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Ms. Margaret Lagorio Page 6 of 8 Feasibility of Air Sparging Utilizing the existing information for the site, Ground Zero has evaluated the potential effectiveness of air Sparging. We have concluded that the interbedded low and high permeability soils would make control and capture of the injected air ineffective for remedial purposes and may present a risk of further dispersion of gasoline hydrocarbons migrating under the site from offsite sources. Additionally, the relatively large mass of sorbed hydrocarbons in saturated soils would be expected to be only marginally affected by air Sparging. Air Sparging would be an expensive and time-consuming effort involving significant uncertainty of success. Finally, any air Sparging effort, once begun, could be anticipated to continue indefinitely. We do not recommend air sparging for this site. OXYGEN RELEASING COMPOUNDS We believe that the analytical data demonstrate that concentrations of dissolved contaminants in wells affected by the Knowles release have generally diminished with time and that the plume has stabilized. This stability and reduction is attributed to natural attenuation mechanisms, in large part biological, but including sorption, dilution and dispersion. These processes should continue to reduce the magnitude and area of impact over time and should ensure that beneficial uses of groundwater are not degraded at the time and point of use. Graphs of TPHg and benzene concentrations in affected wells are included in Attachment C. Nevertheless, we propose to enhance the biodegradation process by the addition of oxygen releasing compounds to the subsurface. During the first quarter 2002 groundwater sampling event (February, 2002) we propose to install Oxygen Release Compound (ORC) "filter socks" in certain monitoring wells at the site. ORC is a proprietary formulation of magnesium peroxide with intercalated phosphate. The magnesium peroxide hydrates on contact with water, releasing oxygen to the subsurface. The intercalated phosphate acts to retard the rate of hydration of the magnesium peroxide creating an extended period of oxygen release and inhibiting detrimental buildups of magnesium hydroxide coatings. The continuous release of oxygen to the groundwater is intended to enhance the abundance and metabolism of indigenous aerobic hydrocarbon-degrading bacteria. The manufacturer of the ORC filter socks (Regenesis) will be provided with information on well construction, contaminant concentrations and groundwater velocity in order to specify the optimal number of socks and the anticipated change-out period for the socks. Prior to installing the socks, monitoring wells will be purged and sampled per the site sampling schedule. ORC socks will then be placed in the following wells in accordance with the manufacturer's instructions: NMI, MW2, MW5, MW6, MW8 and each vapor well. roekklosure\workp1mVespouse.doc