Dakota, SCS is
studying nutrient and pesticide management in combination with
potentials for conservation tillage. In Wisconsin, the Sands
Resource Conservation and Development Project is working with
farmers and other residents to reduce contamination of community
water supplies from agricultural chemicals. Where computers
are available at the field level, SCS also occasionally uses
a model developed by the Agricultural Research Service that
can estimate the potential for ground-water contamination as
individual conservation plans are developed.

Cc. USDA Agricultural Stabilization and Conservation Service

The Agricultural Stabilization and Conservation Service
(ASCS) administers farm commodity, conservation, environmental
protection, and emergency programs related to agricultural
production across the nation. Within ASCS, the Agricultural
Conservation Program (ACP) is charged with helping prevent soil
erosion and water pollution, protecting and improving productive
farm and ranch land, conserving water used in agriculture, pre-
serving and developing wildlife habitat, and encouraging energy
conservation measures. In carrying out this responsibility,
ASCS provides cost-sharing to farmers and ranchers to carry
out conservation and environmental protection practices that


- 40 -

The application of pesticides through irrigation, often
referred to as chemigation, can also be a significant
source of ground-water contamination. An irrigation
pump may shut down due to a mechanical or electrical
failure while the pesticide-adding equipment continues
to operate. This malfunction can cause a backflow of
pesticides into the well or cause highly concentrated
pesticide levels being applied to a field.

Irrigation practices: increase the soil moisture content
and flow through the soil, raising the potential for
chemical leaching. Irrigation can decrease the amount

of volatilization of some pesticides from the soil.
Excess irrigation can also carry pesticides down the

well casings of abandoned or poorly constructed wells,
directly injecting contaminants into an aquifer. The

use of drainage tiles can also lead to direct input of
pesticides into ground water regardless of their leaching
potential.

Cultivation practices: conservation tillage or no-till
practices used to decrease soil erosion and pollutant
runoff into streams will increase water infiltration
and hence potential for pesticides to leach. Further-
more, these practices usually require increased use of
herbicides which may leach. Other soil conservation
practices designed to inhibit runoff may also increase
infiltration.

Spillage/disposal: can result in high concentrations of

pesticides in soil. These "slugs" can overwhelm normal
decomposition processes and soil adsorption capacity,
resulting in high potential for ground-water contami-
nation. Spillage, in particular, can be a common
problem where pesticide mixing and loading take place.

Handling of unwanted pesticides and empty containers
may also pose problems. Rinse water from the cleaning
of spray equipment may also be washed into the soil;
the large amounts of contaminated water associated
with this practice can increase pesticide leaching.

Non-agricultural applications: pesticides used to
control termites are generally injected directly into
foundations or soil and can result in ground-water
contamination due to the large amounts used and the
methods of and potential problems involved in applica-
tion. Oil and gas drilling operations can cause
contamination through the use of pesticides to combat
build-up of scale in well casings.



- 23 -

As USDA's educational arm, CES provides information,
materials, publications, and advice to citizens. It plays a
vital role in educating pesticide users in the safe and proper
use of pesticides. In cooperation with EPA, CES conducts the
training program that pesticide applicators must complete to
be certified for using restricted use pesticides. These
training programs are viewed as a principal mechanism which
can be used to train applicators in ground-water concerns,
and current plans for the program include developing a unit on
ground-water protection. Extension agents also provide advice
on pest control and individual pesticides, and in many States
provide Integrated Pest Management services and advice.

Recently, the Extension Service established a national
Ground-Water Task Force. It surveyed Extension leaders across
the country regarding current activities and future Extension
programming needs related to ground water. Pesticide use and
application ranked as the highest priority, followed by nutrient
use and application, animal wastes, and on-site sewage (septic
tanks). The Extension leaders also see a role for Extension
in providing public education regarding the health effects of
contamination. Other major needs are additional staff training
and better access to technical expertise so that Extension staff
can fulfill their educational role in support of ground-water
protection.

Among current Extension projects addressing pesticides
in ground water are initiatives in New York and Wisconsin to
develop maps on the risk of ground-water contamination using
information from soil surveys and on the properties of commonly
used chemicals. Nebraska is developing an educational program
on chemigation and ground-water protection in general for
national distribution. An educational component is being added
to Iowa's Big Springs Demonstration Project for ground-water
protection, and the State Agricultural Experiment Stations are
conducting a joint initiative on ground-water education and
research.

B. USDA Soil Conservation Service

The Soil Conservation Service (SCS) was created in 1936 to
control erosion that was stripping topsoil from America's farms
at a dangerous rate. Since then, the SCS mission has expanded
to cover three major areas: soil and water conservation, natural
resource surveys, and rural community protection and development.
Since 1982, SCS has recognized water as an inseparable component
of the resource base and has sought to integrate water quality
concerns into all ongoing SCS programs and activities. Among
other activities, the SCS provides direct technical assistance
to landowners in designing and carrying out plans for conserving
soil and protecting water quality.


- 59 -

Since several program offices throughout EPA prepare risk
assessments, over the years, multiple and sometimes conflicting
health numbers have been developed for the same chemical by
different Agency offices. EPA is working to resolve this pro-
blem. A committee has been established to resolve conflicting
health numbers within the Agency and to ensure that for all
future chemical-specific assessments, one Agencywide number is
developed and used.

Cc. Reference Dose as Benchmark

The Reference Dose (formerly known as Acceptable Daily
Intake, or ADI) is the amount of a pesticide or other chemical
that may be taken into the body daily with practical certainty
that injury will not result, even after a lifetime of exposure.
To assess the significance of pesticides in ground water, EPA
has established the Reference Doses for several pesticides which
can be used as benchmarks for determining potential hazard.

The Reference Dose is based on a rigorous evaluation of
animal studies and, when available, human data. Although in
most cases the Reference Dose is based on one or more chronic
feeding studies, other studies such as multigeneration repro-
duction studies may also be used to set a Reference Dose.

The Reference Dose is derived by applying an uncertainty
or safety factor to the results of animal toxicity studies.
More specifically, animal studies are evaluated and the lowest
dose eliciting any type of toxicological response is identified.
This dose is known as the lowest-observed-adverse-effect level
({LOAEL). The dose immediately below the LOAEL in the same study
must, by definition, elicit no toxicologic response and there-
fore is called the no-observed-adverse-effect level (NOAEL).

The NOAEL and thus the Reference Doses are expressed as mg/kg
of body weight per day. The NOAEL from a particular test is
converted into a human Reference Dose by using an appropriate
uncertainty or safety factor, to allow for the uncertainties

in extrapolation from animals to humans and for the differences
in sensitivities which exist within the human population.
Examples of uncertainty factors used by EPA for various types
of effects and durations of testing are listed in the table
below.


I. The Ground Water Resource

Ground water is a vast resource beneath the surface of the
earth. It occurs in aquifers, which are geological formations
that contain enough water to yield usable amounts to wells and
springs. The volume of known ground water in the United States
is about 50 times greater than the total volume of surface
water.

