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Kathleen I{alamen Aquatic Impairment Study Februar}• 1, 1995 Under the requirements of CDPS Permit Number CO-0000132, the Sanborn Creek Mine discharge, Outfall 011, is required to be monitored weekly for flow, total suspended solids, total iron, pH, and oil and grease; monthly for total dissolved solids; and quarterly for whole effluent toxicit}'. Several whole effluent toxicit}• (WET) tests have been performed using water fleas (Ceriodaphnia dubia) and fathead minnows (Pimephelas promelas). All WET tests using Ceriodaphnia dubia have failed. A single WET test using Daphnia magna has passed. Phase 1 toa;icity identification studies on the mine effluent performed by CT&E implicated alkalinity and sodium ions as the major causes of toxicit}•, Subsequent toxicity identification evaluations completed in October, 1993, indicated that the toxicity is most likel}• due to TDS in the form of bicarbonates. Following a request by Somerset Mining Company in Januar}•, 1994, the discharge permit was amended to grant relief from reguired ~+'ET testing until the aquatic impairment study was completed. WET testing was waived for the period between April 1 and December 31, 1994, and is to resume under new requirements beginning the first quarter of 1995. A two-species WET test with Ceriodaphnia sp., and fathead minnows is required. Somerset Mining Company expects the WET test with Ceriodaphnia dubia to fail, and the WET test with fathead minnows to pass, since there has been no significant change in the mine discharge during the suspension of WET testing. Since the aquatic impairment study has concluded the Sanborn Creek Mine discharge does not have a significant impact on the receiving waters of the North Fork of the Gunnison River, Somerset Mining Company requests relief from the required WET testing. If total relief from WET testing cannot be granted, then Somerset Mining Company requests a change in required species, such as Daphnia magna in place of the Ceriodaphnia dubia. Outfall 0]1 has been in compliance with the monitoring requirements and effluent limitations for the past year. A cop}- of t}ie monitoring results is attached. Somerset ?fining Company requests a change in the monitoring frequenc}' for Outfall 011 to monthl}• for total suspended solids, total iron, pH, and oil and grease. If monthly monitoring frequency for all these parameters cannot be granted, then Somerset Plining Compan}- requests a change to monthly for at least total suspended solids and total iron. 411 the other outfalls covered by CDPS Permit Number CO-0000132, are for sedimentation control ponds at various locations around the mine facilities. Outfalls U07, 009, 010, 012, and 013 are required to be monitored weekly for flow, pH, and oil and grease;