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28 Water-Quality Characteristics and Ground-Water Quantity of the Fraser River Watershed, Grand County, Colorado, 1998-2001
<br />dewatering, or damage to the aquifer), more information would
<br />be needed on recharge and discharge rates along with a more
<br />precise understanding of aquifer properties. The estimate of the
<br />amount of water currently available within the Troublesome
<br />Formation discussed in this section is not representative of the
<br />true full potential yield of the aquifer. Factors that will affect the
<br />yield of the aquifer include recharge rate, regional ground-water
<br />flow, discharge rate, specific storage of the aquifer, and location
<br />and pumping rates of proposed water-supply wells. The use of
<br />ground-water-flow modeling combined with more comprehen-
<br />sive aquifer testing would be necessary to refine estimates of
<br />future water availability.
<br />Summary
<br />Increasing urban development, as well as the seasonal
<br />influx of tourists, is placing more demands on the water
<br />resources in the Fraser River watershed. The U.S. Geological
<br />Survey, in cooperation with the Grand County Board of County
<br />Commissioners, conducted an assessment of ground- and
<br />surface-water quality and ground-water quantity in the Fraser
<br />River watershed, Grand County, Colorado. Eleven wells were
<br />sampled semiannually from August 1998 through September
<br />2001. The data were related to aquifer type (alluvial, Trouble-
<br />some Formation), land use (urban, nonurban), and presence or
<br />absence of individual septic disposal systems. One surface-
<br />water site, Fraser River below Crooked Creek at Tabernash,
<br />Colorado, was sampled bimonthly. This site represents the
<br />cumulative effects of natural and human factors that affect
<br />surface-water quality in the Fraser River watershed upstream
<br />from the town of Tabernash. Ground-water-quantity estimates
<br />were made for the surficial alluvial aquifer and the Trouble-
<br />some Formation aquifer.
<br />The ground water primarily was a calcium-bicarbonate
<br />type water. Except for elevated radon-222 activities, no wide-
<br />spread ground-water-quality problems in the watershed were
<br />indicated. The ground-water data were compared to U.S. Envi-
<br />ronmental Protection Agency or State of Colorado water-
<br />quality standards. In general, ground water in the Fraser River
<br />watershed is suitable as a source of drinking water and for
<br />domestic, municipal, industrial, and irrigation purposes. Con-
<br />centrations of dissolved solids, chloride, fluoride, sulfate,
<br />nitrite, and nitrate in the ground-water samples were substan-
<br />tially less than their respective drinking-water or water-quality
<br />standards. Properties and constituents from samples from at
<br />least one well that did not meet the standards were turbidity,
<br />iron, manganese, methylene blue active substances, and
<br />radon-222. The constituent of most concern is radon-222. All
<br />radon-222 concentrations for every well sample exceeded the
<br />U.S. Environmental Protection Agency proposed drinking-
<br />water standard of 300 pCi/L, which is currently (2003) under
<br />review.
<br />Results of the two-tailed Wilcoxon rank-sum tests indi-
<br />cated that there were statistically significant differences
<br />(p-value <_0.05) in values or concentrations of some field prop-
<br />erties and water-quality constituents between aquifer type (allu-
<br />vium, Troublesome Formation), land use (urban, nonurban),
<br />and areas with or without individual septic disposal systems.
<br />Chloride, magnesium, and sulfate concentrations were
<br />significantly higher in the alluvial aquifer, urban areas, and
<br />areas with the septic systems. Orthophosphate concentrations
<br />were significantly higher in the Troublesome Formation aquifer
<br />and in areas without individual septic disposal systems. Dis-
<br />solved organic carbon concentrations were significantly higher
<br />in the alluvial aquifer and areas without individual septic dis-
<br />posal systems than in the Troublesome Formation aquifer and
<br />areas with individual septic disposal systems, although these
<br />concentration differences likely had no environmental signifi-
<br />cance.
<br />An examination of changes in ground-water-quality data
<br />over time revealed that changes were apparent only for one of
<br />nine wells examined. For this well, specific conductance
<br />appeared to increase over time, probably due to increasing con-
<br />centrations of calcium, magnesium, chloride, and sulfate during
<br />parts of the sampling period.
<br />Surface water collected at the Fraser River below Crooked
<br />Creek at Tabernash from August 1998 through September 2001
<br />also was a calcium-bicarbonate type water and had low concen-
<br />trations of dissolved solids. Water quality at this site generally
<br />was good and indicated the suitability of the water for drinking,
<br />residential, industrial, and irrigation purposes. All pH values
<br />and concentrations of dissolved oxygen, chloride, sulfate, iron,
<br />manganese, un-ionized ammonia, nitrite, nitrate, and fecal
<br />coliform bacteria met State of Colorado instream water-quality
<br />standards.
<br />Concentrations of most constituents in the Fraser River
<br />varied seasonally. Maximum values of specific conductance
<br />and maximum concentrations of chloride, sulfate, ammonia,
<br />nitrate, and all phosphorus species typically occurred during
<br />winter or early spring when discharge was minimal and when
<br />local wastewater-treatment facilities were near maximum dis-
<br />charge. Minimum values or concentrations of all constituents
<br />except sulfate generally occurred during snowmelt runoff, indi-
<br />cating the dilution of the surface water with snowmelt. Mini-
<br />mum sulfate concentrations were detected during midsummer
<br />after snowmelt runoff. Ammonia and nitrate concentrations
<br />also were at a minimum during summer and fall, with low
<br />nitrate concentrations probably occurring because of consump-
<br />tion by instream biota. Maximum concentrations of suspended
<br />sediment occurred during early spring or during snowmelt run-
<br />off, and maximum concentrations of dissolved organic carbon
<br />occurred during snowmelt runoff. Concentrations of fecal
<br />coliform bacteria peaked during summer but remained below
<br />the State of Colorado instream standard for the Fraser River.
<br />Estimates of ground-water quantity in the upper Fraser
<br />River watershed were made for the surficial alluvial aquifer and
<br />the Troublesome Formation aquifer, the primary sources of
<br />ground water for domestic and municipal use in the valley. Cal-
<br />culations of the saturated volume of the alluvial aquifer were
<br />made for minimum, average, and maximum potentiometric sur-
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