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�N ESTER \ GEOLOGIC RESOURCES , INC . J. Munoz/3 Apr 1989 3 =C)y 30 March 1988 - Julian Munoz, Safeway An investigation was conducted by WA between 12 and 15 March to determine whether the 13-inch thick concrete slab in the bottom of the excavation - could be left in place. Eleven soil samples were collected from 0.5 ft to 1 ft below the slab. Four samples were analyzed for total petroleum hydrocarbons by Canonie Environmental (CE) . The highest concentration of TPH was detected at 56 ppm in sample SL-D collected at 0.5 ft below the slab in the southwestern corner of the excavation. Analytic results are presented in Table 4 and sample locations are presented in Figure 4. A groundwater elevation contour map for depth-to-water measurements on 28 March 1988 indicated that the estimated direction of groundwater flow was to the north, which was contradictory to the northwestward direction determined on 15 October 1987 (Figure 5) . The variation was attributed to seasonal changes in groundwater recharge conditions. An additional downgradient well MW-4, to be located on the north side of the excavation, was recommended for installation. 19 May 1988 - Hardip Ahluwalia San Joaquin Local Health District A request was made by WA to the San Joaquin Local Health District (SJLHD) to aerate 1000 cubic yards of pea gravel and soil removed from the tank excavation on site. Samples of the pea gravel PG-East and PG-West had been collected on 25 August 1987, and samples TP-B-2A and TP-B-3A had been _ collected on 23 January 1988, prior to the removal of the pea gravel from the excavation pit. One composite of the stockpiled native soil had also been collected on 14 March 1988. The analytic results of these previously collected samples indicated that an average of between 100 ppm and 500 ppm of hydrocarbons remained in the stockpiled material . 10 June 1988 - Gordon Boggs California Regional Water Quality Control Board - Central Valley Region = A request was made by WA to the California Regional Water Quality Control Board - Central Valley Region (RWQCB-CVR) to leave the 13- inch thick concrete slab in the excavation based on the data obtained from past sampling of soil beneath the slab, soil and groundwater sampling related to installation of the three monitoring wells and soil sampling during r excavation of the tank pit. The basic argument presented by WA suggested that hydrocarbons, which leaked from the tanks, had migrated laterally and - downward away from the edges of the slab and are contained in soil ;. adjacent to the southwestern corner of the excavation. 07611ma9 a