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L.c(BLE 1 -CHECKLIST OF REQUIRED DATA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Former Langston ARCO, 15615 S. Seventh St., Lathrop, San Joaquin County(RB 11390520)
<br /> 1. Distance to production wells for municipal, domestic, agriculture, A 2001 sensitive receptor survey reported one water
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<br /> ndustry and other uses within 2000 feet of the site. supply(1,800'southeast)and ten domestic wells
<br /> (nearest are 1090'northwest and 1090'east)within
<br /> 2,000'of the Site. The wells are not threatened by this
<br /> release.
<br /> I, 2. Site maps, to scale, of area impacted showing locations of any In 4-91, three 4,000-gallon gasoline USTs were
<br /> former and existing tank systems, excavation contours and sample removed.
<br /> locations, boring and monitoring well elevation contours, gradients,
<br /> and nearby surface waters, buildings, streets, and subsurface
<br /> utilities;
<br /> Y 3. Figures depicting lithology(cross section), treatment system Site total
<br /> logydept consists of clay,silt,and sand to 50',
<br /> diagrams; the total depth investigated.
<br /> Y 4. Stockpiled soil remaining on-site or off-site disposal Approximately 5,500 tons of excavated soil was transported to ;
<br /> (quantity); _ Forward Landfill in Manteca. 200,000 gallons of pit'water was
<br /> treated and discharged to the City of Lathrop sanitary sewer.
<br /> Y 5. Monitoring wells remaining on-site, fate; Thirteen(13)monitoring wells(OMW-1 through OMW-3, MW-1 through MW-8,
<br /> DPE-1,and DPE-2)will be properly destroyed.
<br /> r - _ -- - - -=Depth-to=groundwater.-varied=from_10--bgs3o=1:g',bgs.-Groundwater flow=direction -
<br />+ - - 6.T s and
<br /> depths
<br /> to w all groundwater vaned from west to southeast at a gradient of 0.0006 ft/ft to 0.001 ft/ft
<br /> k! elevations and de the to water,
<br /> 7. Tabulated results of all sampling All data adequately tabularized in various reports,including closure report.
<br /> and analyses: - -
<br /> �' Y❑ Detection limits for confirmation
<br /> sampling
<br /> it
<br /> �N Lead analyses
<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 is described in the
<br /> available reports.
<br /> ` �Lateral and Y❑Vertical extent of soil contamination
<br /> Lateral and FAVerlical extent of groundwater contamination �!
<br /> 9. Zone of influence calculated and assumptions used for subsurface remediation Over-excavation and treatment of
<br /> system and the zone of capture attained for the soil and groundwater remediation 200,000 gallons of excavation water
<br /> system; were the engineered remediation.
<br /> 10.Reports/information QY Unauthorized Release Form 10QMRs(46)4/93 to 6/10
<br /> pY Well and boring logs ❑y PAR �y FRP ❑Y Other Closure Report(7/11)
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<br /> Y11.Best Available Technology(BAT) used or an explanation for not using USTs removal, over-excavation,and natural
<br /> BAT attenuation(DPE pilot tested but not
<br /> .. im /emented at full scale).
<br /> _I,,._12—Reasons-why-background.wasls_unattainable- _Residu_al soil.and groundwater contamination_iemams on-site.
<br /> _ - BAT;.
<br /> y 13.Mass balance calculation of substance treated Consultant estimated approximately 46.5 lbs of TPHg remain in
<br /> versus that remaining, groundwater and 663 lbs TPHg remain in soil.
<br /> I 14. Assumptions, parameters, calculations and Soil vapor was not measured, due to depth of over-excavation and
<br /> model used in risk assessments, and fate and impacted soil distance to building(50'). Soil results(TPHg)failed
<br /> transport modeling; ESLs for gross contamination and direct contact at 20'bgs,below the
<br /> water table and typical worker depth. Consultant states site does not
<br /> represent a significant risk.
<br /> 7Ir 15. Rationale why conditions remaining at site will Soil and groundwater contamination reportedly are limited in extent.
<br /> not adversely impact water quality, health, or other Groundwater plume is stable but increasing slightly in core of plume.
<br /> beneficial uses;and Land use(commercial)is not expected to change in the foreseeable
<br /> future. TPH in groundwater is estimated to reach WQGs in 4 to 100
<br /> ears.
<br /> By: JL B %4 Comments:In 4-91, three 4,000-gallon gasoline USTs were removed at the subject site. Residual soil and
<br /> !^� groundwater contamination remains on-site. Based upon the limited extent of contamination reported in soil
<br /> Date: and groundwater, a stable groundwater plume with very slowly declining concentrations in core of plume,no
<br /> 6111/2012 foreseeable changes in future land use(commercial),and minimal risks from soil vapor,soil and
<br /> groundwater, Regional Board staff concur with San Joaquin County's Closure Recommendation.
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