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Seneca 11 Mine <br />SL -6 Phase III Bond Release Request <br />Impacts to Alluuial Valley Floors (AVFs) <br />June 2014 <br />Page 7 -279, Tab 7 of the Seneca II Mine permit identifies one AVF where irrigation was <br />practiced on Fish Creek from the point where Cow Camp Creek is confluent with Fish Creek <br />down to where Fish Creek is confluent with Trout Creek. That is a 63 acre parcel located <br />downstream of the confluence with Bond Creek. However, the irrigation ditch for this parcel, <br />with its headgate on Fish Creek just above the Bond Creek confluence, washed out in 1997, and <br />has not been used since. <br />Based on impact projection analysis performed in Tab 7, Section VII.A.1.c., total dissolved solids <br />(IDS) increases in the Fish Creek stream flow as a result of surface water discharges from <br />NPDES8 (Seneca) and NPDES4 (PSCM) will be only on the order of 76 and 74 mg /l for the <br />months of June and July, respectively. This projection equates to TDS concentrations in the Fish <br />Creek streamflow ranging from 497 to 607 mg /1. <br />The significance of these predicted increases in the TDS concentrations in the Fish Creek AVF <br />are negligible. It has been demonstrated in Tab 7, Section VII.B.1.c., that crops grown in the area <br />can tolerate TDS concentrations in excess of 2,000 mg /1. Predicted TDS concentrations of Fish <br />Creek streamflow of only 497 to 607 mg /l will in no way result in water quality changes that <br />significantly and adversely affect the composition, diversity or productivity of the vegetation <br />dependent on subirrigation and in no way limits the adequacy of the water for flood irrigation. <br />Table 9 (Attachment E) _provides June and July TDS values at Site SSF11 (upper Fish Creek) and <br />Site SSF13 (lower Fish Creek) from 2003 to 2013. The maximum increase of TDS between the <br />sites in June was 50 mg /l (average = 25 mg /1), a 76 mg /l increase was predicted. The maximum <br />increase of TDS between the sites in July was 70 mg /l (average = 21), a 74 mg /l increase was <br />predicted. There are less July samples than there were June samples. This is due to the fact that <br />Fish Creek is monitored in July only if either Sites SSC10 (lower Cow Camp Creek) or SSB12 <br />(lower Bond Creek) are flowing. Sites SSC10 and SSB12 usually dry up in late summer, although <br />Outfalls 004 and 008 upstream flow continuously. This reduction in flow is due to stream <br />channel infiltration and evapotranspiration along the lower reaches of Bond Creek. <br />31 <br />