PROTECTING GROUND WATER:
PESTICIDES AND AGRICULTURAL PRACTICES
U.S.  Environmental Protection Agency
           Office of Water
  Office of  Ground-Water Protection
          401 M Street,  S.w.
           Washington, D.C.
              «'.S. Environmental :
              joglon 5, Library (:
              230 S. Dearborn Stre-- -
              OMcago, IL   60604

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                            FOREWORD
    State and local governments throughout the country are
seeking to address the problem of pesticide contamination as
part of their ground-water protection programs.  Encouraging
the sound choice and management of pesticides is generally
recognized as an important element of these programs, but very
little information has been readily available to aid in
selecting management practices to help reduce the risk of
pesticide contamination.  As part of a continuing effort to
provide information to officials in State and local government
involved in ground-water protection, the Office of Ground-Water
Protection of the U.S. Environmental Protection Agency
initiated a project to identify and evaluate the potential
impacts on ground water of various agronomic, irrigation, and
pesticide application practices.  The results of the study are
presented in this report, "Protecting Ground-Water:  Pesticides
and Agricultural Practices."

    Since site conditions, crop and pest patterns, and agri-
cultural practices vary widely, no single set of
recommendations can be developed that would be appropriate for
all situations. The purpose of this report is to explain the
principles involved in reducing the risk of pesticide
contamination and describe what is known about the impact of
various agricultural practices on pesticide leaching.  With
this basic understanding, it is hoped that water qjuality
officials can work with their colleagues in the agricultural
community to design and implement protection programs suited to
specific conditions in their areas.

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                            PREFACE
    This report, "Protecting Ground-Water:   Pesticides and
Agricultural Practices," was prepared by the Office of
Ground-Water Protection (OGWP), U.S.  Environmental Protection
Agency.  Donna Fletcher, Senior Analyst, OGWP,  served as the
Task Manager and Project Officer.  Ron Hoffer, Director,
Guidelines Implementation Staff, OGWP, provided additional
guidance.  The project was conducted as part of a continuing
effort led by Marian Mlay, Director of OGWP, and Susan Wayland,
Deputy Director of the Office of Pesticide Programs, to address
the problem of pesticides in ground water.

    An EPA technical committee comprised of Dr. Robert Hoist of
the Office of Pesticide Programs,  Robert Carsel of the Office
of Research and Development, Carl Myers of the Office of Water
Regulations and Standards, and Ken Adler of the Office of
Policy Analysis provided technical support arid participated in
the review of preliminary drafts.   Drafts were also reviewed
and discussed by a panel of experts from Federal and State
water quality and agricultural agencies and the industrial,
academic, and environmental communities who are listed on the
next page.

    The report was developed with technical support from
Dames & Moore under EPA Contract No. 68-03-3304.  The principal
contributors to the report from Dames & Moore were
Surya S. Prasad, Ph.D., CPSS, CPAg, Senior Soil Scientist and
Project Manager, and Robert Kalinski, Hydrogeologist.
                                11

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                        ACKNOWLEDGMENTS
    The U.S. Environmental Protection Agency expresses its
appreciation to the following individuals who participated in
the review of preliminary draft reports and a workshop held May
20-22, 1987, in Bethesda, Maryland.


                           Panelists
Timothy Amsden, Office of Ground Water,  U.S.  Environmental
    Protection Agency, Region VII

Dr. James Baker, Department of Agricultural Engineering, Iowa
    State University

Fred Banach, Connecticut Department of Environmental Protection

John E. Blodgett, Environmental and Natural Resources Policy
    Division, Congressional Research Service

Katherine Brunetti, California Department of Food and
    Agriculture

Dr. Rodney DeHan, Florida Department of Environmental
    Regulations

Orlo (Bob) Ehart, Wisconsin Department of Agriculture, Trade and
    Consumer Protection

Thomas J. Gilding, National Agricultural Chemicals Association

Dennis Grams, Nebraska Department of Environmental Control

Dr. George Hallberg, Iowa Department of Natural Resources

Dr. Charles Helling, Pesticide Degredation Laboratory,
    Agricultural Research Service, U.S.  Department of
    Agriculture

Dr. Maureen Hinkle, National Audubon Society

Dr. Patrick Holden, Water Science and Technology Board,
    National Academy of Sciences
                               111

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Russell Jones, Rhone-Poulenc Agricultural Company

Lou Kirkaldie, Soil Conservation Service, U.S.  Department of
    Agriculture

Raymond Knox, South Carolina Department of Health and
    Environmental Control

Dr. Terry Logan, Department of Agronomy, The Ohio State
    University

James Lake, Conservation Technology Information Center,
    National Association of Conservation Districts

Dr. William McTernan, School of Civil Engineering, Oklahoma
    State University

Dr. Richard Maas, Water Quality Group, North Carolina State
    University

Dr. James Schepers, Department of Agronomy, University of
    Nebraska and Agricultural Research Service,
    U.S. Department of Agriculture

Dr. David Schertz, Soil Conservation Service, U.S. Department of
    Agriculture

Velma Smith, Environmental Policy Institute

Dr. Fred Swader, Extension Service, U.S. Department of
    Agriculture

Dr. Heather Wicke, Environmental Law Institute
                               IV

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                          DISCLAIMER
    The mention of trade names of commercial products and
instruments in this report is for illustration and does not
constitute preferential treatment or endorsement or
recommendation for use.
                               v

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               TABLE   OF   CONTENTS
                                                        Page
                                                       Number
        PART I:   OVERVIEW AND OBJECTIVES OF MEASURES
                  TO REDUCE PESTICIDE CONTAMINATION OF
                  GROUND WATER	    1

CHAPTER ONE:  INTRODUCTION 	     2

        Pesticides and Ground-Water Protection
         Programs 	    2
        Background of the Project 	    4
        Scope of the Project	    4
        Organization of Report	    5

CHAPTER TWO:  OVERVIEW OF FACTORS CONTROLLING PESTICIDE
   LEACHING  	     6

        Pesticide Properties Conducive to Leaching.  .    6
        Soil Conditions Conducive to Leaching ....    8
        Other Factors	    13

CHAPTER THREE:   OBJECTIVES OF MITIGATION MEASURES TO
   REDUCE PESTICIDE CONTAMINATION
   OF GROUND WATER	     14

        Minimizing Pesticide Usage   	    15
        Using Pesticides with Lower Leaching
          Potential	    15
        Reducing Pesticide Application at Times
          Most Likely to Promote Leaching 	    15
        Preventing Accidents, Spills, and Pathways
          for Pesticides to Reach Ground Water.  ...    16
        Selecting Combinations of Practices  	    17

        PART II:  POTENTIAL IMPACT OF AGRICULTURAL
                  PRACTICES ON PESTICIDE CONTAMINATION
                  OF GROUND WATER	      19

CHAPTER FOUR:  PESTICIDE APPLICATION
   FACTORS	     20

        Fixed Practices	      20
        Application Methods  	    20
                               VI

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               TABLE   OF   CONTENTS
                           (Continued)
                                                        Page
                                                       Number
        Variable Practices 	      22
        Choice of Pest Control Method	    22
        Application Timing 	    23
        Application Rate and Volume	    27

CHAPTER FIVE:  FARMING PRACTICES 	      29

        Fixed Practices	      29
        Tillage Practices	    29
        Contour Farming	    32
        Terracing	    32
        Contour Stripcropping	    32
        Cover Crops	    33

        Variable Practices 	      33
        Crop Rotation	    .  .    33
        Planting Pest-Resistant Varieties	    35
        Adjusting Planting and Harvesting Times.  ...    35
        Integrated Pest Management 	    35

CHAPTER SIX:  IRRIGATION PRACTICES 	      38

        Fixed Practices	      38
        Methods of Irrigation	    38

        Variable Practices 	      41
        Irrigation Timing	    41
        Irrigation Volume and Frequency	    42

CHAPTER SEVEN:  OTHER PRACTICES TO REDUCE CONTAMINATION
   POTENTIAL	    43

        Handling and Disposal of Pesticides and
          Pesticides Products	    43
        Chemical Anti-Backsiphoning Devices	    46
        Buffer Zone Establishment	    48
        Proper Well Sealing and Abandonment	    49
        Avoiding Sinkholes in Areas of Karst or
          Subsidence	    50
        Sealing of Agricultural Drainage Wells ....    52
        Subsurface Drainage and Treatment	    52
        Farm Ponds and Irrigation Reuse Pits	    53
                               VII

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               TABLE   OF   CONTENTS
                          (Continued)
                                                        Page
                                                       Number
                             TABLES

TABLE   2-1  PHYSICAL AND CHEMICAL CHARACTERISTICS OF
             PESTICIDES INFLUENCING LEACHING
             POTENTIAL	9

TABLE   2-2  PESTICIDES AND RELATED CHEMICALS INCLUDED
             IN EPA'S NATIONAL SURVEY OF PESTICIDES IN
             WELL WATER	10

TABLE   5-1  POSSIBLE EFFECTS OF FARMING FACTORS ON
             QUANTITIES OF PESTICIDES USED	34

TABLE   6-1  POTENTIAL FOR PESTICIDE LEACHING WITH
             VARIOUS METHODS OF IRRIGATION AND
             PESTICIDE APPLICATION 	    39

TABLE   B-l  DEGRADATION RATE CONSTANTS FOR SELECTED
             PESTICIDES ON FOLIAGE 	    B-2

TABLE   B-2  SOIL DEGRADATION RATE CONSTANTS FOR
             SELECTED PESTICIDES 	    B-4

TABLE   D-2  SOURCES OF INFORMATION	D-5


                            FIGURES

FIGURE  4-1  PESTICIDE APPLICATION RELATIVE TO
             CROP GROWTH STAGE, WEED AND PEST
             OCCURRENCE	25

FIGURE  7-1  CHEMIGATION SYSTEM WITH ANTI-BACKSIPHONING
             DEVICE	47

FIGURE  7-2  KARSTIC GROUND-WATER CONDITIONS	51

FIGURE  C-l  PATTERNS OF SOIL ORDERS AND SUBORDERS
             OF THE U.S	    C-2
                              Vlll

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               TABLE   OF   CONTENTS
                           (Continued)
                                                        Page
                                                       Number
                           APPENDICES

APPENDIX A   REFERENCES CITED 	  A-l


APPENDIX B   DEGRADATION RATE CONSTANTS FOR
               SELECTED PESTICIDES	B-l


APPENDIX C   DOMINANT SOIL ORDERS OF THE U.S	C-l


APPENDIX D   INFORMATION SOURCES	D-l
                                IX

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                             PART I


                   OVERVIEW AND OBJECTIVES OF

           MEASURES TO REDUCE PESTICIDE CONTAMINATION

                        OF  GROUND  WATER
        Part I describes the context for ground-water
protection efforts addressing pesticides, the factors
influencing the leaching of pesticides, and the objectives of
measures to reduce pesticide contamination of ground water
                               -1-

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                           CHAPTER ONE

                          INTRODUCTION
Pesticides and Ground-Water Protection Programs	

    Increased awareness of the need to protect the nation's
vital ground-water resources has led to the development of
programs at the Federal, State, and local levels to control
potential sources of contamination.  One of the principal goals
of the U.S. Environmental Protection Agency's (EPA)
Ground-Water Protection Strategy,  issued in 1984, was to
control sources of contamination of particular national
concern.  In the Strategy, pesticides were named as a source
needing additional national attention.  Since that time, the
Agency has increased efforts to review the potential
ground-water impacts of pesticides and take regulatory action
on specific chemicals found to pose a risk to ground water.
The Agency has also initiated a National Survey of Pesticides
in Well Water to better characterize the problem.  In addition,
the Agency conducted an extensive review of the magnitude,
sources, and potential health impacts of pesticides in ground
water and the statutory and program authorities available to
help address the problem.  This work led the Agency to select
the topic of agricultural chemicals in ground water for a major
strategic initiative that is still underway.

    During this same period, many States also began efforts to
understand and address pesticide contamination of ground
water.  These efforts have been stimulated, in part, by the
development of State ground-water protection strategies.  EPA
has supported State strategy development through grants under
Section 106 of the Clean Water Act as a means for strengthening
the capacity of State governments to protect ground-water
quality, another principal goal of EPA's Ground-Water
Protection Strategy.  Nearly all of the State strategies
recognize the need to address pesticides as part of the
ground-water protection program.  However, because the
pesticide contamination problem is a relatively recent
discovery and involves complex technical and institutional
questions, programs to address pesticides in ground water are
less developed than for other sources of contamination.

    The enactment of amendments to the Safe Drinking Water Act
(SDWA) in 1986 provided EPA with a statutory basis for
promoting comprehensive protection of the nation's ground water
as a vital resource.  Under the new Wellhead Protection
                               -2-

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Proaram,  States will be delineating areas around public water
supply wells and instituting management programs to protect
these wells from all sources of potential contamination   EPA
may  provide financial and technical support.   Another SDWA
amendment establishes a demonstration program for protecting
cri?icil aquifer protection areas in designated Sole Source
Aquifers. Since pesticides are a potential source of
contamination for public water supply wells a*d Critical
aquifer protection areas, EPA anticipates that many State and
local governments will seek to develop programs that address
this source.

    The recent reauthorization of the Clean Water Act provides
additional  impetus for addressing pesticide contamination as a
nonpoint source for both surface and ground water.  Under the
new Nonpoint Source Management Program,  States can be eligible
?o receive  funding for ground-water protection activities. EPA
expects that many States will  seek to control pesticide
examination  as part  of their comprehensive nonpoint programs-

    Under  the  Federal  Insecticide, Fungicide, and  Rodenticide
Act  (FIFRA), EPA has  regulatory  responsibility  for determining
whether  a  pesticide  can  be  or  remain  registered  and also  for
specifying  by label,  how the  pesticide  can be  used.   This
aSritygis being  used  to  evaluate the  leaching potential  of
individual chemicals.  Regulatory  actions such  as  label
changes,  restricted use  classification,  and  cancellation  will
continue to be made when needed  to protect ground water.   These
actions  on a chemical-by-chemical  basis  will  define the
chemicals  posing a  risk  to  ground  water  and  establish
 requirements for using these chemicals.

     While regulatory actions on specific chemicals are a
 fundamental element of efforts to  control pesticide
 c^Safion  State and local governments will also  be seeking
 to address pesticides in the broader context of their
 around-water protection programs and in a way that is suited to
 ?hHgr!cu!tu?a? conditions in their areas.   These programs
 will be looking beyond the pesticide regulatory Process for
 ways to manage pesticide use to minimize risks to ground water
 resources.
     The Aaencv recognizes that technical information on
 practices^ Ld^hese risks  is needed to help  in the design
 and implementation of programs addressing pesticide
 cont^inatfon at the State  and local  levels.  To help meet  this
 need  EPA's Office of Ground-Water Protection undertook a study
 ?o evaluate the potential ground-water  impacts  of  various
 agronomic  and pesticide  application practices.  Since there has
 Sen  °nly  limited  research  in this area, the Agency  also  drew
                                -3-

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together experts in the field to gain their insights into what
steps can be taken to reduce risks of pesticide contamination.
This report presents the findings of the study and expert panel
discussions.
Background of the Project	

    As mentioned earlier, the Agency is now developing a
strategy for agricultural chemicals in ground water as an out-
growth of preliminary investigations to understand the scope of
the problem and identify policy issues.  Findings of the
initial working group on pesticides in ground water, co-led by
the Office of Pesticide Programs and Office of Ground-Water
Protection, were published in a 1986 report entitled
"Pesticides in Ground Water:  Background Document."  Readers
seeking a detailed discussion of the extent and causes of
pesticide contamination, its potential environmental and human
health impacts, and the statutory authorities and programs
available to address it should obtain a copy from the Office of
Ground-Water Protection, U.S. Environmental Protection Agency,
WH-550-G, Washington, D.C. 20460.

