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Hater Oualitv. Ground eater samples were collected from 18 wells on a biannual basis. In addition, two wells (25-5 and 42P1-LNI> that are required to be sampled did not have enough water to sample. The parameter list used for all wells Sampled in 1991 is given on Table 4 (Appendix A). Analyses have been performed by ACZ Laboratory in Steamboat Springs, Colorado since May 31, 1983. ACZ Laboratory is EPA certified and performs all analyses by EPA or equivalent methods. Samples are delivered the day of col tection to the lab in an 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 data are presented in Appendix D. Sampling techniques far each cell are given in the remarks page in the same appendix. Abbreviations used in the remarks are: CV = casing volume, BHV = bore hole volume, EC = electrical conductivity, end FP = field parameters (pH, temperature, and electrical conductivity). Tables 5 through 10 (Appendix A) tabulate the percentage of milliequivalents per liter of major ions and total dissolved solids (TDS) for each well sampled in 1991. Historical data is provided for comparison purposes. [t is important to note here that percent anions for 1981 and 1982 are not tabulated since the program that generates these tables cannot use the format in which this old data exists. The following discussion of water quality will limit itself to a description of major ions and total dissolved solids (TDS) concentrations. A separate section, Comparison of Ground Hater Quality to Hater USe Standards, will list those samples that exceed water use standards. Alluvium. Nell 32-A, located furthest upstream on Little Grassy Creek, displays a NaMgCa-SO4HC03 type eater. TDS values the past several years have fluctuated, implying that TDS values have stabilized and that changes are due to annual changes in precipitation and subsequent recharge. Progressing down valley, the alluvium picks up spoils water discharge typified by calcium and magnesium replacing sodium as the major cation at Nell 6-A. 7D5 and sulfate concentrations increase as one progresses downstream and with time. NeLI 31-A2 is downstream of the discharge of the Nadge Impoundment. It is similarly ,a CaM g-504 type water. TDS values at this welt also fluctuate from year to year, implying that those changes are due to annual changes in precipitation. The one well completed in the Grassy Creek alluvium, 33-A, has a CaM g-504 type water. TDS values at this cell have gradually increased the last four years, possibly due to a i 6