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Peabody Sage Creek Mine July 2014 <br />SL -3 Phase III Bond Release Request <br />E) Impacts to Alluvial Valley Floors (AVFs) <br />There are two potential AVFs in the Grassy Creek basin. They include a 45 acre parcel near the <br />confluence of Little Grassy Creek and Grassy Creek and a 40 acre parcel along Little Grassy <br />Creek. Per the CDRMS (1/28/2009 email from Tom Kaldenbach), these two parcels are <br />`grandfathered' (per Rule 4.24.3(4)) and are exempt, and are not evaluated. <br />An AVF is present in the Fish Creek basin downstream of PSCM Outfall 004. It was originally <br />discussed on page 7 -279, Tab 7 of the Seneca II Mine permit package, which identifies an AVF <br />where irrigation was practiced on Fish Creek from the point where Cow Camp Creek is confluent <br />with Fish Creek down to where Fish Creek is confluent with Trout Creek. This 63 acre parcel is <br />located downstream of the confluence with Bond Creek. However, the irrigation ditch for this <br />parcel, with its headgate on Fish Creek just above the Bond Creek confluence, washed out in <br />1997, and has not been used since. <br />Based on impact projection analysis performed in the Seneca II Mine permit Tab 7, Section <br />VII.A.1.c., total dissolved solids (TDS) increases in the Fish Creek stream flow as a result of <br />surface water discharges from NPDES8 (Seneca) and NPDES4 (PSCM) and will be on the order <br />of 76 and 74 mg /l for the months of June and July, respectively. This projection equates to TDS <br />concentrations in the Fish Creek streamflow ranging from 497 to 607 mg /1. The significance of <br />these predicted increases in the TDS concentrations in the Fish Creek AVF are negligible. It has <br />been demonstrated in Tab 7, Section VII.B.1.c., that crops grown in the area can tolerate TDS <br />concentrations in excess of 2,000 mg /1. Predicted TDS concentrations of Fish Creek streamflow <br />of only 497 to 607 mg /l will in no way result in water quality changes that significantly and <br />adversely affect the composition, diversity or productivity of the vegetation dependent on <br />subirrigation and in no way limits the adequacy of the water for flood irrigation. <br />Table 14 provides June and July TDS values at Site SSF11 (upper Fish Creek) and Site SSF13 <br />(lower Fish Creek) from 2003 to 2013. The maximum increase of TDS between the sites in June <br />was 50 mg /l (average = 25 mg /1) compared to a predicted 76 mg /l increase. The maximum <br />increase of TDS between the sites in July was 70 mg /l (average = 21) compared to a predicted 74 <br />32 <br />