In 1980, about one-fourth of all the fresh water used
in the United States came from ground water. This was a 162
percent increase in ground water use over 1950; the percentage
continues to increase. The principal uses are for irrigation
and public drinking water. While smaller amounts are used in
industries and rural households, the degree of dependence on
ground water for industrial and rural household use is often
higher. Clearly, ground water is critical to millions of
Americans.

The likelihood of pesticide contamination of ground water
and its impact on the environment depend in part on geologic
and hydrologic characteristics that vary from location to loca~
tion. These characteristics determine how quickly ground water
moves, how and whether it is discharged to surface water, how
deep it is below the surface layer, how withdrawing it affects
surface water, how effectively soils filter out pesticides, and
how easily pesticides can enter aquifers. This complex combi-
nation of factors makes it difficult to predict what level or
duration of ground-water contamination a pesticide may cause
at different sites. Because of this uncertainty, discovery
of relatively localized pesticide contamination of groundwater
may be viewed as an indicator of probable, more widespread
contamination.

Movement of Ground Water

In strata containing unconsolidated sand and gravel,
ground water moves as fast as 800 feet a year or more. Ground
water may move even more rapidly through cavernous limestone
formations. In general, however, ground water moves very
slowly. Formations containing layers of consolidated clays
with little fracturing allow ground water to move only a few
inches a year. These slow rates, in most cases, prevent con-
taminants from spreading or mixing quickly, concentrating them
in slow-moving plumes that may remain undetected until water
wells or surface waters are contaminated. Plumes are typically
present for many years -~- sometimes decades or longer.


- 14 -

B. EPA's Ground-Water Protection Strategy

EPA's Ground-Water Protection Strategy, issued in August
1984, sets forth the Agency's policy framework for ground-water
protection in all programs, including pesticides. To foster
implementation of the Strategy, EPA established a new Office
of Ground-Water Protection in Headquarters and ground-water
offices in each of the 10 EPA Regions.

Central to the strategy is a differential protection policy
designed to ensure a level of protection that is appropriate
to the use, value, and vulnerability of the ground water. The
most stringent protection requirements apply in areas where
the ground water is both highly vulnerable to contamination and
either an irreplaceable source of drinking water or ecologically
vital (Class I). The vast majority of the nation's ground water
will be in Class II, where the water is a current or potential
source of drinking water or has other beneficial uses (such as
for irrigation). In these areas, "baseline" protection measures
designed to reduce the risk of contamination apply. Ground
water of little or no potential for future use because of
natural or man-made contamination is defined as Class III.
Here, some relaxation of baseline requirements might be allowed
if the quality of the water is not harmful to human health or
the environment.

To implement this policy, each EPA program that governs
an activity affecting ground-water quality is devising manage-
ment strategies to afford the appropriate level of protection
to each class. These strategies may include such elements as
siting criteria, engineering and performance standards,
operating requirements, monitoring requirements, and best
management practices.

A second major policy in the strategy acknowledges that
States have primary responsibility for ground-water protection.
EPA's role is to set national policy and standards and to pro-
vide the technical and other assistance needed by the States to
improve State capacity to protect ground water. During FY 85
and FY 86, EPA provided $7 and $6.7 million, respectively, in
Section 106 grants under the Clean Water Act to help the States
develop and implement ground-water protection strategies.

All States are now in the process of developing and/or
implementing strategies for ground-water protection. In
addition to using the supplemental Section 106 grant funds
to enhance interagency coordination on ground water issues
generally -~ including coordination with pesticide and agri-
cultural agencies -- several States are using the funds for


- 50 -

E. Remaining Information Needs

While significant advances have been made in our
understanding the behavior, extent, causes, and exposure to
pesticides in ground water, uncertainty remains. We do not
know how widespread the problem is nationwide. We have trouble
determining where, how long, and how much particular pesticides
have been used. We can locate only generally where soil and
rock will permit movement of pesticides to ground water. We
can make crude estimates, at best, about how long pesticides
will persist underground and in what direction they will move.

Such uncertainties impair our ability to determine whether
it is safe to use a particular pesticide in a specific place.
Following is a discussion of the information needed to refine
our basic understanding and clear up these uncertainties.

o Which pesticides have the potential to leach to
ground water?

The chemical characteristics that determine the prob-
ability a particular pesticide will leach are under-
stood. EPA has identified more than a hundred poten-
tial leachers among the pesticides currently being
used, and has collected additional environmental fate
data on them to allow full evaluation of their ground-
water contamination potential. Information about
leaching potential is now required routinely for
registration of all new chemicals and re-registration
of all existing chemicals. With this information,
EPA is now able to determine which chemicals have the
potentia’ to leach.

o What environmental conditions and farming practices
enhance the potential for a pesticide to leach to

ground water?

These conditions are generally understood and are
described under "Factors Influencing Leaching."
Predictive models have been developed to determine
the potential for a chemical to leach. The models
are now being used to give general estimates of
contamination potential over large areas. The
models were not designed to accurately predict
pesticide movement from individual field sites.



-57 -

EPA's method of risk assessment for potential ground-water
contaminants and other chemicals is based on a process first
characterized by the National Academy of Sciences. This risk
assessment process contains four components:

1)

2)

3)

Hazard identification - The determination of whether
a particular chemical is causally linked to particular
health effects. To make this determination, Agency
scientists review and analyze toxicity data; weigh
the evidence that a substance causes various toxic
effects; and evaluate whether toxic effects in one
setting will occur in other settings. The toxicity
data considered include human studies (case reports,
clinical studies, and epidemiologic studies), animal
studies (general and specialized toxicity studies),
and short-term tests often carried out on micro-
organisms.

Dose-response evaluation - The determination of the
relation between the magnitude of exposure and the
probability of occurrence or severity of the health
effects. Dose-response evaluation is performed to
measure the adverse effect that is likely to occur

at the lowest exposure level. It often involves
extrapolation from high to low dose (in animals),
extrapolation from animals to humans, and occasionally
extrapolation of the dose-response relationship from
one exposure route to another.

Human exposure evaluation - The determination of the
extent of human exposure before or after application
of regulatory controls. Three routes of human expo-
sure are considered: ingestion, inhalation, and skin
contact. Agency scientists determine in which media
the substance may be present (water, food, air, soil),
and how people may be exposed (drinking, eating,
inhalation, skin contact). They then identify popu-
lation groups who may be exposed. Finally, they
determine, by actual measurement or by environmental
fate modeling, the concentration of the substance in
these media and the amount of human intake through
exposure to the media (i.e., the magnitude, duration,
and timing of the exposure). Among the many uncertain-
ties associated with each of these steps is that which
may result from comparisons of modeling and actual
monitoring data.



- 30 -

I. Assessing Ground Water Impacts of Pesticides

Once ground water is contaminated, many years may have
to pass before natural processes can return it to its pre-
vious state. Attempts to accelerate the "cleansing" of an
aquifer can prove very costly, if not impossible. Contami-
nation of an aquifer today could preclude its use as a drinking
water source for some time into the future. Even when treat-
ment of the water is technically feasible, the costs may be
prohibitively expensive, particularly for small water systems
and individual well owners. Ground water deserves protection
as a natural resource for both current and future use. It
may not be necessary (and sometimes, not possible) to deter-
mine the extent of exposures that could result from a current
or potential occurrence of ground-water contamination before
remedial or preventive action should be initiated.

