United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S4-87/019Sept. 1987
x°/EPA Project Summary
Quality Assurance Audits of the
EPA State-Operated Precipitation
Collection Network
W. Gary Eaton and Berne I. Bennett
Networks that collect and quantify
the constituents of precipitation in the
United States have increased in number
and size in recent years. Eleven states
presently participate in the EPA-spon-
sored State-Operated Precipitation
Network that collects weekly samples
at 27 locations. As networks have
grown, so have the development and
application of quality assurance con-
siderations to ensure that accurate,
precise, complete, and representative
data are obtained.
Quality assurance protocols for sys-
tem and performance audits of the
State-Operated Network (SON) of wet
deposition collection sites are outlined.
The protocols address site characteris-
tics, training, precipitation collection
and measurement equipment, sample
retrieval and handling, system audits,
and the use of simulated precipitation
test solutions in performance audits.
Results from quality assurance studies
by Research Triangle Institute in 1985
and 1986 of the 27-site SON sites and
recommendations for corrective action
are given.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering In-
formation at back).
Introduction
In response to the need for data to
determine the extent and nature of acidic
precipitation, wet deposition collection
networks in the United States have grown
in number and size in the last decade. As
the networks have grown, so has the
development of protocols and procedures
for external quality assurance. Benefits
of quality assurance studies of networks
include assuring that established proto-
cols for siting, sample collection, and
analysis are being followed; identifing
non-complying equipment to be fixed and
operators who need further training; pro-
viding a means of documenting the data
base with respect to accuracy, precision,
completeness, and representativeness;
and allowing the data quality of several
networks to be compared in a systematic
way.
The 27-site SON has been in place
since 1982. The full report describes
quality assurance procedures established
for this network and gives results of
1985 and 1986 site visits. Recommenda-
tions for improvement are also given. The
procedures are similar to those developed
and applied earlier by two other networks:
the Utility Acid Precipitation Study Pro-
gram, (UAPSP), that collects on a daily
basis1 and the National Atmospheric
Deposition Program/National Trends
Network, (NADP/NTN), that collects
weekly samples2.
Procedures
Adherence to established siting guide-
lines is checked by comparing each site's
installation and nearby surroundings to
criteria given in urban- or regionally-
sited station checklists designed expressly
for the State-Operated Network. These
checklists are given in the full report.
Important criteria common to either type
station are: (a) type and height of nearby
groundcover; (b) distance of collector and
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rain gauge from obstructions; (c) distance
of the collector from sources of con-
tamination and pollution; (d) proximity of
human or animal activities to the collector;
and (e) nearby land and water features.
During the visit the following system
audit topics are reviewed: (a) sample col-
lection equipment and procedures (in-
cluding plastic bag bucket liners used in
the SON); (b) site laboratory facilities and
cleanliness; (c) analysis procedures; (d)
communication and recordkeeping; and
(e) quality control tests and corrective
action procedures. Technical assistance
is provided whenever an operator is un-
certain of procedures or when equipment
needs maintenance or calibration.
The accuracy of response of each site's
collection and measurement devices is
tested during the visit. The performance
audit techniques and designated toler-
ances for the SON are described in Table
1.
Results and Discussion
Siting Criteria Checks
At least one variation from the desig-
nated siting criteria was found for most
of the SON sites. Many were minor and
should have negligible effect on the
physical and chemical data base. The
most important siting exceptions are
noted below.
Collector/rain gauge obstructions
Several collectors and gauges were
near enough to trees, towers, or other
equipment such that the object projected
onto the collector at greater than a 45
degree angle. Since the sample catch
and chemistry could be affected by this, it
was recommended that the samplers be
slightly repositioned or that the obstruc-
tions be removed.
Proximity to sources
Several sites had sources nearby al-
though the criterion for collector/source
separation was minimally satisfied.
Examples include asphalt plant, animal
stockade, and salt water. It was recom-
mended that data users be made aware
of these facts and that the site be moved
or the source removed if possible.
