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<br />Date: February 20, 2000 <br />To: Wally Erickson <br />From: Harry Posey <br /> <br />Subject: Groundwater monitoring proposal; DGMC, Incas Mine, M-86-076 <br />This letter comprises my review of Bob Hill's water monitoring data from the captioned <br />mine area for 1996-1998. Also provided for your review is a proposed groundwater <br />monitoring schedule and monitoring parameters list. <br />REVIEW: <br />The Incas mine and mill are high and dry facilities stationed together on a steep <br />southerly-facing slope. It is not anticipated that mining will intersect groundwater. <br />Several hundred feet below the mine and mill lies the portal of an historic draining adit; <br />several hundred feet below that portal is an ephemeral stream. The operator indicates <br />that the adit flows at about 3 gpm, and the stream varies from zero, generally, up to <br />several ] Os of gpm during spring snowmelt. Because the stream and adit portal are <br />directly downgradient of the mine/mill area it is presumed that surface or groundwater <br />discharges from the mill would report to the draining adit and portal along with dilution <br />water. The adit water discharges subsurface into alluviumJtalus. Most constituents in the <br />adit water are at or below detection, so are not detected in the ephemeral stream <br />downgradient. <br />Dr. Hill sampled both the adit and surface water during five quarters in 1996 and one <br />quarter each in 1997 and 1998. Those results, provided in your August 30, 1999 packet, <br />are the basis of this review and proposal. <br />Except for surface water pH measured in 1998, concentrations of all parameters were <br />below surface water (aquatic life or agriculture) and groundwater (drinking water or <br />agriculture) standards. All regulated parameters were measured, and all of the detection <br />limits were below the regulated value. The single stream pH, which was reported at 6.38 <br />on 10/3/98, appears anomalous with respect to the other measurements at this site, all of <br />which were about 7.7 or higher. <br />