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Ms.Margaret Lagorio,SJCEHD February 2,2009 Work Plan for Collection of Soil Gas Data Joe's Travel Plaza, 15600 S.Harlan Road Lathrop,California Page 4 (53 µg/L) and MWO-lx (470 µg/L). The current approximated extent of MTBE in Sand B wells is illustrated on Figure 6. Currently, the dissolved-phase MTBE plume in Sand B (exceeding the secondary MCL of 5.0 pg/L) extends from the site (well MWO-lx) to the northeast to the vicinity of well MW-8 and to the north-northwest to the vicinity of well MW-13A/B. The maximum concentration of MTBE (100 µg/L) was reported in wells MWO-lx and MW-13A/B. Historical analytical results demonstrate the natural attenuation of the plume over time in Sand B wells, with the exception of well MW-13A/B (in which insufficient data has been gathered). Currently, the MTBE plume is adequately (and/or practically) assessed to the secondary MCL in all directions in Sand B. Sand C Analytical results of samples collected during the most recent quarterly groundwater monitoring and sampling event (December 29, 2008) indicate no concentrations of GRO, BTEX, or MTBE reported in either of the Sand C wells. Low level (laboratory-flagged) DRO concentrations were reported in both wells at concentrations of 110 µg/L (MW-12C) and 95 µg/L (MW-13C). Based on these results (and analytical results of grab water samples collected from CPT borings 5 to 10 feet deeper than Sand C wells), the vertical extent of impact to groundwater beneath the site is adequately characterized at this time. PROJECT APPROACH FOR PROPOSED SCOPE OF WORK Stratus proposes the advancement of eight (8) direct-push soil borings and subsequent collection of shallow subsurface soil gas samples from the borings. Analytical results of soil gas samples collected during this investigation will be compared against RWQCB-SF's ESLs2 and used to determine the need for a HHRH. The locations of the eight proposed soil gas samples were selected to evaluate if potential health risks to workers at the site property (an active gasoline service station and truck stop) and to occupants of surrounding commercial and residential properties in areas overlying or near known impacted groundwater are present. The surrounding properties that will be considered are the (commercial) Storage Pro facility located at 15550 South Harlan Road and some of the residential properties that adjoin the site property to the east along Lisa Lane/Patricia Place and adjoin the Storage Pro facility along Lottie Way. It should be noted that only extremely low levels of MTBE, if any, are known to underlie the residential properties along Lisa Lane, Patricia Place, and Lottie Way; however, to be conservative, data will be collected from these areas to evaluate potential risk of volatilization of MTBE from shallow groundwater. 'California Regional Water Quality Control Board,San Francisco Region,Screeningfor Environmental Concerns at Sites with Contaminated Soil and Groundwater—INTERIM FINAL—November 2007(Revised May 2008) K:\Joe's Truck Plaza\Work Plans\Work Plan for Collection of Soil Gas Data 2-2-09.doe