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8 ground-water levels have declined gradually across the area such that the ground-water conditions have returned to the southeasterly flow direction observed during 1994 (Figures 8 and 9, respectively). The contour maps were prepared without including the observed water levels from the deep South Tracy#1 or Brown's #1 wells because they are representative of the deep ground water zone. Also, the observed water levels from the Petz well, which is completed in both shallow and deep zones of the underlying aquifer, were not used in preparing the contour maps. Until mid-1998, the Petz well water levels had been in an intermediate elevation range between those measured in wells solely completed in the shallow or deep zones; those measurements have typically represented a "composite" of shallow and deep zone water levels and thus are invalid for use in contouring the shallow or deep ground-water levels exclusively. Ground-Water Quality General mineral analyses of ground-water samples conducted during the last six years indicated that the ground water beneath the area is hard to very hard with intermediate electrical conductivity (EC) and total dissolved solids (TDS) values (Tchobanoglous, 1985), as shown in Table 2. Hardness values ranged from 230 to 360 mg/1 (Figure 10), and EC values ranged from 790 to 1,100 umho/cm with the highest EC values in samples from the shallow wells (Figure 11). Samples from all wells were of a similar sodium/calcium quality, but the proportions of major anions varied with aquifer depth. The shallow ground water appeared to be of a bicarbonate/chloride quality, such as shown by the Hall well analyses (Figure 12), while deep ground water appeared to be of a bicarbonate/sulfate quality as shown by the Brown's#1 well analyses (Collins, 1928; Piper, 1953; Hem, 1959) (Figure 13). HA 9 f > .. 111 In regard to other notable ground-water constituents, nitrate levels were elevated in both shallow and deep well samples, with concentrations in the South Tracy#1 production well fluctuating alternately slightly above and below the drinking water maximum contaminant level (MCL) of 45 mg/1 during © LUHL)ORFF & SCALMANINI A CIMNSULTING ENGINEERS