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RULE 2 - PERMITS <br />Grassy Creek is a perennial tributary of the Yampa River, which it joins approximately five miles <br />downstream of the proposed PSCM facilities, and four miles downstream of its confluence with <br />• Little Grassy Creek. Four streamflow monitoring sites characterize flows along Grassy Creek, and <br />are listed below from upstream to downstream, followed by the single Little Grassy Creek site. <br />Figure 2.04.7 -F13 shows the hydrographs for all streamflow monitoring stations in Grassy Creek <br />and Little Grassy Creek. <br />Site YSGF5, originally established in April of 1991 for the Yoast Mine, is located on Grassy Creek <br />approximately 1800 feet upstream from the Routt County Road 27 in Section 16, T5N R87W (see <br />Map 2.04.7 -M1, Hydrology), and represents inflow to the site from the portion of the watershed <br />upstream of the presently proposed mining. Streamflow in the channel reach at YSGF5 is <br />perennial. From a review of the flow hydrographs, the period of snowmelt influence appears to <br />start in late March and early April and extends into early to mid -June. The largest flows occur <br />during this period and ranged up to 4.9 cfs during the recent monitoring period. Late September <br />low flows were as low as 0.05 cfs. <br />Site SSG1 (or SW- S2 -1), originally established for the Seneca II Mine, is located on Grassy Creek <br />just upstream of its confluence with Little Grassy Creek, in Section 34, T6N R87W, approximately <br />3.5 miles downstream of YSGF5, and within the PSCM permit area. It integrates the effects of <br />proposed mining within the upper Grassy Creek drainage. SSG1 was intermittent during the <br />reported monitoring period, and exhibited seasonal flow similar to YSGF5. Spring flows peaked at <br />between 2.2 to 2.8 cfs in early to mid - April, and receded to zero or near -zero flow in the summer. <br />The occurrence of flow at YSGF5 in 2007, while the downstream station SSG1 was dry, suggests <br />• that summer low flows from upstream may reinfiltrate into the Grassy Creek alluvium. <br />Site SSG2 (or SW- S2 -2), also established for the Seneca II Mine, is located on Grassy Creek at the <br />PSCM permit boundary, and downstream of its confluence with Little Grassy Creek, in Section 27, <br />T6N R87W. Flows are perennial, and due to the influence of Little Grassy Creek tributary inflows <br />and location further downstream, spring peak runoff at SSG2 is higher (up to 7.1 cfs) than SSG1 <br />and YSGF5. Summer flow at SSG2 receded to as low as 0.06 cfs. Pond 003, discussed further <br />below, discharges to Grassy Creek above SSG2, but Pond 003 flows are minimal due to its limited <br />upstream drainage area and pumping between Pond 003 and Pond 002. Figure 2.04.7 -F14 shows <br />the outflow hydrographs for surface impoundments. <br />Site YSG5, originally established for the Yoast Mine, is located on Grassy Creek downstream of the <br />PSCM permit boundary, and downstream of its confluence with Scotchman's Gulch, in Section 28, <br />T6N R87W. It is perennial, with the highest (15.7 cfs) and latest spring peak flows of the gaging <br />sites. <br />Little Grassy Creek is a perennial /intermittent (depending on location) tributary of Grassy Creek <br />that enters the Grassy Creek mainstem just one mile downstream (north) of the proposed PSCM <br />mine facilities, and within the PSCM permit area. One streamflow monitoring site, SSLG5 <br />(formerly SW- S2 -5), and one surface impoundment outflow (NPDES2), characterize flow in Little <br />Grassy Creek. Figure 2.04.7 -F14 shows the outflow hydrographs for surface impoundments. <br />• <br />PSCM Permit App. 2.04 -64 6/15/09 <br />