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<br />Ramboll 2 Environment & Health <br /> <br />Soil Gas Investigations Advisory (Cal/EPA 2015 – the “Advisory”), and the Los Angeles Department of <br />Building and Safety’s “Site Testing Standards for Methane”. At all locations, soil vapor probes will be <br />installed at depths of 5, 10 and 20 feet bgs. A depiction of proposed nested soil vapor probe <br />construction specifications is provided in Figure 2. <br />After waiting a minimum period of 24 hours to allow the soil vapor probes to equilibrate with <br />subsurface conditions, two sequential methane measurements will be recorded at each soil vapor well, <br />using a calibrated methane field sensor capable of ppmv detection. In addition, Ramboll will collect up <br />to four samples from the soil vapor probes with the highest field methane concentrations for analysis <br />of fixed gases (including methane) by a fixed-base California certified laboratory. Fixed gases will be <br />analyzed on a rush 24-hour turnaround time by ASTM Method 1946, or similar. <br />WELL DESTRUCTIONS <br />After completion of sampling activities, soil vapor probes will be destroyed in accordance with SJCEHD <br />requirements, as follows: surface completions will be removed and all soil vapor probe materials will <br />be removed by over-drilling each probe with DPT drilling equipment to the probe total depth. Borings <br />will then be backfilled with neat cement grout. Well destructions will be performed during a separate <br />mobilization to the site, and destructions will be overseen by a SCJEHD inspector. <br />INVESTIGATION DERIVED WASTE (IDW) <br />All IDW generated during drilling and vapor probe destruction activities including soil cuttings and <br />decontamination rinse water will be containerized in 55-gallon drums and stored at the site for future <br />disposal. A soil sample will be collected from the drum(s) and analyzed for waste characterization <br />parameters. Pending the results of IDW characterization, soil will be disposed of at an appropriate <br />disposal facility. <br />SCHEDULE <br />It is our understanding that the expedited permit approval process requires approximately three days <br />to process. This scope of work has tentatively been scheduled for March 10 and 11, 2022. Well <br />destructions will be performed approximately 2 weeks after completion of sampling, anticipated to be <br />late March, 2022. <br />CLOSING <br />Please contact the undersigned if you have any questions or need additional information. <br />Sincerely, <br /> <br /> Tom Winger, PG <br /> Senior Consultant <br /> TWinger@ramboll.com <br /> <br /> <br />