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Thrifty Oil Company#172 / ConocoPhillips page 2 <br /> 7647 Pacific Avenue, Stockton May 25, 2010 <br /> Based on the findings from the groundwater samples to be collected during the third and <br /> fourth quarters of 2010, COP proposes submitting a work plan to the EHD by March 31, <br /> 2011, if further site assessment is needed or if changes to the existing remedial actions <br /> are required. The EHD considers waiting until the end of March 2011 for COP's work plan <br /> to either continue using SVE and GWE or conducting additional site assessment to be <br /> excessive and the extension date for this phase is not approved. <br /> The EHD believes that COP can complete the rebound testing evaluations for SVE and <br /> GWE with a portable unit for the short time period the tests need to be run if the existing <br /> systems can not be put into operation quickly. This way, COP would be able to submit the <br /> report if findings for the rebound testing in August 2010, if not sooner. The report should <br /> contain an estimate and schedule of time needed to repair both systems (if applicable) <br /> and to secure other agency permits, and include a date the systems would be back online. <br /> After the rebound tests are completed, if COP concludes that the dissolved petroleum <br /> hydrocarbon plume is not fully characterized and additional site assessment is needed, <br /> the EHD will allow the SVE and GWE systems to go online as an interim remedial action <br /> (if recommended) pending the results of any additional site investigation. The EHD <br /> considers a plume to be laterally undefined when groundwater samples from monitoring <br /> wells located at the investigated area's periphery consistently contain petroleum <br /> hydrocarbons at significant concentrations. The plume is considered to be vertically <br /> undefined when the deepest screened monitoring wells provide groundwater samples that <br /> are significantly impacted by petroleum hydrocarbons. <br /> The State Water Resources Control Board (SWRCB), Clean Up Fund (CUF) recommends <br /> that a Human Health Risk Assessment (HHRH) be conducted for this site. Please <br /> address this concern in the next proposal submitted to the EHD. <br /> Groundwater analytical data from the April 2010 sampling event revealed that elevated <br /> levels of dissolved petroleum hydrocarbons are still present in many monitoring wells at <br /> this site. Groundwater remediation appears to be needed and extensive delay returning <br /> this site to active and effective remediation (mass removal/meeting water quality <br /> objectives) can not be permitted by the EHD. Please make every effort to complete the <br /> evaluation of the remedial system and provide the EHD with conclusions and <br /> recommendations COP plans to utilize to meet this requirement. <br /> Questions regarding this letter should be directed to Michael Infurna, <br /> minfurna s cehd.com or by phoning (209) 468-3454. <br /> /444WI�4� "I <br /> Michael J. Infurna Jr., REHS Nuel C. Henderson Jr., PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> c: Mr. James L. Barton, CVRWQCB <br /> Mr. Mark Owens, SWRCB <br /> Mr. Louis Mosconi, ConocoPhillips, 3611 S. Harbor Blvd, #200, Santa Ana, 92704 <br /> Ms. Diane Barclay, Stantec, 3017 Kilgore Rd., Rancho Cordova, CA 95670 <br />