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Ground Peter Level Summa rv. Mast aquifers at Seneca II-Y exhibit a typical seasonal fluctuation. Pater levels ere highest (shallowest) after the spring snowpeck runoff • which recharges the aquifer. Often, bedrock (i.e., non-alluvial) aquifers exhibit a lap time between spring runoff and highest water levels. Pater levels then decrease (deepen) as late summer or fall approaches. Several alluvial wells, along with overburden Yell 140V, exhibited for this year their deepest fall water levels on record. All other wells exhibited water levels this year that fell within their historic ranges. Peter quality. Table 3 (Appendix A), Summary of Ground Pater Monitoring Wells, describes the wells that were sampled, the sample frequency during the 7994 water year, end site characteristics. [n 7994, samples were collected from 19 wells. In addition, two wells from which water samples are required (Yells 20A and 160V) were either dry or had not enough water to sample. Table 4 (Appendix A) shows the ground water parameter list used for all wells. Analyses have been performed by A[Z Laboratory in Steamboat Springs, Colorado since May 31, 7983. AC2 Laboratory performs all analyses by EPA or equiveLent methods. Samples ere delivered the day of Collection to the lab in en iced cooler. The following discussion of the analytical data collected during the reporting period is arranged by strata being • monitored and coincides with the format (by aquifer type) in which the analytical date ere presented in Appendix D. Sampling techniques for each well are given in the remarks page in the same appendix. Tables 5 to 7 (Appendix A) tabulate the pe reentage of milliequivalents per liter of major ions and total dissolved solids (TDS) for each well sampled. All data prior to 1990 has been averaged together to provide the baseline (i.e., premining) conditions that existed. In addition, the range of total dissolved solids (TDS) that existed prior to mining is also given. S1nce mining began in August )990, date from the 1990 water year an is fisted separately. The following discussion of water quality will limit itself to a description of major ions. A separate section, Comparison of Ground Mater quality to Water Use Standards, will list those samples that exceed water use standards. Alluvium. Samples from Yell 6A2 display a NeCaNg-NC03 type water with en average TDS value of 395 mg/l in 7994. This is both lower than the 611 mg/l baseline average end the baseline range of 454 to 900 mg/l. This well exists in the Nubberson Gulch alluvium upstream of mine discharges. Irrigation of the pssture surrounding this well began May 6, • 1989. 4