United States
Environmental Protection
Agency
Research and Development
Environmental Monitoring
Systems Laboratory
Research Triangle Park, NC 27711
EPA/600/S4-87/036 Jan. 1988
&EPA Project Summary
Summary Report for the
National Atmospheric
Deposition Program/National
Trends Network (NADP/NTN)
Site Visitation Program -
December 1984 through
September 1986
W. Gary Eaton, Curtis E. Moore, Dan A. Ward, and Berne I. Bennett
The proper collection of
precipitation and the accurate
measurement of its constituents are
important steps in attaining a better
understanding of the distribution and
effects of "acid rain" in the United
States. NAPAP Task Group IV project
4A-15, "Quality Assurance Support
for Wet Deposition Monitoring" is
sponsored by EPA to evaluate the
sample collection process of the
NADP/NTN networks through a site
visitation program.
This document is a summary
report of the findings from the 1985-
1986 Site Visitation Program to the
195 sites that comprise the National
Atmospheric Deposition Program
and National Trends Network
precipitation networks, referred to
collectively as the NADP/NTN
network. The visits were conducted
by Research Triangle Institute.
Protocols and procedures
followed in conducting the site visits
are described. Results of systems
and performance audits are
discussed for siting, collection
equipment, and the field support
laboratories.
Where exceptions are found, the
potential effects of nonstandard
siting, improperly operating
equipment, and improper sample
handling or analysis technique on the
data base are discussed.
Recommendations are given for
improvement and standardization of
individual sites and the network as a
whole.
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 documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Wet deposition collection networks in
the United States have grown in number
and size in the last decade in response to
the need for data to determine the extent
and nature of acidic precipitation. As the
networks have grown, so has the
development of protocols and procedures
for quality assurance assistance through
site visitation programs. The goals of the
visitation program to the NADP/NTN
collection sites are to:
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(1) Provide a qualitative assess-
ment of each site and its
surroundings, the operator's
adherence to sample collection
and analysis procedures, and
the condition of the site's
collection and analysis
equipment through an on-site
systems survey;
(2) Provide a quantitative
assessment of the operation of
the precipitation collector and
the accuracy of response of field
and laboratory measurement
devices for precipitation depth,
mass, temperature, conductivity,
and pH through an on-site
performance survey;
(3) Provide technical assistance to
the operator by verbal
explanation, minor trouble-
shooting, repair and calibration
of equipment, and by making
recommendations for sources of
corrective action;
(4) Prepare brief reports for each
site detailing site characteristics,
results of quality assurance
tests, and technical assistance
provided;
(5) Computerize results of all
information gathered from each
site and submit this to the
NADP NTN Quality Assurance
Manager on a quarterly basis;
and
(6) Document the sites and their
surroundings by assembling a
collection of site maps and color
photographs.
This Project Summary describes
procedures and results from quality
assurance visits made to the sites in
1985 and 1986. Recommendations for
improvement are also given.
Procedures
Each NADP NTN site was to be
visited once in a two-year period. About
one-half of the 1985 sites were visited
each year during the period 1985-1986.
Prior to the scheduling of site visits, RTI
consulted with the NADP/NTN Quality
Assurance Manager and CAL personnel
to determine which sites, if any, should
be seen on a priority basis. Whenever
possible, visits were planned so that
several sites in the same vicinity could
be seen in the same trip. A listing of the
activities carried out in preparation for,
conduct of, and reporting of a site visit is
given in Figure 1.
Systems Survey
A quality assurance systems survey
was conducted at each site to
qualitatively assess the site, its
surroundings, and the operator's
adherence to procedures specified in the
NADP NTN site operator's instruction
manuals1.2 and the NTN design
document3. The operator was asked to
demonstrate sample collection and
analysis procedures. These were
observed with special attention given to
calibration procedures and sample
handling technique. Site equipment was
examined for signs of wear or faulty
operation. It was noted whether solutions
and equipment were properly stored. Site
logbooks and rain gauge charts were
examined for legibility, completeness,
and accuracy. Photographs of the site
were taken.
Performance Survey
A quantitative performance survey
was conducted at each site. Table 1 lists
the equipment that was checked fo
performance and the type of test used.
Criteria for evaluating performance are
specified in the NADP Quality Assurance
IV.
