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TAB 1 - CHECKLIST OF REQUIRED TA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
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<br /> Site Name and Location: Former Shell Station, 141 North EI Dorado Street,Stockton,San Joaquin County
<br /> 1. Distance to production wells for municipal, domestic, agriculture, The nearest sensitive receptor is the Stockton Channel
<br /> industry and other uses within 2000 feet of the site; located directly south of the slte. No water supply
<br /> wells are located within 2,000 feet of the site.
<br /> 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, Site maps are provided in
<br /> Y the various reports. Six
<br /> excavation contours and sample locations, boring and monitoring well elevation contours, LISTS were removed from
<br /> gradients, and nearby surface waters, buildings, streets, and subsurface utilities; the site from 1981 to 1991.
<br /> 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology consists of clay and slit with minor
<br /> sand lenses to 41 feet, the total depth explored.
<br /> 0 4. Stockpiled soil disposed off-site(quantity); The disposition of excavated soil during UST removal was not
<br /> presented. It was likely returned to the tank pit excavation.
<br /> 5. Monitoring wells remaining on-site, fate; All eleven site monitoring and remedial wells were properly destroyed under
<br /> County permit in September 2000. +
<br /> 6. Tabulated results of all groundwater elevations and depths to water; Groundwater levels varied from 16 to 37 feet below 4
<br /> ground surface,and flow is to the east/northeast
<br /> 7. Tabulated results of all sampling and analyses: Samples collected in July 2000, the last groundwater sampling event,
<br /> Ellshowed TPHg at<50lrg/l, benzene at 1.21 ug/1,and toluene at 1.09 pgil.
<br /> Detection limits for confirmation sampling MtBE was detected at a maximum concentration of 2,4401rg/l, which
<br /> Lead analyses has been determined to originate from an off-site source west and
<br /> upgradient of the site. Lead was detected at 10 mg/kg.
<br /> 8. Concentration contours of contaminants found and those remaining in soil Confirmation soil sampling completed in
<br /> 0 and groundwater, and both on-site and off-site: 1996 identified TPHg in 4 of 29 samples,
<br /> © Lateral andVertical extent of soil contamination and BTEX in 1 of 29 soil samples. Minor
<br /> ❑ Latera!and 171 Vertical extent of groundwater contamination benzene and toluene were identified in
<br /> Y Y groundwater during the last sample event
<br /> 9.Zone of influence calculated and assumptions used for subsurface Site remediation consisted of soil vapor
<br /> 0 remediation system and the zone of capture attained for the soil and extraction,air sparging,-.and groundwater
<br /> groundwater remediation system; extraction.
<br /> Reports/information Unauthorized Release Form QMRs 8/92 through 7/00)
<br /> 10.Repo 0 � ( g
<br /> Y❑ Boring logs 0 PAR T] FRP Yn Other(Request for Case Closure, 12/01)
<br /> Y❑ 11.Best Available Technology(BAT) used or an explanation for not using 13A T, Soil vapor extraction,air sparging,and
<br /> groundwater extraction.
<br /> TPHg and minor BTEX contamination remains in soil and groundwaterat the
<br />.,... Y,. ,12.Reasons why_background was/is ._,
<br /> unattainable using BAT,' The reinaining contamination does-not presehf a significant.threat--to
<br /> water quality.
<br /> El13.Mass balance calculation of substance The consultant estimated that approximately 3,277 pounds of TPHg was
<br /> treated versus that remaining, removed from site soils, which is more than.100%of the condsultants original
<br /> contaminant mass estimate.
<br /> 14.Assumptions,parameters, calculations and model used in risk Based on the limited groundwater contamination,a risk
<br /> assessments, and fate and transport modeling, assessment was not required
<br /> 15. Rationale why conditions remaining of site will not adversely Remaining contamination is limited in extent, and only
<br /> impact water quality, health, or other beneficial uses;and trace levels of TPHg and BTEX constituents were
<br /> detected in groundwater during the last sampling events. E
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<br /> Comments: The site is a former Shell station that operated from 1955 to 1981. The site is currently owned by the City of Stockton,and it
<br /> By: has been redeveloped as a waterfront park along the Stockton Deep Water Channel. Five gasoline USTs(4,000 to 7,500 gallon)were
<br /> MH removed from the site in 1981,and one 550-gallon waste oil UST was removed in 1991. A soil and groundwater assessment was
<br /> completed in 1990, and three remedial technologies were used to remove site constituents. A soil vapor extraction(SVE)system
<br /> operated from 1992 to 1996, air sparging was added to the SVE system from 1994 to 1996,and a groundwater extraction and treatment
<br /> system operated from March 1993 to October 1995. Based on confirmation soil sampling and mass balance calculations, the consultant
<br /> Date: estimates that 3,277 pounds of TPHg has been effectively removed from site soils. MtBE was detected in upgradient wells at increasing
<br /> 6124102 concentrations,and based on site history and site hydrogeology, the consultant suggests that the source of MtBE contamination is from a
<br /> former ARCO service station 300 feet upgradient of the site. County staff concur with this determination, and the County has directed
<br /> ARCO to define the extent of MtBE contamination originating from their site. Based on the site investigation and remedial activities
<br /> completed to date,Board staff concur with San Joaquin County's closure recommendation.
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