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• COLORADO DEPARTMENT OF HEALTH <br />Water Quality Control Division <br />Rationale - Page 8 <br />Permit No. CO -0034142 <br />APPLICABLE RULES AND REGULATIONS: <br />pH: (Continued) <br />To consider the impact of the effluent pH upon the Williams Fork River, <br />data provided by Empire Energy for the period of 1981 through part of <br />1983 was considered for the Williams Fork River upstream of the <br />discharge. Data from the USGS Station 09249750, Williams Fork River at <br />Mouth, near Hamilton, Colorado, was also considered for the water years <br />of 1976 through 1980. The data from these two sources is summarized <br />below. <br />Upstream of Discharge, Downstream of Discharge, <br />Empire Energy Data USGS 09249750 Data <br />Sample Sample <br />Parameter Mean Range Number Mean Range Number <br />PH, s.u. 8.42a 7.85-8.79 9 8.1a 7.1-8.7 54 <br />T. Alkalinity, 174 71-225 9 159b 67-270 54 <br />• mg/l as CaCO3 <br />a/ This is the median pH value. The mean Empire Energy value was 8.4 s.u. <br />b/ The lowest stream mean monthly value was 70.3 mg/l as CaCO3 for total <br />alkalinity <br />Using calculation examples from an EPA document (see reference 1), the <br />resultant pH value was determined for a mixture of the upstream pH and <br />alkalinity representative values with the effluent pH and alkalinity <br />values. Three steps are involved in determining the pH mixed value. <br />First the mixed alkalinity value is determined from the following equation: <br />Alk mix = (Alku) (Qu) + (Alkd)(Qd) <br />Qu + Qd <br />where <br />Alk u = total alkalinity upstream <br />Alk d = total alkalinity in discharge <br />Qu Q7-10 flow = 16.7 MGD <br />Qd discharge design flow - 0.012 MGD <br />For the upstream alkalinity value, both the mean valueof 174 mg/1 as <br />• CaCO3 and an assumed minimum value of 70.3 mg/l as CaCO3 were <br />considered. For the alkalinity in the discharge, two assumed higher <br />values were considered: 500 and 700 mg/l as CaCO3. The basis for the <br />assumed alkalinity discharge values is from data of two mine water <br />discharges: 002 (593 mean; 520-624 range) and 003 (656 mean; range = <br />616-709 mg/l as CaCO3 for total alkalinity). <br />