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

Table 3. Distribution of field-blank samples
0 I'~, no sample or not appltcahle; lah, office laborUfory]
-.....J .
en
Co:) Site Land Previous General
use site chemical
constituents
Slate Line Mixed Reed h
Dor.~ero Mixed Baker i
Gunnison Mi;~ed Gunnison near m
near Grand Grand Junction
Junction
Gunnison Mixed Lab cleaned
Tunnel refe.rence2 Lab cleaned
Lab cleaned
East Rural urban. Gunnison at
recreation 32 Road
Gore Rural urban, French
recreatIOn
French Mining French
Dry Agriculture Lab cleaned
Baker Reference. Lab cleaned
srmJ Lab cleaned

Concentration range at previous site1
Dissolved Suspended
Nutrients organic organic
carbon carbon

Trace
elements

h
I

h

h
I

m
In

m

m

In

III

m

h

III

h

'Concenlralion ranges with respe("{ /0 all SIIes wilhin the ~urface-waler network.. I = low. m = medium. h = high.
:Oownslrearn from major reservoir .<.y:~aem.
3Phy.<.iographlc prOVlnl'~, ~nn = Smnhem Rocky Mountain.

different combinations of sources of variability.
The pre-processing split replicate. the concurrent
and sequential replicate. and the post-processing
split-replicate samples collected in surface water of
the UeOl study unit for water years \ 995-96 are
discussed in the following sections.
Data published by the U.S. Geological
Survey are rounded. For example. a calcium value of
ISO mg/l (milligrams per liter) is reponed (rounded)
to the nearest 10 mg/L. A calcium value of 6.5 mg/L
is rounded to Ihe nearest 0.1 mg/L. Data rounding is
incorporated in the assessment of replicate analysis in
this report by using a unit called the lowest rounding
unit. A lowest rounding unit of I would represent
10 mgfl for the 150 mg/L sample and would represent
0.1 mg/L for the 6.5 mg/L sample. A lowest rounding
unit is equal to the magnitude of the least significant
figure reported by the USGS National Water Quality
laboratory. In this report. the differences between the
environmental and replicate values are given in the
units of the constituent and in lowest rounding units.
The use of lowest rounding units for comparison
avoids skewing comparisons when values of conslitu-
ents span orders of magnitude. For example. consider

the two pairs of magnesium values for the French
and Dry sites (table 4). The environmenlal and split-
replicate values for French are 5.5 and 5.6 mg/L,
resulting in a difference of -0. I mg/L. The Dry envi-
ronmental and splil-replicate values are 36 and
37 mg/L. resulting in a difference of -I mg/L. Both
of the differences are -I unit of the leasl significant
figure or -I unit of the lowesl rounding value. The
practical difference between the environmenlal and
replicate values is similar in both of these cases (the
only smaller difference available for each pair of
samples would be zero). A comparison of the actual
magnitude difference between the environmenlal and
split-replicate pairs (-0.1 to -I mg/L) is of little
use. A difference between the environmental and split-
replicate sample for Ihe Dry site could not be 0.1 mg/I.
because the dala are reported to the nearesl whole
milligram per liter.
Percent differences between the environmental
and replicate values do not yield practical significance
for many of the constituents in this data set. For
example. the chloride environmental and replicate
values for French have a -0.] mg/L difference
(table 4). which represents a -lO percent difference.

QUALITY-CONTROL SAMPLING PROGRAM 5