SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Jack Badey -2 - 2 August 2010` • PCE found in a grab groundwater sample at 80 feet bgs upgradient of Unifirst (1 ug/L). • PCE found in soil samples (2,600 ug/kg) at an underground tank excavation two blocks south of the Unifirst facility at the Gene Gabbard site (640 N. EI Dorado Street). • PCE found in shallow groundwater downgradient of this tank excavation (87 ug/L). • Fuel components benzene and ethylbenzene on the south side of the PCE plume in groundwater at 90 feet bgs (240 ug/L and 800 ug/L, respectively). These detections are downgradient of known fuel release sites to the south. Fuel Releases Parisian Industrial Laundry removed several underground fuel tanks in the 1990s, and in 2003 Unifirst discovered another underground tank containing heating oil. Unifirst removed the tank, fuel, and affected soil, and in 2005 installed monitoring wells. On 15 July 2010, Central Valley Water Board staff issued a no further action letter for the fuel portion of the site due to the absence of fuel detections in shallow groundwater. Natural Attenuation The Corrective Action Report gives multiple examples of biological degradation processes that appear to be converting PCE into its elemental components at this site. Degradation intermediaries such as cis- and trans-dichloroethene are common in low concentrations relative to PCE and TCE, and very low concentrations of vinyl chloride are found. These indicators show that insitu biodegradation is occurring and the destruction of TCE appears to be proceeding to complete mineralization without the accumulation of intermediate degradation products. The Corrective Action Plan In the Corrective Action Plan, Unifirst discusses various remediation methods that are used at other sites to remove PCE and TCE from groundwater. It considers enhanced insitu bioremediation, a permeable reactive barrier, air sparging with soil vapor extraction, insitu chemical oxidation, groundwater extraction, treatment, and disposal, and monitored natural attenuation. Of these, monitored natural attenuation was deemed potentially viable, and the other remediation alternatives were deemed infeasible. While Central Valley Water Board staff concur that degradation of PCE and TCE is occurring, the concentrations observed in the core of the plume cannot be degraded in a reasonable amount of time by relying on natural attenuation alone. A substantial reduction of mass must occur first. As embodied in the California State Water Resources Control Board Resolution No. 92-49, Policies and Procedures for Investigation and Cleanup and Abatement of Discharges Under Water Code Section 13304, the following policies are applicable: • Before the Regional Water Board can make a determination that it is technologically or economically infeasible to attain cleanup objectives in a reasonable amount of time, a responsible party must demonstrate that it is not technologically or economically feasible to clean up to water quality objectives. • Technological feasibility is determined by implementing technologies that are known to be effective in reducing the concentration of the contaminants.