Some contamination of ground water by pesticides may,
however, be an unavoidable side-effect of the use of these
chemicals. Such contamination may be acceptable in cases
where there is confidence that no undue risk to human health
or the environment would result either now or in the foresee-
able future. In order to draw conclusions as to presence or
absence of any unreasonable risk, the exposures resulting
from an identified or predicted incidence of ground-water
contamination must be assessed.

As will be shown by the discussion below, significant
strides have already been made in understanding the potential
for ground-water contamination by pesticides. However, there
are also many inherent difficulties in assessing this potential
and limits to the amount of actual monitoring information that
is feasible to collect. Consequently, regulatory decision-
makers base their actions on a mix of information on both
known contamination and predictions of potential drinking
water exposure which could result from the use of pesticides.


- 70 -

CONCLUSION

The potential threat that pesticides pose to ground water
quality -- and thus to an important source of drinking water
for many Americans -- has only recently become widely recog-
nized. The problem raises complex technical, institutional,
and policy challenges for the many agencies at all levels of
government involved in ground-water protection, public health,
and agricultural production. In this report, we have tried
to present the context in which public policy regarding pesti-
cides in ground water will develop.

Steady advances have been made in the last decade, but
many scientific and technical uncertainties remain about the
causes of contamination and under what conditions it is likely
to occur. Relatively little is known about how to reduce the
risk of leaching; the research conducted thus far points to a
few promising directions but has yet to provide conclusive
results. We understand the potential for contamination from
leaks, spills, and disposal of pesticides -- as well as some
techniques for controlling such sources -- but we do not yet
know their relative contribution to the overall contamination
problem.

The health risks presented by trace levels of pesticides
in drinking water can be estimated, but there are inherent
uncertainties built into risk assessment methods as well as a
continuing need for adjustments as new toxicity data becomes
available. Increasing monitoring data and mathematical models
are now available, however, we remain limited in our ability
to predict where and at what levels contamination is occurring
or will occur, and lack information on well locations in
regard to pesticide usage. Thus, it is difficult to estimate
potential human .exposures to contaminated ground water.

There are many efforts now underway to improve our pre-
diction capabilities and exposure calculations. The National
Survey of Pesticides in Drinking Water Wells, in particular,
will provide valuable information. Other monitoring and
research efforts being undertaken by a variety of agencies and
organizations will add to the information base. Clearly, as
more becomes known, we will be in a stronger position to deter-
mine what actions to take both in preventing contamination and
in responding to contamination incidents.


-31-

A. Information Requirements for Contamination and Exposure
Assessment

Determining whether ground water contamination could occur
from the use of pesticides requires information on:

o What pesticides have the potential to leach to ground
water?

Given enough time and the right conditions, many
pesticides are capable of leaching through soil into
ground water. However, some pesticides degrade too
quickly or move too slowly in soil to be considered
much of a threat; others have the capability to move
down into ground water rapidly and intact. The
chemical and physical characteristics of a pesticide
determine its potential as a "leacher."

o What conditions are necessary or enhance the potential
for a pesticide to leach to ground water?

While a pesticide's chemical and physical characteris-
tics determine its potential as a leacher, a number of
factors are involved in determining whether the pesti-
cide will actually leach to ground water. The way a
pesticide is applied, the environment to which it is
applied (soil, rock, topography, water table, weather,
type of crop, etc.), and the other farming activities
being practiced (e.g., irrigation) are just some of
the major determinants in the fate of a pesticide once
released into the environment.

o What conditions other than "normal leaching" can result
in ground-water contamination?

Certain pesticide uses (e.g., biocides in wells) can
result in ground-water contamination by pesticides
which are not usually thought of as being leachers.
Spills or careless disposal of pesticides could also
result in “non-leachers" contaminating ground water.

o Where has pesticide contamination occurred or is
contamination a potential threat?

Years of pesticide use have resulted in contamination
of ground water in several areas around the country.
Efforts must be made to identify other areas where
ground-water contamination by pesticides may require


- 46 -

Extent of Ground-Water Contamination and Exposure. As
discussed in Chapter I, at present we are unable to determine
the extent of the pesticides in ground water problems. While
numerous studies have been conducted for a variety of purposes,
they have provided information about a limited number of pesti-
cides in specific areas.

Table 4 describes some of the current and pending efforts
by EPA, USGS, and some States to monitor for pesticides in
ground water. Other studies are underway in industry and in
other States. Of particular interest are the large~scale
surveys designed to indicate the extent of pesticide contami-
nation in the nation as a whole and in several States (e.g.;
Iowa, Georgia, California).

EPA's National Survey of Pesticides in Drinking Water Wells
is the Agency's major effort to understand how extensive the
problem is nationwide. The survey will give us useful informa-
tion about the distribution of pesticide contamination problems,
some estimates of the number of people affected, and how pesti~
cide usage and hydrogeology relate to pesticide occurrences.
Approximately 50 pesticides are being monitored in 1,500 public
and private wells throughout the country. The survey design
calls for all counties in the U.S. to be categorized according
to four classes of pesticide usage (i.e., high, medium, low,
and uncommon) and three classes of ground-water vulnerability
(i.e., high, medium, low). A predetermined number of counties
will then be selected from each of the 12 strata in the 3x4
matrix. County segments and actual wells to be sampled will
be selected based on criteria which have not yet been specified.
The intent of this survey is to provide a general indication of
the extent of pesticide occurrences across the country as well
as occurrences in areas of particular interest (for example,
farmland where pesticide usage is high and hydrogeological
vulnerability to contamination is high). A final report from

_the national survey is expected in late 1988.

Another broad ground-water "characterization" effort is the
U.S. Geological Survey's Toxic Waste-Ground-Water Contamination
Program. This program will systematically investigate ground-
water quality in relation to human activities, climate, and
hydrogeology within 14 study areas. The intent of these studies
is to help define the type of ground water problems in various
areas of the country. Pesticides will be examined as well as
other organic substances and trace metals. This national
appraisal should be completed in 1988.


- 20 -

Underground Storage Tanks (Subtitle I)

Leaks from underground storage tanks have caused ground-
water contamination in many areas of the country. In 1984,
Congress amended RCRA requiring EPA to established a regulatory
program for prevention, detection, and correction of leaks from
underground tanks storing motor fuels and any chemical on the
"CERCLA list" of toxic substances, which includes many pesti-
cides. Their storage in underground tanks will be governed by
the regulations as they are issued. This will control one
potential source of pesticide contamination of ground water.

F. Comprehensive Emergency Response, Compensation and Liability
Act_(CERCLA)

The Comprehensive Emergency Response, Compensation and
Liability Act of 1980 establishes a trust fund (Superfund) to
finance government responses to releases, or threats of releases,
of hazardous substances that may harm health or the environment.
The Act also authorizes enforcement against those responsible
for the release to require cleanup or to recover the government's
cost of cleaning up. The Act directs EPA to identify a priority
list of at least 400 sites as candidates for remedial action.

