SITE INFORMATION AND CORRESPONDENCE

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TABLE 1 - CHECKLIST OF REQUIRED TA FOR NO FURTHER ACTION REQUESTS AT UNDERGROUND TANK SITES Site Name and Location: Lopez Property,25500 Nowell Road,Thornton,San Joaquin County 1. Distance to production wells for municipal, domestic, agriculture, well survey completed by Tri-Valley Growers(TVG). industry and other uses within 2000 feet of the site; Seven irrigation wells are located within.1,400 feet of the former UST area. Five wells are owned by TVG. 2. Site maps, to scale, of area impacted showing locations of fanner and existing tank systems, One 500-gallon gasoline Y UST was removed in excavation contours and sample locations, boring and monitoring well elevation contours, October 1989. gradients, and nearby surface wafers, buildings, streets, and subsurface utilities; 3. Figures depicting lithology(cross section), treatment system diagrams; Borehole lithology and cross section figures show predominantly silt, clay,and sand. 4. Stockpiled soil remaining on-site or off-site disposal(quantity); No information was provided regarding excavated soils. 5. Monitoring wells remaining on-site, fate; Three monitoring wells currently exist on-site. The monitoring wells and the on-site irrigation well(Lopez well)will be destroyed pending site closure. 1 f. 6. Tabulated results of all groundwater elevations and depths to water;4.Depth to water-varies from 4.5_to 12.5,bgs,and flow varies from southwest to northwest. 0 7.Tabulated results of all sampling and analyses: July 1997 groundwater results in Ng/l show ND for all constituents (TPHg at<50,MtBE<5.0, all BTEX compounds at<0.5). MtBE has not ©Detection limits for confirmation sampling been identified at this site. The Lopez irrigation well was sampled in Lead analyses July 1999 by TVG,and was ND for all constituents. 8. Concentration contours of contaminants found and those remaining in soil Lateral extent of soil contamination 0 and groundwater, and both on-site and off-site: defined. Vertical extent of soil to 33 feet, Lateral andY❑ Vertical extent of soil contamination and groundwater to 20 feet. TVG ❑ Lateral and Vertical extent of groundwater contamination completed a deep well south-of the site, ❑ y N and was ND in July 1999. F9. Zone of influence calculated and assumptions used for subsurface A remediation system was not operated at remediation system and the zone of capture attained for the soil and this site. groundwater remediation system; 10.Reports/information El Unauthorized Release Form QMRs(2/96 to 7197) Welland boring logs N❑PAR N❑ FRP Other(Request for No Further Action, 11/98) 0 11.Best Available Technology(BAT)used or an explanation for not using BAT, Remove UST and contaminated soils, monitored natural attenuation. 12.Reasons why background wasps 0 unattainable using BAT, Low concentrations of TPHg and BTEX exist in site soils and groundwater. 13.Mass balance calculation of substance An estimated 267 cubic yards of impacted soils remain above the water table, treated versus that remaining; and 911 cubic yards remain below the water table. Consultant estimates less than one pound of TPHg remains in groundwater. 14.Assumptions,parameters, calculations and model used in risk assessments, and fate and transport modeling; A risk assessment was not completed. 15. Rationale why conditions remaining at site will not adversely Groundwater monitoring has demonstrated that the impact wafer quality, health, or other beneficial uses;and groundwater plume is stable. Remaining contamination will naturally degrade. NA 16.WET or TCLP results By: • Comments: Tri-Valley Growers(TVG), 26200 Nowell Road, completed a UST investigation 75 feet south of the Lopez site. Supporting data from TVG reports. Low concentrations of TPHg and BTEX remain in on-site soils and groundwater. MtBE and other oxygenates have not been identified at this site. The Lopez irrigation well is Date: approximately 72 feet east of the former UST. This well was sampled in July 1999, and was<DL for petroleum hydrocarbons and fuel oxygenates(TVG data). The remaining irrigation wells are south of the site, and owned by NG. Based on information provided by the County, the Regional Board concurs with the County's closure recommendation.