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CLEARWATER <br />' C K 0 L I' I 1 ( <br /> En,r nmrntui Ser e, <br /> Following further discussion with the SJCPHS/EHD, Clearwater submitted a Revised Remedial Action <br /> Plan dated November 12, 1996, which recommended remediation by only soil vapor extraction and air <br /> sparging The SJCPHS/EHD approved this plan in a letter dated November 6, 1996 <br /> In late summer 1998, the SVE/AS remediation system was installed at the site Wells RW-1, MW-1, <br />' MW-2 and VW-1 through VW-4 were used to extract soil vapors, which were treated by an electric <br /> catalytic oxidizer An air blower was used to deliver air to the subsurface via wells SW-1 and SW-2 <br /> The system was operational from October 1998 to the end of September 1999, which resulted in 6,638 <br /> hours of total system operation Contaminant recovery from the subsurface was dramatic at first, <br /> averaging approximately 2 lbs/hr during the first five months of operation However, by July 1999, <br /> contaminant recovery rates had decreased to approximately 0 02 lbs/hr For the last three months of <br /> operation, influent TPHg levels only slightly exceeded laboratory detection limits Calculations <br /> indicated the SVE/AS system recovered approximately 7,377 lbs (or 1,209 gals) of gasoline from the <br /> subsurface by the end of September 1999 The amount of contamination recovered from the subsurface <br /> compared well to that calculated to be in the subsurface prior to remediation, although slightly higher, <br /> indicating that the system had removed the vast majority of contaminants beneath the site <br /> Remediation efforts were also reflected by a marked decrease, over two orders of magnitude, in <br /> groundwater contaminants in the source area Prior to remediation, maximum concentrations of <br /> TPHg, benzene, and MTBE in groundwater had been 150,000 pg/L, 9,400 lig/L and 3,800 gig/L, <br /> lie respectively Following shut-down of the remediation system, maximum TPHg, benzene, and MTBE <br /> concentrations in groundwater were only 990 pg/L, 13 lig/L, and 150 pg/L, respectively, in November <br /> 1999 Clearwater recommended shut-down of the SVE/AS system at the end of September 1999 because <br /> operational data indicated that it had reached a plateau contaminant recovery The SJCPHS/EHD <br /> approved system shut-down in a letter dated September 20, 1999 In that letter, the SJCPHS/EHD <br /> indicated that groundwater beneath the site should continue to be monitored for several quarters to <br /> evaluate post-remediation trends in residual groundwater contaminants and that confirmation soil <br /> borings would be required in the future to demonstrate remediation of the vadose zone <br /> The mobile catalytic oxidizer was removed from the site in October 1999 However, all vapor extraction <br /> piping remains in the ground, and the above ground manifold was secured (Figure 2) <br /> Purpose of Confirmation Soil Borings <br /> The purpose of the final confirmation soil boiings, presented herein, was to evaluate the lateral and <br /> vertical extent of residual soil contamination present following site remedial activities The soil <br /> borings were advanced in locations where contamination had been previously observed or <br /> documented, enabling a comparison of pre- and post-remediation contaminant levels The extent of <br /> both soil and groundwater contamipation had been effectively delineated, however, it was necessary to <br /> examine post-remediation contaminant levels following the cessation of operation and removal of the <br /> . SVE/AS system <br /> l ZB107C Conf Bonngs/GWMR 1Q00 2 March 27 2000 <br />