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Coal Company Water Quality Assessment 000042161 <br />Total Recoverable Iron, Dissolved Manganese: Mass balance calculations were used to determine <br />• the assimilative capacity for total recoverable iron and dissolved manganese in Fish Creek. <br />Using the equation provided in the beginning of Section IV, the chronic low flows set out in Table <br />A-5, the background concentrations contained in Table A-4, and the in-stream standards found in <br />Tables A-2 and A-3, assimilative capacities for iron and manganese were calculated. The data used <br />and the resulting calculations are contained in Table A-7. <br />Table A-7 <br />Manganese and Iron Assimilative Capacities for Twentymile Coal Company <br />~~::;Pdra»eeter ~Qi`(f./s) '~`Q~~(cfs)` Q;~(6fs) M„(ugR)~ ~M, (u8~),? S1Vf, (u8~) <br />Mn, Dis acute 0.63 1.2 1.83 106 9034 13,721 <br />Mn, Dis chronic 1.3 1.2 2.5 106 3105 6,354 <br />Iron, Trec chronic 1.3 1.2 2.5 2175 1000 0 <br />Note that in-stream ambient water quality data summarized in Table A-4 did not include dissolved <br />manganese analytical results but did contain total recoverable manganese data. The amount ofinetal <br />in total recoverable form tends to be greater than the dissolved portion. Thus, use of the mean <br />ambient total recoverable manganese data results in a conservative analysis of the available <br />assimilative capacity for dissolved manganese. <br />• For total recoverable iron, the ambient background mean concentration is greater than the water <br />quality standazd. This results in a calculation of zero available assimilative capacity. Note that <br />downstream assimilative capacity calculations that include downstream flow contributions also <br />resulted in zero assimilative capacity. In cases where no assimilative capacity is available, it is the <br />standard procedure of the WQCD to assign the in-stream standazd as the assimilative capacity to <br />prevent further degradation while studies of the receiving stream aze conducted to determine <br />appropriate assimilative capacities for all relevant dischazgers. <br />Ammonia: Ammonia is present in the aqueous environment in both ionized and un-ionized forms. <br />It is the un-ionized form which is toxic and which is addressed by water quality standards. The <br />proportion of total ammonia present in un-ionized form is a function of the mixed effluent and in- <br />stream pH and temperature. <br />The Colorado Ammonia Model (CAM) is a software program designed to project the assimilative <br />capacity of ammonia based on upstream and downstream conditions and effluent discharges. To <br />develop setpoint conditions for the CAM, an assessment must be conducted of the receiving water <br />conditions on a monthly basis of the pH and corresponding temperature, over a period of at least one <br />year. <br />There were no data available for Fish Creek that would meet the CAM's needs. In the absence of <br />data, the WQCD standard procedure is to rely on the allowable in-stream total ammonia default <br />values contained in the Colorado Total Maximum Daily Load and R'asteload Allocation Guidance. <br />Appendix A Page 9 of 12 <br />