United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-89/007 Sept. 1989
I V
c/EPA Project Summary
The National Atmospheric
Deposition Program/National
Trends Network (NADP/NTN)
Site Visitation Program (October
1986 through September 1987)
W. Gary Eaton, Curtis E. Moore, Dan A. Ward, and
Richard C. Shores
The proper collection of pre-
cipitation and the accurate meas-
urement of its constituents are im-
portant steps in attaining a better
understanding of the distribution and
effects of "acid rain" in the United
States. One of NAPAP Task Group
IV's major programs concerns wet
deposition monitoring. One of that
program's projects, 4A-15, "Quality
Assurance Support for Wet Deposi-
tion Monitoring," is sponsored by
EPA to evaluate the sample collection
process of the National Atmospheric
Deposition Program/National Trends
Network (NADP/NTN) precipitation
networks through a site visitation
program. Research Triangle Institute,
as contractor to EPA, conducts these
visits. If deficiencies or nonstandard
procedures are noted, the site
operator and supervisor are notified.
Brief reports are sent to the EPA
Principal Investigator and the
NADP/NTN Quality Assurance Man-
ager. 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
three-year span 1986-1989. This docu-
ment is a summary report of the find-
Ings from the 1986-1987 (fiscal year
1987) site visitation program to 62 of
the sites that comprise the
NADP/NTN precipitation networks,
referred to collectively as the
NADP/NTN network. In its present
configuration, the NADP/NTN net-
work's research and monitoring pro-
grams are supported and operated by
the U.S. Geological Survey, State
Agricultural Experiment Stations, the
Departments of Agriculture, Interior,
Commerce, and Energy, and the En-
vironmental Protection Agency. Addi-
tional support is provided by state
agencies, public utilities, and
industry.
Protocols and procedures followed
in conducting the site visits are de-
scribed. Results of systems and per-
formance audits are discussed for
siting, collection equipment, and the
field support laboratories.
Where exceptions are found, the
potential effects of nonstandard sit-
ing, improperly operating equipment,
and improper sample handling or
analysis technique on the data base
are discussed. Recommendations are
given for improvement and standardi-
zation of individual sites and the
network as a whole.
This Profect Summary was devel-
oped by EPA's Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
-------
separate report of tfie same title (see
Project Report ordering Information at
back).
Introduction
This document is the summarizing re-
port of quality assurance assistance and
findings from site visits made to the
National Atmospheric Deposition Pro-
gram/National Trends Network
(NADP/NTN) precipitation collection sta-
tions in the period October 1986 through
September 1987. Each site is located and
operated according to protocols and
procedures as given in the siting and
operating manuals for the networks L2^.4.
The purposes of the site visitation pro-
gram, sponsored by the U.S. Environ-
mental Protection Agency, are to verify
that each site is operated according to
established procedures and to provide
technical assistance as required.
Sixty-two of the 201 sites that were in
operation as of June 30, 1987, were
visited during this time frame.
The goals of the site visitation program
for quality assurance assistance to the
NADP/NTN collection sites are to:
1. Provide a qualitative assessment of
each site and its surroundings, the
operator's adherence to sample cot-
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 de-
tailing site characteristics, results of
quality assurance tests, and technical
assistance provided;
5. Computerize results of all information
gatfiered from each site and submit
this to the NADP/NTN Quality Assur-
ance (QA) Manager on a quarterly
basis;
6. Document the sites and their sur-
roundings by assembling a collection
of site maps and color photographs.
This project summary describes proce-
dures and results from quality assurance
visits made to the sites in 1986 and 1987.
Recommendations for improvement are
also given.
Procedures
Scheduling
Each NADP/NTN site was to be visited
once in a three-year period. About one-
third of the 201 active sites were visited
in the first year (1986-1987). Prior to the
scheduling of site visits, RTI consulted
with the NADP/NTN QA Manager and
Central Analytical Laboratory (CAL) site
liaison to determine which sites, if any,
should be seen on a priority basis. When-
ever possible, visits were planned so that
several sites in the same vicinity could be
seen in the same trip.
