**Guidance for Prospective**

**Ground-Water Monitoring Studies**

Environmental Fate and

Effects Division

Office of Pesticide Programs

U.S. Environmental Protection Agency

December 19, 2007

[CHAPTER 1 - INTRODUCTION 7](#chapter-1---introduction)

[1.1 Environmental Exposure Characterization
8](#environmental-exposure-characterization)

[1.11 Fate and Transport Studies 9](#__RefHeading___Toc184799136)

[1.12 Conceptual Model 11](#conceptual-model)

[1.2. Ground Water Exposure and Estimating Risk
13](#ground-water-exposure-and-estimating-risk)

[1.21 Evaluation of Registered or Proposed Uses
13](#evaluation-of-registered-or-proposed-uses)

[1.22 Available Monitoring Data 14](#available-monitoring-data)

[1.23 Modeling Ground Water Exposure
14](#modeling-ground-water-exposure)

[1.24 Consideration of Risk 15](#consideration-of-risk)

[1.3 CASE STUDY 15](#case-study)

[1.31 Exposure Characterization 15](#exposure-characterization)

[1.32 Monitoring 16](#monitoring)

[1.33 Modeling 17](#modeling)

[1.34 Data Evaluation 17](#data-evaluation)

[1.4 STUDY COMPONENTS 18](#study-components)

[1.5 STUDY RESULTS 19](#study-results)

[CHAPTER 2 - SITE SELECTION 19](#chapter-2---site-selection)

[2.1 STUDY SCOPE 20](#study-scope)

[2.11 Definition 20](#definition)

[2.12 Compounds of Interest and Analytical Methods
22](#compounds-of-interest-and-analytical-methods)

[2.2 A SET OF CANDIDATE SITES 23](#a-set-of-candidate-sites)

[2.21 Unconfined Aquifer 24](#unconfined-aquifer)

[2.22 Shallow Depth 24](#shallow-depth)

[2.23 No Flow Restrictive Layers 24](#no-flow-restrictive-layers)

[2.24 Preferential Flow 25](#preferential-flow)

[2.25 Tile Drains 25](#tile-drains)

[2.26 Single Soil Series Mapping Unit
25](#single-soil-series-mapping-unit)

[2.27 Low Topographic Slope 26](#low-topographic-slope)

[2.28 Stable Hydraulic Gradient 26](#stable-hydraulic-gradient)

[2.3 COOPERATOR INTERVIEW 27](#cooperator-interview)

[2.31 No Prior History of Test Pesticide Use
27](#no-prior-history-of-test-pesticide-use)

[2.32 Long-Term Availability of Study Site
27](#long-term-availability-of-study-site)

[2.4 PRELIMINARY SITE CHARACTERIZATION
28](#preliminary-site-characterization)

[2.41 Absence of Dominant Fracture Flow
28](#absence-of-dominant-fracture-flow)

[CHAPTER 3 - SITE CHARACTERIZATION AND CONCEPTUAL MODEL
30](#chapter-3---site-characterization-and-conceptual-model)

[3.1 EXISTING LOCAL DATA AND BASE MAP
30](#existing-local-data-and-base-map)

[3.11 Compile Existing Local Data 31](#compile-existing-local-data)

[3.12 Develop a Base Map 31](#develop-a-base-map)

[3.13 Information Sources 32](#information-sources)

[3.2 SOIL AND VADOSE ZONE INVESTIGATION
32](#soil-and-vadose-zone-investigation)

[3.21 Exploratory Coring Program and Field Testing
33](#exploratory-coring-program-and-field-testing)

[3.22 Number and Locations of Soil Cores
34](#number-and-locations-of-soil-cores)

[3.23 Field Testing 35](#field-testing)

[3.24 Preservation and Transportation of Formation Samples
35](#preservation-and-transportation-of-formation-samples)

[3.25 Quality Assurance and Quality Control Procedures
36](#quality-assurance-and-quality-control-procedures)

[3.26 Test Pit Excavation 36](#test-pit-excavation)

[3.27 Abandonment of Soil Core Holes
37](#abandonment-of-soil-core-holes)

[3.3 SATURATED ZONE INVESTIGATION 37](#saturated-zone-investigation)

[3.31 Hydraulic Head 37](#hydraulic-head)

[3.32 Direction of Ground-Water Flow and Hydraulic Gradient
38](#direction-of-ground-water-flow-and-hydraulic-gradient)

[3.33 Hydraulic Conductivity 38](#hydraulic-conductivity)

[3.34 Background Water Quality 38](#background-water-quality)

[3.4 CONCEPTUAL MODEL 39](#conceptual-model-1)

[3.41 Soils and the Vadose Zone 39](#soils-and-the-vadose-zone)

[3.42 Saturated Zone and Water Quality
40](#saturated-zone-and-water-quality)

[CHAPTER 4 - MONITORING PLAN DESIGN 41](#__RefHeading___Toc184799189)

[4.1 SETTING UP 41](#setting-up)

[4.11 Agricultural Management Practices
41](#agricultural-management-practices)

[4.12 Irrigation 42](#irrigation)

[4.13 Initial Post‑Pesticide Application Irrigation Event
42](#__RefHeading___Toc184799193)

[4.14 Irrigation After Initial Event
43](#irrigation-after-initial-event)

[4.15 Mixing and Loading Area 43](#mixing-and-loading-area)

[4.16 Control Plot 43](#control-plot)

[4.17 Decontamination Area 44](#decontamination-area)

[4.18 Weather Station 44](#weather-station)

[4.2 Application of Pesticide and Tracer
44](#application-of-pesticide-and-tracer)

[4.21 Pesticide 44](#pesticide)

[4.22 Tracer 44](#tracer)

[4.3 SOIL MONITORING PLAN 45](#__RefHeading___Toc184799202)

[4.31 Soil Sampling Methods and Instrumentation
45](#soil-sampling-methods-and-instrumentation)

[4.32 Number and Location of Soil Cores
45](#number-and-location-of-soil-cores)

[4.33 Soil Sampling Timing and Frequency
46](#soil-sampling-timing-and-frequency)

[4.4 SOIL-WATER MONITORING PLAN 46](#soil-water-monitoring-plan)

[4.41 Soil Water Content Measurements
46](#soil-water-content-measurements)

[4.42 Instrumentation 46](#instrumentation)

[4.43 Location and Frequency of Sampling
47](#location-and-frequency-of-sampling)

[4.44 Soil water Sampling 47](#soil-water-sampling)

[4.45 Instrumentation 47](#instrumentation-1)

[4.46 Depth and Number of Lysimeters
47](#depth-and-number-of-lysimeters)

[4.47 Time of Emplacement 48](#time-of-emplacement)

[4.48 Sampling Frequency 48](#sampling-frequency)

[4.5 GROUND-WATER MONITORING PLAN 48](#ground-water-monitoring-plan)

[4.51 Monitoring Well Design 49](#monitoring-well-design)

[4.52 Number, Emplacement, and Screen Lengths of Wells Within a Cluster
49](#number-emplacement-and-screen-lengths-of-wells-within-a-cluster)

[4.53 Number and Location of Monitoring Well Clusters
49](#number-and-location-of-monitoring-well-clusters)

[4.54 Time of Emplacement 50](#time-of-emplacement-1)

[4.55 Sampling Frequency 50](#sampling-frequency-1)

[4.56 Instrumentation 50](#instrumentation-2)

[4.57 Sampling Methods 51](#sampling-methods)

[4.58 Integrated Sampling Schedule 51](#integrated-sampling-schedule)

[CHAPTER 5 - SITE CHARACTERIZATION AND MONITORING PLAN DESIGN REPORTS
56](#chapter-5---site-characterization-and-monitoring-plan-design-reports)

[5.1 SITE CHARACTERIZATION REPORT 56](#site-characterization-report)

[5.11 Site Base Map 57](#site-base-map)

[5.12 Surficial Soil Characteristics
57](#surficial-soil-characteristics)

[5.13 Field Testing Methods and Results
57](#field-testing-methods-and-results)

[5.14 Historical Water Needs and Net Recharge
57](#historical-water-needs-and-net-recharge)

[5.15 Test Pit Excavation 58](#test-pit-excavation-1)

[5.16 Exploratory Boring Program 58](#exploratory-boring-program)

[5.17 Saturated Zone Investigations 58](#saturated-zone-investigations)

[5.18 Background Water Quality 58](#background-water-quality-1)

[5.19 Conceptual Model 58](#conceptual-model-2)

[5.2 MONITORING PLAN DESIGN REPORT (PROTOCOL)
59](#monitoring-plan-design-report-protocol)

[CHAPTER 6 - MONITORING PLAN IMPLEMENTATION
62](#__RefHeading___Toc184799236)

[6.1 APPLICATION OF PESTICIDE AND TRACER
63](#application-of-pesticide-and-tracer-1)

[6.2 IRRIGATION 63](#irrigation-1)

[6.3 SOIL MONITORING 64](#soil-monitoring)

[6.31 Decontamination of Sampling Equipment
64](#decontamination-of-sampling-equipment)

[6.32 Soil Sample Collection and Handling
64](#soil-sample-collection-and-handling)

[6.4 PORE-WATER MONITORING 65](#pore-water-monitoring)

[6.41 Instrumentation 65](#instrumentation-3)

[6.42 Decontamination 66](#decontamination)

[6.43 Sample Collection 66](#sample-collection)

[6.5 GROUND-WATER MONITORING 67](#ground-water-monitoring)

[6.51 Instrumentation 67](#instrumentation-4)

[6.52 Well Development 68](#well-development)

[6.53 Decontamination 69](#decontamination-1)

[6.54 Sample Collection 69](#sample-collection-1)

[6.6 SAMPLE HANDLING AND TRACKING 70](#sample-handling-and-tracking)

[CHAPTER 7 - REPORTING 72](#chapter-7---reporting)

[7.1 QUARTERLY REPORTS 72](#quarterly-reports)

[7.11 Summary of Site Activities 73](#summary-of-site-activities)

[7.12 Mass Balance 73](#mass-balance)

[7.13 Protocol Deviations 73](#protocol-deviations)

[7.14 Analytical Results 73](#analytical-results)

[7.2 STUDY TERMINATION REPORT 74](#study-termination-report)

[7.3 FINAL REPORT 74](#final-report)

[7.31 Field Practices 75](#field-practices)

[7.32 Sampling Activities 75](#sampling-activities)

[7.33 Analytical Results and Discussion of Findings
75](#analytical-results-and-discussion-of-findings)

[7.34 Quality Assurance 75](#quality-assurance)

[7.4 ELECTRONIC DATA REPORTING GUIDELINES
76](#electronic-data-reporting-guidelines)

[7.41 Study Area and Conceptual Site Model
77](#study-area-and-conceptual-site-model)

[7.42 Application of pesticide and tracer
77](#application-of-pesticide-and-tracer-2)

[7.43 Crop information 78](#crop-information)

[7.44 Soil properties 78](#soil-properties)

[7.45 Ground-water data 79](#ground-water-data)

[7.46 Weather data 79](#weather-data)

[7.47 Irrigation input 80](#irrigation-input)

[7.48 Chemical monitoring results 80](#chemical-monitoring-results)

[CHAPTER 8.0 - REFERENCES 81](#chapter-8.0---references)

**[ACKNOWLEDGEMENT]{.underline}**

Many scientists in the Environmental Fate and Effects Division deserve
thanks for their roles in the design of these studies and development of
this Guidance. We would like to acknowledge Michael Barrett, Elizabeth
Behl, Kevin Costello, and James Wolf, who developed the design of the
field study described in this document and who wrote substantial
sections of the document. Other scientists provided significant
technical input and editing of the guidance and/or participated in the
public workshop and Scientific Advisory Panel meetings were Jonathan
Angier, Mark Corbin, R. David Jones, Robert Matzner, Laurence Libello,
David Wells and Amy McKinnon. Finally, the original concept of designing
a prospective ground-water monitoring study for pesticides was developed
by Stuart Z. Cohen and Catherine Eiden.

# CHAPTER 1 - INTRODUCTION

This document provides guidance for conducting a Prospective
Ground-Water (**PGW) monitoring study** for the registration of
pesticides in the United States (listed as guideline number 166-1 in 40
CFR 158.29). The PGW study, which is required on a case-by-case basis,
is conducted in a controlled setting and provides the Agency with data
for evaluating the impact of legal pesticide use on ground water
quality. After assessing the overall environmental fate of a pesticide,
the Agency may require the pesticide manufacturer (registrant) to
conduct a PGW study, with input from EPA on key aspects of the study
design. The Agency's assessment is based on a review of laboratory data
on mobility and persistence of the compound, estimates of potential
exposure, available monitoring and modeling information, and a
consideration of the potential for risk from drinking water exposure.
Data generated from these field studies have proven valuable to EPA
scientists and risk managers as they are specifically designed to relate
pesticide use specified on the label to measurements of the pesticide
and its degradates in ground water used as a source of drinking water.
This document provides guidance on how to conduct a PGW monitoring
study, describes milestones for consulting with EPA, and describes how
results should be reported to EPA.

EPA uses the results of PGW monitoring studies to help answer questions
such as: (1) Will the pesticide leach in portions of the pesticide use
area that are similar to the study area? (2) How do pesticide residues
change over time? (3) What measures might be effective in mitigating the
pesticide leaching? Monitoring data generated in these studies provide a
time-series of concentrations that can be used in exposure and risk
assessments as a reasonable surrogate for pesticide concentrations in
drinking water drawn from shallow private wells in agricultural areas.
PGW studies have been used to test alternative mitigation strategies for
pesticides that have adversely affected ground water quality to
determine, for example, if a reduction in application rate or specific
irrigation technology will reduce or eliminate the impact. Data from
these studies also have been used to develop the EPA regression
screening model SCI-GROW,
(<http://www.epa.gov/oppefed1/models/water/models4.htm#scigrow> ; see
also ILSI, 1998), which is used to estimate screening-level pesticide
concentrations in ground water used as a source of drinking water.
Currently, the results of these studies are being used to evaluate
models of subsurface pesticide transport, and as a basis for model
scenarios for estimating pesticide concentrations in shallow ground
water.

In the past, the Agency has required both retrospective and PGW studies
on a case-by-case basis. The prospective study was designed to eliminate
factors that confound the interpretation of retrospective monitoring
studies. For example, in the site selection process, sites with prior
use of the pesticide or with point sources of contamination are not
selected for study. Also, since the pesticide is applied according to a
current or proposed label, concentrations observed during the study can
be directly linked to a known and current labeled use. The PGW studies
are conducted at a field scale rather than a larger scale to ensure that
adequate field quality assurance/quality control (QA/QC), collection of
ancillary data (climatic data, soil characteristics), and level of
instrumentation can be implemented at a reasonable cost, while
maintaining a scale that captures the natural variability in soils,
hydrology, and other environmental factors, and under which standard
agronomic practices can be implemented.

The original draft guidance for PGW monitoring studies was developed
primarily in the early 1990s and has been subjected to substantial
public review and comment, including a public workshop sponsored by EPA
in 1995 and a Scientific Advisory Panel (SAP) review in 1998. The
comments received during the workshop and SAP meeting provided valuable
suggestions from both a technical and practical perspective and were
used to revise this guidance and to address other issues identified in
the Agency's review of studies conducted for the registration of over 50
pesticides. The recommendations in this guidance document also represent
the Agency's substantial experience, over the last decade, in developing
and articulating effective procedures for collecting high quality data
on pesticide movement into ground water.

##  1.1 Environmental Exposure Characterization

PGW studies may be required on a case-by-case basis, depending on an
assessment of the pesticide's potential to impact ground water and the
Agency's consideration of risk. Before a pesticide can be sold in the
United States, EPA evaluates its safety to humans and to terrestrial and
aquatic animals and plants, based on a wide range of laboratory and
field studies. The environmental studies examine both the ecological
effects (toxicity) of a pesticide and its chemical fate and transport.
After EPA scientists review all the available information on toxicity,
chemical fate and transport, and proposed use of a pesticide, they
develop an environmental exposure characterization, which includes an
exposure profile and conceptual model. The exposure characterization
estimates the potential exposure of plants, animals, and water resources
to pesticide residues in water, food, and air. The exposure profile
describes:

-   Degradation of the pesticide active ingredient (how fast and by what
    means it is degraded in the environment) and how persistent it is in
    the environment;

-   Breakdown products or degradates that result from the degradation
    processes;

-   Mobility of the pesticide active ingredient and its degradates and
    how these chemicals may be transported from the application site
    (*e.g.* volatilize into the atmosphere, move into ground or surface
    waters, or bind to the soil); and

-   Accumulation of the pesticide and it's degradates in the
    environment.

These environmental fate studies are designed to help identify which
dissipation processes are likely to occur when a pesticide is released
into the environment and to characterize the breakdown products that are
likely to result from these degradation processes. The diagram below
illustrates the potential dissipation pathways for a pesticide after it
is applied.

**Figure 1. Pesticide Dissipation Pathways**

![](media/image1.png){width="3.59375in" height="2.386111111111111in"}

Based upon results of environmental fate and transport studies, EPA
develops a preliminary, qualitative exposure assessment. This, in turn,
may be used to design or trigger additional conditional field studies,
such as the PGW study.

### 1.11 Fate and Transport Studies 

EPA reviews many laboratory and field studies to determine the fate of
pesticides in the environment. The types of studies required depend on
the use of the pesticide. Certain laboratory studies (*e.g.*,
hydrolysis, photolysis, and soil metabolism) are routinely conducted for
all outdoor-use pesticides. Other conditional studies (*e.g.*, PGW
studies, photo-degradation in air, and field volatility) may be
triggered by data from the initially required laboratory studies and/or
use or application patterns and basic product chemistry data. The basic
studies provide the following critical information for a pesticide
active ingredient and its major degradates:

-   Half-life of the parent (persistence)

-   Identity of degradates

-   Rates of formation and decline of degradates

-   Bioconcentration potential

-   Mobility of the parent and degradates

The Agency regulations found in 40 CFR 158.29 describe the types and
amounts of data that the Agency needs for assessing the environmental
fate of a pesticide active ingredient. These controlled laboratory and
field studies, which are conducted under approved Guidelines and Good
Laboratory Practices, are used to determine the persistence, mobility,
and bioconcentration potential of a pesticide active ingredient and its
major degradates. Generally, degradates formed at greater than or equal
to 10% of the amount of applied pesticide are considered significant
(*i.e.*, major degradate) and should be identified in the study. In
addition, degradates of known toxicological or ecotoxicological concern
should be quantified and identified, even when present at less than 10%
of the applied pesticide.

-   **Physicochemical Degradation:** This includes hydrolysis and
    photo-degradation in water, soil, and air. Hydrolysis studies
    determine the potential of the parent pesticide to degrade in water,
    while photo-degradation studies determine the potential of the
    parent pesticide to degrade in water, soil or air when exposed to
    sunlight. During these studies, data are also collected concerning
    the identity, formation and persistence of degradates.

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-   **Biological Degradation:** These studies include aerobic and
    anaerobic soil metabolism, and aerobic and anaerobic aquatic
    metabolism. The soil metabolism studies determine the persistence of
    the parent pesticide when it interacts with soil microorganisms
    living under aerobic and anaerobic conditions. The aquatic
    metabolism studies produce similar data that are generated by
    pesticide interaction with microorganisms in a water/sediment
    system. These studies also identify degradates that result from
    biological metabolism.

