SITE INFORMATION AND CORRESPONDENCE

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Mr. Paul Supple Arco Station No. 6100 25775 Patterson Pass Road Page 2 of 3 MW-1, encountered low hydrocarbon concentrations in Sand 1, suggesting continued down-dip migration toward the southeast, but did not go deep enough to encounter Sand 2. The SCM appears to be technically sound and to be a useful tool for determining additional assessment needs and to guide remediation planning. Delta concluded that additional investigation of Sand 2 toward the southeast is warranted; EHD concurred with that conclusion. In a 15 October 2002 work plan (WP), Delta proposed to advance four soil borings to approximately 150 feet bsg off-site toward the southeast utilizing mud- rotary drilling to delineate and characterize free product and/or impacted ground water in Sand Unit 2 in that direction. The WP also proposed to destroy the obstructed vapor well VW-15 and to continue free product removal from MW-1 on a weekly basis. EHD approved the proposed work as necessary and adequate to continue corrective action for the site. The WP has not been implemented to date due to problems acquiring and access agreement with the adjacent property owner. The RAP evaluated five potential remediation methods to address impacted soil and ground water on the site; the methods evaluated included natural attenuation, excavation, soil vapor extraction with air bubbling (SVE/AB), dual- phase extraction (DPE), and bioremediation. The SCM recounts Resna's SVE test conducted in 1991 on VW-1 through VW-4 which recovered significant hydrocarbon mass and yielded a radius of influence of 35 feet. Delta selected SVE/AB as the most cost effective and implementable remedial alternative that accommodated site conditions. Delta demonstrated in the RAP that the bulk of impacted soil on site can be addressed utilizing the existing network of vapor wells and selected groundwater monitoring wells. In Addendum to Hydrocarbon Mass Evaluation, dated 10 September 1999, IT Group estimated that soil was impacted by 200,575 pounds of total petroleum hydrocarbons as gasoline (TPH-g) and 17,339 pounds of benzene, toluene, ethylbenzene and total xylenes (BTEX). EHD concurs with Delta's recommended remedial action as adequate and necessary to address impacted soil and perched groundwater on the site and approves implementing the proposed scope of work described in the RAP as an interim remediation measure. The RAP . cannot be accepted as final at this time because the extent of impact toward the southeast, potentially involving significant quantities of free product, has not yet been fully characterized. If the SVE/AB operation cannot be implemented by 01 September 2003, please contact EHD with a schedule for implementation. During review of site data for this evaluation, EHD noted that 1,2-dichloroethane (1,2-DCA) and ethylene dibromide (EDB) have not been part of the laboratory analytical routine. 1,2-DCA and EDB were detected in the soil sample collected