At the present time, 124 pesticides are listed as hazardous
substances under CERCLA. Releases of listed pesticides which
exceed the reportable quantity must be reported immediately to
the National Response Center. Reportable quantities are one
pound unless a different quantity has been established by regu-
lation. The reporting requirement does not apply to the appli-
cation of a pesticide or to releases from handling or storing
a pesticide by an agricultural producer. The Agency may respond
to incidents involving other pesticides if they present an
imminent and substantial danger to the public health or welfare.

If ground-water contamination results from lawful applica-
tion of pesticides, the law specifically precludes the use of
CERCLA cost recovery authorities against pesticide applicators
or private users who may be responsible even if their actions
can be fully documented. While the law is clear regarding
cost recovery from pesticide applicators, it does not expressly
preclude use of the Fund for removal, remedial response, or
restoration of the ground water. Several sites contaminated
by pesticides have been proposed for the National Priority List.
In general, however, EPA currently does not plan to initiate
CERCLA responses for sites contaminated by pesticides since
the number of sites is potentially very large and may impose a


- 49 -

TABLE 4, continued

PESTICIDES RESPON-

GRAM PURPOSE LOCATION MONITORED SIBILITY STATUS REMARKS
perfund Hazardous nationwide all haz. OSWER/ ongoing Facility-
nitoring substance substances, states/ spill
clean-up & incl. pesti- owners & oriented.
enforcement cides operators Monitoring
unlikely
where clean-
up is not
feasible.
'RA Haz Detect & eval- nationwide 22? OSWER/ ongoing
ste uate contamin- - uppermost states/
cilities ation; monitor aquifer owners &
mitoring compliance immediately operators
beneath
edge of
waste.
RA Non- Compliance specified In general,  states/ ongoing
z Waste with facility by state contaminants owners &
cilities guidelines regulated operators

nitoring

(Subtitle D)

under the SDWA


- 58 -

4) Risk characterization - The description of the nature
and often the magnitude of human risk, including
attendant uncertainty. Risk characterization inte-
grates the data collected in the first three steps
to characterize the potential risk to humans.

Statistical and biological uncertainties in estimating
the extent of the health effects are always described.

Certain issues are associated with each step of the risk
assessment process, including:

1) Hazard identification issues:
° Use of animal data in evaluating risks to humans
° Negative epidemiological studies

2) Dose-response evaluation issues:

° Extrapolating from high dose to low dose
Extrapolating from animals to humans
° Extrapolating from one exposure route to another

3) Human exposure evaluation issue:

° Modeling vs. ambient monitoring vs.
personal monitoring

4) Risk characterization issue:
° Qualitative or quantitative

Although various uncertainties and issues are involved
at each step of the risk assessment process, it does provide
the Agency with a clear, consistent framework for estimating
the health significance of pesticides in ground water and other
media. This process is sufficiently flexible to permit consi-
deration of different types of data and formulation of different
evaluations and conclusions by different program offices even
in assessing risks associated with the same chemical. This
flexibility is necessary to ensure that the process is useful
to all programs and anyone else who is interested in conducting
risk assessments. However, it is important to recognize that
use of the same basic process can produce different evaluations,
even for the same pesticide, depending upon the data and assump-
tions included.

EPA carries out several risk assessment activities that
are pertinent to pesticides in ground water, and in so doing
generates a variety of health significance numbers. The major
types of these health numbers and their uses are described in
this section.


TABLE OF CONTENTS

INTRODUCTION

CHAPTER 1:
I.

TI.

IIt.

CHAPTER 2:

I.

It.

Ill.

THE PESTICIDES IN GROUND WATER CHALLENGE
The Ground Water RESOULCE. see e cece e eee eee
Sources of Pesticide Contamination.....+...-

TABLE 1: Potential Sources of Pesticide
Contamination of Ground Water.....

Extent of Pesticide Contamination......+..e.

TABLE 2: Pesticides Found in Ground Water
Due to Normal Land Application....

STATUTORY AUTHORITIES AND PROGRAMS
EPA Authorities and ProgramS.+ceessseeeeoeee

A. Federal Insecticide, Fungicide

and Rodenticide Actes cccseeeeseeeeeees
B. EPA's Ground-Water Protection Strategy..
C. Safe Drinking Water Act.rseeeeeesceeeees
D. Clean Water Actecesssssccecccssseeessens
E. Resource Conservation and Recovery Act..
F. Comprehensive Emergency Response,

Compensation and Liability Act........

Programs of Other Federal Agencies.........-

A. USDA Extension Serviceececeeeeccccccveee
B. USDA Soil Conservation Service......+..-
C. USDA Agricultural Stabilization

and Conservation Service. .seesesseeeee
D. USDA Agricultural Research Service......
E. U.S. Geological Survey..sccccececceeeeee

State Programs Addressing Pesticides
in Ground Wateressscessecesecccsucecevesaces

10

10
14
15
16
19

20
22
22
24

25
25

27


- 38 -

Concern for ground-water contamination by pesticides has
led EPA to focus more attention on identifying potential leachers
through the Agency's pesticide registration and re-registration
process. EPA has begun to examine every pesticide for chemical
and physical properties that would, as described above, indicate
their potential to leach. Table 3 provides a summary of the
threshold values for these key factors that would indicate a
pesticide has a high potential to leach. For pesticides identi-
fied as being potential leachers, the Agency will review their
use patterns to assess if other factors may exist that would
increase the likelihood of their leaching (see below).

Soil Factors Affecting Leaching. The type of soil that
receives a pesticide can greatly affect the likelihood of any
leaching. The properties of the soil form one of the two most
important categories of factors affecting leaching potential.
These soil factors include:

o Clay content: refers to the presence of clay minerals.
Clay minerals contribute to cation exchange capacity,
or the ability of the soil to adsorb positively-charged
molecules (i.e. cations). Positively-charged pesticides
will thus be adsorbed to soil containing negatively-
charged clay particles. Clay soils also have a high
surface area which further contributes to adsorption
capacity. Adsorption onto clay colloids leads to
chemical degradation and inactivation of some pesti-
cides, but it inhibits degradation of others.

o Organic matter content: also contributes to adsorption
of pesticides in soil. Organic matter content affects
bioactivity, bioaccumulation, biodegradability, leach-
ability, and volatility of pesticides. Soils with high
organic content adsorb pesticides and therefore inhibit
their movement into ground water. However, pesticides
which are highly adsorbed to organic soil will often be
applied at higher rates by a farmer in order to compen-
sate for the adsorbed portion. There is evidence that
pesticide residues adsorbed to high organic (humus)
soils may eventually be released, intact, to ground
water when microbial degradation of the humus occurs.

o Soil texture: also influences pesticide leaching.
Texture refers to the percent sand, silt, and clay.
Leaching is more rapid and deeper in coarse or light-
textured sandy soils than in fine or heavy-textured
clayed soils.


- 36 -

Following is a summary of what is currently known about
pesticides in ground water and the current efforts underway to
improve our understanding.

