WSP10284

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1998
• Author: USGS
• Title: Water-Quality Assessment of the Arkansas River Basin - Southeastern Colorado - 1990-93
• Water Supply Pro - Doc Type: Report/Study

0230

Table 17. Number of samples that exceeded chronic manganese water-quality standards in the upper Arkansas
River, April 199O-March 1993

[d, no standard available]

Site name
(see table 1)

Number of samples
enalyzed

Leadville
Malta
Granite
Buena Vista
Nathrop
Wellsville
parkdale
Portland

Number of samples that exceeded standard I

Chronic
standard for
dIssolved
manganese2

Chronic
standard for total-
recoverable
mangsnese3
o
o
o
o
o
o
I
o

27
26
27
27
27
27
27
26

7
4
2
o
o
o

JColorado Department of Health. ]994.
2Unless noted: Chronic standard = 50 mkrograms per liter.
] 1 ,000 micrograms per \iler.

Zinc

I,

Zinc concentrations (fig. 15) showed spatial and
temporal patterns similar to manganese (fig. 13).
Median dissolved-zinc concentrations typically were
largest during early-snowmelt runoff. The concentra-
tion of dissolved zinc in unpolluted freshwater typi-
cally ranges from 0.5 to 15 IlglL (Moore and
Ramamoorthy, 1984). The maximum median concen-
tration (320 1lg!L) was at Malta; downstream from
Malta, dissolved-zinc concentrations decreased, prob-
ably because of increased partitioning to the particu-
late phase. The percentage of zinc in the dissolved
phase decreased from about 83 percent at Leadville to
about 19 percent at Portland (fig. 16). Concentrations
of dissolved 'zinc generally increased between Lead-
ville and Malta because of tributary contributions from
California Gulch. Total-recoverable zinc concentra-
tions tended to decrease downstream from Malta,
except during snowmelt runoff (fig. 15) when resus-
pension of fluvial sediment by the elevated streamflow
probably caused total-recoverable zinc concentrations
to increase downstream from Granite. Dilution by
Lake Creek and sedimentation of particulate zinc are
the probable causes for the substantial decreases in
total-recoverable zinc concentrations between Malta
and Granite. An analysis of instantaneous total-recov-
erable zinc loads indicates that the only tributary that
contributed a substantial zinc load (>10 percent) to the
main-stem river during all streamflow regimes was

California Gulch (table 18). Most other tributaries
typically contributed insubstantial loads (<10 percent)
compared to the main-stem loads.
Concentrations of dissolved and totaI-
recoverable zinc had statistically significant decreases
(p ~ 0.05) between the pre-treatment and post-treat-
ment periods at both mine-drainage sites and at four of
the eight main-stem Arkansas River sites (table 19).
With the exception of Parkdale, all main-stem sites
had significantly smaller dissolved-zinc concentra-
tions during the post-treatment period (table \9).
Total-recoverable zinc concentrations decreased
significantly at main-stem sites at Leadville, Malta,
Buena Vista, and Wellsville (table 19). Based on these
results, it seems likely that the treatment plants had a
substantial effect on zinc concentrations.
The acute water-quality standard for dissolved
zinc was exceeded in 18 of28 samples (about
64 percent) collected at Leadville (table 20). Seven of
the 18 exceedances occurred during snowmelt runoff,
and the other II exceedances occurred during the
other three flow regimes. Only one of the exceedances
occurred after the treatment facility at Leadville Mine
Drainage Tunnel began operation. There was no acute
standard for zinc at sites located between Leadville
and Portland. The chronic stream-water-quality
standard for zinc was exceeded in three samples, or
less than 2 percent of the main-stem samples collected
during the study period (table 20).

WATER QUALITY 33