WSP05652

• File Number: 8273.300
• Description: Colorado River Basin Salinity Control - Federal Agency Reports - USGS
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1997
• Author: USGS
• Title: Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water - Quality Assessment Study Unit - Water Years 1995-96
• Water Supply Pro - Doc Type: Report/Study

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A summary of the differences for the constitu-
ents listed in table 4 is given in table 5. Except for
specific conductance and residue on evaporation.
most of the environmental and pre-processing splil-
replicate samples agree within plus or minus I lowesl
rounding unit. The differences for conductance agree
within plus or minus 2 lowest rounding units. These
differences would equal plus or minus 2 ~S/cm
(microsiemens per centimeter at25 degrees Celsius)
for all but the Dry sample (Iable 4) and probably are
well within instrument variation. Differences of
2 ~S/cm are not considered excessive. Differences
between environmental and split-replicate samples for
residue on evaporation are greater Ihan any other of
the constituent differences. It appears that differences
of a few lowest rounding unils for residue on evapora-
tion would be common. and lower differences may
be limited by the precision of the laboratory method.
Results in table 4 that have differences greater than
plus or minus I lowest rounding unit have been
shaded. By observation of Ihe random position of
the shaded cells. it appears that the larger differences
for each constituent do not seem to be relaled to the
concentration or the sampling site. Variabilily associ-
ated with sample processing. handling. shipment.

and analysis for general chemical constituents is low
and will have little effect on interpretation of environ-
mental data.

Comparison 01 Nutrients and Organic Carbon

Results of comparison of the environ menial
and pre-processing split-replicate samples for nutri-
ents, dissolved organic carbon, and suspended organic
carbon are listed in table 6. To determine Ihe differ-
ences between the environ menial and pre-processing
split-replicale sample concentrations for values less
than the laboratory reporting limit (values that
have a less-than symbol), a value of one-half of the
reporting limit was substituted for the less-than value.
A summary of the differences between environmental
and pre-processing split-replicale samples for each
conslituent is listed in table 7. Most of the differences
between the environmental and pre-processing split-
replicate samples for all constituents are within plus
or minus I lowest rounding unit. Variability associated
with sample processing. handling. shipment. and
analysis for nutrients and organic carbon is low and
will have little effect on inlerpretation of environ-
mental data.

Table 5. Summary of differences between environmental and pre-processing split-replicate samples for general chemical
constituents

{Lowest rounding unit is equal to the mugnitude of the least sigmficum figure]

Constituent

Percent of samples
with no difference

Calcium
Magnesium
Sodium
Potassium
Sulfate
Chloride
Fluoride
Laboratory alkaliruty
Silica
Iron
Manganese
LaboraLory pH
Laboratory specific conduclance
ReSidue on evaporalion

57
57
86
29
57
29
86
71
57
71
71
57
14
14

Percent of samples
within plus or minus 1
lowest rounding unit
86
100
100
86
100
86
100
71
100
86
86
71
43
14

Percent of samples
within plus or minus 2
lowest rounding units
86
100
100
100
100
100
100
86
100
86
86
100
lOa
28

QUALITY-CONTROL SAMPLING PROGRAM 9