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I <br /> ENSR AECOM <br /> ENSR <br /> 1 10461 Old Placerville Road Suite 170,Sacramento,California 95827-2508 <br /> T 916 362 7100 F 916 362 8100 www ensr aecom com _ <br /> G <br /> FE 5 r 6 <br /> February 13, 2006 <br /> EN\ARC<:yIENT HEALTH <br /> IMr Jeff Wong pERf�101,'SFWAES <br /> San Joaquin County <br />' Environmental Health Department <br /> 304 E Weber Avenue, Third Floor <br /> Stockton, California 95202 <br />' RE Quarterly Groundwater Monitoring Results Report, Fourth Quarter 2005 <br /> Stockton Scavenger Association Facility <br /> 1240 Navy Drive, Stockton, California <br />' ENSR Project No 05027-031-100 <br /> Dear Mr Wong <br /> ENSR Corporation (ENSR) has been authorized by Norcal Waste Systems Inc (Norcal)to perform <br /> quarterly groundwater monitoring and sampling at the Norcal Stockton Scavenger Association site located <br /> at 1240 Navy Drive, Stockton, California (Figure 1) The locations of former and current site features are <br /> illustrated on Figure 2 Quarterly groundwater monitoring and sampling is intended to evaluate the <br /> lip distribution of petroleum hydrocarbon constituents in groundwater beneath the site This report <br /> summarizes results for groundwater monitoring and sampling conducted at the site during the fourth <br /> quarter 2005 The work was performed in accordance with the field methods and procedures included in <br /> Attachment A <br /> Groundwater Level Measurements <br /> Depth to groundwater was measured in monitoring wells MW-1 through MW-4 on December 12, 2005 <br /> These measurements are presented in Table 1,and were used to construct a groundwater elevation contour <br /> map included as Figure 3 The groundwater in the vicinity of the former excavation pit(MW-2)maybe <br /> I higher in elevation than in areas of undisturbed native soil In general, groundwater appears to have been <br /> flowing south with a gradient of 0 0004 feet per foot(ft/ft)on December 12,2005 This is consistent with <br /> historical groundwater flow direction and gradient observations Copies of the groundwater depth <br /> measurement information sheets are included in Attachment B A summary of groundwater elevations <br /> Imeasured to date is presented In Table 1 <br /> Groundwater Sampling and Analytical Results <br /> Groundwater samples were collected from monitoring wells MW-11 through MW-4 on December 12, 2005 <br /> Groundwater samples and an equipment(pump) blank were submitted to California Laboratory Services <br /> (CLS) in Rancho Cordova, California, a State-of-California certified laboratory, under chain-of-custody <br /> protocols CLS analyzed the samples for benzene, toluene, ethylbenzene and total xylenes(BTEX) by <br /> Environmental Protection Association (EPA) Method 8021 B, for total petroleum hydrocarbons as gasoline <br /> (TPHg)and total petroleum hydrocarbons as diesel (TPHd) by EPA Method 8015M, and for methyl tertiary <br /> butyl ether(MTBE) by EPA Method 82606 Copies of the groundwater sampling information sheets are <br />' included in Attachment B <br /> TPHg and MTBE have remained below the laboratory reporting limits in all wells for a minimum of four <br />' consecutive quarters <br />