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' FINAL RUM31MATION PLAN 1488 West Frontage Road Manteca Callforda 2.3 Soil Conditions The sal profile consists of a yellowish-brown, fine to medium-grained silty sand, ranging rfrom surface to 9 to 15 feet below grade (bg) This sand is underlain by interbedded clays, silts, and fine-to coarse-grained sand that vanes in color from dark yellowish-brown ' to olive gray The lower soils extend from 9 to 15 feet bg to 49 feet bg 2.4 Petroleum Hydrocarbons in Soil ' Analytical results obtained during the various site investigations indicate the soil beneath the site contains concentrations of a) benzene, toluene, ethylbenzene, and total xylenes (BTEX), and b) total petroleum hydrocarbons (TPH), as gasoline To date, a total of twenty soil samples from soil and monitoring well borings drilled by ETS, Delta, NGA, and Aegis have been submitted and analyzed for concentrations of BTEX and TPH, as gasoline Tables 1 and 2 summarize soil analytical results collected to date An inferred zero line of petroleum hydrocarbons in soil is indicated on Figure 3 ' 2.5 Groundwater Level Measurements Groundwater level measurements have been collected from August 1988 to September 23, 1992, from the respective existing wells on and off site All water level measurements were referenced to the surveyed wellhead elevations (top of casing) and . measured to the nearest 0 01 foot Table 3 summarizes the available groundwater Eelevation data Groundwater elevations ranged from 5 25 to 10 07 feet above mean sea level during the observation period Calculated historical groundwater elevations have been plotted on Figure 4 As indicated by the data, the maximum groundwater elevation fluctuation is 4 82 feet This observation was used to evaluate design parameters of a remediation Isystem The potentiometric surface of the groundwater beneath the site on October 20, 1992, is shown on Figure 5 The direction of groundwater flow has varied from northeast to southwest, from August 23, 1990, to October 20, 1992 The calculated hydraulic gradient has fluctuated from 0 0003 to 0 007 ft/ft during the observation period 2.6 Petroleum Hydrocarbons in Groundwater Analytical results obtained during the site investigation indicate the groundwater beneath the site contains concentrations of BTEX and TPH, as gasoline Table 4 summarizes the groundwater analytical results collected to date Appendix C includes the most recent (October 20, 1992) groundwater analytical results Floating liquid hydrocarbons have not been observed in any of the wells Dissolved petroleum hydrocarbons have been detected consistently in wells MW-1, MW-3, MW-4, and MW-5, periodically in wells MW-2, MWA MW-7, and MW-8, but have not been found in well MW-9 An inferred zero line of TPH, as gasoline, and benzene is indicated on Figures 6 and 7, respectively I 90-097A FRP -4- I