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Mr. Mark Clardy <br /> ' Page 3 <br /> April 3,2006 <br /> Petroleum Hydrocarbon-Impacted Soils <br /> During the site investigation, 12 discrete areas were identified with soil impacted by petroleum <br /> hydrocarbons in the TPH diesel range(TPH-d) and TPH-cr,at concentrations greater than 50 <br /> ' milligrams per kilogram(mg/kg). In nine of the areas,petroleum hydrocarbon concentrations <br /> were observed to attenuate at a depth of around 12 to 15 feet. SPH was observed in three borings <br /> (BB-5,BB-40, and BB-176) in soil above 8 feet. Elevated petroleum hydrocarbon <br /> ' concentrations were observed to extend to groundwater in three areas(B-3,B-4, and B-9). <br /> BTEX compounds were generally not detected, and where detected,were present at low <br /> concentrations in the soil samples(<10 mg/kg). Benzene was not detected in any of the soil <br /> samples. As noted above,Attachment 1 presents tables and figures from the November 2005 site <br /> investigation report. <br /> Dissolved Petroleum Hydrocarbons <br /> Groundwater impact was observed exceeding the RWQCB water quality objectives in seven of <br /> ' the 12 areas. TPH was detected at concentrations ranging from 75 micrograms per liter(pg/L)to <br /> 21,000 pg/L(TPH-d or TPH-cr). SPH was observed in one groundwater sample. BTEX <br /> compounds were detected at low concentrations in groundwater samples,with benzene detected <br /> to a maximum of 0.42 pg/L, and the remaining BTEX compounds detected to a maximum of 30 <br /> pg/L <br /> TRANSPORT MECHANISMS <br /> Petroleum hydrocarbons would be expected to migrate vertically through soil, and upon(if) <br /> reaching groundwater,would be expected to migrate with the general groundwater flow. As <br /> ' noted,petroleum hydrocarbon concentrations commonly attenuate at a depth of approximately 12 <br /> to 15 feet,and generally do not extend deeper than 15 feet(except in the areas noted above). <br /> Where groundwater impact was observed,the lateral extent appears to be limited, as groundwater <br /> ' concentrations decreased sharply within 25 feet of the former pipeline alignment. <br /> PATHWAY/RECEPTOR EVALUATION <br /> ' Potential receptors include human and ecological receptors. The remedial efforts described <br /> below will remove shallow impacted soil,which will likely preclude physical contact with <br /> ecological receptors. As the property is to be redeveloped as residential and commercial <br /> property, ecological receptors are not likely following redevelopment. Thus,the following <br /> sections evaluate the human receptor scenarios. Note that while the sections below discuss <br /> groundwater protection separately from human health protection, human health issues are a <br /> component of the groundwater protection policy;however,the groundwater protection policy <br /> also includes a general resource degradation component. <br /> ' Human Health Protection <br /> At the site,potential human health exposure pathways consist of direct contact with and <br /> ingestion of soil, inhalation of vapor from soil and/or groundwater,and direct contact with and <br /> ingestion of groundwater. Direct contact with and ingestion of groundwater are not complete <br /> pathways. Therefore, the remedial approach as it relates to human health protection needs to <br />