SITE INFORMATION AND CORRESPONDENCE

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I (.6LE 1 -CHECKLIST OF REQUIRED DATA U I 111 FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES ] Site Name and Location: C&B Equipment, 7474 Eleventh Street; Tracy, San Joaquin County . Y 1. Distance to production wells for municipal, domestic, agriculture, industry Fifty-six wells were reported within ZOo0 feet of and other uses within 2000 feet of the site; the site. One on-site well was destroyed and replaced with another well 150 feet east(cross- ' - gradient)of the site. Y❑ 2. Site maps,to scale, of area impacted showing locations of former and existing tank systems, In 1988,one 550-gallon/diesel excavation co.Ontours and sample locations, boring and monitoring well elevation contours, and one 1,removed gasoline gradients, and nearby surface waters, buildings, streets, and subsurface utilities; tank were removed from the site. 3. Figures depicting lithology(cross section), treatment system diagrams; No boring logs g submitted. The consultant states - in the closure summary that a thick rine-grained silty clay unit exists between 30 and 40 feet bgs. J Q4. Stockpiled soil remaining on-site or off-site disposal(quantity),, Spread on-site. Eight monitoring wells were installed at the site. The consultant proposed to destroy 5. Monitoring wells remaining on-Site, fate; the wells pending Regional Board's concurrence with the closure recommendation. 0 6 Tabulated results of all groundwater elevations and depths to water, Groundwater elevation varies from 6 to 8 feet bgs,with ft a northerly Flow direction. FYI 7. Tabulated results of all sampling and analyses: In 1988,elevated levels of petroleum contamination were detected in soil and groundwater when the gasoline tank was removed. Monitoring wells were Y❑Detection limits for Confirmation sampling installed in 1995 and 1997. Low levels of TPHg,BTEX,and MTBE were detected in samples from shallow wells MW-1 and MW-2; TPHg and BTEX were found in Lead analyses deep well MW-101. In August 2000,in addition to low concentrations of TPHg and BTEX,MTBE at 18 pgll and 0.73 pg11 only were detected in MW-1 and MW-2, ` respectively. 8. Concentration contours of contaminants found and those remaining in soil and groundwater, and both on-site and off-site: FY Lateral and El Vertical extent of soil contamination mLateral and ❑Y Vertical extent of groundwater contamination r 9. Zone of influence calculated and assumptions used for subsurface No remediation system was installed. remediation system and the zone of capture attained for the soil and groundwater remediation system; t FTJ 10.Reports l information ] Unauthorized Release Form ❑Y QMRs(Dates) 7/95—8/00 ❑N Well and boring logs SPAR ❑N FRP Y❑ Other(report name) GW Monitoring and Closure Report LjjulI:Best Available Technology(BAT) used or an explanation-for not using BAT'S""IThe tankswereremoved from the site.= •--- "` 0 12.Reasons why background waslis unattainable using BAT,' Minor contamination remains in soil and groundwater. 13.Mass balance calculation of substance treated versus that remaining; None submitted. 0 14.Assumptions,parameters, calculations and model used in risk - } assessments, and fate and transport modeling; Q15.Rationale why conditions remaining at site will not adversely Contamination is confined on-site. impact water quality, health, or other beneficial uses;and i F1 16.WET or TCLP results [7at i Comments:During tank removal, elevated levels of hydrocarbons were detected in soil and groundwater samples. Seven shallow ( monitoring wells and one deep well were installedat the site. Groundwater monitoring was conducted from July 1995 to August : 2000. Throughout the monitoring period, low concentrations of TPHg, BTEX,and MTBE were detected in water samples from two shallowwells. With the exception off MTBE,low levels of hydrocarbons also were detected in water samples from the lower water- r/j,-> bearing zone. The absence of contaminants in water samples from the perimeter and deep wells suggests the hydrocarbon plume is confined on-site in the upper aquifer. The low permeable aquatard also should further limit vertical migration of contaminants. Fifty-six domestic wells are within 2,000 feet of the site. The nearest downgradient well is about 500 feet north of the former tanks. Samples from the.on-site well were ND prior to its destruction. Based on the low contaminant concentrations and their confinement on-site,staff concurs with San Joaquin County closure recommendation. I