U.S. Department of the Interior

U.S. Geological Survey

Quality-Assurance Design

Applied to an Assessment of

Agricultural Pesticides in Ground Water

from Carbonate Bedrock Aquifers in the

Great Valley of Eastern Pennsylvania

by Kevin J. Breen

Water-Resources Investigations Report 00-4104

prepared in cooperation with the

PENNSYLVANIA DEPARTMENT OF AGRICULTURE

Lemoyne, Pennsylvania

2000
ii

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of brand names and names of companies, organizations, or individuals in this report is for

identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

For additional information Copies of this report may be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

840 Market Street Box 25286

Lemoyne, Pennsylvania 17043-1586 Denver, Colorado 80225-0286

Email: dc_pa@usgs.gov Telephone: 1-888-ASK-USGS
iii

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Quality-assurance design and application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Data-quality objectives and the types of quality-control samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Design components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Quality-control samples and the role of the USGS laboratories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Field blanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Spikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Replicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Splits (2-lab) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Assessment area for application of the design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Field and Lemoyne laboratory procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Analytical laboratory procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Field blanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Spikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Replicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Splits (2-lab) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Quality-assurance results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Field blanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Spikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Replicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Splits (2-lab). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Assessment results for pesticide concentrations in ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Summary and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

References cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Supplemental data tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

CONTENTS

Page
iv

Figure 1. Map showing the location of data-collection sites used for the quality-assurance

design in the 30 sampling cell areas subdividing the Great Valley agricultural

area underlain by carbonate bedrock aquifers in Berks, Lebanon, Lehigh,

and Northampton Counties, eastern Pennsylvania. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2. Graph showing the percentage recovery of alachlor, atrazine, cyanazine, metolachlor,

and simazine in spiked ground-water samples analyzed by Pennsylvania

Department of Environmental Protection Laboratory and U.S. Geological

Survey, National Water-Quality Laboratory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3. Graph showing the concentration of atrazine in splits of ground-water samples

analyzed using two different methods by Pennsylvania Department of

Environmental Protection Laboratory and U.S. Geological Survey, National

Water-Quality Laboratory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

TABLES

Table 1. Priority (State Management Plan) pesticides for monitoring as specified by the

Pesticides and Ground Water Strategy and concentrations that trigger

actions by Pennsylvania Department of Agriculture. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Quality-control sample types and sampling cell numbers for application of the

quality-assurance design in the agricultural areas underlain by carbonate

bedrock aquifers in the Great Valley of eastern Pennsylvania . . . . . . . . . . . . . . . . . . . . 8

3. Concentrations of selected pesticide compounds in commercial mixtures used

for preparation of laboratory-water and ground-water spike samples . . . . . . . . . . . . 9

4. Analytical reporting levels (quantitation limits) for selected pesticides . . . . . . . . . . . . . . . 9

SUPPLEMENTAL DATA TABLES

S-1. Records of selected wells in Berks, Lebanon, Lehigh, and Northampton

Counties sampled for the Quality-Assurance Project for the Pennsylvania

Department of Agriculture Pesticides and Ground Water Strategy, 1997-98 . . . . . . . 22

S-2. Analytical results for pesticide concentration and surrogate compound

recovery determined by Pennsylvania Department of Environmental

Protection Laboratory for field blanks of pesticide-free laboratory water . . . . . . . . . 24

S-3. Analytical results for pesticide concentration and surrogate compound

recovery determined by U.S. Geological Survey, National Water-Quality

Laboratory, for field blanks of pesticide-free laboratory water . . . . . . . . . . . . . . . . . . 24

S-4. Analytical results for pesticide concentration and surrogate compound

recovery determined by Pennsylvania Department of Environmental

Protection Laboratory for spiked pesticide-free laboratory-water samples

submitted as triplicate-blind samples for assessment of laboratory bias

and variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

S-5. Analytical results for pesticide concentration and surrogate compound

recovery determined by U.S. Geological Survey, National Water-Quality

Laboratory for spiked pesticide-free laboratory-water samples . . . . . . . . . . . . . . . . . 25

ILLUSTRATIONS

Page
v

Table S-6. Analytical results for pesticide concentration and surrogate-compound

recovery determined by Pennsylvania Department of Environmental

Protection Laboratory for spiked ground-water samples and unspiked

ground-water samples and concentration differences calculated from the

analytical results for pesticide concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

S-7. Analytical results for pesticide concentration and surrogate-compound

recovery determined by U.S. Geological Survey, National Water-Quality

Laboratory for spiked ground-water samples, unspiked ground-water

samples, and concentration differences calculated from the analytical

results for pesticide concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

S-8. Spike recovery data and summary statistics for analyses of pesticides in spiked

laboratory-water and ground-water samples by Pennsylvania

Department of Environmental Protection Laboratory and U.S. Geological

Survey, National Water-Quality Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

S-9. Analytical results for pesticide concentration and surrogate-compound

recovery determined by Pennsylvania Department of Environmental

Protection Laboratory and U.S. Geological Survey, National Water-Quality

Laboratory for replicate samples of ground water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

S-10. Analytical results for pesticide concentration and surrogate-compound

recovery determined by Pennsylvania Department of Environmental

Protection Laboratory and U.S. Geological Survey, National Water-Quality

Laboratory for routine ground-water samples and for 2-lab splits of

ground-water samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

SUPPLEMENTAL DATA TABLES—Continued

Page
vi

Multiply By To obtain

Length

foot (ft ) 0.3048 meter

mile (mi) 1.609 kilometer

Volume

gallon (gal) 3.785 liter

Mass

pound avoirdupois (lb) 0.4536 kilogram

Other Abbreviations

μg/L micrograms per liter

mg/mL milligrams per milliliter

L liter

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929—a geodetic

datum derived from a general adjustment of the first-order level nets of the United States and Canada,

formerly called Sea Level Datum of 1929.

CONVERSION FACTORS, ABBREVIATIONS, AND VERTICAL DATUM
1

ABSTRACT

Assessments to determine whether agricultural pesticides are present in ground water are

performed by the Commonwealth of Pennsylvania

under the aquifer monitoring provisions of the

State Pesticides and Ground Water Strategy. Pennsylvania’s Department of Agriculture conducts the

monitoring and collects samples; the Department

of Environmental Protection (PaDEP) Laboratory

analyzes the samples to measure pesticide concentration. To evaluate the quality of the measurements of pesticide concentration for a groundwater assessment, a quality-assurance design was

developed and applied to a selected assessment

area in Pennsylvania. This report describes the

quality-assurance design, describes how and

where the design was applied, describes procedures used to collect and analyze samples and to

evaluate the results, and summarizes the qualityassurance results along with the assessment

results.

The design was applied in an agricultural area

of the Delaware River Basin in Berks, Lebanon,

Lehigh, and Northampton Counties to evaluate the

bias and variability in laboratory results for pesticides. The design—with random spatial and temporal components—included four data-quality

objectives for bias and variability. The spatial

design was primary and represented an area comprising 30 sampling cells. A quality-assurance

sampling frequency of 20 percent of cells was

selected to ensure a sample number of five or more

for analysis. Quality-control samples included

blanks, spikes, and replicates of laboratory water

and spikes, replicates, and 2-lab splits of groundwater. Two analytical laboratories, the PaDEP Laboratory and a U.S. Geological Survey Laboratory,

were part of the design. Bias and variability were

evaluated by use of data collected from October

1997 through January 1998 for alachlor, atrazine,

cyanazine, metolachlor, simazine, pendimethalin,

metribuzin, and chlorpyrifos.

Results of analyses of field blanks indicate that

collection, processing, transport, and laboratoryanalysis procedures did not contaminate the samples; there were no false-positive results. Pesticides

were detected in water when pesticides were

spiked into (added to) samples. There were no

false negatives for the eight pesticides in all spiked

samples. Negative bias was characteristic of analytical results for the eight pesticides, and bias was

generally in excess of 10 percent from the ‘true’ or

expected concentration (34 of 39 analyses, or

87 percent of the ground-water results) for pesticide concentrations ranging from 0.31 to 0.51 μg/L

(micrograms per liter). The magnitude of the negative bias for the eight pesticides, with the exception

of cyanazine, would result in reported concentrations commonly 75-80 percent of the expected concentration in the water sample. The bias for

cyanazine was negative and within 10 percent of

the expected concentration. A comparison of

spiked pesticide-concentration recoveries in laboratory water and ground water indicated no effect

of the ground-water matrix, and matrix interference was not a source of the negative bias. Results

for the laboratory-water spikes submitted in triplicate showed large variability for recoveries of atrazine, cyanazine, and pendimethalin. The relative

standard deviation (RSD) was used as a measure of

method variability over the course of the study for

laboratory waters at a concentration of 0.4 μg/L.

An RSD of about 11 percent (or about ±0.05 μg/L)

characterizes the method results for alachlor, chlorpyrifos, metolachlor, metribuzin, and simazine.

Atrazine and pendimethalin have RSD values of

about 17 and 23 percent, respectively. Cyanazine

showed the largest RSD at nearly 51 percent. The

pesticides with low variability in laboratory-water

spikes also had low variability in ground water.

Quality-Assurance Design

Applied to an Assessment of

Agricultural Pesticides in Ground Water

from Carbonate Bedrock Aquifers in the

Great Valley of Eastern Pennsylvania

by Kevin J. Breen
2

The assessment results showed that atrazine

was the most commonly detected pesticide in

ground water in the assessment area. Atrazine was

detected in water from 22 of the 28 wells sampled,

and recovery results for atrazine were some of the

worst (largest negative bias). Concentrations of the

eight pesticides in ground water from wells were

generally less than 0.3 μg/L. Only six individual

measurements of the concentrations in water from

six of the wells were at or above 0.3 μg/L, five for

atrazine and one for metolachlor. There were eight

additional detections of metolachlor and simazine

at concentrations less than 0.1 μg/L. No well water

contained more than one pesticide at concentrations at or above 0.3 μg/L. Evidence exists, however, for a pattern of co-occurrence of metolachlor

and simazine at low concentrations with higher

concentrations of atrazine.

Large variability in replicate samples and

negative bias for pesticide recovery from spiked

samples indicate the need to use data for pesticide

recovery in the interpretation of measured pesticide concentrations in ground water. Data from

samples spiked with known amounts of pesticides

were a critical component of a quality-assurance

design for the monitoring component of the Pesticides and Ground Water Strategy.

Trigger concentrations, the concentrations that

require action under the Pesticides and Ground

Water Strategy, should be considered maximums

for action. This consideration is needed because of

the magnitude of negative bias.

INTRODUCTION

In areas of Pennsylvania where pesticides are

used extensively for agricultural purposes, there is

concern about pesticides entering aquifers that

supply water to wells and springs. The Pennsylvania Department of Agriculture (PDA) is the

agency responsible for regulating pesticide registration and use, including protecting all environmental resources from deleterious effects of

pesticides. The U.S. Environmental Protection

Agency (USEPA) requires PDA to develop state

management plans for five pesticides—alachlor,

atrazine, cyanazine, metolachlor, and simazine—

identified as either probable or possible human

carcinogens with a potential to contaminate

ground water. PDA developed a Pesticides and

Ground Water Strategy (Pennsylvania Department of Agriculture, 1998) as an approach to

managing pesticide use and preserving groundwater quality. The goal of the Strategy is to protect

all drinking-water sources from degradation.

Monitoring for pesticides in ground water is

an important component of the Strategy and is

done statewide. The monitoring to determine the

occurrence and distribution of pesticides in ground

water of Pennsylvania evolved during 1996-97 to

focus on spatial characterization. This focus has

roots in the U.S. Geological Survey (USGS)

National Water-Quality Assessment Program

(Gilliom and others, 1995, p. 26). Areas of the State

are prioritized on the basis of geologic setting,

hydrogeology, presence of agricultural lands and

pesticide use, and on the availability of data from

previous studies of pesticides in ground water

(Lindsey and Bickford, 1999). In addition to the

five pesticides for which state management plans

are required, PDA tests water samples for the

herbicides pendimethalin and metribuzin and the

insecticide chlorpyrifos due to the quantities that

are used as determined by PDA pesticide-use

surveys. A priority area for sampling is divided

into subareas of equal size, and a single sampling

location is randomly selected to start to represent

each subarea. This is a “stratified random spatial”

selection. To supplement the data from a single

location in a subarea, PDA collects samples from

and monitors additional wells for assurance that

each subarea is adequately represented. The subareas were termed sampling cells.