    In exploring potential solutions, it soon became apparent
that little information was readily available to aid in
selecting management practices that would help reduce the risk
of contaminating ground water from pesticide use.  Recognizing
that encouraging sound choice and management of pesticides
would be an important element of ground-water protection
programs at all levels of government, the Office of
Ground-Water Protection initiated a project to identify and
evaluate the potential impact of various agronomic and
pesticide application practices on ground water.

    This report presents the results of an extensive literature
review and interviews with experts in several disciplines.  The
draft report was reviewed by a panel of experts from the
research community, Federal and State agriculture and water
quality agencies, and industry and environmental organizations
who participated in a three day workshop to discuss the
findings to assure that they represent the best professional
judgement now available on this topic.
Scope of the Project	

    The problem of pesticides in ground water is extremely
complex.  Pesticides can enter ground water from activities at
any point in their manufacture, commercial distribution,
storage, use on land or in industrial settings, and disposal.
                              -4-

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The leaks, spills/ and other releases that can occur wherever
bulk pesticides are stored, handled, or disposed of can result
in ground-water contamination; several laws and regulations
already address these potential sources.

    By far, pesticides are most commonly used to control in-
sect and weed pests on the land.  While they are also used on
lawns and gardens, forest lands, and rights of way, the
greatest use of pesticides is on land in crop production.
Under certain conditions, some pesticides applied to the land
can leach to the ground water from normal application.   Tne
focus of this report is on reducing leaching from agricultural
use of pesticides; some practices to minimize on-farm releases
and spills are also addressed.  It should be noted that many of
the considerations and practices suggested may also apply to
non-agricultural use of pesticides.

    It is recognized that long-term solutions to the problem of
pesticides in ground water could involve changes in how and
where crops are grown, implementation of pest control metnods
that are less chemically dependent, and development and use of
new chemicals that present a lower risk to ground water and
human health.  This report, however, assumes tnat in the more
immediate term, farmers will continue growing crops in areas
where ground water may be vulnerable to contamination and will
be using chemicals that have some potential to leach.  The
purpose of the report is to provide State and local regulatory
officials with technical information pertaining to measures for
reducing pesticide leaching to ground water that can aid in the
design of programs to prevent ground-water contamination from
pesticides.
Organization of Report	

    Part I of this report contains background information on
the pesticide properties, site conditions, and other factors
influencing the likelihood of pesticide contamination.  It also
contains an overview of basic principles for reducing pesticide
contamination that provides a framework for developing and
implementing protection measures.

    Part II of the report contains detailed discussions of tne
potential impacts of various farming, pesticide application,
and irrigation practices on pesticide leaching.  Tnis
information can be used as a starting point for development and
fostering use of management practices that are appropriate to
the conditions in a particular area.

    The appendices contain references, national maps of soils
and climatic conditions, and a list of other sources that can
provide information useful in the development of ground-water
protection programs addressing pesticides.
                              -5-

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                          CHAPTER TWO

       OVERVIEW OF FACTORS CONTROLLING PESTICIDE LEACHING
    A complex set of factors influence the likelihood of
pesticide contamination of ground water in a given location:
the physical and chemical properties of the pesticide, natural
hydrogeologic and man-made features at the site of application,
and the agronomic and pesticide application practices
employed.  The following summary of pesticide properties and
site conditions most conducive to leaching is provided as
background for the more detailed discussion of practices
influencing leaching potential that are the primary focus of
this report.
Pesticide Properties Conducive to Leaching	

    Although ground-water contamination by pesticides is a
relatively recent public concern, a significant amount of
research on the environmental fate of pesticides has either
directly or indirectly provided some understanding of the
problem.  In particular, a great deal of work addresses the
fate of pesticides in soil.   As a result, a better
understanding of the relative leaching potential of various
pesticide classes exists than perhaps any other aspect of the
problem.  Recent monitoring of ground water has provided data
that have improved and confirmed understanding of what makes a
pesticide more likely to leach.  The following are the
important physical and chemical characteristics of a pesticide
that may make it conducive to leaching, based on current
scientific understanding (EPA, 1986) .

         Water solubility:   the propensity for a pesticide to
         dissolve in water.   The higher a non-ionic pesticide's
         water solubility,  the greater the amount of pesticide
         that can be carried in solution to surface water and
         ground water.  Water solubility of greater than 30 ppm
         has been identified as a "flag" for the possibility of
         a pesticide to leach.

         Soil adsorption:   the propensity of a pesticide to
         adhere to soil particles, which is defined as the
         ratio of the pesticide concentration in soil (Cs) to
         the pesticide concentration in water (K^;
         CS/-CW).  There are different mechanisms for
                              -6-

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        pesticide  adsorption  in  soils, with particularly
        important  differences  between  clays and  soil  organic
        matter.  A second  measure,  Koc,  is used  to  help ^
        characterize the mechanism  of  adsorption.   Koc  is  a
        measure  of the pesticide adsorption to the  organic
        component  of the  soil.   The lower  a pesticide s Kd
        and Koc  values, the less likely  these chemicals J^?;
        be adsorbed to soil particles  and  the more  likeJY  they
        will leach to ground water.  Of  the pesticides  found
        In ground  wate? to date, most  have had K£ values  of
        less than  5, and usually less  than 1.  These
        ground-water contaminants have also  generally been
        shown to have Koc values of less than 300.

        Volatility:  the propensity for a pesticide to dis-
        ^r^FTnto the air.  Volatility is primarily a     _
        function of_the vapor_ pressure^^the^hemical^and is ^

                                 r.
        wa?er Solubility  can  cause pesticides with  high vapor
                                         '1
         rainfall.

         ||Mlff^ip-ionm?n1so?l9Sra^ymmeSasu?eras

         ^-ha?f?he^^rent?^lofot°a^s?l&d£often
         referred to as a pesticide's soil half-lite.

                    of pesticides in soil is dependent on a
nunfceoenvr
several decomposition processes that cause chemical breakdown,

^sforma^
wa?er   Photolysis is the breakdown of a chemical from exposure
to the energy of the sun.  And, microbial transformations
resul? f^the metabolic activities of microorganisms within
the soil   When a pesticide resists these decomposition
processes and does^ot readily evaporate, ^^^'^

                                          Le   st?  i e Fi""*

            era
    or three weeks   y have a higher potential  to  leach to
ground water.
                               -7-

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    Concern for ground-water contamination by pesticides has
led EPA to focus more attention on identifying those having the
greatest potential to leach 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 2-1 provides a summary of the threshold values
for those key factors indicating that a pesticide has a high
potential to leach.   It is important to note, however, that no
single threshold will indicate leachability.

    Presently, insufficient data exist to state with certainty
which pesticides have the greatest potential  to leach from
normal application to land.  In preparing for the National
Survey of Pesticides in Well Water, however,  EPA developed a
list of pesticides suspected, of having a potential to leach
based on their properties, use patterns, and available
monitoring data.  The pesticides shown in Table 2-2, along with
selected pesticide metabolites or degradation products, are the
pesticides included in the National Survey.  Pesticides marked
with an asterisk on the list are those for which monitoring
data shows the pesticide has leached .as a result of normal
use.  Other pesticides shown are those that EPA considers,
based on current knowledge, to have the potential to leach to
ground water.
Soil Conditions Conducive to Leaching	

    The site conditions at the area receiving a pesticide can
greatly affect the likelihood of any leaching.  The composition
and properties of the soil are the two most important factors
affecting leaching potential.  These factors are discussed
below.

    Soil Composition

         Clay minerals content:   contributes to cation exchange
         capacity (CEC), the ability of the soil to adsorb
         positively charged ions or molecules (i.e., cations).
         Positively charged pesticides may be adsorbed to soil
         containing negatively charged clay particles.

         Clay soils:   defined as soils with a predominance of
         particles less than 2 micrograms in size; particle
         size is generally proportional to the amount of clay
         mineral contained.  They have a high surface area
         which contributes further to adsorption capacity.
         Adsorption onto clay colloids leads to chemical
         degradation and inactivation of some pesticides, but
         it inhibits degradation of others.
                               -8-

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TABLE 2-1-   PHYSICAL AND CHEMICAL CHARACTERISTICS OF PESTICIDES
                 INFLUENCING LEACHING POTENTIAL
Pesticide Characteristic
Value or Ranged
Water solubility
Koc
Henry's Law Constant
Spec i at ion

Hydrolysis half-life
Photolysis half-life
Field  dissipation half-life
Greater than 30 ppm
Less than 5, usually less than 1
Less than 300 - 500
Less than 10~2 atm-m"3 mol
Negatively  charged, fully or
partially at ambient pH
Greater than 25 weeks
Greater than l week
Greater than 3 weeks
 contamination .
 Source:   U.S. EPA, 1986
                indicating the potential for ground-water
                                 -9-

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 TABLE 2-2:
PESTICIDES AND RELATED CHEMICALS INCLUDED
 IN EPA's NATIONAL SURVEY OF PESTICIDES
              IN WELL WATER
Acifluorfen  (H)
Alachlor  (H)
Aldicarb  (I)
Ametryn (H)
Atrazine  (H)
Bromacil  (H)
Butylate  (H)
Carbaryl  (I)
Carbofuran (I)
Carbofuran-3-OH
Carboxin  (F)
Chloramben (H)
alpha-Chlordane (I)
gamma-Chlordane (I)
Chlorothalonil (F)
Cyanazine (H)
Cycloate  (H)
2,4-D (H)
Dalapon (H)
Dibromochloropropane (N)
DCPA (H)
Diazinon  (I)
Dicamba (H)
3,5-Dichlorobenzoic acid (H,I)
1,2-Dichloropropane (N)
Dieldrin  (I)
                          PESTICIDES
                           Dinoseb (H)
                           Diphenamid (H)
                           Disulfoton (I)
                           Diuron (H)
                           Endrin (I)
                           Ethylene dibromide (I,N)
                           Fluometuron  (H)
                           Heptachlor (I)
                           Hexachlorobenzene(s)
                           Methomyl (I,N)
                           Methoxychlor (I)
                           Metolachlor  (H)
                           Metribuzin (H)
                           Oxamyl (I)
                           Pentachlorophenol (H)
                           Picloram (H)
                           Propachlor (H)
                           Propazine (H)
                           Propham (H)
                           Propoxur (I)
                           Simazine (H)
                           2,4,5-T (H)
                           2,4,5-TP (H)
                           Tebuthiuron  (H)
                           Terbacil (H)
                           Trifluralin  (H)
These pesticides and related chemicals are considered by EPA to
have the greatest potential for leaching to ground water.

F - Fungicide
H - Herbicide
I - Insecticide
N - Nematicide
S - Seed Protectant
                              -10-

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                     TABLE 2-2  (continued)
                     PESTICIDE METABOLITES
Aldicarb sulfone                  Fenamiphos sulfoxide
Aldicarb sulfoxide                Heptachlor epoxide
Atrazine, dealkylated             Hexazinone
Carboxin sulfoxide                Methyl paraoxon
DCPA acid metabolites             Metribuzin DA
5-Hydroxy dicamba                 Metribuzin DADK
Disulfoton sulfone                Metribuzin DK
ETU                               Pronamide metabolite, RH 24850
Fenamiphos sulfone
Source:  U.S. EPA, 1986
                               -11-

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          Organic matter content:  contributes to adsorption of
          pesticides  in soil.  Organic matter content affects
          biological  activity, bioaccumulation, biodegrad-
          ability,  leachability, and volatility of pesticides.
          Soils with  high organic content adsorb pesticides and
          therefore inhibit their movement into ground water.

     Soil  Physical Properties

          Soil texture:  refers to the relative proportion of
          different sizes of soil particles (i.e., percent sand,
          silt, and clay).  Leaching is more rapid and deeper in
          coarse or light (sand textured) soils than in fine or
          heavy (clay) soils.

          Soil structure:  refers to the way soil grains are
          grouped together into larger aggregates - platy,
          prismatic,  blocky, or spheroidal (granular and crumb).
          Structure is affected by texture and percent of
          organic matter.  Pesticides and water can seep,
          relatively  unimpeded, through seams between the
          aggregates.

          Porosity:   is a function of pore size and pore size
          distribution determined by soil texture, structure,
          and particle shape.  Pesticides are more likely to be
          transported to a greater degree through more porous
          soils, all  other things being equal.

          Soil moisture:   refers to the presence of water in
          soil.  The  soil water ultimately transports pesticides
          that are not adsorbed onto soil particles in the
          unsaturated bone to the water table below.  Upward
          movement may also occur through capillary action and
          evapotranspiration (evaporation from open bodies of
          water and soil  surfaces and the uptake of soil
          moisture and release to the atmosphere by plants).

    The factors described above are considered important in
evaluating leaching potential at a site based on standard
concepts  of water and chemical movement through porous media.
However,  recent studies  (Hallberg,  1986) indicate that
preferential flow (of water and solutes) through soil
macropores may be a major cause of pesticide leaching to ground
water under various soil and climatic conditions.

    Under standard concepts of flow through porous media, sandy
soils should provide  a higher potential for pesticide leaching
than clayey soils.   However, clayey soils may tend to be well
structured and contain a high number of macropores which may
enhance the potential for rapid leaching.  In addition,
                              -12-

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dessication of clayey soils may result in prominent  shrinkage
cracks.   Rainfall or irrigation,  water flowing preferentially
along such features may promote leaching,  even when  other
pesticide properties and site conditions are not conducive to
leaching.

    Appendix C contains a national map prepared by the Soil
Conservation Service of the patterns of soil orders  and
suborders of the United States.  More detailed local
information on soils is available from State and district
offices of the Soil Conservation Service.

Other Factors	     ..	—	

    Several other factors also affect pesticide leaching
potential and the likelihood for ground water contamination.
Depth to ground water and permeability of the material in the
vadose (unsaturated) zone are considered particularly important
in determining vulnerability to pesticide contamination.  Areas
of karstic hydrogeologic conditions, found in many regions of
the United States are also particularly vulnerable to
contamination.  Hydrogeologic  information may be available from
State geological survey offices and/or district offices of the
U.S. Geological Survey in some areas of the country.  Well
drilling logs are another possible source of  information,
although they tend to be of  inconsistent quality.

    The  amount and seasonal  variation  in the  amount of
recharge—rainfall and irrigation—is  another  important factor
influencing leaching potential.  Areas with high rates  of
infiltration  from rainfall or  irrigation water  have large
amounts  of water passing through the  soil,  and  therefore  are
more susceptible to  leaching.  Average monthly  precipitation
data are recorded at numerous  stations  around the country  and
are available from several publications,  including van  der
Leeden and Troise  (1974).  Several methods  of  calculating
evaporation and  evapotranspiration are given  in Dunne and
Leopold  (1978).  One of the  more  common methods is  the
Thornthwaite  method, which uses  air  temperature as  an index of
the energy available for evapotranspiration.   Average monthly
air temperature  for  numerous stations  is  also available from
van der  Leeden and Troise  (1974).

