Environmental Protection
Agency
Office of Pesticides ana
Toxic Substances
n 1990
National Pesticide Survey
Quality Assurance/
Qualify Control
What is
QA/QC?
QA/QC
Throughout
ih* Survey
The U.S. Environmental Protection Agency (EPA) has completed its five-year
National Survey of Pesticides in Drinking Water Wells (NPS). A joint project of EPA's
Office of Drinking Water (ODW) and Office of Pesticide Programs (OPP), the Survey
was designed to assess the extent and severity of the presence of pesticides and
nitrate in drinking water welts nationwide, and the relationship of pesticide use and
ground-water vulnerability to the presence of pesticides and nitrate.
In conducting the Survey, EPA sampled over 1300 wells for the presence of 127
analytes, including pesticides, pesticide degradates, and nitrate. Sampling teams
throughout the country collected thousands of water samples and administered
questionnaires on local agriculture, pesticide use, and well construction. Eight
laboratories tested the water samples using eight different analytic procedures. EPA
used a broad array of data management techniques to direct the varied activities and
report results. This fact sheet describes the quality assurance (QA) and quality control
(QC) procedures that were carried out during the design and implementation of the
Survey. These procedures ensured that data derived from the analysis of Survey
samples of drinking water wells and questionnaires were of a known and useful
quality.
Quality assurance/quality control is a system of activities for ensuring the
reliability and validity of data. EPA's QA programs, upon which the NPS QA program
is based, provide Agency decision-makers with data that meet specified standards.
QA refers to the overall management activities conducted to ensure that a project
meets the agreed-upon quality standards. QC refers to the operational-level
management activities conducted to ensure these same standards. Comprehensive
QA/QC activities were carried out throughout the Survey and were managed by a full-
time QA officer. Prior to the implementation of the Survey, QA/QC activities included
determining acceptable quality standards and developing quality assurance plans,
standard operating procedures, and training programs. During the Survey, these
activities included field and laboratory audits, and day-by-day monitoring of well
sampling and laboratory analysis. In addition, to produce reliable and unbiased
Survey results, EPA conducted continuous oversight and evaluation of laboratory
results and field data
QA/QC systems and procedures were implemented for each element of the
Survey - design, field sampling, laboratory analysis, and data management. These
elements are discussed below.
QA/QC In Survey Design. EPA's overall Survey design was independently
reviewed by experts to ensure that it would produce reliable and statisticalry valid data
EPA tested the Survey design, as well as field sampling and analytical methods,
through a pilot study conducted in three States prior to initiation of the full Survey.
The Survey design was also given a scientific peer review by a special subpanel of the
Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel
NPS Quality AitunncefQumltty Control
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Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel
(SAP). The ten-member SAP subpanel reviewed the cveraH Survey design and the
findings of the pilot study. The subpanel commented on tour broad areas of the
design: data collection, well selection for community water systems, effects of
temporal variation on sampling, and anatyte stability. In each of these areas, the
subpanel made recommendations for improving or refining the Survey design. EPA
reviewed and evaluated the subpanel's recommendations and made appropriate
changes.
QA/QC In the Field. EPA developed and implemented extensive QA/OC
procedures for field activities to ensure that water sampling and data collection were
conducted according to specific Standard Operating Procedures (SOPs). All State
and contractor personnel involved in the NPS were fully trained before undertaking
field activities such as sampling and interviewing. Samplers administered specially
designed questionnaires to obtain information about weU construction, pesticide use,
and land use in the surrounding area from well owners, operators, and county
agricultural extension agents. To respond quickly to any sampling questions or
problems, EPA set up a telephone hotline for samplers and Survey participants. EPA
also conducted audits at a number of field sampling sites to assess the effectiveness
of the QC procedures. These audits helped to identify problems or inconsistencies
with the SOPs and maintain a high level of quality throughout the sampling phase of
the Survey. To enhance further the quality of the Survey, EPA's contractors
periodically conducted audits on their own internal operations by their QA personnel
and performed routine quality control checks of field operations,
QA/QC In the Laboratory. Each laboratory selected for the NPS had to
satisfy certain QA/QC criteria In addition to having to meet rigorous standards for
initial selection as an NPS analytical laboratory, each laboratory also had to maintain
the highest analytical chemistry standards throughout the Survey. Day-to-day QA/OC
activities included analysis of method blanks (a portion of reagent water analyzed as if
it were a water sample), shipping blanks (reagent water transferred to a sampling
bottle, shipped to the field, and returned to the laboratory with the samples), spiked
samples (samples to which a known amount of anatyte is added), and instrument and
laboratory control standards. In addition, two EPA laboratories analyzed duplicate
samples for approximately ten percent of the total samples collected and provided
overflow relief to the primary contract laboratories. All of the laboratories were
required to obtain analytical standards from NPS, report results in a standardized
format, and pass an automated audit for compliance with QC criteria for all data sets.
