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001989 i~;~t;t~;~~~t~ ANALYSIS OF STREAM QUALITY IN THE YAMPA RIVER BASIN, COLORADO AND WYOMING By Dennis A. Wentz and Timothy Doak Steele ABSTRACT Historic data show no significant water-temperature changes since 1951 for the Li ttle Snake River or the Yampa River, the two major ,streams of the Yampa River basin. Regional analyses indicate that harmonic-mean temperature is negatively correlated with altitude, thus allowing stream temperatures to be estimated at unmeasured sites in the basin. No change in specific con- ductance since 1951 was noted for the Li ttle Snake Ri.ver; however, specific conductance in the Yampa River has increased 14 percent since that time and is attributed to increased agricultural and municipal use of water. Site- specific relationships between major inorganic constituents and specific con- ductance for the Little Snake and the Yampa Rivers were similar to regional re 1 at i onsh i ps deve loped for the ent i re ba s.i n from both hi stor i c and recen t (1975) data. These relationships provide a means for estimating concentra- tions of major inorganic constituents, from specific conductance, which is easily measured. {;;',: Trace-element and nutrient data collected from August 1975 through September 1976 at 92 sites in the Yampa River basin indicate that water~ qual ity degradation occurred upstream from 3 sites. The degradation resulted from underground drainage from pyritic materials that probably are associated with coal at one site, discharge from powerplantcool ing-tower blowdown water at a second site, and run'off from a small watershed containing a gas fi.e1d at the third site. In the latter instance, it is not'known if the effect was natural or man-induced. Although not critical problems, ambientconcentra- tions of dissolved and total iron and manganese frequently exceeded proposed Colorado water-quality standards. The concentrations of many dissolved and total trace elements and nutrients were greatest during March 1976. These trace-element and nutrient concentrations were associated with relatively larger suspended-sediment concentrations and relatively sma 1 ler pH values than occurred at other times of the year. Seasonal fluctuations in specific conductance were controlled primarily by and were inversely related to stream discharge. ..-.- .~'~~. . ..''; INTRODUCTION ;:..<;r~: ~~:~~:~t.~:~} :'.'("".:~ _....~ }',.,.;:. Energy resources, primari ly coal, rates in the 8,080-mi2 (20,900-km2) Yampa rado and south-central \>Jyoming (fig. 1). are being developed at increasing River basin of northwestern Colo- For example, annual coal production ....-.: " ?:~<':-'-^":';; ....:.,:>./' "; ,>. ..'': ',',': .'. - -',' "c''-'';::.<'