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CLEAkRATER Environmental 5ert 1crs In late summer 1998, the SVE/AS remediation system was installed at the site Wells RW-1, MW-1, MW-2 and VW-1 through VW-4 were used to extract soil vapors, which were treated by an electric catalytic oxidizer An air blower was used to deliver air to the subsurface via wells SW-1 and SW-2 The system was operational from October 1998 to the end of September 1999, which resulted in 6,638 hours of total system operation Contaminant recovery from the subsurface was dramatic at first, averaging approximately 2 lbs/hr during the first five months of operation However, by July 1999, contaminant recovery rates had decreased to approximately 0 02 lbs/hr For the last three months of operation, influent TPHg levels only slightly exceeded laboratory detection limits Calculations indicated the SVE/AS system recovered approximately 7,377 lbs (or 1,209 gals) of gasoline from the subsurface by the end of September 1999 The amount of contamination recovered from the subsurface compared well to that calculated to be in the subsurface prior to remediation, although slightly higher, indicating that the system had removed the vast majority of contaminants beneath the site Remediation efforts were also reflected by a marked decrease, over two orders of magnitude, in groundwater contaminants in the source area Prior to remediation, maximum concentrations of TPHg, benzene, and MTBE in groundwater had been 150,000 gg/L, 9,400 gg/L, and 3,800 gg/L, respectively Following shut-down of the remediation system, maximum TPHg, benzene, and MTBE concentrations in groundwater were only 990 gig/L, 13 gg/L, and 150 gg/L, respectively, in November 1999 Clearwater recommended shut-down of the SVE/AS system at the end of September 1999 because ® operational data indicated that it had reached a plateau contaminant recovery The SJCPHS/EHD approved system shut-down in a letter dated September 20, 1999 In that letter, the SJCPHS/EHD indicated that groundwater beneath the site should continue to be monitored for several quarters to evaluate post-remediation trends in residual groundwater contaminants and that confirmation soil borings would be required in the future to demonstrate remediation of the vadose zone The mobile catalytic oxidizer was removed from the site in October 1999 However, all vapor extraction piping remains in the ground, and the above ground manifold was secured (Figure 2) Groundwater Monitoring Methods On May 8, 2000, wells MW-1 through MW-7 were gauged for depth to water An electronic water level indicator was used to gauge depth to water accurate to within ±0 01-feet The wells were checked for the presence of SPH prior to purging No measurable thicknesses of SPH were observed in any of the wells Following gauging, wells MW-1 and MW-2 were purged for sampling The wells were purged until sampling parameters (e g temperature, pH and conductivity) stabilized, which occurred by approximately three wet casing volumes Groundwater monitoring and well purging information was recorded on Gauge Data/Purge Calculations and Purge Data sheets (attached) ZB107C GWMR 2QOO 2 MayN 2000