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indicate that TPHc in soil is limited to beneath the pipeline with minimal lateral <br /> migration. <br /> • Based on residual Light Non-Aqueous Phase Liquid (LNAPL) sample analysis, the <br /> TPH carbon range distribution is typical of weathered crude oil. The residual <br /> LNAPL is dominated by low solubility and low mobility constituents. <br /> • Zone A groundwater monitoring data indicates there are three discrete locations <br /> with chemicals of potential concern (COPCs) in groundwater. hi general, COPC <br /> plumes are small in aerial extent, relatively low concentration, and stable or <br /> shrinking. COPC plumes variably satisfy the low threat closure policy (LTCP) <br /> groundwater specific criteria. <br /> • The TPHc detections in Zones B and C groundwater are likely attributed to naturally <br /> occurring hydrocarbons based on the previous forensic analysis,but may also be the <br /> result of drag-down from drilling. The TPHc concentrations in Zones B and C do <br /> not pose a risk to receptors based on the incomplete groundwater exposure <br /> pathway. Zone B and C COPC plumes satisfy the LTCP groundwater specific <br /> criteria. <br /> • Based on the soil vapor sampling results, there is not an indoor air vapor intrusion <br /> risk from the residual crude oil impacted soils for potential commercial or residential <br /> occupants. <br /> • A human health risk assessment (HHRA) was completed for development of a <br /> risk-based concentration (RBC) for TPHc in soils for both commercial worker and <br /> construction/utility worker direct contact exposures, which were deemed the only <br /> potentially complete exposure pathways. The RBCS calculated for the commercial <br /> worker direct contact with soil range from 46,142 to 107,561 milligram per kilogram <br /> (mg/kg) and the RBCS calculated for the construction/utility worker direct contact <br /> with soil range from 12,563 to 29,285 mg/kg. <br /> • Exposure pathways are effectively incomplete between chemicals of potential <br /> ecological concern (COPECs) and ecological receptors. Based on the determination <br /> that exposure pathways are functionally incomplete, further ecological risk <br /> assessment(ERA) activities are not warranted. <br /> 2.2 ROLES AND RESPONSIBILITIES <br /> This section outlines the process by which the City of Tracy or the property owner(s) <br /> may request SHELL'S assistance in identifying and managing Affected Soil originating <br /> from the Former Shell Central Valley Crude Oil Pipelines within the Limited Area. <br /> 060223(33) 3 CONESTOGA-ROVERS&ASSOCIATES <br />