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Quik Stop No 121 Closure Report • CCI Project No 12118 Page 12 6. SELECTED REMEDIATION SYSTEM After consultation with Quik Stop, CCI proposed to install the KVA C-Sparger® System (System) ozone generator to remediate the groundwater at the site Due to the relatively flat gradient and localized area of the groundwater compounds at the Quik Stop site, this remediation technique appeared to be appropriate for the subject site due to relatively low system costs, and because the system uses ozone to destroy organic chemicals through the process of chemical oxidation, which breaks the targeted chemical (predominantly MTBE and its daughter products) into carbon dioxide and water The generalized degradation chain is as follows MTBE > tert-Butyl-Formate> tert-Butyl Alcohol > Acetone> Formaldehyde> carbon dioxide The chemical oxidation process takes place in-situ, and no groundwater extraction takes place at the subject site C-Sparge Installation& Operation In late June 2002, CCI installed a 10 sparge well System at the site CCI estimated that 10 sparge wells would be needed to effectively cover the aquifer at the subject site (Tab 1, Figures 5 & 6) The 10 sparge wells were based on an estimated subsurface permeability of 10 1 to 10 centimeters per second (cm/sec) and a 50-foot diameter radius of influence Eight of the sparge wells were installed to a depth of approximately 28 feet (approximately 10 feet into the water table), and two sparge wells were installed to a depth of 40 feet, near monitoring wells MW-4 and MW-3 The purpose of the two deeper sparge wells was to treat groundwater in the lower A-aquifer, which was found to be impacted with MTBE at that time The 10 sparge wells were connected to the master control, via 3-inch diameter PVC conduit placed inside a trench Three eighths-inch, high density polyethylene (HDPE)tubing was then pulled through the trench conduit and hooked to the master control panel, which was located on the south side of the Quik Stop Market The System began operation on July 2, 2002 After 6 months of operation, the contaminant concentrations in the vicinity of the highest groundwater contamination(MW-3 and RW-1) had dropped The MTBE concentration in well MW-3 had dropped by 98 percent, from 130,000 ug/L in July 2002 to 2,600 ug/L in January 2003 MTBE concentrations in well RW-1 also showed a significant decrease of 86 percent, from 150,000 ug/L zn July 2002 to 21,000 ug/L in January 2003 Graphs of contaminant concentrations over time for wells MW-1, MW-2, MW-3, MW-4, MW-5 and RW-1 are in Tab 2. By January 2005, groundwater samples collected from site wells were all free of detectable petroleum hydrocarbons The System operated a total of 9,569 hours, until May 13, 2005, at which time the System was shut-down at the County's request •