To monitor ground water, the PDA regularly

samples wells and submits the water samples to

the Pennsylvania Department of Environmental

Protection (PaDEP) Laboratory to analyze for the

presence of pesticides in ground water at concentrations above the Maximum Contaminant Level

(MCL) (Pennsylvania Department of Agriculture,

1998, p. 2). A concentration of one-third of the

MCL for any of the five pesticides in ground water

triggers action by PDA. The concentrations for five

pesticides that trigger action by PDA as part of the

Strategy are summarized in table 1. The concentration of 1 μg/L (micrograms per liter) for cyanazine

requires that laboratories analyzing ground-water

samples for PDA are capable of measuring

0.3 μg/L of cyanazine. The 0.3 μg/L concentration

is also the reporting level for the other pesticides.

Quality assurance of the laboratory analytical

measurements and aspects of sample collection are

also part of the monitoring component because

data from PDA assessments are for regulatory pur-
3

poses and data quality must be documented.

Because pesticide concentrations in ground water

are usually extremely small (usually smaller than

one part per billion), quality assurance is a critical

part of the monitoring component.

The USGS, in cooperation with PDA, completed the study described herein to demonstrate

the application of a quality-assurance design to an

assessment of an area prioritized for study by the

monitoring component of the Pesticides and

Ground Water Strategy. The USGS role was to

develop the quality-assurance design, assist PDA

in the application of the design to a selected assessment area, evaluate the results, and report the

quality-assurance and assessment results.

Purpose and Scope

This report 1) describes a quality-assurance

design developed primarily to evaluate the quality

of laboratory analytical results for pesticide

concentrations in ground water, 2) evaluates the

bias and variability of laboratory results, and

3) summarizes quality-assurance data and data for

pesticide concentrations in ground-water samples

from the assessment area. The data used for the

evaluation were collected from October 1997

through January 1998. The pesticides include five

herbicides (alachlor, atrazine, cyanazine,

metolachlor, and simazine) for which specific state

management plans are required, two additional

high-use herbicides (pendimethalin and

metribuzin), and a high-use insecticide,

chlorpyrifos. The ground-water data presented

herein are for the 8 pesticides in water samples

collected from 28 wells in the Delaware River Basin

in eastern Pennsylvania. The wells were drilled

into carbonate bedrock aquifers in agricultural

areas of the Great Valley Section of the Ridge and

Valley Physiographic Province.

Acknowledgments

John W. Pari, PDA, is gratefully acknowledged

for assisting with field and laboratory work, for

providing data and insightful comments throughout the study, and for reviewing an early draft of

this manuscript. The author also is grateful for the

encouragement and support of David D. Bingaman, PDA, during the implementation of this

research. P. Ted Lyter, PaDEP, Bureau of Laboratories, contributed substantially to the planning and

review meetings for the study. The author thanks

the following individuals for significant contributions toward the preparation of this report:

Technical review: J. Kent Crawford, USGS,

Lemoyne, Pa.; Kevin M. Beer, USGS, Pittsburgh,

Pa.; Jeffrey D. Martin, USGS, Indianapolis, Ind.;

and Mark W. Sandstrom, USGS, Denver, Colo.

Editorial review and preparation of text and

graphics: James E. Bubb, Kim L. Otto, Kim L.

Shank, and Terriann Preston.

QUALITY-ASSURANCE DESIGN AND

APPLICATION

The primary design goals were to (1) establish

if there was bias in laboratory analytical

measurements of pesticide concentrations,

including determining whether results were free

from field and laboratory contamination, and

(2) define the variability of pesticide-concentration

measurements in ground water. The evaluation of

the bias and variability for measured concentrations had to be documented so that actions by PDA

Table 1. Priority (State Management Plan) pesticides for monitoring as

specified by the Pesticides and Ground Water Strategy and concentrations

that trigger actions by Pennsylvania Department of Agriculture

[MCL, U.S. Environmental Protection Agency Maximum Contaminant Level;

H indicates an MCL is not developed for the pesticide and the U.S.

Environmental Protection Agency Health Advisory Level is used]

Pesticide

Concentration,

in micrograms per liter

MCL One-third of MCL

Alachlor 2 0.7

Atrazine 3 1.0

Cyanazine 1. H .3

Metolachlor 100. H 33

Simazine 4 1.3
4

as part of the Pesticides and Ground Water

Strategy were supported by quality-assurance

information.

The design was used 1) to be confident that

contamination (false-positive detections or

contamination bias) introduced by samplecollection procedures and field and laboratory

sample-processing activities was not the source of

trace amounts of the eight pesticides in groundwater samples, 2) to be confident that falsenegative results would not be a problem and that a

pesticide would be detected in ground water when

the pesticide was present, 3) to quantify bias in

pesticide recoveries, 4) to determine if bias was

related to interferences from the ground water

itself, and 5) to quantify overall variability in

pesticide recovery.

Data-Quality Objectives and the Types of

Quality-Control Samples

Four data-quality objectives are presented. The

types of quality-control samples used to assess the

objective are given in italics.

The first data-quality objective was that bias

due to sample contamination from all processing

sources (field processing, transport, and lab analysis) would not be found (concentration less than

the detection level for the analysis). This objective

was evaluated with field blanks.

The second data-quality objective was for

small numbers (less than 5 percent) of false negatives (negative detection bias). Pesticides deliberately added to the samples of ground water and

laboratory water (spikes) were used to evaluate

this objective. Reagent-grade water was spiked

(laboratory-water spikes) to determine detection and

recovery in a sample matrix free of environmental

interferences. Ground water was spiked (groundwater spikes) to determine detection and recovery in

a sample matrix that may have properties that

interfere with extraction or analysis. Unspiked

ground-water splits submitted to two laboratories

(2-lab splits) were another check on false-negative

results.

The third data-quality objective was that the

bias in the recovery would be within 10 percent of

the ‘true’ (100-percent recovery) result. The laboratory-water spikes and ground-water spikes used

for the second data-quality objective also were

used to evaluate this objective. Recoveries and

recovery percentages for both types of spikes were

used to evaluate overall bias resulting from the

sample matrix and other factors.

The fourth data-quality objective was that

recovery variability would be low or small. On the

basis of data presented by the USEPA (1995, p. 507-

27), a small variability would be 10 percent or less.

This objective was evaluated with split replicate

samples—duplicate samples of ground water and

triplicate samples of spiked laboratory water.

A single volume of water was split for each sample; thus, recoveries and recovery percentages for

both types of replicates were used to evaluate

overall analytical variability with sampling and

sample-processing variability assumed constant

within each replicate.

Design Components

The quality-assurance design had spatial and

temporal components. The spatial design was primary and represented an area comprising 30 sampling cells assessed as part of the monitoring

component for the PDA Pesticides and Ground

Water Strategy during the 1997-98 field season.

A quality-assurance sampling frequency of 20 percent of cells was selected to ensure a sample number of five or more for analysis. Sampling cells for

the blanks, spikes, and replicates collected in the

field were chosen by use of a random number table

(Taylor, 1987, p. 274-275); thus, the term ‘random

spatial’ design.

The temporal design component was intended

to gather quality-assurance information throughout the field season. Because of the complex nature

of pesticide analysis methods, results from laboratories can take months to be completed and made

available. During a 3- to 4-month field season, it

was reasonable to assume that some quality-assurance results might not be returned from the laboratory until after the season had ended. Visiting the

selected randomly chosen cells at the beginning of

the field season and submitting quality-control

samples such as field blanks and selected spikes as

early in the season as possible were emphasized.

Laboratory-water spikes were to be analyzed at

discrete intervals during the study period and

were not randomly chosen cells. In this way,

results were available across the sampling period.
5

Quality-Control Samples and the Role of the

USGS Laboratories

Two analytical laboratories, the PaDEP Laboratory in Harrisburg, Pa., and the USGS National

Water-Quality Laboratory in Arvada, Colo., were

part of the design. The quality-assurance design

was not developed to compare laboratories but to

compare specific types of quality-control samples

that were submitted with routine samples of

ground water to evaluate the objectives. The purpose of using the USGS Laboratory was to provide

(1) an independent check of results from the

PaDEP Laboratory for blank samples to evaluate

false positives, (2) independent confirmation that

preparation of laboratory-water spikes and

ground-water spikes by the USGS field personnel

was valid and resulted in the concentrations

expected based on spike calculations, (3) an independent check of the PaDEP Laboratory results to

evaluate false negatives, and (4) an independent

set of ground-water-sample results to evaluate

whether the sample matrix affected pesticide

recovery. In addition, using two laboratories to

analyze split samples provided additional documentation of the measured concentrations in

ground water.

All quality-control samples were blind samples;

that is, the laboratories did not know the qualitycontrol samples were any different than routine

ground-water samples. Replicate samples were

processed and spike samples were prepared in the

laboratory at the USGS in Lemoyne, Pa., hereafter

termed “Lemoyne laboratory.” The reason the

samples were prepared and how the laboratories

were used are described below.

Field Blanks

Blank samples were used to determine if contamination was occurring in any stage of sample

processing in either the field or laboratory that

would result in false positives. Blanks were for

evaluation of false positives. The random spatial

design called for blanks at 20 percent of the sampling cells. Five field blanks were collected during

the field season at five field sites for analysis by the

PaDEP Laboratory. Four of the five blanks were

split at the Lemoyne laboratory and submitted to

both the PaDEP Laboratory and the USGS Laboratory for analysis.

Spikes

Spikes were for evaluation of false negatives

and bias in pesticide recovery. A spike not detected

was a false-negative result. The random spatial

design called for ground-water spikes at 20 percent

of the sampling cells. Ground water for five spikes

were collected at five field sites. All were split at

the Lemoyne laboratory and submitted to both the

PaDEP Laboratory and the USGS Laboratory for

analysis. The temporal design was to check for

false negatives at 10 percent of the sampling cells

using laboratory waters spiked with pesticides.

These waters were submitted to the PaDEP

Laboratory with samples from three cells—10, 20,

and 30—in an attempt to distribute the information

throughout the field season. Two of the three

laboratory-water spikes were split at the Lemoyne

laboratory and submitted to the PaDEP Laboratory

and the USGS Laboratory for analysis. The

triplicate samples, prepared for cells 10, 20, and 30,

were designated lab spike 10-1, 10-2, 10-3, 20-1,

and so forth. A second aspect of the temporal

design was to compare spike recovery for samples

collected on the same day. This involved analysis

of results for two sets of spikes prepared from

waters on the same day. This was done twice (on

two different days) and involved samples from

four sites.

Spike recovery was used to evaluate bias. Concentrations in a 0.3 to 0.5 μg/L range were selected

for spikes in order to evaluate bias near the trigger

concentration for action by PDA under the Pesticides and Ground Water Strategy. The range also

was selected to match measured concentrations in

ground water determined by earlier studies. Concentrations from earlier studies were summarized

by Lindsey and Bickford (1999). All laboratorywater spikes were prepared at a concentration of

0.4 μg/L.

Recovery results from laboratory-water spikes

and ground-water spikes were used for evaluation

of bias from ground-water matrix interference.

Matrix interference is not expected for laboratorywater spikes. The design compared recoveries of

spikes in laboratory water and in ground water.

The three laboratory-water spikes and five groundwater spikes were again used for this evaluation.

Replicates

Replicates were used for evaluation of overall

variability. The design involved 1) evaluation of

the triplicate results from the PaDEP Laboratory
6

for three laboratory-water spikes and 2) evaluation

of duplicate results from the PaDEP Laboratory for

seven ground-water samples. The triplicates and

duplicates were from the temporal and random

spatial components of the design, respectively.