The Leachers. As stated above, the study of pesticides
in soil and the corresponding development of soil fate models
pre-dates the concern for ground-water contamination. As a
result, we have a better understanding of the relative leaching
potential of various pesticide classes than perhaps any other
aspect of the problem. Recent monitoring of ground water has
provided data that has improved and confirmed our understanding
of what makes a pesticide a high potential leacher. The following
are the important physical and chemical characteristics of a
pesticide leacher:

o Water solubility: the propensity for a pesticide to
dissolve in water. The higher a pesticide's water
solubility, the greater the amount of pesticide that
can be carried in solution to ground water. Water
solubility of greater than 30ppm has been identified
as a "flag" for a possible pesticide "leacher."

© Soil adsorption: the propensity of a pesticide to
"stick" to soil particles, which is defined as the
ratio of the pesticide concentration in soil (Cg)
to the pesticide concentration in water (KgiC5/Cy).
There are different mechanisms for pesticide adsorp-
tion in soils, with particular important differences
occurring in clays as opposed to organic soil matter.
A second measure, Koc, is used to help characterize
the mechanism of adsorption. Ko ¢ is a measure of
the pesticide adsorption to the organic part of the
soil. The lower a pesticide's Kg and Koo values, the
more likely these chemicals will not be adsorbed to
soil particles but leach to ground water. Of the
pesticides found in ground water to date, most have
had Kg values of less than 5, and usually less than
}.0. These ground-water contaminants have also
generally been shown to have Koc values of less than
300.

o Volatility: the propensity for a pesticide to disperse
into the air is primarily a function of the vapor
pressure of the chemical and is strongly influenced
by environmental conditions (e.g., temperature, wind
speed, etc.). Nonvolatile pesticides such as DDT have
low vapor pressures which will increase their persis-
tence on and in the soil. Pesticides with high vapor
pressures have not been considered a threat to ground


- 61 -

o ODW determines Recommended Maximum Contaminant Levels
(RMCLs)*/ by apportioning the Reference Dose according
to the contribution of the chemical through drinking
water, food, and air. If data are available, the RMCL
is determined by subtracting from the Reference Dose
the known contribution of the contaminant in food
(using food tolerances and other data), and air. If
data are not available, ODW uses an estimation of the
percentage of exposure attributable to an exposure route.
For organic chemicals, the percentage of drinking water
exposure used in the absence of known exposures is 20
percent, and for inorganic chemicals a 10 percent con~
tribution is used, since sources other than drinking
water are more likely carriers for inorganics.

o OPP, in setting pesticide tolerances (that is, residues
that can remain on crops treated by pesticides) ,**/
compares the dietary exposure of the pesticide to
the Reference Dose. OPP has developed and is starting
to use a "Tolerance Assessment System" (TAS) which
calculates distributions of exposure, crop group distri~
butions, and exposures to a pesticide on the day that
a commodity is eaten, as well as averaged exposures
over a period of time. This system may be used to
estimate pesticide exposure on a fairly detailed level
and has the capability of estimating consumption of
a pesticide through drinking water as well as food.
Thus, the estimated exposure that is compared to the
Reference Dose is now as accurate as possible.

To assess exposure for new pesticides, OPP estimates
dietary exposure and characterizes as accurately as
possible the potential for ground-water contamination.
OPP proposes that for those pesticides that have a

high leaching potential, ODW will be requested to
establish a health advisory level and this additional
exposure is considered as a “worst case" drinking water
exposure in the overall exposure estimate. To assess
or reassess exposure for existing, registered pesticides
(which have established tolerances, an OPP~established

*/ See discussion of RMCLs which follows.

**/ See discussion of Tolerances for Pesticide Residues which
follows.


ground water due to normal application to the land, in various
States where monitoring has occurred. In 1984, a total of 12
pesticides were detected in ground water in 18 States. By 1985,
17 pesticides had been detected in 23 States. The Agency
anticipates that additional monitoring will reveal more loca-
tions where pesticides have entered ground water.

As many as 50 other pesticides have been detected in ground
water, but the sources of the contamination are uncertain and
in some cases were the result of accidental spills or leaks
rather than leaching from land application.


= 48 -

TABLE 4, continued

PESTICIDES RESPON-
* PROGRAM PURPOSE LOCATION MONITORED SIBILITY STATUS REMARKS
G-Water Determine Northern many; focus Univ of Funding Expect to
study in ground-wate Towa is on Iowa, Iowa recently complete
northern quality in four herbicides Geological approved study &
Town hydrogeological Survey, final report
settings in OPP in late '87.
agricultural
regions of Iowa
California Understand San Joaquin  EDB, DBCP, California Complete Provided key
Pesticide geographic Valley & Simazine, Dept of Food data for
Movement distribution Riverside Carbofuran. & Agric/OPP EDB emergenc
to Ground of g-water Co. suspension
Water study contamination in '83 and
by pesticides for recent
in 4 aquifers. Simazine
regulatory
actions.
DBCP Determine poten- Maui, Hawaii DBCP OPP & Completed
assessment tial for drinking USGS in 1985
in Maui, water contamina-
Hawaii tion from DBCP
to support
regulatory de-
cision.
Single Registration of Lab All Pesticide Study OPP developin
chemical pesticides studies; registered regis- require- quidelines to
leaching field plots pesticides trants ments improve con-
studies as needed being sistency &
increased reliability o
these studies
Will complete
Fall '86.
Public Compliance nationwide Lindane ODW/ RMCLs have be:
Water with maximum Endrin Public proposed for
Supply contaminant Toxaphene Water about a dozen
Program- levels (MCLs) Methoxychlor Systems pesticides,
SDWA Regu- 2-4-D when they are
lated 2-4-5-T issued as fin
Contaminant MCLs, moni-
monitoring toring will

be required.


~ 54 -

Exposure estimates would also be improved by
obtaining more accurate well density and loca-
tion information in areas with a high potential
for contamination,

More routine monitoring of public and private
wells for pesticides used in their vicinities
would also improve the overall information base.

Because testing is very expensive, improved multi-
residue analytic techniques are also needed.

Improvements in the Quality and Accessiblity of Pesticides

in Ground Water Data is a Basic Need. Groundwater quality efforts

are generally plagued with data quality and data management pro-
blems. Data on pesticides in ground water is no exception.

There is a basic need to improve communications

and data management among the various Federal,
State, and local agencies concerned with pesticides
in ground water. Considerable data exists that

are unknown to ground-water managers who could make
good use of it. A national system for coordinating
data collection, storage, and access is essential.

Ground-water monitoring data is of uncertain
guality. Monitoring and testing are conducted
mostly by State and local agencies without
centralized control. Development of testing
protocols and performance of integrity audits
would help assure data reliability.


CHAPTER TWO

STATUTORY AUTHORITIES AND PROGRAMS

Just as the problem of pesticides in ground water is complex,
so is the array of statutory authorities and programs that
may be used directly or indirectly to prevent or mitigate
contamination. This chapter describes the laws and programs
EPA administers as well as programs of other Federal agencies
and the States which provide the institutional framework for
addressing the pesticides in ground water problems.


ACKNOWLEDGEMENTS

This report presents the findings of EPA's Working Group
on Pesticides in Ground Water, established in 1985 to develop
background materials amd identify issues and aptions for develop~
ment of a strategy to address pesticides in ground water. With
the work of this group as foundation, strategy development has
now been broadened into a major Agency strategic initiative on
agricultural chemicals in ground water, including both pesti-
cides and fertilizers.

