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Former Exxon Service Station No. 73942 Page 2 of 4 <br /> 4444 North Pershing Avenue November 3, 2014 <br /> Stockton, California 95207 <br /> chromium, bromate, lead and total dissolved solids in groundwater; and the Regional <br /> Board suggested collecting baseline data from monitoring wells MWA 1 (previously <br /> destroyed) and MW-12 instead of MWA, as proposed by Cardno. <br /> • Approved a quarterly monitoring program that included sampling and reporting the <br /> findings until concentrations of PersulfOx and any by-products had stabilized and had <br /> been shown to be effective in reducing concentrations of contaminants of concern to <br /> achieve background levels in a reasonable amount of time. The Regional Board also <br /> approved reducing the analyses in the monitoring program proposed by Cardno to <br /> include only petroleum hydrocarbons, sodium, sulfate, nitrate, ammonia, iron, <br /> manganese, cadmium, chromium, hexavalent chromium, bromate, lead and total <br /> dissolved solids. <br /> • Approved the proposal by Cardno to use wells MW3, MW6, RW2, SW1, UVB-MW1 and <br /> V4 to monitor the treatment zone. <br /> • Approved use of well V3 to monitor the transition zone, as proposed by Cardno, and <br /> suggested an additional well be installed northwest of V3 to monitor the transition zone <br /> down-gradient of the treatment zone instead of well RW4, as proposed by Cardno. <br /> • Proposed that wells RW4 and MW-10 be used as the compliance zone wells instead of <br /> wells MW12 and MW13, as proposed by Cardno. <br /> • Submittal of a "more aggressive approach to correcting any potential adverse impacts <br /> caused by the injection of PersulfOx". <br /> In Withdrawal of Notice of Intent for Waste Discharge Requirements, Cardno stated that <br /> ExxonMobil Environmental Services (EMES), on behalf of Exxon Mobil Corporation, had <br /> requested the withdrawal of notice of intent for general waste discharge requirements for this <br /> site. EMES' decision was based on the Regional Board's response to Revised Notice of Intent <br /> for Waste Discharge Requirements, as outlined above. Cardno stated that EMES and Cardno <br /> "no longer believe that the use of a chemical oxidant (PersulfOx) is a cost-effective, feasible <br /> remedial alternative for the site." Cardno stated that in a meeting attended by representatives <br /> from EHD, Regional Board, property owners and Cardno on 10 July 2013, Cardno had agreed <br /> "to perform chemical oxidation as a good faith effort by the responsible party to make one more <br /> attempt at active remediation at the site. The scope of chemical oxidation discussed in the <br /> meeting was a cost-effective remedial action using the existing well network, and the site would <br /> be considered for closure regardless of the results of the chemical oxidation given the <br /> acknowledged challenges to remediation." Cardno and EMES have requested another meeting <br /> "to discuss the site and a cost-effective, realistic path towards closure." <br /> In Semi-annual Groundwater Monitoring Report, Second Quarter 2014, dated 25 July 2014, <br /> Cardno presented results from collecting groundwater samples at this site on 9 June 2014. <br /> Benzene concentrations were reported at 8,500 micrograms per liter (pg/L), 2,400 pg/L, and <br /> 2,200 pg/L in wells UVB-MW1, V2, and IP113, respectively. To meet the Low-threat <br /> Underground Storage Tank Case Closure Policy criteria adopted by the California State Water <br /> Resources Control Board (State Water Board), the dissolved concentration of benzene must be <br />