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<br /> TA T - CHECKLIST OF REQUIREDTA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: Lathrop Gas and Food Mart, 14800 B. Hwy 99, Manteca, San Joaquin County (Lustis#391147)
<br /> y 1. Distance to production wells for municipal, domestic, agriculture, industry A well survey in 2005 showed Cone
<br /> and other uses within 2000 feet of the site; domestic well 100 feet east(cross-gradient)
<br /> of the site and one domestic well 200 feet
<br /> south ugradient) of the site.
<br /> Y 2. Site maps, to scale of area impacted showing locations of any former and existing tanks stems Dispenser piping was
<br /> excavation contours and sample locations boring and monitoring well elevation contours removed in 1/03 during
<br /> .gradients, and nearby surface waters buildings, streets and subsurface utilities an u rade.
<br /> Y 13. Figures depicting litholo cross section), treatments stem diagrams' Site lithology consists of sand, silt, and
<br /> clay to 40 feet, the total depth
<br /> investigated.
<br /> N 4. Stockpiled soil remaining on-site or off-site disposal(quantity); Excavated soil(unknown quantity) was disposed at i
<br /> Forward Landfill in Manteca.
<br /> N 5. Monitoring wells remaining on-site, fate; No monitoring wells were installed for this case#2. Case#1 wells were
<br /> abandoned at closure in 1998.
<br /> 6. Tabulated results of all groundwater elevations and depths,to water; Prior to 1998, depth to groundwater varied from 15
<br /> - — -to-.25-feat below ground surface fts).--Historically-
<br /> the groundwater downgradient flow direction was
<br /> towards the north.
<br /> 7. Tabulated results of all sampling and analyses: In 1/03, maximum confirmation soil concentrations were: TPHg,
<br /> 6,100 mg/kg; TPHd, 8,500 mg/kg;ethylbenzene, 11 mg/kg;and
<br /> El Detection limits for confirmation sampling xylenes, 137 mg/kg. In 8/04,maximum soil concentrations were:
<br /> Lead analyses TPHg, 250 mg/kg; TPHd, 190 mg/kg;Xylenes, 0.51 mg/kg; TBA,
<br /> 0.16 mg/kg;and MtBE,0.019 mg/kg. Maximum grab groundwater
<br /> concentrations in 8/04 were: TPHg, 2,100 Erg/L; TPHd, 7,200 Pg/L,
<br /> ethylbenzene; 7.9 Erg/L;xylenes, 63 Erg/L;MTBE, 18 Erg/L;and 1,2-DCA,
<br /> 2.7 /L.
<br /> LyJ 8. Concentration contours of contaminants found and those remaining in soil and The extent of Case#2
<br /> groundwater, and both on-site and off-site., contamination is defined by soil
<br /> borings and grab groundwater
<br /> Y❑ Lateral and 0 Vertical extent of soil contamination samples.
<br /> © Lateral and © Vertical extent of groundwater contamination
<br /> Yi9. Zone of influence calculated and assumptions used for subsurface remediation system Remove piping, overexcavation,
<br /> and the zone of capture attained for the soil and groundwater remediation system; and natural attenuation.
<br /> 10.Reports/information Unauthorized Release Form E QMRs(
<br /> Well and boring logs PAR FRP 0 Other;Site Conceptual Model
<br /> Y 11.Best Available.Technology(BAT)used or an explanation for not using BAT,_ An engineered remediation system was
<br /> not i eguired for this soil-only siteF ` .
<br /> Y 12.Reasons why background wasfis unattainable using BAT,- Limited soil and groundwater contamination remain on-
<br /> site.
<br /> Y 13.Mass balance calculation of substance treated versus that remaining; Consultant estimated 8 gallons of TPHg remain
<br /> in soil from Case 1. In a letter dated 31 March
<br /> 2006, SJCEHD states 2004 grab groundwater
<br /> concentrations are equivalent to 1998 closure
<br /> levels.
<br /> Y 14. Assumptions, parameters, calculations and model used in TPHg exceeds ESLs(gross contamination) for Case 2
<br /> risk assessments, and fate and transport modeling; soil. Fate and transport modeling showed no impacts
<br /> to nearby domestic wells; while well water samples
<br /> analyzed were ND.
<br /> Y 15. Rationale why conditions remaining at site will not adversely Soil contamination is limited in extent. Groundwater
<br /> impact water quality, health, or other beneficial uses;and will attain WQOs before reaching domestic wells
<br /> By. JLB/BK Comments:Dispenser piping was removed from the subject site in 1/03. A soil and grab groundwater investigation
<br /> in 2004 showed soil contamination was limited to the dispenser area, while groundwater concentrations were
<br /> Date: 4/24/06 equivalent to previous site closure levels. Based upon groundwater modeling and analysis showing no impacts to
<br /> sensitive receptors before WQOs are reached, and the limited extent of contamination present in soil under the
<br /> dispensers, Regional Board staff concur with San Joaquin County's Closure Recommendation for Case#2.
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