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880 Victor,Lodi <br /> Former Shell Service Station <br /> Page 2 <br /> the end of 2003 instead. However,EHD concluded the proposal to be inadequate based on the <br /> aquifer pump test conducted in October 2002,which Cambria calculated that 3.33 pounds of MTBE <br /> were removed. Nevertheless,in a meeting with EHD on July 28,2003,Equilon requested that the <br /> limited groundwater extraction be allowed to proceed since there does not seem to be any local <br /> groundwater receptor and hydraulic control is not of priority. <br /> Analytical results of the quarterly samples in the 8 months after completion of the limited <br /> groundwater extraction events indicated negligible reduction of the dissolved oxygenate <br /> contaminants. EHD is most concerned with the continued rising concentrations of TBA and the <br /> reducing concentrations of MTBE. It is unknown if the reduction of concentration of MTBE is a <br /> result of conversion to TBA or contaminant migration in groundwater. The continual decrease in <br /> MTBE concentration in the occasionally downgradient well MW-7 could be a sign of dilution due to <br /> any number of factors such as conversion to TBA,natural attenuation, or dilution due to plume <br /> migration. EHD again directs that an interim remediation to reduce the dissolved mass and to. <br /> established hydraulic control be implemented immediately. Submit a work plan that will remediate <br /> the dissolved contamination plume and prevent further degradation of groundwater to EHD by <br /> September 16,2004. Interim remediation should be implemented within 45 days following approval <br /> of the work plan. <br /> The vertical extent of the contamination at the site is not defined. TBA has been found in the <br /> deepest well MW-11. Due to low the soil retardation factor of the both TBA and MTBE (compared <br /> to the aromatic hydrocarbons such as benzene and toluene)and high solubility, the greatest effort <br /> should be made to define the vertical extent of the plume as soon as possible to prevent further <br /> degradation of deeper aquifers. EHD is also concerned about the large data gap between MW-6 and <br /> MW-7. Although contaminants have not been detected historically in MW-6,it is located about 130 <br /> feet north of MW-7,and therefore too far to be considered a zero line for the eastern edge of the <br /> contamination plume. Furthermore,with the historically high concentration of TBA detected in <br /> MW-2,it is vital that an additional monitoring well between MW-6 and MW-7 be installed in order <br /> to define the lateral extent of the contamination and to provide a sentinel data collection point for <br /> potential dissolved TBA migration to the east. Submit a work plan that will define the vertical and <br /> lateral extent of the contamination by September 16,2004. EHD recommends that the proposal be <br /> included in the interim remediation work plan mentioned-above. <br /> The proposed and EHD-approved MW-12 and MW-13 have not been installed to date due to denial <br /> of access. Provide EHD with copies of correspondence to the off-site property owner and any <br /> letters from the property owner denying access by September 16,2004. EHD will request in writing <br /> that the property owner grant access once this correspondence is provided. <br /> The Geo Z well survey data for NAV-1,MW-2,and MW-3 have not been submitted to the <br /> Geotracker website. Submit the Geo Z Data for these wells to Geotracker as soon as possible. If <br /> you have any question please contact Jeffrey Wong at (209)468-0335. <br /> Donna Heran,REHS,Director <br /> Environmental HealDepartment <br /> effrey Wong,Senior REHS C Margaret gorio,REHS <br /> LOP/Site Mitigation Unit Supervisor <br /> C: CRWQCB,Central Valley Region—James L.L.Barton,RG <br /> C: Cambria Environmental Technologies,Inc.—Aubrey Cool <br />