The following sequence was followed
when arranging a visit to a collection site.
• About two months before the an-
ticipated date of visit, RTI selects a set
of sites in a location suitable for a trip
lasting up to two weeks and sets a
tentative schedule for visits. As many
as eight sites may be visited in this
time frame, depending on the prox-
imity of the sites.
• The NADP/NTN QA Manager, the CAL
of the Illinois State Water Survey, and
the sponsoring agency are notified by
letter of the proposed visits. CAL
supplies pertinent information to RTI
concerning each site.
• Each site's supervisor is telephoned to
set up the visit. Depending on the
wishes of the site supervisor, the
supervisor contacts the operator or
RTI contacts the operator to confirm
the date, time, and place of the visit.
When the supervisor makes the ar-
rangements, he contacts RTI prior to
the planned visit to confirm or alter the
initial plan.
• EA form letter is sent to each site's
supervisor and operator that confirms
the date, time, and place of the visit.
This letter also gives a brief agenda
for the visit and an estimate of the
time to set aside for the visit (usually 4
to 5 hours).
Site Survey Visits
An auditor accompanied the supervisor
and/or operator to each collection site
and field laboratory with the dual aims of
(1) documenting the site and its imme-
diate surroundings, its operation, and tii
accuracy of its instrument's responses 1
various quality assurance tests and (i
providing information, training, an
instruction for operators and supervisor:
equipment calibration and minor mair
tenance as needed, and establishing cot
tacts for further information and/or maj<
repairs.
Systems Survey
A quality assurance systems surve
was conducted at each site to qualiU
lively assess the site, its surrounding!
and the operator's adherence to procc
dures specified in the NTN design doci
ment' and in the NADP/NTN site open
tor's instruction manual3. Criteria fc
siting an NADP/NTN precipitation static
are illustrated in Figure 1. The operate
was asked to demonstrate sample collet
tion and analysis procedures. These wer
observed with specific attention given t
calibration procedures and sample har
dling technique. Site equipment was e>
amined for signs of wear or faulty opera
tion. It was noted whether solutions an
equipment were properly stored. Site log
books and rain gauge charts (if presen
were examined for legibility, complete
ness, and accuracy.
Information from the systems surve
was entered in the systems survey ques
tionnaire. Photographs (color slides) c
the sites were taken. The directions N, E
S, and W were photographed with th
precipitation collector in the foregrouru
Additional views were taken as specific
in the questionnaire.
Performance Survey
A quantitative performance survey wa
conducted at each site. Criteria for eva
uating performance are specified in th
NADP Quality Assurance Plan*. All into
mation was recorded in the performanc
survey questionnaire. Several items hav
ing to do with quality assurance tes
equipment, materials, and procedures an
discussed in the next section.
Sequence Of Site Visitation
Activities
/. Select Site For Visit And Inltla
Communications
• Advise QA Manager, CAL, site spor
sor of plans; request site informatioc
receive go-ahead
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5 m • No objects greater lhan 1 m In height
20m • Stops* 115H
• Natural v«g*Mion<0£m
• No grazing animals
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30m • No sudden changes In (tap* greater thin tISH
Farm aim should be nothing «xcepl mgMMkxi maintoinad H teas
than 06m
100m •Nosunteeiloraoialagricullunlpfoducls.hMls.wniclM.
psfking Ms, of miJntonmca ywds
• No moving ioucoi ol poManH wch n rummy, tailway. road or
navtgibtortvw
500 m • No iMd lot*, dairy bvra or targi eonomiratlon ol anlmalt
10km
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• Contact site supervisor, site operator,
sponsoring agency
• Send letter of confirmation to super-
visor, operator, agency
• Advise EPA that trip plans are
complete
//. Pre-TWp Preparation
• Make travel arrangements (air, car,
hotel)
• Prepare and test quality assurance
materials
• Review site-specific quality control in-
formation (maps, QC test results, etc.)
