Laserfiche WebLink
~. <br />• AQUATIC IMPAIRMENT STUDY OF THE SANBORN CREEK MINE DISCHARGE, <br />SOMERSET, COLORADO <br />ABSTRACT <br />The Colorado School of Mines conducted an aquatic impairment study for the Sanborn Creek <br />Mine near Somerset, Colorado during 1994. The purpose of the study was to assess the effects of <br />the mine dischazge on aquatic macroinvertebrate fauna living in the North Fork River. Sample <br />stations were established at 10 m, 100 m, 200 m, 400 m, and 600 m upstream of the <br />discharge, and the same number at corresponding distances downstream: 10 m, 100 m, 200 m, <br />400 m and 600 m. Aquatic macroinvertebrates were sampled in March and in October using a <br />modified Hess sampler. Field water quality measurements and water samples for laboratory <br />analysis were collected at the same sites during the same periods, and the physical habitat of <br />the stream as well as the condition of the surrounding stream bank and ripazian areas was <br />assessed. The study found that total numbers of aquatic macroinvertebrates were moderately <br />high, between 300 to 1600 organisms per mZ. A total of 14 insect families were identified, with <br />the fauna dominated by large numbers of Trichopterans and Chironomids. ETPlC ratios were <br />calculated, and generally were lower in the downstream stations, mainly due to increases in <br />Chironomids rather than a decrease in the intolerant families. Water quality measurements <br />indicated detectable plume concentrations downstream, with the water quality returning to <br />ambient conditions 600 m downstream or less. There were no obvious conditions related to the <br />physical or stream side habitats that would substantially affect aquatic macrofauna, except for <br />higher observed silt deposition downstream of the discharge. A possible source of the silt is the <br />Sanborn Creek watershed. Presence of the silt could affect macroinvertebrate density and <br />composition. We believe that the discharge from the Sanborn Creek Mine has a minimal effect <br />on stream macroinvertebrates in general, that the discharge has little, if any, effect on the <br />overall food base for fish, and that the use of the river for fishing has not been impaired. <br />INTRODUCTION <br />Purpose and Scope: <br />In March, 1994, Colorado School of Mines was contracted to conduct an aquatic impairment <br />study for the Sanborn Creek Mine requested by the Colorado Department of Health. The purpose <br />of the study was to investigate possible impacts of the mine discharge on the aquatic habitats and <br />organisms of the North Fork of the Gunnison River. The study included water quality <br />• 1 <br />