United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-92/152 October 1992
EPA Project Summary
Summary Report for the National
Atmospheric Deposition
Program/National Trends
Network (NADP/NTN) Site
Visitation Program for the Period
October 1988 through
September 1989
W.C. Eaton, C.E. Moore, R.W. Murdoch, R.C. Shores, D.A. Ward, C.O.
Whitaker, and R.L. Lampe
The proper collection of precipitation
and the accurate measurement of its
constituents are important steps in at-
taining a better understanding of the
distribution and effects of "acid rain"
in the United States. One of the major
programs of the National Acid Precipi-
tation Assessment Program (NAPAP)
Task Group IV concerns wet deposi-
tion monitoring. One of that program's
projects, 4A-15, "Quality Assurance
Support for Wet Deposition Monitor-
ing," is sponsored by the U.S. Environ-
mental Protection Agency (EPA) to
evaluate the sample collection process
and provide technical assistance to the
NADP/NTN network through a site visi-
tation program. Research Triangle In-
stitute, as contractor to EPA, conducts
these visits. If deficiencies or nonstand-
ard procedures are noted, the site op-
erator and supervisor are notified. Brief
reports are sent to the EPA Project
Officer, the NADP/NTN Quality Assur-
ance Manager, and others. In this way,
necessary changes can be made
promptly.
All NADP/NTN sites were visited in
1985-1986. A second round of visits
began in October 1986, with the goal of
visiting approximately one-third of the
200 sites each year over the next three
years. This document is a summary
report of the findings from the 1988-
1989 (Fiscal Year 1989) site visitation
program to 72 of the sites of the NADP/
NTN network. In its present configura-
tion, the network's research and moni-
toring programs are supported and op-
erated by the U.S. Geological Survey;
State Agricultural Experiment Stations;
the Departments of Agriculture, the In-
terior, Commerce, and Energy; and
EPA. Additional support is provided by
state agencies, public utilities, and in-
dustries.
Protocols and procedures followed
in conducting the site visits are de-
scribed. Results of systems and per-
formance audits are discussed for sit-
ing, collection equipment, and the field
support laboratories. Where exceptions
are found, the potential effects of non-
standard siting, improperly operating
equipment, and improper sample han-
dling or analysis technique on the da-
tabase are discussed.
This report was submitted in partial
fulfillment of EPA Contract No. 68-D8-
0001 by Research Triangle Institute.
This report covers site visits made dur-
ing the period October 1,1988, through
September 30,1989. All work was com-
pleted as of September 30,1989.
This Project Summary was developed
by EPA's Atmospheric Research and
Exposure Assessment Laboratory, Re-
search Triangle Park, NC, to announce
Printed on Recycled Paper
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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
The main report summarizes quality as-
surance assistance and findings from site
visits made to the National Atmospheric
Deposition Program/National Trends Net-
work (NADP/NTN) precipitation collection
stations for the period October 1988
through September 1989. Each site is lo-
cated and operated according to proto-
cols and procedures as given in the siting
and operating manuals for the networks.
The purposes of the site visitation pro-
gram, sponsored by the U.S. Environmen-
tal Protection Agency (EPA), are to verify
that each site Is operating within control
limits and according to established proce-
dures, and to provide technical assistance
as required.
Seventy-two of the 199 sites (with du-
plicate sites bringing the total to 208) that
were in operation during 1989 were vis-
ited during this timeframe. Figure 1 shows
the NADP/NTN site locations.
Goals of the Site Visitation
Program
The goals of the site visitation program
for quality assurance assistance to the
NADP/NTN collection sites are sis follows:
1. Provide a qualitative assessment of
each site and its surroundings, the
operator's adherence to sample col-
lection 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 col-
lector and the accuracy of response
of field and laboratory measurement
devices for precipitation depth, mass,
temperature, conductivity, and pH
through an on-site performance sur-
vey;
3. Provide technical assistance to the
operator by verbal explanation, minor
troubleshooting, repair and calibration
of equipment, and by making recom-
mendations for sources of corrective
action;
4. Prepare brief reports for each site
detailing site characteristics, results
of quality assurance tests, and tech-
nical assistance provided. Submit the
reports to the NADP/NTN Quality As-
surance Manager, the Central Ana-
lytical Laboratory's Site Liaison, and
the EPA Project Officer;
5. Computerize results of information
gathered from each site and submit
this to the NADP/NTN quality Assur-
ance Manager on an annual basis;
6. Document the sites and their sur-
roundings by assembling a collection
of site maps and color photographs.
