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Sanborn Creek mine discharges into the river to Somerset is approximately 960 m. The <br />upstream reach from the discharge point to the West Elk Mine (occasional discharge) is <br />approximately 1200 M. Actual sampling was restricted to 600 m above and below the <br />discharge point to minimize effects from these other possible pollutant sources. Two sets of <br />samples and water quality field measurements were collected in 1994 during low flow <br />conditions: the first set was collected on March 16 and 17 and the second during October 14 - <br />23. <br />Macroinvertebrate Sampling and Analysis: <br />Methods used in this assessment generally followed procedures outlined in USEPA (1989, <br />1990). A preliminary reconnaissance was conducted to determine if the discharge plume could <br />be detected in the river. This was be done by wading the river with a conductivity meter and <br />plotting the values on a map of the river. Sample stations were established at 10 m (Station <br />U1), 100 m (Station U2), 200 m (Station U3), 400 m (Station U4), and 600 m (Station U5) <br />upstream of the discharge, and the same number at corresponding distances downstream: 10 m <br />(Station D1), 100 m (Station D2), 200 m (Station D3), 400 m (Station D4) and 600 m (Station <br />D5). Appendix 1 shows the location of each sample station on the North Fork River. <br />Downstream stations were located in the northern third of the river channel and within the <br />plume if it was detectable, to provide a worst -case comparison with upstream data. Three <br />replicate samples were collected at each station. <br />A modified Hess sampler with a 360,a mesh net and 33.6 cm barrel diameter was used to <br />collect macro invertebrate samples. The sampler was firmly inserted into the substrate, which <br />required rocking and pushing to seat it between the boulders and cobbles. Initially, a foam <br />rubber gasket was tried to improve the seal on the bottom, but was later discarded because the <br />sampler was easier to maneuver between the rocks without it. Each rock within the sampler <br />was gently scrubbed with a soft - bristled brush to dislodge invertebrates, then removed from <br />inside the sampler barrel. When all rocks were scrubbed and removed, the loose sediment was <br />gently agitated to a depth of about two inches with the hand to collect additional organisms. <br />Organisms clinging to the net were flushed into the sample chamber with fresh water, and any <br />remaining organisms were plucked off with forceps. The sample chamber was then dumped <br />into an enameled steel tray for picking. The sampler was thoroughly rinsed with fresh water <br />prior to collecting the next sample. Organisms were picked from the tray using forceps and <br />eyedroppers and placed in a labeled sample jar containing 80 percent ethanol and taken to the <br />laboratory for later counting and identification. After about three or four days, the ethanol <br />preservative in the sample bottles was decanted and replaced with fresh 80 percent ethanol. <br />The three replicate samples were collected within a three -meter radius if possible. Some areas <br />were avoided, either because the water death would swamp the sampler or because the <br />substrate materials were too large to be effectively sampled. During the march sampling trip, <br />the river flow had been increasing. Some shallower areas sampled were barren of invertebrates <br />and it was assumed that those places had recently been flooded by the rising water level; those <br />� <br />6 <br />