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1 <br />' 12 December 2006 <br /> • AGE-NC Project No 01-0827 <br />' Page 4 of 14 <br />' SVE wells VW-6 to VW-8 were installed to a depth of 30 feet bsg A soil vapor extraction/in-situ <br /> air sparging system was installed during August and September 2001 The operation of the IAS <br /> system has produced only minor volatilization of the dissolved hydrocarbons in the deep ground <br /> water well samples at the site(VW-2D),and reduced the dissolved hydrocarbon concentration in the <br /> shallow well samples(MW-I and VW-1)as well as the concentrations of hydrocarbons in the SVE <br /> influent samples to below detection levels Soil vapor extraction operation was terminated in May <br />' 2003 Soil vapor extraction operation data and soil vapor extraction samples are summarized in <br /> Tables 2 and 3 <br />' Subsequently, AGE had proposed to augment the IAS system with a low-flow ozone generator in <br /> the Ozone Sparging and Additional Monitoring Well Installation Work Plan dated 07 October 2002 <br /> and Ozone Sparging Work Plan Addendum, dated 28 January 2003 <br />' An ozone air sparging system was installed 01 July 2003 on-site, utilizing the existing IAS system <br /> wells IAS-I through IAS-3 The system had operated continuously since installation Operation of <br />' the ozone infection system had been ongoing since July 2003, resulting in a general downward <br /> concentration trend However, based on the proposed contaminant reduction profile, the use of a <br /> stand alone ozone generator, without using a diffuser, has not meet the reduction goal At the <br /> 10 <br /> direction of the City of Stockton and based on the residual contamination and need to reduce overall <br /> project time (cost)a sparge-diffuser was installed to a depth of approximately 30 feet bsg,the zone <br /> of porous media at the lower portion of the upper aquifer under the former UST area <br /> IAGE had proposed to augment the IAS system with a low-flow ozone generator in Ozone Sparging <br />' and Additional Monitoring Well Installation Work Plan, dated 07 October 2002 An EHD letter <br /> dated 03 January 2003,requested procedures for evaluating the effectiveness of the operation of the <br /> in-situ air sparing(IAS)system with a low-flow,ozone generator Essentially what benchmarks for <br /> I proposed remediation system would be acceptable AGE prepared Ozone Sparging Work Plan <br /> Addendum dated 28 January 2003, outlining the acceptable performance of the ozone sparging <br /> system and the specific modification to the system, including the installation of a micro-diffuser at <br /> Ithe former UST area Ozone sparging was terminated after December 2005 <br /> 3.0. SOIL PROPERTIES-HYDROSTRATIGRAPHY/SITE HYDROGEOLOGIC <br /> CONDITIONS <br />' Based on vertical soil profiles in soil-boring logs acquired during site assessment, the subsurface <br /> stratigraphy consists of a fine-grained,sandy silt and clayey silt,identified generally between surface <br /> grade to a varied depth of 10 feet bsg at the former UST area to a depth of 30 feet bsg at monitoring <br /> well MW-2, located 100 feet east of the former UST area The upper silt is in contact with a silty to <br /> well graded sand, locally with poorly graded gravel cut and fills Generally,the sand was identified <br /> Advanced GeoEnvironmental,Inc <br /> I <br />