    Man-made  site  features  such  as poorly constructed water
supply wells, agricultural  drainage  wells,  and faulty check
valves on  chemigation  systems  also  influence  whether  a
pesticide  will reach ground  water.   These features  can lead to
"short circuiting"  or  the  creation  of pathways for  pesticides
to  enter ground  water  without  filtering though soil.
                               -13-

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                         CHAPTER THREE

          OBJECTIVES OF MITIGATION MEASURES TO REDUCE
            PESTICIDE CONTAMINATION OF GROUND WATER
     Since  site conditions, pest and crop patterns, and
 agricultural practices vary widely, no specific recommendations
 for  practices to reduce the risk of pesticide contamination can
 be developed that are appropriate for all situations.
 Generally, however, measures to protect ground water from
 pesticides achieve one or more of the following objectives:

     --Reduction of the quantity of pesticides used.
     --Use of pesticides with less potential to leach.
     --Avoidance of pesticide application when conditions are
      most likely to promote leacning.
     --Prevention of spills and elimination of pathways for
      entry of pesticides to ground water.

     Tne potential impacts on leaching of various farming,
pesticide application, irrigation, and other agricultural
practices are discussed in detail in Part II of this report,
along with suggestions for measures that can be taken with each
practice to minimize leaching.  Many agricultural practices are
 "fixed";* that is, they are either impractical to change or
serve another important environmental purpose such as reducing
soil erosion or surface runoff.  Other practices are
"variable"; that is, they are more amenable to cnanges in
management such as timing or rate of pesticide application.

     Designing a program to promote tne use of good practices to
reduce pesticide contamination risks requires an understanding
of the type(s)  of agriculture and agricultural practices that
are common or typical in the area.  This knowledge forms the
basis for identifying specific practices that might be promoted
as well as the particular technical assistance needs of tne
area's agricultural producers.


* No practice is ever completely "fixed," since there is always
the potential to change crops, tillage equipment,  etc.  The
term is used because of the major investment likely to be
involved in changing or because they are in place to achieve
other important benefits.
                             -14-

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    An obvious part of any plan to reduce  the  potential  for
leaching of pesticides into ground water  is  minimizing the
   r
                                                        I-
integrated pest management (IPM) system.

    IPM is an integrated approach to pest control that involves
pe
Case studies have shown that pesticide use can  e greatly
      ?
 tha?  inKuence  those  pests;  and after considering  the concepts,
 Extension specialists  or  pest consultants.
 Using Pesticides with Lower beaching Potential
     As described in Chapter Two,  studies have shown that
                    rthe^o^enLKlorlharpestlcide to leach
                  .  NumerouS pesticides have been proven
        I
 with lower leaching potential should be encouraged,
 particularly in areas with vulnerable conditions.
 Reducing Pesticide Application at Times Most i^exy
 Promote Leaching
     While many of  the  site conditions conducive  to  leaching  are
 natural? occurring, various  farming and  irrigation practices
                               -15-

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 can  increase  or  decrease the  likelihood that pesticides will
 leach.  When  soils  are at or  near saturation or have many
 macropores  or  cracks, conditions are particularly conducive to
 leaching.

     Some  farming practices can help reduce the potential for
 pesticide leaching  by enhancing the soil's ability to retain
 moisture  or adsorb  or degrade pesticides.  Other practices,
 however,  may  promote leaching.  Ponding of runoff water high  in
 pesticides may promote infiltration into the ground.  Certain
 tillage practices may foster  the formation of macropores which
 enhance infiltration.  Chapter Five in Part II describes the
 impact of a variety of tillage and other farming practices on
 leaching.

     The method and  timing of  irrigation and pesticide
 application can  also create site conditions that are conducive
 to pesticide  leaching.  With  some irrigation methods, soils are
 kept at or near  full saturation.  This condition can promote
 pesticide leaching  when normally adsorbed pesticides desorb
 from soil particles and become available to leach into ground
 water.  In addition, improper and/or excessive irrigation can
 promote leaching of surface-applied or soil-incorporated
 pesticides by  moving dissolved pesticides through soil.  The
 potential impact of various irrigation methods and timing of
 pesticide applications are discussed in Chapter Four of Part  II

     In many areas of the United States,, site conditions may be
 conducive to  leaching either naturally or as a result of
 irrigation.  In general, site conditions that are conducive to
 leaching  occur when ground-water recharge rates are high and
 significant guantities of water move downward.  This can occur
 in areas  where infiltration is significantly higher than
 evapotranspiration, and/or where soils are highly permeable.
 This is particularly a problem in irrigated semi-arid or arid
 regions of the United States where infiltration of irrigation
 water leaching from agricultural fields is the primary source
 of ground-water  recharge.  High ground-water recharge rates
 alone, however,  do not necessarily indicate that concentrations
 of pesticides will reach levels of concern because the
 pesticides may be sorbed to soil or degraded before reaching
 ground water.
Preventing Accidents, Spills, and Pathways for Pesticides
to Reach Ground Water	

    Contamination of ground water can also be avoided by proper
pesticide handling and by eliminating pathways for pesticides
to enter ground water from the ground surface or from surface
water.   Contamination by any pesticide, regardless of its
leaching potential, can result from spills and leaks or entry
by direct pathways.

                              -16-

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    In the steps between the purchase and application of
pesticides, pesticides may be spilled or released into the
environment at any time or place during transport,  storage or
handling.  Depending on site conditions and the amount of
pesticide involved, movement of the released pesticide to
ground-water can occur.  Ground water contamination is a
particular concern if spilled pesticides build up in soil, sucn
as can happen if application equipment is loaded or cleaned in
one designated area repeatedly.  Careful storage and handling
of pesticides can help to minimize spillage and waste.

    Improperly constructed or abandoned irrigation or drinking
water wells can provide a direct pathway for pesticides to
enter ground water.  In ungrouted wells, especially those
located in topographic depressions susceptible to surface
runoff, water may be able to run down the outside (or even the
inside) of the well casing directly into ground-water
supplies.  In addition, pesticide-laden surface runoff water
may enter ground water through abandoned wells that are not
sealed properly or covered.  Pesticides may also enter ground
water via irrigation wells connected to chemigation systems
unequipped with check valves to prevent back-siphoning of
chemicals into the well.

    In developing measures to reduce the impacts of pesticides,
the relationship between ground water and surface water should
also be considered.  Surface water bodies that are susceptible
to runoff from agricultural fields, such as irrigation reuse
pits or farm ponds, may contain high amounts of pesticides.
Although such surface water bodies may not serve as direct
sources of drinking water, they may recharge ground-water
supplies.  Futhermore, where ground water discharges  to surface
water, it is possible for any ground water that is contaminated
with pesticides to adversely impact surface water supplies.

    Measures to avoid contamination from leaks and spills and
to reduce direct pathways for contamination are discussed in
Chapter Seven of Part II.


Selecting Combinations of Practices	

    While the broad objectives described in tnis chapter  set
forth  an overall framework for reducing the risk of pesticide
contamination from crop production, determining which practices
can and should be promoted involves analysis of the particular
conditions, needs, and capabilities of farms in the area  of
concern.  Design of specific measures may  ultimately  need to  be
done at the individual farm level.  Technical  assistance  in
determining appropriate measures  is available  from a  variety  of
agencies  (see Appendix D) .
                              -17-

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     In the development and external  review of this report  one
 overriding recommendation emerged thajt_Js__apprnpriat-p fnr 311
                                          _
 conditionsj	£esticide_use_should be reducedtoonlT'that which
 is essential.   While biological  methods of~^esT control  have	
 not yet been developed for all crop and pest situations,  the
 principles of integrated pest management, which include  a
 variety of chemical,  biological,  and non-chemical  methods,
 should be applied to the extent  feasible.   Reducing pesticide
 use protects not  only ground water,  but also the environment in
 general—and particularly,  the farm family  and farm community.
 Reduced chemical  inputs  can also  improve farm profitability,
 and may help in addressing the increasing pest resistance
 problem.

     Selection of  appropriate measures is influenced to a  large
 extent by the topography and soil  type of the site.   For
 example,  flat  fields  of  sandy soils  with low adsorptive
 capacity and high permeability, where ground-water is recharged
 primarily from infiltration of irrigation water,  require
 specific  mitigation  measures. In  such cases,  one should
 concentrate  on reducing  the quantity of pesticides used,
 carefully managing water  use, timing applications  for when  site
 conditions are less  likely  to promote leaching,  and increasing
 the  ability  of the soil  to  adsorb  and/or degrade pesticides.

     By contrast,  for  a hilly site  with clay-rich soils of low
 permeability and  high  adsorbtive capacity,  where the  ground
 water  is  generally of  low vulnerability to  contamination,
 practices  to reduce  soil  erosion and control  surface  runoff are
 likely to  be in place.  Here, leaching is less likely, so
 mitigation^would  focus on other pathways to ground-water.   For
 these  settings, mitigation  measures  should  concentrate on
 reducing  the quantity of  pesticide used (so that both surface
 and  ground-water  are protected) and  minimizing the potential
 for  pathways such  as farm ponds and  irrigation re-use pits  to
 adversely  affect ground water.

     In Part  II, the potential impact  on ground water of a wide
 range  of  agricultural practices is discussed  in  detail. The
 information  is presented  to  suggest  possible  measures that,
when tailored  to  local conditions, can  be incorporated into
ground-water protection efforts.    Appendix  D  contains a
description  of agencies and  organizations with expertise  in
agriculture, soil  science,  and hydrogeology who  can provide
more detailed  information on conditions  and practices on  a  more
localized  level.
                              -18-

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                            PART II


                      POTENTIAL IMPACT OF

                     AGRICULTURAL  PRACTICES

                   ON PESTICIDE CONTAMINATION

                        OF GROUND WATER
    This part contains discussions of the potential impact of
pesticide application, farming,  irrigation,  and other practices
on pesticide contamination of groundwater.   Each section
separates "fixed" practices, which are impractical_to change or
otherwise essential, from "variable" practices, which are more
amenable to change to accomplish ground water protection
(and/or other) objectives.  Note that no practice is ever
completely "fixed"; the term is used because of the major
investment likely to be involved in changing or because such
practices are in place to achieve other important benefits.
                              -19-

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                          CHAPTER FOUR

                 PESTICIDE APPLICATION FACTORS
    A carefully adopted plan for pest management can play a
significant role in helping reduce the potential for pesticide
leaching to ground water.  Tne plan should include choosing the
most appropriate pest control method.  Whenever possible/
consider factors such as:  choosing a pesticide with low
leaching potential; properly timing pesticide application
relative to climate, crop stage, and weed and insect
populations; controlling the volume and frequency of
application; and using the correct form of pesticide.
Potential impacts of these factors on pesticide leaching are
discussed individually in the sections that follow.
	Fixed Practices	

    The method of application is generally considered a fixed
practice because it is dependent upon the equipment available
to the farmer and is specific to the type of crop and the type
of pest being treated.
Application Methods	

    The method of pesticide application refers to how the
pesticide is applied on the crop or field.  A pesticide can be
applied to a crop by aerial application, ground application, or
through chemigation.  Ways in which the method of application
can impact pesticide leaching to ground water are described
below.

Aerial Application

    Aerial application involves the foliar or surface appli-
cation of pesticides from a small airplane or helicopter.
Pesticides applied by this method may not always be applied
uniformly over a field and can drift away from the target site
to nearby fields or surface water.  Localized areas may receive
more or less of the application of pesticides, which can result
in over-concentrated areas from which pesticides may leach.

    Aerial application of pesticides, however, is often the
only available method, such as at times of advanced crop stages
when ground application is not feasible.  Methods that may be
                              -20-

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 used  to  increase the uniformity of application and decrease
 drift include  applying pesticides only at times when winds are
 calm,  applying the pesticides at as  low an altitude as
 possible, using swath analysis to evaluate distribution, and
 adjusting spray nozzles and drop sizes to account for air
 turbulence  (propwash) (Maas, et al,  1984).

 Ground Application

    Ground  application involves applying pesticides through
 land  based  vehicles.  Pesticides applied by ground application
 can be foliar  applied, surface applied, or soil incorporated.

    With foliar applied pesticides,  the quantity of pesti-
 cides  used  can be reduced by adjusting spray drop sizes
 relative to the surface of the plant to which they are being
 applied.  This helps pesticides stick to plant surfaces and not
 run off onto soil.  The drop sizes should be small enough to
 avoid  runoff,  but not so small that  they are susceptible to
 drift  and inadequately cover plant surfaces (Roberts, 1982).

    The quantities of pesticides used can also be reduced
 through the use of methods that help foliar applied pesti-
 cides  cling to plant surfaces, such  as by adding crop oil or
 surfactants to the pesticide mixture.  Electrostatic sprayers,
 or sprayers that use ultra-low volumes of pesticides by
 recirculating  pesticides that do not become attached to the
 plant  surface, are also effective.   With electrostatic
 sprayers, pesticide drops are negatively charged before they
 are applied to plant surfaces. The negatively charged pesti-
 cide can then more easily attach to the positively charged
 surfaces of the plant.   In some sprayers, the negatively
 charged pesticides that do not attach to plant surfaces can be
 collected and  recirculated, thus reducing the quantities of
 pesticide used (Mass, et al, 1984).

    The potential for pesticide leaching to ground water is
 higher with surface applied and soil incorporated pesticides
 an for foliar  applied pesticides.   This is particularly true  if
 the pesticide  is applied where site conditions are most
 conducive to leaching.   However,  for many insects and weeds,
 surface application or soil incorporation are the only
 effective means of control.  In irrigated agriculture, the
potential for pesticide leaching with these application methods
depends,  in large part,  on the method of irrigation being used
 (See Chapter Six).

    Where surface application and/or soil incorporation is
necessary,  uneven application of the pesticide can cause an
 increase in the potential for pesticide leaching.   The
uniformity of the application depends,  in part,  on the
                              -21-

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uniformity,  calibration,  spacing,  and height  of  the nozzles
(Roberts,  1982).  Improper calibration can lead to concen-
trated bands of pesticide.

Chemiqation

    Chemigation involves  mixing the pesticide with water
flowing through an irrigation system.  The irrigation system
used is most often a spray or drip system, although chemigation
can also be practiced with flood irrigation.   The potential
impacts of chemigation on pesticide leaching  are discussed in
Chapter Six.
	Variable Practices	

    By choosing appropriate pest control methods and carefully
managing the amount, volume, and timing of pesticide
applications, the risk of ground water contamination can be
reduced significantly.
Choice of Pest Control Method	

    Subsequent sections describe many ways to control pest
populations through management practices that either eliminate
or reduce the need for pesticides.  Further, an overall
recommendation regarding the use of pesticides is to implement
integrated pest management (IPM) techniques, which consider
non-chemical methods of pest control and prescribe the use of
pesticides only as they are needed to keep pest populations
below economic thresholds (see discussion of IPM in
Chapter Five).  Reductions in the use of pesticides will result
in the greatest protection for all environmental media.

