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Geospte& <br /> consultants <br /> 2. INVESTIGATION ACTIVITES <br /> To characterize the soil and groundwater within the former UST excavation and assess the <br /> potential presence of LNAPL within the former UST 817B excavation area, Geosyntec will <br /> conduct the following activities: <br /> • Prior to field activities, the depth to groundwater will be measured in nearby wells <br /> (917-01, 917-03, 917-04, 917-05, 917-06, 917-07, 917-08, 917-09, 917-10, 917-11, <br /> and 917-14). <br /> • Two borings will be advanced within the former UST 817B excavation area to the top <br /> of the concrete slab (presumed to be approximately 7 feet bgs). The slab will not be <br /> penetrated during the boring advancement. <br /> • To assess the vertical distribution of contaminants within the former UST 817B <br /> excavation area, subsurface soil samples will be collected from each boring at depths <br /> of approximately 2 feet bgs, 4 feet bgs, and 6 feet bgs. <br /> • Following soil sample collection, a temporary casing with a 5-foot-long screen <br /> interval will be installed in the boring, and the groundwater will be allowed to <br /> equilibrate within the casing. It will be assumed that equilibration will have been <br /> achieved when the depth to groundwater stabilizes. <br /> • If groundwater is present at depths shallower than 7 feet bgs (the top of the concrete <br /> slab), an oil-water interface probe will be used to assess if LNAPL is present and its <br /> relative thickness. <br /> • A sample of the LNAPL (if present) and a groundwater sample, if present, will be <br /> collected through the temporary casing. <br /> • Soil and grab groundwater samples collected will be chemically analyzed for TPH-g, <br /> TPH-d, volatile organic compounds (VOCs), and total organic carbon(TOC). <br /> LNAPL samples, if collected, will be analyzed for TPH-g and TPH-d. <br /> The analytical results will be compared against the SFBRWQCB's ESLs for commercial uses <br /> (SFBRWQCB, 2019). These ESLs are summarized in Table 1. Target locations, sampling <br /> depths, and target analytes are summarized in Table 2. The remainder of this Work Plan <br /> describes the scope of work for implementing the above activities. <br /> Final Investigation Work Plan Addendum—UST 817B 4 June 24,2022 <br />