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Changes in water quality can be expected to occur as a result of mining. An <br />increase in erosion rates are expected from the disturbance of soils and <br />vegetation, however, these are compensated by deposition of sediment in the <br />sediment pond. An increase in total dissolved solids (TDS) may occur from <br />well water pumped and used for dust suppression (7 gallons per minute) and <br />other operational use (10 gallons per minute). Evaporation of water standing <br />in the pond may also cause an increase in TDS, although the absolute increase <br />above background concentrations of about 1500-2000 mg/1 are not expected to be <br />large. <br />The acidic drainage which has been observed at the mine site has the potential <br />for degradation of water quality in Hay Gulch. The concentration of iron, <br />manganese, copper, lead and zinc, as well as other trace metals and sulfate, <br />can be expected to be elevated due to this condition. It is difficult to <br />attribute the cause of this acid drainage to an identifiable source due to the <br />previous mining activities at the site and possible natural sources of this <br />condition in the area. The magnitude and duration of flow can not be <br />precisely quantified, however, indications are that it is probably seasonal <br />and related to runoff with low flow rates (4 to 5 gallons per minute). A <br />treatment system will be installed which will neutralize the acid condition <br />and should effect a decrease in dissolved metals concentrations of the <br />effluent. <br />The probable hydrologic effects on surface water identified above have been <br />determined to not preclude use of the water below the point of discharge from <br />the mine. This conclusion is based on the small and infrequent flows relative <br />to the large amount of dilution available in receiving waters. The quantity <br />of surface water is limited on site and the treatment systems should act to <br />mitigate any adverse effects on surface water. <br />2. Ground Water Effects <br />There are two potentially impacted ground water systems within and adjacent to <br />the La Plata No. 1 Mine: the Menefee Formation, and the Hay Gulch alluvial <br />system. <br />The probable hydrologic consequences of mining to the Menefee Formation are <br />negligible. The Menefee Formation in the vicinity of the La Plata No. 1 Mine <br />appears to be essentially dry. Abandoned mines along the north side of Hay <br />Gulch near the La Plata No. 1 Mine have not been observed to drain water from <br />the portals. No water has drained from or been encountered in the previously <br />developed entries near the location of the La Plata No. 1 Mine. <br />Due to the hydrogeologic characteristics of the Menefee Formation, perched <br />aquifers which may be located above the mined seam may be dewatered during the <br />course of mining operations. Perched aquifers which may be located above the <br />mine are probably limited both in number and in areal extent. There is no <br />documented use of any of these aquifers nor is there any evidence to suggest <br />that any of these overlying aquifers supply base flow to any local streams or <br />springs. Therefore, impacts to perched aquifers, and the Menefee Formation as <br />a whole, will be minimal. <br />_lg_ <br />