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VI ICVI VII tro-V I ( I <br /> 6633 Pacific Ave., Stockton ry <br /> Stockton, San Joaquin Cour <br /> p, <br /> Residual Mass Calculation <br /> The Report estimated 5.96 pounds of TPHg, 266 pounds of TPHd, and 401 pounds of motor <br /> oil remain in soil, and 0.000045 pounds of MTBE remain in groundwater. The LCERT has not <br /> calculated the mass of petroleum hydrocarbons removed by their extraction wells. <br /> Summary and Recommendations <br /> Chevron has complied with all of the requirements in the Regional Board staff letters. <br /> Concentrations of petroleum hydrocarbons, iincluding MtBE, have decreased significantly since ' <br /> groundwater monitoring started in 1990. As of November 2008, petroleum hydrocarbons <br /> (MtBE, 14 ug/L) will reach WQGs within one year. The petroleum hydrocarbons plume has 3 <br /> been defined both laterally and vertically and poses minimal risk to sensitive receptors, human <br /> health, or other beneficial uses of groundwater in the area. The LCERT continues to operate <br /> the GWP&TS extraction wells at the site for their chlorinated solvent plume (Site well MW-3, <br /> PCE, 6600 ug/L in November 2008). ' <br /> Based on the minimal residual contamination in soil and groundwater, lack of threats from <br /> vapor intrusion, declining soil and groundwater petroleum hydrocarbons concentrations, <br /> compliance with the tasks of Regional Board directives, and a well defined vertical and lateral <br /> extent of pollution, no further action is warranted for the Site. Staff recommends closure of <br /> this Site. The required public participation comment period was conducted with one adverse <br /> comment from LCERT requesting Chevron install new wells for the dry cleaners investigation, <br /> which was later modified to request specific Chevron monitoring wells be transferred to the <br /> LCERT. Chevron complied on 28 September 2009 with the LCERT request to transfer of <br /> MW-2, MW-3, and MW-5 to the dry cleaners investigation. All remaining monitoring wells <br /> were properly abandoned on 28 August 2009 <br /> Attachments: Attachment 1: Site Location Figure 1 <br /> Attachment 2: Site Plan with former USTs and Well Locations Figure 2 <br /> Attachment 3: Sensitive;Receptor Well Survey Figure 6 <br />