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r Page 1 of 1 V �! Nuel Henderson [EH] From: Nuel Henderson [EH] sent: Tuesday, November 02, 2010 3:38 PM To: 'Kirk Larson' Cc: Vicki McCartney [EH] Subject: Five -Year Review Recommendations for 2651 Airport Way Claim Number 2429 Kirk, Thanks for giving me an opportunity to comment on this site after the initial 45 -day comment period. The EHD had reviewed this site for closure consideration in January of this year, and found there are some good reasons to be favorably disposed to site closure; specifically: Sorbed and dissolved plumes appear to be adequately delineated; Dissolved concentrations in outboard wells appear to be declining; Much of the surrounding area is in industrial use; and Modeling predicts limited plume migration and eventual reduction to background levels. The EHD also identified potential issues not favoring immediate site closure: Very high TPHg concentrations in several core area wells do not exhibit significant, sustained declining trends of the last three years and only minimal decline over the last ten years; Benzene concentrations in PZ -1 have remained high for the last ten years; There are several residential lots nearby, one residential structure within 500 feet of the former UST site; and There are twodomesticwells within 600 feet of the former UST area. The EHD has recently approved a pilot test to evaluate insitu chemical oxidation using modified Fenton's Reagent. In view of the persistent high dissolved TPHg and benzene concentrations in the core area, the presence of domestic wells within 600 feet of the former LST. area, and the very long time frame estimated to be required for natural attenuation to reduce the contaminate concentrations to background levels, the EHD believes it would be prudent to attempt some mass reduction in the core area to accelerate the overall rate of return to background conditions. The EHD believes that the CLIF recommendation of April 2008 is still valid. Nuel Henderson 8/16/2011