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Enviro -Chem Analytical, Inc. <br />2493 Hwy 6850 Unit 7 <br />Grand Junction, CO 81505 <br />Introduction <br />Chronic Toxicity Testing <br />OXBOW — July 2013 <br />2 Species <br />At the request of Oxbow Mining LLC, Enviro -Chem Analytical, Inc. conducted <br />biomonitoring test to evaluate the toxicity of the Outfall. The test's purpose was <br />to determine the effluent's NOEC, LOEC, IC25 for larval fathead minnows <br />(Pimephales promelas) and Ceriodaphnia dubia during short-term 7 -day chronic <br />exposures. <br />According to the NPDES permit, a chronic test is failed whenever the 25% <br />inhibition concentration (IC25) calculated on the basis of test organism survival <br />and growth or survival and reproduction, is less than 100% effluent <br />concentration. <br />Methods <br />A two species chronic test was conducted according to the methods described in <br />the USEPA manual :Short-Term Methods for Measuring the Chronic Toxicity of <br />Effluents and Receiving Water to Freshwater Organisms," 2002, Fourth Edition, <br />EPA/821 -R -02 -013, the McClane Canyon Mine NPDES permit CO- 0029599, and <br />the Colorado Department of Public Health and Environment "Guidelines for <br />Conducting Whole Effluent Toxicity Tests ". <br />Sample Collection <br />The effluent samples were collected by Elk Creek Mine personnel and delivered <br />via Hand to the laboratory. Upon arrival, each sample was logged in according <br />to the Sample Receipt procedures and initial chemistry values were obtained. <br />Minimum chemistry included arrival temperature, pH, conductivity, dissolved <br />oxygen, ammonia, total residual chlorine, hardness and alkalinity. <br />Initial chemistry values are found in Table 1. <br />2 <br />