Conclusions
Seventy-two of the 199 active NADP/
NTN precipitation collection sites were vis-
ited over the one-year period, October
1988 through September 1989. About one-
third of the sites were visited during this
third year of a four-year effort. The sites
are located in all regions of the country
and are sponsored and operated by nu-
merous agencies. Each site is located ac-
NADP/NTN Monitoring Network
,^x
ME|\.
Flgun 1. Active sites In the NADP/NTN monitoring network during 1989.
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cording to established siting criteria and
operates according to published proce-
dures. This report assesses the degree to
which criteria and procedures are adhered;.
predicts, where possible, the relative im-
pact on the data that might be expected
from the variances found; and compares
results from the first round of visits to
those documented in the first round of
visits that occurred over the period De-
cember 1984 through September 1986.
Siting
Improvements in adherence to siting cri-
teria were noted at most of the sites vis-
ited in 1989 that were not in compliance
at the time of the first round of visits in
1985-1986. A number of sites had sepa-
rated the collector and rain gauge to the
prescribed 5-m distance and had oriented
the collector's wet-side bucket to the west.
Obstructions and sources of dust such as
animals, parking lots, and chemical stor-
age areas had been removed, or the site's
equipment had been moved away from
them.
For the 13 siting criteria summarized in
this report, 55 of 72 sites (76%) visited in
FY 1989 had at least one variance.
Twenty-one percent of the sites had three
or more variances. However, most of the
variances are expected to have minimal
effects on the database because of the
nature of certain criteria and/or the degree
to which the criteria were exceeded. For
example, network siting criteria require that
the precipitation collector and rain gauge
be separated by at least 5 m but not more
than 30 m. Twenty-four percent of the 72
sites did not meet this criterion, always
because of inadequate separation.
Sample Collection
Designated sample collection proce-
dures were adhered to at almost all the
sites in the network. All operators were
careful not to touch the inside of the col-
lection bucket or lid or contaminate the
sample in any way. All but one of the site
operators stated that they checked the
sample for contaminants (leaves, bird drop-
pings, etc.) at the time of the bucket's
removal from the collector. This proce-
dure was not being well adhered to at the
time of the first round of visits.
To ensure accurate precipitation data, it
is most important that the precipitation
collector and rain gauge are properly work-
ing and well maintained. All sites were
able to make a weekly equipment check.
A properly working, precipitation collector
should uncover the wet bucket at the be-
ginning of a precipitation event and re-
cover the wet bucket shortly after the event
stops to keep matter such as dust out of
the wet bucket when there is no precipita-
tion. There were indications at 17 of 72
sites (24% of the total) that the clutch on
the Aerochem Metrics precipitation collec-
tor was wearing; however, only 3 of these
17 failed to operate properly when tested
with a 1600-g load. Only 3 of 70 sensors
checked were not operating properly.
Forty-nine percent of the rain gauges (34
of 70) were found to be out of calibration
by more than ±0.1 in. at some point on
the 0-12-in. scale. This is not believed to
be a major source of error because the
calibration errors usually occurred at a
depth of 5 in. or more, and the operator is
instructed to empty the catch bucket be-
fore this depth is reached. Calibration
checks showed that 59 of the 70 gauges
(84%) met acceptable calibration criteria
(±0.1 in.) over the range of 0 to 5 in.
Field Laboratory Procedures
Field laboratory procedures for sample
handling, conductivity measurements, and
pH determinations were being carried out
properly and accurately in most cases.
Proper procedures were discussed or dem-
onstrated to site operators as needed.
