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QUARTERLY GROUND WATER MONITORING REPORT 5491 F Street,Banta,California 3.0 QUARTERLY MONITORING RESULTS Presented below is a summary of the results of Aegis' ongoing groundwater elevation monitoring and groundwater sample analytical testing. 3.1 Groundwater Elevations During the 1 February 1991 site visit, groundwater elevations were observed to range from 12.31 to 12.51 feet above mean sea level. The groundwater surface was observed to range from approximately 13 to 14 feet below existing grade. Based on groundwater elevation contouring by the SURFER® computer program using the Kriging method, the hydraulic flow direction is in an easterly direction. The average hydraulic gradient across the site for the 1 February 1991 data was approximately 0.002 feet per foot (ft/ft). A groundwater elevation contour map was drafted from the groundwater elevations measured on 1 February 1991 and is presented as figure 3. This contour map indicates the flow direction and calculated hydraulic gradient. A monitoring well hydrograph has been prepared showing the fluctuation of groundwater levels with time since the installation of the wells. The hydrograph is included as Figure 4. 3.2 Groundwater Analytical Results Monitoring wells were purged and groundwater samples were obtained according to Aegis' SOP, Appendix A. Concentrations of dissolved petroleum hydrocarbons in groundwater were reported below detectable levels in all wells except MW-1 for the 1 February 1991 sampling event. Laboratory analyses of the groundwater samples collected from the monitoring wells are summarized in Table 2. These results will be compared to ensuing groundwater sampling results to determine if the data is reproducible or if there is a changing trend in groundwater chemistry or flow. 4.0 SCHEDULE The next quarterly monitoring is scheduled for May 1991. 90-099A.RFr 9