For the three replicates of spiked laboratory

waters, four-way splits were prepared at the

Lemoyne laboratory for determination of

variability. Three triplicates were submitted to the

PaDEP Laboratory, and twice, a single sample was

submitted to the USGS laboratory as a independent verification check on spike concentration.

Seven replicates of ground waters were prepared at the Lemoyne laboratory, three as two-way

splits of samples and four as three-way splits for

evaluation of variability. The two-way splits were

submitted as duplicate samples only to the PaDEP

Laboratory. The three-way splits of the samples

were used to prepare a duplicate for the PaDEP

Laboratory and a single sample submitted to the

USGS laboratory as an independent verification

check on concentration. A split submitted to both

laboratories is hereafter termed a 2-lab split.

Splits (2-lab)

Four additional samples, not part of other

quality-control sample types, were prepared as

2-lab splits and were used to further evaluate false

negatives and bias. The interest was in determining how often the PaDEP Laboratory detected the

‘true’ presence of a pesticide. The USGS Laboratory results were used to help determine the ‘true’

values. The unspiked ground water analyzed with

each of the five spiked ground waters also was

categorized as a 2-lab split. In total, 11 samples

were prepared as 2-lab splits, including the

5 spike-related ground waters, 2 additional samples prepared as three-way split replicates, and

these 4 additional samples.

Assessment Area for Application of the Design

The 30 sampling cells subdividing the assessment area in Lebanon, Berks, Lehigh, and

Northampton Counties are shown in figure 1 along

with the locations and local well numbers of the

29 wells chosen to represent 28 of the cells. The

wells were assigned a local number and another

identifier for the USGS and PDA computer systems, respectively. The identification numbers and

records of wells sampled for the assessment and

for the quality-assurance design are provided in

table S-1 (Supplemental Data section). Wells representative of agricultural areas could not be located

for sampling in cells 17 and 23. Two wells were

sampled in cell 14. The assessment was completed

with 28 samples from 27 of the 30 cells. The sample

from cell 15 was lost. The cells and local well numbers associated with the types of quality-control

samples are provided in table 2.

Field and Lemoyne Laboratory Procedures

Sample collection for the monitoring component of the Pesticides and Ground Water Strategy

is not restricted to a specific time of year. In well

waters having high concentrations of pesticides,

PDA has found that the concentrations show little

fluctuation with season (John W. Pari, Pennsylvania Department of Agriculture, oral commun.,

1997). The sampling for this assessment started

during the harvest season in October 1997 and

ended in February 1998, months after the primary

pesticide-application period for row crops in the

spring and early summer of 1997.

Sampling supplies were prepared at the

Lemoyne laboratory each day before field work

began. The 3-L Teflon bottles used to collect

samples were cleaned with Liquinox detergent and

triple rinsed with both tap water and deionized

water. The bottles were allowed to dry, and an

empty weight was determined.

Samples for analysis were submitted to the

laboratories in 1-L amber glass bottles. Bottles from

two suppliers were used. I-Chem brand bottles

were provided by the PaDEP Laboratory for use by

PDA and were certified by the manufacturer to be

free of organics. Bottles used for samples submitted to the USGS Laboratory were supplied for field

use by the USGS Quality of Water Services Unit in

Ocala, Fla.

Water for preparation of blank samples and

laboratory-water spikes was obtained through the

USGS Laboratory from commercial sources of

laboratory supplies. Waters from three lot numbers

were used for the study. Each lot was certified as

laboratory water for use in blanks; the eight

pesticides were not detected by independent

analyses of the lots by the USGS Laboratory.

For field preparation of blank samples, pesticidefree laboratory waters were transported to the field

with the bottles and other supplies. The pesticidefree laboratory water was added to the 3-L Teflon

bottles to simulate the procedures used in

collection of ground-water samples.
7

Figure 1. Location of data-collection sites used for the quality-assurance design in the 30 sampling cell areas subdividinGreat Valley agricultural area underlain by carbonate bedrock aquifers in Berks, Lebanon, Lehigh, and Northampton Coeastern Pennsylvania.
8

At the sampling site prior to sample collection,

a raw-water faucet was opened to allow the water

from the well to flow into a bucket. Temperature

and specific conductance of the water were monitored until measurements were stable at 5-minute

intervals. Samples from the raw-water faucet were

then collected in one or more of the 3-L bottles.

If sediment or particulate matter was visible in the

samples, the waters were to be filtered through

glass-fiber membranes with pore-size openings of

0.7 microns. None of the samples required this filtration step. The waters submitted to the laboratories were free of visible sediment and particulates.

No preservatives were added.

Depending on the type of quality-assurance

sample being prepared, the water from the 3-L

bottles was either transferred directly to the 1-L

glass bottles and stored in a cooler on ice or the 3-L

bottles were placed in a cooler on ice for processing

and shipment to the analytical laboratories.

Samples were transported to the Lemoyne

laboratory for processing and shipment.

At the Lemoyne laboratory, spiked samples

were prepared by adding known herbicide

amounts to the samples. The samples in the 3-L

Teflon bottles were weighed for volume determination, using unit density to convert mass to volume. Spike mixtures manufactured by Supelco,

Inc., and certified by the USGS Laboratory were

obtained from the USGS Laboratory. A 100-microliter variable-volume micropipet with replaceable

glass bores was used to dispense predetermined

aliquots of the spike mixture to the water samples

in the 3-L Teflon bottles. Calculations for spike concentrations in the 0.3 to 0.5 μg/L range were made

from concentration data (Supelco, Inc.) for pestiTable 2. Quality-control sample types and sampling cell numbers for application of the quality-assurance design in the

agricultural areas underlain by carbonate bedrock aquifers in the Great Valley of eastern Pennsylvania

[PaDEP, Pennsylvania Department of Environmental Protection; USGS, U.S. Geological Survey]

Quality-control sample type

Sampling cell

identification

number

Local well

number where

sample

collected

Laboratory to analyze

sample Comments

 PaDEP USGS

Blank, field 2 LB 621 X X Before first sample

Blank, field 4 LB 1169 X X --

Blank, field 5 BE 1618 X -- --

Blank, field 12 BE 1621 X X --

Blank, field 27 NP 806 X X --

Spike, laboratory water 10 BE 755 X -- To PaDEP in triplicate

Spike, laboratory water 20 LE 1414 X X To PaDEP in triplicate

Spike, laboratory water 30 NP 807 X X To PaDEP in triplicate

Spike, ground water 4 LB 1169 X X --

Spike, ground water 6 BE 1619 X X --

Spike, ground water 14 BE 1036 X X --

Spike, ground water 19 LE 1413 X X --

Spike, ground water 24 NP 803 X X --

Replicate, laboratory water 10 BE 755 X -- To PaDEP in triplicate

Replicate, laboratory water 20 LE 1414 X -- To PaDEP in triplicate

Replicate, laboratory water 30 NP 807 X -- To PaDEP in triplicate

Replicate, ground water--3-way split 4 LB 1169 X X To PaDEP in duplicate

Replicate, ground water--2-way split 8 BE 1624 X -- To PaDEP in duplicate

Replicate, ground water--2-way split 9 BE 1625 X -- To PaDEP in duplicate

Replicate, ground water--3-way split 16 BE 1622 X X To PaDEP in duplicate

Replicate, ground water--3-way split 19 LE 1413 X X To PaDEP in duplicate

Replicate, ground water--3-way split 29 NP 643 X X To PaDEP in duplicate

Replicate, ground water--2-way split 30 NP 807 X -- To PaDEP in duplicate

2-lab split, ground water 1 LB 1168 X X --

2-lab split, ground water 3 LB 545 X X --

2-lab split, ground water 10 BE 755 X X --

2-lab split, ground water 12 BE 1621 X X --
9

cide spike mixtures. The two lots of spike mixture

used for the study have pesticide concentrations

listed in table 3. The overall errors in measuring

sample volume and the volume of spike mixture

were estimated to be 2 percent of the final spiked

concentration. After spiking, the total sample volume from multiple 3-L bottles was thoroughly

mixed by shaking and stirring and then split by

pouring waters from the 3-L bottles into 1-L glass

bottles in equal-volume aliquots. The water samples in glass bottles were kept chilled and delivered to the laboratories for analysis within

24 hours after collection.

A single water sample submitted to the PaDEP

Laboratory comprised two 1-L glass bottles of

sample. Thus, a duplicate sample to PaDEP (or

intra-lab split) comprised four 1-L glass bottles of

sample all split from two 3-L bottles of the initial

sample. One 1-L glass bottle was submitted to the

USGS Laboratory for each sample.

Analytical Laboratory Procedures

The two laboratories used different methods

for pesticide extraction from water prior to analysis. Extraction methods used by the PaDEP Laboratory involved a liquid-liquid extraction procedure

as described in USEPA Method 507 (U.S. Environmental Protection Agency, 1988). USGS used a

solid-phase extraction procedure described by

Zaugg and others (1995). USGS methods concentrate the extract to about one-fifth of the volume

used in Method 507.

Analytical methods for the eight pesticides

differed between laboratories and resulted in

different method detection limits (MDL’s).

The MDL is statistically determined and is defined

to be the minimum pesticide concentration that

can be identified, measured, and reported with

99-percent confidence that the concentration is

greater than zero. The MDL is intended to protect

against false-positive results.

The PaDEP Laboratory used a modification of

USEPA Method 507; a mass spectrometer detector

was substituted for the nitrogen-phosphorus

detector specified in Method 507. The PaDEP

Laboratory operated the detector in full-scan

monitoring mode. The PaDEP set the reporting

levels for the pesticides to 0.3 μg/L and set the

MDL’s at 0.1 μg/L. USGS used a mass spectrometer detector operated in the selected-ion

monitoring mode. The concentrations measured by

the USGS laboratory were at reporting levels of

0.005 μg/L or less for the eight pesticides. A summary of the reporting levels or quantitation limits

for the two laboratories is provided in table 4.

Table 3. Concentrations of selected pesticide

compounds in commercial mixtures used for

preparation of laboratory-water and ground-water spike

samples

[Data from Supelco, Inc., certificate of composition for

pesticide/herbicide spike mix.]

Pesticide

Spike-mixture concentrations,

(micrograms per milliliter of solvent)

Supelco Lot

LA-62435

Supelco Lot

LA-66096

Alachlor 1.0 1.0

Atrazine 1.0 1.0

Chlorpyrifos 1.0 1.0

Cyanazine 1.0 .9

Metolachlor .9 1.0

Metribuzin 1.0 .9

Pendimethalin 1.0 1.0

Simazine 1.0 1.0

Table 4. Analytical reporting levels (quantitation limits)

for selected pesticides

[PaDEP, Pennsylvania Department of Environmental

Protection Laboratory; USGS, U.S. Geological Survey

National Water-Quality Laboratory]

Pesticide

 Reporting level, by laboratory,

in micrograms per liter

PaDEP USGS

State Management Plan herbicides

Alachlor 0.3 0.002

Atrazine .3 .001

Cyanazine .3 .004

Metolachlor .3 .002

Simazine .3 .005

Additional high-use herbicides

Pendimethalin .3 .004

Metribuzin .3 .004

High-use insecticide

Chlorpyrifos .3 .004
10

Data Analysis

The procedures or statistical methods used to

analyze the results by sample type are described in

this section. The description begins with methods

for blanks and then includes methods for analysis

of data resulting from spikes, replicates, and splits.

Field Blanks

To determine if there was sample contamination and how that may bias an environmental sample, analyses results of field blanks were tabulated

to determine the number of detections (false positives) and obtain summary statistics for the concentrations in blanks. Results from the PaDEP

Laboratory and the USGS Laboratory were compiled for splits of the blank samples submitted to

both laboratories. This compilation ensured that

pesticide concentrations in blanks were described

over the range of reporting limits listed in table 4

for the two laboratories.