• Check equipment and supplies
• Prepare site visit notebook
///. Conduct S/te Visit
• Outline activities to supervisor and
operator
• Assess site and surroundings (map,
photographs, obstructions, sources)
• QA tests of precipitation collector and
gauge
• Adjust or calibrate collection equip-
ment as required
• Assess operator handling and trans-
port of collection bucket
• QA tests of conductivity and pH
meters, temperature, mass
• Examination of site records, rain
gauge charts
• Answer questions; provide information
• Prepare short report; conduct exit
interview
IV. Reporting
• Short report prepared; left with super-
visor or operator
• Copy of short and extended reports
forwarded to NADP/NTN QA Manager,
to CAL, and to EPA Project Officer
• Copy of site visit notebook sent to
NADP/NTN, QA Manager; file original
• Summary reports prepared monthly
and annually
• Report presented to NADP/NTN com-
mittees
Results and Discussion
Siting Criteria Survey
Collector Height Standard—The collec-
tor should be installed on its standard 1-
meter high aluminum base. Any of sev-
eral methods can be used to stabilize or
level the collector such as concrete pads
or stakes. However, the bucket height of
the collector should not vary from its
standard height by more than ±0.5 m.
An exception to this criteria is permitted
in areas with significant accumulations of
snow. In this case, the collector may be
placed on a platfbrm that is no higher
than the highest anticipated snow pack.
To prevent obstructions to wind flow, the
collector base should not be enclosed.
Eleven of 62 collectors checked (18%)
were not at the standard 1-meter above
ground height. Of these 11. all were on
platforms. All of these sites, with the
possible exception of Georgia Station,
were in areas where snow pack ac-
cumulates and warranted being on plat-
forms. The base was enclosed on five
collectors.
In most cases, platforms were short,
not more than 2 to 4 feet in height. The
higher platforms (Buffalo Pass and
Snowy Range) were necessary to raise
the collector above snow packs which
could exceed 10 feet. The effect of
shorter platforms on the sample is be-
lieved 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-side bucket is
generally upwind of the dry-side bucket
(winds generally being from the S to SW
in the eastern United States), and the
sensor is downwind of the wet-side
bucket. This placement is designed to
lessen the chance for contamination and
to minimize the obstruction of the col-
lector itself to sample entry.
Of 61 sites examined in 1987, 47
(77%) were correctly installed with the
wet bucket facing to the SW, W, or NW.
Three were installed with the wet bucket
facing SSW. These southerly installations
probably have no effect on the data.
Eight collectors that were installed with
the collection bucket facing N or E may
cause an aberration in the collection ef-
ficiency or sample chemistry. A statistical
study of the long-term data base would
be required to discern this and may be
complicated by other factors.
Ground Slope—The collector should
not be located on ground with a slope
greater than 15° or 27%. The slope at 7
of 62 sites (11% of the total) exceeded
this criterion. Six of the seven sites were
located in mountainous regions and were
representative of their respective regions.
It is difficult to say what the effect of
the steeper slopes is on collection
efficiencies. However, to adhere too
rigidly to the criterion would effectively
eliminate many regions, especially those
at higher elevations, from this network.
Collector-Gauge Separation—The col-
lector should be located within a distance
of 30 m of the rain gauge but not closer
than 5 m. This guideline is set so that the
collector and gauge "see" the same
precipitation event and so that neith
piece of equipment offers an aerod
namic interference to the other's colle
tion ability.
Twelve of 60 sites (20%) had ra
gauges less than 5 m from the collectc
The collector and rain gauge we
mounted on a platform at several of the:
sites and separating them would requi
the construction of a second platfor
(one site had separate platforms). Son
sites not meeting the distance requir
ments were enclosed by chain-Mr
fences for security; meeting the distam
requirements for these sites would n
quire enlarging the enclosure or buildir
a separate one. Many sites in this ne
work may not be able to comply with th
criterion due to cost. However, thos
gauges which can be removed to th
proper distance should be and the mo\
should be documented. None of the sit<
exceeded the recommended separatic
distance of 30 m. The closest separatic
was 0.5 m.
