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Ground Water Analysis: Ground Water Depth and Gradient The static depth to ground water upon completion of the two water supply wells on the property was 86 feet in the residence well and 80 feet in the dairy well. These depths are consistent with those reported by the San Joaquin County Flood Control and Water Conservation District for the fall of 1994. The same agency reported that the ground water gradient sloped to the northwest at the time. The drop in elevation was approximately five feet per mile. It appears that the aquifer providing the primary water source in the area is the coarse sands and gravel which occur from 75 to 135 feet below the surface. However, Oakdale Irrigation District wells are much deeper-- from 400 to 500 feet and undoubtedly also tap water-bearing units lower in the stratigraphic section. Because of the deep ground water depth, it is difficult to determine seasonal variations in ground water elevation. However,Oakdale Irrigation District reported that the water levels vary only about three feet. The lowest levels occur during the summer months when irrigation wells are actively pumped. Ground Water Sampling Three water supply wells were sampled to determine the baseline nitrate concentration. Two of the wells were located on the property at the Manuel Da Silva residence and at the dairy. The third well sampled was the John Da Silva dairy well which is situated approximately one half mile southeast of the Manuel Da Silva dairy. This third well is upgradient from the two wells on the subject property. Water samples from these three wells were transferred under chain of custody to Geo Analytical _. Laboratories in Modesto. They were analyzed for nitrate,using EPA method 300,with a detection limit of 1.0 mg/liter. The results show that nitrate is present in all of the samples,ranging from a low of 18 mg/liter in the John Da Silva well to a high of 21 mg/Liter in the Manuel Da Silva residence well. Although the presence of nitrate in the ground water indicate that there may be some agricultural contribution contamination,all of these values are well below the maximum contaminant level for drinking water established for nitrate of 45 mg/Liter. Furthermore, the consistent level of nitrate in the ground water indicates that the nitrate in these waters is more a result of a regional infiltration into the water table,rather than contribution from the local source of the Manuel Da Silva dairy operation. 8