REP34327 - Laserfiche WebLink

Home Browse Search

• 2.0 Hydrologic Dara luerpreruion and Impart Assessmru for rhr Permit and Adjacru Arras • North Fork. The level of iron in the sample taken (5/11/95) from the North Fork of the Gunnison River, above the mine, exceeded the baseline maximum (Table D-8). Levels of manganese exceeded the baseline maximum parameter on 5/11/95 with a reading of 0.126 mg/l. MCC is unaware of any specific activity upstream that would necessarily cause these increases, but elevated total suspended solids measure- ments suggest that high sediment levels could be the source of the metals. Iron and manganese concentrations of comparable magnitudes have been observed previously, but did not occur during the baseline period. At the monitoring station below the mine, concentration levels of iron and manganese exceeded the maximum baseline concentrations on5/11/95. Acomparisot}of results from the two stations exhibit differences t~tTil [fie realm of sampling and analytical error. No apparent changes in the water quality of the North Fork of the Gun- nison River are attributed to effects from mining during WY 19D5. 2.4.2 MB-2R Water Quality MB-2R treats surface water runoff from approximately forty percent of the facilities area, including the lower refuse pile. During the WY, mine water discharge was also directed to this pond. Full suite analyses show a slightly alkaline, saline, sodium bicarbonate/sulfate water with a high SAR (Table 2.4-1 and Table D-12). Total iron concentrations were elevated in June due to high sediment levels. AHR~95.210/OS/ I S/96(I:JBpm) 2.5 MINE WATER MANAGEMENT AND IMPACT ASSESSMENT The discussion of the mine water system and hydrologic impact assessment is organized by the four sources of water: • North Fork water • sanitary wastewater • mine water, and • runoff from disturbed areas. Use and discharge of water from these sources is studied for its potential to affect the North Fork. 2.5.1 North Fork Water The annual 1995 WY mean flow on the North Fork of the Gunnison was 709 cfs, higher than the mean flow for the 1934 to present historic recording period, of 462 cfs. The annual seven-day minimum occurred December 27 to January 2 and averaged 49 cfs. The maximum flow occurred June 6 and was 4,600 cfs. The maximum withdrawal at the intake North Fork of the Gunnison galley is 450 gpm with both pumps operating. During 1994, the average withdrawal was 312,816 gpd for 250 working days. This is an increase in usage from 257,291 gpd in WY 1993, but is within the projected estimates for fresh water demand in the PHC of 391,080 gpd. 20