WSP03775

• File Number: 8507
• Description: Rio Grande Project
• State: CO
• Basin: Rio Grande
• Date: 6/1/1996
• Title: Assessment of Metal Transport into and out of Terrace Rervoir/ Conejos County/ Colorado/ April 994 through March 1995
• Water Supply Pro - Doc Type: Publication

Table 2. Statistical summary of water-quality data for sites AR34.5 and AR31.0, April 1994 through March 1995--Continued

[Concentrations in micrograms per liter; <, less than; see fig. 1 for location of sites]
Number of
Number of enalyses 25th 75th
ConeUl\I8I1t enely_ greeter then MInimum percentUe Medlen percenUle MaxImum
reporting
level
SITE ARJI.O-Coottoued
Other trace elements---{;ontinued:
Cobal~ dissolved 25 18 <5 <6 10 18 23
Cob.l~ lotal 25 18 <5 <6 11 16 21
Lead, total 25 9 <2 <2 <2 <2 8
Nickel, dissolved 25 8 <IS <IS <IS <IS 19
Nickel, total 25 6 <15 <IS <IS <IS 23
Vanadium, total 25 I <3 <4 <4 <4 4

This definition of "dissolved" is an operational
on~nly substances that pass through the filter
are considered to be dissolved. However, numerous
investigations of trace-element chemistry have
indicated that water filtered through a 0.45-/!m filter
can contain substantial amounts of colloidal trace
elements (Kimball and others, 1995; Horowitz and
others, 1996). Because colloids can pass through a
0.45-/!m filter, trace-metal concentrations reported
as dissolved might include a substantial percentage
of colloidal-size particles.
Comparisons of reported dissolved to
reported total concentrations of aluminum, iron,
copper, cadmium, manganese, and zinc indicated
that reported dissolved-cadmium, -manganese,
and -zinc concentrations frequently were greater
than the reported total concentrations in samples
collected from sites AR34.5 and AR31.0. Reported
dissolved concentrations of aluminum were greater
than reported total concentrations for samples
collected from site AR31.0 during the summer-flow
and storm-runoff period (July 15-September 30);
reported dissolved concentrations of copper were
greater than the reported total concentrations for
samples collected from sites AR34.5 and AR31.0
during the summer-flow and storm-runoff period.
Because dissolved-metal concentrations cannot be
larger than total-metal concentrations, measurements
of dissolved-metal concentrations that exceeded

the total-metal concentrations resulted from either
sampling and processing errors or laboratory
uncertainties, or both. Laboratory personnel indicated
that laboratory precision and accuracy oflaboratory
quality-control and quality-assurance samples were
within 10 percent (Barbara Dabou, oral cornmun.,
1996). In addition, field quality-control and quality-
assurance samples indicated that no substantial
contamination of environmental samples occurred
during sample collection and processing, and analyses
of replicate samples generally were within 10 percent.
Further review of the data was unable to resolve the
anomalies and resulted in some uncertainty in the
reported metal concentrations. In general, the
dissolved concentration was greater than the total
concentration hy less than 20 percent; the dissolved-
and the total-metal concentration data were used to
describe the metal chemistry and compute metal loads.
However, the reader needs to be aware that uncertainty
exists in the data and that the true error or uncertainty
is unknown.
The metal chemistry section of this report
describes the spatial and temporal variations in
metal concentrations; the spatial and temporal
variations in the percentage of metals that are in the
dissolved and suspended fraction; and correlations
of concentrations of metals of concern, streamflow,
specific conductance, and pH.

METAL CHEMISTRY 11

003168