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TABL�wA - CHECKLIST OF REQUIRED D)�aA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: US IteMals, 1444 Mariposa Road,Stockton,San Joaquin County
<br /> Y 1. Distance to production wells for municipal, domestic,agriculture, A sensitive receptor survey Identified 55 wells within
<br /> industry and other uses within 2000 feet of the site; 2,000 feet of the site. The nearest well Is 150 feet
<br /> downgradient-of the former UST area.
<br /> 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, Four USTs were removed in
<br /> Y July 1992. Site maps are
<br /> excavation contours and sample locations, boring and monitoring well elevation contours,
<br /> gradients, and nearby surface waters, buildings, streets, and subsurface utilities; provided.
<br /> Y� 3. Figures depicting lithology(cross section), treatment system diagrams; Soil borings show clayey silts with silty sands
<br /> lenses to 60 feet
<br /> a 4. Stockpiled soil remaining on-site or off-site disposal(quantity); Excavated soils were aerated on-site and returned to
<br /> the tank pit excavation.
<br /> 5. Moliitorinv wells r+eJrwining site.fate___ Seven r»ontto ng wells cun+atltly exist on-site. The wells will be properly
<br /> Y des"d`follorv1ng-siteclosure. -.
<br /> ❑Y 6. Tabulated results of all groundwater elevations and depths to water, Depth to water varies from 46 to 69 feet The
<br /> groundwater flow direction Is to the southeast
<br /> a 7.Tabulated results of all sampling and analyses: April 2000 maximum groundwater results In pg/1 show TPHg at 50 pg/1,
<br /> MISE at 0.78, TBA at 11,and ethanol at 9.8. All other constituents were
<br /> Detection limits for confirmation sampling non-detect Two wells sampled in 10/00 showed TBA at 13 pg/l, and all
<br /> ®Lead analyses other constituents Including MtBE were non-detect. No indication of
<br /> lead analysis.
<br /> FTI 8. Concentration contours of contaminants found and those remaining in soil
<br /> and groundwater,and both on-site and off-site: Lateral and vertical extent of soil and
<br /> F1Lateral and Y❑ Vertical extent of soil contamination groundwater contamination is defined.
<br /> aLateral and 0 Vertical extent of groundwater contamination
<br /> 9.Zone of influence calculated and assumptions used for subsurface SVE piping was Installed in the tank pit and
<br /> Qremediation system and the zone of capture attained for the soil and excavation trenching,and a pilot test was
<br /> groundwater remediation system; completed to determine the zone of capture.
<br /> The SVE system was never operated.
<br /> Y� 10.Reports/information 0 Unauthorized Release Form 0 QMRs
<br /> Y❑ Boring logs Nl PAR 0 FRP 0 Other(Closure Report)
<br /> Y❑ 11.Best Available Technology(BAT)used or an explanation for not using BA T, Remove USTs and contaminated soils.
<br /> Aerate soils and return to excavation.
<br /> 12.Reasons why background was/fs
<br /> unattainable using BAT, Petroleum hydrocarbons remain In on-site Boll and groundwater.
<br /> 13.Mass balance calculation of substance
<br /> treated versus that remaining; Consultant estimates that 3 gallons of TPHg remains In soil, and 48 gallons of
<br /> TPHg remains in groundwater.
<br /> N❑ 14.Assumptions,parameters,calculations and model used in risk
<br /> assessments,and fate and transport modeling, A risk assessment was not completed.
<br /> YD 15. Rationale why conditions remaining at site will not adversely Soll and groundwater contamination Is limited In extent,
<br /> J mpact water quality,health, or other beneficial uses;and and groundwater monitoring shows the plume is stable.
<br /> The contamination will naturally attenuate.
<br /> By: Comments: The site is a former construction rental property. Four USTs(one 5,000-gallon diesel, one 10,000-gallon, and
<br /> _,,,� two 550-gallon gasoline USTs) were removed from the site in July 1992. Contaminated soils were excavated from around
<br /> �1'1_ the former USTs, then aerated, and returned to the tank pit excavation. Seven monitoring wells were installed from
<br /> March 1993 to May 1999,and decreasing trends are documented in the quarterly monitoring reports. The remaining
<br /> D te: cDntamination is stable and limited to on-site soil and groundwater. The nearest water supply well, reportedly 191 feet
<br /> I deep,Is on-site, about 150 feet downgradlent of the former USTs. This well was sampled in December 1999 and found to
<br /> /B 0l be non-detect for all constituents. The site is paved with asphalt, which should limit further leaching and transport of
<br /> contaminants. Based on the limited extent of soil and groundwater contamination, Board staff concur with San Joaquin
<br /> County's closure recommendation.
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