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Tosco-76/former BP#11192 page 2 <br /> 1403 Country Club Blvd, Stockton. <br /> MtBE was only detected at this site some time after the new underground storage tanks(UST)were <br /> installed further southwest. EHD is concerned that this relatively new release (documented with UAR <br /> #99-UO2—January 7, 1999) is not being adequately investigated. By installing monitoring wells only <br /> down gradient of MW-11 (northeast), the upgradient and cross gradient areas (southwest and west <br /> quadrants)are not being investigated at all depths of concern. Without defining the soil and groundwater <br /> conditions surrounding the known, deep contamination, a complete picture of the status of the MtBE <br /> plume cannot be determined. <br /> In order to collect adequate data to delineate the soil and groundwater plumes,the work plan included in <br /> this CAP should be modified to include additional deep monitoring wells. Additionally, EHD feels that <br /> installing twelve(12) OMS points would be excessive for testing the effectiveness of this method. <br /> TOSCO should reevaluate the locations best suited to test a few wells and not install all 12 at this time. If <br /> it can be shown that this remedial alternative will potentially be successful for returning the site to pre- <br /> release conditions, additional OMS points may be added. <br /> Lastly, EHD advises that the use of Risk Based Corrective Action/Human Health Risk evaluations is not <br /> appropriate for evaluating whether a site is clean enough. Only the Department of Toxic Substances <br /> Control (DTSC) has the authority to evaluate toxicity matters related to human health concerns and UST <br /> remediation efforts should be directed at returning the aquifer to pre-release conditions, not toward <br /> human health risks. Clean up levels for petroleum-impacted groundwater designated as beneficial use <br /> are MCLs. If your chosen remedial method does not successfully clean up this site to those levels, EHD <br /> will make a determination regarding the necessity for TOSCO to continue the clean up. Your consultant's <br /> comment that"remediation will cease when asymptotic concentrations are reached"is unacceptable and <br /> EHD will not allow pre-establishing closure criteria, other than MCLs, for groundwater remedial efforts. <br /> EHD has received the"Groundwater Monitoring and Sampling Report First Quarter—Event of February <br /> 18, 2002"and has the following comments. TBA has risen significantly in MW-3 and MW-7, and no <br /> explanation or professional evaluation was included in the report. Please ensure that all reports <br /> submitted to EHD include a Conclusion and Recommendation section. Confirmation of a sudden and <br /> significant rise in a new constituent(TBA) in the groundwater at this site may indicate a new release on <br /> the site. <br /> TOSCO is to take immediate steps to verify the presence of TBA in the groundwater by re- <br /> sampling MW-3 and MW-7 immediately. TOSCO is to include a professional evaluation along with <br /> the findings of the re-sampling event in a report due at EHD before May 10,2002. <br /> Please continue to mail your correspondence to Michael Infurna and you may phone him at(209)468- <br /> 3454 should you have any questions or wish to discuss the site. Mr. Infurna can be reached by electronic <br /> mail at minfurna(@-sicehd.com also. <br /> Donna Heran, REHS, Director <br /> Enviro mental He+Di ' 01 <br /> Michael J. InfurnaHS Nuel C. Henderson,Jr., R.G. <br /> Site Mitigation Unit IV/LOP Site Mitigation Unit IV/LOP <br /> MI/ <br /> c: Gettler Ryan—Dave Vossler 1364 N. McDowell Blvd, Ste B-2, Petaluma,94954. <br /> c: CVRWQCB—Marty Hartzell, Sacramento. <br /> c: SWRCB-CUF—Mark Owens, Sacramento <br />