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Jeff Whitworth - 2 - 13 December 2006 <br /> subsurface conditions once the target depth is reached and the probe is retracted. A flow <br /> regulator placed between the probe and Summa canister will be operated at a flow rate not to <br /> exceed 200 milliliters per minute (ml/min). Each sample will consist of three sample train <br /> purge volumes. Leak detection testing for ambient air entering the sampling system will be <br /> performed using a leak check compound such as isopropanol. The vapor samples will be <br /> transported to a fixed laboratory and analyzed for volatile organic compounds (VOCs) <br /> according to EPA Method TO-15. Shell will prepare a report describing the field investigation <br /> results and comparing the data to California Human Health Screening Levels (CHHSLs) <br /> established by Cal/EPA. Recommendations will be made in the report for additional site <br /> activities based on the investigation results and planned site development. The field <br /> investigation is currently planned for 11 December 2006. <br /> WORK PLAN REVIEW COMMENTS <br /> DTSC provided work plan review comments for a portion of the site encompassed by <br /> proposed Mountain House High School and conditionally concurred with the activities <br /> proposed by Shell in the school area. Remedial soil excavation Areas 3, 4, and 5 are located <br /> within the proposed high school development. Based on a review of existing soil arid <br /> groundwater chemical data, DTSC recommends that one soil vapor sample location be added <br /> 100 feet northeast of boring EX-513 in Area 3 as the remedial excavation did not extend to the <br /> water table. This was recommended because the nearest groundwater sample, B-231, was <br /> not analyzed for benzene, toluene, ethylbenzene, and xylenes (BTEX) and the western side of <br /> the school area is lacking groundwater data. DTSC also requested that Shell provide the <br /> proposed detection limits for volatile organic compound (VOC) analysis of the vapor samples. <br /> Shell needs to revise the sample location map to add the location northeast of Area 3 and <br /> provide the VOC detection limits as requested by DTSC. <br /> Regional Water Board staff conditionally concurs with the activities proposed by Shell in the <br /> Soil Vapor Work Plan. There was a minor discrepancy in the planned sample locations for <br /> Area 5 (Excavations 8 and 9) as shown in Figure 2b. During the 14 November 2006 meeting, <br /> participants agreed that two locations would be sampled exterior of the excavation area, one <br /> 15-foot deep sample location and one vertical profile location. The sample location map <br /> depicts only one sample location exterior of this area. Shell needs to revise and resubmit the <br /> sample location map for Area 5 to show two sample locations exterior of the excavation. Shell <br /> also needs to provide a schedule for report preparation and submittal following completion of <br /> the field investigation. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4719 or <br /> mclardy@waterboards.ca.gov. <br /> Mark W. Clardy, P.G. <br /> Engineering Geologist <br /> Private Sites Cleanup Unit <br />