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x m c y [4] LOCAL GROUNDWATER AND SURFACE-WATER INFORMATION h. The static water table depth is found at approximately 17.5 ft below grade,according to the sounding Of the domestic well with an electronic water level meter. The 199$ Lines of Equal Depth Map - published by the San Joaquin County Flood Control"District does not illustrate the depth nor elevation of the water #able under the subject property: This is due to the fact that water table elevations change dramatically4hroughout the Tracy area. - A nearby Water Well Drillers Report is attached but does not show the depth of first water in 1988. However, information on the pressure tank on the sub'ect roe a _ J p p rty,says the static water level to be 18 ft on 12/17/90. Therefore, the water table has not fluctuated dramatically in the past 10 years. A 1992 Lines of Equal Elevation Map is attached and reveals the groundwater directional flow to be in a northeast direction. .Consequently;most 'o the°Army Defense Depot can be considered :- _ ;. crossgradient, although a portion of the facility is upgradient to the subject property. There is significant contamination'originating from the Depot. It is our opinion that since the water table is high in elevation in comparison to the land surface,there is probably a very slight possibility of perched water table conditions occurring at a higher elevation than the static water table. A gravel and rock strata from 25 to 30 feet is undoubtedly water bearing. There is no potential for:future septic impact-to surface irrigation waters, provided applicable I; distance requirements are followed,and there is no surfacing of effluent from inundated conditions !T caused by irrigation proximity. Analysis of water'drawn from the domestic well.which supplies-water to the business reveals a comparatively high nitrate concentration-of 34 ppm nitrate (NO3). The Maximum Contaminant Level (MCL) for NO3 in drinking water is 45 ppm; therefore, the underlying aquifers have been affected by nitrate sources. Nitrate sources may include agricultural production, confined animal k facilities,point-source fertilizer applications, and/or surrounding septic-systems. From the USDA aerial photograph, it is evident that there is significant agricultural production upgradient from the subject property. The pesticides DB CP and EDB were below detection limits(BDL}which is equivalent to non-detect (ND). DBCP was found in well water in 1997 in the Banta area,near the intersection of 11t' Street and Grantline Road. Since DBCP was normally applied to grape vineyards up until 1976, it is =unknown as to why it was found in this area. _ The construction details of the subject property well concerning perforation depths is unknown; however, it is known that the well was originally 122 ft deep according to what was written on the pressure tank. It is assumed:the new sanitary seal extends to at least 100 ft�dnd therefore, the perforations must extend from 100 ft to 122 ft_ The Well Log for the repair was not on file at PHS- ii _ EHD as of the date of this report. Page -3- - _ _ Va&y Ag Research