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ABLE 1 -CHECKLIST OF REQUIRED DAT4J
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> I�.
<br /> Site Name and Location: Former Unocal#2859, 1665 Pacific Ave., Stockton, San Joaquin County(RB#390176)
<br /> y 1. Distance to production wells for municipal,domestic, Eight supply and one deep USGS wells are located within
<br /> agriculture, industry and other uses within 2000 feet of the site. 2,000 feet of the Site. The supply wells are upgradient
<br /> while the USGS well is`800 feet downgradient of the Site.
<br /> Y 12. Site maps, to scale, of area impacted showing locations of In January 1988, contamination was found during a site
<br /> any former and existing tank systems, excavation contours and investigation for property sale. In March 1988, two
<br /> sample locations, boring and monitoring well elevation 10,000-gallon gasoline and one 500-gallon waste oil USTs
<br /> contours, gradients, and nearby surface waters, buildings, were removed.
<br /> streets, and subsurface utilities;
<br /> Y 3. Figures depicting lithology(cross section), treatment system Site lithology consist .1of clay, silt, and sand to 90', the
<br /> diagrams; total depth investigated.
<br /> N 4. Stockpiled soil remaining on-site or off-site disposal(quantity); approximately 1,100 to 1,350 y excavated soil was
<br /> removed, although the fate of the soil is not discussed
<br /> in the available reports.
<br /> 7y 5. Monitoring wells remaining on-site, fate; Twenty one monitoring wells(MW-1 through MW-21)and seventeen
<br /> remediation wells(VW-1 through VW-3, SVP-1A/-1B through SVP-7A/-7B)will
<br /> be properly abandoned.
<br /> B. Tabulated results of all groundwater Depth to groundwater varied from 22'to 48'bgs. Groundwater flow
<br /> elevations and depths to water; direction varied from northeast to northwest and groundwater gradient
<br /> varied from 0.002 to 0.005 ft/ft.
<br /> 7. Tabulated results of all sampling All data adequately tabularized in various reports,including closure report.
<br /> and analyses: i
<br /> tDetection limits for confirmation
<br /> sampling
<br /> r.
<br /> 0 Lead analyses
<br /> 8. concentration contours of contaminants found and those remaining in soil and The extent of the identiried
<br /> groundwater, and both on-site and off-site: I? contamination shown in applicable
<br /> reports.
<br /> y❑Lateral and El Vertical extent of soil contamination
<br /> Lateral and FYI Vertical extent of groundwater contamination
<br /> 9. Zone of influence calculated and assumptions used for subsurface remediation Over-excavation, SVE, and ozone
<br /> system and the zone of capture attained for the soil and groundwater remediation injection were the approved remediation.
<br /> s stem;
<br /> YJ 10.Reports/information El Unauthorized Release Form FYI QMRs 27 from 2/97 to,1/10
<br /> Ey Well and boring logs Fy PAR �y FRP Other Sail Vapor Intrusion.Report(11/09)NFAR(11/10)
<br /> Y 11,Best Available Technology(BA 7) used or an explanation for not USTs removal, over-excavation, SVE, ozone
<br /> usin BAT, injection, and natural attenuation.
<br /> Y 12. Reasons why background wasvls Minimal residual soil and groundwater contamination remains on-site.
<br /> ttainable usin BAT,
<br /> Y7ai Mass balance calculation of substance treated The consultant estimates 2,757 lbs TPH removed from soil, and
<br /> 7
<br /> estimates 2,266 lbs of TPH remain in!soil and 34 lbs TPH remain in
<br /> versus that remaining;
<br /> roundwater. �M
<br /> Y 14. Assumptions,parameters, calculations and The shallow soil vapor passed the Region 2 commercial ESLs.Direct
<br /> model Used in risk assessments, and fate and exposure and gross contamination soil ESLs(TPHg, TPHd, BTEX)were
<br /> transport modeling; exceeded at 12.5'bgs, which is below depths associated with normal
<br /> construction.
<br /> Y 15. Rationale why conditions remaining at site Soil and groundwater contamination reportedly are limited in extent.
<br /> will not adversely impact water quality, health;'or Land use(commercial)is not expected to change in the foreseeable
<br /> other beneficial uses;and future. Vapor intrusion risk has been addressed. Water quality goals
<br /> will be reached in 24 years.
<br /> By: JLB Comments:In January 1988, contamination was found during a site investigation for property sale. In
<br /> March 1988, two 10,000-gallon gasoline and one 500-gallon waste oil USTs were removed from the subject
<br /> Date: Site. Based upon 27 quarters of groundwater monitoring showing a stable plume with declining
<br /> 12/30/2010 concentrations, the limited extent of contamination remaining in soil and groundwater, no foreseeable
<br /> changes in land use, and limited threats from groundwater, soil and soil vapor intrusion, Regional Board
<br /> staff concur with San Joaquin County's Closure Recommendation.
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