SELECT SITE FOR VISIT AND INITIAL COMMUNICATIONS
Advise QA manager, CAL, s/te sponsor of plans: request site information: receive go-ahead
Contact site supervisor, site operator
Send letter of confirmation to supervisor, operator
Advise EPA that trip plans are complete
RE-TRIP PREPARATION
Make travel arrangements (air, car, hotel)
Prepare and test quality assurance materials
Review site-specific quality control information (maps, OC test results, etc.)
Check equipment and supplies
Prepare site visit notebooks with survey questionnaires
CONDUCT SITE VISIT
Outline activities to supervisor and operator
Assess site and surroundings (map, photographs, obstructions, sources)
QA tests of precipitation collector and rain gauge
Adjust or calibrate collection equipment as required
Assess operator handling and transport of collection bucket
QA tests of conductivity and pH meters, temperature, balance
Exam/nation of site records, rain gauge charts
Answer questions; provide instruction
Prepare short report; conduct exit interview
EPORTING
Short report prepared; left with supervisor or operator
Copy of short report forwarded to NADPfNTN QA manager, to CAL, and to EPA pro/ecf officer
Copy of site visit notebook sent to NADP!NTN, QA manager; file original
Questionnaire contents placed in computer file; sent to QA manager
Annual report presented to NADP.'NTN committee
Figure 1. Sequence of Site Visitation Activities
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Ian4 and report5. All survey notes and
instrument responses were recorded in
the performance survey questionnaire.
Results and Discussion
Siting Criteria Survey
Collector Height Standard. The
collector should be installed on its
standard 1-meter-high aluminum base.
The bucket height of the collector should
not exceed this standard height by more
than 0.5 m. An exception to this criterion
is permitted in areas with significant
accumulations of snow. Twenty-six
(12%) of 194 collectors checked were on
platforms. In most cases, the platforms
were short, not more than 1 m in height.
The sites were located in the snow belt.
The effect of this extra height on the
sample is believed to be minimal.
Wet Bucket Orientation. The
collector should be mounted with the
wet-side bucket to the West and the
sensor facing North. In this way, the wet
bucket is generally upwind of the dry-
side bucket and the sensor is downwind
of the wet-side bucket. One hundred
and forty collectors (72%) were correctly
installed. For the 37 collectors that were
installed with the collection bucket facing
N or E, a statistical study of the long-
term data base would be required to
discern if the collection efficiency or
sample chemistry were affected.
Ground Slope. The collector should
not be located on ground with a slope
greater than 15 degrees or 27 percent.
The slope at 33 sites (17% of the total)
exceeded this criterion. Note, however,
that all of these sites were located in
mountainous regions and the sites were
representative.
Collector and Ram Gauge at Same
Height. The heights above ground of the
collection bucket and the rain gauge
orifice should be within 0.3 m of each
other. Twenty-two sites (11%) did not
meet this criterion. In all cases, the
criterion was exceeded by small amounts
and the effect is probably negligible.
Distance from Rain Gauge. The
collector should be located within a
distance of 30 m from the rain gauge but
no closer than 5 m. Fifty-eight sites
(30%) had rain gauges less than 4.9 m
from the collector. None of the sites
exceeded the recommended separation
distance of 30 m.
Site Surroundings. Site evaluation
results relative to criteria addressing
potential pollutant sources are discussed
below.
Industry and Urban Areas — Sites
should not be located within 10 km of an
industry or urban area or within 20 km of
an upwind industry or urban area. Based
on the site visitor's best estimates, 54
sites (28%) were too close to industries
and 42 sites (22%) were too near cities
with respect to the siting criteria. The
impact of these influences will vary
considerably. It is difficult to assess the
impact of these siting criteria variances
on the data base.
Grazing Animals or Feedlots --
Site should be more than 30 m from
grazing animals and more than 500 m
from feedlots, dairy farms, or poultry
farms. Thirty-one of the sites (16%)
were too near such sources.
Vegetation within 30 m and the 45
Degree Rule -- Vegetation within 30 m
of the collector should not be more than
two feet tall and no object should project
on the collector from an angle greater
than 45 degrees. The most frequent
exception was the occurrence of
broomstraw at or just above the 2-ft.
height limit. This is not considered a
major source of sample bias. Eighteen
sites (9%) had trees or meteorological
towers too near the collectors.
Parking Lots, Transit Sources, or
Chemical Storage — The site should
not be within 100 m of chemical storage
facilities, parking lots, or transit sources.
Thirty-six sites (18%) did not meet
these criteria.