Spikes

Bias was determined by evaluating how close

the measured concentrations are to the ‘true’ or

known sample concentration. The rate of falsenegative results was determined for the eight pesticides in laboratory water spikes and in groundwater spikes as a percentage of the total number of

each type of spike.

Analysis of the recovery of pesticides spiked

into water at concentrations ranging from

0.31 μg/L to 0.51 μg/L was used to assess bias of

results. The spike-recovery calculations require the

following information for each pesticide:

Cmix, Spike mixture concentration of

pesticide, in micrograms per milliliter (see

table 3);

Vwat, Volume of water sample, in milliliters;

Vmix, Volume of spike mixture added to

water sample, in milliliters;

Cspkmeas, Concentration, in micrograms per

liter, of pesticide measured by laboratory

in the spiked water sample; and

Cunsmeas, Concentration, in micrograms per

liter, of pesticide measured by laboratory

in the unspiked water sample.

Percent recovery was calculated in three steps:

1. Calculate the spike concentration

prepared in the spiked water sample, in

micrograms per liter:

Cprp = Vmix × Cmix × [1/Vwat] × 1,000 (1a)

2. Calculate the spike concentration

measured by the laboratory, in micrograms per liter:

Cdifmeas = Cspkmeas - Cunsmeas (1b)

3. Take the ratio of measured to prepared

concentrations to determine recovery, in

percent:

Recovery Percentage = [Cdifmeas/Cprp] × 100 (1c)

In the calculations for laboratory-water samples,

Cunsmeas was set to zero.

Graphical techniques and summary statistics

were used to compare recoveries among samples

for each pesticide. Recovery results were tabulated,

summary statistics were computed, and results

were compared to the data-quality objective that

recoveries be within plus or minus 10 percent of

the ‘true’ or 100-percent value.

To evaluate the use of internal surrogate recoveries to estimate recoveries of spiked pesticides,

internal surrogate recoveries were correlated with

pesticide recoveries for the same sample. Recoveries of the internal surrogate 1,3-dimethyl2-nitrobenzene were reported by the PaDEP Laboratory, and three other internal surrogates—diazinon-d10, terbuthylazine, and lindane (alpha-HCHd6)—were reported by the USGS Laboratory. The

laboratories monitor these recoveries to determine

if the analysis is within a control-limit range set for

the analytical method. The range for the PaDEP

method was 60-120 percent or 70-120 percent

depending on the sample. Results that show poor

(or out-of-range) surrogate recoveries generally

require samples be reanalyzed by the laboratory.

In some instances, if the original water sample cannot be re-extracted, water may need to be

resampled from the well.

The exact form of the rank-sum test (Helsel

and Hirsch, 1992, p. 120) was used to compare the

recovery summary statistics for laboratory-water

spikes and ground-water spikes to determine if

there was a significant bias caused by interference

from the ground-water matrix.
11

Replicates

Variability is a measure of how well detections,

concentrations, and recoveries can be reproduced.

To evaluate variability of detections, equivocal

detection results (a measured detection and nondetection for splits of the same sample) were tabulated for duplicate ground-water samples

submitted to the PaDEP Laboratory. The result

from the USGS Laboratory for the sample was then

used as an independent check in cases of disparate

results from the PaDEP Laboratory. The USGS

result provided an independent way to determine

if the nondetection or the detection was correct. To

evaluate concentration variability, replicate samples submitted to the PaDEP Laboratory were analyzed two ways. For determination of differences

between duplicate samples where results were

greater than the reporting limit, the Relative Percent Difference (RPD) was calculated. The RPD, a

statistic that represents the difference between two

measurements (X1, X2) relative to their average,

was calculated as follows:

RPD = [(2|X2 - X1|)/(X2 + X1)] × 100 (2)

For determination of differences between triplicate

samples where results were greater than the

reporting limit, the Relative Standard Deviation

(RSD) was calculated as follows:

RSD = s/C-bar (3)

where s is the standard deviation of triplicate

results, and

C-bar is the mean concentration of the

triplicate results.

The RSD is also known as the coefficient of

variation.

Splits (2-lab)

Detection summaries were prepared as part of

the overall assessment of agricultural pesticides in

ground water. The percentages of false negatives

combined with graphical techniques were used to

evaluate results for the 11 ground-water samples

analyzed by both laboratories.

QUALITY-ASSURANCE RESULTS

The results are presented by type of qualitycontrol sample. Discussion of the results focuses on

addressing the design goals and whether the

results met the data-quality objectives.

Field Blanks

The results of analyses of five field-prepared

blank samples of laboratory water showed no evidence of any sample contamination at or above a

concentration of 0.3 μg/L. Data for the blank samples are given in tables S-2 and S-3 (Supplemental

Data section) for the PaDEP Laboratory and USGS

Laboratory, respectively. The data indicate the

three lots of pesticide-free laboratory water used

for quality assurance had no detectable concentrations of the eight pesticides. The results for five

field blanks indicate that collection, processing,

transport, and laboratory-analysis procedures did

not contaminate the samples. In addition, the last

four field blanks were collected following collection of samples in which pesticides were detected,

which demonstrates the cleaning procedures were

effective in decontaminating the sampling equipment. Therefore, pesticide detections in ground

waters were due to the presence of the pesticide in

ground water and were not to be attributed to contamination from sample processing in either the

field, the Lemoyne laboratory, or the analytical laboratories. The first data-quality objective was met.

Spikes

Results for laboratory water are presented first,

then the ground-water results are presented. The

results were evaluated to first address the question

of false negatives (data-quality objective 2) and

then to evaluate bias (data-quality objective 3).

Matrix interference from ground water, as a cause

of bias, was then addressed.

Evaluation of false negatives began with the

results of the analyses by the PaDEP Laboratory of

laboratory-water spikes with pesticide concentrations at 0.4 μg/L (table S-4 in Supplemental Data

section). The results of analyses of two four-way

splits submitted to the USGS Laboratory as independent concentration checks are given in table S-5

(Supplemental Data section) and show the spikes

had concentrations close to that expected from the

spike-preparation calculations. On the basis of

results in table S-4 from 64 analyses for individual

pesticides in 3 samples of laboratory water spiked

with known amounts of pesticides, all spiked pesticides were detected. For laboratory-water spikes,

there were no false-negative results at the 0.4 μg/L

concentration.

The evaluation of false negatives in ground

water used analyses by the PaDEP Laboratory of

spiked samples of ground water at concentrations
12

ranging from 0.31 μg/L (the reporting level) to

0.51 μg/L. On the basis of results from 40 analyses

by the PaDEP Laboratory for individual pesticides

in 5 ground-water samples spiked with known

pesticide amounts, no analytical measurements

failed to detect the presence of a pesticide (table S-6

in Supplemental Data section). The check samples

analyzed by the USGS Laboratory showed the pesticides to be present (table S-7 in Supplemental

Data section).

In summary, there were no false negatives for

the eight pesticides in all spiked samples. The second data-quality objective, for small numbers (less

than 5 percent) of false negatives in analyses of

ground water, was met.

To evaluate bias (data-quality objective 3), the

results in tables S-4, S-5, S-6, and S-7 (Supplemental Data section) were used in equation 1 to

calculate pesticide recoveries. On the basis of

results from the laboratory blanks, setting Cunsmeas

to zero in equation 1b for laboratory water was a

valid procedure. The results of the calculations of

recoveries are given in table S-8 (Supplemental

Data section) along with summary statistics for

recovery in laboratory water and in ground water.

Recovery data for pesticides in addition to the

eight evaluated herein are summarized by Durlin

and Schaffstall (1999, p. 395-399).

Negative bias is a normal and accepted characteristic of analytical methods for pesticides (U.S.

Environmental Protection Agency, 1988, p. 167;

Zaugg and others, 1995). Negative bias comes from

measured concentrations that are generally lower

than expected. In samples with very small concentrations of pesticides, a small (0.1 μg/L) difference

in measured concentration can result in a large difference in recovery. In a sample spiked for example

at 0.5 μg/L, a result of 0.3 μg/L would yield a

recovery of 60 percent; a result of 0.4 μg/L would

yield a recovery of 80 percent. Bias results for

PaDEP analyses were compared against Method

507 results in U.S. Environmental Protection

Agency (1995).

Negative bias was characteristic of results for

the eight pesticides. Spike recoveries in laboratory

water by the PaDEP Laboratory ranged from

medians near 76 percent for alachlor, atrazine,

chlorpyrifos, metolachlor, and pendimethalin to

107 percent for cyanazine. The median recovery for

pesticide spikes in ground water was as low as

65 percent for atrazine and as high as 97 percent

for cyanazine. The results for cyanazine were

dissimilar from the other pesticides and were characterized by high positive bias in 7 of the 13 spikes

analyzed for cyanazine. The recoveries for cyanazine in Lab-Spike-10 were in excess of 250 percent.

The median results for alachlor, atrazine, metolachlor, metribuzin, and simazine in laboratory

water and ground water were lower than the

results, some by as much as 20 percent, reported in

the Method 507 documentation (U.S. Environmental Protection Agency, 1995). The USEPA

results were for recovery of concentrations

between 0.75 μg/L (simazine) and 7.5 μg/L

(metolachlor)—concentrations generally many

times higher than the concentrations used in this

study—and were not directly comparable to the

results presented here. The USEPA results also do

not include data for chlorpyrifos, cyanazine, or

pendimethalin. Standard deviation of recovery

was as low as 7 percent for alachlor and simazine

and as high as 17 percent for cyanazine. The standard deviations of the percent recovery in table S-8

were similar to the USEPA results for ground

water.

A rank-sum test of the results for laboratory

water and ground water showed no significant difference (alpha=0.05) in spike recovery for any of

the eight pesticides. Thus, the ground-water

matrix did not contribute to matrix interference.

The magnitude of the negative bias for the

eight pesticides, with the exception of cyanazine,

would result in reported concentrations commonly

75-80 percent of the expected (‘true’) concentration

in the water sample. To relate recovery results to

data-quality objective 3, spike recovery for the five

state management plan pesticides in ground water

and the 20 percentage point range (from 90 to

110 percent) acceptable for objective 3 are illustrated in figure 2. The results (table S-8 and

figure 2) show that the bias in the recovery was not

within 10 percent of the ‘true’ (100 percent recovery) result for at least half of the results for each

pesticide. The laboratories were unable to consistently provide results to within 10 percent of

known concentrations for ground water over the

course of the study.

The recovery data for the internal surrogate

1,3-dimethyl-2-nitrobenzene (tables S-4 and S-6 in

Supplemental Data section) were checked for correlation with the spike recovery. For the six spikes,

three of laboratory water and three of ground

water, where surrogate recovery and spike recovery were quantified, correlations were too small for
13

Figure 2. Percentage recovery of alachlor, atrazine, cyanazine, metolachlor, and simazine in

spiked ground-water samples analyzed by Pennsylvania Department of Environmental Protection

Laboratory and U.S. Geological Survey, National Water-Quality Laboratory.
14

the relations to be of any practical use. Two other

spikes of ground water analyzed by the PaDEP

Laboratory had “poor” internal surrogate recoveries. Poor internal surrogate recovery did not correspond to anomalous results for spike recovery.

Internal surrogate recoveries for 1,3-dimethyl2-nitrobenzene could not be used to determine the

pesticide recoveries.

Bias from laboratory rounding of measured

concentrations to the tenth of a microgram for

reporting purposes was an issue not addressed for

this study. Rounding, as a source of bias, could

contribute about 10 percent to the overall bias if,

for example, a 0.44 μg/L concentration in a sample

was reported as 0.4 μg/L. This type of bias could

be negative, as in the example, or positive. Relating

to this issue, for the last samples analyzed by the

PaDEP Laboratory for the assessment in April

1998, the results were reported to hundreths of a

microgram.

