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i` TAC 1 - CHECKLIST OF REQUIRED PTA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES
<br /> Site Name and Location: City of Escalon/Former ARCO station, 1305 Escalon Ave., Escalon, San Joaquin County
<br /> IA welf'surve in 2000 shows two public water supply
<br /> Y I. Distance to production wells for municipal, domestic, agriculture, 'a
<br /> industry and other uses within 2000 feet of the site;
<br /> wells re located approximately 1600 feet north and
<br /> 1800 feet southwest of the site. One irrigation well is
<br /> located approximately 750 feetto the northeast.
<br /> 0 2. Site maps, to scale, of area impacted showing locations of former and existing tank One 8,000-gallon and two
<br /> systems, excavation contours and sample locations, boring and monitoring well 10,000-gallon gasoline USTs were
<br /> elevation contours, gradients, and nearby surface wafers, buildings, streets,'and
<br /> removed,in 9198.
<br /> subsurface utilities;
<br /> s Y 3. Figures depicting , Site lithology consists of sand, silt and clay to
<br /> 0 g g lifholo gy(cross section treatment diagrams;) y !1115 feet, the total depth investigated.
<br /> 0 4. Stockpiled so!l disposed off-site (quantity); The fate of approximately 100 cubic yards of contaminated excavated
<br /> soil was not reported.
<br /> 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 property destroyed.
<br /> Y 0 6. Tabulated results of all groundwater elevations and depths to wafer,' 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 /> 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 /> Y® benzene;220 mg/kg, toluene; 140 mg/kg, ethylbenzene; 730 mg/kg,Detection limits for confirmation sampling xylenes,and 8 mg/kg;•MISE. After Soil Vapor Extraction (SVE)in 9103,
<br /> Lead analyses soil results were 3,130 mg/kg, TPHg; 1.9 mg/kg, toluene;30.4 mg/kg,
<br /> i ethylbenzene;and 194 mg/kg,xylenes. Groundwater monitoring
<br /> results on 4/00 were 516 pg/L, TPHg; 62 Fig/L, benzene,42 pg/L,
<br /> toluene; 10 pg/L, ethylbenzene;57 Ng/L,xylenes;and 220 pg/L, MtBE.
<br /> In 5105, groundwater monitoring results were all ND.
<br /> YD 8. Concentration contours of contaminants found and those remaining in soil '
<br /> nad groundwater, both on--s&and off-site: The extent of contamination is defined by
<br /> Y Y
<br /> Lateral and Vertical extent of soil contamination i. on-site soil borings and monitoring wells.
<br /> Y Lateral and Vertical extent of groundwater contamination
<br /> 9. zone of influence calculated and assumptions used for subsurface j
<br /> remediation system and the zone of capture attained for the soil and SVE, the engineered remediation system,
<br /> groundwater remediation system; i[ removed approximately 1,013 gallons of
<br /> gasoline from soil at this site.
<br /> 'I 10.Reports/information Y❑ Unauthorized Release Form QMRs 22 QMRs from 4/00 to 5/05.
<br /> Boring lags El PAR FRP Y❑ Other EF Site Closure Report
<br /> It 11.Best Available_Technology_(BAT) used Dian explanation for not using 6A'T_ Remove U5Ts, SVE and natural attenuation.
<br /> .. . _ r +.. _. - —_
<br /> Q12.Reasons why background walls '4
<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 /> Y� 15. Rationale why conditions remaining at site will not adversely Although minor soil contamination is present onsite,
<br /> impact water qualify, health, or other beneficial uses. based on 22 groundwater sampling events,petroleum
<br /> hydrocarbons are not continuing to leach to
<br /> i
<br /> groundwater.
<br /> By: Comments: One 8,000-gallon and two 10,000-gallon gasoline US Ts;were removed from the subject site in 9/98.
<br /> JLB Confirmation soil results in 11/98 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, MfBE. After Soil Vapor Extraction (SVE)in 9/03, 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 lig/L, TPHg; 62 ug1L, benzene;42 pg/L, toluene; 10 pg/L, ethylbenzene; 57 pg/L, xylenes;and
<br /> 7/27105 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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