2009-05-12_GENERAL DOCUMENTS - C1981025

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Since August 11, 1995, Mine No. 1 and Mine No. 3 portal discharges have been combined and treated. The discharge (Outfall 001) to North Thompson Creek from the water treatment system is no longer subject to the CDPHE CDPS Permit No. CO- 0029599, as it was terminated on or around April 20, 2006. There was no known incident where Outfall 001 discharges failed to meet CDPS discharge requirements. (c) Flows From Other Sources There are a number of inflows, other than from the portals of Mine No. 1 and Mine No. 3, to North Thompson Creek between the upstream and downstream monitoring stations of the mining permit. These include discharges from Mine No. 2, four known springs and seeps, runoff from reclaimed disturbed and undisturbed areas of the contributing watershed, and, perhaps, charge to surface flows from alluvial aquifers, including that section located at the foot of the mine waste refuse pile. The North Thompson Creek Mine No. 2 is abandoned and "pre-law". It was not, historically, a part of Permit C-1981-025, and it is not proposed to be reopened or permitted under this renewal action. A detention pond prior to discharge into North Thompson Creek treats the discharge from this mine. No record of laboratory sampling of the discharge from the pond has been recovered during this review. Mine No. 2 water was once reported as acid and toxic (a field measurement of a 2.5 pH by Division staff). Field measurements of May 20, 2003 (Division staff) of discharge from the treatment pond of pH was 8.2 and of TDS was 1780 mg/1. Flow was measured as 1.09 gallons/minute. Only two springs, Spring 1 and Spring 2, are identified in the PAP. A tributary from the southwest discharges into North Thompson Creek between the upstream and downstream monitoring stations. Alluvial groundwater may flow into North Thompson Creek. In addition, there was no monitoring of a bed-rock seep below Mine No. 1. See the discussion of ground water for these potential contributions. (d) Receiving Stream Standards Monitoring suggests that, at times, some parameters in North Thompson Creek may be above receiving stream standards, but except for sulfate, not a result of Outfall 001 discharges. Baseline and monitoring water quality data are available in the permit documentation from, for various times, at a location upstream and a location downstream of permitted mining activities, Mine No. 1 and Mine No. 2 inflows (during mining), Mine No. 1 and Mine No. 2 untreated discharges, Spring SP-1 and Spring SP-2, and Outfall 001. There is no information on water quality of the seep just below Mine No. 1. It has a strong sulfur smell, and leaves a crust of precipitate in the vicinity of the seep. North Thompson Creek C-1981-025 Permit Renewal 05 12 May 2009 22