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.4ABLE 1 -CHECKLIST OF REQUIRED DATE..
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: ARCO#6020,85 Louise Ave., Lathrop,San Joaquin County (Lustis Case 2,43911094
<br /> y 1. Distance to production wells for municipal, domestic, agriculture, A well survey in 2006 reported that no wells exist
<br /> t industry and other uses within 2000 feet of the site. within 2000 feet of the site.
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<br /> f Y 2. Site maps, to scale, of area impacted showing locations of any fom7er A release was defected during piping and
<br /> and existing tank systems, excavation contours and sample locations, dispenser upgrades conducted in 9199. Three
<br /> boring and monitoring well elevation contours, gradients, and nearby 12,000-gallon gasoline USTs are currently active
<br /> surface waters, buildings, streets, and subsurface utilities; at the site.
<br /> Y1 3. Figures depicting lithology(cross section), treatment system diagrams; Site lithology consists of silt and sand to
<br /> E 26 feet, the total depth investigated.
<br />` Y 4. Stockpiled soil remaining on-site or off-site disposal(quantify); . Approximately 50 yards of over-excavated soil was
<br /> removed and transported to TPS Technologies in
<br /> Richmond
<br /> Y 5. Monitoring wells remaining on-site, fate; Three monitoring wells(MW-lthrough MW-3)remaining on-site will be
<br /> propertyabandoned.
<br />--�. "6.Tatiulafed—results of al!groundwater Depth#o grourfdwater Garled from 7 to 12 feet below ground surface
<br /> -71 elevations and depths to water, (bgs). The groundwater gradient varied from 0.0004 to 0.01 fUft,and the
<br /> downgradient direction varied clockwise on a compass rose from West
<br /> f to Southeast.
<br /> 7. Tabulated results of all sampling In 9199, maximum soil concentrations were TPHg, 6,700 mg/kg;toluene;47 mg/kg;
<br /> and analyses: ethylbenzene, 71 mg/kg;xylenes, 710 mg/kg;and MtSE, 1.71 mg/kg. In 5199 after
<br /> over-excavation,maximum soil confirmation concentrations were TPHg,
<br /> Detection limits for confirmation 9,800 mg/kg;toluene,52 mglkg;ethylbenzene, 78 mg/kg;xylenes;950 mg/kg;and
<br /> sampling MtBE, 0.41 mg/kg. Maximum groundwater concentrations were TPHg, 613 ug1L
<br /> (9100);benzene, 14 ug1L(9/02);ethylbenzene,5.5 uglL(9102);xylenes, 25 ug/L
<br /> ❑N Lead analyses (9102);and MtBE;170 pg/L(6101). In 6107, maximum groundwater concentrations
<br /> were di-iso ro 1 ether (DIPS), 5.4 ug/L;and MtBE, 0.69 u /t.
<br /> 8. Concentration contours of contaminants found and those remaining in soil and The extent of contamination is
<br /> groundwater, and both on-site and off-site: adequately defined by soil borings and
<br /> monitoring wells. €
<br /> 0 Lateral and I Vertical extent of soil contamination
<br /> Lateral and Vertical extent of groundwater contamination
<br /> 9. Zone of influence calculated and assumptions used for subsurface remediation An engineered remediation was not k
<br /> system and the zone of capture attained for the soil and groundwater remediation required by the lead agency. f
<br /> s stem; t
<br /> 10.Reports/information QY Unauthorized Release Form FYI QMRs(28 from 6100 to 3107)
<br /> F Well and boring logs PAR FRP Other,,RBCA Analyses and Closure Summary Report
<br /> Y 11.Best Available Technology(BAT) used or an explanation for riot using.BAT, Removal of piping and dispensers,minor_ ,
<br /> -— _ .�- ;,..� :� -__ d r:atural attenuation.
<br /> -- _. , _, -- .: over-excavation an;
<br /> Y 12.Reasons why background wasrs unattainable using BAT; Limited soil contamination and groundwater pollution
<br /> remains on-site.
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<br /> y 13.Mass balance calculation of substance treated versus that An engineered remediation was not required. In 2006, the
<br /> remaining; residual contamination was estimated in soil as TPHg,
<br /> o 39 gallons and MtBE, 0.04 lb.;and as 1.16 lbs of MtBE in
<br /> groundwater.
<br /> Y14. Assumptions, parameters, calculations and model used in Soil ESLs were exceeded for TPHg and xylenes. The
<br /> risk assessments, and fate and transport modeling; Water Quality Goal(WQG)is exceeded for DIPS(0.8 ug/L,
<br /> taste&odor). In 4/07, a RBCA Tier 1 and 2 analyses '
<br /> supported the request for no further action.
<br /> Y 15. Rationale why conditions remaining at site will not adversely Soll contamination is limited in extent and currently not
<br /> impact wafer quality, health, or other benericial uses;and leaching to groundwater. Results of 28 quarters of a
<br /> E groundwater monitoring show a decreasing trend in
<br /> concentrations. WQG should be reached in two years.
<br /> JLB Comments:A release was defected during piping and dispenser upgrades conducted-in 9199. Three 12,000-
<br /> gallon gasoline USTs are currently in use at the site. Site is an active service station.i;Based upon 28
<br /> Dale: quarters of declining groundwater concentrations,results of a Tier 1 and Tier 2 RBCA analyses which
<br /> 8/9/2007 evaluated all pathways,and the limited extent of contamination present in soil and groundwater, Regional
<br /> Board staff concur with San Joaquin County's Closure Recommendation.
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