Working Group on Pesticides in Ground Water

Co-Chair: Susan Sherman, Deputy Director, Office of Pesticide Programs
Staff Leads: Glen Griser/Carol Panasewich, Special Assistants

Co-Chair: Marian Mlay, Director, Office of Ground-Water Protection
Staff Lead: Donna Fletcher, Senior Analyst

Office Representatives

Office of Pesticides and Toxic Substances
office of Compliance Monitoring-~David Hanneman
Office of Water
Office of Drinking Water--Susan Goldhaber*
Office of Water Regulations and Standards--Carl Myers
Office of Solid Waste and Emergency Response
Office of Emergency and Remedial Response--Rarbara Hostage*
Office of Solid Waste--Reva Rubenstein
Office of Research and Development
Office of Environmental Process and Effects Research--Kenneth Hood
Office of Health and Environmental Assessment--Steven Lutkenhoff
Office of Policy, Planning and Evlatation
Office of Standards and Regulations--Donn Viviani
Office of Management Systems and Evaluation--Peter Truitt*
Office of Environmental and Compliance Monitoring~-Deeohn Ferris
Office of General Counsel--William Jordan
Region IV--Stallings Howell, Kent Williams
Region VII--Timothy Amsden, Leo Alderman

Many, many others participated in the Working Group effort.
We would like to recognize the following individuals whose
contributions were particularly significant: Dennis Athayde,
Robert ‘Barles, Stuart Cohen, Steven Dressing, Richard Hertzberg,
Nancy Parkinson, and Anne Weinberg. Thanks also to Joyce Edwards
and Carolyn Acklin who provided support services to the project.

* Also served as a Subgroup Chair.


CHAPTER THREE
ASSESSING GROUND WATER IMPACTS

AND HEALTH SIGNIFICANCE

The primary reason there is concern about pesticide contamination
of ground water is the potential risks it my pose to human health.
To address this concern, the presence and extent of any actual

or potential risks posed by such contamination must be assessed.
Such assessments must not only identify potential risk, but also
strive to understand the underlying causes of contamination.

This latter objective is necessary, for knowledge of causal
factors provides the basis for both determining appropriate
control measures and developing the capability to predict risks
prior to their realization.

To assess the health risks posed by pesticides, information is
required on both the inherent toxicity of the chemical and the
extent of contact or exposure to the agent. Most of the infor-
mation on the toxicity of a pesticide comes primarily from lab-
oratory animal testing, usually required of the manufacturer for
EPA registration. Exposure information can come from studies of
actual occurrences of environmental contamination and exposures.
Estimates of exposures can also be derived from analyzing the
physical and chemical properties of a pesticide as well as its
current or intended use; these factors are key determinants of
the fate of a pesticide once it is released into the environment.

The primary purpose of this section is to describe the informa-
tion that is critical for identifying or predicting the risks
of pesticide contamination of ground water and for developing
appropriate preventive or remedial measures. The first part

of this chapter focuses on the information required to identify
or predict ground water contamination and subsequent human
exposures. The second part focuses on the toxicity information
required to assess the health consequences of any identified or

predicted exposure.


-71-

From an institutional standpoint, many laws and programs
are already in place to address pesticides in ground water.
The challenge will be to use the existing laws more creatively
and effectively, and to establish workable arrangements between
the many interested Federal, State, and local agencies toward
a common goal of protecting ground (and surface) water quality
while sustaining a viable agriculture. Adjustments in trad-
itional relationships between EPA and the States on pesticide
matters may be needed so that local variability in hydrogeology,
agricultural practices, and pesticide usage can be accommodated
both in determining the risks pesticides pose to ground water
and in designing and implementing appropriate controls.

Especially within the last two years, there has been an
increasing level of interest and commitment to solving the
problem of pesticides in ground water at all levels of govern-
ment. EPA is now developing a national strategy on Agricultural
Chemicals in Ground Water. A majority of States have identified
the problem as a high priority concern, and many are developing
and implementing monitoring programs and control strategies as
part of their State ground-water protection efforts.

Because of the many complex factors involved, it will be
years before the problem of pesticides in ground water will be
fully understood, solutions implemented, and results evidenced.
However, considerable progress is being made -- by EPA as well
as by other Federal, State, and local agencies, researchers,
the pesticide industry, pesticide users, and the interested
public -- toward increasing our understanding of the problem
and finding mutually acceptable solutions. In preparing this
report, a conclusion became apparent: We need to encourage
and take advantage of the best, most innovative thinking about
preventive and remedial approaches and to open new avenues of
cooperation and coordination among all the parties involved to
achieve the greatest overall protection of ground water for
current and future generations. EPA invites all interested
members of our society to join us in meeting the challenges
presented by pesticides in ground water.


- 18 -

and private lands. Local, areawide, and interstate agencies

are responsible for implementing programs in their jurisdic-
tions in coordination with States. The Policy calls for Federal
agencies to integrate nonpoint source concerns, as appropriate,
into their existing programs and delivery systems. EPA, as
required by the CWA, is to serve as the lead Federal agency in
coordinating interagency and State nonpoint source management
actions. And finally, the cooperation and efforts of the private
sector are recognized as a key element.

Agricultural Nonpoint Source Controls. In agricultural
areas, nonpoint source control efforts generally involve devel-
oping and implementing site-specific plans for reducing pollu-
tants from individual farms. Under a variety of arrangements
between Federal, State, and local agencies, the land owner
receives technical and cost-sharing assistance to implement
structural, vegetative, and management practices needed to
reduce soil erosion, and increasingly in more recent years,
to reduce pollution from use of pesticides and fertilizers.
While most of these latter efforts have been designed to
address surface water quality, an increasing number of local
projects are now being refined to control pollutant loadings
to ground water as well. A key feature of some of these efforts
is tying the availability of cost-sharing assistance to partici-
pation in Integrated Pest Management programs.

National Pollutant Discharge Elimination System (NPDES)

Each facility which discharges effluent to the nation's
waterways is required to obtain a permit specifying the amount
of pollutants which may be released. In addition to the dis-
charge permit itself, many facilities are also required to have
plans for handling spills and leaks from materials handling.
While the primary purposes of the National Pollutant Discharge
Elimination System (NPDES) is to protect surface water quality,
reduction in pollutant loadings to surface water also reduce
the risk of ground-water contamination where surface and ground
waters interconnect.

Pesticide manufacturing and formulating facilities as
well as industrial users of pesticides are subject to the NPDES
permit requirements. In late 1985, EPA issued effluent guide-
lines specifically for the pesticides industry which detail the
allowable levels of pesticide ingredients in the waste stream
based on the availability of treatment technology to remove them.


PESTICIDES IN GROUND WATER:

BACKGROUND DOCUMENT

U.S. Environmental Protection Agency

Washington, D.C. 20460

May, 1986


- 41 -

The textile industry uses large volumes of pesticides
to treat finished products for odor control and fungus
growth; poor handling and mixing practices in this
industry could pose threats to ground water. Lastly,
pesticides are widely used to control insect and weed
pests on highway and utility rights of way and on urban
lawns.


