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INTRUDUCTION <br /> Biomonitoring provides an effective method for testing <br /> the toxicity of effluents from municipal and industrial <br /> discharges . Among the advantages of biomonitoring is the <br /> ability to test complex effluents containing a broad range of <br /> contaminants . The biomonitoring methods generate data that <br /> cannot be gotten solely from chemical analyses. At the same <br /> time, chemical analyses often go hand in hand with the <br /> biomonitoring tests. <br /> Because of the value of biomonitoring , states in EPA <br /> Region VIII have begun to use whole effluent toxicity testing <br /> as a means to evaluate industrial and municipal discharges <br /> through the NPDES permit process . As a NNDES permittee, <br /> Midcontinent Resources is required to perform quarterly <br /> biomonitoring for acute effects and semiannually for chronic <br /> effects . This report details the results of acute tests <br /> undertaken during June, 1989 to satisfy the biomonitoring <br /> requirements of the state of Colorado . <br /> MATERIALS AND METHODS <br /> -Sample Collection <br /> Water samples were collected in one-gallon plastic <br /> containers on June 22, 1989. Receiving water from Dutch <br /> Creek upstream of the pond was also collected for use as a <br /> dilution water source in the tests. fhe containers were <br /> packed in ice chests and transported to the lab via an <br /> overnight express carrier . In the lab , samples were <br /> refrigerated at 4- C until use. A chain of custody form <br /> showing collection and lab arrival times is included in <br /> Appendix 1 . <br /> rest Organisms <br /> Ceriodaphnia sp . and the fathead minnow, Pimephales <br /> promelas, were used in the tests . Ceriodaphnia sp . were <br /> cultured in T .H.E. Consultants' laboratory. Fathead minnows <br /> were received from a commercial supplier by overnight express <br /> service. Before use, minnows were allowed to acclimate to <br /> laboratory temperatures in an aquarium. <br /> Test Procedures <br /> Upon receipt at the lab water samples were analyzed for <br /> alkalinity, hardness, ammonia, conductivity, dissolved <br /> oxygen, and pH. Alkalinity and hardness were determined <br /> titrimetrically according to methods described in Hach <br /> Chemical Co . ( 1978) . Ammonia was also determined by <br /> titrimetric methods after distillation (APHA/AWWA/WPCF 1985) . <br /> Acute tests were performed according to the procedures <br /> outlined in Peltier and Weber ( 1985) . Acute Ceriodaphnia <br /> tests were conducted over 48 hours with fathead minnows being <br /> exposed for 96 hours. Exposure concentrations included 100%, <br />