Important changes in NASQAN and HBN field methods, constituent coverage, and field sample contamination from 1973-95
[NASQAN, National Stream Quality Accounting Network; HBN, Hydrologic Benchmark Network. USGS memoranda are identified by the unique number QWyy_nn where yy gives the year of the document and nn is a sequential number of the year's memoranda]
[This file is Table 4 in the accompanying Open-File Report]
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Constituent Date Description of change (memoranda or references)
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Alkalinity 10-01-84 Field determinations of alkalinity by fixed-
endpoint titration (QW84_16) required for
all network samples. Alkalinity
determinations between 1980 and 1984
were most likely made in the lab, but
parameter code 00410 allowed for storage
of field determinations (QW80_27, QW81_04,
QW82_05) that may have been made
by some network field personnel.
Determinations prior to October 1, 1980
were made in the laboratory.
10-01-85 Filtered samples required for field
determinations of alkalinity by fixed-
endpoint titration (QW85_19). Previous
field determinations of alkalinity were
made on unfiltered water samples.
Field determinations of bicarbonate and
carbonate in filtered samples by
incremental titration method (QW85_19)
implemented. Significant differences
found between fixed-endpoint and
incremental methods during 1984-85
study.
Biological 01-01-73 - Periphyton collected.
parameters 10-01-80
01-01-73 - Phytoplankton collected.
10-01-81
10-01-77 Change in phytoplankton sampling from 12
per year to 4 samples collected in June to
Sept. months and 3 samples during the
remainder of the year (QW77_12).
Carbon, 01-01-73 - Total collected.
organic 10-01-81
12-28-76 Evidence of a negative bias of unknown
magnitude in total organic carbon resulting
from various loss processes (e.g.,
adsorption to container walls, biological
activity). Questionable values were deleted
from the data files prior to this time
(QW77_02).
10-01-77 - Dissolved and suspended collected.
10-01-81
Fecal
bacteria 10-01-75 Began sampling.
Coliform 10-01-76 Parameter code changed from 31616 to 31625
with increase in filter pore size from
0.45 to 0.70 micrometer (QW76_25T).
Studies showed that more accurate results
are obtained using 0.70 micrometer pore
size filters.
Streptococci 10-01-76 Parameter code changed from 31679 to 31673
(QW76_25T) with change in media type from
M-enterococcus agar to KF agar (0.45- or
0.70-micrometer filter size accepted for
either parameter code; field personnel
tended to use the same filter pore size
as used for fecal coliform samples).
04-15-91 A filter pore size of 0.45 micrometer is
required to comply with TWRI methods
(QW91_FS). A study of the effects of the
two pore sizes on analytical results based
on data collected at NASQAN and HBN
stations in 1990 indicates no statistically
significant differences in methods (QW91_FS).
The differences in analytical results appear
to reflect random measurement errors with no
evidence of upward or downward bias based
on the symmetry of the distribution of
differences.
Radio- 10-01-75 Began sampling.
chemicals
Trace 04-01-78 - Sample contamination with lead and cadmium
elements 02-28-79 from paint ring on acid ampoules (QW79_12).
10-01-82 Discontinued analyses for total recoverable
trace elements (QW82_18).
Before 1991 Contamination detected in trace-element
samples from 1989 to 1991 related to field
sampling and processing procedures.
Discontinued analyses for arsenic,
beryllium, cadmium, chromium, copper,
lead, mercury, and zinc in 1991 (QW91_11,
QW91_10, QW92_05). The evidence of
contamination raised important concerns
about the accuracy of the data for these
constituents prior to 1991.
Before 1993 Studies beginning in 1987 showed trace-
element contamination associated with the
interior components of some samplers
(Horowitz and others, 1994). Previously,
the exterior of samplers had been routinely
coated with epoxy paint to avoid
contamination. The following samplers
were phased out beginning in 1993: DH48,
DH59, DH76, D74, P61, P63, and P72.
10-01-93 Capsule filters (0.45 micrometer) began to be
used at many stations. Higher concentrations
of trace elements may be expected due to the
transmission of more colloid-sized particles
(QW93_05).
02-01-94 New sampling and processing protocol
implemented at some stations for low-level
inorganic analyses (QW94_09, QW94_05 ,
QW93_11). Several USGS studies documented
the need for revisions in sample collection
and field processing procedures for trace
elements (Horowitz and others, 1994; QW93_06;
QW93_05; QW93_03; QW92_13, QW92_12, QW94_13).
Samplers with Teflon or plastic components
(DH81, D77) were recommended for use.
Trace Period of Caution should be exercised in the interpretation
elements record of mercury data (QW94_10). Possible
(mercury) contamination sources include mercuric chloride
tablets (QW80_26), manometers, thermometers,
and blue-silicon seals and stoppers of
Kemmerer and Van Dorn samplers.
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revised 01/28/97