- 26 -

costs shared equally by the USGS and cooperating State and

local agencies. Much of the information used for planning,
developing, and managing the nation's water resources is
derived through this program. Areas of investigation are
selected through a collaborative effort between USGS personnel,
with support from outside contractors for drilling and sampling.

The USGS has also proposed a program to describe water
quality on a national scale, called the National Water Quality
Assessment Program (NAWQAP). Other existing USGS activities
include the Regional Aquifer System Analysis Program (RASA),
which focuses on describing ground-water flow and natural
ground-water chemistry in the systems; a National Water
Resources Conditions Program (NWRC) designed to provide infor-
mation about the availability, quantity, quality, and use of
water resources; and a Toxic Waste Ground-Water Contamination
Program, which supports regional field studies, intensive
investigations, and research focused on specific contaminants,
and provides Federal and State agencies with earth-science
information that relates land use and hydrogeology to contami-
nant fate in ground water.

Recent activities under RASA include studies of aquifer
systems in the northern Great Plans, the High Plains, California's
Central Valley and the Snake River Plain. NWRC recently developed
an information system to support the identification of water
issues, characterize current water conditions, and evaluate the
water resources assessment activities of other agencies. The
Toxic Waste Program is investigating the ground-water transport
mechanisms under field conditions for contaminants such as oil,
gasoline, organic chemicals (e.g., pesticides and solvents),
sewage, and heavy metals.

The Department of Interior and EPA have signed a Memorandum
of Understanding (MOU) which covers the two agencies’ relation~
ships and activities related to ground water. Under this MOU,
the USGS and EPA's Office of Pesticide Programs signed an
interagency agreement in 1984 to allow and promote cooperation
in the gathering of information on and assessment of the hydro-
geology of various areas of the nation. This agreement supports
projects that address the vulnerability of the nation's ground-
water supplies to pesticide leaching.


- 34 -

Hence, large-scale monitoring efforts depend, in part, on
statistical designs to estimate the general extent of occur-
rence of contaminants in wells over a large area. Large-scale
efforts also depend on models to provide inferences as to the
dimensions of contamination.

The Role of Modeling. The need to understand the complexity
of the interacting factors that affect pesticide movement and
persistence in soil and in ground water has led to the develop-
ment of mathematical models that quantify and integrate these
factors. These models attempt to simulate the fate of pesti-
cides in the soil environment and their movement to and within
ground water. The two general types of models are ranking
models and dynamic fate models.

The ranking models assign relative weights to a series
of key factors in terms of their importance in determining
the potential for ground-water contamination. Such models
have been used by EPA to identify and rank pesticides for
their potential to leach or locations for their vulnerablity
to such leaching.

Dynamic fate models are much more complex than static
models for they attempt to simulate the transport and trans-
formation of pesticides in the environment over time. They thus
require sophisticated mathematical formulations and are usually
set up on a computer. Dynamic models for predicting ground-
water contamination by pesticides have been developed for the
Saturated zone (below the water table) and the unsaturated zone
(located between the ground surface and above the water table).

o Unsaturated zone fate models predict the amount of
pesticide to leach below a certain point in the soil,
either below the root zone, below one or two meters,
etc. Such models try to predict the solution concen~
tration of a pesticide at a certain depth over time.
Or, a multi-year model simulation can be interpreted
statistically to provide probabilities of certain
occurrences. For example, one may predict that 15%
or more of an applied pesticide will leach below the
root zone 10% of the time. This "10% of the time”
may be interpreted as the worst year in ten.

o Saturated zone fate models attempt to predict the
horizontal and vertical movement of pesticides in and
among aquifers, or the saturated zone. The saturated
zone, lying under the unsaturated zone, has all spaces
or pores filled with water. Output from an unsaturated
zone fate model can be direct input for a saturated zone



- 21 -

disproportionate demand upon the Fund. It should be noted

that nothing in the present law precludes use of enforcement
and cost recovery authorities or Fund expenditures to clean up
pesticide contamination sites caused by a spill, leak, improper
disposal, or other activity not a part of lawful pesticide
application.


III. Extent of Pesticide Contamination

At present, the extent of pesticide contamination of ground
water cannot be determined. Numerous surveys have been under-
taken for different reasons using different design strategies.
These studies have provided information about a limited number
of pesticides in specific areas, but they are small pieces of
a very large and intricate puzzle.

Past monitoring for pesticides in ground water has been
minimal. Before 1979, relatively little systematic water
monitoring was focused on ground water. Surface water and
urban drinking water supplies received almost all the attention.
While a number of urban water systems draw on ground water, they
have been required to routinely monitor for only six pesticides
since 1975: endrin, lindane, methoxychlor, toxaphene, 2,4-D and
2,4,5-T. Of these pesticides, only lindane, methoxychlor, and
2,4-D are still being used to any appreciable extent; most or
all uses of the others have been removed from the marketplace
by EPA. Other ground-water monitoring efforts have focused on
contaminants other than pesticides such as nitrates from
fertilizers, or more recently, organic chemicals from hazardous
waste disposal sites.

Testing of pesticides for their potential to leach through
the soil and contaminate ground water has also been very limited.
Most pesticides on the market today were registered for use
before sophisticated environmental fate testing was routinely
required.

Several major episodes of ground water contamination by
pesticides brought the problem to national attention. Prior to
1979, there was a general belief that ground water was protected
from pesticide contamination by chemical degradation processes
in and on the soil and by impervious layers of subsoil, rock, and
clay. The discovery of DBCP in numerous wells of California's
Central Valley was the first big step in the dismantling of this
long-held belief.

The first discoveries of DBCP in wells were traced to
unlined holding ponds used for disposal by a company producing
the pesticide. Initial reaction was that pesticide contamina-
tion of ground water would only be a problem when large amounts
of these chemicals were placed on the soil as a result of hazard-


- 56 -

pesticides are lacking or inadequate, they are being required
of pesticide registrants for product re-registration and tol-
erence reassessment.

Estimates of human populations actually or potentially
exposed to pesticides through ground water used as drinking
water are less certain, though the Agency is actively working
to increase the information base on this side of the hazard
assessment equation. In the absence of actual exposure data,
the different EPA programs are taking different approaches and
making different assumptions about exposure. These different
assumptions result in the variety of "health numbers" or
safety/acceptable risk levels generated and used throughout
the Agency.

This section describes the risk assessment process used
by EPA to assess the health significance of pesticides in
ground water, and discusses the different health risk numbers
and issues that have resulted as Agency program offices have
brought several statutes, sets of data, and assumptions to
bear on the matter of risks posed by pesticides that may be
found in ground water.

B. Health Risk Assessment for Pesticides in Ground Water

Before an Agency manager may initiate regulatory or
response action on a pesticide posing an unreasonable risk
through its actual or anticipated presence in ground water,
the nature and extent of the risk must be known and charac-
terized. That is, pertinent data and information about the
pesticide and its hazards must be compiled, analy 7, and
evaluated. The resulting risk assessment will be considered
along with other economic, political, and social factors by
the decision maker in arriving at a risk management conclusion.

