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presented in the following section titled "Ground Yater Suitability". • Cressy Creek. Vells YGAL75 through TGAL18 monitor alluvial water quality et different lotetions progressing upg radiant in the Grassy Creek watershed. Alluvial water quality is variable in this upper basin. Yells YGAL 78, YGAL77, and YGAL76 monitor ground water influenced by alluvial end totluvial materiels in small, unnamed tri6ut cries to Grassy Creek (see Exhibit 7-7). Yell YGAL75 is located furthest downgradien t, and water quality monitored et this site is cumulatively influenced by the alluvial end colluviel materiels in ell upgredient tributaries. Yell YGAL78 exhibits three water types, most commonly CeNgNaSO4XC03. Sulfate is the dominant anion during the spring and summer, and bicarbonate increases es the fell progresses into winter. No. ration is dominant; however, sodium does exhibit some influence during the winter. Yell YGAL77 shows four water types, end no dominant cation or anion, although calcium end sulfate generally exert the greatest influence. Contrastingly et Yell YGAL77, bicarbonate has the greatest influence during the spring and summer months, and sulfate replaces bicarbonate es the year progresses to fall end winter et YGAL77. Well YGAL76 is typically a CaNgHC03504 water type and shows no seasonal • variability. YGAL75 is consistently a NeCeNg504 (one exception; see Table 7-12) end similar to YGAL76, shows virtually no seasonality in water type. TDS ranges from 546 mg/l (YGAL76) up to 4030 mg/l at YGAL75. Both YGAL77 end YGAL76 exhibit similar ranges in TDS, end winter TDS levels et both wells were the lowest emon9 all four. YGAL75 typically exhibits TDS levels three times higher then the other three alluvial wells, and TDS only slightly lowers et this well after the spring season progresses into summer. Sulfate values measured et YGAL75 ere also et least Three to four times higher than the three upg radiant alluvial wells. Mean field pX values range from 7.02 at TGAL 15 up to 7.42 et YGAL76. Field pX measurements conducted et the three upgredient alluvial wells indicate that slightly alkaline waters commonly contribute to downgradient alluvium along Grassy Creek, end that the highest values are measured in late fell and winter. However, field pH a[ YGAL75 generally becomes slightly acidic as the seasons progress into winter. Mean hardness as CeC03 for the three upgredient Grassy Creek wells range from 537 to 572 • mg/l. The furthest downgradient well, YGAL75, exhibits very hard water with values three times higher, ranging from 7525 to 1830 mg/l. 42 Revised 03/01/95