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The groundwater gradient under the subject site is estimated to be -19.60 ft - (-21.0 ft) _ 1,390 ft = 0.0010 ft/ft. The velocity of the groundwater under the site can be estimated by the following formula. This corresponds with the velocity determination found in the groundwater report for the Harney Landfill: -1i21 Va,,uifer= L 7.5 Where: K = Hydraulic conductivity of aquifer formation in gals/day/ft, =500 gals/day/ft- (est. based on a silty clay formation) h,= -19.6ft h, — -21.0 ft L = 1,690 ft p = porosity of aquifer = 35% (est.) V2yU,,,,— 0.16 ft/day or 58 ft/yr During the drilling procedures for the deep pert test borings, no saturated soil conditions were encountered down to the depths of 25 feet. However, it is a possibility that perched water table conditions exist above the static water table depth. A water sample was obtained from the domestic well head that serves the Diamond residence. Nitrate testing of this water sample reveals a very low nitrate concentration of 4 ppm. The Maximum Contaminant Level (MCL) for nitrate (as NO,,) is 45 ppm. The agrichemicals dibromochloropro pane (DBCP) and ethylene dibromide (EDB) concentrations were found to be non-detect. The MCL for DBCP is 0.0002 ppm or 0.2 kcg/L. Nitrate concentration from a previous study directly to the north of the subject site also revealed a comparatively low nitrate concentration at 14 ppm. Explanations for this difference in nitrate concentrations may include varying well perforation elevations, total depth of each well, and grouting or sanitary seal depth. It is most likely a combination of all these factors. In addition, the vineyard to the north was deep-ripped which may have created a conduit to facilitate the downward movement of nitrate. B. SURFACE WATER INFORMATION Surface water consists of all other water sources originating on the surface of the project, other than septic system effluent. These sources include rainfall, surface runoff domestic irrigation and stormwater retention. "The San Joaquin County of Public Works - Isohyetal Map indicate 13 inches of rainfall to be the Mean Annual Precipitation in the area of the project. There should be no impact to surface waters from septic effluent provided applicable distance requirements are followed. There are aerated sewage ponds adjacent to the south of the Migrant Farm Labor Camp and directly east of the subject site. At no time during this investigation was any odor detected. 5