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TABLES CHECKLIST OF REQUIRED DATA'
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Former Shell Station, 1071 N. Main Street, Manteca, San Joaquin County
<br /> 0 1. Distance to production wells for municipal, domestic, agriculture, A well survey in 2004 shows one public water supply
<br /> industry and other uses within 2000 feet of the site; well located approximately 1,500 feet south
<br /> (upgradient)and four domestic wells over 1100 feet
<br /> (downgradient)of the site.
<br /> 0 2. Site maps, to scale, of area impacted showing locations of former and existing tank Two 8,000-gallon and one 10,000-
<br /> systems, excavation contours and sample locations, boring and monitoring well gallon gasoline USTs were
<br /> elevation contours, gradients, and nearby surface waters, buildings, streets, and removed in 8/96. Two 15,000-
<br /> subsurface utilities; gallon gasoline and one 550-gallon
<br /> waste oil USTs were removed in
<br /> 12/04.
<br /> a 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology consists of sand,silt and clay to
<br /> 45 feet, the total depth investigated..
<br /> 0 4. Stockpiled soil disposed off-site(quantity); The excavated soil and pea gravel was aerated and reused as backfill.
<br /> 5. Monitoring wells remaining on-site, fate; Three monitoring wells(MW-1 through MW-3))installed for this investigation
<br /> will be properly destroyed.
<br /> 6. Tabulated results of all groundwater elevations and depths to water,• The depth to water varied from 15 to 29 feet,and
<br /> the down-gradient direction of groundwater varied
<br /> from south to west at 0.002 ft/ft.
<br /> 7.Tabulated results of all sampling and analyses. In 8/96,maximum soil results were: TPHg, 1,300 mg/kg;benzene,
<br /> ®Y0.055 mg/kg;toluene, 29 mg/kg;ethylbenzene, 20 mg/kg;xylenes,
<br /> Detection limits for confirmation sampling 140 mg/kg;and MtBE,34 mg/kg. All soil results were ND in 12/00.
<br /> Lead analyses Maximum groundwater monitoring results in 10/98 were: TPHg,460
<br /> Ng/L;ethylbenzene, 2.1 Ng/L;xylenes, 2.3 Ng/L;and MtBE, 1,700 Ng/L.
<br /> In 10/05,all groundwater monitoring results were ND.
<br /> Q8. Concentration contours of contaminants found and those remaining in soil
<br /> and groundwater, both on-site and off-site: The extent of contamination is defined by
<br /> Rateral and 8 Vertical extent of soil contamination on-site soil borings,grab groundwater
<br /> ateral and Vertical extent of groundwater contamination samples and monitoring wells.
<br /> 0 9. Zone of influence calculated and assumptions used for subsurface A groundwater remediation system was not
<br /> remediation system and the zone of capture attained for the soil and required for this site.
<br /> groundwater remediation system;
<br /> 10.Reports/information Unauthorized Release Form F QMRs 4/98 to 10/05.
<br /> 0 Boring logs Y❑ PAR N❑ FRP 0 Other Closure Report
<br /> Q11.Best Available Technology(BAT) used or an explanation for not using BAT, Remove USTs and natural attenuation.
<br /> 12.Reasons why background wasrs Decreasing concentrations have been attained at all monitoring wells. Minor
<br /> unattainable using BAT- soil contamination remains on-site.
<br /> 0 13.Mass balance calculation of substance The consultant did not estimate the remaining mass in soil and groundwater.
<br /> treated versus that remaining;
<br /> 14.Assumptions,parameters, calculations and model used in risk A risk assessment was required(VLEACH). Remaining
<br /> assessments, and fate and transport modeling;and concentrations do not exceed Region 2 ESLs.
<br /> yTJ 15. Rationale why conditions remaining at site will not adversely Soil contamination is limited in extent,and based on
<br /> impact water quality, health, or other beneficial uses. thirty one sampling events, contamination is not
<br /> continuing to leach to groundwater. Groundwater
<br /> monitoring shows a decreasing trend in concentrations.
<br /> By: Comments: Two 8,000-gallon and one 10,000-gallon gasoline USTs were removed in 8/96. Two 15,000-gallon gasoline
<br /> JLB and one 550-gallon waste oil USTs were removed in 12/04. In 8/96, maximum soil results were: TPHg, 1,300 mg/kg;
<br /> benzene, 0.055 mg/kg;toluene, 29 mg/kg;ethylbenzene, 20 mg/kg;xylenes, 140 mg/kg;and MtBE, 34 mg/kg. All soil
<br /> Date: results were ND in 12/00. Maximum groundwater monitoring results in 10/98 were: TPHg, 460 Ng/L;ethylbenzene, 2.1
<br /> Ng/L;xylenes, 2.3 Ng/L;and MtBE, 1,700 Ng/L. In 10/05, all groundwater monitoring results were ND. Based on limited
<br /> 12/28/05 soil contamination and declining concentrations in groundwater, Regional Board staff concur with San Joaquin County's
<br /> Closure Recommendation.
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