Results were improved over those noted
at the time of the first round of visits. For
example, all 67 sites with operational pH
meters were able to determine the pH to
within ±0.1 unit of the designated value.
Five sites had inoperative pH meters and
could not be checked. All three of the
sites that were outside of tolerance for pH
measurements in Round 1 were within
tolerance in Round 2. Overall, 100% of
the 67 field laboratories checked in 1989
agreed within ±0.1 pH unit with the audit
solution's designated value.
For conductivity measurements, 65 of
the 67 sites checked (97%) determined
the audit solution's conductivity to within
±4 uS/cm of the designated value. Four
sites had exceeded the limit of agreement
during Round 1 visits. Five sites had mal-
functioning or broken equipment and thus
could not be audited.
The solution balances were operating
properly in all cases checked. Of 71 bal-
ances checked, more than half agreed
within ±1 g with the designated weight
over the range of 823 to 5116 g. All but
one balance agreed within ±5 g with the
designated weight over the same range.
In terms of percent variation with respect
to weight, the worst case for the 70 bal-
ances that operated with ±5 g agreement
would be ±0.4% at a loading of 823 g and
±0.1% at a loading of 4943 g.
Recom mendations
The site precipitation collector and rain
gauge are central to the successful op-
eration of the network. However, the equip-
ment in the NADP/NTN network is aging
and will require increased maintenance.
Therefore, weekly equipment checks by
the operator should continue to detect
problems as early as possible. The
collector's clutch assembly should be in-
spected for signs of wear. The failure rate
of the precipitation collector's sensor heat-
ers has greatly diminished. A simple check
of the collector's sensor heater, by acti-
vating the collector with water and, after 5
min, lightly touching the sensor surface to
verify it is heating, should continue.
A number of rain gauges were found to
be out of calibration. However, many of
those calibrated in 1985-1986 met speci-
fications in 1989. It is recommended that
a simple, on-site calibration check of the
rain gauge be carried out every six months.
A copy of the gauge chart used for the
check should be forwarded to the network's
Central Analytical Laboratory (CAL) for re-
view.
Recommendations for improving site lo-
cations center on those siting criteria that,
if violated, may affect the catch efficiency
or chemistry of the precipitation samples.
Specifically, it is recommended that the
NADP/NTN Coordination Office take the
following steps to correct conditions at
several sites:
• Relocate the collector or remove the
obstruction (tree, etc.) that causes the
45° angle rule to be violated (four sites).
• Relocate the collector or restrict use of
nearby parking lots and storage facili-
ties so that a 100-m separation is
achieved (three sites).
• Relocate the collector or install fencing
so that animals are kept at least 30 m
away (12 sites).
• Relocate the collector so that transpor-
tation roadways and sources are at least
100 m away (six sites).
• Reorient the collectors whose wet-side
collection bucket faces north or east so
that all wet-side buckets face west (15
sites).
• Where expedient and inexpensive to do
so, relocate collectors or rain gauges
so that a minimum separation distance
of 5 m is achieved (17 sites).
• Emphasize to site operators and super-
visors that grass, weeds, and small trees
or bushes should be kept at a height of
2 ft or less in a circle with a radius of 30
m from the collector (13 sites).
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• Level any collectors or rain gauges that
are out of tolerance (12 sites).
• Investigate whether or not the resistivity
required to activate the collector sensor
should be set closer to the factory value
of 80K ii for several of the collectors.
• Supply rain gauge damping fluid (sili-
cone oil) to those sites that may need
to fill reservoirs to within 0.25 in. of the
top.
Site Survey Visits
A quality assurance systems survey was
conducted at each site to qualitatively as-
sess the site, its surroundings, and the
operator's adherence to procedures speci-
fied in the NTN design document and in
the NADP/NTN site operator's instruction
manual. Criteria for siting an NADP/NTN
precipitation station are illustrated in Fig-
ure 2. The operator was asked to demon-
strate sample collection and analysis pro-
cedures. These were observed with spe-
cial attention given to calibration proce-
dures 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 (if present) were examined for leg-
ibility, completeness, and accuracy.
