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Shell notes that soil impacts extend deeper than 15 feet bgs in Areas B-3, B-4, and B-9; <br /> however, excavations in these areas will not extend vertically beneath the target depth of 15 <br /> feet. Shell is committed to addressing additional contamination related to the former pipeline if <br /> it becomes apparent during site grading. <br /> Soil will be segregated in stockpiles based on visual and olfactory signs of contamination. Soil <br /> disposal characterization samples collected from the stockpiles will be composited at a 4:1 <br /> ratio for every 1,000 cubic yards of soil. Soil samples will be tested according to analytical <br /> requirements of the landfill. If contaminants are detected in stockpiles segregated as clean <br /> soil, the level of contamination will be discussed with Regional Water Board staff to evaluate <br /> whether reuse as backfill is appropriate. Remaining excavations not backfilled with native soil <br /> will be backfilled with clean imported soil. The backfill will be compacted in 6-inch lifts to 90 <br /> percent relative compaction in excavations less than 10 feet bgs and to 95 percent relative <br /> compaction in excavations greater than 10 feet bgs. <br /> Soil samples for possible leachability testing will be collected from borings beneath the former <br /> pipeline using direct-push equipment. Soil samples will be analyzed for TPHd and TPHcr <br /> using EPA Method 8015. Based on the soil sample TPH concentrations, selected samples <br /> may be tested for leachability using the Soluble Threshold Limit Concentration (STLC) <br /> methodology utilizing de-ionized water. <br /> A written report will be submitted summarizing the investigation findings and providing <br /> recommendations for additional work, if warranted. Leachability data generated from the soil <br /> samples will be used to evaluate TPH concentrations that may pose a threat to groundwater <br /> quality. <br /> The Well Installation Plan proposes the installation of three groundwater monitoring wells in <br /> Areas B-3 and B-4 to evaluate the depth to groundwater. Borings for the wells will be <br /> advanced using hollow-stem auger equipment. The wells will be constructed installed to about <br /> 30 feet bgs using 2-inch-diameter polyvinyl chloride (PVC) casing with approximately 15 feet <br /> of 0.020-inch slotted casing at the bottom. The annular space will be backfilled with No. 2-12 <br /> filter sand to approximately 1 foot above the well screen followed by a 6-inch thick layer of <br /> hydrated bentonite pellets. The remaining annular space will be backfilled with neat cement to <br /> 1 foot bgs. The wellheads will be completed in traffic-rated well vaults. The top of the well <br /> casings will be land surveyed for horizontal and vertical position by a California licensed <br /> surveyor. The wells will be developed using a combination of surging and bailing until physical <br /> parameters of pH, temperature, electrical conductivity, and turbidity have stabilized or a <br /> minimum of 10 well casing volumes of water have been removed. Well installation activities <br /> will be documented in the report of the site remedial soil excavation activities. According to <br /> SAIC, groundwater level data will be used to evaluate the viability of excavating soil down to <br /> the groundwater table in Areas B-3 and B-4. <br /> Regional Water Board staff concurs with the Well Installation Plan and conditionally concurs <br /> with the activities proposed in the Soil Removal Plan. To clarify the Soil Removal Plan, Shell <br /> should provide a written description of the frequency of confirmation soil sampling and <br /> propose a suite of chemical analyses for these samples. In addition, Shell should describe <br /> where soil borings are to be completed for possible leachability testing. For future reference, <br /> the Soil Removal Plan states that Water Quality Objectives (WQOs) established by the <br />