Selection of Pesticide

    When use of a pesticide is necessary to control damaging
pest populations, careful selection can help avoid
contamination of ground water.  As described in Chapters Two
and Three, persistent pesticides with high water solubility
that do not adsorb readily to soil have the highest potential
to leach.  Table 2-2 (Page 11) lists the pesticides EPA has
determined as having greatest potential to  leach based on
current data and understanding.  The Agency will monitor these
pesticides in the National Survey of Pesticides in Well Water.
Until better information is available, this list represents the
pesticides for which there is some concern  that they may leach
to ground water as a result of normal application to the land.
                              -22-

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Form of Pesticide

    The form of pesticide can affect the potential for leaching
into ground water.   Pesticide forms include powders,  dusts,
granules,  timed-release encapsulated forms, concentrated
emulsions,  liquid concentrates,  and aqueous solutions.  The
particular form used is generally dictated by the pesticidal
effect desired.

    Different spraying formulations may be prepared by
dissolving a solid in water,  by mixing a liquid solution with
water, by mixing a wettable powder to form a suspension, by
mixing an emulsifiable concentrate with water to form an
emulsion,  or by mixing an oil-miscible formulation with an
oil.  All these forms of application have variable impacts on
the leaching potential of pesticides.  For example, surfactants
made of oils are added to foliar-applied herbicide/insecticide
sprays to increase the penetration and translocation of the
chemicals within the plant tissue.  This process increases the
effectiveness of the pesticide,  thus allowing a smaller
application of the active ingredient.  These additives also
help the pesticide stick to the plant surfaces, thus reducing
the amount washed off onto the soil and the potential for
leaching to ground water.  However, the surfactants may
increase the potential for pesticide leaching of washed off
pesticides by decreasing their ability to adsorb to soil
particles.

    Pesticide solubility can also impact leaching potential.
Pesticides with low solubility and high adsorbtive capacity are
prone to be transported in the sediment phase rather than in
dissolved runoff and thus have lower potential to leach. More
soluble pesticides can be carried to ground water in solution
where runoff is not significant.

    Because of their high solubilities, wettable powders,
dusts, and microgranules are generally susceptible to surface
runoff or to leaching.  These solid forms of pesticides also do
not volatilize as readily as do pesticides in liquid and
aqueous solutions and may persist in soil, potentially
affording more time when leaching might occur.
Application Timing	

    The time that a pesticide is applied can be a major factor
in pesticide leaching potential, depending on local environ-
mental conditions, temperature, and rainfall.  Leaching
potential is minimized when the applied pesticide is fully
utilized or when the soil conditions promote degradation.
                              -23-

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Timing of pesticidal application should be relative to climatic
conditions, crop stage,  and weed and insect populations.
Figure 4-1 presents, for illustration purposes,  a summary of
the concepts presented in this discussion; note  that actual
timing decisions will vary based on climate,  crop,  and pest
control needs.

Climatic Conditions

    The degree of pesticide leaching at a particular site
depends on the amount and nature (e.g., drizzle  vs. downpour)
of local precipitation events.  The temperature  of the soil and
surrounding air at a site can also greatly affect the processes
that result in a pesticide's movement and degradation in the
environment.  These climatic factors are governed by the season
and the geographical location.  In general, pesticides are more
likely to leach below the root zone when the soil is at or near
full saturation after heavy precipitation.  This condition can
result in pesticide desorption from soil particles, or downward
movement of dissolved pesticides.  As such, leaching can be
minimized by limiting pesticide application during wet
seasons.  Leaching potential can also be minimized by observing
weather patterns and avoiding pesticide application before
major precipitation events.  In either situation, proper timing
of pesticide application relative to climatic conditions
involves knowledge or understanding of the period(s) of heavy
precipitation for the geographical area in general (e.g., late
spring or fall).  The immediate weather forecast, is, of
course, of primary importance in making a specific application
decision.

Crop Stage

    Pesticides are usually applied at pre-planting, at
pre-emergence, or during post-emergence.  Pesticides applied
during pre-planting and pre-emergence stages have higher
potentials to leach than those applied post-emergence.  The
potential for post-emergent applied pesticides to  leach depends
upon the crop stage.  In general, mature crops have a higher
capacity for uptake of pesticides.  During this stage of crop
growth, water is absorbed at the root zone, thus limiting
downward movement of water and the potential for pesticide
leaching.  For some weeds and pests, however, the benefits  of
pre-plant and pre-emergent application may outweigh the higher
potentials for leaching associated with these methods.  This
would be true when, for example, a single application per
season is effective in controlling weeds  that would otherwise
require multiple applications.
                              -24-

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I
NJ
Ln
   150-

   140-

   130-

   120-

   110-
  I
  t 100-

  S 90-

  2 M-
  UJ
  I 70"l
  I 60-|
WJ o
>   50-

    40

    30

    20

    10
                                                            CROP GROWTH
                               CRITICAL WEED GROWTH-  /
                               FIRST CYCLE        \  '
CRITICAL PERIOD FOR
POST-EMERGENCE
PESTICIDE APPLICATION^,
                                   APR
                                                                CRITICAL WEED GROWTH-
                                                                SECOND CYCLE
CRITICAL PERIOD FOR
POST-EMERGENCE
PESTICIDE APPLICATION
                                        / ^CRITICAL PERIOD FOR
                                       /   PRE PLANT OR
                                      /    PRE-EMERGENCE
                                     /     PESTICIDE APPLICATION
                                                        SEP       OCT
                                                       MONTH OF YEAR
                                                     •CRITICAL PERIOD FOR
                                                     PRE PLANT OR
                                                     PRE EMERGENCE
                                                     PESTICIDE APPLICATION
                                                                                                                    CRITICAL WEED GROWTH-
                                                                                                                    THIRD CYCLE
                                                                                                                 DEC
                                   CRITICAL PERIOD FOR
                                   POST-EMERGENCE
                                   PESTICIDE APPLICATION
150

140

130

120

110

100

90

so

70

-60

50

-40

-30

-20

-10
                                                                                                                                     _L
                                                                                                                                                     >
                                                                                                                                                     <
                                                                                                                                                     D
                                                                                FIGURE  4-1
                                                             PESTICIDE  APPLICATION  RELATIVE  TO  CROP
                                                           GROWTH  STAGE, WEED  AND PEST OCCURRENCE
                                                         (ILLATION  ONLY;  ACTUAL WILL  VARY BASED ON
                                                              CLIMATE  CROP AND PEST CONTROL NEEDS)

-------
    For post-emergent application,  the timing of pesticide
application relative to crop stage  should consider the inter-
action between growth stages of the crop and the time that the
pest species does the most damage.   Many pests cause damage to
crops only during a specific period of the crop cycle (Maas,  et
al, 1984).  The alfalfa seed-crop,  for example, can be best
protected from the lygus bug, which attacks alfalfa buds,
floral parts, and immature seeds,  by application of insecticide
during the early bud stage of the  crop (Martin and Leonard,
1967). In addition, pesticide application can be reduced by
eliminating application at crop stages where pests do not feed
on the crop.  For example, the tobacco budworm, which only
affects buds, cannot cause economic damage to tobacco after
plant leaves emerge, thus eliminating the need for insecticide
application after that point (Maas, et al, 1984).

Thresholds and Pest Cycles

    Pesticide application can be reduced through insect and
weed scouting and by being aware of economic thresholds—that
is, the levels at which pest numbers become economically
injurious to crops.  Proper timing of pesticide application
relative to economic thresholds and pest cycles can
significantly reduce the quantity of pesticides applied.  With
the new pest resistant varieties on the market, most crops can
generally tolerate a high number of pests before yields and/or
crop quality are affected.  In addition, many weeds and insects
reach critical growth stages where their numbers can be
drastically reduced with a relatively low amount of
pesticides.  Extension specialists  with expertise in weed and
insect monitoring can provide advice on proper timing of
pesticide applications.

    In several studies, pesticides  were found to have been
applied unnecessarily at times when pest scouting indicated
that economic thresholds had not been reached  (Maas, et al,
1984).  A four-county study in Illinois found that 19 and  11
percent of corn acreage actually required insecticide usage
while 67 and 57 percent, respectively, received it (Luckman,
1978).  In addition, a three-year study in the Midwest showed
that only 9 percent of corn fields even contained wireworm,  a
commonly treated pest, and only 1.2 percent actually had
wireworm damage (National Science Foundation,  1975).  Studies
with soybeans have shown that this crop can have a remarkably
high ability to tolerate insects without significant loss  of
yield (Newsom, 1978), thus requiring the use of only small
quantities of pesticides.

    Application of pesticides relative to pest growth cycles
can also be useful in reducing the quantities  of pesticides
used.  The times in pest cycles where they can be best
                              -26-

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controlled can be identified with the help of Extension
specialists,  by consulting pesticide label directions,  or from
the reports "Weed Control Manual and Herbicide Guide"  and
"Insect Product Guide"  (published by Ag Consultant and
Fieldman, respectively).  For example, Canada thistles  and many
broadleaf weeds in corn  fields can be effectively controlled
only by applying herbicides in early weed or pre-emergent
stages (Ag Consultant,  1986).  In fact, nearly all weeds can be
most effectively controlled by application of pesticides at
times early in growth stages when they are most susceptible.
In addition,  pests such  as cutworm, corn earworm, cottom
bollworm, sorghum headworm, soybean podworm, tobacco budworm,
and tomato fruit worm are best controlled when the larvae first
appear (Ag Consultant,  1986).


Application Rate and Volume

    Proper choice of pest control method and application timing
can reduce the quantity  of required pesticides as described in
the previous sections.   In addition, other measures help assure
the most effective use of minimum amounts of pesticides,
including proper maintenance and calibration of pesticide
application equipment,  consideration of recommended ranges of
pesticides, and band application of pesticides.

Proper Mixing

    Label directions for mixing the pesticide should be
carefully followed to assure the most efficient use.
Under-dilution of the pesticide will result in use of excessive
quantities; more pesticide may be available to leach since
normal degradation processes are likely to be less effective.

Equipment Maintenance and Calibration

    Pesticide application equipment should be maintained and
properly calibrated to ensure even application of pesticides
and to ensure that pesticides are applied at volumes intended
by the user.   Poorly maintained and/or calibrated equipment can
discharge excessive quantities of an improperly diluted mixture
of pesticides which can  result in inefficient use and subse-
quent leaching into ground water.  Ensuring the proper rate and
volume of pesticide application can be made easier with the use
of automatic volume regulating devices which cause spray
pressure to vary accordingly with change  in speed of the
application equipment.

    Pesticide application equipment should be maintained and
calibrated on a periodic basis to achieve the desired
application rates and volumes.  The Agricultural Training  Board
                              -27-

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of England recommends that calibration should take place at the
beginning of each season;  after every 100 hectares sprayed; and
after changes of tractor wheels,  nozzles, or pressure (Roberts,
1982).

    Detailed information on calibration procedures can be
obtained from Extension specialists and equipment
manufacturers.   The calibration procedure for spray equipment
should first include selecting nozzles to give the required
application rate at the intended pressure and speed,  based on
the label instructions of the pesticide being applied.  The
sprayer should then be adjusted to the intended spray pressure,
and the nozzles should be checked for visual alignment.   All
worn or bent nozzles should be repaired or replaced.   The
nozzle output should then be checked for uniformity with
flow-measuring devices or by recording the time it takes each
nozzle to fill a container to a specified depth.   In a trial
run with the pesticide application equipment filled with water,
the spray width of the nozzles should be checked for the
desired width.   If the desired width is not obtained, the boom
height or nozzles can be adjusted accordingly.

Consideration of Dosage Recommendations

    Pesticide label instructions recommend a specific dosage,
which is generally expressed in a range of active ingredients
per acre.  If pest numbers are relatively low, the lower end of
the recommended range may give adequate results while resulting
in lower quantities of pesticide used.  It is illegal to use
greater than the maximum dose shown on the label.

Band Application

    Applying pesticides in a band on crop rows rather than on
the entire field is an effective method for reducing the amount
of pesticides used.  Band application with corn, for example,
can be used to apply pesticides along the crop row at the time
of planting with a sprayer located behind the planter.  Drop
nozzles can also be used to spray below the crop canopy,
allowing use of less pesticide and more effective application.
The band application will control weeds along the row, while
mechanical cultivation or lesser amounts of pesticides can be
used to control weeds between the rows (Martin and Leonard,
1967).
                              -28-

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                          CHAPTER FIVE

                       FARMING PRACTICES
    Farming practices can help reduce the quantities of
pesticides used and make site conditions less conducive to
leaching.   Farming practices employed at a given farm are
usually influenced by soil conditions,  topography,  rainfall
pattern, cropping pattern, economic status of the farmer, and
individual knowledge of various agricultural practices.  A
combination of farming practices can be used to set up an
integrated pest management (IPM) system, in which the
quantities of pesticides used can be greatly reduced.

    Many farming practices are also used for the purposes of
preventing soil erosion and surface runoff.  Because in some
situations there may be tradeoffs, the choice of farming
practices  should consider impacts on all environmental media.
For example, one farming practice may be useful in reducing the
leaching potential of pesticides, but may promote soil erosion,
with subsequent negative impacts on surface water quality.


	Fixed Practices	

    Since  different tillage methods require different types of
capital equipment and are often selected as a means for
controlling erosion and surface runoff, tillage practices are
considered, for this publication, to be "fixed" practices.
When a decision to change tillage method is being made,
however, the potential impact of alternative methods on both
ground and surface water should be considered.


Tillage Practices	

    The fundamental purposes of tillage are to:  provide a
suitable seedbed, reduce competition from weed growth, and make
conditions in the soil more favorable for crop growth  (Martin
and Leonard, 1967).  Tillage practices can impact the potential
for pesticide leaching by influencing the quantity of
pesticides used and by making the site more or less conducive
to pesticide leaching.  Details of how conventional and
conservation tillage can impact the potential for pesticide
leaching to ground water are discussed below.
                              -29-

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 Conventional Tillage

     In conventional tillage, land is cultivated mechanically
 often in both fall and spring prior to planting for seed bed
 preparation.  Mechanical cultivation is also one of the oldest
 forms of weed control known.  In addition to weed control,
 cultivation between crop rows provides aeration to crop roots
 and  can help in reducing insect numbers by exposing insects to
 the  surface where they can be controlled by natural predators.
 Conventional tillage can be effective in the control of weeds
 that grow between crop rows before the crop can shade the
 ground (Martin and Leonard, 1967).

    Herbicide use can be relatively low with conventional
 tillage, although herbicides are generally used in conjunction
 with mechanical cultivation to control weed competition.  In
 addition, conventional tillage may be useful in eliminating
 macropores and animal burrows through which pesticides can
 rapidly infiltrate into ground water.

    However, because the soil is left exposed, conventional
 tillage can promote soil erosion and surface runoff if
 practiced on steep slopes (greater than 3%) without contouring
 or terraces.  Erosion is particularly a problem in areas of the
 United States where steep slopes are combined with soils of
 relatively low permeability, and rainfall amounts are high and
 occur in high-intensity events (storms).

 Conservation Tillage

    Conservation tillage is defined as any tillage practice
 that leaves at least 30 percent of the soil surface covered
 with crop residues after planting (Conservation Technology
 Information Center, 1987).   Conservation tillage is generally
 employed as an inexpensive, effective method for reducing soil
 erosion and surface runoff.  At the present time, considerable
 controversy exists over the impact of conservation tillage on
 ground water.

