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Sent- By: RWOCB; 2553439; Dec-28-40 5:25PM; Page 2;3 California Regional Water Quality Control Board Central Valley Region Steven T.Butler,Chair Gray Davis Winston H.Hiekux rovernar Seeretaryfar Sacramento Main Office 8nvironmenhd Internet Address: http://www.swreben ppv/mgeh5 Protection 3443 Routier Road,Suite A,Sac,to,California 95527-3003 Phone(916)255.30W-FAX(916)255.3015 draft Durhim Ali Jubari Nasi Saleh-Ali Mohamed&Huda Gubary 667 O'Farrell Street#10 PO Box 1322 25 Poncetta Drive#201 San Francisco,CA 94109 Riverbank,CA 95367 Daly City,CA 94015 PROBI-F.M ASSESSAfENT REPORT AEVIFW RANCH MARKET,23569 SOUTH SANTA FE ROAD, RIVERBANK,SAN JOAQ UINCOUNTY I reviewed your 8 November 2000 problem Assessment Report(PAR) and 18 December 2000 Addendum to the Problem Assessment Report(PAR Addendum)submitted by Secor Tntemational Incorporated(Secor)for the subject site. The PAR presents the extent of soil and groundwater contamination at the site,the results of the soil vapor extraction(SVF,) and air sparge(AS)testing,and an evaluation of remediation alternatives. The Addendum presents cost estimates for remediation alternatives evaluated. Soil contamination has been defined to a maximum depth of 60 feet below the former underground storage tanks (USTs),and laterally from the Ranch Market property south across part of the adjacent property at 23565 South Santa Fe Road. The extent of groundwater contamination has been defined in the shallow water-bearing zone; however,low concentrations of benzene and MtBE were identified in the one deep monitoring well(Mw-5D). Additional deep monitoring wells may be required based on future groundwater monitoring results. Secor installed six SVE wells and one AS well at the site in September 2000, and conducted a SVE/AS test in October 2000- Results indicate a 40-foot radius of influence for the SVE test, and a 30-foot radius of influence for the AS test. Influent air samples show TPHg concentrations ranged from 1,500 to 8,200 parts per million by volume(ppmv),and an estimated 102 pounds (17 gallons)of TPHg was removed during the two-day testing. During the five hour SVE/AS test, six SVE wells operated at a combined flow rate of 154 standard cubic feet per minute(sefm),and purge air was injected into the AS well at 6 scfm. As presented in the PAR Addendum,Sccor reports that air sparging may have resulted in lateral transport of dissolved constituents to the perimeter groundwater monitoring wells, as shown in forth quarter monitoring results,and that future air sparging rates must he very low to avoid lateral transport of dissolved constituents. Secor evaluated the following remedial altematives in the PAR and PAR Addendum: • Soil excavation; • Passive biodegradation; • 1n-situ biologic/chemical treatment; • Dual phase extraction and treatment; • SVE combined with groundwater extraction and treatment; • SVE combined with AS; and • SVE combined with Ozone sparging- California Environmental Protection Agency 04 RecyNed Ynper