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Jeff Baker • - 2 - • 19 December 2006 <br /> biodegradation rates are sufficient to destroy remaining petroleum hydrocarbons downgradient <br /> of the remedial observation wells. In conclusion, STTC stated that the work plan for <br /> installation of additional ozone injection wells as described in the contingency plan and <br /> requested by the Regional Water Board will not be submitted as the threshold criteria has yet <br /> to be exceeded. <br /> The Third QMR describes groundwater monitoring performed in August 2006 and remediation <br /> activities performed during the third quarter 2006. Groundwater is monitored in four separate <br /> zones designated Zone A, Zone B, Zone C, and Zone D. Localized water table mounding at <br /> well PS/WC-1 S and radial inward flow at well SP/WC-1 S were observed within an overall <br /> shallow zone flow pattern to the east at an average gradient of about 0.003 foot per foot (ft/ft). <br /> Separate phase hydrocarbons (SPH) were reported at wells AR/MW-23A (0.01 ft.), TS-4 (0.03 <br /> ft.), and TS/M-2 (1.61 ft). Maximum groundwater chemical concentrations were reported in <br /> Zone A with 100,000 ug/L Total Petroleum Hydrocarbons (TPH) as gasoline; 64,000 ug/L TPH <br /> diesel; 14,000 ug/L benzene, 16,000 ug/L methyl tertiary butyl ether (MTBE); and 8,300 ug/L <br /> tertiary butyl alcohol (TBA). There reportedly appears to be some correlation between <br /> seasonal groundwater level fluctuations and chemical concentrations with increasing <br /> concentrations during rising groundwater levels. The West OS was operational most of the <br /> reporting period except from 4 August 2006 to 29 September 2006 due to compressor shutoff <br /> between maintenance visits. The East OS was non-operational during the reporting period <br /> due to a mechanical malfunction associated with the oil separator of the compressor. On 5 <br /> October 2006, the East OS compressor was replaced and the system restarted. <br /> REGIONAL WATER REVIEW COMMENTS <br /> Regional Water Board staff acknowledges the comments provided in the Response Letter. <br /> Based on full-scale startup of the ozone injection systems in the fourth quarter 2005 and no <br /> exceedance of the threshold criteria as stated in the Response Letter, Regional Water Board <br /> staff concurs that the requested work plan to implement the contingency plan is not required at <br /> this time. <br /> Monitoring and Reporting Program (MRP) No. R5-2004-0823 requires that the Regional Water <br /> Board shall be notified within 48 hours of an unscheduled shutdown of any soil vapor and/or <br /> groundwater extraction system operated at the site. This requirement applies to any soil or <br /> groundwater remediation system operated at the site including the OS. In the future, STTC <br /> needs to notify Regional Water Board staff within 48 hours of the unscheduled shutdown of <br /> either ozone injection system operated at the facility. The next groundwater monitoring and <br /> remediation status report for the fourth quarter 2006, including the 2006 annual report, is due <br /> to this office by 1 February 2007. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4719 or by <br /> email at mclardy@waterboards.ca.gov. <br /> Mark W. Clardy, P.G. <br /> Engineering Geologist <br /> Private Sites Cleanup Unit <br />