    The term conservation tillage encompasses five basic
methods:  no-till,  ridge-till,  strip-till, mulch-till, and
 reduced-till.  With no-till, the soil is left undisturbed prior
 to planting, and the planting is completed in a narrow
 seedbed.   With ridge-till and strip-till, the soil is left
undisturbed prior  to planting,  although a portion of the soil
 surface is tilled  at planting.   With ridge-till, however,
planting is completed on ridges which are higher than the row
middles,  and cultivation is used to rebuild ridges.  In
mulch-till, the total soil  surface is disturbed by tillage
prior to planting  with tillage tools such as chisels, field
cultivators, discs, sweeps, or blades.   Reduced-till refers to
                              -30-

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any conservation tillage practice not covered above.   With
conservation tillage practices,  weed control  is  accomplished
with a combination of herbicides and cultivation (Conservation
Technology Information Center,  1987).

    The controversy surrounding the effects of conservation
tillage on pesticide leaching centers around the fact that
conservation tillage may require additional herbicides  in some
cases, compared to conventional tillage (Maas, et al, 1984)^
However  experience has shown that much of the increase is due
to a desire for a hedge against uncertainty.   Some producers
are using less herbicides than they did when practicing
conventional tillage, often after they have gained experience
and confidence in the new system.  Studies on corn have shown
that more herbicides may be required with reduced tillage
compared to conventional tillage (Hanthorn and Duffy, 1983).
For soybeans, however, only no-till was found to cause an
increase in herbicide usage, while there was no significant
differences in herbicide use between reduced till and
conventional tillage.

    Different methods of conservation  tillage require different
quantities of herbicide  and have different effects on leaching
potential.  Generally,  it appears  that no-till  requires the
greatest herbicide  usage and may  lead  to  site conditions  most
conducive to  leaching when  compared  to other  conservation
tillage methods.   If no-till is  used continuously for several
years  on the  same land,  the  likelihood for the  presence of soil
macropores  is higher than for  other  conservation tillage
methods, thus  increasing the potential for pesticide leaching
 (Dick   et al.,  1986).   Ridge-till  and  mulch-till may generally
 require the  least amount of  herbicides because  some  mechanical
 cultivation  is  done with these methods.

     In some  instances,  higher  amounts  of  insecticides may also
 be required  with conservation  tillage, compared to  conventional
 tillage (Smith,  et al.,  1979).   The additional  amounts  involved
 are generally greater  for no-till.

     Although conservation tillage may require the use of  more
 pesticides  in some cases, the  overall impact of this practice
 on the potential for pesticide leaching  remains unclear.
 Studies have also shown that conservation tillage,  although
 sometimes requiring the use of more pesticides, can also help
 in reducing the potential  for  pesticide  leaching by making site
 conditions  less conducive to leaching by enhancing
 microbiological activity and degradation of pesticides in the
 upper three inches of the soil layer  (Helling, 1986).
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Contour Farming
    Contour farming involves the planting of crops along
contour lines across slopes.  Contour farming is effective at
reducing soil erosion by slowing water movement on the soil
surface and allowing for increased infiltration.  It is most
effective on fields of moderate slopes (less than 8 percent)
that are free of depressions and gullies.  Runoff volumes may be
reduced up to 50 percent depending on crop and soil type (Maas,
et al., 1984) in comparison to other farming practices.

    Although contour farming can decrease surface runoff, this
practice can cause ponding of runoff between rows.  Subsequent
increases in infiltration may increase the potential for
leaching of soluble pesticides (Maas, et al., 1984).
Terracing	

    Terraces are ridges and channels constructed across a
slope.   They are divided into two general classes—graded
terraces and level terraces.   Graded terraces divert water to a
grassed waterway or to some other non-erosive drain.  Level
terraces hold water on the field, thereby increasing
infiltration water and allowing redeposition of eroded soil.
Both types of terraces help reduce surface runoff, with the
greatest reductions occurring in dry areas with level terraces
(Maas,  et al.,  1984).

    Increased infiltration from terracing may result in an
increased potential for leaching of pesticides to ground water.
This is due to the minimized surface runoff, which allows more
water to infiltrate into the ground.  Level terraces are often
used in semi-arid areas to supplement the general lack of
moisture in the root zone; in such areas the depth to ground
water is greater so the likelihood of pesticides reaching the
water table is reduced.
Contour Stripcropping	

    Stripcropping consists of alternating rows of the main crop
with strips of either a grain crop, sod, or a legume.  It is
effective in controlling surface runoff and soil erosion by
wind and water (Maas, et al., 1984).  Stripcropping can also
help in reducing insect, nematode, and weed problems in some
cases, thus reducing the amounts of required pesticides
(National Science Foundation, 1975).  Stripcropping also helps
reduce the total area of land to which pesticides are applied,
thus reducing the quantity of pesticide used.
                              -32-

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Cover Crops
    The purpose of cover crops is to provide vegetative cover
to the soil to control soil erosion during the non-growing
season. Insecticide requirements are generally unchanged from
those with conventional tillage, although with no-till, a
contact herbicide may be required to kill the cover crop
(Smith, et al., 1979).
	Variable Practices	

    Farming involves making a large number of choices regarding
where, when, and how crops are planted and harvested; the
variety of plants to be grown; and pest management.   Depending
upon the tillage practices used, such variable practices can
have different impacts on the quantities of pesticides used,
and thus, the amount that might be available to leach.  Table
5-1 shows the possible impacts of each variable practice on
insecticide and herbicide use when practiced with each of the
fixed practices.  The table shows whether pesticide use would
likely increase or decrease as compared to not employing the
particular variable practice.
Crop Rotation	

    Crop rotation involves periodically changing the crops
grown on a particular area.   This practice can reduce the
quantities of pesticide used when practiced with any of the
tillage methods.   In addition, crop rotation can help to
improve soil structure, organic matter content, and
infiltration, thereby making conditions more favorable for crop
growth (Smith, et al., 1979).  The principle behind crop
rotation and pest control is to eliminate insect pests of a
specific crop by introducing non-host crops into the crop
rotation program. Crop rotation is most effective in reducing
numbers of pests that are poor competitors and have low
survivability and mobility.

    Crop rotation has proven to be especially effective against
corn rootworm.  Corn rootworm numbers have been found to be
dramatically reduced by rotating crops with corn on consecutive
years (Maas, et al.,  1984).   Crop rotation has also proven
useful in controlling nematodes and billbugs in wheat (Martin
and Leonard, 1967).
                              -33-

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                        TABLE 5-1:   POSSIBLE  EFFECTS OF  FARMING  FACTORS  ON  QUANTITIES OF PESTICIDES USED*
I
OJ
Practice



Crop Rotation

Contour Stnpcropping

Cover Crops

Pest Resistant Varieties

Adjusting Planting and
  Harvest Times

IPM
                                               Conservation
   Other
Conventional
Tillage
In
D/3
D/2
N
D/2
D/2
D/3
H
D/l
D/2
N
N
D/l
D/l
No-Till
In
D/3
D/2
I/I
D/l
D/l
D/2
H
D/3
D/2
I/I
N
D/3
D/2
Ridge-Till
In
D/3
D/2
N
D/2
D/2
D/2
H
D/2
D/2
N
N
D/l
D/l
Tillage
In
D/3
D/2
N
D/2
D/2
D/2
H
D/l
D/2
N
N
D/2
D/2
          In - Insecticide
          H - Herbicide

          I - Increase
          N - No Significant Impact
          D - Decrease
                                      1 - Minor Impact
                                      2 - Moderate Impact
                                      3 - Major Impact
          *  The table bhuws generally whether pesticide use would likely increase  or  decrease compared to not
             employing the practice.   The effect on actual  amounts used at a  given  location  is dependent on
             site-specific conditions.

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Planting Pest-Resistant Varieties
    A non-chemical pest control method that is steadily
 increasing is the planting of pest-resistant varieties.  About
 75 percent of the total U.S. acreage is planted with pest- and
 disease-resistant crop varieties.  Insecticide use in the
 United States was significantly reduced between 1971 and 1982
 (Maas, et al., 1984), partly due to the use of pest-resistant
 varieties.  Resistance can help the plant to either inhibit
 pest growth or recover from injury inflicted by the pest.
 However, to reduce the quantity of pesticides used with
 pest-resistant varieties, pest scouting and monitoring are
 still necessary to ensure that pesticides are applied only when
 pest numbers approach economic thresholds.
Adjusting Planting and Harvesting Times	

    Planting can often be timed to give crops a competitive
edge over insects and weeds, thus decreasing the requirement
for pesticide use.  A study in Wisconsin, for example, showed
that corn planted before weed emergence required minimal use of
herbicides.  Herbicides were needed in only two out of ten
locations investigated.  The study showed that early crop
canopy, particularly in narrow rows, gave the corn a
competitive advantage over weeds and slowed water movement in
soil, thus reducing the potential for pesticide leaching
(Kogan, 1982).

    Adjustments in planting and harvesting times can also help
in reducing damage from insects and the use of insecticides.
Planting as soon as the soil is warm enough to permit rapid
plant growth can help corn to avoid corn borer attack.
Planting of winter wheat late enough for the main brood of
hessian flies to have emerged and died can reduce damage from
these pests (Martin and Leonard, 1967).  For soybeans, early
planting is encouraged so that a plant canopy can form before
the flight of second generation moths of the corn earworm
(Maas,  et al.,  1984).

    Timing of harvesting can also reduce the need for
pesticides.   Early harvesting, before insects reach economic
thresholds,  has proven effective for a variety of pests,
including sugarcane borers,  sweet potato weevils, potato tuber
worms,  and cabbage loopers (Maas, et al., 1984).
Integrated Pest Management	

    All farming practices discussed above can be incorporated
into an integrated pest management (IPM) system of controlling
                              -35-

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pests with minimal use of pesticides.   IPM is  a pest control
strategy that utilizes appropriate control methods to keep pest
populations below economic thresholds  with the least
undesirable impacts on the environment.   It includes both
chemical and non-chemical means of pest control.

    Practicing IPM can reduce the overall quantities of
pesticides used, leading to a decreased potential for pesti-
cide leaching to ground water and transport to other environ-
mental media.  It has been estimated that a 40 percent reduc-
tion in current pesticide use may result from IPM programs that
are now available, with an estimated projection to a 60 percent
reduction in the next decade by continuing these programs
(USDA, 1985).

    An effective IPM system requires extensive knowledge of the
ecology of the system of interest (Maas, et al., 1984) and
generally will require the use of Extension specialists or pest
consultants.  One text that includes discussion of  IPM (van der
Bosch, 1978) suggests the following general guidelines for
setting up an IPM system:

    1)   Understand the biology of the crop, and how  it is
         influenced by the surrounding ecosystem.

    2)   Identify the key pests; know their biology;  recognize
         the kind of damage they inflict;  and  initiate studies
         on the economic  impact of these  damages.

    3)   Identify the key environmental  factors  that  impinge
         upon the pest.

    4)   Consider concepts, methods, and materials  that
         individually or  in combination  will help  suppress
         permanently or  restrain pest  species.

     5)   Structure  IPM programs  so that  they will  have the
         flexibility needed to adjust  to ecosystem changes.

     6)   Anticipate unforeseen developments;  expect setbacks;
         move with  caution;  and remain aware  of  the ecosystem
         complexity.

     7)   Seek the weak  links  in the key pest  life cycle  and
         narrowly direct control  practices at  these weak links,
          avoiding broad  ecosystem impacts.

     8)   Whenever possible,  use methods that  preserve,
          complement,  and augment biotic and physical mortal-
          ity factors  of  the  pest.

     9)    Whenever feasible,  attempt  to diversify the ecosystem.


                               -36-

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    IPM systems for reducing pesticide use have proven
effective for a number of crops including corn, soybeans,  and
cotton (Maas et al.,  1984).   Crop rotation has been combined
with pest scouting and monitoring to help eliminate corn
rootworm beetle populations (Luckman, 1978).   Monitoring and
scouting, optimal planting dates, natural control agents,
resistant varieties,  trap crops, selective use of insecti-
cides, and treatments based on economic thresholds have proven
effective for controlling pests  (Rudd, et al., 1980).

    Note-  At present, IPM methods for insect pest control,
while still not available for all crops and all pests, are
generally more developed than for weed control.  Since many of
the commonly used herbicides are considered to have  significant
leaching potential, many workshop participants and reviewers
from the agricultural and environmental communities  noted  a
particular need for research to  develop IPM methods  for weed
control.
                               -37-

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                           CHAPTER SIX

                      IRRIGATION PRACTICES
    Irrigation is the practice of applying water to the land to
provide sufficient moisture for crop production.  Irrigation is
needed because rainfall is either insufficient for crop needs
or does not occur at the ideal time during the growing season.
Proper use of irrigation can increase crop yields and quality
by counteracting high or low temperatures, eliminating short
droughts, and aiding germination and continuous plant growth
(Soil Conservation Service, 1983).

    A proper irrigation strategy can also help to make site
conditions less conducive to pesticide leaching and help reduce
the quantities of pesticides used.   The goals of the strategy
are to apply pesticides when site conditions are less likely to
promote leaching and to ensure the most efficient use of the
pesticides.

    With all methods of irrigation, water inputs should be
managed to limit the potential for pesticide leaching (Helling,
1986).  Water conservation practices, such as the use of soil
moisture monitors to determine field water requirements, will
help avoid over-watering and minimize the potential for
dissolved chemicals to leach with the excess water.

    Irrigation practices that can influence the potential for
pesticides to leach to ground water include the method of
irrigation (fixed practice) and the timing, volume, and
frequency of irrigation (variable practices).  The potential
for pesticides to leach is also dependent upon the relationship
between the method of irrigation and the method of pesticide
application (See Chapter Four).  Table 6-1 shows the potential
for pesticide leaching of various irrigation methods practiced
with various pesticide application practices.  For leaching
potentials listed in Table 6-1, it is assumed that the applied
pesticide has a high potential to leach, based upon its
physio-chemical properties.
                        Fixed Practices
Methods of Irrigation	

    Irrigation methods commonly used in commercial agricul-
ture can be categorized generally into three basic types:
                              -38-

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                                TABLE 6-1:   POTENTIAL FOR PESTICIDE LEACHING WITH VARIOUS METHODS
                                            OF IRRIGATION AND PESTICIDE APPLICATION*
I
OJ
  Application Method

Foliar Application

Surface Application
  Pre-Plant/Emergent
  Post Emergent

Soil Incorporated
  Pre-Plant/Emergent
  Post Emergent

Chenugation
                                                       Irrigation Method  - Soil Type
Sprinkler Drip
thod Clay
on L
ion
gent L
L
d
gent M
L
Loam
M
M
M
M
M
Sand
M
M
M
H
H
Clay
L
L
L
L
L
Loam
L
L
L
M
M
Sand
L
M
M
M
M
Clay
L
M
M
M
M
Flood
Loam
L
M
M
H
M

Sand
L
H
M
H
H
M
H
M
M
M
H
H
          L   Low Leaching Potential
          M -- Moderate Leaching Potential
          H - High Leaching Potential
          *  The table assumes that a pesticide with chemical-physical properties  indicating  leaching potential  is
             being used.  Actual leaching potential will depend on the specific pesticide and site properties.

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flood or furrow,  sprinkle,  and trickle or drip.   There are many
variations within these categories and there are other methods
designed for specific crop needs and site conditions.   A
growing practice, known as chemigation,  is to apply pesticides
and/or fertilizers through the irrigation systems.

