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CAB R I A samples from downgradient wells S-2 and S-3 have not contained petroleum hydrocarbons and MTBE, except for low levels of BTEX detected during the fourth quarter of 1998 Well S-1 contained 0 01 foot of separate-phase hydrocarbon during its first groundwater sampling event Since then it has contained TPPH concentrations as high as 200,000 parts per billion (ppb), benzene concentrations up to 5,300 ppb, and has not contained detectable concentrations of MTBE WORK PLAN Technical Rationale for Proposed Scope of Work ® The petroleum hydrocarbon source area appears to be the northern dispenser island Soil data from borings drilled in the vicinity of this dispenser suggest petroleum hydrocarbons have migrated vertically from the dispenser island down to groundwater No upgradient source is suspected o Groundwater flow direction has been monitored for five quarters and has predominantly been to the south and southeast Groundwater gradients have been very flat (ranging between 0 001 and 0 005) Soils encountered beneath the site consist primarily of fine grained soils (clay and silt) These conditions suggest a slow groundwater and contaminant migration rate SJCPHSIEHD requested we install an upgradient monitoring well Cambria does not recommend installing an upgradient well due to logistical and safety concerns An upgradient well would have to be locate on the sidewalk or in Fremont Street Overhead power lines are located above the sidewalks on either side of Fremont Street Installing a well in the sidewalk is not possible because of the overhead power lines Using a limited access drilling rig is one option often selected when drilling beneath power lines, however a limited access drilling rig was used at this site to drill boring SB-2 and the rig was not able to drill deep enough to install a well Installing a well in Fremont Street is a safety concern for drilling crews during installation, groundwater sampling personnel in the future, and the public (vehicle traffic) during drilling and future sampling activities • Soil samples collected 60 and 65 fbg from S-1 did not contain detectable levels of benzene or MTBE, however the detection limits for these analytes were elevated Cambria proposes drilling a deep boring (SB-4) using cone penetrometer testing (CPT) equipment in the vicinity of the northern dispenser island to assess the vertical extent of petroleum hydrocarbons in soil Cambria proposes drilling two additional soil borings (SB-5 and 241-0797 4