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San Joaquin County DIRECTOR <br /> Environmental Health Department Donna Her an, REHS <br /> ). '_� ASSISTANT DIRECTOR <br /> Z. 600 East Main Street Laurie Cotulla, REHS <br /> TO <br /> Stockton , California 95202-3029 <br /> PROGRAM COORDINATORS <br /> -- Carl Bergman, REHS <br /> r . P <br /> Mike Huggins,Huggins, REHS, RDI <br /> H � / FOPS\ Website: www.sjgov. org/ehd Margaret Lagorio, REHS <br /> Phone : (209) 468-3420 Robert McClellon, REHS <br /> Fax: (209) 464-0138 Jeff Carruesco, REHS, RDI <br /> Kasey Foley, REHS <br /> April 28, 2008 <br /> Mr. Jay Coffey <br /> City of Stockton <br /> Department of Housing and Redevelopment <br /> 22 East Weber Avenue, Room 350 <br /> Stockton, California 95202-2317 <br /> Subject: Former San Joaquin County Motor Pool <br /> 130 North Hunter Street <br /> Stockton, California 95202 <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed <br /> Investigation Summary Report and Groundwater Monitoring Work Plan, dated February <br /> 6, 2008, submitted by Treadwell & Rollo, Inc. (Treadwell & Rollo) on your behalf. In <br /> the work plan, Treadwell and Rollo proposes to install six monitoring wells at locations <br /> illustrated in Figure 9 . The data from these wells will assist in characterizing the extent <br /> of the petroleum hydrocarbon plume in two purportedly distinct groundwater zones <br /> (shallow and deep), monitor natural attenuation, and provide information to evaluate the <br /> need for future site assessments and possibly site remediation. <br /> A technical justification for differentiation of two aquifer zones was not provided in the <br /> work plan, but the data distribution for impacted groundwater does support installation of <br /> monitoring wells in the proposed depth intervals. The EHD approves the installation of <br /> the six proposed monitoring wells. Three wells will be screened at approximately twenty <br /> to thirty-five feet below surface grade (bsg), and three wells will be screened at <br /> approximately fifty to sixty-five feet bsg. In addition to these wells, the EHD believes <br /> one deep monitoring well should be installed in the vicinity of former monitoring wells <br /> MW- 1 , MW-2, and MW-3 , or close by in the assumed down-gradient direction and <br /> screened at approximately seventy to eighty-five feet bsg. The screened interval is based <br /> on the lithologic logs for SB-6 and SB-7 demonstrating a silty sand interval at <br /> approximately seventy to eighty feet bsg. The vertical extent of impacted soil has not <br /> been fully addressed; if a deeper well (approximately 70-85 feet bsg) is installed as <br /> described, soil samples should be collected and analyzed to complete the vertical <br /> assessment of impacted soil. <br /> H:1130 North Hunter.Street.doc <br />