Flood or Furrow Irrigation

    In this method of irrigation,  water is retained within some
type of ridge or  dike and infiltrates into the ground in
response to gravity.   Water is pumped or allowed to flow from
ground or surface sources into the ridged or diked area.  In
level or graded basin irrigation,  for example, all or part of
the crop is flooded temporarily until the soil absorbs the
water.  In furrow irrigation,  water is ponded between crop rows
in furrows created during planting and cultivation (Soil
Conservation Service, 1983).   Flood or furrow irrigation may
promote leaching of soil incorporated and surface applied
pesticides because it is difficult to avoid over-application of
water with this method (Helling, 1986).   Over-watering may
promote downward movement or desorbtion of pesticides,
particularly where soils are highly permeable.

Sprinkle Irrigation

    In sprinkle irrigation, water is sprayed into the air
through perforated pipes or nozzles operated under pressure.
Sprinkle systems can be classified into three broad
categories:  portable, solid-set,  or self-propelled (Soil
Conservation Service, 1983).

    Sprinkle irrigation offers the greatest potential to
promote pesticide leaching when it washes foliar applied
pesticides from crop and weed surfaces before they are
effectively utilized.  When foliar applied pesticides are used
with sprinkle irrigation, therefore, proper timing of
irrigation with regard to pesticide application  is essential.

Trickle or Drip Irrigation

    In trickle irrigation, water  is applied slowly on or
beneath the surface  layer—usually as drops,  tiny streams,  or
miniature spray—through emitters or applicators placed along  a
water delivery line.  Trickle systems are normally designed to
apply light, frequent applications of water and  to wet  only
part of the soil  (Soil Conservation Service,  1983).

    Since trickle irrigation  is a relatively  conservative  user
of water, the potential for over-application  of  water and
subsequent  leaching  of pesticides can also  be relatively  low.
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Chemiqation

    With chemigation,  pesticides  (or  fertilizers)  are mixed
with irrigation water  before they are applied to the field,  and
irrigation and application is done simultaneously.   Chemigation
can be done with any irrigation system and method as long as
the pesticide and the  method of application are compatible.
For example, surface applied pesticides should only be applied
with drip or flood irrigation.   While it is common practice to
irrigate at the same time as pesticide application, some
experts recommend that only the amount of water needed to
activate the pesticide should be applied when chemigating (see
Irrigation Timing, below).

    Although research is  limited on this subject, there is some
concern that the practice may promote leaching because the
pesticide (or fertilizer) is being applied continuously or in
pulses when it is already dissolved (Helling, 1986). The
potential impact of chemigation when practiced with drip
irrigation systems, however, may be lower because  less water  is
used with this method compared with flood and sprinkler_
irrigation, and the pesticide  is being applied  in  localized
areas nearer the crop.  Another possible source of ground-water
contamination associated  with  chemigation is faulty,  leaky, or
non-existing anti-back-siphoning devices  (see section on
Chemigation Back-Siphoning Devices in Chapter Seven).
                       Variable Practices
 Irrigation Timing
     The  proper  timing  of  irrigation  relative  to  pesticide
 application  can enable the  pesticides  to  be utilized most
 effectively.  Under  relatively  dry conditions,  soil  incorpor-
 ated or  surface applied pesticides will remain  in the root zone
 or  be adsorbed  onto  soil  particles before significant leaching
 can occur.   However, when excessive  water is  applied before
 pesticides degrade or  can be taken up  by  plants, mobile
 pesticides may  move  with  infiltrating  irrigation water and
 leaching may occur.  Because of this possibility, irrigation
 should be delayed, when practical, following  pesticide
 application.  The delay time is a function of,  among other
 factors, the rate of plant  uptake of the  pesticide and the
 pesticide degradation  rate.

     The rate of plant  uptake of soil applied  pesticides is
 generally a  function of the transpiration rate of the plant.
 In addition,  plant uptake also  increases  as the root zone depth
 increases (Carsel, et  al.,  1984).  Therefore, for post-emergent
                               -41-

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pesticides applied to mature crops,  a shorter  delay time is
necessary than for post-emergent pesticides  applied to young
plants or pre-emergent or pre-plant  applied  pesticides.   The
necessary delay time is also shorter for pesticides with faster
degradation rates in soil,  which is  an inverse function of the
pesticide half-life.  Appendix B shows degradation rates for
selected pesticides in soil.

    For foliar applied pesticides which rely on contact with
the plant surface for effectiveness, sprinkle irrigation too
soon after application may wash pesticide off onto the soil
before the full benefit of the pesticide is  obtained.   Again,
by delaying irrigation which may wash pesticides from plant
surfaces, the pesticide can be fully utilized and the potential
for pesticide leaching reduced.  The delay time between foliar
application and irrigation is generally a function of the
degradation rate of the pesticide on foliage.  For pesticides
with short half-lives, the necessary delay time is shorter.
Appendix B shows degradation rates for selected pesticides on
foliage.
Irrigation Volume and Frequency	.

    As stated earlier, avoiding excess water inputs can be an
effective method of limiting the potential for pesticide
leaching.  Studies have shown that fields are often irrigated
at unnecessarily high volumes and frequencies (University of
Nebraska, 1984), and irrigation amounts can almost always be
reduced with no significant impacts on yield.

    Irrigation volumes and frequencies can be limited through
soil moisture monitoring and with the help of various water
conserving best management practices  (BMPs).  Soil moisture
monitoring can be done with portable moisture meters and probes
that indicate soil moisture levels.  This practice can help
determine the water requirement in a field and will identify
when water contents become low enough to cause crop stress.
                               -42-

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                         CHAPTER SEVEN

       OTHER PRACTICES TO REDUCE CONTAMINATION POTENTIAL
    In many areas of the country,  natural  hydrogeologic
conditions make pesticide leaching to ground water  more  likely
to occur than in other areas.   Factors that are generally
conducive to pesticide leaching include high ground-water
recharge rates, highly permeable soils, soils with  low
capacities to adsorb or biologically degrade pesticides,  and
shallow ground water depths.  In karst areas, ground water can
also become contaminated by surface water  running into
sinkholes.

    The potential for pesticides entering ground water can be
increased by man-made alterations to the land such as poorly
constructed, improperly sealed currently used or abandoned
wells, and agricultural drainage wells.  The potential can also
be increased from chemigation systems that are improperly
equipped.

    This  chapter describes actions, not all strictly manage-
ment practices, that can be taken either to minimize the
likelihood of pesticides entering ground water or to minimize
the impact on water supplies if contamination  should occur.

    Note:  Workshop participants  and  reviewers generally  agreed
that the  practices  described in this  chapter  should be employed
everywhere,  regardless  of hydrogeologic vulnerability.
 H<
dling and Disposal of Pesticides and Pesticide Productj
     Spills  and  improper  disposal  of  any pesticide,  not  just
 those pesticides  considered  to  have  high  leaching  potential,
 can  result  in ground-water contamination.   If  a  spill or
 release  occurs,  "slugs"  of the  pesticide  can overwhelm  normal
 decomposition processes  and  soil  adsorption capacity, resulting
 in a high potential  for  pesticide leaching.  Careful  handling
 and  disposal of pesticides are  critical parts  of an overall
 effort to reduce the risk of ground  water contamination.

     Studies in  Wisconsin, Iowa, California,  North Carolina,  and
 other  states suggest that incidents  in which pesticide
 concentrations  in ground water  exceed State standards are often
 the  result  of pesticide  spills  and leaks  during loading,
 handling, or storing of  pesticides,  and from pesticide
 equipment rinsing.
                               -43-

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    Pesticide storing,  mixing,  or loading activities should be
conducted as far from wells as  possible to prevent
contamination.   These activities should take place,  whenever
feasible, on an impervious foundation or on a ground cover to
retain spilled materials.   The  USDA Soil Conservation Service
can provide information to farmers interested in constructing
special facilities for mixing and loading designed to minimize
the potential for ground water  contamination.  Care should be
taken that storm drains and any routes of runoff from the area
are protected by berms or diking.

    Closed-system transfer, mixing, and loading of pesticides
can substantially reduce worker exposure and facilitate
pesticide handling.   In these systems the chemical is delivered
through gravity flow, suction,  or pumping, thus eliminating the
need to open and handle pesticide containers.  Closed systems
meter and transfer pesticide products from shipping container
to mixing or application tanks, and often rinse the emptied
containers as well.   Closed systems can also provide greater
accuracy in measuring the dosage, and reduce or eliminate fill
site contamination from spillage.  Mechanical failures such as
hose breaks, and backsiphoning  into water sources, however, may
occur with these systems,  depending on their design and
operation.

    Recommendations for pesticide handling have been summarized
by the University of Wisconsin  (1987):

    1)   Open pesticide containers carefully.

    2)   When adding water to a spray mixer, the hose or pipe
         should remain above the level of the mixture at all
         times to avoid the possibility of back-siphoning into
         the water source.  An input line should be submerged
         in the mix only when it is equipped with a reliable
         anti-siphoning device.

    3)   If an emulsifier or spreader-sticker is used, it
         should be added before the tank is full because these
         materials tend to cause foaming.

    4)   Be careful to avoid overflow and never leave a spray
         tank unattended while it  is being filled.

    5)   Always have materials  for containing or cleaning up a
         spill close at hand.  Know ahead of time what to do to
         contain a spill of the particular chemical being
         used.  A spill must be controlled, contained and
         cleaned up.  Since different chemicals require
         different actions, it is  a good  idea to have on hand
         the "Emergency Response Information Sheets" or  "Safety
                              -44-

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         Data Sheets"  from manufacturers  that  have  them
         available.   These provide detailed information about
         what to do  in case of  a spill.

    Significant ground-water contamination can result  if
pesticide containers break from rough handling,  weathering,
corrosion, or age.   Proper storage can help avoid these
problems. The label  instructions for  each registered pesti-
cide contain brief  but explicit instructions regarding storage
and disposal. Pesticide containers and materials may be stored
ideally in a separate fire-resistant  facility on a  pallet or^on
a raised impervious  or concrete platform.  The storage facility
should be hydrologically downgradient and a safe distance from
the drinking water  well and any other sensitive areas.  Spill
containment measures,  such as paving  and diking the area, will
prevent releases to  the environment.   Routine inspection of  the
condition of pesticide containers and the storage facility can
minimize the potential for leaks or spills.  Additionally,
maintaining an inventory of stored and used pesticides can be
helpful in this regard.

    Damage to containers and spills can occur during trans-
portation.  Precautions should be taken to avoid such
accidents, for example, by examining  the condition of  the
containers, fastening containers to prevent shifting and
damage, and protecting against weather conditions.

    Steps should be taken to minimize pesticide-related waste
and reduce disposal problems.  Reduction in left-over  tank
mixes, rinse water,  and the number of pesticide containers
requiring disposal  will enhance ground water protection
efforts.  In all cases, label directions should be followed
exactly.  Only the required amount of pesticide solution should
be mixed and equipment must be carefully calibrated.  Rinse
water can be sprayed on cultivated fields where feasible and
consistent with label directions.  Fresh water can be carried
and used to flush spraying equipment in  the field.

    Federal law requires triple rinsing  of pesticide
containers, or jet-spray cleaning, before disposal  (Federal
Insecticide, Fungicide and Rodenticide Act).  Rinsed  containers
should be stored securely prior to disposal to minimize  the
chance of inadvertent exposure to humans or the environment.
Metal containers may be recycled through scrap metal  dealers;
those not suitable for recycling or  refilling by distributors
should be disposed of  in a sanitary  landfill.

    The potential for pesticide contamination of ground  water
may be significantly reduced by employing  common sense,
caution, and the methods and procedures  discussed  above.
                              -45-

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Chemigation Anti-Backsiphoning Devices
    A growing practice in many areas of  the country is  the
application of fertilizers and pesticides  through irrigation
systems, often termed "chemigation".   Although there are
systems specifically designed for chemigation, in most  cases an
existing irrigation system is modified to  mix the chemical with
irrigation water for application to  crops.   Pesticides  (or
fertilizers) are generally stored in large tanks located near
wells drawing ground-water for irrigation.   Pesticides  flow
from the storage tanks into the irrigation water (see Figure
7-1) .

    Concerns about pesticide ground-water  contamination from
this practice rise from two potential problems:  (1) if the
system is not well designed and therefore  not operating
properly, the chemical-laden water may be  applied unevenly or
at an improper rate, resulting in inefficient use of the
chemical and a greater potential for leaching; and  (2)
accidental backflow or siphoning of chemicals into the well may
occur when the irrigation pumping system shuts down
unexpectedly (Schepers and Hoy, 1987).

    The importance of careful timing and application of
pesticides and irrigation water in reducing risks of pesticide
contamination due to leaching are discussed in Chapters Four
and Six.  Because of the potential for ground-water
contamination from backflow  into wells, this  section discusses
requirements for anti-backsiphoning equipment on  irrigation
systems used for pesticide application.

    Many States already  require the use of  anti-backsiphoning
devices on chemigation systems.  The State  of Nebraska  requires
also that chemigation systems contain inspection  ports  built
into the chemigation system  pipelines to allow visual
inspection of the check  valves  (State of Nebraska,  1986).   In
addition, EPA recently notified pesticide  registrants  that  they
must place specific chemigation use directions  on the  label  of
any  pesticide they wish  to be eligible  for  use  in such systems.

     Unless the pesticide user's  equipment  meets  these  EPA label
requirements, it will be a violation  of the Federal pesticide
law  to  use the pesticide in  the  chemigation system.  Labeling
requirements, PR Notice  87-1,  for chemigation systems  connected
to  sprinkler, flood,  and drip irrigation  systems include:

     1)   The system must contain a  functional check valve,
         vacuum  relief valve,  and low pressure drain appro-
         priately  located on the irrigation pipeline to prevent
         water  source  contamination from  backflow.
                               -46-

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                Bickflow
                prevention
                device
                            Irrigation pipe lint
trrigttion pump
                  Check
                  valvt
    should
    be property
    shielded
                       Discharge
                       line
                                FIGURE 7-1
       CHEMIGATION SYSTEM WITH ANTI-BACKSIPHQNING DEVICE
SOURCE: ASAE1980
                                   -47-

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    2)    The  pesticide  injection pipeline must contain a
         functional,  automatic, quick-closing check valve to
         prevent  the  flow of  fluid back toward the injection
         pump.

    3)    The  pesticide  injection pipeline must also contain a
         functional,  normally closed  solenoid-operated valve
         located  on the intake side of the  injection pipe and
         connected to the system interlock  to prevent fluid
         from being withdrawn from the supply tank when the
         irrigation system  is either  automatically or manually
         shut down.

    4)    The  system must contain functional interlocking
         controls to  automatically shut off the  pesticide
         injection pump when  the water pump motor stops.

    5)    The  irrigation line  or water pump  must  include  a
         functional pressure  switch,  which  will  stop  the water
         pump motor when the  water pressure decreases to the
         point where  pesticide distribution is  adversely
         affected.

    Readers who wish  to obtain a  copy of  the EPA labeling
requirements  for  pesticides to be  used  in chemigation should
write to the  Registration  Division,  Office  of Pesticide
Programs, TS767C, U.S.  Environmental  Protection Agency,
Washington, D.C.  20460  and  refer  to  PR Notice 87-1.


Buffer-Zone Establishment	

    A buffer  zone is  an established area or distance between a
polluting activity (e.g.,  nonpoint source of entry of
pesticides into ground water) and a point of ground-water
discharge such as a well.   The purpose of the buffer zone is to
allow adequate space and/or time for dilution,  dispersion,  or
degradation of the pesticide before it reaches the ground water
to minimize its potential  adverse impacts.   The concept of
altering activities to protect the ground water in portions of
the recharge area to a well  is fundamental to the new Wellhead
Protection Program established under the 1986 Safe Drinking
Water Act amendments,  rthile buffer zones  are generally useful,
they protect primarily existing wells, not future or potential
sources of drinking water (some future wells may be located in
wellhead protection  areas).

