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. Trout Creek Sandstone. dell GU-SS-TC is used as the potable water supply for the Seneca <br />It Mine facilities. [t displays a Na-SO4MC03 type eater. TDS values show no discernable <br />trend. <br />Spoils. Three wells that are used for monitoring eater quality in the spoils above the <br />Nadge Impoundment are 25-5, 26-5, and 27-5. Well 25-S, the upper spoils eel 1, did not <br />have enough eater in its casing to sample this year, although in the past it displayed e <br />MgCa-504 type water. (Jell 26-5, the middle spoils eel 1, displayed a MgC a-S04 type eater. <br />well 27-5, the loner spoils well, also displayed a MgCa-504 type note r. TDS decreases as <br />one progresses downgradien t. This is,due to the diluting effect of the lower TDS Nadge <br />Impoundment water in direct communication with spoils aquifer eater. Year to year trends <br />in TDS are difficult to delineate probably due to the effects of fluctuating cadge <br />reservoir eater levels. <br />Seven spoils wells were comet eted in the summer of 1987. Three (welts 59-5 to 61-s1 were <br />completed above Spoils Spring #3 (also known as the Spring Creek area). Four (Neils <br />62-5 to 65-5) were completed above Spoils Spring #1 (also known as the Cow Camp Creek <br />area>. In 1990, the furthest downgradient well in each area was sampled for water quality <br />(Neils 67-5 and 62-5). Data collected by PCC and the U.s- Geological survey (uSGS) in <br />prior years indicate that eater quality from the spoils wells in each respective area are <br />simiLa r. Nell 61-5 displays a MgL a-504 type water, Nhile Nell 62-5 displays a CaMg; S04 <br />type water. TDS values have increased at both wells this year (see Table 10). These <br />increases may be the result of the extended drought conditions and/or the spoils aquifer <br />not yet achieving TDS stability. <br />Comoarison of Ground Nater Oualitv to Water Use Standards. The Colorado Department of <br />Neal th (CDON) drafted basic standards. for ground water, including standards for <br />agricultural use (irrigation) in 1986 (COON, 1966). These standards have been summarized <br />and are presented in Table it in Appendix A. Results of analyses performed on samples <br />obtained from monitoring wells during the 7990 water year have been compared to th¢se <br />standards, and the comparison results are presented in Table 12 (Appendix A). <br />Table 72 shoos that Spoils Neils 526, 527, and 561 all have exhibited manganese levels <br />higher than the CD ON irrigation standard. Alluvial Neils 56, 531, 532, 533, 546, 568, end <br />S69 also were analyzed to have higher manganese levels Than [he irrigation standard. gosh <br />pH and fluoride in underburden Nel is s8P1 and 511, and cadge Coal Nell S19 were measured <br />9 <br />