Collector and Rain Gauge at San-
Height—The heights above ground of tf
collection bucket and the rain gauj
orifice should be within 1 foot of eac
other. Seven of 61 sites (11%) did n
meet this criterion. However, in all case
the criterion was exceeded by snru
amounts and the effect on the data ba:
is probably negligible.
Immediate Site Surroundings — Th
purpose of these criteria is to prevei
sample contamination or obstruction froi
occurring. The presence of urban are*
or industry at distances of 10 km i
greater from the site is not considered
this report since this information he
already been given in the report of th
first round of site visits made in 1985 ar
1986, and the site locations have m
changed. Documentation of the presenc
of new sources after 1980 is not yet aval
able as an NPAP emissions inventory.
Vegetation Within 30 m and the 4
Degree Rule—Vegetation within 30 m i
the collector should not be more than tw
feet tall, and no object should project c
the collector from an angle greater the
45°. These criteria are intended to kee
windblown contaminants such as seec
or splashing water out of the collectic
bucket. Fourteen of 62 sites (23%) he
vegetation of height greater than two fe<
within 30 m of the collector. Six site
(10%) had trees or meteorological towe!
too near the collectors that violated th
45° siting criterion. Under certain win
conditions, it is possible that rai
splashing from these objects into th
collection bucket could significantly alt
the sample chemistry.
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Parking Lots, Chemical Storage-The
site should not be within 100 m of
parking lots or chemical storage. Ten of
62 sites (16%) did not satisfy this
criterion.
Transit Sources Closer than 100 m —
Transit sources such as well-traveled
roads, railroads, and shipping channels
should be no closer than 100 m to the
sample collector. Five of 61 sites (8%)
were judged to be too near such sources.
Grazing Animals or Feedlots—The site
should be more than 30 m from grazing
animals and more than 500 m from large
concentrations of animals such as
feedlots, dairy farms, or poultry farms.
These criteria are intended to keep
sources of compounds which could buffer
acidic solutions removed from the site.
Five of the 62 sites examined in 1987
were only affected by grazing animals,
and the effect here is probably negligible
since animals in these situations tend to
roam over large areas and are not
concentrated near the site. None of the
sites, however, were near feedlots or
other large concentrations of animals
which could affect the sample chemistry.
Equipment and Sample
Collection Survey
System and performance checks were
made at each site to assess the opera-
tional fitness of the Aerochem Metrics
precipitation collector* and the Belfort rain
gauge. The process of sample retrieval
and care was also examined. These are
discussed below.
Precipitation Collection System
Checks
Collector Level—The precipitation col-
lector should be level so that the
collection efficiency will not be biased by
wind direction or variations in effective
bucket opening areas. Only five of 60
collectors examined (8%) were not level.
In most cases, the collectors were off
level by small amounts. It is not believed
the effect of this variance would be
measurable.
Collector Stable—The precipitation col-
lector should be mounted firmly so that it
will not move in strong winds. Each of the
61 collectors examined was judged to be
stably mounted (i.e., it could not be
rocked easily by hand).
•Mention of trade names or commercial products
does not constitute endorsement or recom-
mendation for use.
Sensor Clean—The collector's sensor
should be clean. Each of the 61 collector
sensors examined was clean. The usual
effect of a dirty sensor is to prolong the
length of time the wet bucket stays
uncovered after an event, increasing the
likelihood of contamination.
Counferwe/ghf—The moving bucket lid
should be properly counterweighted so
the lid can be moved without excessive
motor strain or clutch slippage. Improper
counterweighting is usually found at sites
which have added snow roofs. Only two
of 61 site collectors were found to have
improper counterweights. For these two,
there was no sign of excessive clutch
wear.