    Establishing  a buffer zone adequate in size and
configuration to  provide protection against pesticides entering
into ground water that  supplies a well depends upon a number  of
factors.  First,  pesticides  vary in the speed and degree to
                               -48-

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which they degrade in ground water.   Also important are
hydrogeologic conditions—such as the depth to ground water,
ground-water flow velocities,  ground-water flow patterns,
ground-water recharge rates, aquifer types,  recharge and
withdrawal rates, and assimilative capacity of the aquifer.   A
larger buffer zone may be required for groundwater that is
particularly vulnerable to contamination.  Vulnerable
ground-water resources may include aquifers with shallow ground
water or permeable soils with little or no adsorptive capacity
and/or high recharge rates.   In addition, consolidated rock
aquifers that are highly fractured present particular
challenges to protection, in many cases comparible to the karst
problem discussed later.  Readers interested in more
information regarding methods for determining size of wellhead
areas (buffer zones) should obtain a copy of "Guidelines for
Delineation of Wellhead Protection Areas," published by the
Office of Ground-Water Protection, U.S.Environmental Protection
Agency, WH-550G, Washington, D.C.  20460.

    Drinking water wells most likely to be impacted by
pesticides leaching to ground water are the domestic supply
wells located in rural areas near agricultural fields and
community supply wells where there is a high degree of
interface between agricultural and residential land use.  Wells
that are hydrologically downgradient from crop lands have the
greatest potential to be impacted.  For private wells at risk
to pesticide contamination, stopping the use of pesticides in
the area around the well can be an effective means of providing
extra protection to current sources of water supply.  Of
course, other practices, such as those described  in this
report, should be used to protect all  other ground water to
help assure its quality for future use.

    Many experts recommend  that pesticides should not be mixed,
stored, handled, or applied in the immediate vicinity of a well
(e.g., 25 to 50 feet) to avoid direct well contamination and
run-in from the land surface.
Proper Well Sealing and Abandonment
    Water wells with improper sealing around the well  casings
can provide a direct conduit for pesticides to enter ground
water from the land surface (Exner and Spalding, 1985).   If  a
well casing is backfilled with gravel, sand, or other  permeable
materials, pesticides can run down the side of the  casing and
into ground water.  Inadequate grouting and sealing can  also
lead to contamination of confined aquifers which would
otherwise be protected from surface contaminants.   Inadequate
grouting and sealing can be a problem particularly  if  the well
is located in a topographically  low area  susceptible to  surface
runoff.
                               -49-

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    State standards for well construction should be  followed.
Generally,  to prevent ground-water contamination via improperly
sealed wells, the well should be sealed with bentonite grout or
some other  form of relatively impermeable material.   In
addition, the well should be sealed with concrete for at least
two feet below ground surface.

    As is the case with wells that are inadequately grouted and
sealed, abandoned wells can also provide a direct conduit for
pesticides  to reach ground water, particularly if the well is
located in an area susceptible to runoff or chemical spills.
Also, abandoned wells may be used to dispose of chemicals by
parties unaware of the environmental or legal implications.

    Although many States have strict codes regarding the
abandonment of wells, these codes are difficult and sometimes
impossible to enforce.  Proper well abandonment often requires
pressure grouting and the blocking of casing perforations to
adequately seal off different aquifers and to prevent movement
of water through annular spaces.  It may involve removal of the
well casing or the pump above the ground.


Avoiding Sinkholes in Areas of Karst or Subsidence

    Karstic hydrogeologic conditions are found  in agricul-
tural areas, especially in the midwest and southeastern United
States. Under so called "conduit karst" conditions, ground
water may flow through openings  (see Figure  7-2) such  as caves,
rather than through porous or highly fractured  material  as
diffuse  flow (Quinlan  and Ewers,  1985).  In  karst areas,
sinkholes may form at  the surface allowing runoff water  to  flow
into ground water  in underground  conduits  (Hallberg and  Hoyer,
1982).   Subsidence due to excessive ground water extractions
can cause fractures  and cracking  in the ground,  increasing
opportunity  for movement of pesticides  into  ground  water.

    Sinkholes, when  located  in  areas susceptible to runoff from
agricultural fields, provide a  direct  path  for  pesticides  to
reach  ground water.  Also,  pesticides  entering  ground water in
karst  areas  can travel  for  long distances  with  little or no
dilution or  attenuation.

     Several  methods  are  available to help  ensure that pesti-
cide-contaminated surface  runoff  does  not  enter sinkholes.
Runoff  can be  channeled away from the  sinkhole; cover crops not
requiring pesticides can be planted around the sinkhole; and
pesticide use  in  the immediate  area of the sinkhole can be
stopped by use of a  buffer  strip made  of grass or  non-crop
vegetation.
                               -50-

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                                 FIGURE 7-2
                     KARSTIC GROUND-WATER CONDITIONS
SOURCE Hallberg. et al. 1984
                                  -51-

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Sealing of Agricultural  Drainage  Wells
    Agricultural drainage wells  (ADWs)  are sometimes  used to
drain excess water from fields,  particularly during wet
seasons, providing a direct route for pesticides to enter
ground water (Grahm, et.  al.,  1977).   Although installation of
new ADWs is illegal in most States,  many old wells still exist.

    ADWs are usually located in  topographically low areas
susceptible to surface runoff.   The  wells generally consist of
a cistern or basin to collect  water  and a well that drains
directly into the ground.  Generally, ADWs are found  in areas
that have underlying consolidated aquifers with high  secondary
porosities.  Relatively few are  found in unconsolidated
aguifers because those wells frequently clog.

    To prevent ground-water contamination from ADWs,  new wells
should not be constructed and old wells should be properly
abandoned.  Proper abandonment involves removal of old well
casing where possible, overreaming the borehole to greater than
its original diameter, and plugging the boring with impermeable
materials.
Subsurface Drainage and Treatment	

    Subsurface drains are often used to draw off excess water
from agricultural fields (Hallberg, et. al., 1986).  The
drained water is then discharged to surface water or allowed to
drain  into ground water through agricultural drainage wells
(see the discussion of ADWs above).  When  subsurface drainage
contains high concentrations of contaminants, treatment,  such
as carbon treatment, may be needed before  final discharge of
the drainage water to minimize adverse  impacts on either  ground
or surface water (Stryk, et. al.,  1977).

    Tile drains can be used to drain large areas without
disrupting the natural soil structure  (Stryk, et. al.,  1977).
The tile drains are designed to  lower  the  water table to  allow
drainage and cultivation and to  improve plant rooting.  Tile
drains are used extensively throughout  the corn belt  States  to
improve  soil drainage  in seasonally or  perennially  wet  soils.
Tile drains help to collect unused or  excessive pesticides
applied  to a crop  land.  The  leachate  may  be  recycled for use
as  irrigation water, or  it may  be  diverted to grass waterways
where  soil adsorption  and degradation  processes  can take
place.  (Note that  some  herbicides will kill  the  grass,
however.)
                               -52-

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Farm Ponds and Irrigation Re-Use Pits
    Farm ponds are often constructed on farm facilities by
damming up small streams.   These ponds form reservoirs of water
for irrigation,  for livestock use,  or for fish culture.  They
often collect surface runoff which may contain high
concentrations of pesticides.  Since the ponds may be deeper
than the water table, the possibility of contaminating adjacent
ground water exists.

    A measure to reduce risks that may result from pesticide
contamination of farm ponds is to establish a buffer zone
between the pond and nearby drinking water wells.  The potential
for ground water contamination from the ponds can also be
minimized by limiting pesticide use in nearby fields.

    Irrigation re-use pits are often built in topographic low
areas adjacent to agricultural fields.  The pits are used to
store runoff from fields for re-use as irrigation water.
Because the pits contain direct runoff, the water often con-
tains high concentrations of pesticides.

    Lining of irrigation re-use pits with low permeability
clays such as bentonite can help minimize the potential impacts
the pits may have on ground-water quality.  In addition,
mitigation measures should also include locating the pits as
far as possible from drinking water wells.
                              -53-

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                           APPENDIX A

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Hallberg, G. R., R. D. Libra, E. A. Bettis III,  and  B,  E.
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    Regulation and Control in Major Crop Ecosystems. Progress
    Report.  Volume 1.  1975.

Nebraska, State of.  Legislative Bill 284.   1986.

Nebraska, University of.   farm, Ranch,  and  Home Quarterly.
    30:  No. 3.  Special Edition 1984.   Institute  of
    Agriculture and Natural Resources.   1984.

Newson, L. D.  Progress in Integrated Pest  Management of
    Soybean Pests.  Pest Control Strategies, F. H. Smith and D.
    Pimentel, eds.  pp.  157-180.   Academic  Press,  New York,
    N.Y.  1978.

Quinlan, J. F. , and R. D.  Ewers.   Ground Water Flow in
    Limestone Terrains:   Strategy Rationale and Procedure for
    Reliable, Efficient Monitoring of Ground Water Quality in
    Karst Areas.  Proceedings of the Fifth  National Symposium
    and Exposition on Aquifer Restoration and Ground Water
    Monitoring.  National Water Well Association.   Dublin,
    Ohio.  1985.

Roberts, H. A.  Weed Control Handbook and Principles.
    Seventh Edition.  Blackwell Scientific  Publications.
    Boston, Massachusetts.  1982.

Rudd, W. G., Revsink, W. G., Newson, L. D., Herzog, D. C.,
    Jensen, R. L. and N. F. Marsolan.  Tne  Systems Approach to
    Research and Decision Making for Soybean Pest Control.
    New Technology of Pest Control.  C. B.  Huffker, ed.
    pp. 99-122.  John Wiley and Sons.  New York, N.Y.  1980.

Schepers, J.S. and D.R. Hay,.  Impacts of Chemigation on
    Groundwater Contamination.  Rural Groundwater
    Contamination.  Frank M. D'Irti and Lois G. Wolfson,  eds.
    Lewis Publishers, Inc.  Chelsea, Michigan.  1987.

Smith, E. E., Lang, E. A., Casler, G. L., and  R. W. Hexem.
    Cost-Effectiveness of Soil and Water Conservation Practices
    for Improvement of Water Quality.  Effectiveness of Soil
    and Water Conservation Practices for Pollution  Control.
    U.S. Environmental Protection Agency, Office of Research
    and Development, Athens, Georgia.  1979.
                              A-4

-------
Stryk, Y., et.  al.  Atrazine Residues in Tile Drain Water as
    Affected by Cropping Practices and Fertility Levels.
    Canadian Journal of Soil Science 57:249-259.  1977.

U.S. Department of Agriculture.  Cooperative Extension
    and Agricultural  Profitability—Integrated Pest Management
    Reduces Costs and Increases Income.  U.S. Dept.  of
    Agriculture, Cooperative Extension Service.  Washington,
    D.C.  April 1985.

U.S. Department of Agriculture.  Irrigation.  Engineering
    Field Manual.   Soil Conservation Service.  U.S.  Department
    of Agriculture.  Washington, D.C.  1983.

U.S. Environmental Protection Agency.  Effectiveness of Soil
    and Water Conservation Practices for Pollution Control.
    U.S. Environmental Protection Agency, Office of Research
    and Development.  Athens, Georgia.  1979.

U.S. Environmental Protection Agency.  Pesticides in Ground
    Water:  Background Document.:   U.S. Environmental Protec-
    tion Agency, Office of Ground-Water Protection,  Washington,
    D.C.  1986.

van der Bosch,  R.   The Pesticide Conspiracy.  Doubleday Company,
    Inc., Garden City, New York  1978.

van de Leeden,  Frits, and F. L. Troise.  Climates of the
    States.   Water Information Center, Inc., Port Washington,
    New York.  1974.

Wisconsin, University of.   Agriculture Management Practices to
    Minimize Groundwater Contamination.  Environmental
    Resources Center.  Madison, Wisconsin.  1987.
                               A-5

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                           APPENDIX B


       DEGRADATION RATE CONSTANTS FOR SELECTED PESTICIDES
    Tables B-l and B-2 present degradation rate constants for
selected pesticides on foilage and for selected pesticides in
soil respectively.  These constants express the rates at which
pesticides decay or breakdown when present on plant surfaces or
in the soil.   Knowledge of these degradation rates can aid in
preventing ground-water contamination.  Pesticides which
degrade relatively fast should be chosen over those which
degrade slower, assuming that performance and applicability are
consistent with intended use.
                               B-l

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                                       TABLE B-l:   DEGRADATION RATE CONSTANTS FOR SELECTED
                                                      PESTICIDES ON FOLIAGE
              Class
                                              Group
                                                            Decay Rate
                                                             (days'1)
          Organochlorine
CO
I
M
Oiyanophosphate
          Carbamate
                    Fast

(aldrin, dieldrin, ethylan, heptachlor, lindane
methoxychlor).

                    Slow

(chlordane,  DDT, endrin, toxaphene).

                    Fast

(acephate, chlorpyrifos-methyl,  cyanophenphos,
diazinon, dipterex,  ethion, fenitrothion,  leptophos,
malathion, methidathion, methyl  parathion, phorate,
phosdrin, phosphamidon, quinalphos, alithion,
tukutliion, triazophos,  trithion).

                    SJow

(azinphosmethyl, demeton, dimethoate, EPN, phosalone).

                    Fast
                (carbofuran)

                    Slow
                 (carbaryl)
                                                                               0.231 - 0.1386
                                                                                         0.1195 - 0.0510
                                                                                         0.2772 - 0.3013
                                                                                         0.1925 - 0.0541
                                                                                         0.630
                                                                                         0.1260 - 0.0855

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ro
i
              Class
                                      TABLE B-l:  DEGRADATION  RATE CONSTANTS FOR SELECTED

                                                      PESTICIDES ON FOLIAGE

                                                           (Continued)
	Group
    Decay Rate

     (days~l)	
          Pyrethroid



          Pyridine



          Benzole acid
(permethrin)



(pichloram)



 (dicamba)
0.0196



0.0866



0.0745
          Source:  Knisel, 1980.

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         TABLE  B-2:
SOIL DEGRADATION RATE CONSTANTS FOR
  SELECTED PESTICIDES
   Chemical Name

Alachlor
Aldicarb
Atrazine
Benanyl
Bifenox
Carbaryl
Carbofuran
Chlordane
Chloropropham
Cyanazine
Dalapon
Diazinon
Dicamba
Dichlobenil
2,4-Dichlorophenoxy-
  acetic Acid
Dinoseb
Diuron
Fenitrothion
Fluometuron
Linuron
Malathion
Methoxychlor
Methyl Parathion
Monuron
Parathion
Permethrin
Phorate
Picloram
Propachlor
Propanil
Propazine
Simazine
Toxaphene
Trifluralin
Zineb
    Degradation Rate
   Constant  (days"1)
0. 0384
0.0322
0.0149
0 . 1486
0 . 1420
0. 1196
0.0768
0. 0020
0 . 0058
0.0495
0.0462
0.0330
0.2140
0.0116
0.0693
0.0462
0.0035
0.1155
0.0231
0 .0280
0 .291
0.0046
0.2207
0 . 0046
0.2961
0.0396
0.0363
0.0354
0 .0231
0.693
0.0035
0 . 0539
0 . 0046
0 . 0956
0.0512

- 0. 0116
- 0.0063
- 0.0023

- 0.0768
- 0.0079
- 0.0007
- 0.00267

- 0.0231
- 0.0067
- 0.0197
- 0.0039
- 0 .0231
- 0.0231
- 0.0014
- 0.0578

- 0. 0039
- 0.4152
- 0.0033

- 0. 0020
- 0.0046

- 0. 0040
- 0. 0019
- 0. 0139
- 0.231
- 0.0017
- 0.074

- 0.0026

Reference

      a
      a
      a
      a
      a
      a
      a

      d
      c
      d
      a
      a
                                 d
                                 d
                                 d
                                 a
                                 c
                                 a
                                 a
                                 a
                                 a
                                 d
                                 a
                                 e
                                 a
                                 a
                                 d
                                 d
                                 d
                                 a
                                 e
                                 a
                                 a
                               B-4

-------
    TABLE B-2:  SOIL DEGRADATION RATE CONSTANTS FOR
                  SELECTED PESTICIDES
                       (Continued)
Nash, R.G.,  1980.  Dissipation Rate of Pesticides from
Soils.  Chapter 17.  IN CREAMS:  A Field Scale Model for
Chemicals Runoff, and Erosion from Agricultural Management
Systems.  W. G. Knisel, ed.  USDA Conservation Research
Report No.  26.  643 pp.

