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run NU r-UKIHkH ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> .� Site Name and Location: San Joaquin Co Courthouse, 222 E.Weber Ave., Stockton, San Joaquin County(Case 390610)
<br /> Y Distance to production wells for municipal, domestic, A 2002 well survey reported no supply or domestic wells
<br /> culture, industry and other uses within 2000 feet of the site. within 2000'of the site.
<br /> r. Y 2. Site maps, to scale, of area impacted showing locations One 10,000-gallon gasoline UST and associated piping were
<br /> of any former and existing tank systems, excavation removed 8/96. TPHg,benzene, toluene, ethylbenzene,
<br /> contours and sample locations, boring and monitoring well xylenes, and MTBE were detected in soil beneath the UST.
<br /> elevation contours, gradients, and nearby surface waters, No new USTs were installed.
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<br /> buildings, streets, and subsurface utilities;
<br /> Y1 3. Figures depicting lithology(cross section), treatment Site lithology consists of clay, silt, and sand to
<br /> system diagrams; 39 feet the total depth investigated.
<br /> Y 4. Stockpiled soil remaining on-site or off--site disposal(quantity); The fate of the excavated soil is not discussed in the
<br /> reports.
<br /> Y 5. Monitoring wells remaining on-site, fate; Three monitoring wells(MW-1 through MW-3)remaining on-site will be
<br /> erl abandoned.
<br /> +••e 6. Tabulated results of all groundwater Depth to groundwater varied from 11 to 29 feet below ground surface
<br /> elevations and depths to water; (bgs). The groundwater gradient varied from 0.006 to 0.01 ft/ft, with the
<br /> downgradient direction towards the northeast.
<br /> 7. Tabulated results of all sampling Maximum confirmation soil concentrations(8/96) were TPHg, 1,600 mg/kg;
<br /> .r and analyses: benzene, 0.8 mg/kg; toluene,42 mg/kg;ethylbenzene, 26 mg/kg;xylenes,
<br /> Y❑ 140 mg/kg;and MTBE, 0.2 mg/kg. In 2/01, soil boring after results were TPHg,Detection limits for confirmation 400 mg/kg;benzene,-0.3 mg/kg; toluene, 5.9 mg/kg;ethylbenzene, 11 mg/kg;
<br /> sampling xylenes, 43 mg/kg;and MTBE, 0.065 mg/kg. Maximum grab groundwater
<br /> concentrations(2/01) were TPHg, 36,000 ug/L;benzene, 1,700 ug/L;toluene,
<br /> QY Lead analyses 4,600 ug/L;ethylbenzene, 1,400 ug/L;xylenes, 5,900 ug/L;and MTBE;25 pg/L.
<br /> in 12/07, maximum groundwater concentrations were TPHg, 112 ug/L;benzene,
<br /> 7.9 ug/L;ethylbenzene, 1.6 ug/L;xylene 8.9 ug/L;and MTBE, 0.8 ug/L.
<br /> 8. Concentration 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
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<br /> reports.
<br /> Lateral and .Y❑Vertical extent of soil contamination
<br /> Lateral and Vertical extent of groundwater contamination
<br /> 9. Zone of influence calculated and assumptions used for subsurface remediation The regulatory agency did not require an
<br /> system and the zone of capture attained for the soil and groundwater remediation engineered remediation.
<br /> system;
<br /> .. 10.Reports/information ❑Y Unauthorized Release Form ❑Y QMRs(22 from 2102 to 2108)
<br /> ` Well and boring fogs � PAR a FRP Other Site Conceptual Model, 8/04;Additional Site
<br /> Investigation, 2/07;Soil Vapor Sampling and Human Health Risk Assessment,4108
<br /> Y 1 11,Best Available Technology(BAT) used or an explanation for not using Removal of USTs and natural attenuation.
<br /> BAT;
<br /> r.r Y 12. Reasons why background warms unattainable Limited soil contamination remains on-site.
<br /> BAT,
<br /> Y 13.Mass balance calculation of substance treated The consultant estimated approximately 294 pounds of TPHg
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<br /> versus that n=mainin contamination remain in soil.
<br /> Y 14. Assumptions, parameters, calculations and No soil vapor ESLs were exceeded during the soil vapor analyses.
<br /> _ model used in risk assessments, and fate and
<br /> transport modelin ;
<br /> Y15. Rationale why conditions remaining at site will Soil contamination is limited in extent and not leaching to
<br /> not adversely impact water quality, health, or other groundwater. Results of 23 quarters of groundwater monitoring show
<br /> beneficial uses;and a decreasing trend in concentrations.
<br /> By: JLB Comments: One 10,000-gallon gasoline UST and associated piping were removed 8196 at the subject site.
<br /> w Maximum confirmation soil concentrations(8/96) were TPHg, 1,600 mg/kg;benzene, 0.8 mg/kg;toluene,
<br /> Date: 42 mg/kg; ethylbenzene, 26 mg/kg;xylenes, 140 mg/kg;and MTBE, 0.2 mg/kg, In 2/01, soil boring after results
<br /> 8/21/2008 were TPHg, 400 mg/kg; benzene, 0.3 mg/kg;toluene, 5.9 mg/kg;ethylbenzene, 11 mg/kg;xylenes,43 mg/kg;
<br /> and MTBE, 0.065 mg/kg. Maximum grab groundwater concentrations(2/01)were TPHg,36,000 ug/L;benzene,
<br /> 1,700 ug/L;toluene, 4,600 ug/L;ethylbenzene, 1,400 ug/L;xylenes,5,900 ug/L;and MTBE;25 fig/L. In 12/07,
<br /> maximum groundwater concentrations were TPHg, 112 ug/L;benzene, 7.9 ug/L;ethylbenzene, 1.6 ug/L;
<br /> xylenes, 8.9 ug/L;and MTBE, 0.8 ug/L. Based upon 23 quarters of declining groundwater concentrations, no
<br /> reported threat from vapor intrusion, no anticipated threats to sensitive receptors, and the limited extent of
<br /> contamination present in soil, Regional Board staff concur with San Joaquin County's Closure
<br /> Recommendation.
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