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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> !— � Donna K. Heran, R.E.H.S. Unit Supervisors <br /> Director 304 East Weber Avenue,Third Floor Carl Borgman,R.E.H.S. <br /> Laurie A. Cotulla, R.E.H.S. Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I. <br /> Program Manager Telephone: (209)468-3420 Douglas W. Wilson, R.E.H.S. <br /> F o a Margaret Lagorio,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellon, R.E.H.S. <br /> Website:www.sjgov.org/ehd/ Jeff Carruesco, R.E.H.S. <br /> DANIEL SILVA APR 1 a 2006 <br /> WEST CLAY PROPERTIES <br /> PO BOX 6152 <br /> STOCKTON CA 95206 <br /> RE: West Clay Properties Site Code: 1065 <br /> 639 West Clay Street <br /> Stockton, CA 95206 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Additional <br /> Monitoring Well Installation Mork Plan dated December 23, 2005,prepared by <br /> Advanced GeoEnvironmental Inc. (AGE). AGE proposed installing two additional <br /> monitoring wells south and southeast of the former underground storage tank (UST) cluster <br /> located on the north side of the above-referenced property. The purpose of the two wells is <br /> to cover the data gap between monitoring well MW-14 and MW-15. The two wells will be <br /> completed to 40 feet below surface grade (bsg) with 20 feet of screen. EHD approves the <br /> above-mentioned proposal as adequate and necessary elements (H&S 25296.10(c)(3)). <br /> EHD has reviewed Revised Ozone Injection Pilot Study Mork Plan(the work plan) <br /> dated October 27,2005 prepared by AGE. The work plan is a follow-up to the Ozone <br /> Injection Pilot Study Work Plan dated January 4, 2005, and concluded that based on the bench <br /> scale study conducted at the site in April 2005, the injection of ozone and subsequent effect <br /> on the contaminants would have minimal adverse side effects. The work plan included a <br /> observations and interpretations of the bench scale study authored by McCampbell <br /> Analytical, Inc. (McCampbell). McCampbell stated the generation of water soluble <br /> hexachrome was not found at detection limit <20 parts per billion (ppb) before or after <br /> introduction of ozone, and concluded the reduction of chromate in the environment to <br /> hexachrome by ozone is unlikely to occurred to concentrations above <0.2ppb. <br /> AGE proposed conducting a 24-week in-situ ozone sparge (IOS) pilot study in the area of <br /> the above-mentioned former UST cluster. The pilot study includes installation of 4 ozone <br /> sparge wells around the UST cluster, and incorporation of the existing well MW-9 into the <br /> IOS system. The ozone sparge wells will be completed to approximately 35 feet bsg with a <br /> manufacturer-assembled 2-inch by 30-inch microporous section. EHD approves the in-situ <br /> ozone injection pilot study as adequate and necessary elements of the work plan (H&S <br /> 25296.10(c)(3)). <br /> DATED April 14, 2006 BY l `' <br /> Cc: RWQCB, Central Valley Region—James L. L. Barton, PG <br /> Cc: Advanced GeoEnvironmental, Inc. —Bill Little, PG <br />