Clutch Wear—The motor box clutch
assembly should not show signs of
excessive slippage or wear as evidenced
by a shiny clutch surface or rounded-off
indent. Fourteen of 60 sites (23%) had
evidence of clutch wear or slippage.
However, other tests, such as the
assembly's ability to lift two or more
Belfort gauge weights without slipping,
showed that eight of these 14 were
operating properly. There are several
causes of clutch slippage in addition to
improper counterweighting discussed
above. The usual result of serious clutch
slippage is that samples are not collected
because the bucket lid fails to move off
the wet bucket at the start of a
precipitation event.
Bucket Tie-Down—Both the wet and
dry collection buckets should be secured
to the collector with tie-down straps to
prevent their being blown out during
strong winds. Nine of the 61 sites (15%)
did not secure the buckets. However, the
actual incidence of sample loss due to
this variance is probably rare.
Precipitation Collector
Performance Checks
Cover Seats Properly on Wet Bucket—
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 (and so that the
lid liner is protected during wet periods).
None of the 58 collectors that could be
examined in 1987 had bucket lid seal
problems.
Lid Tension—The force that the bucket
cover exerts against the rim of the
collection bucket may be assessed by
lifting the lid slightly above the bucket
and reading the force (in grams) required
to do so. A spring scale is used.
Generally, tensions of 1500 g or greater
are found. Three sites had lid tension of
1500 g. The average lid tension was 2384
± 434 g.
Lid Drop Distance—Another measure
of adequate lid/ bucket seal tension is the
lid drop distance -- the distance the lid
drops when the wet bucket is
momentarily removed. The CAL of the
NADP/NTN network has found that a
distance of 3 mm or greater is required to
give good, dust-free seals.
Not all collectors were checked in this
manner because the test was not used
initially in the program. Of 56 site
collectors checked, none had a lid drop
distance of 3 mm or less. Minimum,
maximum, and mean distances were 5,
21, and 14.2 ± 3.7 mm.
Voltage to Event Marker—\n the wet-
side open mode, the Aerochem Metrics
unit should send signal of 14 ± 3 volts to
the event marker solenoid of the Belfort
rain gauge. Zero voltage or values
outside the prescribed range are
indications of problems with the
Aerochem Metrics motor box or the
battery, when one is used to power the
unit. Of 58 units checked, three were
lower and one higher than the acceptable
range. The mean voltage was 12.74 ±
1.15. The highest voltage was 173 at the
Snowy Range-Glacier Lake site. It may
be that the solar panel there is over-
charging the battery. The low voltages
were found at the Niwot Saddle, Quincy,
and Verna Well Field sites.
Unactivated Sensor Temperature —
Generally, the temperature of the pre-
cipitation collector sensor is at ambient
level when there is no precipitation. If the
ambient temperature is below 4°C, the
sensor heater should come on, at a lower
power level, to melt ice or snow that may
fall. A sensor should not be heating at
ambient temperatures above 4°C unless
it is raining. If it is heating prior to the
rain, light rainfall striking the sensor may
evaporate before the circuit can be made
to open the lid. None of the 53 sensors
checked showed irregular heating at am-
bient temperatures.
Activated Sensor Temperature—When
activated by precipitation, the Aerochem
Metrics sensor causes the cover to move
off the wet-side collection bucket. To
speed precipitation evaporation and thus
reduce the time the wet-side bucket is
open after precipitation ceases, a heater
circuit beneath the base plate of the
sensor is energized and the temperature
of the sensor (as measured at the base
plate) rises. The circuit is thermistor-
limited and is adjusted to 50-60°C (122-
140°F) at the factory.
