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confluence with Fish Creek. Instantaneous flow measurements aze collected at all <br />three creeks. Like the Grassy Creek drainage, streamflows in the Fish Creek basin <br />are seasonally variable with peak flows occurring in the spring in response to <br />snowmelt runoff. <br />F. Probable Hydrologic Consequences <br />A determination of the probable hydrologic consequences of the mining and <br />reclamation activities at the Seneca II Mine site has been made by the applicant and <br />is found in Volume 4, Tab 7, Section VII.B of the permit application. This section <br />includes an evaluation of quantity and quality effects on ground and surface water <br />systems and mitigative measures to be taken both during and after mining. <br />The Probable Hydrologic Consequences section of this document is divided into two <br />main subsections; Surface Water Effects and Ground Water Effects. <br />Surface Water Effects <br />The Seneca II Mine is located in the upper Yampa River basin on the north flank of <br />the Williams Fork mountains. The mine is located on a watershed divide between <br />the Fish Creek drainage basin to the east and the Grassy Creek drainage basin to the <br />west. Most of the previous mining at the site has occurred in the Little Grassy Creek <br />basin which is tributary to Grassy Creek, a perennial tributary to the Yampa River. <br />Mining in the Fish Creek basin began in 1982, in [he Cow Camp Creek tributary <br />basin. As mining in this drainage was completed, an area in another tributary basin <br />of Fish Creek, Bond Creek, was disturbed. Mining activity will occur throughout <br />the life-of-mine in this basin. The effects of mining on the water quality and <br />quantity in each of these surface water basins is discussed below. <br />Grassy Creek Drainage Basin <br />Grassy Creek is a northerly flowing minor tributary of the Yampa River east of <br />Hayden, Colorado. The Seneca II Mine is located about three miles upstream of [he <br />confluence with the Yampa River, and includes about 860 acres of disturbed lands <br />within this drainage basin. Surface water monitoring sites are located above and <br />below the mine to quantify mine-related impacts. Two ponds, NPDES 002 and 003, <br />dischazge between these two stati:,:is to Little Grassy Creek. <br />The operator has conducted monitoring of discharge and water quality at the two <br />surface sites in the Little Grassy Creek drainage since 1981. At the station above the <br />mine (SW-S2-1) a mean discharge of 0.9 cubic feet per second (cfs) is characteristic <br />of stream flow during the period June through September, the historic irrigation <br />25 <br />