Abstract Groundwater pollution is an emerging environmental concern in the Rocky Mountain region. In this two-year study, we evaluated the utility of two sublethal toxicity tests for detecting migration of contaminated ground water into streams and rivers.
During Year 1, we tested groundwater or surface-water samples from five locations at each of two study sites; 1) the Laramie River as it flowed past a former railroad tie treating plant south of Laramie, Wyoming, from June 1985 to October 1985; and 2) Crow Creek as it flowed past an oil refinery in Cheyenne, Wyoming, from June 1985 to April 1986. During Year 2, we tested groundwater and surface-water samples only at the Crow Creek site, from June to September 1986. Each water sample was tested for its effects on survival and reproduction of Ceriodaphnia dubia (an aquatic invertebrate) and survival and growth of fathead minnow (Pimephales promelas) larvae. Chemical analyses of water samples included routine water chemistry parameters, major inorganic ions, II trace elements, dissolved organic carbon, reverse-phase HPLC gradients, and GC-MS analyses of organics.
At the Laramie River, toxic ground water underlaid sediments adjacent to the tie treating plant. However, migration of ground water into the Laramie River did not adversely affect fathead minnows and Ceriodaphnia. Some groundwater and surface-water samples from Crow Creek also were toxic. The oil refinery's effluent appeared to cause much of the adverse effects in surface water downstream from that discharge. Adverse effects upstream from the refinery discharge may have been caused by contaminated ground water or storm sewer runoff.
Results of this study indicate that (1) ambient toxicity tests can be used in alkaline surface waters of the western U.S.; (2) they are sensitive enough to detect migration of contaminated ground water into surface waters; (3) they may be more sensitive in some cases than routine, inexpensive chemical analyses for detecting the presence of contaminants; (4) toxicity of contaminated ground water and an industrial discharge varied considerably during the two-year study; and (5) toxicity of interstitial ground water did not always correspond with toxicity of the overlying surface water or downstream surface water.
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