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Chapter IV <br /> The maximum discharge of the mines coincides with the maximum spring melt runoff <br /> period. This mitigates the higher TDS levels by immediate dilution. The mine <br /> discharges (Nos. 1 and 2) enter the Dutch Creek drainages some 4 miles above their <br /> junction with Coal Creek, thus again diluting and mixing. Stream gauging station No. 5, <br /> Dutch Creek, above Coal Creek, has the following averages (1976-1985). <br /> Maximum Mean Minimum <br /> TDS 1155 393 2.09 <br /> TSS 12398* 689 0 <br /> Iron 59.4 1.3 0 <br /> pH 8.9 8.03 6.8 <br /> Conductivity1390 571 160 <br /> *Summer thunderstorm with stream bank failure. <br /> Compare this with Sutey Creek, which is an unaffected drainage at a point north of the <br /> main coal refuse pile. <br /> Maximum Mean Minimum <br /> TDS 632 528 320 <br /> TSS 2880 721 6. <br /> Iron 45.6 5.5 .02 <br /> pH 8.4 7.8 7.1 <br /> Conductivity 900. 721 410. <br /> Such a comparison indicates that normal dilution mitigates the effect of discharge from <br /> the mines and other disturbed areas. All disturbed areas of the mine have runoff water <br /> routed through sediment ponds which release water with suspended solids levels well <br /> below that of the natural undisturbed streams during high flow conditions. <br /> The alluvium of Coal Creek and its tributaries consists of sands and gravels derived <br /> from the Mesaverde Group, Mancos Shale, and reworked glacial and terrace deposits. <br /> This alluvium is discontinuous, varies between 0 and 75 feet and is moderately <br /> permeable. The Coal Creek alluvium is isolated into separate narrow alluvial bodies by <br /> water gaps formed by the resistant sandstone strata and by layers of clay deposited <br /> from the Mancos Shale. Wells do not produce as much as would be expected, ranging <br /> from 5 to 15 GPM. The alluvial ground water is predominantly a calcium, sodium, <br /> magnesium bicarbonate type. The total dissolved solids concentration is about 350 <br /> mg/l. Alluvial ground water is utilized for domestic and industrial uses. The alluvial <br /> ground water discharges to Dutch, Coal, Bear and Porcupine Creeks, providing base <br /> flow in the creeks during low flow periods. The alluvium is recharged directly from the <br /> streams during snowmelt and during precipitation events. <br /> 12 <br /> �I <br />