In summary, the majority of results did not

meet data-quality objective 3. For analytical results

from the PaDEP Laboratory, bias was nearly

always negative (38 of 39 analyses or 97 percent of

the ground-water results) and generally in excess

of 10 percent from the ‘true’ or expected concentration (34 of 39 analyses or 87 percent of the

ground-water results) for pesticides at concentrations ranging from 0.31 to 0.51 μg/L. Cyanazine

results were unusual, meeting the data-quality

objective in three of the five ground-water spikes

yet overall exhibiting the largest (50 point) range in

recovery percentage. Results were better for

laboratory-water spikes than for ground water;

63 percent of laboratory-spike results were in

excess of 10 percent from the ‘true’ or expected

concentration. A rank-sum test of the results for

laboratory water and ground water showed no

significant difference (alpha=0.05) in spike

recovery for any of the eight pesticides. From this

test result, the ground-water matrix did not

contribute to bias.

To put the negative bias in the context of concentrations that would trigger actions by PDA

(0.7 μg/L of alachlor, for example; see table 1),

a 75-percent recovery value means an alachlor concentration of 0.53 μg/L measured by the PaDEP

Laboratory would be equal to an environmental

concentration of 0.7 μg/L. Thus, a laboratory

report showing a concentration of 0.53 μg/L

alachlor should prompt PDA to trigger action for

the Pesticides and Ground Water Strategy.

Replicates

Spiked replicates (laboratory water) were used

for evaluating variability in pesticide recovery.

Unspiked replicates (ground water) were used for

evaluating variability in pesticide concentration.

Results for laboratory water are presented first,

then the ground-water results are presented.

The results were evaluated to determine if variability was small (10 percent or less, data-quality

objective 4).

Variability was estimated using the results for

the laboratory-water spikes submitted in triplicate

to the PaDEP Laboratory (table S-4). The RPD was

calculated for lab-spike 10 and the RSD for labspikes 20 and 30. The RPD was zero for all pesticides except cyanazine (RPD of 10 percent) in

lab-spike 10. In the two triplicates, the RSD was

zero for chlorpyrifos, metolachlor, metribuzin, and

simazine; the RSD for alachlor, cyanazine, and

pendimethalin ranged from zero in lab-spike 30 to

as high as 20 percent in lab-spike 20; and the RSD

for atrazine in the two triplicates ranged from 13 to

18 percent. The recovery percentages that characterize these samples are shown in table S-8. In both

cases, the result for one sample of the three in the

triplicate series was different.

No ground-water samples were prepared as

replicate spikes for this study. Summary statistics

for variability in recovery for laboratory-water

spikes, including the RSD, for the eight samples

are listed in table S-8. The RSD in table S-8 is a

measure of variability of the method over the

course of the study for laboratory waters at a concentration of 0.4 μg/L. An RSD of about 11 percent

(or about ±0.05 μg/L) characterizes the method

results for alachlor, chlorpyrifos, metolachlor,

metribuzin, and simazine. Atrazine and pendimethalin have RSD values of about 17 and

23 percent, respectively. Cyanazine showed a large

RSD at nearly 51 percent.

The statistics summarizing variability in recovery results for spiked ground-water samples also

are listed in table S-8. The pesticides with low variability in laboratory-water spikes also had low

variability in ground water. The RSD for PaDEP

lab results is about 10 percent for alachlor, chlorpyrifos, metolachlor, metribuzin, and simazine

(table S-8). The RSD values for atrazine, pendimethalin, and cyanazine are high relative to the

five other pesticides. Ground-water results were

consistent with results for laboratory water.
15

By combining the results for laboratory water

and ground water in table S-8, a combined RSD

was calculated for the eight pesticides. The combined percent RSD was 11 for alachlor, 19 for atrazine, 12 for chlorpyrifos, 52 for cyanazine, 12 for

metolachlor, 13 for metribuzin, 22 for pendimethalin, and 13 for simazine. The combined RSD for

alachlor, chlorpyrifos, metolachlor, metribuzin,

and simazine is considered low enough to meet the

requirement of data-quality objective 4. Results for

atrazine, cyanazine, and pendimethalin do not

meet data-quality objective 4. The nature and magnitude of RSD values for the different pesticides

underscores the importance of using spikes and

the results of spike recovery when evaluating

pesticide concentrations in ground water.

Concentration variability in unspiked ground

water was difficult to determine because of the

large proportion of “less than quantitation limit”

results (table S-9). For seven ground-water samples

submitted to the PaDEP Laboratory in duplicate,

only one duplicate analysis had two measured

concentrations greater than the reporting level

(atrazine in samples from BE 1622). Two other samples had estimated concentrations in duplicate

atrazine analyses (samples from LB 1169 and

NP 643). Metolachlor also was detected in the

duplicate from NP 643. In an attempt to quantify

the differences, the RPD was calculated for these

samples. The RPD was zero for atrazine and

40 percent for metolachlor. Two samples in seven

had an inconsistency in results between duplicate

analyses—an estimated detection of 0.2 μg/L and a

“less than reporting level” result for atrazine in

samples from well BE 1624 and well BE 1625.

The samples from wells BE 1624 and BE 1625 were

not among the 3-way split samples analyzed by the

USGS Laboratory and the disparate results could

not be further qualified. For two of the seven

duplicate samples or about 25 percent, the presence of atrazine remained in question. Again, these

results for atrazine do not meet data-quality objective 4.

The evaluation of variability from the perspective of the temporal design was accomplished primarily with the triplicate samples of laboratorywater spikes. In addition, the variability of

recovery results among ground-water samples

collected on the same day is shown in figure 2 and

provides additional insight on use of a temporal

design. The five samples included in figure 2 were

collected on 3 days; bars showing recovery for

samples collected on the same day are labeled with

the date of collection. Although the spike concentrations were different for each sample on the 2

days, the within-day variability is apparent. The

magnitude of variability for samples on a single

day contributes to and appears to be described

well by the overall variability summarized above.

The description of variability reinforces the

point that the only way to assure the quality of the

concentration data is to regularly submit spike

samples to evaluate recovery in ground water.

Both random spatial and temporal designs could

be used to guide submission of these samples.

Splits (2-lab)

The results for the 11 samples are listed in table

S-10 (Supplemental Data section). In the split

samples, there were eight detections of atrazine,

one detection of metolachlor, and no detections of

alachlor, chlorpyrifos, cyanazine, metribuzin,

pendimethalin, or simazine by the PaDEP Laboratory. The results from the USGS Laboratory

supported the PaDEP results and showed no

detections for the 11 splits at concentrations greater

than 0.05 μg/L for alachlor, chlorpyrifos,

cyanazine, metribuzin, pendimethalin, or

simazine. For metolachlor, the results from the

USGS Laboratory supported the PaDEP results in

the one sample where metolachlor was detected by

the PaDEP Laboratory. The eight other metolachlor

detections by USGS were at concentrations too

small (less than 0.06 μg/L) to be reported even as

estimated concentrations in the PaDEP Laboratory

results. Atrazine concentrations less than

0.13 μg/L reported by the USGS Laboratory were

not detected or reported as estimated concentrations by the PaDEP Laboratory (fig. 3). Atrazine

concentrations greater than 0.13 μg/L reported by

the USGS Laboratory also were reported as

detections by the PaDEP Laboratory. These results,

no false-negative results for atrazine and

metolachlor, support the earlier findings for dataquality objective 2.

ASSESSMENT RESULTS FOR PESTICIDE

CONCENTRATIONS IN GROUND WATER

Results showed measured concentrations of

the eight pesticides in ground water from wells in

carbonate bedrock aquifers in the assessment area

were generally less than 0.3 μg/L. In water samples from 28 wells, only 6 individual measurements of the concentrations in water from 6 of the

wells were at or above 0.3 μg/L, 5 for atrazine and
16

1 for metolachlor. No well water had more than

one pesticide at concentrations at or above

0.3 μg/L. In addition, the assessment results

showed:

• No chlorpyrifos, cyanazine, metribuzin, or

pendimethalin was detected in ground water.

• Atrazine was detected in water from 22 of

the 28 wells sampled. Two of the 22 detections

were in question on the basis of results of duplicate

analyses.

• The atrazine concentration of 0.5 μg/L in

water from well NP 805 was the largest atrazine

concentration measured. The atrazine

concentration that triggers action by PDA under

the Pesticides and Ground Water Strategy would

be a measured concentration of approximately

0.75 μg/L if the spike-recovery data from this

study hold true at concentrations greater than

0.5 μg/L.

• At four wells, resampling in April 1998

confirmed atrazine detections from November

1997 and indicated atrazine concentrations were

the same or differed less than 0.1 μg/L in groundwater samples collected 5 months apart.

• Metolachlor was reported at a concentration

of 0.3 μg/L in water from well NP 643. The

0.3 μg/L metolachlor concentration is well below

the 33 μg/L trigger concentration for metolachlor.

Eight additional detections of metolachlor were at

concentrations below 0.06 μg/L in other well

waters. All eight were in waters where atrazine

was detected.

• Simazine was detected in water from eight

wells at concentrations of 0.04 μg/L or less. Seven

of the eight detections were in water where

metolachlor also was detected. All eight waters

where simazine was detected contained atrazine.

• Evidence exists for a pattern of cooccurrence of metolachlor and simazine at low

concentrations with higher atrazine

concentrations.

SUMMARY AND CONCLUSIONS

The U.S. Geological Survey (USGS) in cooperation with Pennsylvania Department of Agriculture

(PDA) completed a study to demonstrate the

application of a quality-assurance design to the

monitoring component of the Pesticides and

Ground Water Strategy. The design was to evaluate

the bias and variability of laboratory measurements of pesticide concentration. The USGS role

was to develop the quality-assurance design, assist

PDA in the application of the design to a selected

assessment area, evaluate the results, and report

the quality-assurance and assessment results. This

report describes the quality-assurance design,

describes how the design was applied to a selected

assessment area in eastern Pennsylvania, describes

procedures used to collect and analyze samples

Figure 3. Concentration of atrazine in splits of ground-water samples analyzed using two

different methods by Pennsylvania Department of Environmental Protection (PADEP)

Laboratory and U.S. Geological Survey (USGS), National Water-Quality Laboratory.
17

and to evaluate the results, and summarizes the

quality-assurance results along with the assessment results.

The design had random spatial and temporal

components. Four types of quality-control samples

were used to evaluate data-quality objectives:

1) field blanks were used to test for false-positive

results, 2) spikes of laboratory water and ground

water were used to test for false-negative results

and determine bias, 3) replicates of laboratory

water and ground water were used to determine

variability, and 4) 2-lab splits were used as an

additional check for bias. The design included use

of two laboratories. The Department of

Environmental Protection (PaDEP) Laboratory

analyzes the samples collected by PDA for the

monitoring component of the Pesticides and

Ground Water Strategy to determine pesticide

concentration. The second laboratory, a USGS

Laboratory, was used to provide supporting

information and an independent check on results

for the four types of quality-control samples.

The design was applied to an assessment area

that included agricultural areas of the Great Valley

Section of the Ridge and Valley Physiographic

Province in Berks, Lebanon, Lehigh, and

Northampton Counties. Wells drilled into carbonate bedrock aquifers were sampled. Bias and variability were evaluated using data collected from

October 1997 through January 1998 for five herbicides (alachlor, atrazine, cyanazine, metolachlor,

and simazine) for which specific state management

plans were required, two additional high-use herbicides (pendimethalin and metribuzin) and a

high-use insecticide chlorpyrifos.

Results of the evaluation of bias showed:

• False positives (analyses reporting pesticides

to be present when there actually were none

present) were not a problem. Results for five field

blanks indicate collection, processing, transport,

and laboratory-analysis procedures did not

contaminate the samples. The last four field blanks

were collected following collection of samples in

which pesticides were detected. These results

demonstrate the cleaning procedures were

effective in decontaminating the sampling

equipment. The first data-quality objective was

met; there were no false-positive results.

• Pesticides were detected in water when

pesticides were spiked into (added to) samples.

There were no false negatives for the eight

pesticides in all spiked samples. The second dataquality objective, for small numbers (less than

5 percent) of false negatives in analyses of ground

water, was met.

• Negative bias is a normal and accepted

characteristic of analytical methods for pesticides.