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A total of 58 sensors were checked
during the 1987 visits. Sensors at four
sites were not checked since heavy rains
were occurring at the time of the visit. Of
the 58, two were not heating (3%), one
(Snowy Range-Glacier Lake) was over-
heating (90°C), and 55 were judged to be
heating properly. Temperatures at 51 of
the 55 sites were checked using a
thermo-couple and digital meter. Of these
51, the lowest temperature was 33°C
(Meridian), the highest was 76°C (Sugar-
loaf), and the average temperature was
58.2 ± 10.8°C. Of those 51, ten (20%)
heated below 50°C, 22 (45%) were in the
manufactured range of 50-60°C, and 19
(37%) were above 60°C.
Resistance to Trigger Sensor—The
sensor of the Aerochem Metrics collector
activates circuitry to open the cover when
water droplets bridge the gap between
the grid and the base plate elements of
the sensor assembly. According to
factory specifications, this occurs when
the resistance between the elements is
reduced to 80 Kohms. This resistance is
sufficiently sensitive to cause activation
by relatively pure water (i.e., water of
very low conductivity, such as deionized
water).
All of the 56 sensors checked caused
the circuit to activate when distilled water
was applied to the grid and base plate.
The low, high, and average resistances
measured by bridging the grid and the
base plate through a variable resistance
box were 59.1, 110.0, and 82.3 ± 10.3
Kohms.
Rain Gauge System Checks
Gauge Level—The rain gauge should
be level so that precipitation collection
efficiency is not biased by wind direction
or by variation in effective exposure area.
Five of the 61 rain gauges inspected
(8%) were out of level by small amounts.
Alter Shields—Alter shields may be
used with rain gauges in the NAOP/NTN
network to abate strong winds near the
gauge and improve collection efficiency.
Fourteen of 62 sites (23%) were so
equipped.
Chart Recorders—When checked at
the time of the visit, the chart recorders
should indicate the correct time ± one
hour. The rain gauge chart recorders
were off by more than one hour at only 1
of the 61 sites checked.
Dampening Fluid Levels—The Belfort
gauge dampening fluid reservoir should
be filled to within 0.25 inch of the top to
reduce pen "noise" created by strong
winds. Charts showing excessive pen
noise are difficult to read accurately. The
dampening fluid level was low at 10
(17%) of the 60 sites checked.
Rain Gauge Performance Check
The rain gauge calibration was
checked using Belfort gauge calibration
weights. Fifty-five of the 59 gauges (93%)
were in calibration (within ±0.1 inch) up
to 5 inches depth. At a depth of 6 inches,
only 76 percent were in calibration. Errors
associated with the crossover point
increased rapidly at the 6-inch depth
point. Because most rain amounts are
measured in the 0-5 inch range (except
when winterized), and because the event
depth is measured as the difference in
chart reading before and after the event,
few measurable errors in precipitation
mass measurements are expected due to
inaccurate rain gauge calibration. Twenty
of the 51 rain gauges checked (34%)
were calibrated during the site visits.
Sample Collection Procedures
Most operators were using proper col-
lection procedures and no instances of
contamination were noted. Operators
were also checking for sample contami-
nation while at the site.
Only one site operator was not able to
make a weekly equipment check. Seven
operators did not bag and box the bucket
before transporting it to the field
laboratory. In those cases, the sites were
within walking distance of the field
laboratory.
Field Laboratory Survey
Systems Check of Field
Laboratory
Field laboratories had adequate space
and were clean. Fourteen sites (23%) did
not have air conditioning, but were
usually in areas that would need it only
rarely. Required records were kept and
report forms were filled out correctly in all
cases. Rain gauge charts were annotated
fully with site name, date, time on, time
off, etc. Field samples were shipped to
CAL, generally within three days. Proper
techniques for weighing samples were
followed in all instances.
pH and Conductivity
Measurement Techniques
In order to make accurate and precise
pH and conductivity measurements, the
analyst must be familiar with the meas-
urement equipment, follow appropriate
calibration procedures, and use measure-
ment techniques consistent with good
laboratory practices. Field person
were observed while making pH and c
ductivity measurements and adherei
to technique was noted.