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-   **Mobility:** These studies include leaching and
    adsorption/desorption, laboratory volatility, and field volatility.
    The leaching study assesses the mobility of the parent pesticide and
    its' degradates through columns packed with various soils. The
    adsorption/desorption study determines the potential of the parent
    pesticide and its' degradates to bind to soils of different types.
    The potential mobility of the parent pesticide and each degradate is
    determined by examining the data from both of these studies and may
    range from immobile to highly mobile.

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-   **Bioconcentration:** These studies use aquatic organisms to
    estimate the potential of a pesticide, under controlled laboratory
    conditions, to partition to the organisms from respiratory and
    dermal exposures. These studies also provide information on the
    degree a pesticide or degradate can be depurated should levels of
    the pesticide in the surrounding aquatic environment be reduced.

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-   **Field dissipation:** These studies track the dissipation of a
    pesticide from the surface soil layer, and the formation and
    dissipation of degradates. While laboratory environmental fate
    studies are designed to assess one dissipation process at a time,
    field dissipation studies assess pesticide loss as a combined result
    of chemical and biological processes (*e.g.*, hydrolysis,
    photolysis, microbial transformation) and offsite transport (*e.g.*,
    volatilization, leaching, runoff) as well as loss from plant uptake.
    These studies provide a field dissipation half-life, a lumped
    parameter that takes all routes of dissipation into account. Several
    field studies are usually conducted for each pesticide in typical
    use areas.

EPA's assessment may also identify whether pesticide mobility or
persistence is affected by pH, temperature, or other factors. The
exposure profile, combined with an evaluation of use and consideration
of risk may trigger a PGW monitoring study.

### 1.12 Conceptual Model

The potential for pesticide movement to ground water depends on a
variety of factors, including hydrologic properties of the overlying
soil and vadose zone that affect downward movement of water and
chemicals, travel time through the unsaturated zone to ground water,
aquifer properties (conductivity, porosity, depth, type, location of
recharge area), leaching potential of the pesticide (persistence and
mobility), and type of well drawing water for drinking purposes (Focazio
et al, 2002). These factors can vary significantly throughout the use
area of a pesticide. While pesticide persistence and mobility parameters
derived from laboratory studies are useful as a starting point for
assessment, these parameters are not always sufficient to adequately
characterize leaching of chemicals under actual field conditions. Data
collected in PGW monitoring studies represent the integration of effects
of multiple environmental and agronomic practices at a site where a
specific crop is grown. The term *prospective* is based on a key aspect
of the study design, namely, the pesticide has not been used previously
at the site. If the pesticide is detected, then it is the result of the
application during the study rather than a prior application (*e.g.,* at
a different label rate) or mishandling of the pesticide during mixing,
loading, or disposal activities.

A PGW monitoring study begins with the application of a pesticide and a
mobile tracer compound to a site that has been instrumented (i.e. wells
and other monitoring equipment has been installed) and where the crop is
(or will be) planted. The crop is grown in a field during the study,
following standard agronomic practices (*e.g.,* tillage, irrigation,
crop cultivation). Figure 2 below depicts a generic conceptual model for
pesticide transport to shallow, private rural wells in an agricultural
area. Following pesticide application, residues can be washed off plant
surfaces by precipitation or irrigation. They may adsorb to soils to
varying degrees and may degrade as a result of chemical or biological
processes. As water infiltrates through the vadose zone to the water
table, pesticide residues can be transported to the subsurface and can
adsorb and degrade further. Pesticides can be transported from a field
in runoff after precipitation or irrigation, adsorbed to eroded soil, or
volatilized in air. Pesticides also can be taken up to a varying extent
by plants. A PGW study is designed to minimize the effect of some of
these transport processes (i.e., runoff or the impacts of artificial
drainage) in the site selection process and to track the overall impact
of other processes on water quality.

**Figure 2. Conceptual Model for Pesticide Transport to Shallow, Private
Rural Wells.**

![](media/image2.jpeg){width="6.5in" height="4.875in"}

The vadose and saturated zones under the field are monitored over time
(usually at least two years) for residues of the pesticide, significant
degradates, and a conservative tracer. The tracer identifies the depth
to which recharge has moved following the application of the pesticide.
Weather data is also collected during the study. The pesticide and
tracer are only applied one time, to enable the movement of the
pesticide and the tracer to be tracked without interference. These
studies track the movement of the pesticide, degradate, and applied
water (using a tracer compound) through the soil into the water table
and produce a time-series of concentrations over a period of several
years. Adequate ancillary data are collected (*e.g.,* climate, timing
and mass of pesticide applied, irrigation, soil characteristics) to
enable the results to be interpreted. Study results should be evaluated,
and concentrations adjusted accordingly to take into consideration the
numbers and frequencies of application allowed on the label. The goal of
the study is to determine whether a pesticide will move to ground water
in some locations where it can be applied, and to determine the
time-course concentrations in ground water of the pesticide, major
degradates, and degradates of toxicological concern.

In order for the results to be applicable to regulatory decisions, the
site selected for study should have certain characteristics. Depending
on the objective of a particular study, a study site may be selected to
represent an environment that is highly susceptible to leaching (*e.g.*,
sites with coarse-textured soils that facilitate rapid transport) or a
site that represents other conditions under which the pesticide is most
typically used. Sites selected for study represent a specific use (or
set of uses) of the pesticide, as well as soil, hydrology, and climatic
conditions common to a use area; these conditions should be explicitly
described in the site selection report. Site selection should also
include consideration of other factors that dominate ground-water flow
systems, e.g. regions dominated by karst topography or tile drains,
especially if such factors dominate in an important use area. Ideally,
multiple sites should be selected for monitoring that exhibit a range of
characteristics of the broader use area. For example, selecting several
sites that are highly vulnerable to leaching along with several sites
presenting more typical vulnerability for a spatially diverse pesticide
use area can provide a more complete understanding of the potential
range of pesticide movement. Having results from a range of sites will
enhance the Agency's ability to extrapolate results across the composite
use area. When a single site is chosen for monitoring, the site should
represent a highly vulnerability site. If the behavior of a pesticide
(*i.e.,* its soil mobility and persistence) varies greatly from site to
site, EPA may request site-specific measurements of degradation rates or
sorption coefficients in the PGW study test soil. These data would aid
in interpreting study results and in modeling.

## 1.2 Ground Water Exposure and Estimating Risk

Some pesticides and pesticide degradates pose a high risk at very low
concentrations, while others pose less risk at these same low
concentrations. Because of the substantial costs associated with
conducting a PGW study, consideration is given to potential risk based
on estimates of exposure from available monitoring data and from
screening-level models.

### 1.21 Evaluation of Registered or Proposed Uses

The way in which a pesticide is used can play a critical role in
determining its impact on the environment. For example, pesticides that
are exclusively used indoors pose negligible risk of direct ground-water
contamination in comparison to those with outdoor uses. Some typical
indoor uses include baits, greenhouse uses, and use in food handling
establishments. While ground-water impacts associated with those uses
can occur from improper handling or disposal, the PGW study focuses on
water quality impacts resulting from use according to the registered
label. Thus, a consideration of how the pesticide will be used is an
important factor in assessing whether a study would provide data needed
to reduce uncertainty in water exposure assessments.

### 1.22 Available Monitoring Data

For the pesticide of concern, EPA may have available ground-water
monitoring data collected by academic institutions, federal and state
agencies, or pesticide registrants. Sources of these data include state
monitoring databases, other federal agencies \[e.g., United States
Geologic Survey (USGS) monitoring programs like the National Water
Quality Assessment Program (NAWQA) or the Toxic Substances Hydrology
Program\], Office of Pesticide Program\'s (OPP) Pesticides in Ground
Water Database (USEPA, 1992), reports submitted to EPA under FIFRA §
6(a)(2), EPA's STORET database, the open literature, and monitoring
conducted by public water supply facilities in compliance with the Safe
Drinking Water Act. OPP compiles and evaluates available water
monitoring data and examines the quality of the studies. In general,
most monitoring studies are not designed to target and document impacts
from the use of a specific pesticide at a specific rate, nor are they
conducted with the level of quality assurance and quality control of a
PGW study. Monitoring data typically provide a lower bound on potential
exposure, especially where data are available to determine the amount of
a pesticide applied (both the rate and numbers of applications) and the
location of treated areas relative to sampling sites.

While most available monitoring data are not likely to be of adequate
spatial and temporal resolution to address uncertainties in exposure for
a specific pesticide, data are useful in EPA's determination of the need
for a PGW study and may also be helpful in determining preferred test
sites. These data may highlight uses for which impacts appear to be
lower, and, thereby help EPA focus evaluation efforts or further
monitoring on specific uses or geographical areas where impacts may be
higher.

### 1.23 Modeling Ground Water Exposure

EPA routinely uses the screening-level model (SCI-GROW) to estimate
potential ground water exposure for pesticide water assessments.
SCI-GROW is an empirical regression model developed by EPA and is based
on monitoring results of PGW studies. This model requires limited input
parameters (e.g., K~oc~, aerobic soil metabolism half-life, and annual
pesticide application rate). Using these values, the model estimates the
concentration of the pesticide (90-day peak) in shallow, unconfined
aquifers that are subject to relatively rapid recharge and under
conditions similar to sites where the monitoring was conducted). The
model can simulate multiple applications of the pesticide and the
results are useful when reviewed in conjunction with the field study. A
detailed description of this model can be found at EPA\'s Web site:
[www.epa.gov/oppefed1/models/water/index.htm](http://www.epa.gov/oppefed1/models/water/index.htm).

When the screening model estimates that a particular pesticide may leach
into ground water at levels of concern, risk managers may determine that
a PGW study will provide quality data to reduce the uncertainty in the
assessment.

EPA is currently evaluating mechanistic models such as LEACHM (Hutson
and Wagenet, 1992), PRZM (Carsel et al., 1997), RZWQM (DeCoursey et al.,
1989), and PEARL (Leistra, et. al., 2001) and comparing estimates to
monitoring data from PGW studies and other studies. OPP's overall ground
water modeling approach and conceptual model has been peer reviewed by
the FIFRA Scientific Advisory Panel at meetings in February 2005 (USEPA,
2005a) and August, 2005 (USEPA, 2005b). This methodology was implemented
in water modeling conducted for the Revised N-Methyl Carbamate
Cumulative Risk Assessment (USEPA, 2007).

### 1.24 Consideration of Risk

Before requiring a PGW study, risk managers at EPA take into
consideration the potential for human exposure to pesticide residues in
drinking water and related uncertainties. Consideration of risk may also
take into account the potential for ground water containing pesticide
residues to impact the quality of ecologically sensitive surface water,
as well as the intrinsic value of ground water as an important natural
resource. Ground water contamination can be difficult and costly to
remediate, and it can take many years for contaminants to naturally
degrade even when point sources are removed. Water from private rural
wells is typically not treated prior to consumption, and over 27 million
people in the United States rely on private rural wells as their primary
water source.

## 1.3 CASE STUDY

The following case study is an example of the exposure assessment
process that occurs before a ground-water study is required for a
(hypothetical) herbicide, Chemical H, proposed for use on corn and
soybeans.

### 1.31 Exposure Characterization

The registration standard for Chemical H required the full complement of
environmen­tal fate studies, and data submitted by the registrant were
acceptable. Overall, Chemical H is characterized as a potentially
persistent pesticide (half-lives up to a few months) that can be mobile
in a variety of soils. However, field dissipation studies suggest that
Chemical H degradation may be more rapid (*i.e.*, within a few weeks)
under certain condi­tions in some soils.

The aerobic soil metabolism half-life was determined to be 35 to 70 days
in studies conducted in several soils, and the anaerobic soil metabolism
half-life averaged about 170 days. Based on these studies, it appears
that Chemical H could be persistent enough in the field for significant
leaching to occur. However, at some field dissipation study sites,
Chemical H dissi­pated more rapidly (half-lives were less than three
weeks at four of the eight study sites) than other soil-applied
pesticides that have been found to reach ground water. Overall, at eight
study sites, field dissipation half-lives for the upper six inches of
soil ranged from 8 to 46 days. The field dissipation data indicates that
Chemical H appears to degrade more rapidly in acidic soils in the
southern part of its use range; however, it is not clear whether the
enhanced dissipa­tion in these soils was entirely due to more rapid
degradation as opposed to soil leaching or other dissipation routes.
Although residues were analyzed to a 3-foot depth at several of the
field dissipa­tion study sites, there were no consistent detections of
Chemical H or its major degradate, Chemical H-acid, below 18 inches at
any of these sites. The minimum detection limit was 10 μg/L for both
compounds (the maximum application rate for Chemical H is 0.10 lb ai/A).

Chemical H is fairly resistant to abiotic hydrolysis. It hydrolyzes
slowly in sterile water at pH 5 (extrapolated half-life is 91 days) and
does not appreciably hydro­lyze at pH 7 and 9 over the 30-day study
period. Chemical H, though, is very susceptible to photolysis, with an
aqueous photolysis half-life of 1 day and a soil photolysis half-life of
7 days.

In general, the laboratory data show that Chemical H is persistent in
most soils with a degrada­tion half-life of 5 to 10 weeks. Chemical
H-acid, the primary degradate, appears to persist for several months or
longer in neutral or alkaline soils. However, this degradate has not
been found to persist in photolysis studies. No other degradates were
found to accumulate at more than 5% of the applied parent compound. In
the field, the accumulation of Chemical H-acid residues was highly
variable, ranging from a maximum of 5% of the applied Chemical H at one
site to a maximum of 50% of the applied Chemical H at another site.

Chemical H partitions primarily into the soil water in most soils. In
soil column leaching studies, it is mobile in a sandy soil containing
1.4% organic matter (5% to 10% leaching through the column) and
moderately mobile in sandy loam (1.1% O.M.) and loamy sand (2.0% O.M.)
soils (1% to 5% leaching through the column). In batch equilibrium
studies, K~d~ (in this case equivalent to Freundlich adsorp­tion
con­stants) values ranged from 0.8 to 3.4 in five soils tested. The
degree of adsorption was roughly propor­tional to soil organic matter
content. The K~oc~ ranged from 34 to 72; the median K~oc~ was 47. The
only K~d~ greater than 1.4 in four soils tested was associated with a
soil containing 12% organic matter. It should also be noted that
Chemical H solubility is considerably reduced in alkaline soils.

Chemical H-acid is even more mobile than Chemical H, with K~oc~ values
from batch equilibrium studies ranging from 4 to 17 in the same four
soils in which Chemical H sorption was studied. The degradate was not
confirmed to leach below 18 inches in field dissipa­tion studies sampled
to a 3-foot depth, but the soil analyti­cal method could only detect
residues exceeding about 20% of the applied pesti­cide, even if it was
applied at the maximum rate and was fully retained in the upper six
inches of soil.

### 1.32 Monitoring

Chemical H parent was detected in ground water sampled in a small number
(5) of studies reported in the Office of Pesticide Program's (OPP\'s)
Pesticides in Ground Water Database (USEPA, 1992). Although three
detections exceeded the pesticide\'s Maximum Contaminant Level (MCL) and
Health Advisory Level (HAL) of 7 μg/L, the majority of the detections
(75%) were below 1 μg/L. No monitoring data are avail­able for Chemical
H-acid in ground water. Sufficient monitoring data, though, are
available for the parent to demonstrate that Chemical H does leach to
ground water after regis­tered applications in some areas. However, some
of the higher concentrations reported may be due to chemical spills or
other accidents. The monitoring data have not been collected in a
sufficiently systematic way to determine under what specific conditions
Chemical H is most likely to reach ground water. Based on a gross
examination of the monitoring data, it appears that ground-water
contamination may be more likely in the northern part of the Chemical H
use area.

### 1.33 Modeling

Initially, evaluation of Chemical H was performed with the screening
model SCI-GROW. Screening modeling demonstrates that Chemical H has the
characteristics (at least in the majority of use sites) of other
pesticides with long-established uses that have been found in ground
water. This is especially true of Chemical H-acid, which is both more
mobile and more persistent than Chemical H parent. The soil half-life of
this degradate has not been directly measured, but it appears to be much
longer than 6 months in at least some soils. Based on SCI-GROW
concentration estimates, residues of Chemical H alone exceed the
aggregate risks for drinking water alone in OPP's human dietary risk
assessment; similar exposure estimates for the degradate, which is
assumed to have similar toxicity, will add to the risk.

PRZM modeling was conducted at 10 representative use sites. A simulation
of leached residues for Chemical H was compared with simulated Chemical
P residues, the corn and soybean herbicide most commonly detected in
ground water. Twenty separate application years were simulated at each
site. At 1 of the 10 sites, measured Chemical P residues from a vadose
zone and ground-water monitoring study were compared with simulations
for both chemicals. PRZM only roughly predicted the overall amount of
Chemical P and its chemical behavior as it leached through the soil
profile. At this, and at most other sites, when aerobic metabolism
half-lives and average K~oc~ values were used, modeling always predicted
that Chemical H would leach to a depth of 3 or 6 feet more than Chemical
P (as a percentage of the applica­tion rate). However, if the Chemical H
degradation half-life was shorter (*e.g.*, less than two weeks), then
predicted leaching as well as the magnitude of residues was generally
less than that of Chemical P. Chemical H-acid, when formed in sufficient
quantities, was also predicted to leach substantially at many use sites.

### 1.34 Data Evaluation 

The weight-of-evidence of the environmental fate properties of the
pesticide are enough to raise concern about its potential to reach
ground water. Since the photolysis half-life for Chemical H is short,
the foliar application for this chemical is consid­ered less of a concern
than the soil-incorporation method.

Modeling shows that there is a significant risk of Chemical H residues
leaching to ground water. Based on a comparison with monitoring data,
both Chemical H and Chemical H-acid residues may impact the quality of
ground water and exceed EPA's regulatory endpoint in at least a portion
of the use area. Moreover, Chemical H-acid has been found in tissues of
laboratory animals in studies used to calculate the MCL and has also
been found in tissues of fish, which appear to be among the most
sensitive non-target organisms. Eco­toxicity studies indicate that
concentra­tions of 1 μg/L in water over a period of a few weeks exceed
Levels of Concern (LOCs) for freshwater fish (Risk Quotient (RQ) of
12-30). This exceedance may pose a risk in areas where ground water
dis­charges to surface water bodies. A more definitive analysis of the
scenarios under which Chemical H residues leach significant­ly to ground
water cannot be made at this time because of the uncertainty regarding
the subsurface behavior of Chemical H and Chemical H-acid. Such data
could be obtained, however, from PGW studies.

Given the large potential use area (corn and soybeans) for this
pesticide, at least two ground-water monitor­ing studies are recommended
to characterize potential exposure: one in a high-exposure area and
another in a more typical-use area. For these studies, the pesticide
should be applied by soil incorporation at the maximum rate allowed on
the label. EPA is also requesting that a more sensitive analytical
method be developed for Chemical H and Chemical H-acid in water, which
detects residues at 0.1µg/L rather than the current 0.5 μg/L.

This case study illustrates the complex analysis that is involved in
determining the environmental fate of a pesticide and in evaluating its
potential to impact the quality of ground water as a result of normal
agricultural use. The uncertainty in this analysis may be greater for
chemicals that have never been used and for degradation products that
have little environmental fate data. In these cases, scientists should
rely exclusively on the environmental fate assessment to determine the
likelihood of leaching, and on predictions of models to estimate the
concentrations that may occur. PGW studies may provide EPA risk
assessors and risk managers with particularly valuable information in
these circumstances.

