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STABLE 1 -CHECKLIST OF REQUIRED DATA %-W
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: 7-Eleven#21756, 853 E. Yosemite Ave., Manteca,San Joaquin County(Lustis Case 390711)
<br /> Y Distance to production wells for municipal. domestic. A 1999 well survey reported 1 public well exists 1,980 feet
<br /> iculture, industry and other uses within 2000 feel of the site. northwest of the site.
<br /> Y 2. Site maps, to scale, of area impacted showing locations Three 10,000-gallon gasoline USTs and associated
<br /> of any former and existing tank systems, excavation piping/dispensers were removed 12/96. MtBE was detected in
<br /> contours and sample locations, boring and monitoring soil beneath the USTs. No new USTs were installed,
<br /> well elevation contours, gradienlS. and nearby surface
<br /> waters, buildings, streets, and subsurface utilities:
<br /> Y 3. Figures depicting lithology(cross section), treatment Site lithology consists of clay,silt and sand to
<br /> system diagrams: 40 feet, the total depth investigated.
<br /> y4. Stockpiled soil remaining on-site or off-site disposal(quantity); The fate of the excavated soil is not discussed in the
<br /> reports, although it was reported as non-detect.
<br /> :y:1 5. Monitoring wells remaining on-site, fate; Six monitoring wells (MW-1 through MW 6) and two soil vapor extraction
<br /> wells SPV-1 and SPV-2 remainin on-site will be properly abandoned.
<br /> 6. Tabulated results o1 all groundwater Depth to groundwater varied from 17 to 24 feet below ground surface
<br /> elevations and depths to water; (bgs). The groundwater gradient varied from 0.001 to 0.002 ft/ft,and the
<br /> downgradient direction varied from northwest to northeast.
<br /> 7. Tabulated results of all sampling Maximum boring(6/99)sample soil concentrations were xylenes, 0.003.2 mg/kg and
<br /> and analyses: MtBE,0.175 mg/kg. Soil after result(10/07) was TBA, 0.0063 mg/kg. In 1/01,
<br /> maximum groundwater concentrations were TPNg, 16,000 ug/L;benzene, 440 ug/L;
<br /> Detection limits for confirmation ethylbenzene, 710 ug/L;xylenes, 1,310 uglL;and MWE;3,400 pg/L. In 7/07, all
<br /> sampling groundwater monitoring sample results were non-detect. In 10/07, the grab
<br /> groundwater sample result was non-detect.
<br /> 0 Lead analyses
<br /> 8. Concentralion contours of contaminants found and those remaining in soil and The extent of the identified
<br /> groundwater, and both on-site and off-site: contamination shown in applicable
<br /> 7Fyi reports.
<br /> 1_?_1 Lateral and l r J Vertical exlent of soil contamination
<br /> FYI Lateral and Vertical extent of grouadwaterconternioation
<br /> 9. Zone of influence calculated and assumptions used for subsurface remediation The required engineered remediation
<br /> system and the zone of capture attained for the soil and groundwater remediation was soil vapor extraction;however, only
<br /> system, two pilot tests were conducted.
<br /> 10.Reports/information �' Unauthorized Release Form 0 QMRs(21 from 1100 to 7107)
<br /> Well and boring logsPAR �� FRP 7 Other; Site Closure Requests, 6106 and 10107; RBCA and
<br /> Well Destruction Work Plan, 2108
<br /> Y 1?.Best Available Technology(BAT)used or an explanation for not using Removal of USTs,limited(2 pilot tests)soil
<br /> BAT, vapor extraction, and natural attenuation.
<br /> Z12. Reasons why background wasCs unattainable Limited soil contamination remains on-site.
<br /> ng BAT;
<br /> YD 13.Mass balance calculation of substance treated The consultant did not estimate the amount of residual contamination
<br /> versus that remainin in soil or groundwater. i
<br /> T14. Assumptions, parameters, calculations and No soil ESLs were exceeded during the RSCA analyses. Soil vapor
<br /> model used in risk assessments, and fate and intrusion was evaluated;and no threat was indicated due to the
<br /> transport modeling; distance(30 feet) from former USTs to store and low soil
<br /> _ concentrations,
<br /> Y 15. Rationale why conditions remaining at site will Soil contamination is limited in extent. Results of 21 quarters of
<br /> not adversely impact water quality, health, or other groundwater monitoring show a decreasing trend in concentrations to
<br /> beneficial uses:and non-detect. WQOs have been reached.
<br /> By. JLB Comments: Three 10,000-gafton gasoline USTs and associated piping/dispensers were removed 12/98 at the
<br /> subject site. No new USTs were installed. Maximum boring(6/99)soil concentrations were xylenes,
<br /> Date: 0.0032 mg/kg and MtSE, 0.175 mg/kg. Soil boring after result(10/07)was TBA,0.0063 mg/kg, In 1/01,
<br /> 611012008 maximum groundwater concentrations were TPNg, 16,000 ug/L;benzene, 440 ug/L;ethylbenzene, 710 ug/L;
<br /> xylenes, 1,310 ug/L;and MtBE;3,400 fig/L. In 7/07, all monitoring well sample results were non-detect. In
<br /> 10/07,a grab groundwater sample result was non-detect. Based upon 21 quarters of declining groundwater
<br /> concentrations to ND, no exceedence of ESLs in soil for residual contamination, the lack of threat from vapor
<br /> intrusion as a result of the distance from the former USTs to the store, no anticipated changes in land use
<br /> (commercial), and the limited extent of contamination present in soil, Regional Board staff concur with San
<br /> Joaquin County's Closure Recommendation. r
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