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i TAi."_E 1 - CHECKLIST OF REQUIRED IA
<br /> FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SiTES
<br /> Location: M 8 K Market, 8960 W.Walnut Grove Rd.,Thornton, San Joaquin County
<br /> Site Name and t
<br /> A sensitive receptor survey conducted in 2001 reported
<br /> Eli. Distance to production wells for municipal, domestic, agriculture, seventeen private wells located within 2000, which include
<br /> industry and other uses within 2000 feet of the site; 1 crossgradient, NW(280 ft) and 1 upgradient, E(520)of
<br /> the site. No wells are located within 2000'downgradient.
<br /> g locations of former and existing tank
<br /> Two 10,000-gallon unleaded
<br /> 0 2. Site maps, to scale, of area impacted showingasoline and one 10,000-gallon
<br /> systems,excavation contours and sample locations, boring and monitoring well elevation iesel USTs were removed in
<br /> contours, gradients,and nearby surface waters, buildings, streets, and subsurface utilities; 1199
<br /> I Site lithofogy consists of sand,silt and clay,.
<br /> 0 3. Figures depicting lithology(cross section), treatment system diagrams; The Iotal depth investigated was 20 feet.
<br /> :F Over 3,000 cubic yards of soil was excavated, aerated and spread onsite.
<br /> 0 4. Stockpiled soil disposed off-site (quantity);
<br /> Y 5. Monitoring wells remaining on-site, fate; Seven monitoring wells,installed for this investigation, will be properly
<br /> abandoned.
<br /> The depth to water varied from 5 to 9 feet. The
<br /> - MY 6. Tabulated results of ali groundwater elevations and depths to�wat�erg _.groundwater flaw direction-.s-to-the-west-��.
<br /> . - � � ,�
<br /> Maximum soil boring results in 1999 reported TPHg(1,800 mg/kg),
<br /> �Y 7.Tabulated results of all sampling and analyses: TPHd(1,100 mg/kg),benzene(2.4 mg/kg),and MtBE(4.5 mg/kg). In
<br /> Y Detection limits for confirmation sampling 2001, confirmation soil analyses reported ND for all constituents.
<br /> ®Lead analyses Groundwater maximum grab sample from 3101 reported TPHg
<br /> (320,000 pg/L), TPHd(46,000 lig/L),benzene(1,900 Pg/L), and MtBE
<br /> (3,500 pg/L). In 1104,all groundwater analysis reported ND except
<br /> MtBE(88 Ng/L).
<br /> 8. Concentration contours of contaminants found and those remaining in soil The extent of contamination r defined by
<br /> soil borings and groundwater monitoring
<br /> -aad groundwater, both on ' and off-site: wells.
<br /> Y Lateral and Y Vertical extent of soil contamination
<br /> Lateral and. Vertical extent of groundwater contamination
<br /> Based on the limited extent of groundwater
<br /> 0 9. Zone of influence calculated and assumptions used for subsurface contamination and soil overexcavation, an
<br /> remediation system and the zone of capture attained for the soil and engineered remediation system was not
<br /> groundwater remediation system; required at this site.
<br /> 10.Reports/information Unauthorized Release Form [9 QMRs, 5/01 to 1104
<br /> PAR 0 FRP � Other (Risk Assessments/Conceptual Site Models))
<br /> Boring logs
<br /> ED11.Best Available Technology(BA T) used or an explanation for not using BAT, Remove UST, overexcavation,and natural
<br /> attenuation.
<br /> Y 12.Reasons why background was/is Minor groundwater contamination remains on-site.
<br /> unattainable using BAT;
<br /> 13.Mass balance calculation of substance Mass balance was not estimated for this site.
<br /> treated versus that remaining;
<br /> 14.Assumptions,parameters, calculations and model used in risk A risk assessment was not required.
<br /> assessments, and fate and transport modeling;and
<br /> 15. Rationale why conditions remaining at site will not adversely Soil contamination is limited in extent,and based on
<br /> t water quality, health, or other beneficial uses, twelve quarterly sampling events, contamination is not
<br /> impact r continuing to leach to groundwater. Groundwater
<br /> L
<br /> monitoring shows a decreas 141 trend in concentrations.
<br /> P
<br /> omments: Two 10,000-gallon unleaded gasoline,and one 10,000-gallon diesel USTs were removed from the subject
<br /> ite in 1/99. Over 3,000 cubic yards of soil were excavated, treated onsite, and spread onsite. Multiple borings were
<br /> ompleted from 1999 to 2002, to delineate contamination at this site. Maximum soil boring results in 1999 reported TPHg
<br /> 1,800 mg/kg), TRHd(1,100 mg/kg), benzene(2.4 mg/kg), and MISE(4.5 mg/kg). !n 2001, confirmation soil analyses
<br /> eported ND for all constituents. Groundwater maximum grab sample from 3/01 reported TPHg(320,000 ug/L), TPHd
<br /> (46,000 pg/L),benzene(1,900 pg/L),and MtBE(3,500 pg/L). in 1104, all groundwater analysis reported ND except MtBE
<br /> 3/1/04 (88 pg/L). Based,on the limited extent of soil and groundwater contamination and twelve quarters of groundwater
<br /> analysis, which show a decreasing trend in concentrations, Board staff concur with San Joaquin County's Closure
<br /> Recommendation.
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