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� M <br /> r <br /> importantly, shallow soil vapor samples were collected from Area 5 and concentrations <br /> were below applicable screening levels. <br /> Groundwater flow directions were generally north-northwesterly with the exception of <br /> Areas 3 though 7 in Neighborhoods C and D where north-northeasterly and <br /> southeasterly flow directions were observed. Gradients were shallow ranging from <br /> 0.002 to 0.006. Groundwater samples did not contain any detectable TPHc, TPHd, <br /> BTEX, or naphthalene. The groundwater analytical data demonstrate that the prior <br /> remedial excavation activities were successful in protecting groundwater. <br /> Sulfur compounds in soil and groundwater samples were evaluated and demonstrated <br /> no significant increase in sulfur concentrations as a result of the former crude oil release. <br /> According to the RWQCB sulfate and sulfur concentrations were determined to be <br /> within background levels (RWQCB letter regarding Subsurface Investigation and Third <br /> Quarter 2009 Groundwater Monitoring Report, Former Shell Central Pipelines, Neighborhoods <br /> B, C, & D, Mountain House, San Joaquin County, April 8, 2010). Based on these findings <br /> no further testing of these constituents was warranted. <br /> 2010 Soil Vapor Sampling. CRA performed soil vapor sampling activities in July 2010 in <br /> the vicinity of the proposed Mountain House High School as recommended by the <br /> RWQCB in an August 13, 2008 letter to Shell. Soil vapor samples from SVP-1 were <br /> collected from each screened interval (5 fbg and 16 fbg). The soil vapor samples were <br /> analyzed for BTEX and naphthalene. None of these compounds were detected in any of <br /> the soil vapor samples collected. <br /> Groundwater Monitoring. Quarterly groundwater sampling and monitoring has been <br /> performed at Neighborhoods B, C, and D the site since September 2009. Groundwater <br /> samples have contained no constituents above reporting limits with the exception of <br /> seven samples collected in March 2010. Groundwater samples from Neighborhood B <br /> MW-19 and Neighborhoods C and D MW-3, MW-4, MW-6, MW-9, MW-13, and MW-14 <br /> contained TPHd ranging from 54µg/L (MW-4) to 79µg/L (MW-6). All TPHd <br /> concentrations were below the water quality objective of 100µg/L (water quality <br /> objective referenced in August 11, 2010 RWQCB letter regarding Second Quarter 2010 <br /> Groundwater Monitoring Report, Former Shell Central Pipelines, Neighborhoods B, C&D). <br /> 060222 p 1I B-4 CONESTOGA-ROVERS&ASSOCIATES <br />