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"'--fABLE 1 -CHECKLIST OF REQUIRED DAT
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Ripon Shell Service Station,341 Main St., Ripon,San Joaquin County (Lustis Case#390898)
<br /> Y1 1. Distance to production wells for municipal, domestic, agriculture, industry and other uses There are 7 water wells within
<br /> within 2000 feet of the site; 2,000 feet of the site. The
<br /> nearest well(Caltrans)is
<br /> located 150'from the site.
<br /> Y Site maps, to scale, of area impacted showing locations of any former and existing tank One 10,000-gallon and two
<br /> systems, excavation contours and sample locations, boring and monitoring well elevation 8,000-gallon gasoline UST
<br /> contours, gradients, and nearby surface waters, buildings, streets, and subsurface utilities; were removed 4196.
<br /> Y1 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology consists of silt and sand to
<br /> 76 feet, the total depth investigated.
<br /> Y 4. Stockpiled soil remaining on-site or off-site disposal(quantity); An unspecified volume of soil was removed and was
<br /> transported offsite Closure Report).
<br /> 7Y 5. Monitoring wells remaining on-site, fate; Nine monitoring wells(MW-1 through MW-3, -4A,-4B,-5A, -5B, -6A,-6B)and
<br /> two extraction wells(EW-1 and EW-2)remaining on-site, will be properly
<br /> abandoned.
<br /> 6. Tabulated results of all groundwater Depth to groundwater varied from 25 to 36 feet below ground surface(bgs). The
<br /> elevations and depths to water- groundwater downgradient direction was reported to vary from all directions in
<br /> the shallow zone and in the deep zone 50'-70'b s from Northwest to Southeast.
<br /> 7. Tabulated results of all sampling and In 4196, maximum soil concentrations were: TPHg,4,800 mg/kg;benzene,
<br /> analyses: 68 mg/kg;toluene, 500 mg/kg;ethylbenzene, 140 mg/kg;xylenes, 770 mg/kg,
<br /> Y and MtBE, 250 mg/kg. In 2199 all soil confirmation sample results were ND,�
<br /> Detection limits for confirmation Maximum grab groundwater concentrations in 7198 were:benzene, 13.8 ug/L';
<br /> sampling toluene, 0.9 ug/L;and MtBE, 170,000 ug/L. In 3107,all groundwater monitoring
<br /> concentrations were ND.
<br /> ❑Y Lead analyses
<br /> 8. Concentration contours of contaminants found and those remaining in soil and The extent of contamination is
<br /> roundwater, and both on-site and off-site: adequately defined by soil borings
<br /> Y Lateral and 8 Vertical extent of soil contamination and monitoring wells.
<br /> Lateral and Vertical extent of groundwater contamination
<br /> 9. Zone of influence calculated and assumptions used for subsurface remediation Soil overexcavation to 18 ft bgs,
<br /> system and the zone of capture attained for the soil and groundwater remediation groundwater pump and treat, and
<br /> system; natural attenuation were the
<br /> required remedial actions.
<br /> 10.Reports/information ❑Y Unauthorized Release Form FYI QMRs(25 from 1998—2007)
<br /> 0 Well and boring logs ❑Y PAR � FRP ❑Y Other,•Case Closure Summary, Fate and Transport Model,
<br /> Va or Intrusion Analysis.
<br /> Y 11.Best Available Technology(BAT) used or an explanation for not using BAT; BAT was soil removal to 18 ft bgs,
<br /> groundwater pump and treat,and natural
<br /> attenuation.
<br /> Y 12.Reasons why background was/is unattainable using BAT, Reportedly no soil contamination and groundwaterpollution remain on-site.
<br /> Y1 13.Mass balance calculation of substance treated versus that The consultant did not estimate mass remaining.
<br /> remaining;
<br /> Y 14. Assumptions, parameters, calculations and model used in The latest data show that soil ESLs are not exceeded.
<br /> 7
<br /> risk assessments, and fate and transport modeling; Water Quality Goals are not exceeded.
<br /> I, 15. Rationale why conditions remaining at site will not adversely Soil contamination was limited in extent and residual
<br /> impact water quality, health, or other beneficial uses;and contamination will continue to decline. Results of 25
<br /> quarters of groundwater monitoring show a sustained,
<br /> decreasing trend in concentrations to non-detect.
<br /> By: JLB Comments: One 10,000-gallon and two 8,000-gallon gasoline UST were removed 4/96 from the subject site.
<br /> Remediation consisted of overexcavation of contaminated soil to 18 ft bgs, groundwater pump and treat from 2000-
<br /> Date: 2001, and natural attenuation. The consultant reports that no soil contamination remains on-site. Groundwater
<br /> 7!9!2007 concentrations declined to ND and have not rebounded, indicating that MtBE is not continuing to leach into
<br /> groundwater. Region 2 soil ESLs are not exceeded. Based upon successful completion of active remediation, with
<br /> 25 quarters of declining or non-detect groundwater concentrations, no threats from vapor intrusion, and the lack of
<br /> residual soil contamination, Regional Board staff concur with San Joaquin County's Closure Recommendation.
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