In general, specified procedures w
adhered to and laboratory technique i
good. Only two sites (3%) had a variai
with pH measurement technique. Not
sites use the inverted cell technique
measuring conductivity. This is usu.
due to the fact that the site does not
the type of electrode that may
inverted.
Each site operator rinsed the cond
tivity cell with sample before taking
second reading. Only one site measu
the standard, deionized water, and s«
pie in the wrong order. NADP/NTN f
cedure requires the measurement of
ionized water after the 75 jiS/cm stand
and before the precipitation sample
ensure there is no carry-over from
standard to the lower ionic strength r
sample. Proper analysis procedures w
always discussed with site operat
whenever the need was evident.
Results of Field Stte Analysis c
Simulated Precipitation
Each field laboratory was asked
analyze a performance audit solution
conductivity and pH. These solutic
were prepared by dilution of EF
supplied performance test solutions;
audit value is that designated by E
and lies between pH 3.8 and 4.8 and I
a conductivity between 20 and 77 pS/c
Designated quality limits are ± 0.1 t
for pH and ± 4 iiS/cm for conductivity
Ninety-seven percent of the 60 fi
laboratories checked had pH rest
within ±0.1 unit of the designated val
The average absolute difference v
0.036 ± 0.03 pH unit. Of the two si
that exceeded the accuracy requirenru
one had a faulty pH electrode and
other had a faulty meter. Two sites I
inoperative pH electrodes and could
be tested. Ninety-seven percent of
field laboratories obtained conducts
values which varied by no more than :
nS/cm from the designated value. 1
average absolute difference was 1.46
1.34 nS/cm.
Balances are used at the sits to we
the mass of precipitation collected by
Aerochem Metrics collector. They
usually triple beam-balances. The t
ances were checked with weights rang
from approximately 800 to 4000 grai
Only three of 58 sites checked had err
of greater than 5 grams over the range
test weights. The worst case was
+ 10.9 g disagreement at a loading
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3292 g. This was discovered to be due to
inding of the beam arm dampening at-
ichment in the mechanism of the mag-
netic damper. This was corrected and the
Jisagreement was only 4.4 g.
Of 58 balances checked, the absolute
iverage of the worst case differences
was 2.2 g. This usually occurred at the
naximum load applied and corresponded
o less than 0.1 percent of the average
load of 3736 g, or to less than 0.002 inch
of rain (where 1724 grams = 1 inch of
rain for the Aerochem Metrics collector).
The full report was submitted in ful-
fillment of Task 231B of EPA Contract
No. 68-02-4125 by Research Triangle In-
stitute. This report covers site visits made
during the period October 1, 1986
through September 30, 1987, and all
work was completed as of September 30,
1987.
References
1. Bigelow, D.S. "NADP Instruction
Manuel - Site Operation." National
Atmospheric Deposition Program, Ft.
Collins, CO. January 1982.
2. Bigelow, D.S. "Instruction Manual:
NADP/NTN Site Selection and In-
stallation." National Atmospheric
Deposition Program, Ft. Collins, CO.
July 1984.
3. Robertson, J.K. and J.W. Wilson.
"Design of the National Trends Net-
work for Monitoring the Chemistry of
Atmospheric Precipitation." U.S.
Geological Survey Circular 964.
1985.
4. "The NADP Quality Assurance Plan."
NADP Quality Assurance Steering
Committee. 1984.
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W. Gary Eaton, Curtis E. Moore, Dan A. Ward, and Richard C. Shores are with
Research Triangle Institute, Research Triangle ParH, NC 27709.
Berne I. Bennett is the EPA Project Officer (see below).
The complete report, entitled "The National Atmospheric Deposition
Program/National Trends Network (NADP/NTN) Site Visitation Program (October
1986 through September 1987)," (Order No. PB 89-151 5421 AS; Cost: $15.95,
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 Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-89/007
000085833 PS
fC*lO
«M
60604
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