Audits were conducted periodically to check that all laboratory procedures and
instrumentation were accurate and properly maintained, that the laboratories were
following the established operating standards, and that data could be tracked and
verified from sample collection to the final reporting of results. Performance evaluation
studies were conducted to verify the laboratories' on-going analytical capabilities.
QA/QC In Data Management Data management for the NPS was
conducted using the NPS Information System (NPSIS), a computerized management
information system. NPSIS was used to develop and monitor sampling schedules,
track samples, record data generate reports, and provide a communications link
between the laboratories and the contractor in charge of coordinating the Survey's
implementation.
All information obtained from questionnaires was checked for completeness and
accuracy. NPS staff made follow-up cafls to questionnaire respondents to complete
missing information or to confirm responses that appeared to be incorrect. The
Survey staff used a standard statistical approach to account for the unavailable,
inconsistent, and out-of-range information. All data from the questionnaires were
Control
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Problems
Identified and
Corrected
through
QA/QC
Summary
entered into the NPSIS twice and compared, using a computer software program, to
control for data entry errors. QA for data entry was implemented through the
performance of random audits of the data entry process. After completion of all
QA/QC checks, the data were transferred to NPSIS.
The NPS quality assurance program identified and corrected potential problems
that could have affected data quality. Quality control checks and quality assurance
audits worked together to ensure that sampling, data collection, and laboratory
analysis continued on schedule and that field and laboratory staff followed specific
procedures. Rigorous reviews and quality assurance audits at each phase of the
Survey - initial planning and design, the pilot study, the full Survey, and data
analysis - assisted management staff in monitoring the progress of the Survey to
prevent problems that could compromise data quality. For example, EPA revised the
Survey design, based on the pilot study results and SAP recommendations, to correct
implementation problems by:
• adopting a two-stage design for identifying community water system
wells;
• allocating sampling randomly within the Survey schedule to minimize the
possibility of seasonally-induced bias;
• dropping the laboratory method for volatile organic compounds due to
problems with sample aeration under Survey conditions; and
• expanding the Survey's questionnaires to collect additional information on
well characteristics, cropping, and pesticide use.
The Survey's QA program also provided criticaJ information that prevented
serious data losses during sampling and data collection. These situations were rare
and were corrected immediately. For example, early in the Survey QA staff identified
that the laboratories were receiving an overload of samples. If this problem had not
been discovered and resolved, sample data and analysis results would have been
lost EPA quickly provided analytic support to the laboratories and corrected sample
storage procedures. EPA also identified trace amounts of chlorine in some well water
samples, which adversely affects detecting pesticides. In response, EPA quickly
initiated additional procedures to test for chlorine in the field as well as in the primary
laboratories.
Quality assurance staff identified other technical problems such as incorrect
interpretation of questionnaire terms, an inaccurate instrument calibration standard,
and inappropriate delays in computer database backups. Again, as a result of early
detection, these minor problems were corrected before serious loss of information or
data quality occurred.
EPA was diligent in supporting and implementing a quality assurance program
for the NPS. The Survey's key QA/QC elements - expert review, pilot studies, training,
specific standard operating procedures, detailed quality assurance plans for each
major phase of the study, and routine audits - are now recognized throughout EPA as
models for other EPA studies. The direct benefit for the policy analysts, scientists, and
others who will use NPS results is an information base of documented, consistent,
high quality data on drinking water wells, pesticide use, and ground-water vulnerability.
NPS Quality AMuranc«/Ou»/fty Control
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When to Go
for More
Information
This fact sheet is pan of a series of NPS outreach materials, fact sheets and
reports. The following additional fact sheets are available through EPA's Public
Information Center (401 M Street SW, Washington DC 20460, 202-382-2080):
Project Summary
Analytical Method*
foot Sheet for aach
detected anafyta
Summary Ratultt
Survay Anatytai
How EPA Will Una
The NPS ftetuAt
Survey Des/gn
G/o**an/
Additional information on the Survey and on pesticides in general can be
obtained from the following sources:
U.S. EPA Safe Drinking Water Hotline
1-800-426-4791 (In Washington, DC - 382-5533)
Monday-Friday, 8:30 am to 4:30 pm Eastern Time
National Pesticide Telecommunications Network
1-800-858-7378
24 hours a day
U.S. EPA Office of Pesticide Programs (OPP) Docket
Public Information Branch (H7506C)
401 M Street, SW
Washington, DC 20460
Telephone: (703) 557-2805
National Technical Information Service (NTIS)
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
Information on regulation of
pesticides in drinking
water
Information on health
effects and safe
handling of pesticides
Background documents
for Survey (available
for review)
Copies of the
NPS Phase I Report
(available 1991) and
NPS Phase II Report
(when available)
If you are concerned about the presence of pesticides and nitrate in your private water
well, contact your local or State health department. Other experts in your State
environmental agency or agriculture and heaJth department may also be helpful to
you. If you receive your drinking water from a community water system and have
questions about your water quality, contact your local community water system
owner/operator or the State water supply agency.
NPS Qutltty Ae«urenc«/Oua//ry Control
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