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• • 20 March 2012 <br /> ` Flag City Chevron - � - <br /> 6421 Capitol Ave., Lodi, San Joaquin County <br /> • Groundwater pump and treat was the only remedial effort at Site; that Soil Vapor <br /> Extraction (SVE) was not performed (Shallow groundwater[5' to 15'bgs]made <br /> SVE impractical. Soil overexcavation was chosen at the Site to remediate <br /> contaminated soiO, <br /> • Lack of evidence for a New West release (The source of the New West release <br /> has not been definitively identified. While "no alarms sounded"or records show <br /> a release at New West, the monitoring well concentration data correlates to a <br /> New West MtBE release to groundwater that appeared to move towards the Site <br /> under Site pumping influence.), <br /> • The Site remediation was unsuccessful (Site soil and groundwater remediation <br /> was successful in reducing petroleum hydrocarbons concentrations originating <br /> from the Site), <br /> • Residual contaminant plume thickness used for the Site Fate and Transport <br /> Model should be 80 feet (The Model used 10 feet as the plume thickness, which <br /> was based on available Site residual contaminant cross-sections for groundwater <br /> and the analytical data. The New West consultant mistakenly identified the <br /> neighboring 3 B's Truck Stop MtBE plume as Site's.), <br /> • Residual mass of soil and groundwater contaminants incorrectly calculated <br /> (Residual mass estimate was adequate, based on available data), and <br /> • Groundwater flow direction from Site was to the north towards New West <br /> (Groundwater has varied in all directions prior to Site remediation, due to a flat <br /> gradient and pumping influences from now-destroyed private well and municipal <br /> well. The Site remediation caused groundwater to flow radially inwards towards <br /> the Site extraction wells. Post-remediation groundwater flow direction has <br /> primarily been to the southeast (one quarter to the east) from the Site. New <br /> West monitoring shows the same southeast flow direction for their MtBE plume <br /> beyond the influence of their extraction wells.) <br /> 2) SJCEHD comments recommend: <br /> • Collection of additional quarterly groundwater samples from Site extraction wells <br /> and selected monitoring wells (The CAO requires quarterly sampling of Site <br /> wells), <br /> • Collection of grab groundwater or install new wells downgradient of Site's MW-8A <br /> and MW-2 (The Site Fate and Transport Model addressed the rationale for the <br /> comment— to clarify the threat to CSA-31, Well 2, as did installation and <br /> sampling of additional New West downgradient monitoring wells MW-8A and <br /> MW-8B, which are also downgradient of the Site). <br /> • Concurrent monitoring of New West and Site (Site and New West consultants <br /> attempted, but could not agree to concurrent sampling dates, due to conflicting <br /> schedules), and <br /> • Determine whether pumping from CSA-31 wells influences Site wells (Post- <br /> remediation Site and all New West groundwater level monitoring data show that <br /> groundwater direction is primarily to the southeast from the Site and New West <br /> towards CSA 31-2. However, since the SJCEHD issued their comments, New <br /> West installed three multi-level guard wells (MW--9B, MW 9C, and MW-9D) and <br />