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U-14aul#709-50 ' Additional Site Charactenzation Blaes Environmental ' 5. SUMIARVAN ) CONCLuSIONS On January I I through January 20, 2000, Blaes Environmental conducted an additional subsurface site characterization program at U-Haul Facility #709-50 located at 2701 North Wilson Way, Stockton, Califomea (Figures 1, 2 and 3) The objectives of the site characterization program were to further evaluate the vertical and lateral extent of detectable petroleum hydrocarbons in the soil below the former dispenser island and former USTs, and to determine the extent of dissolved hydrocarbons in groundwater beneath the site Since previous characterization activities had been performed by ETS (1990), Applied Consultants ' (1990) and SOTA (1995), this additional site characterization program further defines the degree and extent of hydrocarbons in soil using direct-push and cone-penetrometer soil sampling methods Blaes ' Environmental also installed eight new monitoring well screened across the groundwater interface to better define the degree and extent of hydrocarbons in groundwater 5 1 PREVIOUS INV_ESTIC` ATInI\TS ' Previous investigations determined the presence of hydrocarbons in soil samples collected from the trenched area of the former product piping from the USTs to the dispenser island (ETC, 1990) Further investigation performed by ETC (1990) involved the installation of three soil borings, which were converted into groundwater monitonng wells Results indicated that hydrocarbons were present in soil at depths of 60 to 75 ' feet bgs and that groundwater samples collected from the monitoring wells contained hydrocarbons above the California action levels ' In 1993 Applied Consultants conducted further investigations with the installation of eight soil borings and three monitonng wells Results indicated that soil bonng B7 was located nearest the release area Soil from this bonng contained hydrocarbons from 10 feet bgs to 70 feet bgs, the depth to groundwater at that time Groundwater sampling and analysis of the six wells at that time indicated that groundwater from MW-4 and MW-6 contained the highest concentrations of hydrocarbons At that time, the higher concentration on of the hydrocarbon plume appeared to stretch east to west across the site In 1995 SOTA installed two additional wells (MW-7 and MW-8) to further define the extent of hydrocarbons in groundwater Monitoring groundwater of the wells indicated that the depth to groundwater was between approximately 63 to 66 feet bgs and the groundwater flow direction was toward the southwest Analytical results of groundwater samples collected in October 1995 indicated that hydrocarbon concentrations exceeded California action levels in groundwater samples from five of the seven on-site 20