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Confirmation Sampling Investigation Work Plan STAND Affordable Housing Page 3 A more detailed summary of the Passive Soil Gas Investigation can be found in October 12, 2018 report prepared by Condor, "Report of Findings Passive Soil Gas Survey STAND Affordable Housing, 2222 and 2244 S.Airport Way,Stockton,CA". 4.0 CONFIRMATION SAMPLING FIELD PROCEDURES Four semi-permanent soil vapor test wells are proposed as shown on Figure 3, Appendix A. The semi- permanent soil gas probes will be placed as follows: 1. In the southwestern corner of the Site where the highest mass of PCE was found in the passive soil gas survey conducted at the Site; 2. At the location of the former dry cleaner on Site where PCE was previously detected in soil gas collected from a temporary soil gas probe at a concentration that exceeded the California Human Health Screening Level (CHHSL); 3. At a location to be determined based upon proposed development plans to evaluate potential vapor intrusion concerns to future structures;and, 4. At a second location within the proposed building footprint or, alternatively, near well MW-1 at the eastern property boundary to evaluate soil gas vapors where concentrations in groundwater were found to be highest on Site. 4.1 SITE PREPARATION The proposed monitoring 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. Condor will prepare all permit applications for submittal to San Joaquin County Environmental Health Department(EHD)for the installation of the proposed soil vapor test wells. Condor will receive all permit applications prior to initiating any fieldwork. 4.2 FIELDWORK PREPARATION Prior to commencement of fieldwork, a tailgate safety meeting will be held and a site-specific Health and Safety Plan 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. 4.3 SOIL VAPOR PROBE CONSTRUCTION Semi-permanent soil vapor probes will be installed to a depth of approximately 5.5 feet bgs using the direct push drilling method. Condor and the drilling contractor will install the soil vapor probes 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 semi-permanent soil vapor probe will te. 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 6-inch 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 grout to near the ground 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 ;�� CONDOR