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Hess-Dubois Cleaners, Stockton - 3 - 12 July 2023 <br /> a. Collect crawl space (or indoor air) sample under the northeast corner of <br /> house. <br /> b. Collect only one outdoor air sample between the crawl space sample and <br /> the SG2 locations. <br /> c. Perform the pre-sampling inspection prior to collecting the crawl space <br /> and outdoor air samples. The inspection should be done in accordance <br /> with the Work Plan and the 2023 Guidance. <br /> d. Submit an off-Site vapor intrusion evaluation by 13 October 2023. This <br /> evaluation should present the results of the crawl space and outdoor air <br /> sampling and present an evaluation of the risk of vapor intrusion to the <br /> house on the adjacent residence. This evaluation should be done in <br /> accordance with the 2023 Guidance, and utilize crawl space air, outdoor <br /> air, and soil gas data. If a vapor intrusion risk is identified, please include <br /> recommendations for a scope of work to mitigate that risk. <br /> 8. Please proceed with completing the confirmation sampling of the existing soil gas <br /> wells. Please perform the confirmation sampling using the same methodology as <br /> used for the February 2022 soil gas sampling, including oxygen analysis, use of <br /> a shroud, and quantification of the leak detection compound concentration in <br /> both the sample and under the shroud. Please submit a confirmation sampling <br /> report by 13 October 2023. This report should include technical conclusions <br /> based on the data and an evaluation of the data in comparison to CVOC human <br /> health risk and to the Low Threat UST Case Closure Policy (LTCP) for petroleum <br /> compounds. This report may be combined with the off-Site vapor intrusion <br /> evaluation. <br /> If you have any questions or concerns regarding comments in this letter or regarding the <br /> Site, please contact Alan Buehler at (916) 464-4615 or by email at <br /> alan.buehler(a�_waterboards.ca.gov. <br /> Alan M. Buehler, P.G. *aIvVin ffman, P.G. <br /> Engineering Geologist Senior Engineering Geologist <br /> < CS\pNAL G�O�0 C RICK <br /> 4 ALAN M. BUEHLER <br /> No.9340 9542 r <br /> OFCA1AFC jFOP CX Vl <br /> cc: Jasleen Singh & Brian Millman, AdvancedGeo Inc., Stockton (email) <br />