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C3eo(ogir,,dTwhnics 2nc. `... Page 4 City of Escalon Project No. 750.3 February 26,2001 2.1.1 Excavation In September 1998, Wright Environmental Services Inc. (Wright)removed the former USTs at the site. Wright completed additional excavation around the former dispenser islands during December 1998. Approximately 213.55 tons (as documented on the landfill ticket) of impacted soils were subsequently hauled off site for disposal at the Manteca Forward Landfill on May 20, 1999. At that time, the extent of the gasoline contamination was undefined. On March 22, 1999, a meeting was held at the PHS/EHD with the City of Escalon's Mr. Doug Stidhain and GTI's Mr. Ray Kablanow in attendance. Further excavation was discussed at the meeting and PHS/EHD staff indicated that remediation activities conducted prior to plume definition would be classified as an "interim" remedial action. PHS/EHD staff further stated that interim remedial actions may not be subject to reimbursement from the Underground Storage Tank Cleanup Fund Program (USTCFP) and they required that the City of Escalon (City) state in writing its' responsibility for the costs of interim remedial actions. Mr. Stidham indicated that the City would not do additional work without USTCFP pre-approval. The participants also discussed the status of the road-widening project currently underway. PHS/EHD staff stated that the City could either continue the investigation (and delay the road construction activities) or delay the investigation. The City reiterated the need to complete the road project and a decision was made to defer the investigation. The - participants agreed that it was possible to install vapor extraction wells and/or groundwater •..� monitoring wells in the proposed roadway to facilitate future remedial activities. PHS/EHD staff documented the above synopsis in their March 26, 1999 letter. In their March 26, 1999 letter, it is apparent that PHS/EHD staff disagreed with further excavation as a remedial alternative. This is evident by their referring to the fact that soil contamination was present at a depth of 46 feet at the site and their conclusion that no shallow source of contamination was present in the area of the dispenser islands. Therefore, due to the following factors: V • the economic savings of continuing the shallow excavations while the equipment was mobilized in 1998 — 1999 has been forfeited, — • the contamination has been shown to extend to a depth of at least 46 feet at the site, • the existing transportation corridor existing at the site would be severely disrupted and at great costs to replace, excavation as a remedial alternative is rejected as technologically and economically infeasible. V 2.1.2. Remediation by Natural Attenuation Remediation by natural attenuation (RNA) is a process in which naturally occurring `+ mechanisms are utilized to reduce contaminant concentrations in the environment. These processes include aerobic and anaerobic biodegradation, volatilization, dispersion and absorption. Since the concentrations of contaminants leaching to groundwater at the site exceed the drinking water maximum contaminant levels (MCLs), it is apparent that RNA is V . V