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U-Haul#709-50 8laes Environmental Preliminary Site Conceptual Model December 15,2006 Note The Frontier Motel located immediately south of the U-Haul facility is no longer considered a sensitive receptor since the domestic well supplying the motel was properly abandoned under the supervision of SJC EHD on September 13, 2005 2 7 PREVIOUS ASSESSMENT ACTIVITIES Following the detection of petroleum hydrocarbons in soil at the site, ETS completed a "Preliminary Investigation and Evaluation Report" in October 1991 This report included results of drilling and sampling three soil bonngs (B-1, B-2, and B-3) to approximately 100 feet bgs, and the installation of the three monitoring wells (MW-1, MW-2, and MW-3) within the borings Results of this investigation indicated that petroleum hydrocarbons were present in soil at depths of approximately 60 to 75 feet bgs Subsequent groundwater monitoring performed by ETS in May 1992 (Appendix B) indicated concentrations of hydrocarbons above the California action levels in groundwater samples from the three wells Applied Consultants of San Diego, California, began managing the site for U-Haul in 1992 Quarterly groundwater monitoring conducted in September 1992 indicated that the depth to groundwater across the site ranged from 85 5 to 86 74 feet bgs and the groundwater flow direction was to the north at a gradient less than 0 001 feet/foot Analytical results of groundwater samples indicated that groundwater at two of the three wells (MW-1 and MW-3) contained benzene at concentrations greater than the California action level (Appendix B) Applied Consultants completed further assessment of hydrocarbons in soil and groundwater in 1993 This work involved drilling and sampling five additional soil borings and the installation of three additional on-site monitoring wells (MW4, MW-5, and MW-6) Applied Consultants report concluded that the source of hydrocarbons in soil was located near boring B7 Analytical results of soil samples from B7 indicated that hydrocarbons were present from 10 feet bgs to approximately 70 and 75 feet bgs (the depth to groundwater at that time) The laboratory analytical results are presented in Appendix B Analytical results of groundwater samples indicated that the hydrocarbon plume in groundwater was centered near monitoring well MW-4 Benzene concentrations in samples from each of the six monitoring wells (MW-1 through MW-6) exceeded the California action level SOTA was contracted by U-Haul in 1995 to conduct further assessment of groundwater conditions with the installation of two additional wells (one on-site and one off-site groundwater monitoring well) These monitoring wells (MW-7 and MW-8) were included in the quarterly monitoring program in October 1995 Page 5