## 1.4 STUDY COMPONENTS

This guidance is intended to be performance-based, rather than a
definitive description of how to install wells and how to collect
samples. The goal is to provide the study director with adequate
flexibility in selecting equipment and methods needed to provide high
quality results, while at the same time standardizing the study design.
This flexibility also allows the study director to install more sampling
devices and collect more samples than stipulated to meet the goal of the
study, when needed. For example, if EPA approves a site where the
hydrology is more complex and the depth to ground water is greater, for
the study to be successful, more site instrumentation may be needed, and
the term of the study is likely to be longer in order to determine the
concentrations of the pesticide and major degradates

The major design components for PGW monitoring studies and guidance on
how to carry out these studies are explained in detail in the following
chapters of this document:

-   Site Selection

-   Site Characterization and Site-Specific Conceptual Model

-   Monitoring Plan Design

-   Site Characterization and Monitoring Plan Design Reports

-   Monitoring Plan Implementation

-   Reporting

## 1.5 STUDY RESULTS

As specific stages of a PGW study are completed, results should be
reported to EPA. These different reports require varying levels of
effort and detail and are described more fully in subsequent chapters of
this guidance. The reports should include the following information:

-   [Site Selection Report]{.underline}: Maps, tables, and a brief
    interpretive text. EPA will select the study site from the set of
    candidate sites proposed by the registrant.

-   [Site Characterization and Monitoring Plan Design
    Reports]{.underline}: Site-specific data, more detailed
    interpretation, and a proposed monitoring plan, including maps. The
    Site Characterization and Monitoring Plan Design Reports should be
    submitted to and approved by EPA before the monitoring plan
    implementation phase of a ground-water study can begin.

-   [Quarterly Progress Reports]{.underline}: Brief data summary relying
    on summary tables and graphs. New data for the quarter are
    highlighted in these reports, and any deviations from protocol,
    equipment failures, or other complications are identified.
    Typically, reviews of these quarterly reports will not prompt any
    action, unless results of analysis or irregularities in the
    perfor­mance of the study warrant further action.

-   [Termination Report]{.underline}: Brief letter report that indicates
    study results and rationale for termination along with accompanying
    data summary.

-   [Final Report]{.underline}: The final report will consist of a final
    review of study results and appendices, containing earlier
    submissions. This final report will serve as a comprehen­sive primary
    reference for the study.

The following chapters describe, in more detail, the components of a PGW
monitoring study.

# CHAPTER 2 - SITE SELECTION

Careful selection of ground-water monitoring study sites is critical in
ensuring that study results are useful to aid risk assessors and
regulatory managers in pesticide regulatory decisions. The soils,
hydrogeology, and climate at the study site (or sites) should be
accurately described or characterized in order to properly instrument
the site and to interpret the results of the study. Also, the range of
soils, hydrogeology, and climatic characteristics represented by the use
site should be established to properly interpret the data collected. The
characteristics of candidate sites will depend on the specific use and
the conditions the study is intended to explore (*e.g.*,\"high
exposure\" or \"typical use,\" irrigated or dryland sites). For example,
a site may be selected because it has the combination of environmental
characteristics typically associated with ground water quality problems.
Another aspect to consider in site selection is that the conditions are
such that the study can be conducted within a reasonable and predictable
time frame. Ultimately, the success of the site selection will be
performance based. The study should be able to clearly track an applied
tracer through the vadose zone to the saturated zone and track any
downward movement of pesticide residues.

OPP recommends that the registrant consider a number of sites in the
preliminary site selection process. The following four-step process for
the selection of field sites is suggested. These steps are described in
detail in the following sections:

-   Study Scope

-   A Set of Candidate Sites

-   Cooperator Interview

-   Preliminary Site Characterization

All proposed sites that meet the criteria discussed in this chapter
should be suitable for study. Sites should be ranked according to soil
type, hydrogeologic characteristics and other relevant factors, and this
information should be submitted to EPA in tabular form. Pesticide
application and data collection cannot begin before the study site is
approved in writing by EPA. Therefore, in the interest of saving time
and resources, the study director should take special care during site
selection to identify candidate sites. Full site characterization
activities (Chapter 3) may begin following EPA approval of the study
site(s).

## 2.1 STUDY SCOPE

### 2.11 Definition

The first step in selecting a study site is for the registrant to
describe where and how the pesticide will be or is used. Included in the
preliminary assessment should be usage (application rates, number of
applications, maximum application) information for all use sites,
stratified by geographic area (region, state, and county). The
registrant should also provide information on the pesticide formulation,
relevant agronomic practices (*e.g.*, application timing or irrigation
requirements), mode of action and environmental fate characteristics of
the pesticide or soil properties that affect the mobility or persistence
of a pesticide in the field.

Since a pesticide use area may have some locations with a greater
probability for contamination of ground water than others, the
registrant should assess the ground-water \"vulnerability\" throughout
the use area. Ground-water vulnerability depends on many factors, and
can be characterized using overlay (GIS) and indexing methods (Leaching
Potential) (Kellog et al., 1992; Diaz-Diaz et al., 1998), process-based
methods (modeling), or statistical methods. The assessment can be as
simple as county-scale ranking, or as sophisticated as layered GIS data
layer maps (Burkart et al., 1994) or vulnerability surfaces. Appropriate
State Agencies may be contacted to determine whether areas highly
susceptible to contamination of ground water have already been
identified in the usage areas. The registrant should use any of these
methods to: 1) describe the overall vulnerability of the pesticide use
area to contamination of ground water; 2) identify the vulnerability
associated with a \"typical use site\"; 3) identify sites throughout the
use area that are most vulnerable to contamination of ground water; and
4) characterize the vulnerability of the sites they propose to study.
The registrant should provide a complete description of the tool used to
assess vulnerability and how this tool was used to select the candidate
sites.

Based on this information, EPA will determine the uses for which the
monitoring study is required, the number of studies for each use, the
implementation schedule, and the conditions of the study (application
method, soil type, geographic area). More than one study site may be
needed because of major differences between uses (*e.g.* rice or corn),
or if use occurs in very different geographic areas (*e.g.*, CA and NY).
A careful definition of study scope will assure that the answers to
regulatory questions such as these are obtained:

-   Will the pesticide leach at any location in the pesticide use area?
    Will fate properties be important or influence study results
    (*e.g.*, soil pH and pesticide hydrolysis)?

-   Which uses pose the greatest risk of leaching?

-   Is there a high risk that leaching will occur in a specific
    geographic area or for a specific use; if so, what measures can
    mitigate this risk?

It is important to design individual prospective ground-water studies to
answer questions particular to the pesticide in question. The chemical
properties of a pesticide may require that the registrant evaluate
leaching potential for application to different soil types, for
different application methods, formulations or for applications at
different label rates. If a single study is performed on a site
representing high vulnerability for leaching within a pesticide\'s use
area, and pesticide residues are not found in the ground water or deep
within the soil column, it can be assumed that this chemical is not
likely to leach unless subsequent monitoring data show otherwise. On the
other hand, studies performed on a highly vulnerable site and at a less
vulnerable site that may be more \"typical\" of the pesticide\'s use
would provide some basis for extrapolation of leaching potential between
these different scenarios, perhaps through the use of computer models.

This preliminary assessment is intended to identify acceptable sites
that are candidates for extensive site characterization activities. The
regional assessment of candidate areas should yield a list of areas
where vulnerable and relatively homogeneous sites might be found. Study
sites that are approximately 2 to 5 acres are then identified within
these candidate regions.

### 2.12 Compounds of Interest and Analytical Methods

All pesticides, major pesticide degradates in the study and the
conservative tracer compound to be used on the site are considered
compounds of interest. A major degradate is one accounting for
[\>]{.underline} 10% of the applied at any time during the laboratory
studies, or one that has been identified as of potential toxicological,
environmental or ecological concern. The test pesticide should be
applied only once using the method of application stated on the product
label. The application should be made at the highest recommended label
rate for the crop used in the study.

A comprehensive description of the methods (USEPA, 1992) selected for
the analysis of all compounds of interest should be provided.
Information on the analytical procedures to be used for both water and
soil samples, and on the method detection limits (MDL) (USEPA, 1992)
should also be reported. Any background information and references that
might assist EPA in the evaluation of the nature, accuracy, and
selectiveness of all proposed analytical methods should also be
included. If no standard analytical method is available for the
compounds of interest, methods should be developed, validated, and
approved by EPA before beginning the prospective study, to ensure that
the study is acceptable.

Since the enactment of the Food Quality Protection Act of 1996 (FQPA),
the Agency is required to conduct an assessment of human exposure from
all routes (aggregate exposure). This requires a consideration of
exposure from chemicals with similar modes of action, including
degradates (common mode). Therefore, to obtain an indication of the
human health risk associated with a pesticide in ground water, the
cumulative exposure of multiple chemicals should be determined. When
selecting an analytical method for a specific pesticide, several factors
should be considered. The MDL and practical quantitation limit (PQL)
should be appropriate for the objectives of the analysis. MDL refers to
the minimum concentration of the compound of interest that can be
measured and reported with a specified confidence (99% probability) that
the concentration is above zero (USEPA, 1992). The registrants should
provide or develop an analytical method for water for the parent
pesticide and its' degradates that has an MDL of 0.01% of the label
application rate (calculated as the average concentration in the top six
inches of soil), or 0.051 μg/L, whichever is lower**.** PQL refers to
the lowest concentration at which the laboratory can confidently
quantify the concentration of the compound of interest. The study
authors should report all samples with concentrations above the MDL as
detections, including those below the PQL in which the concentration
cannot be quantified. In addition, the study authors should provide
sample equations to demonstrate how the PQL was calculated.

Analytical methods used should also be selective for the compound of
interest and free of any interference problems from other substances
likely to be present in the sample. If less selective methods are used
(*e.g.*, ELISA (immunoassay) methods, gas chromatography (GC) with
electron capture detection or nitrogen/phosphorous detection for sample
screening), all detections should be confirmed using a different method
(*e.g.*, a second GC column with a different polarity). The procedure
used to analyze significant degradates identified in the Subdivision N
Environmental Fate studies should also be reported.

## 2.2 A SET OF CANDIDATE SITES

The second step in the site selection process is a regional assessment
of sites within the pesticide use area and identification of candidate
sites. The characteristics of candidate sites will depend on the
specific use and the conditions the study is intended to explore (\"high
exposure\" or \"typical use,\" irrigated or dryland, etc.).

A regional assessment for candidate sites involves several steps. It is
important to first investigate certain general factors including
pesticide use, vulnerability of the use area, soil type, and general
hydrologeology including aquifer type and depth, and climate. Aquifers
are herein defined as a saturated geologic unit that can transmit
significant quantities of water under ordinary hydraulic gradients.
However, many individuals rely on shallow ground water sources (*i.e.*
shallow saturated soils) that do not necessarily meet this definition.
The term "aquifer" used throughout this guidance is intended to cover
both types of drinking water sources. This reconnaissance work can be
done easily using spatially distributed data such as a GIS display. Once
an area is found that appears to meet these factors, the next step is to
look for individual fields that might be appropriate for the study. At
this time, it is important to focus on specific site characteristics
including aquifer characteristics and other criteria listed below.

With few exceptions, all candidate sites for a prospective ground-water
study should meet the following criteria (ordered by expected
significance):

-   Unconfined aquifer,

-   Less than 30-foot depth to the water table,

-   No flow restrictive layers between the surface and water table,

-   Single Soil Series Mapping Unit

-   Less than or equal to 2% topographic slope (generally level),

-   Two to five acres in area, and

-   Sufficient distance from drainage features to ensure stable
    hydraulic gradient conditions.

### 2.21 Unconfined Aquifer 

Prospective ground-water monitoring studies are designed to monitor the
downward movement of pesticides toward the water table. The quality of
ground water in shallow, unconfined aquifers where recharge is rapid is
most likely to be affected by pesticide use. The impact of pesticide use
under these conditions is manifested reasonably quickly. Under different
conditions, for example, where the aquifer is deep or recharge is not
rapid, it may take several years for the impact of a pesticide to be
measured in ground water. Therefore, the time it takes for a pesticide
to leach from its point of application to ground water (its travel time)
can be quite variable and highly dependant upon transport pathways. It
is therefore important to consider the "travel time" of the tracer or
pesticide residues to reach ground water when selecting a site. Travel
time will most likely increase with increasing depth. Thus, the study
maybe required to continue for a longer period of time. Registrants
should therefore consider travel time while the site selection process
is occurring.

Unconfined aquifers are defined here as those where the water table
forms the upper boundary and where no significant low-permeability
layers overlie that boundary. The water table is defined as the top of
the saturated zone, where the fluid pressure is approximately equal to
atmospheric pressure (Freeze and Cherry, 1979).

### 2.22 Shallow Depth

Depth to the uppermost aquifer material is an important variable in
determining the vulnerability of shallow unconfined aquifers to
contamination of agricultural chemicals. Kolpin et al. (1993) stated
that the greater the depth to the top of the aquifer, the smaller the
frequency of herbicide detection. In Mehnert et al. (1995), study
results showed that the occurrence of agricultural chemicals was higher
when the well depth was less than 30 feet. Therefore, to determine the
potential for a pesticide to leach during the time frame in which the
study occurs, shallow is defined here to be an average depth to ground
water of less than or equal to 30 feet and the depth to the water table
suggests a recharge zone. While no specific depth is considered "too
shallow," sites with shallow water tables may actually have an upward
flux rather than downward flux. Therefore, professional judgment should
be exercised to avoid picking a site with too shallow a ground water
table. Sites with drain tiles, drainage ditches, etc. may also need to
be considered for some pesticide uses particularly in those geographic
use areas where they dominate. As noted above, sites with preferential
flow and tile drains will require specialized protocols which will need
to be reviewed on a case-by-case basis.

### 2.23 No Flow Restrictive Layers

Sites with soil layers that may restrict the downward movement of water
should be avoided. Often the definition of restrictive zones is limited
to those layers such as clays and hard pans that restrict downward water
movement. These are soil layers that normally have low hydraulic
conductivity values (less than 0.5 cm per hour (Soil Survey Staff,
1992). Soil particle size distribution (texture), soil structure, and
pore size distribution are factors that significantly influence the
leaching of pesticides through the soil profile to ground water (USEPA,
1990). However, soil layers with highly contrasting soil textures may
also inhibit water flow (*e.g.*, sandy loam overlying a coarse sand or
fine gravel) and should not be considered. Sites should be carefully
evaluated for soil properties that may inhibit water flow.

### 2.24 Preferential Flow

Consideration should be given to selecting sites with a documented
history of preferential flow where the pesticide may be used in that
area. Pesticides which will be used in areas dominated by preferential
flow (*i.e.* soils with macropores or fingered flow in sandy soils) may
leach faster in these soils than conventional flow transport processes
and may be more representative of a "high exposure" scenario for that
chemical. The consideration of sites dominated by preferential flow
should be considered on a case by case basis.

Completion of test pits are a quick and inexpensive method for
evaluating soil variability and determining if preferential flow is
likely to be an important process at a site. Data collected during a
study may also indicate if preferential flow processes are important.
Site specific data can answer questions which provide insight into the
presence of preferential flow processes. Examples of the types of
questions are "did the tracer reach ground water quicker than expected,
or not at all?", "did pesticide leach to ground water faster than
expected from modeling?", and "is there variability in occurrence time
and concentration of tracer and pesticide in lysimeters?". The answers
to these questions can provide information which suggests that
preferential flow process may, or may not, be important at a specific
site.

### 2.25 Tile Drains

In some instances, a pesticide may be proposed for use in an area
dominated by tile drains. Site selection should consider the occurrence
of tile drains. However, care should be used when considering a site
with tile drains. Installation of tile drains can fundamentally alter
the structure of subsurface soils and result in "artificial" pathways
for leaching. In no cases, should a site selected with tiles drains
eliminate ground-water monitoring as part of the design due to the
presence of tile drains. Sampling of tile drains may be considered as a
supplement to the study, but not as a substitute to other required
elements. The consideration of sites dominated by tile drains should be
considered on a case by case basis.

### 2.26 Single Soil Series Mapping Unit

Single soil series mapping units in the field are desirable to best
define the conditions represented by multiple samples collected over the
extent of the field. While no field is truly homogeneous, sites can be
selected to minimize site variability and sampling designs can be used
to better understand pesticide fate. The site should have uniform soil
characteristics in three dimensions: aerially or spatially (same series)
and vertically (similar properties from the soil surface to the water
table). It is likely to be easier to ensure that soils are uniform
spatially, than that they do not vary with depth.

The study director should at least ensure that each 2- to 5-acre study
site be a single soil mapping unit as defined by the National Resource
Conservation Service (NRCS) (formerly Soil Conservation Service or SCS).
The mapping unit should be a consociation, which is a delineated unit
dominated by a single soil series and similar soils. In general, at
least three-quarters of the mapping unit consists of the named soil
series and similar soils (from a hydrologic standpoint). The total
amount of dissimilar inclusions are generally less than 15 % if the soil
properties are more limiting and 25 % in not limiting (Soil Division
Staff, 1993).

Once a particular study area has been identified, specific soil mapping
units containing the soil series on the candidate site can be found by
consulting county soil surveys published by NRCS. Refinement of NRCS
maps may be necessary to achieve the level of detail necessary for site
selection and characterization. The soils maps should be evaluated and
refined as needed by a qualified soil scientist.

In addition to being relatively homogenous over the candidate study
site, the soil physical properties should be consistent with the
conditions the study is intended to evaluate. For instance, soils
appropriate for high-exposure ground-water monitoring studies should be
among the most vulnerable soils allowed on the product label for a
particular use. Two types of soils are appropriate in these situations:

-   Coarse-textured soils with low organic matter content: These soils
    are characterized by high sand content, low silt and clay content,
    and low organic matter (less than 2%) in the uppermost soil
    horizons; or

-   Structured soils with high hydraulic conductivity.

Sites that do not consist of either of these types of soils would be
removed from further consideration.

The selection of a \"typical use\" study site would be carried out in a
similar fashion, but the main selection criteria would favor a site
representative of the most common conditions to which the pesticide will
be applied, which might not reflect the highest vulnerability to
leaching. A determination of the areas with the greatest use cannot be
the sole criterion in the selection of a study site. \"Typical use\"
studies will only be requested if there is a question as to whether the
pesticide will leach under those conditions.

### 2.27 Low Topographic Slope

The site should be as level as possible to minimize runoff or run-on.
The topographic gradient of proposed study sites should not exceed 2%.
In addition to slope, the shape of the land surface should also be
considered. For example, concave land surfaces will encourage
infiltration and convex land surfaces would tend to encourage runoff,
and should therefore be avoided.

### 2.28 Stable Hydraulic Gradient

It is recommended that study sites not be located within the radius of
influence of irrigation or production wells. Sites also should not be
located near surface-water bodies or tides that control the direction of
ground-water flow. The Agency has a concern that surficial water bodies
could cause extreme fluctuations in the direction of ground-water flow.
Whatever information that might be gained concerning the leaching
potential of a pesticide would be obscured by the effects of outside
influences on the height of the water table and direction of
ground-water flow. Further information on local conditions may be
obtained from area reconnaissance and an investigation of wells and
surface drainage features on surrounding properties.

## 2.3 COOPERATOR INTERVIEW

The third step in the site selection process is to interview farmers
(\"cooperators\") to investigate the history of pesticide use at each
site and to secure permission to use individual fields as study sites.
Once the registrant has narrowed the search for appropriate study sites
to the county or soil-series level, individual candidate sites can be
identified. Individual farmers should be contacted about past
agricultural practices and the long-term availability of the site for
extended monitoring. If the farmer has not owned the property for at
least the past five years, the previous owner should be contacted if
possible to establish additional site history.

