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-15- The proposed mining operation would not materially damage the quantity or qualit,~of _surface and round water which supply the alluvial valley 1• oor. Worst case projections o~ impact, ue o mim ng in3ic-~ sa inity rising in Harvey Gap during the non-irrigation season from 755 mgjl TOS to 1054 mgjl. A sample from a well in the Colorado River alluvium had a TDS level of 760 mg/1. Any recharge from Harvey Gap into the alluvium could slightly raise the level of salinity in the AVF. This would only occur in those portions of the AVF is immediate contact with Harvey Gap waters. As worst case predictions account for the extreme conditions (see Section VIII, Probable Hydrologic Consequences), no material damage to water quality or quantity is expected. 3. The essential h drolo is function of the alluvial valle floor would be ~~r~~es-er~ved-. The critical characteristics of the designated a uvia valor are the integrity of the present irrigation system and the ability of the surface water system to Supply sufficient irrigation water to farming activities on the alluvial valley floor. As discussed previously, neither surface facilities nor underground workings will be located on or beneath the AVF. Mine entries will be driven along strike to the east, away from Harvey Gap Drainage. As a result, there is no potential for depletion of flows in Harvey Gap Drainage (which is the conduit for irrigation water from Grass Valley Reservoir to the AVF). The integrity of the existing water supply and irrigation system will be preserved. Alluvial Valley Floor Monitoring Monitoring as outlined in Section V of this document will be sufficient to detect any potential for impact to the productivity of irrigated lands on the AVF as a result of mining activity. Due to the low potential for impact, monitoring is not warranted at this time. VIII. Probable Hydrologic Consequences The Eastside Mine is located in Garfield County, approximately 3.5 miles north of Silt, Colorado. The proposed mine will affect 167 acres of non-federal land during the life of mine, with 54 acres being affected during the five-year permit term. This underground mining operation will result in 12 acres of surface disturbance with the surface facilities and roads. The mine is located in the Harvey Gap area is very steep, with the elevation the mine along the Grand Hogback doo Slopes in the area range from 10% to 5C incised north-south trending stream va sandstone of the Grand Hogback. Drainage. The topography in the mine ranging from 7,846 feet to the east of n to 6,350 feet at the portal area. d. The Harvey Gap Drainage is a deeply Iley, which cuts through the resistant