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1 <br />' Historical Background & Site Conceptual Model <br /> g P <br />' AGE-NC Project No 01-0827 <br /> Page 3 of 9 <br /> tests,the 1994 Final Remediation Plan included justification for the use of ground water extraction <br /> and soil vapor extraction for site remediation <br />' In November 1998,based on a new November 1998 directive by the EHD,a fourth SVE remediation <br /> feasibility pilot study and an in-situ air-sparging(IAS)pilot study were conducted on the site,at well <br />' VW-5d However, the sparge test indicated a defective grout seal in well VW-2, the upper screen <br /> of well VW-2 was later abandoned with grout The SVE pilot test was conducted at vapor well <br /> VW-1 for 1 5 hours <br /> In April 1999, a full scale IAS pilot study was conducted on the site The IAS pilot test was unable <br /> to produce air-flow into the subsurface at monitoring well MW-I and therefore was teri-ninated Also <br />' in April 1999, a fifth SVE rernediation feasibility pilot study was conducted on vapor well VW-1 <br /> for 2 hours <br />' In June 1999, an additional full scale in-situ air-sparging pilot study was conducted on the site <br /> without a positive result and therefore the test was terminated at 80 minutes <br />' In January 2000, a feasibility study including justification for the use of in-situ air sparging and soil <br /> vapor extraction for site remediation was submitted to the EHD Additionally, a second Final <br /> Remediation Plan dated 02 April 2000 was submitted to the EHD Both of the proposals for site <br />' remediation were approved by the EHD <br />' 23 SITE REMEDIATION PROGRESS <br /> The site is presently being remediated by procedures outlined in Design Plans and Specifications For <br />' Soil and Groundwater Remediation, prepared by ATC Associates Inc (ATC) and approved by the <br /> EHD by Ietter dated 03 January 2001 <br />' A soil vapor extraction/in-situ air sparging system was installed during August and September 2001 <br /> The operation of the TAS system has produced only minor volatilization of the dissolved <br />' hydrocarbons in the deep ground water well samples at the site (VW-2d), but has reduced the <br /> dissolved hydrocarbon concentration in the shallow well samples(MW-1 and VW-1) as well as the <br /> concentrations of hydrocarbons in the SVE influent samples to below detection levels <br /> An ozone air sparging system was installed 01 July 2003 on-site, utilizing the existing IAS system <br /> wells IAS-1 through IAS-3 The system has operated continuously since installation (July 2003), <br /> resulting in a general downward concentration trend However,based on the proposed contaminant <br /> reduction profile,the use of a stand alone ozone generator,without using a diffuser,has not met the <br /> reduction goal At the direction of the City of Stockton and based on the residual contamination and <br /> Advanced GeoEnvironmental,Inc <br />