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w N <br /> ENSR ( AECOM <br /> ENSR <br /> 10461 Old Placerville Road,Suite 170,Sacramento,California,95827-2508 <br /> T 916.362.7100 F 916.362.8100 w .ensr.aecom.com <br /> February 15,2007 <br /> Mr. James L. Barton <br /> Central Valley Regional Water Quality Control Board <br /> 11020 Sun Center Drive, Suite 200 <br /> Rancho Cordova, CA 95670-6144 <br /> Subject: Revised Work Plan for Decommissioning of Monitoring Well MW-15 <br /> Chevron Site No. 306620 <br /> 5606 Pacific Avenue, Stockton, California <br /> ENSR Project Number 01231-154-OM1 <br /> Dear Mr. Barton: <br /> On behalf of the Chevron Environmental Management Company(Chevron EMC), ENSR Corporation <br /> (ENSR)has prepared this Work Plan for the permanent decommissioning of monitoring well MW-15. Well <br /> MW-15 is an off-site, upgradient well associated with a former Unocal service station located on the <br /> northeast corner of Pacific Avenue and Robinhood Drive at 5606 Pacific Avenue in Stockton, California <br /> (Figure 1). The former Unocal facility and a former Montgomery Wards auto service center located at <br /> 5400 Pacific Avenue in Stockton, California are collectively referred to as the 'Site'(Figure 2). <br /> ENSR prepared this work plan upon learning of City of Stockton street widening activities along the south <br /> bound section Pacific Avenue immediately north of Robinhood Drive. A modified Site Plan showing the <br /> extent of construction along Pacific Avenue is included as Figure 3. An access agreement between <br /> Unocal, a direct subsidiary of Chevron EMC, and the property owner(Stone Bros. and Associates) is <br /> included as Attachment A. If well MW-15 is not property decommissioned, it would be inadvertently <br /> destroyed and paved over during the street widening project. This would result in a potential migration <br /> pathway to groundwater. <br /> Well MW-15 was installed by Woodward Drilling, Inc., under the supervision of Kaprealian Engineering, <br /> Inc. (KEI)on July 13 through July 14 in 1994. A copy of the soil boring log, including well construction <br /> details, is included as Attachment B. Soil samples collected during the installation of well MW-15 were <br /> below laboratory detection limits for total petroleum hydrocarbons as gasoline (TPHg); and benzene, <br /> ethyl-benzene, toluene, and xylenes (BTEX). Methyl-tertiary butyl-ether(MTBE)was not analyzed from <br /> soil samples collected from the MW-15 boring. MW-15 soil analytical data (KEI, May 22, 1996)is included <br /> as Table 1. Groundwater samples collected from well MW-15 have been consistently below laboratory <br /> reporting limits for petroleum hydrocarbon constituents,with intermittent detections, since the first <br /> sampling event on September 14, 1994. Table 2 summarizes the MW-15 historical groundwater sampling <br /> data,through the fourth quarter 2006 groundwater sampling event. <br /> ENSR I AECOM <br />