Negative bias comes from measured

concentrations that are generally lower than

expected. Negative bias was characteristic of

results for the eight pesticides. The magnitude of

the bias was large enough that the third dataquality objective—for pesticide recovery to be

within 10 percent of the ‘true’ (100 percent

recovery) result—was not met. For analytical

results from the PaDEP Laboratory, bias was

nearly always negative (38 of 39 analyses or

97 percent of the ground-water results) and

generally in excess of 10 percent from the ‘true’ or

expected concentration (34 of 39 analyses or

87 percent of the ground-water results) for

pesticides at concentrations ranging from 0.31 to

0.51 μg/L (micrograms per liter). The results for

cyanazine were unusual, meeting the data-quality

objective in three of the five ground-water spikes

yet overall exhibiting the largest (50 point) range in

recovery percentage. The magnitude of the

negative bias for the eight pesticides, with the

exception of cyanazine, would result in reported

concentrations commonly 75-80 percent of the

expected (‘true’) concentration in the water

sample. Therefore, data from calculations of spike

recovery need to be used when interpreting

measured pesticide concentrations in ground

water.

• Neither the pesticide analysis method used

by the PaDEP Laboratory nor the method used by

the USGS Laboratory could always provide

unbiased results to within 10 percent of known

concentrations for ground water over the course of

the study. Expecting concentrations to be within

10 percent of a true value is unrealistic at the

extremely small concentrations at which pesticides

commonly are present in ground water.

Determining the magnitude of the bias is more

important than setting a numerical data-quality

objective.

• Even though the third data-quality objective

may have been too stringent a requirement, the

magnitude of the negative bias, especially for

atrazine, was important to document. Atrazine

was the pesticide most commonly detected, and

recovery results for atrazine were some of the
18

worst (largest negative bias). Atrazine had

recoveries in ground water ranging from 58 to

97 percent and a median recovery of 65 percent.

• The magnitude of negative bias indicates the

importance of incorporating a quality-assurance

design that periodically and routinely includes

samples spiked at concentrations expected in

ground water as part of the monitoring component

of the PDA Pesticides and Ground Water Strategy.

Random spatial and temporal designs that provide

at least five recovery results to evaluate bias are

desirable. The recovery results need to be

evaluated before making conclusions about the

atrazine concentrations (and other pesticides) in

ground water.

• Trigger concentrations, the concentrations

that require action under the Pesticides and

Ground Water Strategy, should be considered

maximums for action. This consideration is needed

because of the negative bias in concentration

results. Concentrations of alachlor, atrazine,

chlorpyrifos, metolachlor, pendimethalin, and

simazine measured by the PaDEP laboratory were

commonly 20 to 25 percent less than expected in

the 0.31 to 0.51 μg/L range.

• Interference in laboratory analyses caused

by the composition of the ground-water matrix

was not a source of bias for this assessment.

Results for spiked laboratory water (no matrix

interference) and ground water were compared.

A rank-sum test of the results for laboratory water

and ground water showed no significant difference

(alpha=0.05) in spike recovery for any of the eight

pesticides. Thus, the ground-water matrix did not

contribute to matrix interference.

Results of the evaluation of variability showed:

• Large variability for recoveries of atrazine,

cyanazine, and pendimethalin. Data for the

laboratory-water spikes submitted in triplicate to

the PaDEP Laboratory were evaluated to

determine if variability was small (10 percent or

less, data-quality objective 4). The relative

standard deviation (RSD) was used as a measure of

variability of the method over the course of the

study for laboratory waters at a concentration of

0.4 μg/L. An RSD of about 11 percent (or about 

0.05 μg/L) characterizes the method results for

alachlor, chlorpyrifos, metolachlor, metribuzin,

and simazine. Atrazine and pendimethalin have

RSD values of about 17 and 23 percent,

respectively. Cyanazine showed the largest RSD at

nearly 51 percent. The pesticides with low

variability in laboratory-water spikes also had low

variability in ground water. The RSD’s for alachlor,

chlorpyrifos, metolachlor, metribuzin, and

simazine are considered low enough to meet the

requirement of data-quality objective 4. Results for

atrazine, cyanazine, and pendimethalin do not

meet data-quality objective 4.

• Large variations in pesticide recovery from

spiked samples further indicate the need to use

data for pesticide recovery in the interpretation of

measured pesticide concentrations in ground

water. Data from replicate samples spiked with

known pesticide amounts are a critical component

of a quality-assurance design for the monitoring

component of the Pesticides and Ground Water

Strategy.

• Variability of concentrations in unspiked

ground water was difficult to determine because of

the large proportion of samples with pesticide

concentrations too small to be detected by the

PaDEP Laboratory. In addition to the types of

quality-control samples used for this study,

replicate samples of spiked ground water would

add quality-assurance information. These samples

can provide important data on bias and variability.

Although no matrix interference from ground

water was significant for this assessment area, the

quality assurance is especially important as the

monitoring is done in the varied geologic settings

where variations in the chemistry of the groundwater matrix would be expected.

The use of two laboratories in the qualityassurance design was useful for:

• Certification that spike mixtures obtained

from a commercial supplier were manufactured

according to the concentration specifications.

• Certification that laboratory water obtained

from commercial suppliers for preparing field

blanks and laboratory-water spikes did not contain

pesticides at concentrations greater than the

method detection limit.

• Verification that spikes were prepared

correctly by field personnel and had

concentrations that were expected on the basis of

spike-concentration calculations.

• Verification of pesticide detections. The

atrazine results showed that concentrations greater

than 0.13 μg/L measured by the USGS Laboratory

were detected by the PaDEP Laboratory.
19

REFERENCES CITED

Durlin, R.R., and Schaffstall, W.P., 1999, Water

resources data, Pennsylvania, water year 1998,

v. 1, Delaware River Basin: U.S. Geological

Survey Water-Data Report PA-98-1, 405 p.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995,

Design of the National Water-Quality

Assessment Program—Occurrence and

distribution of water-quality conditions:

U.S. Geological Survey Circular 1112, 33 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical

methods in water resources: New York,

Elsevier Science Publishing Company, Inc.,

522 p.

Lindsey, B.D., and Bickford, T.M., 1999,

Hydrogeologic framework and sampling

design for an assessment of agricultural

pesticides in ground water in Pennsylvania:

U.S. Geological Survey Water-Resources

Investigations Report 99-4076, 44 p.

Pennsylvania Department of Agriculture, 1998,

Pesticides and ground water strategy, January

2, 1998: Harrisburg, Pa., 36 p.

Taylor, J.K., 1987, Quality assurance of chemical

measurements: Boca Raton, Fla., CRC Press,

Inc. (Lewis Publishers, Inc.), 328 p.

U.S. Environmental Protection Agency, 1988,

Methods for the determination of organic

compounds in drinking water: EPA-600/4-

88/039, 382 p.

_____1995, Methods for the determination of

organic compounds in drinking water,

Supplement III: EPA-600/R-95/131, 552 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and

Fehlberg, K.M., 1995, Methods of analysis by

the U.S. Geological Survey National WaterQuality Laboratory—Determination of

pesticides in water by C-18 solid-phase

extraction and capillary-column gas

chromatography/mass spectrometry with

selected-ion monitoring: U.S. Geological

Survey Open-File Report 95-181, 49 p.

21

SUPPLEMENTAL DATA TABLES

A listing, by topic, of the tables of data that appear in this section is as follows:

Topic

 Laboratory

PaDEP USGS

Well records

Table S-1

Field Blanks

Pesticide concentration and surrogate recovery, laboratory water Table S-2 Table S-3

Spikes

Pesticide concentration and surrogate recovery, laboratory water Table S-4 Table S-5

Pesticide concentration and surrogate recovery, ground water Table S-6 Table S-7

Spike recovery percentages and summary statistics, laboratory water and ground water Table S-8

Replicates

Pesticide concentration and surrogate recovery, laboratory-water spikes (triplicates) Table S-4 --

Pesticide concentration and surrogate recovery, ground water (duplicates) Table S-9

2-lab splits and routine samples

Ground water Table S-10
22Table S-1. Records of selected wells in Berks, Lebanon, Lehigh, and Northampton Counties sampled for the Quality-Assurance Project f

Department of Agriculture Pesticides and Ground Water Strategy, 1997-98

Local well number - Well number shown on index map and county prefix (BE, Berks; LB, Lebanon; LE, Lehigh; NP, Northampton).PDA sample identifier - Sample-identification number assigned by Pennsylvania Department of Agriculture (PDA).Cell number - Sampling-cell number in study area.Latitude and longitude - Location, to the nearest second, of well as determined by USGS personnel from topographic maps and confirme

System.

Aquifer code - Abbreviation of carbonate rock geologic unit where well is completed.

Middle Ordovician:364BKMN, Beekmantown Group; 364HRSY, Hershey Formation; 364JKBG, Jacksonburg Formation;364MRSN, Myerstown Formation; 364ONLN, Ontelaunee Formation.Lower Ordovician:367EPLR, Epler Formation; 367RCKB, Rickenbach Formation; 367SNNG, Stonehenge Formation.Upper Cambrian:371ALNN, Allentown Formation; 371MDCK, Maiden Creek Member of Allentown Formation; 371RCLD, Richland Formation; 371SZC371TCKR, Tuckertown Member of Allentown Formation.

Depth to top - Depth, in feet, to bedrock as reported on driller’s log.Use of water - The primary way water from the well is used: C, commercial; H, rural domestic; P, public supply; S, livestock; T, institutionDepth of well - Depth of drilled well, in feet, as reported on driller’s log.Casing length - Feet of casing used to complete well, as reported on driller’s log.Casing material - S, steel; P, PVC plastic.Date well constructed - Date of well construction as reported on driller’s log, in mm-yy or mm-dd-yy format.Elevation of land surface - Land surface at well site, in feet above sea level (National Geodetic Vertical Datum of 1929).Water-level date - Date of water-level measurement, in mm-dd-yy format.Water level - Depth of water, in feet below land surface, as measured by USGS personnel.All columns - A double dash indicates no information was obtained.
23

Table S-1. Records of selected wells in Berks, Lebanon, Lehigh, and Northampton Counties sampled for the Quality Assura

Pennsylvania Department of Agriculture Pesticides and Ground Water Strategy, 1997-98—Continued

Local well

number

PDA

sample

identifier

Cell

number Latitude Longitude Aquifer code Depth to top (feet) Use of water Depth of well (feet) Casing length (feet) Casing material Date well constructed Elevation of land surface (feet) W

BE 755 06002 10 40°22'20" 76°08'58" 367EPLR -- H, S 128 -- -- 01-65 410 BE 1036 06016 14 40°29'23" 75°47'29" 371MDCK -- S 192 58 -- 01-63 400 BE 1537 06003 11 40°20'30" 76°06'46" 364MRSN -- P 90 -- -- -- 390 

