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Quarterly Groundwater Monitoring Results Quarterly groundwater samples and water level measurements were collected on December 19 and 20, 1996 by Del Tech of Oakdale, California. Groundwater Elevation Data Water elevation data from December 18, 1996 and previous monitoring events are summarized on Table 1. As shown by Table 1,water levels have risen by approximately 1 foot since the previous monitoring event conducted in August 1996. However,the recent monitoring data indicates that water levels are approximately 18 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 1 monitoring wells. Groundwater currently begins at approximately 60 feet below ground surface (bgs). 1 . Figure 2 shows an interpretation of shallow groundwater elevation contours which indicate that the groundwater is flowing in a southeasterly direction with a gradient of 0.10%.The apparent shallow groundwater flow direction has varied widely in past measurements. Generally,during the past two years, the groundwater gradient has been flat and dipping slightly in the southerly direction. The gradient has ranged from 0.06%to 0.27%. G TPH as Gasoline/BTEX Analytical Results In December 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 December 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 December 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 order of magnitude below the concentrations that existed prior to operation of the AS/SVE system (i.e.,prior to February 1995). As indicated on Table 2,each well was sampled by two different methods and analyzed by different laboratories. One sample was collected after a rapid well purge typical for quarterly monitoring. The other sample was collected after minimum aeration purging used 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 with one notable exception. TFH gasoline in MW- DIS-2 is higher in the rapid purge result. MTBE Analytical Results At the request of PHS/EHD,Del Monte sampled wells for methyl tert-butyl ether (MTBE). These samples were collected by the minimum aeration technique. MTBE results are 1 presented in Table 3. No MTBE concentrations were found this quarter in any of the wells SFO/G:TROJECTSIDELMONTE PLANT_331QRPT2_971QTR_REP.DOC 4