Collector and rain gauge
positioning
Ideally the collector and rain gauge
orifices should be at the same height
above ground (~1 m) and be separated by
at least 5 but no more than 30 m. Several
sites had the collector and gauge posi-
tioned within 1 m of each other in the
horizontal; others were separated by
several meters in the vertical dimension.
It was recommended that the rain gauges
be repositioned and inoperative gauges
be repaired or replaced.
System Audits
System checks were made of the
precipitation collector, the rain gauge,
sample collection procedures, and the
field laboratory. Results are noted below.
Precipitation collector
Eleven of 27 collectors were higher
above ground than the prescribed one
meter. This exception was due to place-
ment on platforms or roofs to avoid
snowpack, for security, and to avoid ob-
structions. The effect on the sample is
thought to be minimal. Ten collectors
were installed with the wet bucket facing
N or E rather than the prescribed W. If
rainstorms approach predominantly from
the S or SW, the collector itself may
influence the collection process. Eight
collectors lacked the event marker cap-
ability. Knowing when and for how long
the collector is open is an important
quality control consideration. All but two
sites had properly seating bucket covers.
A dry-site bucket was missing at one site;
another site had a deteriorated liner.
Proper seating is necessary to keep out
dust.
Rain gauge
Variations from the desired distance
from the collector and height with respect
to the collector were noted at about half
of the sites. Six sites do not have record-
Table 1. Audit Techniques and Tolerance Limits For Collection and Measurement Methods
Audit Technique or Test
Measurement Device and
Audit Observable
Expected Results
1. Recording Rain Gauge
- Accuracy of precipitation depth on gauge
2. Precipitation Collector
- Lid liner-bucket-rim seal
- Sensor activation and heating
- Use calibration weights simulating
precipitation.
- Determine lid drop distance
(Bucket in - bucket out).
- Observe open/close cycle. Determine
temperature with thermistor 5 min. after
activation.
Agreement within ±0.10 inch of audit weight.
- Distance >3 mm.
- Ambient temperature, prior to activation.
Temperature of50-70°C attained after
activation.
3. Conductivity Meter
- Accuracy of response to simulatd
precipitation samples
- Deionized water quality
4. pH Meter
- Accuracy of response to simulated
precipitation samples
5. Mass by Solution Balance
- Accuracy of response to calibrated weights
• Have operator determine conductivity of
simulated sample.
- Have operator determine.
Have operator determine pH of
simulated precipitation sample.
Have operator determine mass of
weights in the range 800 g to 330O g.
Agreement within ± 4 nS/cm.
- Conductivity <10 nS/cm.
- Agreement within ±0.1 pH unit of established
value.
- Agreement within ±5 g of stated mass.
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ing rain gauges; several sites had mal-
functioning tipping bucket gauges.
Same collection procedures
Proper sample collection procedures
were followed in virtually all instances. It
was noted that not all operators visually
check the sample for contamination
before returning it to the field laboratory.
It was recommended that this be done;
otherwise contaminants may dissolve and
be unnoticeable later.
Field laboratory
The field laboratories had adequate
space, were clean, and temperature-con-
trolled. Operators and analysts were
trained and familiar with their duties.
Variations in measurement technique
were noted and discussed. It was recom-
mended that smaller sample aliquots be
used, that the network's central laboratory
have first priority for samples, and that
samples be shipped within three days of
collection.
Performance Audits
Performance evaluations were made
of the rain gauge; the precipitation col-
lector; and the pH meter, conductivity
cell, and solution balance. Results are
given in Table 2 and discussed briefly
here.
Rain gauge
All 13 weighing-type recording rain
gauges agreed within 0.1 inch of the
designated audit value over the range 0
to 5 inches. Eight of the 13 gauges were
out of tolerance above 5 inches. However,
this is a seldom-used range as the guage
bucket is usually emptied before this
depth is reached. Most of the gauges
were recalibrated to meet specifications.
Precipitation collector
All collectors operated when the sensor
was activated. The lid-liner/bucket rim
seal was adequate. Several problems
were noted with sensor temperature
range and control. If the sensor does not
heat during and immediately following a
rain, the collector's bucket cover will not
close promptly and contamination of the
sample by dust or debris may occur.
