United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-92/151 September 1992
& EPA Project Summary
The National Atmospheric
Deposition Program/National
Trends Network (NADP/NTN)
SITE Visitation Program
(October 1989 through
September 1990)
W.C. Eaton, C.E. Moore, R.W. Murdoch, R.C. Shores, D.A. Ward, 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 NAPAP
Task Group IV's major programs con-
cerns wet deposition monitoring. One
of that program's projects, 4A-15,
"Quality Assurance Support for Wet
Deposition Monitoring," is sponsored
by the U.S. Environmental Protection
Agency (EPA) to evaluate the sample
collection process and provide techni-
cal assistance to the NADP/NTN net-
work through a site visitation program.
Research Triangle Institute, as contrac-
tor to EPA, conducts these visits. If
deficiencies or nonstandard procedures
are noted, the site operator and super-
visor are notified. Brief reports are
sent to the EPA Project Officer, the
NADP/NTN Quality Assurance 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
1989-1990 (Fiscal Year 1990) site visi-
tation program to 67 of the sites of the
NADP/NTN network. In its present con-
figuration, the network's research and
monitoring programs are supported and
operated by the U.S. Geological Sur-
vey; State Agricultural Experiment Sta-
tions; the Departments of Agriculture,
the Interior, Commerce, and Energy;
and EPA. Additional support is pro-
vided by state agencies, public utili-
ties, and industries.
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 Project Summary was developed
by EPA's Atmospheric Research and
Exposure Assessment Laboratory, Re-
search 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
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 1989
through September 1990. Each site is
located 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-
Printed on Recycled Paper
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duras, and to provide technical assistance
as required.
Sixty-seven of the 196 sites (with dupli-
cate sites bringing the total to 205) that
were in operation during 1990 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 as follows:
1. Provide a qualitative assessment
of each site and its surroundings,
the operator's adherence to sample
collection and analysis procedures,
and the condition of the site's col-
lection 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 re-
sponse of field and laboratory mea-
surement devices for precipitation
depth, mass, temperature, conduc-
tivity, and pH through an on-site
performance survey;
3. Provide technical assistance to the
operator by verbal explanation, mi-
nor troubleshooting, repair and cali-
bration of equipment, an by making
recommendations 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 Qual-
ity Assurance Manager, the Central
Analytical Laboratory's Site Liaison,
and the EPA Project Officer;
5. Computerize results of information
gathered from each site and sub-
mit this to the NADP/NTN Quality
Assurance Manager on an annual
basis; and
6. Document the sites and their sur-
roundings by assembling a collec-
tion of site maps and color photo-
graphs.
Conclusions
Sixty-seven of the 196 active NADP/
NTN precipitation collection sites were vis-
ited over the one-year period, October
1989 through September 1990. About
one-third of the sites were visited during
this fourth year of a four-year effort. The
sites are located in all regions of the coun-
try and are sponsored and operated by
numerous agencies. Each site is located
according to established siting criteria and
operates according to published proce-
dures. This report assesses the degree
to which criteria and procedures are ad-
hered; predicts, where possible, the rela-
tive impact on the data that might be ex-
pected from the variances found; a.nd com-
pares results thus far from the third round
of visits to those documented in the sec-
ond round of visits that occurred over the
period October 1986 through September
1987.
Siting
Improvements in adherence to siting cri-
teria were noted at most of the sites vis-
ited in 1990 that were not in compliance
at the time of the second round of visits in
1986-1987. A number of sites heid 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, 45 of 67 sites (67%) visited in
FY 1990 had at least one variance. Six-
teen 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 de-
gree to which the criteria were exceeded.
For example, network siting criteria re-
quire that the precipitation collector and
rain gauge be separated by at least 5 m
but not more than 30 m. Fifteen percent
of the 67 sites did not meet this criterion,
nine because of inadequate separation.
Sample Collection D
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 site operators stated
that they checked the sample for contami-
nants (leaves, bird droppings, etc,) at the
time of the bucket's removal from the col-
lector. This procedure 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 6 of 66
sites examined that the clutch on the
Aerochem Metrics precipitation collector
was wearing; however, all of these oper-
ated properly when tested with a 1600-g
load. Seven of 62 sensors checked were
not operating properly. Twenty-eight per-
cent of the rain gauges (18 of 64) were
found to be out of calibration by more
than ±0.1 in. at some point on the 0-12-in.
scale, usually above a 5-in. depth. This is
not believed to be a major source of error
because the operator is instructed to empty
the catch bucket before a 5-in. depth is
reached. Calibration checks showed that
63 of the 65 gauges (97%) met accept-
able 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.
