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QUARTERLY MONITORING RESULTS I Quarterly Groundwater Monitoring Results Quarterly groundwater samples and water level measurements were collected on August 15 and 16, 1996 by Del Tech of Oakdale,California. Groundwater Elevation Data Water elevation data from August 15, 1996 and previous monitoring events are summarized on Table 1. As shown by Table 1,water levels have dropped by approximately 1 foot since the previous monitoring event conducted in June 1996. However,the recent monitoring data indicates that water levels are approximately 17 feet higher than when the majority of wells were installed in September 1991. Due to the rise in water levels,shallow groundwater currently exists at approximately 6 to 10 feet above the screens of the monitoring wells. Groundwater currently begins at approximately 60 feet bgs. Figure 2 shows an interpretation of shallow groundwater elevation contours which indicate that the groundwater is flowing in a southerly direction with a gradient of 0.06%. This flow direction is consistent with data collected since June 1994. However,between September 1991 and September 1993, the apparent shallow groundwater flow direction varied between north and west-northwest. Generally,the groundwater gradient has been very flat,ranging between 0.06%and 0.27°/6. i TPH as GasolinelBTEX Analytical Results In August 1996,groundwater samples were collected from monitoring wells MW-DIS-1,2, 3, 8S,8D,9,and 10 for analysis of TPH as gasoline and benzene,toluene,ethyl benzene,and xylenes(BTEX). The August 1996 groundwater analytical results and analytical results from previous monitoring events are presented in Table 2. The laboratory reports and chain of custody forms from the August 1996 sampling event are attached. The results indicate that TPH as gasoline and BTEX concentrations in the plume area(as monitored by MW- DIS-1 and MW-DIS-2) continue to remain one to two orders of magnitude below the concentrations that existed prior to operation of the AS/SVE system(i.e.,prior to February 1995). The results indicate that TPH as gasoline and BTEX concentrations at the outer fringe of the plume (as monitored by MW-DIS-3,8S,8D,9,and 10)continue to remain non- detectable. As indicated on Table 2,MW-DIS-2 was sampled by two different methods and analyzed by different laboratories.One sample was collected after a rapid well purge typical for fquarterly monitoring.The other sample was collected after minimum aeration purging used I for intrinsic bioremediation demonstration monitoring.As expected,the samples collected by minimum aeration technique show BTEX concentrations higher than the concentrations reported for the normal purge sample. In addition to the normal monitoring well sampling,the shallowest screen intervals of nested piezometers NP-1 and NP-2 were sampled this quarter. The locations of the piezometers are shown on Figure 1. The purpose of sampling NP-1 and NP-2 was to assess { TPH as gasoline and BTEX concentrations at shallower depths. The analytical results of the groundwater samples collected from NP-1 and NP-2 are included in Table 3. The 1 SFO\G:1PAOJECTs'oELmowE1PLANT_3MTF7-REP.DOC 4