Equipment And Sample
Collection Survey
System and performance checks
were made at each site to assess the
operational fitness of the Aerochem
Metrics precipitation collector and the
Belfort rain gauge The process of
sample retrieval and care was also
examined.
Precipitation Collector System
Checks. The precipitation collector
should be level. Only 13 collectors (7%)
were slightly unlevel. The effect of this
variance on collection efficiency is
probably not measurable. The collector's
sensor should be clean. Only six
collector sensors were dirty. Thirty
collectors (15%) had evidence of
excessive clutch wear. This is one of the
clearer indications that a site's data set
may be incomplete. The usual result of
clutch slippage is that a sample is not
collected because the cover fails to
move off the wet bucket at the start of a
precipitation event.
Precipitation Collector Performance
Checks. The collector's bucket cover
should fit tightly and evenly on the rim of
the wet (and dry) bucket so that dust
cannot enter during dry periods. Only
four collectors were noted to have
bucket-lid seal problems. A measure of
adequate lid/bucket seal tension is the lid
drop distance -- the distance the lid
drops when the wet bucket is
momentarily removed. A distance of 3
mm or greater is required to give good,
dust-free seals. Of 167 site collectors
checked, only four (2%) had lid drops of
3 mm or less.
The temperature of the precipitation
collector sensor should be at ambient
level when there is no precipitation
unless the ambient air temperature is
below 4°C, during which time the low
power sensor heater should come on to
melt ice or snow. When precipitation
occurs, the high power heater should
come on and sensor temperature should
rise to about 50 to 70°C within 10
minutes. Thirty-two collector sensors
(16%) were found to have malfunctioning
sensor heaters based on one or more of
the above performance characteristics.
Rain Gauge System Checks. The
rain gauge should be level. Fifteen rain
gauges (8%) were off level by small
amounts. The chart recorder should
indicate the correct time within one hour.
Recorders were off by more than 1 hour
at 12 sites (6%). The damping fluid
reservoir should be filled to reduce pen
"noise" created by strong winds. The
damping fluid levels were low at 29 sites
(15%).
Rain Gauge Performance Check.
Rain gauge calibration was checked
using Belfort gauge calibration weights.
One hundred and one of 195 gauges
were in calibration (within ± 0.1 inch) up
to at least 10 inches of rain. Sixty-nine
gauges had calibration errors in the 0 to
6 inch range but of these, only 19 were
out of calibration below four inches.
Because most rain amounts are
measured in the 0 to 4 inch range and
because the depth is measured as the
difference in chart reading before and
after the event, few measurable errors in
precipitation depth measurements are
expected due to inaccurate rain gauge
calibration.
Sample Collection Procedures. Most
operators were using proper collection
procedures and no instances of
contamination were noted. The most
frequently neglected procedure was the
check of the bucket and sample for
contamination during the visit to the site.
Another check that was not done with
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Tato/e 1. NADP/NTN Site Measurements and Performance Survey Methods
Site Measurement Measurement Device Performance Survey Method
Designated Performance Criteria
Rain depth
Precipitation sample collection
Mass
pH
Conductivity
Rain gauge (Belfort) Challenge with known weights that
simulate depth.
Precipitation collector (Aerochem Measure resistance across
Metrics)
Triple beam balance
pH meter and electrode
Conductivity meter and cell
sensor, measure tension and
drop of bucket lid, measure
temperature and voltage of
activated sensor.
Challenge with traceable weights.
Challenge with simulated
precipitation sample of known
pH.
Challenge with simulated
precipitation sample of known
pH.
Agreement within ± 0.1 inch of
test weight value.
Lid drop distance > 3mm.
Sensor temperature ambient
prior to activation; temperature of
50 - 70 "C after activation.
Agreement within ±5 g of test
weight value.
Agreement within ±0.1 pH unit of
test solution's designated value.
Agreement within ± 4^S/cm of
test solution's designated value.
regularity was to ascertain if the sensor
heater is working five minutes after
activation by touching the baseplate
lightly with a finger.
Field Laboratory Survey
Systems Check of Field Laboratory.
Laboratories that support the field
collection sites were generally clean with
adequate space and temperature control.
Required records were kept and report
forms were filled out correctly in all but a
few cases.
pH and Conductivity Measurement
Techniques. Field personnel were
observed while making pH and
conductivity measurements and key
elements of their technique were noted.
In general, specified procedures were
adhered to and laboratory technique was
good.
