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Mr. Roger Smith - 3 - 9 September 2021 <br /> Following completion of soil vapor sampling, groundwater samples will be collected from <br /> monitoring wells MW-513 and MW-713 for analysis of 1,2-DCP and chloroform by EPA <br /> Method 8260B; 1,2,3-TCP by EPA Method 8260 in selected ion monitoring mode; and <br /> DBCP by EPA Method 504.1. Site-specific correlation factors will be developed for 1,2- <br /> DCP, 1,2,3-TCP, DBCP and chloroform by evaluating the soil vapor and groundwater <br /> sample results. These correlation factors will be used to evaluate potential vapor <br /> intrusion risk to residents based on groundwater VOC concentrations in samples <br /> collected from off-Site monitoring wells and determine whether off-Site investigation is <br /> warranted. <br /> COMMENTS <br /> 1 . Central Valley Water Board staff concur with the proposed on-Site investigation work <br /> as an initial step in assessing soil vapor intrusion for the adjacent residential area. <br /> Because on-Site conditions may not be fully representative of the conditions beneath <br /> the off-Site residential area (e.g., presence of utility and sewer lines that may act as <br /> preferential pathways for VOCs to the residential homes), off-Site soil gas <br /> investigation may still be necessary to better evaluate vapor intrusion for the off-Site <br /> residential area. Glenn Springs and Simplot/Geosyntec will need to demonstrate that <br /> on-Site conditions and Site-specific correlation factors that will be developed are <br /> applicable for evaluating off-Site vapor intrusion and determining whether off-Site <br /> soil gas investigation is warranted. <br /> 2. You may proceed with the proposed field work. Please notify our office 72 hours <br /> prior to initiation of the field work to provide staff the opportunity to observe the work. <br /> 3. The soil vapor investigation report should be submitted to GeoTracker by <br /> 15 November 2021. <br /> If you have any questions regarding this letter, you may contact Aimee Phiri at (916) <br /> 464-4746 or by email at aimee.phiriCa).waterboards.ca.gov. <br /> oQROFESS/ON <br /> Digiit 11 signed by Aimee �E C. P <br /> Aimee C. � <br /> c ,\4� P�� HPC fy�, <br /> Phiri <br /> Dal 02,.09.09 !� 2 <br /> 0:44:38-07'00' W C 72612 r+i <br /> AIMEE PHIRI, P.E. <br /> Water Resources Control Engineer sf civic <br /> Federal/Private Site Cleanup Unit �Tf OF CA01 <br /> Digitally signed by Nathan NAL�EO� <br /> Caeb 02 ¢� NpM CASE ` \` <br /> /! Dalt e 2021.09.09 Q h <br /> 11:05:58-07'00' <br /> i <br /> NATHAN CASEBEER, P.G. 8359 <br /> Senior Engineering Geologist <br /> Federal/Private Site Cleanup Unit <br />