BE 1618 06001 5 40°23'27" 76°14'36" 364HRSY -- S 220 60 P 11-01-95 475 10

BE 1619 06015 6 40°29'34" 75°48'18" 371MDCK 25 H 150 120 S 06-26-89 400 1

BE 1620 06030 7 40°29'07" 75°51'39" 367RCKB 3 H 225 41 S 05-10-85 424 12

BE 1621 06028 12 40°20'32" 75°45'24" 371RCLD 52 H 238 60 S 05-01-88 310 12

BE 1622 06005 16 40°32'32" 75°41'39" 367RCKB 53 H 180 100 S 10-07-96 480 1

BE 1624 06010 8 40°26'45" 75°54'35" 367SNNG 40 H 200 92 S 08-03-89 320 1

BE 1625 06008 9 40°24'32" 75°57'57" 367EPLR 41 H 436 63.5 S 03-01-90 270 1

BE 1626 06029 13 40°23'11" 75°44'40" 371ALNN 18 H 95 39 S 09-29-92 320 12

BE 1627 06017 14 40°30'05" 75°47'52" 364ONLN 53 C 180 80 S 06-11-88 430 1

BE 1628 06007 15 40°31'22" 75°44'00" 367EPLR 12 H 172 45.5 S 12-01-89 440 

BE 1631 06035 22 40°30'40" 75°40'02" 371TCKR 70 H 100 100 S 04-05-95 430 

LB 545 38012 3 40°21'03" 76°16'47" 367EPLR -- H 200 -- S -- 480 10

LB 621 38007 2 40°20'28" 76°15'59" 367RCKB -- H 300 -- -- -- 510 

LB 1168 38011 1 40°19'33" 76°14'28" 371SZCK 25 H 70 34 S 02-01-88 520 10

LB 1169 38008 4 40°22'43" 76°16'25" 364MRSN -- H 137 106 S 07-21-77 470 10

LE 1412 39001 21 40°31'48" 75°36'52" 371ALNN 100 H 150 120 S 04-17-97 395 12

LE 1413 39004 19 40°34'09" 75°35'29" 364BKMN 33 H 125 100 S 03-17-95 438 

LE 1414 39003 20 40°33'52" 75°35'25" 364BKMN 39 T 105 100 S 04-26-94 428 12

LE 1415 39002 18 40°39'00" 75°33'05" 364BKMN 87 H 165 100 S 12-27-93 430 12

NP 643 48003 29 40°43'40" 75°17'00" 367EPLR -- H 200 95 S 10-04-80 380 

NP 803 48001 24 40°40'54" 75°27'30" 367EPLR -- H 200 60 S 03-13-97 360 

NP 804 48007 25 40°40'28" 75°24'22" 367EPLR -- H 120 -- S 01-72 400 0NP 805 48006 26 40°41'44" 75°24'15" 367EPLR 115 H 140 114 S 05-01-95 400 0

NP 806 48002 27 40°42'33" 75°21'42" 367EPLR -- H 125 103 S 07-01-89 370 12

NP 807 48008 30 40°48'52" 75°06'10" 364JKBG -- H -- -- -- 01-72 370 0NP 812 48005 28 40°43'29" 75°21'43" 367EPLR 28 C 300 60 S 03-01-84 405 
24Table S-2. Analytical results for pesticide concentration and surrogate compound recovery determined by Pennsylvania Department of 

Laboratory for field blanks of pesticide-free laboratory water

[<, indicates compound was analyzed for but not detected and the quantitation limit is reported]

Lot number of

pesticide-free

laboratory

water

Local well

number where

blank prepared

Date

(yyyymmdd)

Time

(hhmm)

Blank concentration, in micrograms per liter 

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine 

Lot L01251 BE 1618 19971021 1536 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 Lot G51317 BE 1621 19971204 1206 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 Lot 37149 LB 621 19971016 0946 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 Lot 37149 LE 1412 19971209 1413 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 Lot 37149 NP 806 19971229 1040 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 

Table S-3. Analytical results for pesticide concentration and surrogate compound recovery determined by U.S. Geological Survey, Natio

Laboratory, for field blanks of pesticide-free laboratory water

[<, indicates compound was analyzed for but not detected and the quantitation limit is reported]

Lot number of

pesticide-free

laboratory

water

Local well

number where

blank prepared

Date

(yyyymmdd)

Time

(hhmm)

Blank concentration, in micrograms per liter 

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine Diazino

d10 

 Lot L01251 BE 1618 19971021 1535 <0.002 <0.004 <0.004 <0.004 <0.002 <0.004 <0.004 <0.005 104  Lot G51317 BE 1621 19971204 1205 <.002 <.001 <.004 <.004 <.002 <.004 <.004 <.005 98. Lot 37149 LB 621 19971016 0945 <.002 <.001 <.004 <.004 <.002 <.004 <.004 <.005 89.8  Lot 37149 LE 1412 19971209 1425 <.002 <.001 <.004 <.004 <.002 <.004 <.004 <.005 107 
25

Table S-4. Analytical results for pesticide concentration and surrogate compound recovery determined by Pennsylvania Department of E

Laboratory for spiked pesticide-free laboratory-water samples submitted as triplicate-blind samples for assessment of laboratory bias and 

[E, indicates an estimated value below the quantitation limit but above the method detection limit. --, No data received. For a 1-liter samplequivalent to the prepared spike concentration, Cprp, in micrograms per liter (see equation 1a).]

Sample

identifier

Local well

number of

sample

preceding

preparation

of spiked

blank

Date

(yyyymmdd)

Time

(hhmm)

Analyzed concentration of spiked blank, in micrograms per liter Spike volume,

in milliliters

per liter

of sample

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine 

Lab Spike 10-1 BE 755 19971023 1101 0.3 0.3 0.3 1 0.3 0.3 0.3 0.4 0.40 ± .01 

Lab Spike 10-2 BE 755 19971023 1102 .3 .3 .3 .9 .3 .3 .3 .4 .40 ± .01 

Lab Spike 10-3 BE 755 19971023 1103 -- -- -- -- -- -- -- -- .40 ± .01 

Lab Spike 20-1 LE 1414 19971217 1622 .3 .2E .3 .4 .3 .3 .2E .3 .39 ±. 01 

Lab Spike 20-2 LE 1414 19971217 1623 .3 .3 .3 .3 .3 .3 .3 .3 .39 ± .01 

Lab Spike 20-3 LE 1414 19971217 1624 .3 .3 .3 .3 .3 .3 .2E .3 .39 ± .01 

Lab Spike 30-2 NP 807 19980127 1333 .4 .3 .4 .4 .4 .4 .4 .4 .42 ± .01 

Lab Spike 30-3 NP 807 19980127 1334 .4 .4 .4 .4 .4 .4 .4 .4 .42 ± .01 

Lab Spike 30-4 NP 807 19980127 1335 .3 .4 .4 .4 .4 .4 .4 .4 .42 ± .01 

Table S-5. Analytical results for pesticide concentration and surrogate compound recovery determined by U.S. Geological Survey, Natio

Laboratory for spiked pesticide-free laboratory-water samples

[For a 1-liter sample, the spike volume is equivalent to the prepared spike concentration, Cprp , in micrograms per liter (see equation 1a).

Sample

identifier

Date

(yyyymmdd)

Time

(hhmm)

Analyzed concentration of spiked blank, in micrograms per liter Spike volume, in

milliliters per liter

of sample

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine Diazin

d10 

Lab Spike 20-4 19971217 1625 0.409 0.442 0.398 0.442 0.405 0.404 0.343 0.432 0.39 ± .01 110 

Lab Spike 30-1 19980127 1332 .487 .454 .470 .467 .464 .384 .288 .444 .42 ± .01 108 
26Table S-6. Analytical results for pesticide concentration and surrogate-compound recovery determined by Pennsylvania Department of 

Laboratory for spiked ground-water samples and unspiked ground-water samples and concentration differences calculated from the ana

concentration

[Shaded rows are recovery values for concentration (by difference); E, indicates an estimated value below the quantitation limit but abolimit; <, indicates compound was analyzed for but not detected, the quantitation limit is reported, and zero was used for difference calcurecoveries reported as “poor” were quantified as less than 60 percent by the PaDEP Laboratory. For a 1-liter sample, the spike volume prepared spike concentration, Cprp , in micrograms per liter (see equation 1a).]

Local well number

and lot number

of Supelco Brand

pesticide

spike mix

Sample type Date (yyyymmdd) Time (hhmm)

Concentration, in micrograms per liter Spike v

in mil

per 

of sa

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine 

BE 1036LA-66096

Spiked ground water 19971113 1233 0.4 0.6 0.4 0.4 0.4 0.4 0.4 0.4 0.46

Ground water 19971113 1239 <.3 .3 <.3 <.3 <.3 <.3 <.3 <.3 -

Difference -- -- .4 .3 .4 .4 .4 .4 .4 .4 -

BE 1619LA-62435

Spiked ground water 19971113 1112 .4 .6 .4 .3 .4 .4 .3 .4 .51±

Ground water 19971113 1109 <.3 .3 <.3 <.3 <.3 <.3 <.3 <.3 -

Difference -- -- .4 .3 .4 .3 .4 .4 .3 .4 -

LB 1169LA-62435

Spiked ground water 19971016 1233 .4 .5 .4 .5 .4 .4 .3 .4 .51±

Ground water 19971016 1239 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 -

Difference -- -- .4 .3 .4 .5 .4 .4 .3 .4 -

LE 1413LA-66096

Spiked ground water 19971222 1303 .2E .3 .2E .3 .2E .2E .2E .2E .31±

Ground water 19971222 1309 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 -

Difference -- -- .2 .3 .2 .3 .2 .2 .2 .2 -

NP 803LA-66096

Spiked ground water 19971222 1133 .4 .6 .4 .4 .4 .4 .4 .4 .50±

Ground water 19971222 1139 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 -

Difference -- -- .4 .4 .4 .4 .4 .4 .4 .4 -
27

Table S-7. Analytical results for pesticide concentration and surrogate-compound recovery determined by U.S. Geological Survey, Natio

Laboratory for spiked ground-water samples, unspiked ground-water samples, and concentration differences calculated from the analytic

concentration

[Shaded rows are recovery values for concentration (by difference); E, indicates an estimated value below the quantitation limit but above <, indicates compound was analyzed for but not detected, the quantitation limit is reported, and zero was used for difference calculationsspike volume is equivalent to the prepared spike concentration, Cprp , in micrograms per liter (see equation 1a).]

Local well number

and lot number

of Supelco Brand

pesticide

spike mix

Sample type Date (yyyymmdd) Time (hhmm)

Concentration, in micrograms per liter Spike volume,

in milliliters

per liter

of sample

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine Di

BE 1036LA-66096

Spiked ground

water

19971113 1232 0.463 0.713 0.390 0.254 0.443 0.309 0.235 0.433 0.46 ± .01 

Ground water 19971113 1230 <.002 .234 <.004 <.004 .004 <.004 <.004 .011 -- 

Difference -- -- .463 .479 .390 .254 .439 .309 .235 .422 --

BE 1619LA-62435

Spiked ground

water

19971113 1102 .527 .802 .454 .308 .569 .341 .288 .485 .51 ± .01 10

Ground water 19971113 1100 <.002 .259 <.004 <.004 .007 <.004 <.004 .011 -- 10

Difference -- -- .527 .543 .454 .308 .562 .341 .288 .474 --

LB 1169LA-62435

Spiked ground

water

19971016 1232 .612 .753 .478 .350 .617 .319 .292 .475 .51 ± .01 1

Ground water 19971016 1230 <.002 .242 <.004 <.004 .029 <.004 <.004 .008 -- 

 Difference -- -- .612 .511 .478 .350 .588 .319 .292 .467 --

LE 1413LA-66096

Spiked ground

water

19971222 1302 .314 .453 .239 .303 .322 .234 .195 .332 .31 ± .01 

Ground water 19971222 1300 <.002 .105 <.004 <.004 .010 <.004 <.004 .006 -- 

Difference -- -- .314 .348 .239 .303 .312 .234 .195 .326 --

NP 803LA-66096

Spiked ground

water

19971222 1132 .514 .871 .298 .487 .540 .384 .309 .525 .50 ± .01 

Ground water 19971222 1130 .005 .294 <.004 <.004 .034 <.004 <.004 .003E -- 

Difference -- -- .509 .577 .298 .487 .506 .384 .309 .522 --
28Table S-8. Spike recovery data and summary statistics for analyses of pesticides in spiked laboratory-water and ground-water sample

Department of Environmental Protection Laboratory and U.S. Geological Survey, National Water-Quality Laboratory

[PaDEP, Pennsylvania Department of Environmental Protection Laboratory; USGS, U.S. Geological Survey, National Water-Quality Labanalyzed or statistic not calculated; cnbd, could not be determined; SD, Standard Deviation; RSD, Relative Standard Deviation]

