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18 August 2021 dvanc Yee-Owned Company Project No. 21-6555f Page 3 of 4 2_X continue to be added to approximately 4.5 feet bsg. Following placement of the filter pack, approximately 12 inches of dry granulated bentonite will be placed atop the filter pack to 3.5 feet bsg. The remaining space will be sealed with hydrated bentonite to near surface grade. Following soil-vapor well installations, a minimum 2-hour stabilization period will be observed prior to soil-vapor sample collection from the vapor points. A one-liter Summa canister and 60ml purge syringe will be connected with a dedicated and serialized sampling inlet manifold to the vapor point tubing. The sampling inlet manifold will consist of an air/vapor-tight valve; a particulate filter; a flow restrictor calibrated to 150 milliliters per minute (ml/min), a stainless-steel tee-fitting, two vacuum gauges at either end of the controller and connections for both purge syringe and sampling canister (manifold assembly). Prior to sample collection, each soil-vapor well will be purged a total of three purge volumes. The purge volume will be determined by calculating the sum of the internal volume of the Teflon tubing and the volume of the boring trace. Upon achieving the targeted purge volume, the purge syringe will be disconnected, and the sample canister valve will be opened. Each canister's initial vacuum will be measured and recorded between -26 and -30 inches of mercury (in hg). Each soil-vapor well location will be isolated from ambient air by enclosing the borehole, tubing and manifold/canister assembly in a 100-liter shroud. Isopropyl alcohol (IPA) will be emitted into the shroud surrounding the well borehole, tubing and manifold/canister assembly and acts as a tracer gas to evaluate if leaks in the sampling apparatus have allowed infiltration of ambient air. Upon reaching at least -5 in hg or less, the sample canister valve will be closed, and final pressure and time recorded. The sampling port on the sampling canister will be capped with a brass end-cap. The soil-vapor sample will be labeled with sample ID, project name, date, time, and samplers' initials. The soil-vapor samples may be transported under chain-of-custody procedures to a California Environmental Laboratory Accreditation Program (ELAP)- certified laboratory for analysis. Analysis shall be performed at the sole direction of AGI. 2.3. BORING ABANDONMENT All soil borings will be permanently sealed to prevent vertical migration of potential contaminants. Soil borings shall be abandoned by backfilling with cement grout from the total depth to surface grade. The top three to six inches of the boring abandonments will be completed flush to surface grade with concrete or native material. The EHD will be notified for grout inspection at least 48 hours prior to conducting grouting procedures.