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The only significant ground water in the permit area occurs in sandstones of <br />the lower Burro Canyon Formation. The applicant has installed 3 monitoring <br />veils, designated BW-l, 8W-2, and BW-3, in this aquifer. Alluvial ground <br />water along Naturita Creek will be monitored in four wells installed by the <br />applicant. A well has also been installed in order to monitor alluvial ground <br />water quality in Section 33 Creek. The applicant has collected baseline water <br />level and quality data, and upon commencement of mining all wells will be <br />sampled quarterly for field parameters and full-suite samples will be <br />collected twice per year. <br />The applicant has committed to a spoil spring survey following <br />snowmelt each year. The applicant will sample for water quality any spoil <br />acquifer spring which discharges at least 10 GPM. A report submitted to the <br />Division by June 15 each year will document the survey and report any <br />analytical results. <br />The appiicatfon is in compliance with the requirements of this section. <br />Hydrologic Balance: <br />Surface Water <br />The Hamilton Mine is located in the San Miguel River drainage basin <br />approximately three quarters of the distance between its source 1n the San <br />Juan Mountains and its confluence with the Dolores River. The San Miguel <br />River drains an area of 1,080 square miles. The proposed permit area <br />constitutes 0.1 percent of the San Miguel River drainage. The area disturbed <br />by mining activities will be 0.04 percent of the same drainage basin. It <br />traverses the interior portions of a basin within the Uncompahgre Plateau. <br />This basin trends southeast to northwest and fs chiefly underlain by Dakota <br />and Burro Canyon Sandstones, the Morrison Formation and Mancos Shale. The <br />source area is primarily composed of teritary volcanic intrusives. The <br />Morrison Formation and Mancos Shale have the greatest potential for <br />influencing San Miguel river water chemistry. Iorns, et al. (1965) indicate <br />that the waters draining from this area are of a calcium bicarbonate - sulfate <br />type during high flow periods. These waters contain less bicarbonate during <br />low flows while the calcium and sulfate concentrations increase. This <br />concentration increase is caused by less dilution from snowmelt runoff. In <br />addition, approximately 15,500 acres of irrigated land lies between <br />Placerville (near the headwaters to the southeast) and Naturita, Colorado. <br />Naturita is approximately 1 1/2 miles downstream of the proposed Hamilton Mine <br />permit area. Iorns, et al (1905) estimated that 2.8 tons of total dissolved <br />solids (TDS) per acre are contributed to the waters annually from this area. <br />This results in increased levels of magnesium, potassium, sulfate and <br />chloride. Water quality samples taken from the San Miguel River at Naturita <br />have a weighted average of 316 milligrams per 11 ter (mg/1) TDS. Specific <br />conductivity varies between 318 and 730 millimhos (mmhos>. The mean sodium <br />adsorption ratio (SAR> is about 0.7 according to U.S.G.S data from samples <br />taken at Naturita. Discharge records indicate that flow in this river exceeds <br />60 cubic feet per second (cfs) 907. of the year, while flows exceed 1,000 cfs <br />about 107. of the. year. The mean discharge of the river is 351 cfs. San <br />Miguel River waters are suitable for domestic use except during low flow <br />periods when sulfate levels exceed EPA domestic use standards. <br />-7- <br />