SITE INFORMATION AND CORRESPONDENCE

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Mr. James Barton ' October 31, 2002 Page 2 of 5 hydrocarbons in the subsurface and to select boring locations. The results of the soil vapor survey indicated an apparent area of free-product on the levee, which extended from the fuel dispenser (near ' MW-3) westward towards well MW-5. The geophysical survey identified an abandoned sewer line located parallel to the building fronting the slough, which presumably acted as a preferential pathway for contaminant migration. ' In May and June 1993, ten soil borings were advanced to depths ranging between 15 to 25 feet below ground surface (bgs); soil samples from two of the borings contained TPHg at concentrations up to 1,200 mg/kg (in boring B-2 located near the roadside dispenser), soil samples from three of the borings were ' found to contain TPHd at concentrations up to 89 mg/kg (in well MW-3), and soil samples from three of the soil borings were found to contain BTEX components at concentrations up to 296 mg/kg (in boring B- 2 located near the roadside dispenser). Installation of Groundwater Monitoring Wells ' Five of the soil borings were converted to groundwater monitoring wells MW-1 through MW-5 (Figure 2). Groundwater flow measurements conducted since 1993 indicate that groundwater flow is consistently away from the slough. In June 1993, benzene was detected in all collected groundwater samples and ' TPHd was detected in three of the collected samples. Subsequently, free-phase petroleum product (free- product) was found in well MW-3. Free-product was bailed from monitoring well MW-3 on a bi-weekly basis during June through August of 1993. In May 1994, a passive free-product recovery system was installed in well MW-3. Marina personnel monitored this system on a regular basis and recovered free- product was contained on-site in drums, pending appropriate disposal by marina personnel. This system was removed in October 1995 after it appeared that the free-product thickness was reduced to a slight sheen. The system was replaced in October 1996 since the free-product level rebounded after the device ' was removed; subsequently, the skimmer was removed in June of 1999 due to lack of effectiveness. The monitoring wells are located on a levee that has been designated as intrinsically unsafe by the Army Corps of Engineers. Because of this, Reclamation District #548, which regulates activities on the levee, will not allow work on the levee unless they are fully indemnified, without regard to fault, for possible failure of the levee. In past correspondence, the RWQCB has requested that remedial efforts, if ' necessary, be focused on those that can be accomplished in-situ. Thus, in November 1995, ORC Filter Socks were installed in monitoring wells MW-2, MW-3, and MW-4 ' to potentially enhance the natural bioremediation process in the vicinity of these wells by the slow release of oxygen into the groundwater; dissolved oxygen measurements were collected to evaluate the effectiveness of the socks. Based on the variability in DO measurements and TPHd concentrations since sock installation, it did not appear that the ORC Filter Socks were effective; it is likely that competing ' oxygen demand exists between hydrocarbon-oxidizing bacteria and the peaty, organic-rich soil types beneath the Site. The socks were removed from the wells in July 1996 and dissolved oxygen monitoring was discontinued. ' Groundwater monitoring has been conducted since June 1994 in accordance with RWQCB requirements. The current MRP consists of analyzing for TPHd and TPHg. Historically, the predominant contaminant ' identified has been TPHd, with non-typical TPHg and low concentrations of BTEX components typically present in well MW-3, which previously has contained free-product. Groundwater was monitored for dissolved lead and methyl tertiary butyl ether (MtBE) during the early investigation, and neither was detected. MtBE has subsequently been detected at low concentrations in wells MW-2 and MW-3. ' 1:\Tower Park\QMR\2002 QMMQ3_2002\3rd QTR 2002.doc SECOR Intemational Inc. SECOR Job No.050T.02926 I1/1/02 1:56 PM