Risk assessment incorporates both qualitative and quanti-
tative assessments: the qualitative assessment of whether the
risk will occur and the quantitative assessment of the magnitude
of the risk. The need for risk assessment is usually prompted
by the results of research or human experience which suggests
that adverse effects may be caused by the exposure. Assessing
the risks of chronic chemical exposure is complex because the
association between cause and effect is difficult to identify,
particularly when the risk is low or the number of people is
small (as is often the case with pesticide contamination of
particular wells). Risk assessment often involves making
inferences from limited scientific data on the basis of what
we currently know about the underlying biological processes.


- 72 -

SELECTED REFERENCES

Agriculture and Ground Water Quality, 1985. Council for
Agricultural Science and Technology (CAST), Ames, IA

DRASTIC: A Standardized System for Evaluating Ground Water
Pollution Potential Using Hydrgeologic Settings, 1985.

National Water Well Association for Office of Research and
Development, U.S. Environmental Protection Agency, Ada, OK

Evaluation of Existing EPA Methods to Predict, Ground-Water
Pollution Potentials from Pesticide Applications, 1985.
William F. McTernan, EPA/AAAS Environmental Science and
Engineering Fellow (Summer 1985), School of Civil Engineer-
ing, Oklahoma State University, Stillwater, OK

Final Report on the Federal/State/Local Nonpoint Source

Task Force and Recommended National Nonpoint Source Policy,
1985. Office of Water, U.S. Environmental Protection Agency,
Wasington, DC

Groundwater Contamination by Pesticides: A California
Assessment, 1983. Ramlit Associates, Inc., for State Water
Resources Control Board, Sacramento, CA

Ground-Water Protection Strategy, 1984. Office of Ground-
Water Protection, U.S. Environmental Protection Agency,
Washington, DC

Monitoring Ground Water for Pesticides in the "ISA, to be
published in Spring, 1986. S.2. Cohen, C. Eiden, and
M.N. Lorber, Office of Pesticide Programs, U.S. Environ-
mental Protection Agency, Washington, DC

Pesticides and Groundwater Quality: Issues and Problems in
Four States, 1986. Patrick W. Holden, Board on Agriculture,
National Research Council, National Academy of Sciences,
Washington, DC

Potential Pesticide Contamination of Groundwater from
Agricultural Uses, 1984. R.F. Carsel, S.Z. Cohen, S.M.
Creeger and G.C. Enfield, U.S. Environmental Protection
Agency, Wash! gton, DC; Athens, GA; and Ada, OK

State Program riefs: Pesticides in Ground Water, 1986.
Office of Ground-Water Protection, U.S. Environmental
Protection Agency, Washington, DC

Users Manual for the Pesticides Root Zone Model (PRZM),
1984. R.F. Carsel, C.N. Smith, L.A. M,ulkey, J.D Dean, and
P.P. Jowise, Office of Research and Development, U.S.
Environmental Protection Agency, Athens, GA

BUS. Government Printing Office, 1986—671.795 00501


- 42 -

Table 3: Chemical/Physical Properties of Pesticides:
Values Which Indicate Potential
for Ground-Water Contamination

Water solubility ~- greater than 30 ppm

Kg -- less than 5, usually less than 1

Koc -- less than 300-500
Henry's Law Constant -- less than 1072 atm-m73 mol
Speculation ~- negatively charged, fully or

partially at ambient pH
Hydrolysis half-life -- greater than 25 weeks
Photolysis half-life -- greater than 1 week

Field dissipation ~- greater than 3 weeks
half-life



- 44 -

resources, both on a broad-scale and on a local or site-specific
scale where particular problems have been identified. EPA has
agreements with USGS for several cooperative research and moni-
toring efforts and exchange of information in the ground-water
area. Of particular note, USGS will be providing field data

to EPA that should greatly assist further develoment and refine-
ment of predictive ground-water contamination models.

In addition, EPA is also supporting work by others to
develop better understanding of the problem in areas where
ground-water vulnerability to pesticide contamination may be
exceptionally high. For example, EPA has provided assistance
to the study of Iowa's Big Spring Basin area where the ground
is dominantly underlain by carbonate (limestone and dolomite)
rock which holds the region's primary source of drinking water.
In this area, much of the ground water lies close to the surface
and the carbonate rock is highly fractured. The Big Springs
Basin has karst topography where numerous sinkholes, sinking
streams, and blind valleys allow surface water to move rapidly
into the ground water. As a result, karst areas have been
believed to be highly vulnerable to ground-water contamination.
Results from the Big Springs project, however, have shown that
less than a third of the pesticide levels in the area's ground
water is due to the karst condition. Most of the contamination
appears to be due to "normal" leaching from agricultural fields.
The additional contamination due to "run-in" (i.e., contaminated
surface water directly enters ground water through sinkholes)
may, however, result in pesticide levels exceeding thresholds
of basic concern.

EPA is also assessing the impacts of changing agricultural
practices on ground water guality. Of particular interest is
the increasing use of minimum or no-till practices to limit soil
erosion and nonpoint source pollution of surface waters. Such
practices may require a somewhat larger use of herbicides to
control weeds. The heavier use of herbicides and limited run-
off may actually increase pesticide leaching to ground water.
EPA is using its modeling capabilities with extensive field
data in a pilot assessment of the implications of such farming
practices in the Eastern Cornbelt/Lake Erie Drainage Basin.

The pesticides in ground water problem is also being
researched by a number of other Federal and State agencies in
addition to EPA and USGS. The U.S. Department of Agriculture,
through its Agricultural Research Service and through the
funding of State Agricultural Experimental Stations, is a major
sponsor of ground-water research. Research supported by USDA
includes characterization of the source (i.e., quantities of
pesticide used, agricultural practices), examining the fate


Table 2: Typical Positive Results of Pesticide Ground-Water
Monitoring in the U.S.t as a
Result of Normal Land Application

Pesticide Use* State(s) Typical
Positive,
Vo _ —|peb

Alachlor H MD, IA, NE, PA 0.1-10
Aldicarb I, N AR, AZ, CA, FL, 1-50
(sulfoxide MA, ME, NC, NJ,

& sulfone) NY, OR, RI, TX,

VA, WA, WI

Atrazine H PA, IA, NE, WI, MD 0.3-3
Bromacil H FL 300
Carbofuran I, N NY, WI, MD 1-50
Cyanazine H IA, PA 0.1-1.6
DBCP N Az, CA, HI, MD, SC 0.02-20
DCPA (and acid Hq NY 50-700
products)

1,2-Dichloro~ N CA, MD, NY, WA 1-50
_propane

Dinoseb H NY 1-5
Dyfonate I IA 0.1
EDB N CA, FL, GA, SC, 0.05-20
WA, AZ, MA, CT __

Metolachlor H IA, PA 0.1-0.4
Metribuzin H IA 1.0-4.3
Oxamyl I, N NY, RI 5-65
Simazine H CA, PA, MD 0.2-3.0
1,2,3 Trichlor- N CA, HI 0.1-5.0
opropane (impority)

tTotal of 17 different pesticides in a total of 23 different States.

*H = herbicide
insecticide
nematicide

4
"