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TABLE -1 - CHECKLIST OF REQUIRED DA,A
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> V
<br /> ate Name and Location: City of Escalon/Former ARCO station, 1305 Escalon Ave., Escalon,San Joaquin County
<br /> 1.Distance to production wells for municipal, domestic, agriculture, A well survey in 2000 shows two public water supply
<br /> '—' industry and other uses within 2000 feet of the site; wells are located approximately 1600 feet north and
<br /> 1800 feet southwest of the site. One irrigation well is
<br /> located approximately 750 feet to the northeast.
<br /> a2. Site maps, to scale, One 8,000-gallon and two
<br /> of area impacted showing locations of former and existing tank
<br /> systems, excavation contours and sample locations, boring and monitoring well 10,000-gallon gasoline USTs were
<br /> elevation contours,gradients, and nearby surface waters, buildings, streets, and removed in 9/98.
<br /> subsurface utilities;
<br /> te
<br /> FTJ 3.Figures depicting lithology(cross section), treatment system diagrams; 11.5 /ethology consists of sand,silt and clay to
<br /> 115 feet, the total depth investigated.
<br /> 0 4. Stockpiled soil disposed off-site (quantity); The fate of approximately 100 cubic yards of contaminated excavated
<br /> soil was not reported.
<br /> 0 5. Monitoring wells remaining on-site, fate; Six monitoring wells(MW-1 through MW-5,and MW-101),installed for this
<br /> investigation, will be properly destroyed.
<br /> 6. Tabulated results of all groundwater elevations and depths to water, The depth to water varied from 61 feet(2000) to
<br /> 65 feet(2005). The groundwater flow direction
<br /> varied from west to northwest.
<br /> F 7.Tabulated results of all sampling and analyses: Confirmation soil results in 11/98 were 6,200 mg/kg, TPHg;2.64 mg/kg,
<br /> benzene;220 mg/kg, toluene;140 mg/kg, ethylbenzene; 730 mg/kg,
<br /> 8 Detection limits for confirmation sampling xylenes, and 8 mg/kg, MtBE. After Soil Vapor Extraction(SVE)in 9/03,
<br /> N Lead analyses soil results were 3,130 mg/kg, TPHg; 1.9 mg/kg, toluene;30.4 mg/kg,
<br /> ethylbenzene;and 194 mg/kg,xylenes. Groundwater monitoring
<br /> results on 4/00 were 516 Ng/L, TPHg; 62 Ng/L,benzene;42 Ng/L,
<br /> ` toluene;10 pg/L, ethylbenzene;57 pg/L,xylenes;and 220 Ng/L, MtBE.
<br /> In 5/05, groundwater monitoring results were all ND.
<br /> 8. Concentration contours of contaminants found and those remaining in soil
<br /> ... nad groundwater, both on-gite and off-site: The extent of contamination is defined by
<br /> Hateral and Y Vertical extent of soil contamination on-site soil borings and monitoring wells.
<br /> ateral and Y Vertical extent of groundwater contamination
<br /> 9.zone of influence calculated and assumptions used for subsurface
<br /> remediation system and the zone of capture attained for the soil and SVE, the engineereii remediation system,
<br /> groundwater remediation system; removed approximately 1,013 gallons of
<br /> gasoline from soil at this site.
<br /> 10.Reports/information 0 Unauthorized Release Form QMRs 22 QMRs from 4100 to 5/05.
<br /> Q Boring logs rq PAR El FRP 0 Other Site Closure Report
<br /> 0 11.Best Available Technology(BAT)used or an explanation for not using BAT; Remove USTs,SVE and natural attenuation.
<br /> 12.Reasons why background was is
<br /> unattainable using BAT; Groundwater contamination is no longer present Minor soil contamination
<br /> remains on-site.
<br /> Q13.Mass balance calculation of substance
<br /> treated versus that remaining; Approximately 56 gallons of gasoline remain in soil onsite.
<br /> 14.Assumptions,parameters, calculations and model used in risk A limited risk assessment was conducted in the Site
<br /> assessments,and fate and transport modeling;and Closure Report.
<br /> yo15. Rationale why conditions remaining at site will not adversely Although minor soil contamination is present onsite,
<br /> impact water quality, health, or other beneficial uses. based on 22 groundwater sampling events,petroleum
<br /> hydrocarbons are not continuing to leach to
<br /> groundwater.
<br /> By: Comments: One 8,000-gallon and two 10,000-gallon gasoline USTs were removed from the subject site in 9198.
<br /> JLB Confirmation soil results in 11198 were 6,200 mg/kg, TPHg;2.64 mg/kg, benzene;220 mg/kg, toluene; 140 mg/kg,
<br /> ethylbenzene,• 730 mg/kg,xylenes, and 8 mg/kg, MtBE. After Soil Vapor Extraction(SVE)in 9103,soil results were
<br /> Date: 3,130 mg/kg, TPHg; 1.9 mg/kg, toluene;30.4 mg/kg, ethylbenzene;and 194 mg/kg, xylenes. Groundwater monitoring
<br /> results on 4100 were 516 pg1L, TPHg; 62 Ng1L, benzene;42 Ng/L, toluene; 10 pg/L, ethylbenzene;57 Ng/L, xylenes;and
<br /> 7/27/05 220 ug1L, MtBE. In 5105, groundwater monitoring results.were all ND. Based on the low levels of residual soil
<br /> contamination and no petroleum hydrocarbons leaching into groundwater, Regional Board staff concur with San Joaquin
<br /> Countv's Closure Recommendation.
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