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Soil Vapor Monitoring Wells Installation and Sampling Work Plan San Joaquin County Public Works 1810 E. Hazelton Avenue,Stockton,CA Page 3 5.0 FIELDWORK ACTIVITIES 5.1 SITE PREPARATION The proposed soil vapor well locations will be marked with white paint and Underground Service Alert (USA) will be notified so that utilities can be located and marked at least 48 hours prior to drilling. Additionally,Condor will utilize a private utilities locator contractor to clear the proposed drilling locations. Condor will prepare all permit applications for submittal to San Joaquin County Environmental Health Department (EHD) for the installation of the proposed soil vapor wells. Condor will receive all permit applications prior to initiating any fieldwork. Prior to commencement of fieldwork, a tailgate safety meeting will be held, and the site-specific Health and Safety Plan (Appendix C) will be discussed with, and presented to, all field personnel for their signatures. Drilling activities will be performed under the supervision of a Condor geologist in accordance with the provisions of the EHD permits. Descriptions of soil types encountered will be recorded in general accordance with the Unified Soil Classification System (USCS) on geologic logs. Soil samples will be collected from the drill cuttings for the purpose of characterizing the cuttings for disposal, if warranted. 5.2 SOIL BORING AND SOIL VAPOR WELL CONSTRUCTION Soil vapor wells will be installed approximately five to six feet bgs using the direct push drilling method. Condor and the drilling contractor will install the soil vapor wells following guidelines in the Advisory — Active Soil Gas Investigations (Advisory) prepared by the Department of Toxic Substances Control, the Los Angeles Regional Water Quality Control Board, and the San Francisco Bay Regional Water Quality Control Board (July 2015) for typical permanent soil vapor probes. Each soil vapor well will be constructed within a 2.25-inch borehole with rigid 0.125-inch outside diameter (OD) Teflon® or Nylaflow tubing. The bottom of the tubing will be fitted with a soil vapor probe filter tip to prevent water from entering the sample tubing. The filter tip will be installed within an approximately one-foot column of pre-washed #3 silica sand, or equivalent, placed within the borehole. The filter tip will rest near the midpoint of the sand column. Approximately one foot of dry granular bentonite will be placed immediately above the sand. The remainder of the borehole will be backfilled with neat cement or bentonite to near the grand surface. The top of the tubing will be sealed with a gas tight fitting to prevent infiltration of water or ambient air. The surface completion will be flush with the pavement and constructed to prevent accidental damage or vandalism. A Typical soil vapor well construction diagram is included on Figure 8, Appendix A. 5.3 SOIL VAPOR SAMPLING PROCEDURES The purpose of the soil vapor sampling is to evaluate the soil vapor intrusion risk to the Site office and maintenance building. The soil vapor wells will be purged, leak tested, and sampled at least 48 hours after installation. The soil vapor samples will be collected into laboratory-supplied Summa canisters for laboratory analysis by TO-15. Prim to soil vapor sample collection, the monitoring point and tubing will be purged at a rate not exceeding 200 mL/min. The total volume purged prior to sample collection will equal approximately three volumes of air in the open space of tubing and the sample point. Helium will be used as a field tracer during sampling. Soil vapor samples will be collected into Summa canisters with a capacity of no more than 1-liter. Negative pressure readings from a pressure gauge will be recorded both before and after the sub-slab soil gas samples are collected. Other quality assurance and quality control A �i� CONDOR