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• • Mr. Ron Rowe <br /> Page 3 of 4 <br /> Northwest of the tankpit, soil samples from vapor well VW4/VW5 were contaminated <br /> from 15 feet to 40 feet but were non-detect from 45 to 60 feet. We propose to advance <br /> confirmation boring CB3 to a depth of 60 feet near this location (see figure). Soil samples <br /> from the depths of 20, 30, 40, 50 and 60 feet will be collected and analyzed. Soil samples <br /> from these depths will allow a comparison of current conditions with those predating soil <br /> vapor extraction. Additional soil samples may be analyzed depending upon subsurface <br /> conditions. No groundwater samples will be collected from this boring. <br /> Southeast of the tankpit, soil samples from vapor well VW1/VW2 were contaminated <br /> from 25 feet to 55 feet. No samples were analyzed below 55 feet in this boring. We <br /> propose to advance confirmation boring CB4 to a depth of 60 feet at the location depicted <br /> on the attached figure. Soil samples from the depths of 25, 40, 45, 55 and 60 feet will be <br /> analyzed to allow a comparison of current conditions with those predating vapor <br /> extraction. Additional soil samples may be analyzed depending upon subsurface <br /> conditions. No groundwater samples will be collected from this boring. <br /> East and northeast of the tankpit, soil contamination was not present in samples between <br /> the depths of 10 and 50 feet in well MW5 and between the depths of 10 and 55 feet in <br /> well MW 13. Groundwater contamination is present in each well. The purpose of <br /> sampling at this location is to assemble additional information on the vertical distribution <br /> of soil and groundwater contamination downgradient of the source area. Borin <br /> CPT5/CB5 will be advanced to a minimum depth of 110 feet. A CPT hole will be <br /> advanced as a preliminary lithological identification tool. The CPT boring will be twinned <br /> and soil and groundwater samples collected from intervals of interest as identified from the <br /> CPT data and previous data. Soil and groundwater sampling intervals will be agreed upon <br /> in consultation with PHS/EHD and RWQCB. No vadose soil samples will be analyzed. <br /> We do not propose a boring west of MW 1 and MW6 at this time. Well MW 1 is screened <br /> from 39 to 59 feet below grade and well MW6 is screened from 58 to 73 feet. These <br /> wells function as a cluster to monitor different saturated depth intervals. Information to <br /> date does not indicate encroachment of MTBE containing hydrocarbons from offsite and <br /> the relative potentiometric surfaces in the two wells indicates an upward vertical gradient. <br /> If this situation should change in the future a boring or well may be appropriate. <br /> roekMosure\nodaddenJtr <br />