Information from the systems survey was
entered in the systems survey question-
naire. Two sets of photographs (color
slides) of the sites were taken. The N, E,
S, and W views were photographed with
the precipitation collector in the foreground.
Additional views were taken as specified
in the questionnaire.
A quantitative performance survey was
conducted at each site. Table 1 lists the
equipment that was checked for perfor-
mance and the type of test used. Criteria
for evaluating performance ;are specified
in the NADP Quality Assurance Plan.
No Residential ^.., „ .
Structures No Object
VithinSOm, "^Should Project
VJthin 30°
,Cone of Mean
IWind Direction
0.3-1.0
0.6 - 2.0
5-16
20 - 6.6
30-98
500-1640
Residential
Buildings
Preferred
That No
Wet Bucket —
Collector
Project Beyond
10-6.2
20-12.4
40 - 24.8
5 m • No Objects Greater Than 1 m in Height
20 m • Slopes ± 15%
Natural Vegetation <0.6 m
No Grazing Animals
30 m • No Sudden Changes in Slope Greater Than ±15%
Collector and
Gauge Inlet
Within 0.3 m
Notes
* Platforms Discouraged, However, No Higher Than
Anticipated Snow Pak
• Spacing Between the Gauge and Collector at 5 to 30 m
• No Residential Buildings within Upwind 30° Cone
• If More Than 20% of Precipitation Is Snow, Gauge Must Have
an Alter Wind Shield, Pivot Axis at Same Elevation As Gauge
Inlet
• In Snow Areas, Collector Roofs Should Be Properly Counter
Weighted
• Question Future Land Use
• Changes Must Be Submitted to Coordinator's Office
Farm Area Should Be Nothing Except Vegetation Maintained at
Less Than 0.6 m
No Surface Storage of Agricultural Products, Fuels, Vehicles.
Parking Lots, or Maintenance Yards
No Moving Source of Pollutants Such as Runway,
Taxiway, Road or Navigable River
• No Feed Lots, Dairy Barns or Large Concentration of Animals
10 km • No Downwind Industries, Factories, Chemical or
Power Plants
• No Downwind Urban Areas Greater Than 10,000
20 km • No Upwind Industries, Factories, Chemical or
Power Plants
• No Upwind Urban Areas Greater Than 10,000
• No Downwind Urban Areas Greater Than 75,000
40 km • No Upwind Urban Areas Greater Than 75,000
Figure 2. NADP/NTN siting criteria.
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Table 1. NAPD/NTN Measurements and Performance Survey Methods
Site Measurement Measurement Device Performance Suurvey Method
Designated Performance Criteria
Rain depth
Precipitation sample
collection
Mass
pH
Conductivity
Rain gauge (Belfort)
Precipitation collector
(Aerochem Metrics)
Triple beam balance
pH meter and electrode
Challenge with known weights
that simulate rainfall.
Measure resistance across sensor,
measure tension and drop of bucket lid,
measure temperature and resistance of
activated sensor.
Challenge with traceable weights.
Challenge with simulated precipitation
sample of known pH.
Conductivity meter and cell Challenge with simulated precipitation
sample of known conductivity.
Agreement within ±0.1 in. of test weight value
over the range 0-12 in.
Resistance in range oiGO-QOKn. Lid drop
distance >3 mm. 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 uS/cm of test solution's
designated value.
•U.S. Government Printing Office: 1932— 648-080/60114
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W.C. Eaton, C.E. Moore, R.W. Murdoch, R.C. Shores, and D.A. Ward are with
Research Triangle Institute, Research Triangle Park, NC 27709.
Robert L Lamps is the EPA Project Officer (see below).
The complete report entitled "Summary Report for the National Atmospheric
Deposition Program/National Trends Network (NADP/NTN) Site Visitation Pro-
gram for the Period October 1988 through September 1989," (Order No. 92-
219823; Cost: $26.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Off her can be contacted at:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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