Fifty-seven of 65 sites were able to de-
termine the pH of an audit solution to
within ±0.1 unit of the designated value.
Two sites had inoperative pH meters and
could not be checked. Overall, 88 per-
cent of the 65 field laboratories checked
in 1990 agreed within ±0.1 pH unit with
the audit value.
For conductivity measurements, each
of the 65 sites checked (100%) deter-
mined the audit solution's conductivity to
within ±4 |iS/cm of the designated value.
Two sites had malfunctioning or broken
equipment and thus could not be audited.
The solution balances were operating
properly in all of the 67 cases checked.
Of 67 balances checked, almost half
agreed within ±1 g with the designated
weight over the range of 823 to 4938 g.
All but three balances 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 any
balance was 5.5 g at a loading of 4115 g,
corresponding to only a 0.1 percent dis-
agreement.
Recommendations
The site precipitation collector and rain
gauge are central to the successful op-
eration of the network. However, the
equipment in the NADP/NTN network is
aging and will require increased mainte-
nance. Therefore, weekly equipment
checks by the operator should continue to
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NADP/NTN Monitoring Network
Figure 1. Active sites in the NADP/NTN monitoring network during 1990.
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
heaters was still significant. A simple
check of the collector's sensor heater,
made by activating the collector with wa-
ter 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 at some point in the
12-in. range. However, many of those
calibrated in 1987 met specifications in
1990. 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 Cen-
tral Analytical Laboratory (CAL) for review.
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 (five
sites).
Relocate the collector or restrict use
of nearby parking lots and storage
facilities so that a 100-m separation
is achieved (five sites).
Relocate the collector or install fenc-
ing so that animals are kept at least
30 m away (three sites).
Relocate the collector so that trans-
portation roadways and sources are
at least 100 m away (one site).
Reorient the collectors whose wet-
side collection bucket faces north or
east so that all wet-side buckets face
west (ten sites).
Where expedient and inexpensive to
do so, relocate collectors or rain
gauges so that a minimum separa-
tion distance of 5 m is achieved (nine
sites).
Emphasize to site operators and su-
pervisors 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 (five
sites).
Level any collectors or rain gauges
that are out of tolerance (three sites).
Investigate whether or not the resis-
tivity required to activate the collector
sensor should be set closer to the
factory value of 80K Q for several of
the collectors.
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Tablo 1. NADP/NTN Sita Measurements and Performance Survey Methods
Site Measurement Measurement Device Performance Survey Method
Designated Performance Criteria
Rain depth
Rain gauge (Belfort)
Precipitation sample collection Precipitation collector
(Aerochem Metrics)
Mass
pH
Conductivity
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 of 60-90K 0.
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,
Supply rain gauge damping fluid (sili-
cons 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.
This report was submitted in partial ful-
fillment of EPA Contract No. 68-D8-0001
by Research Triangle Institute. This re-
port covers site visits made during the
period October 1, 1989, through Septem-
ber 30, 1990. All work was completed as
of September 30, 1990.
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No Residential,
Structures _No Object
Vithin 30 m,
Should Project
Beyond
0.3-1.0
0.6 - 2.0
5-16
20-66
30-98
500 -1640
Overhead
Wire, Tree,
Building, etc.
Residential
Buildings
45° 3? That No
Wet Bucket
Collector
Objects Project Beyond
10-6.2
20 -12.4
40 24.8
5 m No Objects Greater Than 1 m in Height
20m'Slopes ±15%
Natural Vegetation <0,6 m
No Grazing Animals
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
30. m No Sudden Changes in Slope Greater Than ±15%
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
500 m No Feed Lots, Dairy Bams 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.
U.S. Government Printing Office: 1993 648-060/60129
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IV.C. Eaton, C.B. Moore, R.W. Murdoch, R.C. Shores, and D.A. Ward are with
Research Triangle Institute, Research Triangle Park, NC 27709.
Robert L Lampe is the EPA Project Officer (see below).
The complete report, entitled "The National Atmospheric Deposition Program/
National Trends Network (NADP/NTN) SITE Visitation Program for the Period
October 1989 through September 1990," (Order No. PB92-217298/AS; Cost:
$19.00, 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 Officer 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
Official Business
Penalty for Private Use
$300
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POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-92/151
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