### 2.31 No Prior History of Test Pesticide Use

The history of the site should be known in order to identify use of the
test pesticide, degradates, tracer, or other compounds which could
interfere with analytical procedures or interpretation of the study
results. Therefore, the registrant should demonstrate that there has
been no use of the test pesticide on the test site during the previous
five-year period. For pesticides with extremely long half-lives (greater
than six months), study directors should investigate a longer prior use
history (an additional two to five years of site history, when
possible).

Pesticide use information should be verified using the cooperator\'s
written records. In addition, the study director should be thorough in
inquiring if any pesticide spills, pesticide storage near wells, or
other point sources have occurred at or near the site. In addition,
sites that have received fill material from off-site sources should be
identified due to potential contamination issues. It is incumbent upon
the study director to fully investigate the site and report results
[before]{.underline} the commencement of the monitoring study. Sites
where such potential point sources occur should be eliminated from
further consideration at this stage.

### 2.32 Long-Term Availability of Study Site

Ground-water monitoring studies are typically conducted over a 2 to 3
year period. The length of the required monitoring period is determined
by several factors, the most important of which is the pattern of
movement of both the pesticide and tracer through the soil column, as
determined by the analysis of pore-water and well-water samples. The
site owner should be made aware that time estimates are imperfect, and
that study conditions or chemical properties (i.e. very persistent
chemicals) may require the site to be available for more than 3 years.
Additionally, in cases where leaching of the pesticide is being
investigated at multiple sites or in cases where application to sandy
soils has already been excluded from the registration label, then
studies may need to be conducted at sites where travel times to ground
water are longer. If a site is not available for a minimum 2 to 3 years,
the site should be eliminated from further consideration at this stage.

## 2.4 PRELIMINARY SITE CHARACTERIZATION

The fourth step in the site selection process is to undertake a
reconnaissance of candidate sites. The final result should be a set of
proposed study sites. Once a set of candidate fields has been identified
and access is secured, preliminary characterization should be carried
out. This investigation includes estimations of soil characteristics and
variability, a description of site hydrogeology, identification of
topographic and surface features that could impact the study, and site
access considerations. Utilizing benchmark soil series as established by
the NRCS will provide the registrant with additional soils data. Because
these Benchmark series fall within a specified range of criteria and is
available in GIS coverage, the spatial distribution of the soil and the
range of properties could be characterized to identify how vulnerable
the site actually is and how it fits within the entire use area.

Information about pesticides used on and near the site should be
gathered to ensure that contamination of the aquifer has not occurred.
In addition, it is important to ensure that no chemicals were applied
that would be difficult to analytically separate from the test compound.
The results of these investigations should be submitted to the Agency in
the form of tables presenting the characteristics of the candidate
sites, maps indicating locations of candidate sites, a description of
which sites are most preferred, and why. The presence of compounds that
interfere analytically with the test pesticide will result in rejection
of the site.

Ranking of the various sites should be based on how likely each site
would be to meet study guidelines after full characterization. A small
number of soil samples should be collected for analysis from each
candidate site, with the intent of determining the texture, organic
matter, and permeability of the uppermost soil layers. Local water table
depth should be determined by consulting the local NRCS office,
examining existing wells on the site, or by installing piezometers. The
natural configuration of the land surface should also be considered;
sites containing depressions or low-lying areas that could facilitate
ponding should be avoided. Any additional information that can be
collected during this phase of the characterization should further the
goal of ensuring that a chosen site will be accepted after a more
resource-intensive, full site characterization.

Upon receiving the preliminary site characterization data from the
registrant, EPA will give conditional acceptance of sites that appear to
be consistent with study guidelines. Full site-characterization can then
commence.

### 2.41 Absence of Dominant Fracture Flow

The hydraulic gradient, the configuration of the piezometric (or
potentiometric) surface, and textural variations in the aquifer media
are typically used to estimate the average direction and velocity of
ground-water flow. This technique is not appropriate for the
determination of ground-water flow and velocity in karst or highly
fractured regions. For this reason, areas where prevalent ground-water
flow occurs along karst or fracture-flow features are generally
unacceptable for highly vulnerable study sites, unless significant use
of the pesticide is anticipated in such an environment. Special
monitoring techniques should be planned for such situations.

# CHAPTER 3 - SITE CHARACTERIZATION AND CONCEPTUAL MODEL

Interpretation of the results of a prospective ground-water monitoring
study largely depends upon whether the hydrogeology of the study site is
adequately understood. Site characterization data are necessary to more
accurately assess site vulnerability, thereby placing into context
results of the study relative to conditions throughout the pesticide use
area.

Site characterization includes a description of topography at the site
and in the vicinity, soil characteristics, and vadose and saturated zone
hydrogeology. Descriptions of agronomic practices (including irrigation
and tillage) and climate (rainfall frequency, amount, and seasonal
distribution) are also fundamental. This information is needed before
monitoring equipment is installed. Information collected in this phase
of the study may be used as input parameters for computer models.

A conceptual model should be developed to understand how the site
characteristics may affect the fate of the test pesticide. This model
involves the analysis and interpretation of data collected during site
characterization for soils, the vadose zone, and the saturated zone.
Various methods exist to compile, analyze, and present these data in
both graphical and tabular form. Visual displays of data are usually the
most convenient and useful for presenting site characterization data.
Once the flow system is understood, and the conceptual model is
developed, a monitoring plan can be designed that is suited to the study
site (Chapter 4).

Site characterization activities are divided into four steps. These
steps are described in detail in the following sections:

-   Existing Local Data and Base Map

-   Soil and Vadose Zone Investigation

-   Saturated Zone Investigation

-   Conceptual Model

Products of site characterization are: 1) a summary of existing local
data; 2) a detailed base map; 3) site- specific characterization data;
and 4) a conceptual hydrogeologic model of the site. All these data and
the conceptual model should be summarized and described in the Site
Characterization Report (Chapter 5).

## 3.1 EXISTING LOCAL DATA AND BASE MAP

The first step in the site characterization process is to gather all
available information about the geology, topography, soils, hydrology,
climate, and agricultural practices that could affect the fate and
transport of the pesticide at the study site. These data are used to
characterize the local hydrogeologic and agricultural conditions, and
relate site-specific conditions to the regional framework. The base map
of the study site provides a spatial reference for all site
characterization information and monitoring results.

### 3.11 Compile Existing Local Data

A description of the regional hydrogeology is important background
information for developing the conceptual model of flow and transport at
the study site. An understanding of the hydrogeologic framework is
typically needed to interpret the results of monitoring and to
understand field observations.

Soil is a primary factor in regulating whether rainwater runs off or
infiltrates. Data obtained from soil surveys are used to create maps of
soil classes, where average values of soil properties are estimated
within a defined region of a mapping unit (Webster, 1985; Cambardella et
al., 1994). Thus, an initial set of possible study site locations can be
determined in part with a published United States Department of
Agriculture (USDA) Soil Conservation Survey. Site-specific soil
characterization and delineation, in addition to the Soil Survey, will
normally be necessary.

The timing and intensity of rainfall has a strong impact on the
transport of pesticide residues off a field due to leaching or runoff.
National Oceanic and Atmospheric Administration (NOAA) has a nationwide
system of weather stations that measures rainfall and computes
statistics (averages, return frequencies). During the course of a
prospective ground-water study, an onsite weather station to measure
rainfall amount and intensity, soil and air temperature and pan
evaporation is strongly recommended. Historical rainfall at or near the
study site should be determined to ensure that water input during the
study is consistent with historical data. A water balance should be
developed to provide an estimate of the net historical recharge at the
site.

### 3.12 Develop a Base Map

An accurate base map of each study site should be developed to provide a
spatial reference for site characterization observations and for
subsequent monitoring data. The base map should fully represent the
significant features of the study site and the surrounding area;
particularly those that may affect ground and surface water flow
systems. It is strongly recommended that all base maps include:

-   The location of the test site by latitude and longitude (and by
    township range, and section). The use of more exact methods, such as
    a Global Positioning System (GPS) or standard survey methods should
    also be considered,

-   The location of nearby roads, surface water bodies, fences, and
    municipal boundaries,

-   The location of nearby wells (including identification of irrigation
    source), canals, and drainage systems,

-   The date the base map was developed and the sources of base map
    information,

-   The organization and individual responsible for the base map,

-   The area and slope of the control plot and test plot,

-   Ground surface elevations and topographic features in the vicinity
    of the study site, and

-   Map scale, map title, county name, and complete legend including
    topographic contour interval, explanation of map symbols, and north
    arrow.

Detailed information on site topography is needed to identify areas
within a field where leaching is more likely to occur. Although a study
site should have a low slope overall, small-scale natural variations in
slope within a field can direct the flow of water to runoff or cause it
to pond. Identification of these areas is important for developing a
conceptual model of the site, and in interpreting results of monitoring.
We strongly recommend surveying the study site and adjacent areas to
provide elevation data at a one foot or less contour interval (depending
on the slope of the site).

Base maps are used to record the locations of all pertinent study
features and sampling sites including the location of soil cores,
infiltration tests, piezometers, monitoring wells, lysimeters, drinking
and irrigation wells, buried drainage tiles, weather stations, pesticide
mixing and loading areas, pesticide storage facilities, disposal areas,
and buildings. In addition, the location of a control area
hydrologically upgradient of the study site should be identified and
located on the base map, as well as a site for the test pit excavation.
The Site Characterization Report should include this base map.

### 3.13 Information Sources

Sources of information on soils, geology, hydrology, topography and
climate include: local experts, USDA agricultural extension service, the
USGS and state geologic surveys, USDA NRCS soil surveys, and the NOAA
climatic databases. Information on pertinent surficial features obtained
from aerial photogrammetric surveys may also be of use in base map
development. State transportation departments, environmental protection
departments, and county planning departments often maintain such
information for land areas under their jurisdiction. Private companies
may also be a source for aerial photogrammetric information in some
areas.

## 3.2 SOIL AND VADOSE ZONE INVESTIGATION

Soil structure and variations in soil texture, surficial geology,
topography, hydrology, and the impact of years of agricultural practices
(e. g. tillage, irrigation, drainage structures) influence the extent to
which precipitation or irrigation will infiltrate or runoff from a
field. If site characterization is inadequate, these real-world
complexities will limit the interpretation of the monitoring data. Thus,
characterization of the subsurface is fundamental and necessitates
substantial sampling, particularly between the soil surface and the
saturated zone. The following sections group the investigation into two
categories: an exploratory coring program in which sampling and testing
occur throughout the study site, and a test pit excavation, located
adjacent to or near the study site. The sections below describe
parameters that should be characterized during the coring and test pit
investigations. There is significant flexibility as to which methods can
be used to measure the parameters for site characterization. The
emphasis is on performance-based methods as dictated by site specific
conditions. Techniques are to be approved by the EPA prior to use.

### 3.21 Exploratory Coring Program and Field Testing 

All site characterization programs should include an exploratory coring
program to directly investigate and characterize the vadose zone. The
purpose of the exploratory coring program is to obtain information about
selected soil properties which reflect a soil\'s capacity to hold and
transmit water, to bind or retain a pesticide, and to degrade or
transform a pesticide; or those factors which considered together affect
a pesticide\'s mobility and persistence at a specific study site. The
soil coring program is also a means to assess the vertical and
horizontal homogeneity of these parameters across a study site. Data
collected from exploratory coring is used to develop an initial
conceptual model of subsurface conditions at the test site. In this
phase of the study, soil heterogeneities or barriers to leaching not
discovered in preliminary site selection can be identified. Before
initiation of the exploratory coring program, an effort should be made
to identify and locate utilities, irrigation systems, tile drains, etc.
to avoid damage and costly repairs.

At least one continuous soil core (from the surface to the water table)
from at least eight locations throughout the study site, as well as one
continuous core from a control area assumed to be up-gradient of the
study site, will be collected. A detailed drilling log should be
prepared by a trained soil scientist or geologist to describe the
texture, color, structure, and moisture content of the soils as they are
collected over the complete core. Methods for collecting soil samples
(such as split spoon or thin-walled Shelby tube) can be found in the
open literature. A soil core log should give special attention to
confining layers, abrupt changes in texture or color, and other features
needed to characterize the physical and chemical properties of the
vadose and saturated zones. In addition, depth to the water table should
be recorded.

Soil sub-samples should be taken from each core for laboratory analysis.
Special attention is to be paid to the top six feet of the soil column,
to allow comparison with NRCS soil surveys (which describe soils to a
depth of six feet). The top six feet of the core should be divided into
either six-inch intervals or by soil diagnostic horizon, whichever is
less. Emphasis is placed on the surface six feet because soil texture,
porosity, structure, and organic matter content have a large influence
on the persistence and mobility of the applied pesticide. Below the top
6 feet of the soil core, sub-samples should be collected every four
feet, except when a visible change in soil properties (color, texture,
structure) is observed. In this case, at least two sub-samples should be
taken from the 4-foot interval, to characterize the differences between
soil types. Each sample should be described in the field by an
experienced geologist and/or soil scientist. In addition, all soil
sub-samples should be analyzed for the following information:

-   soil texture class, particle density, bulk density, porosity,
    fraction sand, fraction silt and fraction clay,

-   organic matter content or organic carbon content,

-   field capacity (1/3 bar), 1 bar, 5 bar, and wilting point (15 bar)
    (all measured on undisturbed soil samples),

-   saturated hydraulic conductivity,

-   hydraulic conductivity vs. soil water content and matric potential,

-   field soil water content, residual water content and saturated water
    content,

-   matric potential vs. soil water content (water characteristic
    function)

-   Munsell color (specify moisture condition, *i.e.*, wet or dry), and

-   pH and cation exchange capacity or anion exchange capacity (if
    appropriate).

These samples should not be composited. Compositing of samples precludes
obtaining information about the variability of these important
parameters across the field. Standard methods for the parameters listed
above are available from ASTM and are described in Mason (1983), Klute
et al. (1986), Jury et al. (1991) and Wilson et al. (1995).
Consideration should be given to conducting these tests on undisturbed
samples where possible.

The compounds of interest (ie. pesticide, degradates and tracer), should
also be analyzed for from soil collected in each horizon to ensure there
has been no prior use of these compounds at the study site. If the test
compound has not been registered, this need not be done.

### 3.22 Number and Locations of Soil Cores

Given that the study will be conducted in a field that is approximately
two to five acres in size, a minimum of eight soil cores are needed to
characterize the vadose zone. A greater number of cores will likely
increase the reliability of interpretations of subsurface conditions.

There are a number of ways of determining where these soil cores should
be collected. The most important factor to consider is that core
locations be distributed throughout the field in such a manner that a
strong conceptual model can be developed. This can be accomplished by
locating the cores randomly, along a grid, or stratifying them according
to some predetermined criterion. The grid may be oriented perpendicular
or parallel to the ground-water flow field. The field may be segmented
into sectors, gridded and cores randomly located in each sector. If
piezometers will be installed at core locations, these locations should
be located at or near the corners of the study site.

Coring methods should be selected based on consideration of the
anticipated textures of the vadose and saturated zones, the anticipated
borehole depth, stability of the borehole, and ease of collection of
samples for analysis. Drilling methods appropriate for these
considerations are described in the ASTM standards manual.

### 3.23 Field Testing

The description or prediction of processes which influence pesticide
dissipation, specifically leaching, in the field requires an
understanding of infiltration, recharge, and internal drainage (water
redistribution). Thus there is a need to characterize soil hydraulic
properties, such as soil water content, matric potential vs. soil water
content (water characteristic function) relationships and hydraulic
conductivity. Because soils in a field are typically heterogeneous,
solute transport is controlled by properties which vary both spatially
and temporally, and these are also often scale dependant. Therefore, it
is important that these parameters be measured in the field.

In these two to five acre study sites, we recommend that the saturated
and unsaturated hydraulic conductivity be measured at a minimum of six
locations dispersed across the study site (and indicated on the site
base map) to take into account field variability of soils. If
significant variability in hydraulic conductivity is evident, then
measurements should be made in additional locations to further define
the range of variability across the site. In general, measurements are
made for at least two depth horizons at each measurement location - one
at the soil surface and for each soil horizon below the surface to a
depth of six feet. The soil water content should also be measured at
these sites from the surface to the water table. These data will be
correlated with the water characteristic function determined in the lab
and the matric potential will be estimated for these locations. The
matric potential indicates the direction of water movement in the vadose
zone. The field determined soil water content will also be correlated
with the hydraulic conductivity and compared to the lab results from the
soil cores. This will provide insight into how well the results of the
lab tests represent actual conditions in the field. Consideration should
also be given to developing breakthrough curves to determine
dispersivity and the likelihood for preferential flow and to estimate an
effective porosity for soil samples.

### 3.24 Preservation and Transportation of Formation Samples 

ASTM provides guidance for preserving and transporting soil samples for
analysis. Although some flexibility in these procedures might be
necessary due to the practical considerations in sampling a farm field,
certain procedures should be followed in every case. The field personnel
should follow all relevant Department of Transporation (DOT) and
International Air Transport Association (IATA) hazardous materials and
dangerous goods regulations concerning the shipping of dry ice. These
samples should be sent by overnight mail the day they are collected, or
kept frozen until they arrive at the laboratory.

### 3.25 Quality Assurance and Quality Control Procedures 

Procedures for ensuring the quality of all soil samples and the data
derived from those samples are an integral part of the exploratory
coring program. Mason (1983) and Barth et al. (1989) present details on
quality assurance for soil and formation sampling activities. Good
laboratory practices relevant to field investigations should be
followed.

All soil core logs and subsurface descriptions recorded during the
drilling operation should be included in the Site Characterization
Report. State or local regulations concerning the permitting and/or
documentation of exploratory coring activities should be followed.
Chain-of-custody forms should be prepared and archived for all
subsurface samples, and subsurface samples that are not destroyed by
analytical procedures should be retained as reference samples for the
duration of each study.

### 3.26 Test Pit Excavation

The Agency views the completion of test pit excavations during the
initial phases of the site characterization process as a quick and
inexpensive way to assess the heterogeneity of a site and the potential
for preferential flow. The 1998 Scientific Advisory Panel (SAP)
identified the presence of preferential flow as a critical element to be
assessed in the site selection/site characterization process. If a
pesticide is to be used in an area dominated by preferential flow (e.g.
in a karstic region or with extensive tile drainage) then site
characterization should evaluate this process and consider sites with
documented preferential flow. The completion of test pits at the subject
site is a quick and inexpensive way to assess whether preferential flow
is likely (at least in the near surface) at a site. Unusual conditions
which may prove problematic for a Prospective Ground-Water Study (*i.e.*
restrictive layers) can quickly be identified and result in significant
cost savings. Test pits may also be considered during the course of the
study when unusual conditions are noted. Test pits should not be located
within the active monitoring area but should be located in close
proximity to the area of pesticide application (*i.e.* immediately
adjacent to the site or within a control plot).

Test pit excavations are particularly useful in characterizing the
lateral extent or thickness of low-permeability layers noted during soil
survey and exploratory boring activities or in identifying dominant
patterns at a site (Mason, 1983). Soil structure or other features that
may result in significant preferential flow should be noted and
reported. Such features are common and should be investigated through
use of test pits when considering a site. The excavation should be
located adjacent to or near the area of the site where the compounds of
interest are to be applied and monitored. The locations of the test pits
should be indicated on the base map. The walls of the test pits should
be described using methodology and nomenclature which is consistent with
the Soil Survey Manual (Soil Survey Division Staff, 1993), Soil Taxonomy
(Soil Survey Staff, 1975), and Keys to Soil Taxonomy (Soil Survey Staff,
1992). Photographs of pit walls could also be considered.

