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TABLE 1 - CHECKLIST OF REQUIRED 67�TA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Pershing Shell,4445 North Pershing Avenue,Stockton,San Joaquin County
<br /> 0 1. Distance to production wells for municipal, domestic, agriculture, Two municipal wells were identified at 1,400 to
<br /> industry and other uses within 2000 feet of the site; 1,700 feet from the site. The wells are cross gradient
<br /> to groundwater flow.
<br /> 2. Site maps, to scale, of area impacted showing locations of former and existing tank systems, Five USTs were removed
<br /> Y excavation contours and sample locations, boring and monitoring well elevation contours, between 6/87 and 5/90. Site
<br /> gradients, and nearby surface waters, buildings, streets, and subsurface utilities; maps are available in the
<br /> various reports.
<br /> Y� 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology consists of silt with sand and clay
<br /> to 51 feet, the total depth investigated.
<br /> y� 4. Stockpiled soil disposed off-site(quantify); Approximately 70 cubic yards of excavated soil were disposed of at
<br /> West Contra Class ill Landfill in May 1990.
<br /> 5. Monitoring wells remaining on-site, fate; Four monitoring wells and two soil vapor wells remain on-site. The wells will
<br /> Y be properly destroyed pending site closure.
<br /> � - .a....-� the depth-to-water varied-from 1-3 to 32 feet,'and- -
<br /> 6. Tabulated re—suds—of ati gr'oundwafer elevations and depths to water, the groundwater flow is to the northeast.
<br /> 7. Tabulated results of all sampling and analyses: The maximum soll concentrations show TPHg at 4,300 mg/kg and
<br /> benzene at 10 mg/kg at the bottom of the tank pit excavation. The
<br /> MDefection limits for confirmation sampling maximum groundwater contamination in Shell's monitoring wells
<br /> Y❑Lead analyses showed TPHg at 230 Ng/1 and benzene at 57 pg/l in 1/93. MtBE was
<br /> Identified at a maximum of 32 pg/1,and is currently at 1.41rg/l.
<br /> 8. Concentration contours of contaminants found and those remaining in soil Soil contamination is defined by on-site
<br /> 0 and groundwater, both on-site and off-site: soil borings and monitoring wells, and
<br /> Y� Lateral and Vertical extent of soil contamination groundwater contamination is defined by
<br /> Lateral and El Vertical extent of groundwater contamination Exxon monitoring wells at 4444 North
<br /> Y❑ 9 Pershing Avenue(see comments below).
<br /> 9.Zone of influence calculated and assumptions used for subsurface An extended SVE pilot test was completed
<br /> 0 remediation system and the zone of capture attained for the soil and in 12/91, and a ROI was observed at 20 to
<br /> groundwater remediation system; 25 feet. Due to low soil vapor influent
<br /> concentrations, SVE was not initiated.
<br /> y� 10.Reports/information ] Unauthorized Release Form 71 QMRs(7/90 to 2/02)
<br /> 71 Boring logs ❑ PAR N❑ FRP 0 (NFAR Request, 9/02)
<br /> 11.Best Available Technology(BAT) used or an explanation for not using BAT; Remove USTs and impacted soil, natural
<br /> a ttenua tion.
<br /> 12.Reasons why background wasrs Minor soil and groundwater contamination remains on-site at the former UST
<br /> unattainable using-BAT,•---- areas and down gradient_of_the.former.UST areas.
<br /> 13.Mass balance calculation of substance Based on soil samples collected in 1989 to 1991, the consultant estimated that
<br /> treated versus that remaining; 759 pounds(123 gallons)of TPHg and approximately 3 pounds of benzene
<br /> remained in site soils.
<br /> ❑ 14.Assumptions,parameters, calculations and model used in risk
<br /> assessments, and fate and transport modeling; A risk assessment was not required.
<br /> Y 15. Rationale why conditions remaining at site will not adversely Soil contaminated with gasoline is limited to the tank pit
<br /> 0 impact water quality, health, or other beneficial uses;and area, and will continue to degrade.
<br /> By: Comments: The site is an active Service Station. One 550-gallon waste oil UST-was removed in June 1987, and four
<br /> MH gasoline US Ts(two 5,000-gallon;one 7,500-gallon;and one 10,000-gallon) were removed and replaced in May 1990.
<br /> Multiple soil borings were completed, and four monitoring wells and two soil vapor wells were installed. The wells have
<br /> Date: been monitored since July 1990, and TPHg and benzene have been non-detect for the last four sampling events in all
<br /> wells. MtBE was identified at a maximum of 32 pg/l, and is currently at a maximum of 1.4 pg/l. The former Exxon Station
<br /> 10/28/02 at 4444 Pershing downgradient of the subject site installed one monitoring well(MW-8)in the sidewalk northeast of the
<br /> subject site in early 1988. TPHg in MW-8 has decreased from 120,000 pg/1 in April 1988 to 215 Ng/l in March 2002, and
<br /> benzene has decreased from a maximum of 1,100 pg/1 in February 1993 to 0.60 pg/1 in March 2002. MTBE is non-defect
<br /> in MW-8 at appropriate detection limits. Based on the decreasing groundwater contamination in on and off-site monitoring
<br /> wells, Board staff concur with San Joaquin County's Closure Recommendation.
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