Laserfiche WebLink
E11�yt® <br /> Mr James Barton <br /> ' June 14, 2004 <br /> Page 4 <br /> hydrocarbon concentrations in groundwater <br /> On October 23, 2003, the SVE remediation system was shut off as approved by the RWQCB <br /> ' The AS system is operates on a "week on-week off" basis in all aquifer zones <br /> On February 26, 2004, the groundwater flow direction for Unit A was generally to the northeast, <br /> with the hydraulic gradient ranging from approximately 0 002 feet per foot (ft/ft) to 0 007 ft/ft The <br /> groundwater flow direction for Unit B was generally to the southeast, with the hydraulic gradient <br /> ranging from approximately 0 002 ft/ft to 0 004 ft/ft The boring log and lithology data indicate that <br /> the site is underlain by interlaced silts, clays and sands Based on the data and information <br /> ' reviewed, it is expected that infiltration (rain) travels vertically through portions of the higher <br /> permeable silts and sands that are interbedded with the clays The groundwater in turn travels <br /> horizontally within the higher permeable sands Historic groundwater elevations are within 2 feet <br /> ' of each other across the entire site <br /> PROPOSED REMEDIAL APPROACH <br /> ' Groundwater monitoring data collected since the SVE system was shutdown, in October 2003, <br /> indicate that the extent of detectable benzene concentrations in Unit B has migrated beyond the <br /> existing monitoring well network to the south and east On May 13, 2004, the RWQCB issued a <br /> letter to Unocal requesting that a Work Plan and Schedule be submitted with details on the <br /> proposed approach to be used in defining the new plume limits and actions to be implemented to <br /> ' control and/or cease plume movement <br /> Although the SVE system may no longer be effective at removing petroleum hydrocarbon mass <br /> ' due to low soil vapor concentrations, it may continue to be useful to contain soil vapor pressure <br /> gradients generated by air sparging which may assist in controlling groundwater plume migration <br /> ' The first step in moving remedial activities along at this site should involve resuming operation of <br /> the existing remedial system <br /> e <br /> t <br /> 0 <br /> J IProjects10694015098-2931FinaRReports15098 Work Plan doe <br /> Over 30 Years of Excellence rn Envuormentai Services <br />