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TA6 1 - CHECKLIST OF REQUIRED IATA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Mid Valley Trailer Sales,2421 North Wilson Way, Stockton,San Joaquin County
<br /> Seven water supply wells were identified within 2,000
<br /> 1. Distance to production wells for municipal, domestic, agriculture,
<br /> industry and other uses within 2000 feet of the site; feet of the site. The nearest well is approximately 200
<br /> feet south of the former USTs.
<br /> One 1,000-gallon UST was
<br /> 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, removed in August 1991.
<br /> excavation contours and sample locations, boring and monitoring well elevation contours, Site maps are provided.
<br /> gradients, and nearby surface waters, buildings, streets, and subsurface utilities;
<br /> Boring logs show silt and silty sand to 30 feet,
<br /> 3. Figures depicting lithology(cross section), treatment system diagrams; the total depth of investigation.
<br /> Excavated soil from the UST was most likely returned
<br /> N 4. Stockpiled soil remaining on-site or off-site disposal(quantify); to the tank pit.
<br /> QN 5. Monitoring wells remaining on-site, fate; Contamination was limited to soil. Monitoring wells were not required.
<br /> a 6. Tabulated results of all groundwater elevations and depths to water,- Groundwater was not encountered during the soil
<br /> investigation.Depth to water is estimated at 45 feet.
<br /> 7.Tabulated results of all sampling and analyses: Maximum concentrations of soil samples from four borings completed
<br /> in December 1999 show TPHg at 11,000 mg/kg, ethyl benzene at
<br /> ©Detection limits for confirmation sampling 8,9 mg/kg, and xylenes at 1,500 mg/kg. Benzene, toluene, and all fuel
<br /> Lead analyses oxygenates including MtBE were non-defect at appropriate detection
<br /> limits. Lead analysis was not required.
<br /> 8. Concentration contours of contaminants found and those remaining in soil The lateral and vertical extent of soil
<br /> 0 and groundwater, and both on-site and off-site: contamination is defined. Groundwater was
<br /> Lateral and 0 Vertical extent of soil contamination not encountered at a total depth of 30 feet.
<br /> 0 Lateral and Vertical extent of groundwater contamination
<br /> 9. Zone of influence calculated and assumptions used for subsurface A remediation system was not required at
<br /> Qremediation system and the zone of capture attained for the soil and this site.
<br /> groundwater remediation system;
<br /> FE10.Reports/information 19 Unauthorized Release Form 0 QMRs
<br /> f9 Boring Boring logs � PAR FRP Other(PIER, 1/31/99)
<br /> 11.Best Available Technology(BAT)'used or an explanation for not using BAT; Remove USTs, natural attenuation.
<br /> 12.Reasons why background wasrs Contamination remains in on-site soils. Remediation is not cost effective. The
<br /> unattainable using BAT, remaining concentrations do not present a significant threat to water quality.
<br /> N 1 13.Mass balance calculation of substance
<br /> treated versus that remaining; Based on the limited contamination identified in soil,a mass balance was not
<br /> required.
<br /> N❑ fi
<br /> 14.Assumptions,parameters, calculations and model used in risk Based on the limited contamination identied in soil,a
<br /> assessments, and fate and transport modeling, risk assessment was not required.
<br /> 15. Rationale why conditions remaining at site will not adversely Contamination is limited to soil at one boring location.
<br /> impact water quality, health, or other beneficial uses,and Contamination will naturally attenuate.
<br /> By: Comments:Pacific Towing Company currently occupies the site. One 1,000-gallon gasoline UST and dispenser piping
<br /> were removed in August 1991. Soil was excavated to 7 feet bgs at the former dispenser, and TPHg was identified in soil
<br /> samples at that depth. Four soil borings were completed in December 1999 to 30 feet,and TPHg, ethyl benzene, and
<br /> xylenes were identified in one boring to a depth of 15 feet. Benzene, toluene, and all fuel oxygenates including MtBE were
<br /> Date: non-detect at appropriate detection limits. Soil samples collected at 20 and 25 feet were non-detect for all constituents.
<br /> Due to no staining, odor, or detectable concentrations in soils at 20 feet, a groundwater investigation was not required.
<br /> l/ ®t The County states that the minimum depth to water is 45 feet. Based on the limited contamination identified in soil and the
<br /> reported depth to groundwater, Board staff concur with San Joaquin County's closure recommendation.
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