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ITABLL�I - CHECKLIST OF REQUIRED DU
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Regal#603, 6425 Pacific Avenue, Stockton,San Joaquin County
<br /> 1.Distance to production wells for municipal, domestic, agriculture, industry A well receptor survey was completed in
<br /> and other uses within 2000 feet of the site; 1998. Three water supply wells within 4
<br /> 2,000 feet of the site have been destroyed. 1
<br /> FTI 2. Site maps,to scale, of area impacted showing locations of former and existing tank systems, Three 10,000-gallon gasolineI
<br /> excavation contours and sample locations, boring and monitoring well elevation contours, USTs were removed and !
<br /> gradients, and nearby surface waters, buildings, streets, and subsurface utilities; replaced in October 1988.
<br /> Site maps provided.
<br /> FTI
<br /> 3. Figures depicting lithology(cross section), treatment system diagrams; Lithology figures show a shallow sand
<br /> aquifer overlain with silty clay sediments.
<br /> Q4. Stockpiled soil disposed off-site(quantity); An estimated 550 cubic yards of excavated soil was transported to the
<br /> y Jackson Road Landfill(Sacramento County)in November 1988. I
<br /> F7Y 5. Monitoring wells remaining on-site, fate,, Thirteen monitoring wells remain on-site and off-site. The wells will be
<br /> destroyed pending site closure.
<br /> 71 6. 0 results of all groundwater elevati ns andddddepths to waterGroundw`aterWevationsvary fiorn 31 to 567eei`bgs,
<br /> and groundwater flow is to the east/northeast.
<br /> �y 7.Tabulated results of all sampling and analyses: December 2000 maximum groundwater monitoring results in pg/1 show
<br /> TPHg at 7,000,benzene at 16, toluene at 62, ethyl benzene at 260,
<br /> ©Detection limits for confirmation sampling xylenes at 1400,and MtBE at 38. Lead was identified at 12 mg/kg in
<br /> 0 Lead analyses one overexcavation soil sample.
<br /> 8. Concentration contours of contaminants found and those remaining in soil The extent of soil contamination has been f
<br /> 0 and groundwater, and both on-site and off-site: defined. The lateral and vertical extent of
<br /> Lateral and Vertical extent of soil contamination TPHg and BTEX is defined in groundwater.
<br /> ❑ Lateral and ❑ Vertical extent of groundwater contamination grow has been defined n the shallow
<br /> y y groundwater at 18 pg/I in boring CPT1.
<br /> TI 9.Zone of influence calculated and assumptions used for subsurface A SVE system operated from October 1991
<br /> remediation system and the zone of capture attained for the soil and to December 1998, and an air sparging
<br /> groundwater remediation system; system operated from December 1997 to
<br /> December 1998. The maximum zone of R
<br /> influence is reported at 150 feet.
<br /> 10.Reports/information -,E] Unauthorized Release Form OMRs(8/91 through 1/99)
<br /> y❑ Well and boring logs y❑PAR y❑ FRP y❑ Other(Overexcavation of Soils, 4/00;Add.Assessment, 5/01)
<br /> Y7 11.Best Available Technology(BAT)used or an explanation for not using BAT; Free product removal, SVE/AS to remove an
<br /> estimated 99% of contaminants.
<br /> F7112.Reasons why background wash's Contamination remains in soil and groundwater both on-site and off-site.'""'
<br /> unattainable using BAT; Remaining concentrations do not present a significant threat to water quality.
<br /> y013.Mass balance calculation of substance The consultant estimates the initial mass was approximately 62,000 pounds
<br /> treated versus that remaining; of TPHg,and the remaining mass determined from confirmation borings in '
<br /> June 1997 show 212 pounds of TPHg, a 99%reduction.
<br /> y❑ 14.Assumptions,parameters, calculations and model used in A RBCA evaluation was completed to determine the F
<br /> risk assessments, and fate and transport modeling; leachability of contaminated soil left in place, and these
<br /> results were used to direct additional soil excavations. j.
<br /> ETI 15.Rationale why conditions remaining at site will not adversely Remaining contamination is stable and decreasing.
<br /> impact water quality, health, or other beneficial uses. Contamination will naturally degrade.
<br /> By: Comments: Three USTs were removed and replaced in 1988, an on-site remediation operated from 10/91 until 12/98, and
<br /> groundwater monitoring has been completed from 12/88 to 12/00. The site was submitted to the Regional Board for closure
<br /> on 5 June 2000. Closure was not granted because the extent of contamination downgradient of existing monitoring wells f
<br /> had not been determined,groundwater analyses for fuel oxygenates and fuel additives were not presented, and the status
<br /> Date: of identified water supply wells was not presented. Regal completed additional monitoring and investigation activities from
<br /> 12/00 to 4/01. Regal identified the extent of TPHg and BTEX contamination, sampled and analyzed groundwater samples l
<br /> 7 z%I for fuel oxygenates and additives, and determined that the three water supply wells within 2,000 feet of the site were i
<br /> destroyed. The results of 12/00 sampling show the groundwater plume is stable. Based on the investigation completed to
<br /> date, Board staff concur with San Joaquin County's closure recommendation.
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