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21 March 2003 AGE-NC Project No. 95-0114 Page 3 of 10 • TPH-ss has been detected in on-site ground-water monitoring well samples. The vertical extent of low TPH-ss concentrations have not been defined on-site below a depth of 120 feet bsg. TPH-ss has been detected in down-gradient monitoring wells at the boundary and outside of the site(MW6 and MW-10). The most recent CPT investigation indicated that the TPH-ss plume is still not defined east or north of wells MW-6, CPT2 and MW-10, CPT6, respectively. • Additionally,tetrachloroethene(PCE),cis 1,2-dichloroethene(1,2 DCA)and vinyl chloride have been detected in the water samples collected from wells MW-4,MW-5,MW-6,MW-7 and MW-10. The lateral extent of dissolved PCE and TCE concentrations has been defined to concentrations below 20 µg/1 (CPT6-50); the vertical extent has been defined to concentrations below 5.0 µg/1. The lateral extent of the dissolved cis 1,2-DCE plume has been defined to on-site boring SB2 and off-site boring CPT4, monitoring well MW-10 and CPT5; the vertical extent has been defined, at approximately 80 feet bsg. The lateral and vertical extent of vinyl chloride has been defined. 2.3. GROUND WATER DEPTH AND FLOW DIRECTION Based on the map titled Lines of Equal Depth to Groundwater Spring 1999 published by the San Joaquin County Flood Control District and Water Conservation District(FCD&WCD),the estimated depth to ground water at the site is approximately 30 feet bsg; the map Lines of Equal Elevation of Groundwater Spring 1995 (FCD&WCD) indicates that the regional ground water flow direction is towards the northwest and west. On-site ground water measurements between May 1995 an,' the present indicate that the depth to ground water has risen, from 50 feet bsg to approximately 22 feet bsg, and the general ground water flow direction has been towards the east and northeast.Ground-water elevation contour maps for the site were included in previous quarterly reports prepared by AGE. Based on ground water monitoring data at the site and historical depth to ground water maps (FCD&WCD) dating back to 1971, the depth to ground water at the site has fluctuated between 40 feet bsg and 60 feet bsg. 2.4. HYDROGEOLOGIC FLOW UNITS Based on the CPT results, AGE has developed a preliminary site hydrogeologic model comprised of seven informal zones,a vadose(unsaturated)zone and six hydrological units;the model presented is interpretational and will be modified as more data is collected.Hydrological units may be defined as significant vertical intervals of sediments having significant lateral extent and having similar Advanced GeoEnvironmental,Inc.