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The areas which were reexamined as potential AVFs within the Fish Creek basin <br />include alluvial bodies along two tributaries of Fish Creek, referred to as <br />Cow Camp Creek and Bond Creek, and the reach of Fish Creek between Cow Camp <br />Creek and the confluence with Trout Creek. Based on the Division's review of <br />materials submitted by the applicant on May 27, 1981 and infrared aerial <br />photography reviewed more recently, the alluvial bodies adjacent to Cow Camp <br />and Bond Creeks were determined to not meet the requirements for AVFs. This <br />negative determination was made in both instances due to the fact that the <br />meandering nature of the channels severely limits the farmable acreage within <br />each drainage. <br />During the Division's review of the adjacent Foidel Creek life-of-mine permit <br />revision (C-82-056), the Division reevaluated potential AVFs in Twentymile <br />Park. <br />Infrared photography and field investigations indicate that the Fish Creek <br />alluvial body is, in places, flood irrigated, is generally sub-irrigated, and <br />is potentially farmable land. Based on these investigations, the Division has <br />determined that the Fish Creek alluvial body meets the criteria of an AVF. <br />This AYF extends the length of Fish Creek to its confluence with Trout Creek <br />and along the length of Trout Creek to its confluence with the Yampa River. <br />Effect of Mining on Identified Alluvial Yalley Floors <br />Water quality data were supplied in the renewal application from monitoring of <br />surface water stations on Cow Camp and Bond Creeks, the two streams tributary <br />to Fish Creek. Mining in the Fish Creek drainage basin began in 1982. Since <br />that time increases in both flow and total dissolved solids (TDS) <br />concentrations have been observed. Whereas flow in the channel immediately <br />below the mine, Cow Camp Creek, was ephemeral prior to mining, perennial flow <br />is now observed at the permit boundary. This effect is attributable to spoils <br />aquifer discharge, as well as an increase in runoff from mined lands, and a <br />decrease in evapotranspiration due to removal of vegetation from mining <br />areas. Recent observations have indicated, however, that stream flow is not <br />maintained in the channels of the two tributaries during the months of August <br />and September near their confluences with Fish Creek. The surface effects of <br />water discharged from the mine on the downstream AVF locations is restricted <br />to the months of June and July. Subsurface effects are expected to <br />predominate in August and September. <br />Water quality constituents of concern to the AVF identified on Fish Creek <br />include trace metals, sulfate, and TDS. An evaluation of concentration levels <br />present in the mine discharge indicate TDS to be the constituent most likely <br />to place a restriction on the quality of irrigation water. Rule 2.06.8(5)(b) <br />refers to potential increases in electroconductivity of water suppling AVFs to <br />levels above a threshold value at which crop yields decrease as constituting <br />material damage. The relationship between electroconductivity and TDS is <br />demonstrated level by Peabody Coal Company in the permit renewal application. <br />-16- <br />