Smith, C.N., Partition Coefficients (Log Kow) for
Selected Chemicals.  Athens Environmental Research
Laboratory,  Athens, GA.  Unpublished report, 1981.

Herbicide Handbook of the Weed Science Society of America,
4th ed. 1979.

Control of Water Pollution from Cropland, Vol. I, a manual
for guideline development, EPA-600/2-75-026a.

Smith, C.N.  and R. F. Carsel.  Foliar Washoff of  Pesticides
(FWOP) Model:  Development and Evaluation.  Accepted  for
publishing  in Journal of Environmental Science and
Health - Part B.   Pesticides,  Food Contaminants,  and
Agricultural Wastes, B  19(3),  1984.

Source:  Carsel, et  al.  1984
                            B-5

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                           APPENDIX C

                DOMINANT SOIL ORDERS OF THE U.S.
    Figure C-l shows patterns of dominant soil orders and
suborders of the U.S. and identifies crops and topographic
conditions that are associated with each.  This figure provides
information useful in the identification of topographic and
soil conditions which is necessary for the selection of
mitigation measures to reduce pesticide leaching.  How these
factors should be considered in the selection of mitigation
measures is described in Part I of this report.
                               C-l

-------
o
 I
                                                               FIGURE C-1

                                         PATTERNS OF SOIL ORDERS AND SUBORDERS OF THE U.S.
    SOURCE U S Soil Coci'.prvalion Srvu-p

-------
U  S  DEPARTMENT OF AGRICULTURE
                         LEGEND
                                    *ho*n  E*e* d»lit»**uon MI
            ni af otiwt kind* of *oil  G«ii«f*l dcfini'ion* tor '-h« ort**«
             follow  For coaplti* d*finiuo*» •*« Soi. Sufv*y Suff
  Son CiMtiiicmon, * Caapr^i^tiv* Svt'm "ch Appro^iajdor. Sou
  •"an»«rv«ue» S*r*ici L'  S  D*p*rtrB*m ol AfneaiTu*  196C  for **!• bv
  .  S Oov*r«*nt Prifltint Ofhct j *ad ib* H«trfi l W iupplMtM-- ( «»«..•
  • e i c* horuarM
|         j  of cbr •ceuauuiiM  a*u*uy «oi*t but ruy M dry dwi*i


  * I   AQUALFS  (••MM»UT Mtmvd wit* •«l»rl |*etly tlopiat
         M»*r«]  eroM if dr«i»*d M*TUM Md •wdlwid if «ndr«ia*d
         ( SO*M LOT-HMOIC SI*? toil* Md PUeocoL* )

  * 2   BORALPS  ( cool or cold ) fMnly tlaoiat maKlf woodlMd
         M*t«r*. mi to»* HMil pua < CW*T Io°d»d M»U }

  v.^  BOKALtt  B-*f —uy voodLj^

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                             Miaui u4 R«d-Yclio« Podjouc  toi
           ABIQI50LS     SoiU -it*
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            ENTISOLS      SoU« witbor*
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                                                                            MlSTOSOLS     Ornate Mill
                                                                                    d or idl* ., F»*«u |

                                                                      SAPftlSTS  .' MctMMMd rMCU ( mck cran J
                                                                            INCEFTl&OLS     Soifc
                                                                  US   AJ4DCPT3 i ">t* ••orptiowi tl*
                                                                          p«Mic* i |»f!ly »lo«ia| 10
                                                                          H«*«II •0*1 ly tut*) CUM p
                                                                          MiU, (OM* Toads* »ou)

                                                                  U    ACCEPTS
                                                                  QP  AQUEPT! (WithcoBiut
                                                                          llopkJI to *t**9 w«ortlMd or tdkt ( T«
                                                                  13   OCHKCPTS  (
                                                                          p«Mv«  »a«n cr*i«  Md h«y ( Soil Bran* AtidM «
                                                                          AliMTUl »0lll )
  L3S  OCHJTEFTS M»UT ikMUf to «*<
         (ntM



         i4«d i S-M* a«tMot*}

M  •  mi ^^



III    AQUOLLS  UMBM-iUy Mm»t»d with ••tui |.mly il^n


M2    BOKOLLS  i cool or rold '; MB' 1 y « »OMT«(«)T ilo»*l  M
                                                                       UTX3LLS i t««p
                                                                          l»«iiy lo »
                                                                          vMtvn pwt.  *to>
                                                                          MM* tm^Md erof
                                                                          Md Brow «ojl»)

                                                                  H4S  USTOL-L3 ariiTT'T

                                                                  US   XCJrOLU (comiMO
                                                                          x *i«t*i) fMtlr 1
                                                                  •&S   XEROLLJ


                                                                  RW'TTJ 3POOO4OLS     SoiU wit* »cc»*-« .<=«.'
                                                                                                                                  Ul   AQUUL'H  rMMOMlly Hnntwj "it* »«tn >  i^tl
                                                                                                                                          *«odLMd Md p«tnir« ,f uidn^cd '«wl knd 'rv
                                                                                                                                  U2S  HUWULTS  f
                                                                 U3   UtXJLT? ( «t* 'vm ar^ax- ••IIBT coot.n- i
                                                                         Md Mout i  ft i If to »oi**™l»ly tio^LBt »
                                                                         (••d crop«  'oOacco  Md conn   R*4-Y«
                                                                         •«•• Rt4di*k-Bnm LMtrax *ou» )

                                                                 UJ5  UTXILTS

                                                                 U4S
                                                                                                                                            VgOTiSOLS   .  Soil* »nh hit** cawt«t si twi, Lflf c
                                                                          nc*  ( So«« GnMOM

                                                                  VTI    USTRRITt  (cr^to o
                                                                                                                                             AREAS  •>* "n*
                                                                                                                                          ackl«fld ic* field*
                                                                                                                                    •OJML »«" )  I (  ALFISOL Md CCWUUI
                                                                                                                                    M tb* fiA«l «yLl«bl« f n>aTi ''«- c t^y
                                                                                      • Ui • baruo*. oi ci*y •ectMui

                                                                            bar     - G<  ky»«i. ttarUvra  cool

                                                                            fibr     - L  'itr*. tlb*r LMK teca*pa

                                                                            hwi     - L.  iMW*. **rUi
                                                                                                                                                     -  Gf

                                                                                                                                                     -  Oi
                                                                                                                                                        orfiuic «*n«r

                                                                                                                                               id      - L  Mtv*. bvnt ci* 4
                                                                               FIGURE C-1  (cont.)
                                        PATTERNS  OF SOIL  ORDERS AND  SUBORDERS  OF THE  U.S.
                                                                                           C-3

-------
                           APPENDIX D

                       INFORMATION  SOURCES
    To design an appropriate State or Local program to reduce
 risks of pesticide contamination, consideration must be given
 to hydrological conditions, cropping patterns, agricultural
 practices, pest control needs, and alternatives.  Information
 on these topics is available from a variety of sources; the
 guide which follows describes several sources including Key
 agencies and organizations and the information they can provide
 (see Figure D-l for a summary).
    The Cooperative Extension Service  (CES), a joint program of
the U.S. Department of Agriculture  (USDA),  States, and
counties, serves the American agricultural  community tnrough
dissemination and application of information generated by
research efforts.  The CES is the most extensive and readily
available source of information on agriculture and plays an
important role in educating pesticide users.  Local offices of
the CES may be found in the telephone directory, usually listed
under the U.S. Department of Agriculture.

    The U.S. Soil Conservation Service (SCS), among other
activities, provides direct technical assistance to landowners
in designing and carrying out plans for conserving soil and
protecting water quality.  SCS soil surveys provide detailed
information on soil type and distribution as well as other data
useful in assessing the potential for ground water
contamination from pesticides.  Local offices of the SCS may
also be found in the telephone directory, usually under
U.S. Department of Agriculture.

    Land Grant Universities generally nave  major agriculture
and science programs and represent excellent sources of
information.  Federal and State governments and industry
sponsor many projects conducted by leading  researchers at these
institutions.  Firsthand knowledge of local or regional
agricultural practices may be obtained through contact with
these investigators.  Land Grant Universities are also linked
to the Cooperative Extension Service.

    Agricultural Experiment Stations and Water Resources
Research Institutes are sources of local and regional
information and are usually associated with major universities
                              D-l

-------
or colleges.  Results of research typically are available as
technical reports documenting findings and observations of
agricultural and water resource investigations.

    States generally have a Department of Natural Resources,
Water Quality, Environmental Protection,  or similarly named
agency responsible for managing and protecting ground water.
These agencies are potential sources of information,  as are
State Soil and Water Conservation Agencies.  Offices  of State
agencies can be found in the telephone directory.  State
Geological Surveys generally have major ground water  programs,
and in light of the recent interest in pesticide contamination,
many may have ongoing research projects in this area.  State
surveys are sometimes located in capital cities out may also be
associated with colleges or universities.

    Tne U.S. Geological Survey (USGS)  is the principal Federal
agency conducting ground water resources investigations.
Technical details concerning the geology and water resources of
many areas of the country are presented in USGS Water Supply
Papers.  These reports, usually available at major college or
university libraries, provide information essential for
evaluating the vulnerability of the study area to ground water
contamination.  The USGS headquarters is located in Reston,
Virginia, with numerous offices in other locations.

    U.S. Geological Survey
    12201 Sunrise Valley Drive
    Reston, Virginia  22091
    (703)860-7000

    The Conservation Technology Information Center is a
clearinghouse for information encouraging conservation  systems
for soil and water on croplands.  Information  relating  to
conservation tillage and water quality protection  is currently
available; fact sheets on pesticide and nitrate contamination
of ground water are under development at the time  of this
writing.  For specific information, contact:

    The Conservation Technology Information Center
    1220 Potter Drive
    Room 170
    Purdue Research Park
    West Lafayette, Indiana  47906-13314
    (317)494-9555
                               D-2

-------
    The National Agriculture Library publishes a series of
commodity-oriented environmental bibliographies.  Two recent
bibliographies -- "Conservation Tillage and "Chemigation" --
include the latest available information from United States
publications  involving commodity protection relating to these
two aspects of ground water contamination, pesticides use, and
alternative agricultural practices.  These, and other
publications, can be obtained through:

    National Agricultural Library
    U.S. Department of Agriculture
    Beltsville, Maryland  20705

    Resources For The Future, a non-profit research
association, has compiled a data base of pesticide use
estimates for a typical year in the 1980s.  It details tne
percent of acreage treated with pesticides and the application
rate per acre on a State and county level.  Information
concerning this data base can be obtained from:

    Resources For the Future
    1616 P. Street, N.W.
    Washington, D.C.  20036
    (202)328-5000

    National Pesticide Information Retrieval System  (NPIRS)  is
a data base produced by Purdue University.  It contains
pesticide chemical and registration data for 50,000 products
registered by EPA, as well as thousands of State
registrations.  Facts sheets for each registered pesticide
contain data on product names, pesticide use patterns, EPA
registration numbers, formulations, active ingredients, and
sites and crops where the pesticides are used.  Information on
NPIRS, including accessing information, can be obtained oy
contacting:

    User Services Manager, NPIRS
    Entomology Hall
    Purdue University
    West Lafayette, Indiana  47907
    (317)  494-6614

    The Institute for Alternative Agriculture is an
organization dedicated to advancing agricultural economics,
resource conservation, and environmental protection.
Information on alternative farming practices which may be
implemented to reduce the potential for ground water
contamination from pesticides is available from the Institute:
                              D-3

-------
     Institute for  Alternative  Agriculture
     9200  Edmonston Road
     Suite 117
     Greenbelt,  Maryland   2U770
     (301)441-8777

     Farm  Chemicals Handbook, published annually,  is a directory
 and  reference for  fertilizer and pesticide users.  It contains
 information  on  specific pesticides,  including cnemical names,
 trade  names,  common names, chemical  properties, toxicity,
 applications,  and  formulation.  The  handbook can  be obtained by
 contacting:

     Meister  Publishing Company
     37841 Euclid Avenue
     Willoughby, Ohio  44094
     (216)  942-2000

     The Weed  Science Society of America produces  the "Heroicide
 Handbook.1   It  contains an alphabetical listing of all
 available  herbicides and  includes information on  common names;
 chemical  names; chemical  and physical properties, including
 structural and  molecular  formulae, vapor pressure, and
 adsorption parameters; herbicide use, including application
 methods,  associated crops, and application rates; toxicology;
 and  behavior  in soil and  general potential for leaching.  This
 publication can be obtained by contacting:

    Weed Science Society  of America
     309 West Clark Street
    Campaign, Illinois  61820
     (217)  356-3182

    Weed Control Manual and Insect Product Guide  contain
 listings of insecticides  and herbicides by various crop types.
Also included are mixing  instructions, use instructions, and
 lists of weeds and insects controlled by each pesticide.  The
guides can be obtained by contacting:

    Ag Consultant and Fieldman
    37841 Euclid Avenue
    Willoughby, Ohio 44094
     (216)  942-2000
                              D-4

-------
                                TABLE D-1
                       SOURCES OF INFORMATION
              SOURCES
                                               TYPES OF INFORMATION
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COOPERATIVE EXTENSION SERVICE
SOIL CONSERVATION SERVICE
LAND GRANT UNIVERSITY
STATE AGRICULTURAL EXPERIMENT STATION
STATE WATER RESOURCES RESEARCH INSTITUTE
STATE GEOLOGICAL SURVEY
STATE GROUND WATER AGENCY
STATE SOIL AND WATER CONSERVATION AGENCY
U.S. GEOLOGICAL SURVEY
CONSERVATION TECHNOLOGY INFORMATION CENTER
NATIONAL AGRICULTURAL LIBRARY
RESOURCES FOR THE FUTURE
NATIONAL PESTICIDE INFORMATION RETRIEVAL SYSTEM
INSTITUTE FOR ALTERNATIVE AGRICULTURE
FARM CHEMICALS HANDBOOK
HERBICIDE HANDBOOK
INSECT PRODUCT GUIDE

-------