Laserfiche WebLink
Jeff Whitworth - 3 - 8 May 2007 <br /> concentrations have been found within the proposed school area. As all school sites need to <br /> Le designated for unrestricted land use, DTSC reserved the right to evaluate the remainder of <br /> the school site, including delineation of the groundwater plume, to develop a cumulative health <br /> risk determination. DTSC commented that there appears to be no significant human health <br /> risk associated with residual soil TPH concentrations or a significant cancer risk related to the <br /> soil vapor to indoor air intrusion pathway according to the reported benzene soil gas data. <br /> DTSC expressed some concern regarding the potential presence of biogenic methane vapor <br /> because of excavation backfill exceeding 10 feet in thickness. DTSC requests an evaluation <br /> of total organic carbon (TOC) content of the backfill and an evaluation of biogenic methane if <br /> the TOC content exceeds 0.5 percent. A copy of DTSC's review comments is attached. <br /> Shell concludes that based on established Water Quality Objectives and the confirmation soil <br /> and soil gas sample data that no further action is required for soil or groundwater remediation <br /> related to the former Shell crude oil pipelines in Neighborhoods C and D of the Mountain <br /> House residential development. While Regional Water Board staff concurs with this <br /> conclusion for direct contact with soil and the threat to indoor air quality, the extent of the <br /> groundwater plumes previously identified beneath the pipeline has not been fully delineated. <br /> Groundwater plume delineation and potential groundwater remediation are necessary before <br /> the Regional Water Board can grant a no further action determination for groundwater <br /> beneath areas previously identified as impacted by petroleum hydrocarbons. <br /> Based on the data provided in the RAR, Regional Water Board staff concurs with Shell that <br /> development of the Mountain House community residences overlying the former Shell pipeline <br /> areas does not pose a significant health risk from direct contact with soil or a threat to human <br /> Health due to soil gas migration to indoor air. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4719 or <br /> rnclardy@waterboards.ca.gov. <br /> 4 <br /> Mark W. Clardy, P.G. <br /> Engineering Geologist <br /> Private Sites Cleanup Unit <br /> /\,ttachment <br /> cc Ms. Kamili Siglowide, Department of Toxic Substances Control, Sacramento <br /> Mr. Michael Hurd, Scientific Applications International Corporation, Oakland <br /> Mr. Mike Infurna, San Joaquin County Environmental Health Department, Stockton <br /> Ms. Eileen Nottoli, Allen Matkins Leck Gamble & Mallory LLP, San Francisco <br /> Mr. Manuel Oliveira, Escalon <br /> Mr. Duane Grimsman, Trimark c/o Sterling Pacific Assets, Roseville <br /> Ms. Mary Maria Rocha, Tracy <br /> Mr. Nader Shareghi, Mountain House Community Services District, Stockton <br /> Mr. Alex Dewitt, Condor Earth Technologies, Inc., Stockton <br /> Mr. Kevin Peters, Shea Homes, Livermore <br /> ,11,aC VJ clic dod\AustinStaff\Mark\Shell Mtn.House Pipeline Tracy\3-13-07 Shell Mtn House C-D soil exc rept.doc <br />