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The stratum immediately below the lowest minable coal seam consists of a soft, gray to blue <br />shale with sparse shaley siltstone lenses. This strata is generally 26 feet thick throughout the <br />permit area. Below this strata there are four coal seams that are not considered minable within <br />the permit area. These coal seams are referred to as Naturita Seams 1 through 4, in descending <br />order. <br />Hydrologic Balance -Ground Water <br />Information on the occurrence and quality of ground water in the permit and surrounding area <br />is provided in Sections 2.04.7(1) and in Exhibit 3 of the Hamilton Mine permit application. The <br />hydrologic monitoring plan is presented on page 2.05-35, and is approved as proposed. <br />The only significant ground water in the permit area occurs in sandstones of the lower <br />Burro Canyon Formation. The applicant has installed 3 monitoring wells, designated BW-1, <br />BW-2, and BW-3, in this aquifer. Alluvial ground water along Naturita Creek will be monitored <br />in four wells installed by the applicant. A well has also been installed in ordec to monitor <br />alluvial ground water quality in Section 33 Creek. The applicant collected baseline water level <br />and quality data, and continues to sample all wells quarterly for field parameters and full-suite <br />parameters twice per year. <br />The applicant has committed to a spoil spring survey following snowmelt each year. The <br />applicant will sample water quality for any spoil aquifer spring which discharges at least 10 <br />gpm. A report submitted to the Division by June 15 each year will document the survey and <br />report any analytical results. <br />Hydrologic Balance: -Surface Water <br />The Hamilton Mine is located in the San Miguel River drainage basin approximately three <br />quarters of the distance between its source in the San Juan Mountains and its confluence with <br />the Dolores River. The San Miguel River drains an area of 1,080 square miles. The proposed <br />permit area constitutes 0.1 percent of the San Miguel River drainage. The area disturbed by <br />mining activities will be 0.04 percent of the same drainage basin. It traverses the interior <br />portions of a basin within the Uncompahgre Plateau. This basin trends southeast to northwest <br />and is chiefly underlain by Dakota and Burro Canyon Sandstones, the Morrison Formation and <br />Mancos Shale. The source area is primarily composed of tertiary volcanic inttusives. The <br />Morrison Formation and Mancos Shale have the greatest potential for influencing San Miguel <br />river water chemistry. Waters draining from this area are of a calcium bicarbonate -sulfate type <br />during high flow periods. These waters contain less bicarbonate during low flows while the <br />calcium and sulfate concentrations increase. This concentration increase is caused by less <br />dilution from snowmelt runoff. In addition, approximately 15,500 acres of irrigated land lies <br />between Placerville (near the headwaters to the southeast) and Na[urita, Colorado. Naturita is <br />approximately 1 1/2 miles downstream of the proposed Hamilton Mine permit area. It is <br />estimated that 2.8 tons of total dissolved solids (TDS) per acre are contributed to the waters <br />annually from this area. This results in increased levels of magnesium, potassium, sulfate and <br />chloride. Water quality samples taken from the San Miguel River at Naturita have a weighted <br />average of 316 milligrams per liter (mg/]) TDS. Specific conductivity varies between 318 and <br />5 <br />