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6 SUMMARY OF FINDINGS The air sparging and soil venting remediation system, in operation from April 25, 2001 to December 2002, has reached a level where its effectiveness in removing additional contaminants from the subsurface is currently limited PSC requests that the EHD review current conditions and consider granting case closure for this UST site A summary of site activities and conditions are as follows • A gasoline release occurred at the facility, apparently from one of two 6,000- gallon USTs that were removed in April 1987 • The facility is a bakery products plant located in an area that is primarily industrial/commercial and agricultural in nature The closest private residences are at least 1,000 feet away from the former gasoline UST • The closest surface water body is the intermittent Duck Creek, situated about 900 feet south (in a hydraulically upgradient location) of the facility ' 0 Subsurface lithology at the site comprises primarily silt and clay with some interbedded fine-grained sand ' • Recent depths to groundwater average about 40 feet Groundwater flows east- northeasterly at a gradient of about 2 2 x 10-3 feet per linear foot Hydraulic conductivities measured within the groundwater zone range from 1 04 x 10-5 cm/s to 4 15 x 10-6 cm/s There are no potable or commercial wells located at the Earthgrain's facility, nor are there any plans for one in the future One irrigation water well has been identified from DWR records, situated about 400 feet south (in a hydraulically cross-gradient location) from the former UST This irrigation well is surface- cased and completed at a depth below the vertical extent of groundwater impact delineated at the facility One domestic water well, identified from EHD records, no longer exists • PSC initiated operation of an air spargmg and soil venting remediation system at the facility on April 25, 2001 Soil vapor analytical data suggests that a total of over 1,000 pounds of contaminants have been removed The system was disengaged in December 2002 to evaluate whether petroleum concentrations in groundwater would remain stable • Data suggests that overexcavation performed in 1987 removed most of the impacted soil in the vicinity of the gasoline USTs It is PSC's opinion that residual petroleum hydrocarbon impact in soil is relatively limited ' • Data indicates that the lateral extent of petroleum impacted groundwater is 2 confined within the facility's property boundaries The vertical extent of ,¢S groundwater impact is less than 60 feet Tor+gut Gil 10,.E -A"CA G� rn�I 01 20 } s b-.N Remedial Action Completion Report The Earthgrains Company Facility 0jm W f 1 Yl• LFh 1 jf 2651 South Airport Way Stockton Cahfomia Prepared for THE EARriiGRAINS COMPANY Prepared by Philip Services Corp HTNV\624001321121382EGNStockionNSt ckton�RemedialCompleLionRepo,ido April 14 2003