2008-10-07_PERMIT FILE - C1981047 (4)

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. 2.05.6(3) Another way to analyze the impact on Hubbard Creek is to analyze how the addition of 7 acre feet of relatively high conductivity water impacts the quality of ,water in Hubbard Creek. It is estimated that Hubbard Creek discharges 24,700 acre feet per year (ref. page 43). Introduction of 7 acre feet per year with a conductivity of 4900 into a 24,700 acre feet per year discharge with a conductivity of 150 increases the conductivity of Aubbard Creek about 1 umhos/cm. Clearly this 1 umhos/cm increase is an insignificant impact to Hubbard Creek and the downstream receiving waters. The results of local studies on impacts of water quality from coal mines and agriculture are pertinent here, for example: water yields and quantity in the North Fork are strongly influenced by water control through Paonia Reservoir, by water withdrawal from several irrigation canals, and by return flows from irrigated lands back into the river. Withdrawals at Somerset (Fire Mountain Canal), between Bowie and Paonia (Stewart's Ditch) and just above Paonia (Farmer's Ditch), withdraw significant flows and cause significant dewatering of the North Fork of the Gunnison. Flow in Hubbard Creek is significantly reduced by withdrawals to the Terror Creek and Overland ditches above the mine and by the Deer Trail Ditch (see data provided in Table W-4) between the mine and the North Fork River. Approximately 77 percent of the consumptive water use in the North Fork Valley is used for irrigation. Irrigation is also the primary • factor causing increasing salinity, nutrients, sediment, and herbicide/pesticide levels. Municipal, recreation, and evaporation account for about six percent of the consumptive uses. There is little industrial use or discharge of water. However, several coal mines have operated in the past and are presently operating. Of these, Mountain Coal Company, Somerset Mining Company and the Bear Mines in the vicinity of Somerset are the most significant. The effects of mining on the water quality of the North Fork of the Gunnison are small compared to agriculture. Analysis of the river above and below the now reclaimed Hawksnest Mine by the Colorado Department of Health indicate increases in total hardness of 1.1 percent, calcium hardness of 1.3 percent, electrical conductivity of 1.0 percent, suspended solids of 1.4 percent, and chlorides of 175 percent. Analysis of the irrigation return flow below Paonia by the Colorado Department of Health resulted in increase in total hardness of 817 percent, calcium hardness of 998 percent, electrical conductivity of 630 percent, suspended solids of 1200 percent, and chlorides of 157 percent (Colorado Department of Health, 1975). Sampling station numbers used in this comparison are NF 12 and 13 for the Hawksnest Mine and NF 607 for irrigation return flows. Also, lower flows due to irrigation dewatering of the North Fork of the Gunnison River contribute to higher summer water temperatures. • 122 (Rev. 12-16-92)