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'"TABLE 1 -CHECKLIST OFREQUIRED DATA'
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: TOSCONNOCAL#5447; 1700 E.Yosemite Avenue, Manteca, San Joaquin County
<br /> Y 1. Distance to production wells for municipal, domestic, agriculture,in dustry one documented municipal well is located
<br /> and other uses within 2000 feet of the site; approximately 1,500 downgradient of the site.
<br /> The well is screened from 90 to 150'bgs.
<br /> 0 2. Site maps, to scale, of area impacted showing locations of former 6 nd existing tank systems, This case involves
<br /> contamination detected i
<br /> excavation contours and sample locations,boring and monitoring wel elevation contours, sail
<br /> the
<br /> gradients, and nearby surface waters, buildings, streets, and subsurface utilities; and groundwater during t
<br /> removal of the dispenser island
<br /> ❑ andr rn
<br /> Y 3. Figures depicting lithology(cross section), treatment system diagrams, No treatment system was used. The area
<br /> beneath the dispensers was overexcavated.
<br /> 0 4. Stockpiled soil remaining on-site or off--site disposal(quantity); proximately 150 yds'of soil was removed and hauled off-site.
<br /> i
<br /> �Y Three monitoring wells a e installed at the site. San Joaquin County has proposed !
<br /> 5. Monitoring wells remaining on-site, fate; decommissioning these Wells pending the Regional Board's concurrence with the
<br /> closure recommendation.
<br />. .t 6. Tabulated results,of all groundwater elevations-and deptlhs_to�watA Groundwater elevations vary from 12 to 15',with a NNE -
<br /> Soil sample from beneath the dispensers showed TP14g as high as
<br /> 7. Tabulated results of all sampling and analyses: 15,000 mg/kg and elevated levels of BTEX. The area was overexcavated to
<br /> Detection limits for confirmation sampling -5'bgs,reducing TPHg to 12,000 mg/kg and BTEX to low concentrations.in
<br /> N(1 Lead analyses 1998, 10 soil bori gs and three wells(MW-1,2,3)were installed. Minor
<br /> t� contamination was found in soil,and MtBE at 0.002 mg/l, TPHg at 2.1 mg1l,and
<br /> low levels of SEX were found in samples from MW-2.No contaminants were
<br /> detected in MW-1 and 3. To date,only TPHG at 0,5 mgll was found in MW-2. J
<br /> 8..Concentration contours of contaminants found and those remaining,in soil No system was installed to define vertical extent
<br /> L and groundwater, and both on-site and off-site: of groundwater contamination.
<br /> Lateral and 0 Vertical extent of.soil contamination
<br /> Lateral and 0 Vertical extent of groundwater contamination
<br /> i
<br /> 9. Zone of influence calculated and assumptions used for subsurface No subsurface remediation system was used at
<br /> remediation system and the zone of capture attained for the soil and this site. The area under the former fuel
<br /> groundwater remediation system; dispensers was overexcavated.
<br /> 0 Y t
<br /> 10.Reports/informationF Unauthorized Release Form Y❑ Q Rs(Dates) 7/98-2199
<br /> y❑ Well and boring logs [flPAR. FRP fl Ott er(report name)July 13, 1999 Request for Closure
<br /> Y 11.Best Available Technology(BAT) used or an explanation far not us ng BAT,• Contaminated soil was excavated from the site.
<br /> 12.Reasons why background wasrs unattainable using BAT; Ov rexcavation was limited due to existing dispenser island
<br /> canopy supports.
<br /> 0 13.Mass balance calculation of substance treated versus that remainir g; The mass of TPHg initially present at the site was `
<br /> estimated at 253 kg. The estimated mass of TPHg
<br /> remaining is 79.2 kg.
<br /> 14.Assumptions,parameters, calculations and model used in risk No risk assessments or modeling conducted at this site,
<br /> assessments, and fate and transport modeling;
<br /> 15.Rationale why conditions remaining at site will not adversely Law concentrations of TPHg, TEX,and MtBE only have been
<br /> impact wafer quality, health, or other beneficial uses;and
<br /> detected in one well(MW-2)since July 1998. Benzene and MISE
<br /> have not been detected in 1999.
<br /> NA 16.WET or TCLP results
<br /> Comments: In January 1998,the fuel dispensers and associated piping were removed and replaced with upgraded equipment.
<br /> Elevated levels of TPHg,BTEX,and MtBE were detected undem ath the dispenser island. The area was overexcavated,reducing
<br /> D8 i contaminant concentrations. In July 1998, to Geoprobes®and three monitoring wells were installed at the site. TPHg at
<br /> j 3,800 pglkg, sxylenes at 8.7 pglkg,and MtBE at 8.1 pgkg were the only contaminants found in soil. Groundwater monitoring began
<br /> yin 1998. During this time, TPHg at 2,100 pg/l,benzene of 0.51p ,ethyl benzene at 4.0 pg 1,xylenes at 6.5 ugA, and MtBE at I
<br /> 1.6 vgll were detected in well MW-2. During the February 1999 monitoring event, TPHg at 500 ug/1 was the only contaminant found
<br /> in MW-2. No constituents,including MtBE were detected the other wells during this event. Based on the information provided and
<br /> the declining hydrocarbon concentrations in the plume,staff concurs with San Joaquin County's closure recommendation.
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