SITE INFORMATION AND CORRESPONDENCE FILE 1

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GEORGE AND MEI TERANISHI • 1600 Durham Ferry Rd. Page 3 of to augment the excavation remedial effort by installing a low-flow blower and carbon canisters to initiate bio-venting and vapor extraction to address hydrocarbons impacting the excavation backfill that are thought to have been introduced via migrating impacted ground water. EHD cannot approve this portion of the work plan at this time for the following reasons: • There has been no demonstration that the excavation backfill has been significantly impacted by fuel components; • There has been no presentation of data or a calculation of the contaminant mass impacting the backfill; and • The planned scope of work will not directly address the contaminant mass impacting soil, and therefore ground water; that was left in place; • Other than the redox potential data, there has been no demonstration that bioremediation is a viable process that could be stimulated through the introduction of supplemental oxygen, or that such biological processes that may be currently operating in the area of concern will address hydrocarbons and/or fuel additives; EHD notes that the 1QR02 proposed to collect "natural attenuation parameters" from water samples from the 12 monitoring wells and three domestic wells to ascertain that natural attenuation is occurring at the site. This data will help address the fourth point above and EHD will approve its collection, but requests specification of the parameters to be collected and a brief justification for each monitored point to be so assessed. Soil samples from the impacted area should also undergo the analyses. EHD's analysis of the site data has identified two concerns that should be addressed. EHD notes that the vertical extent of impacted soil east of the probable release point has been delineated by samples from borings MW-102 and MW-202, but the area that appears to have been most impacted, near SE sidewall 9.5, SB-1 , HBA SW sidewalls, and MW-1 (concentrations increasing with depth) does not have a delineated vertical extent. Shallow ground water conditions and the previously mentioned vertical gradients have probably limited the vertical extent of impacted soil in this area of concern to depths similar to the MW-102 area, but EHD recommends a boring between the former pump island and the building near the edge of the excavation to delineate the vertical extent of impacted soil. Of greater concern is the potential lateral extent of impacted ground water. Monitoring wells MW-6, MW-7 and MW-107 appear to provide down gradient limits to the plume of impacted ground water, but EHD notes that MW-6 and MW-7 are completed in the shallow soil with calculated ground water velocities of 0.1 to 1.03 feet per year, so an impact in these wells is not likely to occur until