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GOLDEN STATE ENVIRONMENTAL <br /> Cultural,Environmental&Litigation Support Services 402 W Broadway,Fourth Floor San Diego,CA 92101 <br /> Certified SBA 8(a)/SDVOSB(DVBE)/WBE/SBE Phore:(619)757-9031/Fax:(888)310-3390 <br /> June 10, 2005RECO_ _E(1fL l <br /> California Regional Water Quality Control Board JUN 9!15 <br /> Central Valley Region <br /> 11020 Sun Center Drive, #200 F1fViRQNMENT HEALI I <br /> Sacramento,CA 95670 PERMIMISERVICES <br /> RE: Review of DISC Memorandum—"Survey Using the Combustible Gas Indicator Meter at <br /> Delta View Apartments on May 25, 2005"and Secor's "Revised Work Plan for Soil Vapor <br /> Assessment and Response to RWQCB Letter Dated May 3, 2005" <br /> Aim:Ms. Depra Lewis <br /> Dear Ms. Lewis: <br /> On behalf of the City of Stockton Redevelopment Agency(RI A), Golden State Environmental <br /> (GSE) is providing the following response to the two reports referenced below. <br /> 1. DISC Memorandum titled"Survey using the Combustible Gas Indicator Meter at Delta <br /> View Apartments on May 25, 2005"dated June 6, 2005 (copy attached);and <br /> 2. Secor's "Revised Work Plan for Soil Vapor assessment and Response to RWQCB Letter <br /> Dated May 3,2005." <br /> This review is specific to the adequacy of the air monitoring to dismiss concerns regarding <br /> explosivity and exposure to residents of the Delta View Apartments (DVA). <br /> On May 25, 2005,DISC monitored for combustible gases in Apartment 193,the easternmost <br /> laundry room,and Apartment 171. GSE was encouraged to read the DTSC's conclusion that <br /> "the measured reading of percent of the LEL did not indicate the presence of combustible gases <br /> (including methane) at locations evaluated." <br /> To further understand the correlation of readings by DTSC with the presence of VOCs in soil <br /> and LNAPL on groundwater, GSE compared the concentrations of TPH reported in the bottom <br /> and sidewalls of the excavation performed by Secor with the probable distribution of LNAPL, <br /> and then with the locations of the DISC readings. Concentrations of TPH in soil at greater than <br /> 500 mg/kg collected during the soil excavation performed by Secor correlate 1 to 1 with the <br /> presence of LNAPL (see hand drawn figure—attached). Comparing this probable distribution of <br /> LNAPL with the locations of Apartment 193 and the laundry room, these two spaces are not <br /> directly above a high soil TPH concentration area and not a probable LNAPL area Therefore, <br /> these two areas would not be indicative of readings in a space that is above soil having a high <br /> 1 <br /> Los Angeles,San Diego and Houston Golden State Envmonmental <br /> File: Review DTTC.1lenro and Seror 2OOi0520 Ilok Plan <br />