Field workers should take care when entering a test pit to characterize
soil properties. All test pit activities should be conducted under the
supervision of an Occupational Safety and Health Administration (OSHA)
required "competent person". OSHA standards state that test pits should
not be excavated to deeper than five feet unless a shoring system
(*e.g.* trench box or trench shield) is installed to support the pit
walls. However, since the stability of pits five feet deep and shallower
can also vary with soil texture and moisture, safety precautions should
be considered in these scenarios as well. Proper abandonment procedures
for test pits should be undertaken and documented in the First Quarterly
Report.

### 3.27 Abandonment of Soil Core Holes 

Characterization of the shallow saturated zone requires the installation
of at least four piezometers. Some of the cores drilled for soil
characterization may be converted into piezometers. The holes created by
soil coring that are not converted to piezometers should be properly
abandoned prior to the application of the compounds of interest.
Guidance on proper abandonment of soil coring locations may be found in
Aller et al. (1990) and American Water Works Association (1984). Boring
abandon­ment procedures should also comply with any state or local
regulations for agricultural fields. If additional fill material is
required to complete the abandonment process, "pesticide-free" soil
should be used.

## 3.3 SATURATED ZONE INVESTIGATION 

A limited investigation of the saturated flow regime should be conducted
for each study site. This information is needed to develop the
conceptual model and to interpret monitoring data. The following
sections de­scribe the recommended procedures for characterizing the
ground-water flow characteristics of the aquifer. These procedures
include collecting hydraulic head data and conducting pumping tests
and/or slug tests. The data derived from these activities are then used
to estimate the direction of ground-water flow, the hydraulic
conduc­tivity of the aquifer, and the ground-water velocity at the study
site.

### 3.31 Hydraulic Head

Piezometers should be installed at the site to measure the hydraulic
head. If done simultaneously, piezometers may be placed in the same
borehole where the exploratory soil cores were collected, to save
resources. At least four piezometers should be installed at the corners
of the study site to establish the water-table surface. These
piezometers should remain in place for the duration of the study so that
these simple measurements can continue to be made. Since suitable sites
for ground-water monitoring studies should exhibit low topographic
relief, small errors in surface elevation measurements can seriously
impact the interpretation of subsurface conditions. Therefore, care
should be taken to measure and record elevation data accurately. A small
cut or indelible mark should be placed on the piezometer well casing for
use as a measur­ing point (MP), and this point should be surveyed
relative to the local U.S. Geodetic Vertical Datum. The location and
height of this point should be measured to an accuracy of plus or minus
0.01 foot.

Procedures for measuring depth to water in monitoring wells are detailed
in ASTM Standards. Initial measurements of water levels should not be
collected until after the piezometer or well has had time to stabilize
from the effects of construction and development activities. Piezometer
locations should be specified on the base map, and initial water level
data should be presented on a map in the Site Characterization and
Monitoring Plan Report.

### 3.32 Direction of Ground-Water Flow and Hydraulic Gradient 

A map of the potentiometric surface of the surficial aquifer should be
prepared for each study site. This map should use the site base map for
location information and should include the locations of piezometric
head measuring points. Contour lines representing equal hydraulic head
should be constructed. Methods for constructing water-table maps and
estimating hydraulic gradient and ground-water flow direction from these
maps are provided in Freeze and Cherry (1979).

### 3.33 Hydraulic Conductivity

The hydraulic conductivity of an aquifer controls the rate at which
ground water flows under a given hydraulic gradient. The velocity of the
ground water can be used to approximate how long it will take a
conservative tracer (or pesticide) to travel beyond the test site
boundaries.

Hydraulic conductivity is typically measured in the field by means of
slug tests or pumping tests. Slug tests should be conducted at locations
where the soil cores indicate very low hydraulic conductivity aquifer
materials. A pumping test under these conditions is usually not possible
because the yield of the aquifer is too small to collect sufficient data
to analyze using typical methods. Slug tests sample a very small region
around the well and the results only represent the aquifer properties in
that region. Therefore, they are of limited value and one should be done
at every well. Pumping tests should be used when the hydraulic
conductivity values are large enough to collect sufficient data to
analyze using typical methods. Pumping tests sample a much larger region
of the aquifer and give a more representative hydraulic conductivity
value for the aquifer. Also, fewer pumping tests would have to be
conducted because they do sample a much larger portion of the aquifer.
Methods for conducting and analyzing slug tests and pumping tests are
provided in Freeze and Cherry (1979), Walton (1987) and Fetter (1988).
The results and interpretations of all slug tests and pumping tests
should be included in the Site Characterization Report.

### 3.34 Background Water Quality

Basic data should be collected to establish the background quality of
ground water, irrigation water and precipitation at the study site.
Analyses should include major ions (dissolved oxygen, alkalinity, etc.),
major nutrients (nitrate, nitrite, ammonia, organic nitrogen, and
phosphate), temperature, electrical conductivity and pH. Additionally,
water should be analyzed for the test compound (to ensure that there are
no residues, and to check the analytical method) and the tracer compound
(typically bromide).

If the irrigation source is a well within a quarter mile of the test
plot, the study director should determine if pumping this well has any
effect on the water table below the test site. This can be accomplished
by using a data logger probe in the monitoring well nearest the
irrigation well, and monitoring any drawdown of the depth to water when
the irrigation well pump is turned on. Ensure that the irrigation well
is run long enough to ensure communication with the underlying aquifer.

## 3.4 CONCEPTUAL MODEL

Site characterization data are analyzed and interpreted to produce a
three-dimensional representation of the characteristics of the study
site. The site-specific conceptual model should include graphical
displays of interpreted hydrogeologic characteristics that illustrate
the relationship between soil and hydrogeologic features. The conceptual
model should be discussed with reference to graphs, figures, and maps
and the data collected during site characterization. The discussion
should integrate site hydrogeology, surface hydrology, and historical
climatic data. The minimum graphical tools and analyses needed to
develop the model are described in the following sections.

### 3.41 Soils and the Vadose Zone

The results of the soil analyses including preliminary surface
investigations and NRCS information, exploratory coring program, and
test pit excavation should be analyzed and integrated. At a minimum, the
following are needed to interpret these data:

-   At least two stratigraphic cross sections (or fence diagrams) for
    each study site, one parallel to the direction of ground-water flow
    and one perpendicular to ground-water flow,

-   A detailed map of surface soils (1:100 to 1:1,000),

-   Graphs or tables of particle-size distribution vs. depth for each
    core,

-   Graphs or tables of matric potential head vs. depth and soil water
    content,

-   Graphs or tables of hydraulic conductivity vs. soil water content,

-   Graphs or tables of organic matter content vs. depth for each core,

-   Tables and/or graphs that display ranges of hydraulic conductivity,

-   Ranges of bulk density and hydraulic conductivity values for
    significant subsurface horizons,

-   An estimate of the amount of water needed for the tracer to reach
    ground water in two years and

-   An estimate of travel time needed for the tracer and/or pesticide to
    reach ground water.

A brief discussion of the above information should identify areas in the
study site (at the surface or at depth) where variations in topography,
soil texture, or other factors could cause differences in recharge. All
data analysis techniques and the results of those techniques should be
documented in the Site Characterization Report.

### 3.42 Saturated Zone and Water Quality

The results of saturated zone investigations and background water
quality analyses are used to interpret the subsurface hydrogeology of
the site. At a minimum, the following are needed to interpret these
data:

-   Contour map of the water table surface indicating the direction of
    ground-water flow,

-   Analyses of slug tests and/or pump tests

-   Estimate of hydraulic gradient and flow velocity of the aquifer,

-   Comparison of the spatial distribution of hydraulic conductivity
    using data obtained from laboratory and field investigations,

-   Graphical display of water quality data from the onsite wells, the
    irrigation source and precipitation and

-   Sample chromatogram from an analysis of the test compound(s) and
    tracer in onsite water.

These and other data analysis techniques and the results of those
techniques should be documented in the Site Characterization Report. The
discussion accompanying these data should address water table
fluctuations based on the collection of local historical data. Regional
recharge and discharge areas should also be discussed, including nearby
features such as irrigation wells and canals that could influence the
flow system. The discussion should also include a description of the
variations in hydraulic conductivity, the presence of confining layers,
and the overall aquifer flow system at the site, using historical data
where necessary. Any interferences identified when analyzing the water
collected at the site should also be discussed.

# CHAPTER 4 - MONITORING PLAN DESIGN

Once the site has been characterized, the variability of soil properties
and the ground-water flow system are understood, and a conceptual model
developed, a monitoring plan can be designed that is suited to the study
site. The number of wells and other sampling devices required to provide
a high degree of statistical certainty in the study results would likely
prevent the cooperating farmer from growing a crop on the field using
standard agronomic practices, and would make the study prohibitively
expensive. However, with a good conceptual model and a reasonable number
of sampling locations, monitoring data will be adequate to answer
regulatory questions. The clear advantages of testing a pesticide in the
field under conditions that as closely as possible resemble those in
which it will actually be used, as discussed in Chapter 1, outweigh any
disadvantages. Additional tools such as lysimeters and computer models
can provide useful data to augment the field data obtained. It is
strongly recommended that studies be conducted under FIFRA GLP, as
described in 40CFR160. Written standard operating procedures (SOP)
should be developed and maintained by the study director.

The compounds of interest (Chapter 2) will be monitored in surface
soils, the vadose zone, and the saturated zone. A conservative tracer
will be used to follow water movement through the system and weather
will be monitored throughout the study. Aspects to consider, and minimum
data collection needs, are described in the following sections:

-   Setting Up

-   Soil Monitoring Plan

-   Soil Water Monitoring Plan

-   Ground-Water Monitoring Plan

Design decisions should be integrated into one Monitoring Plan Design
Report for the Prospective Ground-Water Monitoring Study.

## 4.1 SETTING UP

### 4.11 Agricultural Management Practices

Standard agricultural practices for the target crop and the intended use
of the test pesticide should be followed while conducting the
Prospective Ground-Water Monitoring Study. All pesticides, fertilizers,
and farming, maintenance, and sampling equipment should be stored away
from the study site so as to eliminate the possibility of contamination.

### 4.12 Irrigation

The following guidelines assume that leaching of the pesticide is being
investigated at a site selected because conditions exist at that site
that are more likely to promote ground-water vulnerability and will
provide data on the leaching of the pesticide under those conditions.
Some alterations may be approved in the irrigation scheme at selected
sites when leaching at multiple sites representing different levels of
ground-water vulnerability is being investigated. Irrigation should be
scheduled at regular intervals, as well as applied at critical periods
in the growing season, to meet the target water input. The initial
irrigation event should be scheduled to occur within three days after
the pesticide application, unless sufficient precipitation occurs during
this time. Following the first irrigation event, dates should be
established when additional water will be applied to the field if
monthly targets of total applied water are not reached as a result of
natural precipitation. The schedule should be flexible enough to ensure
that adequate water is applied to meet the needs of the crop,
particularly in critical moisture periods (such as the period of
tasseling through silking for corn, or during fruit development for
orchard crops). The Monitoring Plan Design Report should indicate the
irrigation method, rate, schedule, and duration. Actual dates of
irrigation events should be documented and reported in the Final Report.

[]{#__RefHeading___Toc184799193 .anchor}Estimate target water
requirement by month (120% of crop water demand or 120% of historical
rainfall data, whichever is greater). These goals should be maintained
at the study site through each and every agronomic season starting from
the initial pesticide application date throughout the entire monitoring
period for the study unless alternate goals are agreed to by the Agency
during the latter years of the study. Calculations for target water
requirements should be based on 20-year data distributions (crop, study
site/region, rainfall, irrigation, etc). Document calculations,
assumptions, and reference 20-year data used in determining target water
demand. Procedures used to determine the timing and amounts of water as
a function of rainfall and other climate conditions should be provided.
The type of irrigation system, the frequency of irrigation, and the
minimum amount of irrigation applied should conform with local agronomic
practices for the specific crop and study soil. All irrigation events
should be conducted so as to minimize surface pooling and runoff while
maximizing the potential for infiltration.

### 4.13 Initial Post‑Pesticide Application Irrigation Event

In general, the timing and rate of irrigation is more important during
the initial days and weeks after application than it is as the study
progresses into the second year and beyond. The relationship between
rainfall timing and intensity and pesticide leaching has been reported
by a number of researchers (Isensee et al, 1990; McLay et al., 1991,
Shipitalo et al., 1990; Sigua et al., 1993;1995). Since rainfall is both
spatially and temporally variable, it is necessary to supplement
rainfall so that a study can be conducted within a reasonable time
period. Therefore, it is recommended that an initial irrigation be
applied to the study area within three days after the pesticide
application.

After initial pesticide application, a minimum of 1.0 inch of natural
rainfall or irrigation should occur within 3 days and the application
rate should be between 0.5 and 1.0 inches per hour. The first month's
targeted rainfall plus irrigation amounts should be divided into four
periods of 7-8 days each, and at least one fourth of the target monthly
water requirement should occur in each of the four periods (apply
additional irrigation water amounts in increments of 0.3 inches or
greater as needed to meet the total month's targeted amount).

### 4.14 Irrigation After Initial Event

The intent of the Prospective Ground-Water Monitoring Study is to
evaluate a pesticide's potential to contaminate ground water and to
provide an idea as to the concentrations that could be seen in ground
water through normal agricultural activities. It is therefore necessary
that enough water be added to the site so that ground water is recharged
during the study. Due to the stochastic nature of precipitation, to rely
strictly on precipitation may result in the study having to be conducted
for many years. Thus irrigation can be applied to reduce the length of
time that a study may need to run.

Beginning with the second month after application, at least the target
water requirement for the specific month (as specified in
Agency-approved Monitoring Plan Design report) should occur either in
the form of natural rainfall or applied as irrigation. Irrigation does
not have to be applied when the crop is not present. For example,
irrigation should not be applied during winter months when freezing
would destroy irrigation equipment. On occasion, at sites where
precipitation has fallen well below historical norms for months or
longer, some irrigation water might be applied during fallow months in
order to meet the previously established water balance targets.
Irrigation is not required at times when damage to the crop would occur
(during times when drying is essential).

Sprinkler irrigation is preferred except in instances where other
crop-specific methods (flood irrigation as an example) are required to
assess movement under typical agronomic practices. Documentation should
be provided, including references and names, for such crop-specific
irrigation practices.

### 4.15 Mixing and Loading Area

The location of pesticide mixing and loading activities should be
identified on the base map. Ideally these activities should take place
down gradient and down slope from the site to minimize the possibility
of point-source contamination. Other activities that could take place in
this area include calibration of the sprayer equipment with water,
sampling of the application (tank) mixture, and sampling equipment
cleaning.

### 4.16 Control Plot

To establish background ground water quality, at least one well should
be placed hydraulically up gradient of the field where the test
pesticide will be applied. Control plots should be planted and
maintained the same as the treated field. Control wells should be
sampled on the same schedule as monitoring wells in the treated field.
The control area and control well location(s) should be identified on
the base map.

### 4.17 Decontamination Area 

Prior to sampling soils or ground water, equipment should be cleaned to
minimize the likelihood of cross-contamination. This should be done far
enough away from the study site so that activities and onsite disposal
of rinsate will not affect study results. The decontamination area
should be identified on the base map. Additionally, rinsate should not
be disposed of in "ecologically sensitive" areas, such as wetlands or
down other wells.

### 4.18 Weather Station

Onsite climatic monitoring is essential in evaluating pesticide leaching
relative to the timing and magnitude of precipitation. Precipitation
data are also needed to determine the required amount of monthly
irrigation. Daily rainfall amount and intensity, pan evaporation, and
temperature data are also key input parameters for several computer
simulation models. A variety of automated weather stations and data
logging equipment are commercially available that record daily
precipitation, pan evaporation, wind speed, solar radiation, minimum and
maximum air temperature, and soil temperature. Special care should be
taken to protect parts of the weather station that can easily be damaged
by birds and other animals, such as rain gauges and evaporation pans.

## 4.2 Application of Pesticide and Tracer

### 4.21 Pesticide

Decisions about pesticide application rates are made when the study
scope is defined. Application method, calibration procedures and the
amount applied should be documented for the test pesticide and reported
in the Site Characterization and Monitoring Plan. Only one application
of the pesticide should be made. The tank mixture should be sampled and
the concentration confirmed. The pesticide application rate should be
verified using pan samplers, shallow soil samples, application cards or
other in situ collection devices. Nominal and actual application rates
should be reported.

### 4.22 Tracer

A conservative tracer should be applied along with the test pesticide to
provide information on the direction and rate of movement of water
through the vadose and saturated zones.

When selecting a tracer, the chemistry of the compound should be
considered along with potential sources of background interference,
achievable detection limits, and potential losses due to adsorption,
volatilization, and plant uptake. Bromide and chloride have typically
been used to trace the movement of soil water in agricultural studies.
Other tracers may be acceptable if approved by EPA.

[]{#__RefHeading___Toc184799202 .anchor}Appropriate tracer application
rates should be determined prior to initiation of the study, taking into
consideration analytical methods and limits of detection and
quantification, and concentrations in background soil and water samples
(higher background levels of bromide, for example, at a study site can
interfere with the ability to track the subsurface movement of the ion
unless a relatively high initial application rate is used). Analytical
methods, calibration procedures and amount of tracer applied should be
documented and reported in the Monitoring Plan Design and Final Reports.
The tracer should only be applied once at the same time as the initial
pesticide application.

## 4.3 SOIL MONITORING PLAN

The primary purpose of soil sampling in these studies is to verify
pesticide application rate and to provide information on the dissipation
of the compounds of interest in the zone of application, and not to
track the movement of the test compound through the subsurface.
Experience with prospective studies over the past 10 plus years
indicates little correlation between pesticide detections in soil cores
and detections in ground water. Some subsurface soil samples are
collected early in the study to identify residues that remain in top
meter of the soil column, above the uppermost lysimeters. Deeper
vertical transport will be tracked using suction lysimeters and wells
and not soil cores. Soil samples are to be analyzed for residues of the
test pesticide, degradates, and tracer compounds. The soil moisture
content should be measured for each sample collected.

### 4.31 Soil Sampling Methods and Instrumentation 

Soil samples to verify the application rate should be collected using
methods that ensure that pesticide-free soil does not dilute the samples
to which the pesticide has been applied. When the pesticide is applied
as a spray, soil samples for application verification should be
collected from the surface soil without adding deeper pesticide-free
soil. In this case, a sampler such as the box sampler will allow the
collection of a wide (30 cm) and shallow (8 cm) sample. If the pesticide
is soil incorporated, the initial soil samples should be collected to
the depth of the disturbed zone. If a banded application is used, soil
samples should be collected in the band to the depth of the disturbed
zone. To avoid discarding any of the applied pesticide, surface plant
residue should not be removed from these samples.

### 4.32 Number and Location of Soil Cores

A sufficient number of soil samples should be collected from a study
site to qualitatively demonstrate the variability in pesticide
application rates across the study site. The distribution of soil
sampling locations across each study site should be dictated by the
method of pesticide application and the degree of soil homogeneity on
the site. For example, the collection of a minimum of 15 individual soil
cores is required at each sampling period for a 2- to 5-acre study site
with relatively homogeneous soil conditions. Sites that exhibit marked
soil heterogeneities will require a greater number of soil samples.

