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Ms. Lori Duncan & Mr. Nuelfnderson December 14, 2006 Page 2 Shaw anticipates that an active groundwater remediation effort will be needed at the property. Some methods for remediation of gasoline hydrocarbons in groundwater may result in increased volatile flux to the subsurface - for example, air sparging - and hence there is a potential that groundwater remediation might temporarily increase risk to site occupants. Shaw recommends an evaluation of the current risk and potential risk during remediation, to human health via inhalation, before determining the removal of the SVE equipment from the property. Recommendations for Site Work Shaw recommends that five tasks be performed at the site: ■ Modify Groundwater Sampling Frequency ■ Modify Groundwater Monitoring Network ■ Evaluate In -Situ Remediation of the Silty Shallow Saturated Zone (-20-40 feet bgs) ■ Evaluate In -Situ Remediation of the Sandy Intermediate Saturated Zone (--20-40 feet bgs) ■ Evaluate Current Human Health Risk Details on each of these tasks are provided below. Modify Groundwater Sampling Frequency Reduce the frequency of testing water samples from wells MW -2R and MW -3R from quarterly to once annually. Samples from these wells have been consistently free of analytes since November 2003, and the well locations are such that little potential exists for site -related fuel contaminants to migrate towards them. Modify Groundwater Monitoring Network The existing monitoring network does not adequately evaluate the two lithologically-different submerged zones of hydrocarbon that were identified by Shaw in the August 2006 report and in your letter of October 13, 2006. Because of the lithologic distinctness of the two zones, it is likely that they will be remediated in different manners and it may be appropriate to distinctly monitor each of them to verify remediation progress and success. Shaw recommends that each of the two zones should have a monitoring network that includes the following: ■ At least three wells that are not in a line, so that groundwater flow direction may be evaluated. ■ At least one well that monitors impacted hydrocarbons in that zone, so that the fuel analyte content of water in that zone may be monitored for improvement during the course of remediation. Shaw also recommends a resurvey of the tops -of -casing of all the site groundwater monitoring wells, following the construction of new wells. This recommendation is made for the following reasons: KA120221 Don Rodgers\Ltrs\Recommendations.doc Shaw Environmental, Inc.