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r ~ LJ Hy~ologic Ohta lntapriaadon and lmpau Aaemrou fa rht Pamir and Adjatrnr Aiear Comparison of Baseline Water Quality with Operational Data Of the ten parameters selected for baseline charac- tervation, seasonal trends are apparent for TDS, ~yTSS, and total iron. The other parameters do not pS ~, III `'~,~r„ hxhtbit seasonal variation. Total dissolved solids are least concentrated in the North Fork during f ~ ~' ~W~rd~YJ~.~the period between about May and July. The likely ,~ , t .~ Treason for this pattern is during this period high- 155 ~'~°~ r' TDS groundwater is diluted by snow runoff. Total ~u~ `~ iron is most concentrated during this period. Total suspended solids are most concentrated from April to July. n U A comparison of baseline water quality data in the North Fork of the Gunnison River with 1991 monitoring data shows no significant 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 of priority Cram July to Septem- ber. In 1977, it would have been out of priority from April to September. In water year 1986, MCCs Mt. Gunnison Pipeline water right met quadrennial diligence for the conditional portion. Aooordiagly, as additional portion was deemed absolute by the Division 4 Water Court. That decision brought the absolute portion to 0.88 cts. The 10-acre-foot capacity pond (FW-1) provides Cor water storage during the current permit term; an additional pond (FW-2) is antiripated for subsequent permit terms. Water can also be stored in Sediment Ponds M13-1, M13-2, 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 likely to be on the order of 200,000 gpd during start-up of longwafl operations in the West Elk Mine and depending on production levels and re- quirements. During 1991 average withdrawal was 154,115 gpd for 250 working days. This increase in range can be attributed to increased production and the surface construction projects (water was used for dust control, compaction, concrete pro- duction, 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 its 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 can 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 ran be treated to meet potable and sani- tary water requirements, used, and then treated as sanitary waste water. Or, it can be withdrawn for dust suppression in the mine, in which case it then becomes mine water. MCC's Mt Gunnison pipeline water righu were out of priority during a portion of water year 1991 (from approximately 15 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