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~ throughout its entire length. Therefore, every point along the length of the stream may <br />• be treated as a point source cf contamination, Durinc spring runoff, relatively dilute <br />surface water, along with melted snowpack above the alluvium, serve to dilute the <br />• <br />I~• <br />concentration of TDS in the alluvial ground water. After runoff, TDS in the ground water <br />increases, presumably due to additional leaching of minerals in the alluvi un and <br />evapotranspiration (evaporation from soil and transpiration by plants, ET). This <br />phenomenon is especially noticeable at well GYi-531-A2. Because this well is situated in a <br />marsh with thick vegetation, and also has a high water table (D.5 to 1.S feet below the <br />ground surface), one would expect a hich ET rate. Dissolved solids are concentrated by <br />removal of pure water by ET. This effect is not noticed at GW-533 since it is located at <br />the confluence of Little Grassy Creek and Cra ssy Creek, which is relatively low in TDS. <br />This low TDS water serves to dilute the TDS in the alluvium below the level observed in <br />the Little Grassy Creek alluvium (CW-531-A2). Therefore, it may be stated that the mine <br />does not act as a point source of pollution for the alluvium, but rather, every point <br />along the stream acts as a source. Dissolved solids micrate perpendicular to the stream <br />when flow is high in the spring, and are concentrated in the alluvium by additional <br />leaching and ET. <br />PCC believes that, after five years of study, monthly monitoring of these two wells is <br />excessive since its obvious purpose is to show seasonal variations that have now been <br />demonstrated. Long term trends may be seen from monthly surface water, weekly NPDES, and <br />semiannual ground water quality monitorinc. Therefore, Peabody recues is reducing water <br />quality sampling at these two wells from monthly to semiannual. This semiannual <br />monitoring frequency should be more than sufficient to allow detection of any measurable <br />impacts before they would become significant regionally. The concern raised by <br />Stipulation 8 has been addressed. Peabody requests that CMLRD acknowledge this fact in <br />the response to this ANR, <br />62 <br />