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M t a 6 The direction of shallow ground-water flow has consistently been to the southeast during 1994 with only slight fluctuations of ground-water levels beneath the area. The ground-water elevation contour maps for March and October 1994 (Figures 5 and 6, respectively) illustrate the ground- water flow direction and areal change in shallow ground-water levels between the spring high and � i fall low levels. Comparison of the contour maps also illustrates a slight steepening of the ground-water gradient between spring and fall. The contour maps were prepared without including the observed water levels from the deep South Tracy #1 well 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. The Petz well water levels have been in an intermediate elevation range between those measured in wells solely completed in the shallow or deep wells, and may represent a "composite" of shallow and deep zone water levels. Ground-Water Quality General mineral analyses of ground-water samples conducted through 1994 indicated that the ground water beneath the area is hard to very hard with intermediate electrical conductivity (EC) n. and total dissolved solids (TDS) values (Tchobanoglous, 1985), as shown in Table 2. Hardness values ranged from 239 to 360 mg/1 (Figure 7), and EC values ranged for 800 to 1,100 umbo/cm with the highest EC values in samples from the shallow wells (Figure 8). 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 9), while deep ground water appeared to be of a bicarbonate/sulfate quality as shown by the Brown's 91 well analyses (Collins, 1928; Piper, 1953; r, Hem, 1959) (Figure 10). In regard to other notable ground-water constituents, nitrate levels were elevated in both shallow and deep well samples with concentrations just exceeding the maximum contaminant level (MCL) e� of 45 mg/1 in the South Tracy #1 production well during June and October. The nitrate concentration subsequently declined below the MCL during January 1995. The lowest nitrate © LUh DIDRFF S SCALMANINI CONS U I.T I N G E N G I N E E R 5