Conductivity meter
Meter readings at 3 of 20 field labora-
tories varied by more than 4 fiS/cm from
the designated value of the audit solution.
Results were quite acceptable otherwise.
The quality of deionized water in use at
the sites also met specifications.
pH meter
Only 2 of 21 field laboratories had pH
results that varied by more than 0.1 pH
unit from the designated value. The
average absolute variation was 0.054 pH
unit.
Mass
Sixteen of the 19 balances checked
agreed within 1 g of the designated value
at a loading of 1646 g. The worst case
was a 10 g variation corresponding to 1.2
percent at an 823 g loading or 0.3 percent
at a 3292 g loading.
Conclusions
The EPA-sponsored SON is a weekly
precipitation collection network of 27 sites
located primarily in the eastern and
southeastern United States. State
agencies have provided personnel to ser-
vice the sites and laboratories and to
analyze and submit samples to a central
laboratory for analysis. The site super-
visors, operators, and analysts were
familiar with their duties, handled the
precipitation samples carefully, analyzed
the samples accurately in most cases,
and seemed genuinely interested in the
network and the data.
Several of the sites should be improved
upon in terms of siting and maintenance
of sample collection and analysis equip-
ment. Emphasis should be placed on
proper placement and operation of pre-
cipitation collectors, installation and
TaWe 2. Performance Audit Results: EPA State-Operated Network, 1985-1986
Measurement Device Audited
Number
Audited
flange of Response;
Average Response
Comments
1. Rain Gauge
- accuracy of precipitation depth
2. Precipitation Collector
-lid liner/bucket rim seal
- sensor activation and heating
3. Conductivity Meter
- accuracy of response
- deionized water quality
4. pH Meter
- accuracy of response
5. Solution Balance Mass
- accuracy of response
13 All within ±0.1 inch from OtoS
inches.
16 Range 7 to 33 mm; avg. 13.6 mm.
27 All respond and open collector.
Range 23 - 100°C; avg. 55°C.
20 0.3 to 5.80 nS/cm; " avg. 1.63
±7.3
14 0.35 to 3.80 nS/cm; avg. 1.75
21
19
0.01 to 0.18 pH unit;' avg. 0.054
± 0.04 pH unit.
Out-of-tolerance readings occurred on 8 of 13
but only at 6 inches or greater depth, a seldom-
used range.
All met 3 mm criterion of acceptability.
Eight heated at all times. Six did not heat.
Twenty-one heat; of these 10 attain temperature
<50°C. three > 70°C.
EPA performance audit sample; value is 20 or 24
EPA performance audit samples; designated
value is 4.28 or 4.39 pH units.
16 of 19 agree within ±1 gat 1646 17 of 19 are accurate within ± 5g over 823 to
g loading. 3292 g range. All are within ±10 g agreement.
' Range of differences where difference = \ (site value) - (designated value) \.
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proper operation of rain gauges, and
standardization of field laboratory
techniques.
References
1. W. C. Eaton, K. A. Daum, E. D. Estes,
and F. Smith, "Quality Assurance
Results for the Utility Acid Precipitation
Study Program (UAPSP), 1982 to
1984," Transactions: Quality Assur-
ance in Air Pollution Measurements,
APCA Publication TR-3, Pittsburgh, PA
(1985), pp. 488-499.
2. D. S. Bigelow, "Quality Assurance
Report; NADP/NTN Deposition Moni-
toring. Field Operations, July 1978
through December 1983." National
Atmospheric Deposition Program,
Coordinator's Office, NREL, Colorado
State University, Fort Collins, CO,
(August 1986).
W. Gary Eaton is with Research Triangle Institute, Research Triangle Park. NC
27709; and the EPA author, Berne I. Bennett (also the EPA Project Officer,
see below), is with Environmental Monitoring Systems Laboratory, Research
Triangle Park, NC 27711.
The complete report entitled "Quality Assurance Audits of the EPA State-
Operated Precipitation Collection Network," fOrder No. PB 87-208 740/AS;
Cost: $13.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S4-87/019
0000329 PS
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