### 4.33 Soil Sampling Timing and Frequency 

In general, soil samples should be collected until a pattern of
persistence or decline of the compounds of interest has been
established. Soil cores collected during the first two soil sampling
rounds (pre-application and immediately post-application) should only
sample surface soil. Shallow soil cores (0 - 10 cm) should be collected
during rounds 3 and 4. Slightly deeper cores (0 - 100 cm) may be
collected following the initial irrigation event, or earlier if a
precipitation event occurs. Analysis of soil samples for pesticide and
tracer residues should be continued until at least three consecutive
(normally monthly) samples show no residues above the minimum detection
(not quantitation) limit or until termination of soil sampling is
approved by EPA.

## 4.4 SOIL-WATER MONITORING PLAN

Tracer and pesticide residues in soil water are monitored to provide an
indication of the movement of water and the test pesticide through the
vadose zone. Soil-water samples, collected with soil-solution samplers,
suction lysimeters, or other devices, qualitatively track the downward
transport of pesticide residues. Analytical methods for pesticides in
soils commonly have higher minimum detection limits than those in water,
typically by more than an order of magnitude. Also, water is likely the
medium via which the solutes will be transported. Thus, soil-water
samples can be used to better track the movement of pesticide residues
or tracer in vadose zone media with a greater power of detection than in
soil samples.

### 4.41 Soil Water Content Measurements 

The amount of water in soil, or the soil water content, is an important
component of assessing a site\'s overall water balance. It is also
important for providing water to plants and for transporting solutes.
Evaporation of water from the soil, transpiration by plants, movement of
water, and the transport of solutes in soil are functionally related to
the soil water content. Soil water, therefore, is a dynamic property
which varies both spatially and temporally.

Soil water content throughout the site should be measured at least
monthly (preferably more frequently). Soil moisture measurements are a
necessary piece of information needed for modeling flow and for onsite
water management; for example, to determine when irrigation is needed.
Soil water content should be determined for soil samples collected for
pesticide and tracer residue analysis because these parameters should be
reported on a dry-weight basis.

### 4.42 Instrumentation

A number of direct and indirect methods are available to measure soil
water content (Gardner, 1986; Topp, 1993). The gravimetric method (a
direct, destructive procedure) is a standard technique commonly used to
collect reference data on soil water content. Indirect methods include:
electrical conductivity, capacitance and resistance, neutron
thermalization, and gamma ray and neutron attenuation. Of these methods,
the three that appear to have the greatest use and utility are:
gravimetric soil-water content; Time Domain Reflectometry (TDR), an
electrical capacitance method; and neutron probe (neutron
thermalization). Techniques such as TDR or frequency domain capacitors
have the advantage of real-time readouts and no radioactive source.

Tensiometers or other suitable methods should be used to determine the
availability of soil water for sample collection (Cassel and Klute,
1986; Rawlins and Campbell, 1986). Stannard (1990) provides a summary of
the theory, design, installation, and use of vacuum-gauge, manometer,
and pressure-transducer tensiometers in field investigations. The types
of tensiometers used at each study site, and their locations, should be
documented and reported in the first quarterly report.

### 4.43 Location and Frequency of Sampling

Soil water content measurements should be collected near the suction
lysimeters and wells. Soil water content should be measured when
lysimeters are sampled to at least a depth of one meter.

### 4.44 Soil water Sampling

Because water in the vadose zone is held at negative matric potentials,
water will not flow freely into sampling devices. Suction, in excess of
the soil matric potential, should be applied to induce the flow of water
into sampling devices. Therefore, suction lysimeters or other
pore-liquid samplers are required. There is an extensive body of
literature on the function and limitations of different devices and
techniques for extracting water from soil using a pressure differential.
Reliable, documented methods should be used to collect samples of soil
water for analysis of the applied chemical, degradation products,
tracers and other species of interest.

### 4.45 Instrumentation

The operation and effectiveness of suction lysimeters have been
described by Morrison (1983); Everett, Wilson and Hoylman (1984); and
Everett and McMillon (1985). The function and limitations of various
suction sampler designs are presented in Wilson (1990). Vacuum samplers
can be used to obtain soil-liquid samples from up to 6 feet below the
ground surface. Pressure-vacuum lysimeters are recommended for water
sample collection to a depth of 50 feet (Parizek and Lane, 1970).
Limitations are discussed by Litaor (1988).

The porous sampling membrane of suction lysimeters can be constructed
from a number of materials. Testing has shown that sampling membranes
constructed of PTFE (Teflon) cannot sustain a sufficient vacuum to
collect samples under high matric potentials. Prior to installation,
however, laboratory studies should be conducted to assess the degree of
sorption exhibited by the compounds of interest onto the ceramic
membranes.

### 4.46 Depth and Number of Lysimeters

A minimum of eight clusters of four lysimeters each should be installed
within the boundaries of the treated study site. The lysimeters at each
cluster should be installed at four different depths (*e.g.* 3, 6, 10
and 15 feet) to provide the greatest coverage of the vadose zone. If the
study is conducted at a site with a ground water table less than 15 feet
below grade, fewer lysimeters will be required per cluster.

### 4.47 Time of Emplacement

Lysimeters should be in place a minimum of 2 weeks, and preferably one
month, prior to the application of the test pesticide to the study site.
In most cases, this will allow materials in the lysimeter to seal the
annular space and to equilibrate with soil-moisture conditions. In some
instances, a longer period of time may be necessary to achieve reliable
and consistent samples from suction lysimeters. It should be noted that
Litaor (1988) generally recommended that solution sampler systems be
installed one year before sampling begins so that the samplers can
equilibrate with the surrounding soil. Suction lysimeters should
therefore be tested for operational effectiveness prior to the field
application of the compounds of interest.

### 4.48 Sampling Frequency

Tensiometers should be regularly monitored to assess the availability of
soil water for collection, and to determine the level of suction
required to draw water from soil pores. Samples should be collected from
lysimeters prior to pesticide application and frequently in the early
part of the study. Soil pore water sampling activities should be
coordinated with the collection of ground-water samples. A typical
sampling scheme is as follows:

  -----------------------------------------------------------------------
  **ROUND**         **TIMING**                    **DEPTH**
  ----------------- ----------------------------- -----------------------
  Sample 1          Pre-application               3, 6, 9, 15 feet (ALL
                                                  DEPTHS)

  Sample 2          7 days after application      3, 6 feet

  Sample 3          14 days after application     3, 6, 9 feet

  Sample 4          1 month after application     3, 6, 9 feet

  Sample 5          2 months after application    3, 6, 9 feet

  Sample 6          3 months after application    3, 6, 9, 15 feet

  Sample 7 - ?      continue monthly sampling     3, 6, 9, 15 feet (ALL
                                                  DEPTHS)
  -----------------------------------------------------------------------

Samples should be drawn from lysimeters at each sampling period and
analyzed individually. In the event that an insufficient volume of water
is collected from a lysimeter, samples from two lysimeters located at
the same depth increment may be composited. Criteria for termination of
sampling are presented in Chapter 6. Approval for termination of
monitoring should be received from EPA in writing.

## 4.5 GROUND-WATER MONITORING PLAN

The purpose of monitoring tracer and pesticide residues in ground water
is to provide an indication of the movement of water, the test pesticide
and its degradates through the vadose zone to ground water. Ground-water
samples should be collected and analyzed for all compounds of interest
(Chapter 2).

### 4.51 Monitoring Well Design

The success of a ground-water monitoring program for a prospective
monitoring study depends in part on the proper installation of
monitoring wells. Installation of these wells by licensed professional
monitoring well installers, according to published standards
specifically related to the construction of monitoring wells, should
ensure that the wells will provide representative ground-water samples.
Auger, direct push and other acceptable methods of well installation may
be used provided the wells are installed and constructed to ensure
reliable sampling of ground water, and that well materials do not affect
sample quality. Local and state monitoring well construction,
installation and location requirements should be taken into account in
planning well design. Studies have recommended against using existing
drinking water wells for monitoring pesticide concentrations, finding a
significant difference in detections between existing wells and
stainless steel monitoring wells (Smith et al., 1998). Well abandonment
at the completion of the study should be done in accordance with local
and state regulations. To minimize site disturbance, borings completed
for site characterization should be used to install monitoring wells.

### 4.52 Number, Emplacement, and Screen Lengths of Wells Within a Cluster

Ground-water monitoring wells should be installed as clusters. At each
ground-water sampling location [at least]{.underline} two depths should
be sampled. The magnitude of seasonal fluctuations in the water table
should be determined prior to monitoring well installation. The
shallowest well at each location should be placed to intercept the
shallowest occurrence of ground water. This generally means that it will
be screened across the water table. The top of the screen for the second
well should be placed at the depth of the bottom of the shallow well
screen.

In order to avoid excessive dilution of a pesticide residue or tracer
and to focus on a discrete portion of the aquifer, screen lengths should
be no longer than 1.5 meters; generally a smaller screen is preferable.
If the depth to the water table does not fluctuate drastically, each
cluster should monitor the top 3 meters of the aquifer. Where the water
table fluctuates due to seasonal or other influences a greater thickness
of the aquifer should be screened.

### 4.53 Number and Location of Monitoring Well Clusters

Monitoring wells should be located up gradient of the treated field in
the control plot, within the treated field and down gradient of the
treated field. A minimum of eight monitoring well locations should be
spatially distributed within the treated field. State and local
requirements for ground-water monitoring should be included in planning.

The locations of wells should be randomly distributed within the field.
They may be placed at randomly chosen nodes on a regular grid to
simplify data analysis and to reduce interference with agronomic
practices such as planting, pesticide applications, and irrigation.
Alternatively, the field may be divided into sectors and more wells
located in selected sectors based upon the site characterization data
and the conceptual model. Factors that might induce differential rates
of infiltration and solute transport through the soil and subsoil
include soil texture and structure, surface topography (shape and
gradient), and hydraulic conductivity. Monitoring wells should not be
placed in areas susceptible to runoff.

### 4.54 Time of Emplacement 

Wells should be installed a minimum of 2 weeks prior to pesticide
application. Time should be allowed for development and stabilization of
the wells prior to use. They should be in place to allow background
sampling of ground water for site characterization prior to pesticide
application.

### 4.55 Sampling Frequency

Ground-water samples should be collected more frequently in the early
part of the study and coordinated with the collection of soil and soil
water samples and irrigation events. One pre-application sample should
also be collected from all wells. Ground-water samples should be
collected 14 days after the initial application, and at least once a
month after that time from all monitoring wells. Additional samples
should be collected before 14 days if there is reason to believe the
compounds of interest may move rapidly (for example, following a large
rainfall or irrigation event). Some researchers have indicated that
pesticides may leach to very shallow ground water beneath agricultural
fields shortly after major recharge events. Based on analytical results
of soil and soil water sampling, additional ground-water sampling events
may be scheduled. Criteria for termination of sampling are presented in
Chapter 6. Approval for termination of monitoring should be received
from EPA in writing. A typical sampling scheme is:

  -----------------------------------------------------------------------
  **ROUND**                     **TIMING**
  ----------------------------- -----------------------------------------
  Sample 1                      Pre-application

  Sample 2                      14 days after application

  Sample 3                      1 month after application

  Sample 4                      2 months after application

  Sample 5                      3 months after application

  Sample 6 - ?                  continue monthly sampling
  -----------------------------------------------------------------------

### 4.56 Instrumentation 

The study director should ensure that all sample collection equipment
will not alter the quality of ground-water samples during transfer or
collection activities. A wide range of sampling devices suitable for
sampling nonvolatile organic chemicals in ground water is available, but
only a few are suitable for volatile organic compounds. For instance,
most pumps and bailers are not suitable for the collection of volatiles.
Also, certain types of sampling equipment may not be appropriate in any
situation: *i.e.*, peristaltic pumps generally cannot sample as deep as
30 feet. Sampler parts should be constructed of materials that will not
contaminate or alter sample integrity. Typically teflon or stainless
steel sampling equipment is preferred (USEPA, 1986b). In addition,
pesticides may adsorb to certain types of tubing such as silicone
rubber, Nalgene 180, Tygon R-3603, and low-density polyethylene. Teflon
or stainless steel bailers should alleviate this problem in most
situations. Dedicated sampling pumps are recommended to avoid
cross-contamination. If these will not be used, then decontamination
procedures which are appropriate for the situation should be used.

### 4.57 Sampling Methods

Before any well is sampled, the static water levels should be obtained.
Water levels should also be measured in each piezometer during the
sampling round. This information will be used to construct a water table
map for each sampling period. Wells should be purged before sampling.
Samples should be drawn from each monitoring well during each sampling
period and analyzed individually. The first ground-water samples from
each round should be drawn from the furthest up gradient well clusters.
Sampling should then progress down gradient. Sampling for subsequent
events should remain in the same order unless analytical results
indicate contamination of up gradient wells. In this case, sampling
should progress from the well displaying the lowest pesticide residues
to the well displaying the greatest pesticide residues.

### 4.58 Integrated Sampling Schedule

Once design decisions have been made about how and when to sample soil,
soil water, and ground water, these decisions should be integrated into
one monitoring plan for the ground-water monitoring study. An example of
a coordinated monitoring schedule is given below:

  ------------------------------------------------------------------------
  **ROUND**   **TIMING**                  **MEDIA SAMPLED**
  ----------- --------------------------- --------------------------------
  Sample 1    Pre-application             Soil (0 - 3 inches), ALL Soil
                                          Water, ALL Monitoring Wells.

  Sample 2    Immediately                 Soil (0 - 3 inches)
              post-application            

  Sample 3    1 day after application     Soil (0 - 1 foot),

  Sample 4    3 days after application,   Soil (0 - 1 foot),
              (irrigate)                  

  Sample 5    7 days after application    Soil (0 - 1 foot), Soil Water
                                          (3, 6 feet)

  Sample 6    14 days after application   Soil (0 - 1 foot), Soil Water
                                          (3, 6, 9 feet), ALL Monitoring
                                          Wells

  Sample 7    1 month after application   Soil (0 - 2 feet), Soil Water
              (irrigate)                  (3, 6, 9 feet), ALL Monitoring
                                          Wells

  Sample 8    2 months after application  ALL Soil Water, ALL Monitoring
              (irrigate)                  Wells

  Samples 9 - 3 months after              ALL Soil Water, ALL Monitoring
  ?           application - study         Wells
              termination (irrigate)      
  ------------------------------------------------------------------------

Sampling of soil water and ground water should continue until the
patterns of transport and decline have been established for the test
pesticide and associated degradates. No study will be terminated before
the questions for which the study was designed have been reasonably
answered. The registrant may suspend sample analysis with EPA approval
(but not continued sample collection) if they believe these criteria
have been met while awaiting formal response from EPA as to whether the
Agency agrees that the criteria for study termination have been met.

# CHAPTER 5 - SITE CHARACTERIZATION AND MONITORING PLAN DESIGN REPORTS

Reports summarizing the site characterization process and the
development of monitoring plans for each study site should be submitted
to EPA for approval prior to the installation of the monitoring system.
The Monitoring Plan Design Report should be prepared simultaneously with
the Site Characterization Report. Although both reports should be
submitted before the implementation phase of the study can begin, they
do not have to be submitted together. Final approval of monitoring plans
will be provided after review. Required elements of both of these
reports are described below. All reports and supporting data should be
submitted in an editable electronic format and as many hard copies as
required by Registration Division or Special Review and Reregistration
Division.

## 5.1 SITE CHARACTERIZATION REPORT

The Site Characterization Report should be completed after the site
characterization process. The required elements of this report have been
described in detail in Chapter 3. They will be briefly summarized here
and include:

-   A summary of regional conditions,

-   A site base map,

-   Description of surficial soil characteristics,

-   Description of field testing methods and results in the vadose zone
    (saturated and unsaturated hydraulic conductivity, soil water
    content)

-   Description of historical water needs of crop and net recharge at
    the site,

-   Descriptions and results of test pit excavations,

-   Description of the design, implementation, and results of the
    exploratory boring program,

-   Results of shallow saturated zone investigations,

-   Description of the irrigation, ground water and precipitation water
    quality,

-   Development of a conceptual model of the site, and

-   Any additional information that may impact the design, performance,
    or conclusions of the study.

-   Summary of Regional Conditions

Regional hydrogeology and agriculture should be described to provide a
framework for interpreting the site-specific data collected during the
site characterization process. A description and map depicting the site
location with respect to geographic features, regional topography,
dominant soil types, major aquifers (including those used for drinking
water), regional water table depths and direction of ground-water flow,
regional irrigation trends, and other regional agricultural practices
should be included. Maps and figures to illustrate the regional
conditions are encouraged.

### 5.11 Site Base Map

An accurate base map of each study site displaying the information
collected during the site characterization process should be included in
the Site Characterization Report. The required elements of a site base
map are listed in Chapter 3, Section 1.

### 5.12 Surficial Soil Characteristics

The results of detailed soil investigations conducted by a qualified
soil scientist should be presented. A map depicting the soil series
present at each study site should accompany a description of the
characteristics of the soils present on each site. A site-specific soil
profile describing the various soil horizons typical at each study site
should be included. Soil profile descriptions should follow the
conventions established by the U.S. Department of Agriculture.

### 5.13 Field Testing Methods and Results

The procedures used to determine the hydraulic conductivity, matric
potential head and soil water content of each test site should be
reported. A map indicating the locations of test sites should be
presented along with the results of the tests.

### 5.14 Historical Water Needs and Net Recharge

The data used to establish a baseline value for the average historical
water needs of the crop and net recharge at the site should be
summarized. If historical weather data is derived from readily available
sources, such as the nearest NOAA weather station, the average of the
monthly precipitation and evaporation data should be summarized in a
concise table, and the data source cited. If these data were derived
from a local source near the study site, the summary table should be
accompanied by a more detailed description of the data source, as well
as the name of a contact that is willing to discuss and verify the data.
If historical irrigation records are available, these should be
described in text and summary tables. If such data are not available,
the method used to estimate irrigation requirements should be described
in detail. Copies of the historical irrigation records or calculations
used to estimate irrigation needs should be included as an appendix to
the Site Characterization Report.

### 5.15 Test Pit Excavation

Test pit investigation results should be reported. All excavations
should be located on a site map, and sketches and descriptions of
significant features in the test pit walls should be included in the
report.

### 5.16 Exploratory Boring Program

The design of an exploratory boring program is described in Chapter 3,
Section 2. Documentation of all exploratory borings is critical to the
characterization of subsurface conditions at each study site. This
documentation should include a reference to the boring methods and
subsurface sample collection methods used, copies of all drilling logs,
reference to the preservation and transportation procedures for soil
samples, a summary of the methods used to analyze soil sample
properties, and the physical and chemical characteristics of all soil
samples. Quality assurance procedures ensuring the integrity of soil
samples and the data derived from those samples should also be reported.

### 5.17 Saturated Zone Investigations

The procedures used to gather information on the hydraulic
characteristics of the shallow saturated zone should be reported.
Contour maps illustrating the potentiometric surface of the shallow
aquifer at each study site should be constructed, and estimates of the
hydraulic gradient at each site should be reported. Any information on
water-table fluctuations associated with each study site should be
reported, along with estimates of the magnitude and potential impacts of
the fluctuations on the study. Hydraulic conductivity estimates obtained
at each study site should be reported, and the methods used to determine
these estimates should be described. The range of hydraulic conductivity
values obtained from different locations across the site, the results of
pump testing, if used, and the results of laboratory permeability tests
should be compared to obtain an estimate of the variability in hydraulic
conductivity at the site.

### 5.18 Background Water Quality

Basic data should be collected to establish the background quality of
ground water, irrigation water and precipitation at the study site.
Analyses should include major ions, major nutrients, temperature,
electrical conductivity and pH. Additionally, water should be analyzed
for the test compound (to ensure that there are no residues, and to
check the analytical method) and the tracer compound (typically
bromide).

