Upper Los Pinos Water Quality Report

• Document ID: hr_0007
• Contract/PO #: PO 05-64
• County: La Plata
• County: Hinsdale
• County: San Juan
• Stream Name: Los Pinos River
• Basin: San Juan/Dolores
• Sub-Basin: Upper San Juan 14080101
• Water Division: 7
• Title: Water_Quality Data Synthesis for the Upper Los Pinos River Watershed, SW Colorado, and Suggestions for a Watershed Plan, 2005
• Date: 1/1/2005
• Prepared For: CWCB
• Prepared By: Southwest Hydro-Logic
• Watershed Pro - Doc Type: Planning Report

The linear regression equation between SC and TDS
for streams and Vallecito Reservoir is eipressed as
TDS=0.56*SC+4. The linear regression equation
between SC and TDS for ground water is eipressed as
TDS=0.51*SC+; L For general use, the TDS of a
water sample in the upper Los Pilios River watershed
can be estimated as about half of the specific
conductance; however, TDS or SC measurements are
not a substitute for laboratoi-~- measurements to
indicate the effects of land use changes or other trends.
We will begin at the headwaters of the basin at
the high-altitude lakes in the Weminuehe Wilderness,
move do~~m the watershed through the streams, and
end up in Vallecito Reservoir--the sink for everything
that occurs in the upper Los Pinos River watershed.
All of the water-quality sites in the upper Los Pinos
River watershed are shown in figure ~.
High-Altitude Lakes
The USGS collected ~~-ater-quality samples from
high-altitude lakes, located east of the summit of
Windom Peals at the headwaters of Vallecito Creek
(fig. ~). The water-quality data were collected to
describe long-tern trends and effects of atmospheric
deposition. Sample dates range from 1985 to 2002.
Graphs of selected water-quality parameters indicate
that there is an improving trend in some water-quality
parameters (chloride, iron. and pH) (fig. 6).
Constituents t<-pically used for detection of
atmospheric deposition from power plants such as
nitrate and sulfate (Turk and others, 1993) did not
shotiv strong trends. Trend analysis of the data using
the Maim-Kendall test (Helsel and Hirsh, 1992; Salmi
and others. 2002) indicated that the improving trends
are significant. The significance leve10.001 means
that there is a 0.1 % probability that the values are from
a random distribution, and with that probability we
make amistake when rejecting the null hypothesis of
no trend. Thus the significance leve10.001 means that
the existence of a monotonic trend is very probable
(Salmi and others, 2002). The sigiuficaiice level 0.1
means that there is a 10% probability that we make a
mistake when rejecting the null hypothesis (Salmi and
others, 2002). The cause of the improving trends are
unknown; holvever, because of the isolation of these
lakes, very few factors could affect the water quality
of the lakes. These factors could include chemical
erosion of rocks and soils, sheep grazing, human
recreational use, atmospheric deposition, cloud
seeding, and climate change. The trine line for the
Clean Air Act of 1990 is indicated on the graphs;
details involved with the Clean Air Act, and whether
this could affect the upper Los Pinos River watershed,
are beyond the scope of this report.
Streams
In tributaries to Vallecito Creels, most of the
samples showed good water quality eicept for Rock
Creels (site number 8, figure ~). On July 25, 1990, a
water sample from Rock Creels sho«-ed pH = ~.8,
dissolved iron concentration = 270 µg/L (micrograms
per liter), and dissolved manganese concentration =
170 ug/L. Pyrite (fools gold) occurs in the
Uncompahgre Formation throughout the upper
Vallecito Creels basin. Ground water that issues from
the pyrite-bearing formation leaves a coating of iron
(fei7-ic hv_ dro~ide) on stream boulders in Rock Creels
(Barker, 1969). Springs ofiron-sulfate water issue
from the schist that underlies the north-facing
mountain slope southeast of the junction of Rock and
Vallecito Creeks. The water has lulled trees, stained
the cliffs, and caused fish to leave the lower part of
Rock Creek (Bailser, 1969, p. 14). A water analysis of
the springs indicated the following concentrations:
aluminum 18 ppm (parts per million); iron 12 ppm;
manganese 12 ppm; copper 0.13 ppm; zilic 1.5 ppm;
sulfate 1,270 ppm; specific conductance 2,440 µmhos
(micromhos at 25°C), and pH 2.6 (Barker, 1969).
Hikers or recreationists that drink from Rock Creek
may eiperience an iron taste, and other heav<T metals
are probably present in Rock Creek because of the
mineralization. At Vallecito Creek upstream from the
reservoir, the dissolved metals are diluted by other
streams in the Vallecito Creek basin; therefore-
dissolved-metal concentrations are relatively low in
water at the USGS Vallecito Creek gaging station.
The USGS streamflow gaging station at Vallecito
Creek upstream from the Forest Service campground
(fig. ~) is a Hydrologic Benchmark Neti`vork (HBN)
station for the USGS. Stre~unflow and water-quality
data have been collected from the site since 1958. The
goal of the HBN is to detect continental-scale, long-
term trends in ~yater qualit<- by analysis of samples
from streams throughout the United States. Graphs of
selected water-quality- parameters for Vallecito Creek
at the USGS gaging station (fig. 7) sho~y improvuig
trends in chloride, ammonia, and gross beta activity (a
measure of Cesium-137 radioactivity). It is significant
that decreasuig trends also ~yere noted for chloride in
16 Water-Quality Data Synthesis for the Upper Los Pinos River Watershed, In cooperation with the Colorado Watershed Protection Fund and
Southwestern Colorado, and Suggestions for a Watershed Plan, 2005 the San Juan Resource Conservation and Developrnent Council