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T' S E C 0 R from 64 ppb (MW-4) to120 ppb (EW-2). Di-isopropyl ether (DIPE) was detected in one well (DMW-1) at a concentration of 1.3 ppb. Ethylene dibromide (EDB) and ethyl tert butyl ether(ETBE) were not detected this quarter. Chemical concentrations were generally consistent with historical data, except for a decrease in concentrations in MW-1 and MW-4; and an increase in concentrations in EW-2. A liquid phase hydrocarbon (LPH) sheen was observed in well EW-1. Groundwater elevations across the site decreased by an average of 2.34 ft. Groundwater flow for the shallow water bearing zone was to the northeast at an approximate gradient of 0.003 ft/ft, and for the deep water bearing zone was to the northeast at an approximate gradient of 0.003 ft/ft, consistent with historical data. Sampling dates were not coordinated with the Tosco station 4409 located across the street from Arco 4932; therefore the groundwater elevation maps were not combined this quarter. The sampling and gauging events will be coordinated for future quarters. Attachment C contains the Monitoring and Sampling report for Tosco Station 4409 (Gettler-Ryan). Interim remediation by groundwater batch extraction was performed at this site on October 1 and October 21, 2002. A total of 3,490 gallons were extracted from wells MW-1, MW-4, EW-1, and EW-2 during these extraction events. Groundwater extraction data is presented in Tables 4 and 5. Groundwater elevation contour maps for before and after each event are presented as Figures 6 through 9. The contour maps from after extraction show a localized cone of depression around well EW-1. Groundwater batch extraction events were discontinued after the October 21 event. Field Data Sheets are included in Attachment B. This report presents our understanding of existing conditions at the subject site. The conclusions contained herein are based on the analytical results, and professional judgment in accordance with current standards of professional practice; no other warranty is expressed or implied. SECOR assumes no responsibility for exploratory borings or data reported by other consultants or contractors. i ATTACHMENTS: !? • Table 1 - Groundwater Elevation and Analytical Data • Table 2 - Fuel Oxygenates Analytical Data • Table 3-Groundwater Gradient Data • Table 4--Batch Extraction-Total Groundwater Volume Removed • Table 5—Batch Extraction Groundwater Elevation Data • Figure 1 - Groundwater Elevation Contour Map—Shallow Water Bearing Zone • Figure 2—Groundwater Elevation Contour Map—Deep Water Bearing Zone • Figure 3—Groundwater Chemical Concentration Map • Figure 4--MtBE Isoconcentration Contour Map—Shallow Water Bearing Zone • Figure 5— MtBE Isoconcentration Contour Map-Deep Water Bearing Zone • Figure 6-Groundwater Elevation Contour Map-Before Batch Extraction October 1, 2002 • Figure 7- Groundwater Elevation Contour Map-After Batch Extraction October 1,2002 • Figure 8 - Groundwater Elevation Contour Map-Before Batch Extraction October 21, 2002 • Figure 9-Groundwater Elevation Contour Map-After Batch Extraction October 21, 2002 • Attachment A- Field and Laboratory Procedures • Attachment B - Certified Laboratory Analytical Reports, Chain-of-Custody Documentation, and Field Data Sheets • Attachment C--Former Tosco (Unocal) Service Station #4409 Groundwater Monitoring and Sampling Report (Gettler-Ryan) cc: Mr. Marty Hartzell, Regional Water Quality Control Board -Central Valley Region (RWQCB-CVR) Ms. Lori Duncan, SJCPHS I:\ARCO149321QMRs1200214QMR02.doc -3-