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• yydrofogie Qva buapetadan and Impact Ammnat for nc~ Pomir and Adjacnv Arcar Comparison of Baseline Water Qualiiy with Operational Data Of the ten parameters selected for baseline charao• ~ teriration, seasonal trends are apparent [or TDS, Ml tyyTSS, and total iron. The other parameters do not 7i15 ~, ~'~r 1 bxhtibit seasonal variation. Total dissolved solids are least concentrated in the NorW Fork during ~ ~'.i 1: if1; )the period between about May and July. The likely ,t., , {reason for this pattern is during this period high- s 5 ~ ~ x~ ~'' TDS goundwater is diluted by snow runoff. Total ,,u~`~ iron is most concentrated during this period. Total suspended solids are most concemrated from April to July. A comparison of baseline water quality data in the North Fork o! the Gunnison River with 199] monitoring data shows no signifipnt changes in water quality in the North Fork. No apparent changes in the water quality of the North Fork of the Gunnison River can be attributed to affects of mining during water year 1991. Mine Water Management and Impact Assessment expected to be out o[ priority from July to Septem- ber. In 1977, it would have been out of priority from April to September. In water year 1986, MCC's Mt Gunnison Pipeline water righ[ met quadrennial diligence for the conditional portion. Accordingly, an additional portion was deemed absolute by the Division 4 Water Court. That decision brought the absolute portion to 0.88 cfs. The 10-aae-foot capacity pond (FW-1) provides for water storage during the current permit term; an additional pond (FW-2) is anticipated for subsequent permit terms. Water nn also be stored in Sediment Ponds M13-1, Mli-2, and M13-3 under a separate decree. Storage is usually limited to the maximum sediment level elevation. Transfer to FW-1 is possible as outlined in the M & R Plan. Average withdrawals are not expected to exceed 400,000 gpd during the term of permit and are likety to be on the order of 200,000 gpd during start-up of longwall operations in the West Elk Mine and depending on production levels and re- quiremenu. During 1991 average withdrawal was 154,115 gpd for 250 working days. This inaeaze in usage can be attributed to increased production and the surface construction projecu (water was used for dust control, companion, concrete pro- dunion, etc). 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 iu potential to affect the North Fork. North Fork Water During water year 1982, the conditional right to withdraw water from the North Fork was deemed absolute. When this water right is in priority, water ran be pumped from the intake point to the freshwater storage pond(s) within the surface facilities area. In average years, this water right is Water from the freshwater pond(s) is used in two ways. It pn be treated to meet potable and sani- tary water requiremenu, used, and then treated az sanitary waste water. Or, it can be withdrawn for dust suppression in the mine, in which case it then becomes mine water. MCCs Mt. Gunnison pipeline water righu were out of priority during a portion of water year 1991 (from approximately 75 August to 1 October). Average daily low flow in the North Fork during water year 1991 was 395 cfs. The maximum with- drawal at the intake is 450 gpm with both pumps operating. This is about 0.3 percent of the ob- served average daily low flow in the river during the water year. Sanitary Waste Water The sanitary waste water treatment plant has been operating since the fall of 1982 During water year • 14