Results of Field Site Analysis of
Simulated Precipitation. Each field
laboratory was asked to analyze a
performance audit solution for
conductivity and pH. These solutions
were prepared by dilution of EPA-
supplied performance test solutions; the
audit value is that designated by EPA.
Designated quality limits are ± 0.1 unit
for pH and ±4pS/cm for conductivity.
Eighty-seven percent of the laboratories
had pH results within ±0.1 unit of the
designated value. Ninety-five percent
obtained conductivity values which did
not vary by more than ±4pS/cm from
the designated value.
Laboratory Balance Results. The
balances were checked with weights
ranging from 800 to 3200 grams.
Ninety-seven percent of the sites had
errors of less than 5 grams over the
range of test weights. In terms of
precipitation, this translates into a
measurement error of less than 0.003
inch of rain.
Conclusions
Siting
All 195 sites had at least one
variance with respect to siting criteria.
Most of the variances, due to the nature
of certain criteria and/or the degree to
which the criteria were exceeded, are
expected to have minimal effects on the
data base. Variances with respect to
pollutant sources may have measurable
effects on the data, but because the
type, magnitude, and proximity of the
sources vary widely from site to site, a
measure of the effects is not possible
from the data gathered in this site
visitation program.
Sample Collection
Designated sample collection
procedures are adhered to at almost all
the sites in the network. To ensure
accurate precipitation data, it is most
important that the precipitation collector
and rain gauge are properly working and
well-maintained. A properly working
precipitation collector should uncover the
wet bucket at the beginning of a
precipitation event, recover the wet
bucket shortly after the event stops, and
keep dust, etc. out of the wet bucket
when there is no precipitation. There
were indications at 66 sites that the
Aerochem Metrics precipitation collectors
could not properly perform all these
functions.
Field Laboratory Procedures
For the most part, correct
procedures were used by operators,
especially those who had attended the
field operations training course. Eighty-
seven percent of the sites agreed with
the audit solution's designated pH value
within ± 0.1 pH unit. Ability to measure
conductivity accurately within ±4u.S/cm
was outstanding; ninety-five percent of
the sites were within ± 4 u.S/cm of the
audit solution's designated conductivity
value. The precipitation collector and rain
gauge are central to the successful
operation of the network. Based on noted
problems with collector operation and
rain gauge calibration, it is recommended
that the importance of weekly equipment
checks, such as sensor heater operation,
be re-emphasized to site operators. It is
also recommended that a calibratio
check of the rain gauge be instituted and
carried out every six months with a copy
of the gauge chart used for the check
forwarded to the central analytical
laboratory.
Sample collection procedures are
generally well understood and adhered to
across the network. One procedure,
inspection for sample contamination at
the site, is frequently omitted. The
importance of this check should be
restated to site operators.
It was observed that those site
operators who had attended the field
operations training course generally had
a better understanding of procedures. It
is recommended that this course be
continued and that site operators be
encouraged to attend.
References
1. Bigelow, D. S. NADP Instruction
Manual-Site Operation, National
Atmospheric Deposition Program, Ft.
Collins, CO. (January 1982).
2. Bigelow, D. S. Instruction Manual:
NADP/NTN Site Selection and
Installation, National Atmospheric
Deposition Program, Ft. Collins, CO
(July 1984).
3. Robertson, J. K. and J. W. Wilson.
Design of the National Trends
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Network for Monitoring the
Chemistry of Atmospheric
Precipitation, U.S. Geological Survey
Circular 964 (1985).
The NADP Quality Assurance Plan,
NADP Quality Assurance Steering
Committee (1984).
Bigelow, D. S. Quality Assurance
Report: NADP NTN Deposition
Monitoring. Field Operations, July
1978 through December, 1983.
National Atmospheric Deposition
Program, Coordinator's Office.
NREL, Colorado State University,
Fort Collins, CO. (August 1986).
W. Cary Eaton, Curtis. E. Moore, and Dan A. Ward are with Research Triangle
Institute, Research Triangle Park, NC 27709; the EPA author Berne f. Bennett
(also the EPA Project Officer, see below) is with the Environmental Monitoring
Systems Laboratory, Research Triangle Park, NC 27711.
The complete report, entitled "Summary Report for the National Atmospheric
Deposition Program A/a ton al Trends Network (NADPINTN) Site Visitation
Program (December 1984 through September 1986)," (Order No. PB 88-132
519HAS: Cost: $19.95, sub/eel 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
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