SITE INFORMATION AND CORRESPONDENCE FILE 2

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GEORGE AND MEI ANISHI 1600 Durham Ferry Rd. Page 2 of 2 dissolution of the gas in the groundwater. EHD believes it possible that not enough of the injected 03/02 will remain in a gaseous phase long enough to create sufficient force to cause groundwater mounding, stripping of contaminants with migration to the vadose zone, or significant lateral migration of gases. To address these issues; EHD recommends the following: • Prior to any 03/02 injection testing, utilize a portable SVE unit to conduct a test on the two SVE wells previously installed in the excavation backfill to ascertain that contaminant vapor is present and to evaluate the sustainability of the contaminant vapor response to the SVE system in the absence of an operating ozone/oxygen injection system. This test data should demonstrate the presence of contaminant vapor in the backfill and provide a background response against which to measure the effect of the ozone/oxygen injection system to move contaminants into the backfill. • Install only one to three test 03/02 injection wells at this time, with either existing or new observation wells situated to measure the effects of the injection, such as contaminant concentration changes, groundwater mounding, mobilization of metals, dissolved oxygen, etc., within a reasonable time frame. Under the proposed test design, the closest down-gradient observation wells from the Durham Ferry Road injection points would be MW-6 and MW-7, located approximately 50 to 60 feet down-gradient of the proposed injection points. GTI has previously calculated that the groundwater seepage velocity is only 0.104 to 1.04 feet per year in the soil between the ground surface and 30 feet below surface grade (bsg) and is 5.25 to 134 feet per year in soil between 30 and 50 feet bsg, thus it would take as much as 50 to 60 years to detect the effects in the down-gradient wells of the 03/02 injection at 20 to 22 feet bsg. MW-2 and MW-5 are closer to proposed injection points (approximately 15 feet), but are up-gradient of the proposed injection points. A field test of 03/02 injection should be designed with injection and observation well placements assigned such that the desired effects can be measured in a reasonable time-frame. Please provide a feasibility work plan to EHD by 18 July 2005 that will provide sufficient field data to further evaluate the proposed remedial actions discussed in the Plan and in this letter. Questions or comments may be directed to Nuel Henderson at (209)468-3436. Donna Heran, REHS, Director Environmental Health Division Nuel C. Henderson, Jr., PG Unit IV- Site Mitigation C: James L.L. Barton— CVRWQCB Mandeep Singh —Geological Technics Inc.