### 5.19 Conceptual Model

Information required for each study site is presented in Chapter 3,
Section 4 and includes:

-   A topographic map of the site,

-   A detailed map of surface soils (1:100 to 1:1,000),

-   Graphs or tables of particle-size distribution vs. depth,

-   Graphs or tables of matric potential head vs. depth and soil water
    content,

-   Graphs or tables of hydraulic conductivity vs. soil water content,

-   Graphs or tables of organic matter content vs. depth for each core,

-   An estimate of the amount of water needed for the tracer to reach
    ground water in two years

-   An estimate of travel time needed for the tracer and/or pesticide to
    reach ground water.

-   Graphs or tables of infiltration rates and saturated and unsaturated
    hydraulic conductivity measured across each study site, and

-   Contour maps of site hydraulic conductivity, soil water content,
    matric potential head and hydraulic head. The latter map should
    illustrate the direction of ground-water flow and give estimates of
    the hydraulic gradient.

Geologic cross-sections should be constructed from soil core information
collected during site characterization. At least two cross-sections
should be prepared for each study site that depicts significant
stratigraphic and hydrogeologic features. One cross-section should be
oriented parallel to the direction of ground-water flow; the other
should be perpendicular to the flow direction. The following information
should be included on each cross-section:

-   Orientation of the section across the site,

-   Description of all stratigraphic units,

-   Structural features,

-   Zones of high and low hydraulic conductivity,

-   Location of each borehole intersecting or projected into the
    section, with the total depth of the borehole and the depth to the
    water table indicated,

-   Indication of the rate and direction of ground-water flow.

## 5.2 MONITORING PLAN DESIGN REPORT (PROTOCOL)

In contrast to the level of site-specific detail required in a Site
Characterization Report, extensive detail in the Monitoring Plan Design
Report should only be provided for chemical-specific information, or
when elements of the proposed study design vary from the recommendations
provided in the remaining chapters of this Guidance Document. Study
directors are discouraged from submitting \"draft protocols.\" If the
design requirements spelled out in this guidance document are met, then
timely approval of the Monitoring Plan Design Report will allow the
experimental phase of the study to begin on schedule. Most subsequent
changes to the study design can be addressed in a series of memoranda,
rather than by submitting a series of draft reports.

If the study director believes that some aspect of the Monitoring Plan
Design cannot be consistent with the guidelines in this document, a
detailed description and justification should be submitted. This
situation may be caused by the conditions of the study site or chemical
characteristics of the pesticide or degradates.

The Monitoring Plan Design Report should clearly detail how the
pesticide application, sampling, and analysis will provide the data
necessary to evaluate the leaching potential of the pesticide and its
degradates under the site-specific study conditions. The following
chemical-specific data should be provided:

-   Application rates,

-   Compounds to be analyzed, including degradates and tracer,

-   Analytical methods,

-   Application method,

-   Equipment calibration methods, and

-   Method used to confirm the application rate.

The above information should be provided in summary form, with reference
to readily available standard operating procedures. Field personnel
should document referenced procedures in official field notebooks to
comply with Good Laboratory Practice requirements.

The design of the proposed monitoring program for each study site should
also be fully described in the Monitoring Plan Design Report. The
following information, detailed in Chapter 4, should be provided in the
Monitoring Plan Design Report:

-   The number of monitoring wells and suction lysimeters that will be
    installed,

-   A diagram showing proposed well and lysimeter locations,

-   A description of the proposed soil water sampler design,

-   A schematic diagram of the proposed well construction details,

-   Intended method, rate, schedule, and duration of irrigation,

-   Proposed experimental start and finish dates, and

-   Soil, soil water, soil water content, matric potential and
    ground-water sampling schedules.

The Monitoring Plan Design Report should also detail the field
procedures that will be used to instrument the site, conduct the
sampling, and abandon the site at the conclusion of the study. These
required elements are described in Chapter 4. These procedures should be
described in summary form, with reference to readily available standard
operating procedures.

# CHAPTER 6 - MONITORING PLAN IMPLEMENTATION

Once the Monitoring Plan Design has been approved, work on
instrumentation can begin. At this stage all design decisions have been
made. What remains is to install monitoring devices, apply the pesticide
and tracer, to collect samples, and to send them off for analysis. This
chapter describes factors to be considered in the field during
instrumentation, application, sample collection, and sample handling.

EPA anticipates that field-scale ground-water monitoring studies will be
conducted over a minimum of a 3-year period. This period includes 1 year
for site selection, site characterization, the development of a
monitoring plan, and the installation of the monitoring system, and at
least 2 years for post-application monitoring. Additional time will
likely be required for the preparation of the final study report. The
duration of these studies may vary depending on the results obtained.
Termination of monitoring at study sites requires EPA approval.
Generally, conditions appropriate for termination of the study include:

-   The tracer has peaked in concentration in all monitoring wells at
    the site, and has shown a marked decline for at least three months
    and

-   Residues of the pesticide (parent and degradates of concern) have
    completely degraded and dissipated in the entire profile (vadose
    and, if applicable, saturated zone). This is generally defined as no
    detections for three consecutive sampling times over an interval of
    at least two months, or

-   Pesticide residues have clearly peaked (parent and degradates of
    concern) in ground water beneath the treated field (for each of the
    well clusters) or concentrations have leveled off for an extended
    period (usually about 4 to 8 months) while significant pesticide
    residues and tracer substance no longer remain in the vadose zone.

Sampling of soil water and ground water should continue until the
patterns of transport and decline have been established for the test
pesticide and associated degradates. No study will be terminated before
the questions for which the study was designed have been reasonably
answered. The registrant may suspend sample analysis with EPA approval
(but not continued sample collection) if they believe these criteria
have been met while awaiting formal response from EPA as to whether the
Agency agrees that the criteria for study termination have been met.

This chapter is divided into the following sections:

-   Application of Pesticide and Tracer

-   Irrigation

-   Soil Monitoring

-   Soil Water Monitoring

-   Ground-Water Monitoring

-   Sample Handling and Tracking

## 6.1 APPLICATION OF PESTICIDE AND TRACER

The field crew should document that the application of the test
pesticide and tracer corresponds to the rates and methods defined in the
Monitoring Plan Design Report. Background concentrations of the tracer
in the vadose and saturated zones need to be established ahead of time
and the application rate should be sufficient that breakthrough of the
tracer into shallow ground water can be clearly detected with the
analytical method used. Application methods, calibration procedures,
amount applied, and the date and time of each application should be
documented carefully in the field notebook and reported in the First
Quarterly and Final Report. The tracer identified in the Monitoring Plan
Design Report should be applied the same day as the test pesticide.

Field notes should record the climatic conditions on the day of
application, including wind speed, temperature and precipitation. It is
particularly important to document in detail soil water content and
temperature conditions on the day of application and for following days.
The field crew should take detailed notes (supported by photographs when
appropriate) on the amount, type, and positioning of plant residues or
organic amendments relative to the planting rows (if applicable),
surface roughness, row spacing, ridge height and depth and method of
plowing, crop stage and vigor, weed composition and cover, and other
factors which may significantly influence pesticide dissipation
especially in the critical first few hours and days after application.
Application should not take place on a day when conditions could cause
pesticide loss due to spray drift or runoff, or if conditions are
inconsistent with label directions. All entries to the field notebook
throughout the study should be consistent with FIFRA Good Laboratory
Practices (GLP).

## 6.2 IRRIGATION

Detailed guidance on how to determine the amount of irrigation water
needed throughout the course of the study is provided in Chapter 4. The
cooperating farmer tending the study field should be familiarized with
the schedule and method of irrigation identified in Monitoring Plan
Design. With the exception of the irrigation event during the first week
after pesticide application, times when irrigation is needed will not
necessarily correspond to days field personnel are scheduled to conduct
sampling. Soil water content determinations up to a one meter depth
should always be made prior to any irrigation event as well as for all
sampling events (normally several in the first month after application
and once a month thereafter). The Study Director should keep in close
communication with the cooperating farmer to ensure that monthly
irrigation targets are being met, and that records of the dates and
amounts of irrigation are being kept.

## 6.3 SOIL MONITORING

Soil sampling is important for verification of field application rate.
For at least the month after application (normally including samples
taken 0, 1, 3, 7, 14, and 30 days post-treatment) samples should not be
composited before analysis in order to establish spatial variability of
the application. Analysis of soil samples for pesticide and tracer
residues should be continued until at least three consecutive (normally
monthly) samples show no residues above the minimum detection (not
quantitation) limit.

For soil monitoring, permanent equipment will not be installed in the
field. Therefore, the first step in the field procedure is
decontamination of sampling equipment, followed by sample collection and
handling. Careful attention to avoid cross contamination of samples is
important, especially in the early sampling intervals when pesticide
residues on the field are highest. The field crew should carefully
document procedures in the field notebook, noting any problems or
deviations from the Monitoring Plan Design.

### 6.31 Decontamination of Sampling Equipment

Decontamination minimizes the likelihood that pesticide or tracer
residues will be introduced into deeper soil horizons during sampling. A
decontamination area should be designated in a location downgradient of
the study plot. Soil-sampling equipment should be cleaned prior to
sample collection at each sampling interval. Field-blank water samples
should be taken with each sampling round to test the effectiveness of
the soil-equipment decontamination methods. All rinsate used in the
decontamination process should be disposed of away from the study site.
Additionally, rinsate should not be disposed of in "ecologically
sensitive" areas, such as wetlands or down other wells.

Field personnel can take additional precautions beyond equipment
decontamination to prevent sample cross-contamination. For example, each
person collecting samples should wear a clean pair of gloves during
collection of each soil core. Decontaminated sampling equipment should
never come in contact with the ground until the actual sample
collection. Decontaminated sampling equipment should be placed in a
clean plastic bag between uses to avoid accidental contact with
contaminated soil or water.

### 6.32 Soil Sample Collection and Handling 

The primary concern at the time of soil sampling is that representative
samples be collected, being careful not to cross-contaminate samples
from different depths or cores. Surface plant residue should be included
with shallow soil samples to account for pesticide residues clinging to
this material. When collecting successive samples for a deeper core, the
top portion of each core should be carefully scraped to remove soil from
the previous depth increment. The locations of sampling cores should be
carefully measured and recorded in the field notebook, to avoid
re-sampling in a location previously disturbed by coring. After
sampling, core holes should be refilled with pesticide-residue free soil
according to State and local regulations.

## 6.4 PORE-WATER MONITORING

The primary purpose of soil water monitoring is to track the movement of
dissolved pesticide and tracer toward the water table. Detection of
tracer in the soil column indicates that downward movement is occurring;
detection of tracer in the ground water indicates that recharge has
occurred. Monitoring pesticide residues gives an indication of the
relative rate of transport of the pesticide.

### 6.41 Instrumentation

The proper installation of soil water content monitoring devices is
described in manufacturer\'s materials and in USEPA (1986b), ASTM
(1994), Nielsen and Johnson (1990), Everett, Wilson, and Hoylman (1984),
and Morrison (1983). All lysimeters should be cleaned and leak tested
before installation in the field to ensure that they will be able to
hold sufficient vacuum to draw a soil-water sample. Testing of
lysimeters prior to installation is of special practical importance,
since any lysimeter that does not function properly during the study
will require that a replacement be installed. Recommended methods for
pre-installation cleaning and leak testing of pore-water samplers are
described in US EPA (1986b). In some instances, the manufacturer of the
sampling device may recommend other cleaning procedures that are
appropriate for the specific device.

The maximum suction that can be applied to a lysimeter before contact
with soil-water is broken is the bubbling pressure (or air entry
pressure). If a suction greater than the bubbling pressure is applied to
a lysimeter, only air will be drawn into the collection cup. If the
bubbling pressure for a lysimeter is not provided by the manufacturer,
this value should be determined before lysimeters are installed in the
field. This can be done by saturating the collection cup with water,
immersing the cup in water, and applying pressure to the lysimeter. The
bubbling pressure is the pressure at which air escapes from the ceramic
cup into the surrounding water.

Pressure-vacuum lysimeters offer some advantages over suction
lysimeters. For example, the maximum operating depth of pressure-vacuum
lysimeters is 15 meters, as opposed to 6 meters for suction lysimeters.
Also, pressure-vacuum lysimeters collected samples through tubing which
is part of the sample equipment, thus tubing is not reused eliminating
this as a potential source of contamination. Good hydraulic contact
between the porous segment of the sampler and the unsaturated media is
needed to minimize leakage along the annulus of the borehole. This may
be accomplished by packing silica flour around and beneath the porous
segment of suction samplers. The use of other materials, such as sand or
soil backfill will not provide as strong a hydraulic connection and may
necessitate equipment replacement. Bentonite powder should be used to
form a tight seal in the annular space immediately above the porous
component of the sampler to prevent contamination from the surface. The
supervising scientist should record problems encountered during
installation or deviations from procedures and describe them in the
First Quarterly Report and in the Final Report.

### 6.42 Decontamination

Sample collection tubing in a pressure-vacuum lysimeter is a dedicated
part of the sampling device, and need not be decontaminated. Other types
of lysimeters, for example suction lysimeters, have sampling tubing that
is attached at the time of sampling and should be decontaminated if it
is used for multiple lysimeters. In all cases, sampling tubing should
not be allowed to come in contact with the ground and should be handled
with clean gloves during sample collection. Any rinsate should be
disposed of away from the study area. Additionally, rinsate should not
be disposed of in "ecologically sensitive" areas, such as wetlands or
down other wells.

### 6.43 Sample Collection 

The following procedures pertain to the collection of samples from
pressure-vacuum lysimeters. Methods for the collection of pore-water
samples are generally provided by the equipment manufacturer and are
summarized in ASTM (1994), Nielsen and Johnson (1990), and USEPA
(1986a).

Pore-water samples should be collected from suction lysimeters by
maintaining a constant level of suction on the porous cup of the
lysimeter for at least 24 hours. The suction induces the flow of water
from the surrounding unsaturated media into the sampler. To collect a
sample, pressure is applied to the second line and water is forced from
the porous cup through the dis­charge tubing into the collection bottle.

The appropriate amount of suction for each lysimeter depends upon the
type of soil and the ambient soil moisture at the time of sampling. The
suction placed on the lysimeter should be greater than the suction
naturally occurring in the soil in order to induce flow into the
collection container and to prevent backflow from the porous sampling
cup to the soil matrix. The pressure applied to the lysimeter to force
sample water from the collection cup to the surface should not exceed
the bubbling pressure of the lysimeter, or the collected sample will be
forced from the ceramic cup back into the surrounding soil.

The following should be included in the field notes for each lysimeter
sampled:

-   Amount of suction applied,

-   Date and time that suction was applied,

-   Remaining suction at time of sampling,

-   Date and time of sampling,

-   Pressure applied for sampling and

-   Volume of sample collected

If the volume of available pore water or ground water is not sufficient
for both pesticide and tracer analyses, pesticide analyses should be
given first priority. If sample volume allows, duplicate and field-spike
samples should be collected. A trip blank sample should be included to
ensure cross-contamination of samples does not occur during shipment to
the laboratory.

Any problems or variations in pro­ce­dures in the Monitoring Plan Design
Report should be described in the Quarterly Reports and in the Final
Report. Reasonable effort should be made to follow the prescribed
sampling program. Adjustments may have to be made during periods of bad
weather but samples should still be collected according to the
prescribed intensity (*i.e.*, still at an average frequency of once
every month unless a deviation from the protocol is approved by the
Agency) and at times closest to the scheduled date that are feasible.

## 6.5 GROUND-WATER MONITORING

As with the soil pore-water sampling devices, monitoring well design
decisions have been made and described in the Monitoring Plan Design
Report. Problems or variances from these procedures should be documented
and discussed as they arise in each Quarterly Report and in the Final
Report.

### 6.51 Instrumentation 

The ability to collect representative ground-water samples depends on
the proper installation of monitoring wells. Most states require that a
permit be filed prior to the installation of monitoring wells and that
well construction records are returned to the state within a specific
time following the emplacement of monitoring wells. States may also have
specific monitoring-well construction requirements that should be
followed. Wells should be installed by licensed drillers familiar with
all relevant state and local requirements and supervised by an
experienced geologist, professional engineer or environmental scientist.
In addition, before initiation of the monitoring well installation
program, an effort should be made to identify and locate utilities,
irrigation systems, tile drains, etc. to avoid damage and costly
repairs.

All information pertaining to work performed during the well
construction should be recorded in detail in a bound project notebook
using waterproof ink. Field-book entries for each monitoring well should
be sufficiently detailed to allow the preparation of a detailed well
log. The following minimum information should be provided on every well
log:

-   Well number and permit number,

-   Well location,

-   Well depth,

-   Elevation of the top of the casing,

-   Depth to the water table,

-   Well construction details including: materials; length and diameter
    of the casing, screen, and surface casing,

-   Well annulus construction details including: depth, thickness, and
    materials selected for the filter pack, plug, and surface pad,

-   Geologist\'s field observations of soil characteristics from
    continuous split-spoon samples including: soil texture, color,
    moisture, and structure,

-   Geotechnical information, such as blow counts necessary to advance
    the split spoon and sample recovery and

-   Names of the drilling contractor and supervising geologist and,

-   Weather conditions during the drilling activities.

Any deviations should be recorded and described in the First Quarterly
Report and in the Final Report.

### 6.52 Well Development

Well development procedures should be undertaken once a monitoring well
has been installed and sufficient time has passed to allow the annular
seal to cure. The purpose of developing a monitoring well is to improve
the hydraulic characteristics of the filter pack by removing
fine-grained materials from the pack, and causing coarser materials to
settle around and stabilize the screen. Once this is accomplished, the
monitoring well can be used to collect representative ground-water
samples.

Removal of fine materials may be more difficult if the surrounding soil
itself is fine-textured, or if the soil water is naturally turbid. In
these cases, indicator parameters such as pH and conductivity should be
monitored during development (Driscoll, 1986). Development should
continue until parameters stabilize or the turbidity of the discharge
water is less than 5 nephelometric turbidity units (NTU), as recommended
in USEPA (1986b). If the parameters do not stabilize, this is an
indication that the development method is not effective and an alternate
method is needed. Information recorded during the development of each
well should include: date of development and development method, volume
of water removed, and a log of parameters monitored.

### 6.53 Decontamination 

Unless dedicated pumps are used for sampling, all ground-water sampling
equipment should be cleaned before use, and between wells. Non-dedicated
sampling equipment should be washed with a nonphosphate detergent,
rinsed with tap water then distilled water, and finally rinsed with a
pesticide-grade acetone (or hexane or methyl alcohol) to aid in drying
and to remove any organic residue (Barcelona at al., 1985). Other
options are given in Driscoll (1986). All solvents used in
decontamination activities should be disposed of in accordance with
State or local regulations.

If a single pump will be used to purge multiple wells or collect
ground-water samples, tubing should be dedicated to individual
monitoring wells. Any non-dedicated equipment should be designed so that
it can be disassembled for cleaning at the decontamination area before a
different well is sampled. Tubing removed from a well after each purging
or sampling event should be rinsed with deionized water before placing
in a clean storage container and sealed. Field blanks should be
collected from sampling equipment between wells to test the
effectiveness of decontamination. Bailers should be filled once and then
decanted into sample collection bottles. If non-dedicated pumps are used
for sample collection, spectrographic-grade water should be pumped
through equipment after decontamination and a sample collected for
analysis.

Some States have developed guidelines for decontamination protocols
(Mickam et al., 1989). State regulatory agencies should be consulted to
obtain current information on standard decontamination practices for
saturated and vadose zone monitoring programs. These standards should be
used to supplement the guidelines outlined in this document.

