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TABLt 1 - CHECKLIST OF REQUIRED DATA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Unocal#0123, 1034 Central Avenue, Tracy, San Joaquin County
<br /> 0 1. Distance to production wells for municipal, domestic, agriculture, Eight water supply wells were identified within 2,000
<br /> industry and other uses within 2000 feet of the site; feet of the site. A municipal well is 1,400 feet north of
<br /> the site and screened from 490 to 980 feet.
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<br /> 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, Six USTs were removed, and
<br /> excavation contours and sample locations, boring and monitoring well elevation contours, one UST was closed in
<br /> gradients, and nearby surface waters, buildings,streets, and subsurface utilities; place. Site maps provided.
<br /> 0 3. Figures depicting lithology(cross section), treatment system diagrams; Boring logs and cross-sections show clay and
<br /> silty sand to 26 feet.
<br /> 4. Stockpiled soil disposed off-site(quantity); AAproximately 75 cubic yards of contaminated loll was disposed at
<br /> Forward Landfill.
<br /> 5. Monitoring wells remaining on-site, fate; Eight monitoring welll currently exist on-site. The wells will be properly
<br /> Ell destroyed following site closure.
<br /> 0->�6.Tabulated results-of all groundwater-elevations-and depths-to water, Groundwater levels varied from 8_to,12 feet below
<br /> ground surface, and flow is to the northeast.
<br /> 7.Tabulated results of a!!sampling and analyses:
<br /> Maximum groundwater monitoring results for December 2000 in Ng11
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<br /> show TPHg at i49, TPHd of 370, benzene at 3.68, and ethyl benzene at
<br /> ©Detection limits forconfrrmation sampling 0`,969. Toluene,xylenes, MtBE, and other oxygenates were non-detect
<br /> El Lead analyses at appropriate detection limits. Maximum lead in soil is 16 mg/kg.
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<br /> 8. Concentration contours of contaminants found and(hose remaining in soil The lateral and vertical extent of soil and
<br /> and groundwater, and both on-site and off-site: groundwater contamination has been
<br /> © Lateral and Y❑ Vertical extent of soil contamination defined.
<br /> Lateral and Vertical extent ofgroundwater contamfnation
<br /> 9. Zone of influence calculated and assumptions used for subsurface A remediation system was not required at
<br /> remediation system and the zone of capture attained for the soil and I this site.
<br /> groundwater remediation system;
<br /> FE 10.Reports/information El Unauthorized Release Form 0(Z'Qtr 1995 to 4' Qtr 2000)
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<br /> Boring logs N� PAR FRP Y❑ Other(Closure Request, 4/01)
<br /> Y� 11.Best Available Technology(BAT)used or an explanation for not using BAT, Remove USTs, natural attenuation of
<br /> contaminants.
<br /> 12.Reasons why background was/1'sContamination remains in shallow soil and groundwater both on-site and north
<br /> of the site into 11 Stre
<br /> unattainable using BAT; et. Further remediation is not cost effective. The
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<br /> groundwater contamination is limited in extent;and remaining concentrations-,—
<br /> do not pr`,esent at significant threat to water quality.
<br /> 0 13.Mass balance calculation of substance The consultant estimates the initial mass was approximately 500 pounds of
<br /> treated versus that remaining, TPHg. About 75 cubiclyards of contaminated soil was removed with the USTs.
<br /> Confirmation borings were not required.
<br /> 14.Assumptions, parameters, calculations and model used in risk
<br /> Based on the limited extent of groundwater
<br /> assessments, and fate and transport modeling; contamination,a risk assessment was not required.
<br /> 15. Rationale why conditions remaining at site will no(adversely Remaining contamination is limited in extent.
<br /> impact wafer quality, health, or other beneficial uses;and Contamination will naturally degrade.
<br /> ByComments: Four 500 to 6,000-gallon waste oil to gasoline USTs were removed from the site prior to 1865. Two 550-gallon
<br /> gasoline USTs were removed in 11/96, and one 500 to 1,000-gallon UST was closed in place in 12196. Soil contamination was
<br /> identified during the UST removals, soil borings and monitoring wells were installed, and groundwater monitoring has been
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<br /> conducted from 6/95 to 12100. MtBE was identified in a water sample from monitoring well U-1 at a maximum of 5.6 ug/!by EPA
<br /> Date: Method 8260B. All other fuel oxygenates are non-detect at appropriate detection limits. PCE and TCE were identified in
<br /> upgradient and downgradient monitoring wells at maximum concentrations of 17.8 pg4 and 8.42 pg4, respectively. The source of
<br /> '�II�� solvent contamination is unknown;however,the remaining concentrations do not present a significant threat to water quality. The
<br /> /' r site is covered with asphalt, which should limit further leaching of contaminants into groundwater. Based on the investigation
<br /> completed to date, Board staff concur with San Joaquin County's closure recommendation.
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