Sample

identifier

Lot number

of Supelco

Brand

pesticide

spike mix

Spike recovery, in percent

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendi

PaDEP USGS PaDEP USGS PaDEP USGS PaDEP USGS PaDEP USGS PaDEP USGS PaDEP 

Laboratory Water

Lab Spike 10-1 LA-66096 75.2 -- 75.2 -- 75.2 -- 278 -- 75.2 -- 83.5 -- 75.2 Lab Spike 10-2 LA-66096 75.2 -- 75.2 -- 75.2 -- 251 -- 75.2 -- 83.5 -- 75.2 Lab Spike 10-3 LA-66096 cnbd -- cnbd -- cnbd -- cnbd -- cnbd -- cnbd -- cnbd Lab Spike 20-1 LA-66096 76.3 -- 50.9 -- 76.3 -- 113 -- 76.3 -- 84.8 -- 50.9 Lab Spike 20-2 LA-66096 76.3 -- 76.3 -- 76.3 -- 84.8 -- 76.3 -- 84.8 -- 76.3 Lab Spike 20-3, 4 LA-66096 76.3 104 76.3 112 76.3 101 84.8 125 76.3 103 84.8 114 50.9 Lab Spike 30-2 LA-66096 96.2 -- 72.1 -- 96.2 -- 107 -- 96.2 -- 107 -- 96.2 Lab Spike 30-3 LA-66096 96.2 -- 96.2 -- 96.2 -- 107 -- 96.2 -- 107 -- 96.2 Lab Spike 30-4,1 LA-66096 72.1 117 96.2 109 96.2 113 107 125 96.2 112 107 103 96.2 

Median 76.3 -- 75.8 -- 76.3 -- 107 -- 76.3 -- 84.8 -- 75.8 Mean 80.5 -- 77.3 -- 83.5 -- 142 -- 83.5 -- 92.8 -- 77.1 SD 9.2 -- 13.5 -- 9.9 -- 72 -- 9.9 -- 11.0 -- 17.6 RSD, percent 11.4 -- 17.4 -- 11.8 -- 50.8 -- 11.8 -- 11.9 -- 22.8 

Ground Water

BE 1036 LA-66096 87.0 101 65.2 104 87.0 84.7 96.6 61.3 87.0 95.4 96.6 74.6 87.0 BE 1619 LA-62435 78.0 103 58.5 106 78.0 88.4 58.5 60.0 86.6 122 78.0 66.4 58.8 LB 1169 LA-62435 78.4 120 58.8 100 78.4 93.6 98.0 68.6 87.1 128 78.4 62.5 58.8 LE 1413 LA-66096 64.5 101 96.7 112 64.5 77.0 108 108 64.5 100 71.7 83.7 64.5 NP 803 LA-66096 80.0 102 80.0 115 80.0 59.6 88.9 108 80.0 101 88.9 85.3 80.0 

Median 78.4 102 65.2 106 78.4 84.7 96.6 68.6 86.6 101 78.4 74.6 64.5 Mean 77.6 105 71.8 107 77.6 80.7 90.0 81.2 81.0 109 82.7 74.5 69.8 SD 7.3 7.3 14.7 5.4 7.3 11.8 16.9 22.1 8.7 13.1 8.9 9.1 11.6 RSD, percent 9.4 7.0 20.4 5.1 9.4 14.7 18.8 27.2 10.7 12.0 10.7 12.2 16.6 
29

Table S-9. Analytical results for pesticide concentration and surrogate-compound recovery determined by Pennsylvania Department o

Laboratory and U.S. Geological Survey, National Water-Quality Laboratory for replicate samples of ground water

[E, indicates an estimated value below the quantitation limit but above the method detection limit; <, indicates compound was analyzethe quantitation limit is reported. Surrogate for PaDEP Laboratory: Surrogate 1, 1,3-dimethyl-2-nitrobenzene. Surrogate recoveries repquantified as less than 60 percent by the PaDEP Laboratory. Surrogates for USGS Laboratory: Surrogate 1, diazinon-d10; Surrogate 2

Surrogate 3,alpha-HCH-d6 ]

Local

well

number

Analyzing

laboratory

Date

(yyyymmdd)

Time

(hhmm)

Ground-water concentration, in micrograms per liter Su

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine Surrogate 1 

BE 1622 PaDEP 19971103 1249 <0.3 0.4 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 Poor 

PaDEP 19971103 1247 <.3 .4 <.3 <.3 <.3 <.3 <.3 <.3 Poor 

USGS 19971103 1240 <.002 .313 <.004 <.004 .057 <.004 <.004 .041 98.1 

BE 1624 PaDEP 19971104 1530 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 Poor 

PaDEP 19971104 1532 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 Poor 

BE 1625 PaDEP 19971104 1230 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 Poor 

PaDEP 19971104 1232 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 Poor 

LB 1169 PaDEP 19971016 1239 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 96.78 

PaDEP 19971016 1231 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 98.95 

USGS 19971016 1230 <.002 .242 <.004 <.004 .029 <.004 <.004 .008 92.3 

LE 1413 PaDEP 19971222 1309 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 72.26 

PaDEP 19971222 1301 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 69.57 

LE 1413 USGS 19971222 1300 <.002 .105 <.004 <.004 .010 <.004 <.004 .006 71.7 

NP 643 PaDEP 19971229 1439 <.3 .2E <.3 <.3 .3 <.3 <.3 <.3 69.50 

PaDEP 19971229 1437 <.3 .2E <.3 <.3 .2E <.3 <.3 <.3 69.91 

USGS 19971229 1430 <.002 .241 <.004 <.004 .288 <.004 <.004 .021 94.4 

NP 807 PaDEP 19980127 1100 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 83.31 

PaDEP 19980127 1102 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 80.02 
30Table S-10. Analytical results for pesticide concentration and surrogate-compound recovery determined by Pennsylvania Departme

Protection Laboratory and U.S. Geological Survey, National Water-Quality Laboratory for routine ground-water samples and for 2-la

samples

[R, in date column indicates resample; E, indicates an estimated value below the quantitation limit but above the method detection l<, indicates compound was analyzed for but not detected and the quantitation limit is reported. Surrogate for PaDEP Laboratory:Surrogate 1, 1,3-dimethyl-2-nitrobenzene. Surrogate recoveries reported as “poor” were quantified as less than 60 percent by the PSurrogates for USGS Laboratory: Surrogate 1, diazinon-d10; Surrogate 2, terbuthylazine; Surrogate 3,alpha-HCH-d6]

Local

well

number

Analyzing

laboratory

Date

(yyyymmdd)

Time

(hhmm)

Ground-water concentration, in micrograms per liter Su

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine Surrogate 1 

BE 755 PaDEP 19971023 1109 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 101.54 BE 755 USGS 19971023 1100 <.002 .129 <.004 <.004 <.002 <.004 <.004 .004E 109 BE 1036 PaDEP 19971113 1239 <.3 .3 <.3 <.3 <.3 <.3 <.3 <.3 Poor BE 1036 USGS 19971113 1230 <.002 .234 <.004 <.004 .004 <.004 <.004 .011 97.2 BE 1036 PaDEP 19980407 R 1140 <.3 .3 <.3 <.3 <.3 <.3 <.3 <.3 69.62 BE 1537 PaDEP 19971023 1445 <.3 .09E <.3 <.3 <.3 <.3 <.3 <.3 111.77 BE 1618 PaDEP 19971021 1539 <.3 .1E <.3 <.3 <.3 <.3 <.3 <.3 No data 

BE 1619 PaDEP 19971113 1109 <.3 .3 <.3 <.3 <.3 <.3 <.3 <.3 Poor BE 1619 USGS 19971113 1100 <.002 .259 <.004 <.004 .007 <.004 <.004 .011 104 BE 1619 PaDEP 19980407 R 1045 <.3 .35 <.3 <.3 <.3 <.3 <.3 <.3 91.37 

BE 1620 PaDEP 19971204 1550 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 87.74 

BE 1621 PaDEP 19971204 1239 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 97.35 BE 1621 USGS 19971204 1230 <.002 .009 <.004 <.004 .003E <.004 <.004 .002E 109 BE 1622 PaDEP 19971103 1249 <.3 .4 <.3 <.3 <.3 <.3 <.3 <.3 Poor BE 1622 USGS 19971103 1240 <.002 .313 <.004 <.004 .057 <.004 <.004 .041 98.1 BE 1622 PaDEP 19980407 R 1355 <.3 .31 <.3 <.3 <.3 <.3 <.3 <.3 77.01 

BE 1624 PaDEP 19971104 1530 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 Poor BE 1625 PaDEP 19971104 1230 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 Poor BE 1626 PaDEP 19971204 1440 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 98.65 BE 1627 PaDEP 19971113 1305 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 Poor BE 1627 PaDEP 19980407 R 1115 <.3 .24E <.3 <.3 <.3 <.3 <.3 <.3 90.80 

BE 1628 PaDEP 19971103 1500 no data received -- 
31

BE 1631 PaDEP 19971209 1140 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 94.52 

LB 545 PaDEP 19971021 1409 <.3 .1E <.3 <.3 <.3 <.3 <.3 <.3 87.08 LB 545 USGS 19971021 1400 <.002 .142 <.004 <.004 .015 <.004 <.004 <.005 99.1 

LB 621 PaDEP 19971016 0949 <.3 .3 <.3 <.3 <.3 <.3 <.3 <.3 99.02 

LB 1168 PaDEP 19971021 1129 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 100.48 LB 1168 USGS 19971021 1120 <.002 .209 <.004 <.004 <.002 <.004 <.004 <.005 107 LB 1169 PaDEP 19971016 1239 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 96.78 LB 1169 USGS 19971016 1230 <.002 .242 <.004 <.004 .029 <.004 <.004 .008 92.3 

LE 1412 PaDEP 19971209 1420 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 96.54 

LE 1413 PaDEP 19971222 1309 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 72.26 LE 1413 USGS 19971222 1300 <.002 .105 <.004 <.004 .010 <.004 <.004 .006 71.7 

LE 1414 PaDEP 19971217 1545 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 104.84 LE 1415 PaDEP 19971217 1250 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 92.58 NP 643 PaDEP 19971229 1439 <.3 .2E <.3 <.3 .3 <.3 <.3 <.3 69.50 NP 643 USGS 19971229 1430 <.002 .241 <.004 <.004 .288 <.004 <.004 .021 94.4 

NP 803 PaDEP 19971222 1139 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 69.58 NP 803 USGS 19971222 1130 .005 .294 <.004 <.004 .034 <.004 <.004 .003E 68.6 

NP 804 PaDEP 19980114 1220 <.3 .1E <.3 <.3 <.3 <.3 <.3 <.3 87.91 NP 805 PaDEP 19980114 1025 <.3 .5 <.3 <.3 <.3 <.3 <.3 <.3 94.28 NP 806 PaDEP 19971229 1050 <.3 .2E <.3 <.3 <.3 <.3 <.3 <.3 73.40 NP 807 PaDEP 19980127 1100 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 83.31 NP 812 PaDEP 19971229 1525 <.3 <.3 <.3 <.3 <.3 <.3 <.3 <.3 84.02 

Table S-10. Analytical results for pesticide concentration and surrogate-compound recovery determined by Pennsylvania Departme

Protection Laboratory and U.S. Geological Survey, National Water-Quality Laboratory for routine ground-water samples and for 2-la

samples—Continued

[R, in date column indicates resample; E, indicates an estimated value below the quantitation limit but above the method detection l<, indicates compound was analyzed for but not detected and the quantitation limit is reported. Surrogate for PaDEP Laboratory:Surrogate 1, 1,3-dimethyl-2-nitrobenzene. Surrogate recoveries reported as “poor” were quantified as less than 60 percent by the PSurrogates for USGS Laboratory: Surrogate 1, diazinon-d10; Surrogate 2, terbuthylazine; Surrogate 3,alpha-HCH-d6]

Local

well

number

Analyzing

laboratory

Date

(yyyymmdd)

Time

(hhmm)

Ground-water concentration, in micrograms per liter Su

Alachlor Atrazine Chlorpyrifos Cyanazine Metolachlor Metribuzin Pendimethalin Simazine Surrogate 1