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\\ .4 JBM 9 August 11 , 2006 Victoria McCartney Environmental Health Department , San Joaquin County Cy 304 East Weber Avenue, 3 `d Floor `p ;1 , Stockton, CA 95202-2708 RE : Frontier Transportation, Inc. ; 425 Larch Road; Tracy, CA 95376 Subject: Interim Corrective Action Plan Revisions SITE CODE : 2251 The Environmental Health Department of San Joaquin County on July 17, 2006 requested the corrections to the Interim Corrective Action Plan for Frontier Transportation, Inc . BEA offers the following details to be incorporated into the Interim Corrective Action Plan and Addendum. The EDH commented that "TPH-5 detected in the water sample from MW-2 is not , suggestive of the close proximity of significant quantities of free phase gasoline ." BEA has not identified or measured amounts of free product in MW-2 . MW-2 was found to have sheen droplets on the surface during initial groundwater purging in the 2006 first quarter monitoring event. BEA drew attention to this because in the past MW-2 had been a clean well from March 1998 to June 2006, and the presence of any contamination demonstrates plume migration. BEA concurs with the EHD that there is no direct evidence of soil between 15 ' bgs and below being impacted with free phase gasoline. The appearance of free product in MW-21 indicates that the source area must still have elevated levels of contamination. BEA calculated a maximum free phase amount based on unavailable data and assumed a potential maximum. However, BEA concurs with the EHD that the source amount of free product is likely less than 300 gallons. Partial excavation in the northern part of the former UST area will be useful in removing a considerable portion of the contaminant source. Based on the distance of the source area to MW-21 (with small amounts of free product) it seems that excavation could remove from one-fourth to half of the contaminant mass . < Contaminated soil and groundwater removed during the excavation would encompass a maximum area of approximately 600 square feet, but would likely only be approximately 200 square feet. The excavation would only continue as deep as contamination is still indicated by odor (PID detections) or staining, which may be to approximately 14 ' bgs or a few feet below. However, this estimate cannot be substantiated since the remaining amount of contamination in the source area is unknown. Samples collected during excavation will provide information useful in determining how deep to discontinue excavating. If soil samples collected are found BIOPHYSICS ENVIRONMENTAL ASSESSMENTS, INC:. / 3577 W Philadelphia Avenue, Chino, CA 91710 / 909,364-2192 / FTx 909.364-2193