The water purged from the wells should be discharged away from all well
clusters. Additionally, purge water should not be disposed of in
"ecologically sensitive" areas, such as wetlands or down other wells.
Field personnel can take precautions beyond decontamination of sampling
equipment to ensure that cross-contamination between wells does not
occur. Decontaminated equipment should be handled using rubber
laboratory gloves, and should not be placed directly on the ground. It
is best to store equipment in clean sealed containers after
decontamination (*e.g.*, plastic bags or coolers) for relocation to the
well site. If bailers are used for purging and sampling wells, bailer
cords should be discarded after a single use.

### 6.54 Sample Collection

Prior to sampling any of the monitoring wells at a study site, field
conditions should be described in the field notebook. This includes
observations of weather and soil surface conditions, and the height of
the water table in all wells and piezometers.

In order to collect a ground-water sample from a monitoring well that is
representative of the water in the surrounding aquifer, standing water
should be removed from the well casing, screen, and surrounding filter
pack. This procedure is called purging. The volume of water purged, the
rate at which it is withdrawn, and the location of the sampling intake
all determine how representative the sample is to the water in the
aquifer. Typically parameters such as dissolved oxygen, specific
conductivity, oxidation-reduction potential, turbidity and pH are
continuously monitored throughout purging. When these parameters
stabilize, the well is considered purged (Driscoll, 1986).
Alternatively, a specific number of well casing volumes can be removed.
Meters used to monitor pH, temperature, and specific conductance should
be calibrated before each use.

Bailers should be gently lowered into the water column to a measured
depth just below the water table. Samples for volatile pesticides should
be headspace-free. Only a bladder pump is suitable for sampling for
volatile pesticides.

Ground-water samples should be collected in containers that will not
interact with the sample. Consult with the laboratory that the samples
will be analyzed at to determine if preservation methods beyond the use
of ice will be necessary to prevent additional degradation of the target
compounds. Ensure that use of chemical preservatives will not interfere
with analysis of target compounds. Ground-water samples should not be
composited, but placed directly into sample collection bottles. The
techniques used need to be validated for providing a representative
sample in which the analytes are stable under the conditions of
transport and subsequent storage before analysis. A trip blank sample
should be included to ensure cross-contamination of samples does not
occur during shipment to the laboratory.

If the volume of available pore water or ground water is not sufficient
for both pesticide and tracer analyses the pesticide analyses should be
given first priority. The analytical procedures described in the
Monitoring Plan Design should be used and documented. Duplicate samples
and field spike samples should be collected.

## 6.6 SAMPLE HANDLING AND TRACKING

Water and soil samples should be placed directly into coolers after
collection. To ensure against breakage and temperature fluctuations in
the samples, the following sample packing and shipping procedures should
be followed:

-   Samples should be shipped in insulated boxes or coolers. Devices are
    available to automatically monitor and record temperature while the
    samples are in transit.

-   Individual glass sample containers should be wrapped either in
    plastic bubble wrap, placed in Styrofoam holders, or somehow
    packaged to separate the sample bottles during shipping.

-   Gel-Cold packs or other materials to maintain stable temperatures
    can be placed in each cooler, but should not be in direct contact
    with any of the glass sample containers. To help maintain the
    Gel-Cold pack temperature and keep the temperature of the coolers
    around 4 °C, ice sealed in plastic bags may be added. The ice should
    be bagged to prevent seep­age during transport. Soil samples should
    be packed in a container at or below 0 °C as soon as possible after
    collection. If dry ice is used to preserve soil samples during
    shipment, field personnel should follow all hazardous material
    labeling requirements.

-   It is important that all sample tracking paperwork (i.e.
    chain-of-custody) be included with the shipment and that the chest
    be sealed according to chain-of-custody procedures.

All samples should be stored after collection according to GLP-compliant
procedures and the stability should be validated by a storage stability
study. Coordination with the laboratory concerning frequency and number
of samples is important for sample preservation and to ensure that
sample holding times are not exceeded. The laboratory should therefore
be notified prior to sample collection to ensure that samples will be
processed and analyzed quickly.

The sample tracking procedure described in the Monitoring Plan Design
portion of the Study Protocol should be followed. A number should be
assigned to each sample collected. That number should be marked on the
sample container and recorded on the tracking form and in the project
notebook. Weather conditions or field comments should also be recorded
on the tracking form or in the field notebook. A three-part label should
be used that includes numbered descriptive information to be placed on
the sample container. In general, sample labels should be placed in
duplicate on the sample container and should include:

-   Date and time of collection,

-   pH, temperature, and specific conductance,

-   Identification of sample location,

-   Analytes, and

-   Signature of field technician.

If samples are shipped to a laboratory, samples should be shipped in
such a way as to avoid breakage of sample containers and maintain sample
integrity.

# CHAPTER 7 - REPORTING

Quarterly status reports for each prospective ground-water monitoring
study should be submitted following the application of the compounds of
interest. Required elements of these status reports are described in
Section 7.1. These status reports are required to allow adjustment to
the study design, if necessary, and for the determination of when the
stated goals of the study have been fulfilled. However, in the interest
of efficiency, quarterly reports will not be formally reviewed (i.e. no
formal write-up of review will be submitted to registrant from the US
EPA) unless the results presented warrant further action.

The monitoring plan implementation phase of a prospective ground-water
study may end once the EPA approves a Study Termination Report submitted
by the registrant. While ground-water sampling in a prospective study
would ideally be completed two years after the application of the test
chemical, the appropriate termination point of a study is a function of
site-specific and chemical-specific characteristics. Section 7.2
describes milestones in the ground-water study that should occur before
the Study Director considers submitting a Study Termination Report.

At the conclusion of each study, a Final Study Report should also be
submitted to EPA. Required elements of this report are described in
Section 7.3. As this document should be able to stand alone as a full
report on the small-scale prospective study, it will include information
already presented in previous submissions. This report is the vehicle in
which the registrant can provide interpretation of the study results,
suggest further mitigation measures, and extrapolate the results through
modeling, or comparison to other available data. All information
referenced to sampling locations should conform to EPA\'s minimum data
elements standards which can be found at the US EPAs' Water Quality Data
Submissions: OPP Standard Operating Procedure home page
([http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm#appendix_a](http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm%23appendix_a )[)]{.underline}.
All reports and supporting data should be submitted in an editable
electronic format and as one hard copy.

## 7.1 QUARTERLY REPORTS

Quarterly status reports should be submitted to EPA beginning with the
first quarter following the application of the compounds of interest to
each study site. The required elements of these reports include:

-   A summary of the activities at the site during the quarter,

-   Concentrations or mass accounting for the conservative tracer and
    total pesticide residues at each cluster,

-   Protocol deviations from the approved monitoring plan, and

-   Results of all chemical analyses for samples (including quality
    control samples) collected during the quarter. Individual results
    should be reported. Results should not be averaged over samples or
    time.

-   Provide graphical representation of chemical analysis

These report elements are described further in the following sections.
The submittal of additional information that may impact the design,
conduct, or findings of the study is encouraged.

### 7.11 Summary of Site Activities

The summary of site activities should include all activities related to
agronomic practices, monitoring, and irrigation. The application dates
for fertilizers or other compounds applied to the study area should be
reported along with information on other agronomic practices conducted
during the quarter. Similarly, the dates of sample collection should be
reported along with information on weather conditions during the
quarter. If irrigation water was applied to the study site during the
quarter, then the dates and amounts of water applied should be reported,
and compared to the targets set in the Irrigation Plan. The results of
field measurements such as soil water content and matric potential
should be reported along with a water budget indicating the amount of
net recharge to the site.

### 7.12 Mass Balance

A mass balance for the conservative tracer and total pesticide residues
should be reported for each cluster. The mass balance at each lysimeter
and monitoring well should be approximated.

### 7.13 Protocol Deviations

Any deviations from the protocol established and approved as part of the
Monitoring Plan Design should be reported for each quarter. Reporting of
deviations should include a discussion of the proposed and approved
procedures, a description of the revised procedures that were
implemented during the quarter, the reasons for the revisions, and the
anticipated effects on the study.

### 7.14 Analytical Results

The results of all chemical analyses (*i.e.*, analyses for the test
pesticide, degradates, and tracer) conducted on samples should be
reported in tabular format. MDLs and the results of quality control
analyses should also be reported. Comments and a brief discussion of the
analytical results for the quarter may be included.

## 7.2 STUDY TERMINATION REPORT

The sampling program of a prospective ground-water monitoring study
would ideally last two years. However, in reality the duration of a
successful study is a function of how long it takes for applied water to
recharge to ground water and of how long it takes for the pesticide and
its degradates to leave the vadose zone by degradation and/or
dissipation. This time frame is a function of the soil type, properties
of the pesticide, and the amount of net recharge at the site.

In order to consider proposing an end to the sampling phase of a
prospective study, the study director should assess whether the
following criteria have been met:

-   The tracer has peaked in concentration in all monitoring wells at
    the site, and has shown a marked decline for at least three months,
    and

-   Residues of the pesticide (parent and degradates of concern) have
    completely degraded and dissipated in the entire profile (vadose
    and, if applicable, saturated zone). This is generally defined as no
    detections for three consecutive sampling times over an interval of
    at least two months, or

-   Pesticide residues have clearly peaked (parent and degradates of
    concern) in ground water beneath the treated field (for each of the
    well clusters) or concentrations have leveled off for an extended
    period (usually about 4 to 8 months) while significant pesticide
    residues and tracer substance no longer remain in the vadose zone.

The Study Termination Report should detail the fact that the above
conditions have been met, give a brief summary of study results, and
propose a date for the termination of the sampling phase of the
monitoring study. Sample collection should continue until EPA reviews
the Study Termination Report and concurs that sampling can end. EPA will
review the Study Termination Report within sixty days of receipt of the
report. No study will be terminated before the questions for which the
study was designed have been reasonably answered.

## 7.3 FINAL REPORT

A Final Report should be submitted to EPA at the conclusion of each
study. This report should include

-   Documentation of the application of the compounds of interest,
    climatic monitoring, and irrigation practices;

-   Documentation of all sampling and sample analyses activities;

-   Results of all chemical analyses and discussion of findings.
    Individual results should be reported. Results should not be
    averaged over samples or time; and

-   Documentation of quality assurance activities.

These report elements are described in more detail in the following
sections. The submittal of additional information that may impact the
interpretation of study results is encouraged.

### 7.31 Field Practices

The agricultural practices conducted during the course of the study
should be summarized in the Final Report. Information on the application
methods, rates, and dates for the compounds of interest should be
reported. The results of climatic monitoring at each study site should
be reported along with information on the irrigation methods used, and
irrigation rates, dates, and duration.

### 7.32 Sampling Activities 

Information collected during each sampling episode should be reported,
including

-   Static water levels in monitoring wells and piezometers,

-   Weather conditions and field comments,

-   Tensiometer readings and the amount of suction used to collect
    lysimeter samples, and

-   Soil moisture content at the time of sample collection.

### 7.33 Analytical Results and Discussion of Findings

The results of all chemical analyses should be presented. Analytical
results for all compounds of interest should be presented along with
information on analytical detection limits that were achieved. The study
findings should be summarized, and the significance of the findings with
respect to the demonstrated environmental fate of the test pesticide and
degradates should be discussed. The use of graphics and/or computer
models to illustrate this discussion is encouraged.

### 7.34 Quality Assurance

Compliance with good laboratory practices (GLPs) should be documented.
For field activities, a description of the system for sample numbering
and/or identification should be presented

For laboratory operations, the following should be reported:

-   Identification of responsible party who acted as sample custodian,

-   Copies of laboratory sample custody logs consisting of serially
    numbered standard lab-tracking report sheets, and

-   Description of laboratory sample custody procedures for sample
    handling, storage, and dispersion for analysis.

## 7.4 ELECTRONIC DATA REPORTING GUIDELINES 

Data generated from PGW studies have proven valuable to OPP scientists
and risk managers in better understanding the potential for a pesticide
to: (1) impact ground water quality, (2) contaminate drinking water, and
(3) reach ecologically important surface water systems, when used in
accordance with label directions. As part of an effort to update the
Agency guidance for the PGW studies OPP has developed specific guidance
for data submissions to improve the reliability, completeness,
transparency, and consistency in the PGW reports and facilitate further
use of these data for complete assessments of exposure to pesticides
through ground water (*e.g.*, using leaching models to explore the
potential for the pesticide of interest to leach under a variety of
conditions). Specific requirements on the submission of electronic data
are a matter that will be addressed for each study by EPA when
Prospective Ground-Water study candidate site information is submitted
to the Agency for approval. In general though, submission of this data
electronically is likely to be requested and will help the Agency not
only in the specific interpretation of the implications of the study
results for the overall potential to impact ground water of the test
pesticide but also to develop higher tier models and continue the
advancement of pesticide risk assessments.

The following guidelines have been developed to assist in reporting of
PGW monitoring information in electronic format. Listed below are eight
major information fields which focus on the key areas for prospective
ground-water monitoring data collection and reporting. These major
information fields are;

-   study area and conceptual site model;

-   application of pesticide and tracer;

-   crop information;

-   soil properties;

-   ground water data;

-   weather data;

-   irrigation application and

-   chemical monitoring results.

Each major information field lists specific data types and requested
data formats which serve as guidelines for submission of prospective
ground-water monitoring study data.

### 7.41 Study Area and Conceptual Site Model 

The following study area information is requested to provide background
information as well as to develop a study-site conceptual model. The
conceptual model should include graphs, charts, maps and data collected
during site characterization. Integration of site hydrogeology, surface
hydrology, and historical climatic data is acceptable.

Study Area Information

-   Base map in GIS readable format (E.g., Arc shape files, \*.dxf
    files, a format specifically approved by EPA);

-   NRCS soil surveys;

-   Other historical information and

-   Site Characterization Data of Study Area.

-   Sample locations identified and reported in consistent coordinate
    system format (GPS; x,y coordinates; northing,easting; lat,long).

-   Soil cores (coordinates) see soil properties below for listing of
    data to be reported, unsaturated and saturated hydraulic
    conductivity measurements at a minimum of 6 locations (coordinates)
    and soil horizons with depth (bgs, ft) and soil water content
    measurements at same 6 locations.

-   Piezometers - if not placed in soil core holes need coordinates,
    measuring point surveyed with U.S. Geodetic Vertical Datum,
    hydraulic head measurements, hydraulic conductivity (slug tests
    and/or pumping test results), potentiometric surface diagrams,
    background water quality data from upgradient well and influence of
    existing irrigation wells in the area on subsurface hydraulics.

### 7.42 Application of pesticide and tracer

The following pesticide and tracer information is requested.

Pesticide information

-   Chemical properties of test substance;

-   molecular weight;

-   CAS number;

-   formulation and

-   verification of formulation (method and results).

-   Date(s) of pesticide application;

-   Incorporation depth;

-   method of application;

-   total amount applied;

-   rate;

-   area covered (coordinates of locations where pesticide applied
    and/or boundary where pesticide applied) and

-   soil monitoring results after application (field dissipation data).

-   Topographic map detailing results of all surface soil samples
    collected to confirm application rate of pesticide. Determine if any
    hot spots of pesticides were detected post-application. This may be
    used to determine if any detection of pesticides in monitoring
    wells, lysimeters, etc. can be correlated to a "hot spot" detected
    in surficial soil samples.

-   If determined, any site-specific measurements of degradation or soil
    sorption should be reported

Tracer information

-   Chemical;

-   Formulation;

-   locations where tracer applied (coordinates);

-   method of application;

-   rate of application and

-   total amount applied.

### 7.43 Crop information 

The following crop information is requested (include this for the entire
course of the study, not just the year in which the pesticide is
applied).

-   Type of crop;

-   planting dates;

-   emergence dates;

-   harvest date;

-   date when chemicals applied (pesticide, herbicide, fertilizer, etc.)
    and

-   other relevant crop maintenance activities and crop growth / land
    cover information.

### 7.44 Soil properties

All data need to be separately reported for each depth increment of each
soil core analyzed. Some soil characteristic data may have been
collected as part of the site characterization testing of the study
area. If so, there is no need to repeat that information here. Pesticide
property data essential for modeling of leaching of the test pesticide
(K~OC~ and other measures of soil sorption and measures of soil
degradation rate) for the specific test soil should be provided (along
with background data relevant to the determination of these properties)
if specifically collected in association with the prospective
ground-water monitoring data in electronic format. In cases where
pesticide property data are not specifically collected for the test
soil, the extrapolated property data should be submitted along with the
methodology for their calculation and citations for the studies these
property data are derived from.

-   Soil core location (coordinates);

-   Minimum depth of the soil sample;

-   Maximum depth of the soil sample;

-   textural properties;

-   sand/silt/clay fractions (%);

-   CEC, or AEC;

-   Mineralogy;

-   bulk density;

-   K~OC~ of the pesticide in the test soil or extrapolated from data
    for other soils;

-   K~d~ of the pesticide in the test soil or extrapolated from data for
    other soils;

-   K~f~ (Freundlich) adsorption constant of the pesticide in the test
    soil or extrapolated from data for other soils;

-   degradation rate of the pesticide in the test soil or extrapolated
    from data for other soils, organic matter content;

-   field capacity (1/3 bar);

-   1 bar soil water content;

-   5 bar soil water content;

-   wilting point (15 bar);

-   saturated hydraulic conductivity;

-   soil water content;

-   matrix potential;

-   Munsell color and

-   pH.

### 7.45 Ground-water data 

Some of these data may have been collected as part of the site
characterization of the study area. If so, there is no need to repeat
that information here.

-   Well location (coordinates);

-   total depth of well;

-   depth to water table;

-   screened interval;

-   background water chemistry;

-   hydraulic head;

-   flow;

-   subsurface geology,;

-   cross sections (descriptions, fence diagrams) and

-   location (in 3-dimensions) of known aquitards.

### 7.46 Weather data

The following site-specific weather data collected during the PGW study
is requested;

-   location of monitoring station (coordinates);

-   rainfall, daily time step or shorter;

-   air temperature and

-   soil temperature (including depth measured at).

In addition, site-specific historical weather data for the previous
20-years (or as recent a 20+ year period that is available) should be
provided or referenced for analyses purposes.

### 7.47 Irrigation input

The following site-specific irrigation information is requested;

-   irrigation method;

-   irrigation application date (days after treatment (DAT));

-   rate and

-   total amount applied.

### 7.48 Chemical monitoring results 

The following chemical monitoring data for soil and ground water is
requested. All headings should be clearly labeled and explanations
provided in an accompanying text file for clarity. See attached template
for example. All analyses above the minimum detection limit should be
reported as the nominal concentration. If the nominal concentration of a
sample is below a Minimum Reporting Limit or Minimum Quantification
Limit is applicable (whether calculated as a uniform limit or on a
sample-by-sample basis) this information should be captured in a
separate data field. Specific data fields are;

-   study identifier;

-   study type;

-   media sampled;

-   analytes (CAS numbers for parent compound and metabolites);

-   sample location (coordinates);

-   date of sample;

-   depth of sample;

-   analytical result (not averaged over samples or time) and

-   analytical QA/QC data (method description, method quantification
    limit, method reporting limit, sample quantification limit, data
    qualifiers).

-   At a minimum, provide analytical results for each monitoring well in
    bar-graph format so a trend in increase and/or decrease will be
    easily visualized. Graph results for each monitoring well separately
    for entire sampling period (i.e. 24 months).

All tabular data should be in either ASCII or MS Access format (or a
format specifically approved by EPA).

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