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Environmental Protection Plan, Schwartzwalder Mine 11-4 <br />C = WER• e°''°(x)+bA • Ka <br />'" <br />• <br />(acute) <br />C =WER enr-in(H)+bc • KC <br />(chronic] <br />where WER= Water effect ratio <br />MA = Metal-specific constant for acute toxicity (e.g, MA for uranium is 1.1021) <br />mc = Metal-specific constant for chronic toxicity (e.g, mc for uranium is 1.1021) <br />H = Hardness (mg/L as CaCO3) <br />bA = Metal-specific constant for acute toxicity (e.g, bA for uranium is 2.7088) <br />bc = Metal-specific constant for chronic toxicity (e.g, be for uranium is 2.2382) <br />K = Freshwater conversion factor <br />The numeric criteria shown in Table 11-4 have been calculated based on a hardness of 163, which is the <br />low-flow average at station SW-BPL since sump shut-off in June 2002. The calculation assumes a water <br />effect ratio (WER) of 1.0 unless otherwise noted. <br />The uranium drinking water standard of 0.03 mg/L applies to all reaches of Ralston Creek, which is based <br />on a 70-kg human consuming 2 liters of water per day for 30 years. Hardness-based aquatic toxicity <br />standards are based potential environmental effects on cold water aquatic biota (including fish and <br />macroinvertebrates). Using a hardness of 163 mg/L, the acute toxicity standard for uranium is 4.12 mg/L <br />and the chronic toxicity standard is 2.57 mg/L. <br />The hardness value used in calculating numeric criteria is the average of the calculated hardness values for <br />station SW-BPL during low flow months from June 2002 to February 2007. The use of average of <br />hardness values during low-flow season is in accordance with the CDPHE WQCCs "Basic Standards and <br />Methodologies for Surface Water," Document 5 CCR 1002-31, Table III, footnote (3). At Station SW- <br />BPL, the low-flow season occurs between July and February. Hardness values were calculated from <br />magnesium and calcium concentrations, and the calculated values were similar to laboratory-determined <br />hardness values, when reported by the lab. Because values for many analytes, including calcium and <br />magnesium, were different before and after the sump shut-off, only data from post sump shut-off were used <br />to determine the mean hardness value used in the numeric criteria calculations. Calculated hardness values <br />for these distinct periods are presented in Table 11-3. <br />• <br />4109C.100731 Whetstone Associates •