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f 1.0 INTRODUCTION 1.1 SITE DESCRIPTION Tower Park Marina (the Site) is located at 14900 West -Highway 12 on Little Potato Slough near Terminous (near Lodi), California (Figure 1-1). The 50 acre Site consists of a marina, automobile and boat dock fuel dispensing facilities, aboveground .petroleum hydrocarbon storage tanks, campground restaurant, store, small beach, boat storage/repair facility, and a domestic wastewater collection/treatment plant. The Site was historically used.as a railroad depot for:agricultural products grown in the area; the storage buildings have since been converted to the restaurant, store, and the boat storage/repair areas. 1.2 BACKGROUND The presence of petroleum hydrocarbons was visually detected in soil during aboveground petroleum hydrocarbon storage tank and underground conveyance line replacement activities in September 1991_ Site investigations which.have been conducted to assess the extent of contamination and interim remedial activities which have been implemented include the following: • In November 1991, five soil samples were collected from beneath the trenches which contained the former underground conveyance piping between the fuel tanks,the roadside dispenser, and the dock dispenser. • In January 1992, a geophysical survey was conducted to assess the presence and extent of underground piping systems. A soil vapor survey was conducted to preliminarily assess the subsurface presence of petroleum hydrocarbons. • In May and June 1993, ten soil borings were constructed to depths ranging from 15 to 25 feet; five borings were converted to monitoring wells MW-1 through MW-5. The wells were subsequently monitored. Well locations are shown on Figure 1-2. • was hand bailed from monitoring From June through August 1993, free product g well MW-3 on a bi-weekly basis. In May 1994, a passive free product recovery system was installed in well MW-3. The • Y P p passive system consists of a device suspended inside the well which is designed to capture Lfree product only if the device is appropriately located inside the well. The device is periodically removed from the well and its contents drained to an appropriate container. In June 1994, the wells were monitored, slug tests were conducted, and a sample of free product obtained from well MW=3 was analyzed. The results of these activities are detailed in the reports listed in`Appendix A. The major findings of the May/June 1993 soil/groundwater investigation were the presence of benzene in all groundwater samples and free product in well MW-3. The predominant area of contamination and four of the five monitoring wells are located on the levee which separates the campground from Little Potato Slough;MW-2 is located in the campground downgradient of the.aboveground tanks. . Additional site investigation and remedial actions were proposed in the "Work Plan/Remediation Action Plan" prepared by Law/Crandall, Inc. on September 30, 1993 (RAP). The RAP was approved by the Regional Water Quality Control Board,, G ASUS AMTOW ERMW KPLAN 50114-001-01 1-1