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Phase II Environmental Site Assessment Report Satellite Apartments 530 N.Stanislaus Street APN 139-224-090 Page 2 3.0 SAMPLING PROCEDURES AND RATIONALE 3.1 SITE PREPARATION Condor obtained a boring permit from the San Joaquin County Environmental Health Department (EHD) prior to the start of field activities. A copy of the permit issued by EHD is included in Appendix B. Underground Services Alert(USA)was notified at least 48 hours in advance to identify utilities in and near the work area.Prior to performing work,all Site personnel conducted a tailgate safety meeting and reviewed the site-specific health and safety plan(HASP). Condor geologist, Luke Castle (CA Professional Geologist number 9945), observed drilling and collected samples at the Site on May 13, 2024. All drilling was conducted by TEG Norcal, a California licensed drilling contractor(C57-706568),under Permit#WP0045465 issued by EHD. 3.2 ACTIVE SOIL GAS SAMPLING PROCEDURES TEG Norcal, under Condor's oversight, installed vapor implants at two locations (ASG-1 and ASG-2) at depths of 5.5 feet bgs.ASG-1 was installed near Grant Street on the eastern portion of the Site parking lot, and ASG-2 was installed in the parking lot between ASG-1 and the apartment complex(Figure 3,Appendix A). The vapor implants were installed by advancing a 1-inch diameter stainless steel rod using the Direct Push rig to depth and lowering 1/8-inch diameter Nylaflow tubing with the implant probe at the tip. The annular space was then constructed with 1 foot of sand pack around the sample probe followed by 0.5 inches of dry bentonite, then hydrated bentonite to the surface. Prior to purging and sampling, the wells were allowed to rest for at least two hours to equilibrate. Shut-in tests were performed to confirm that no leaks were present in the sample train. The wells were then purged of three void volumes (tubing and sandpack) and sampled with a 1,000-milliliters (mL) Summa canister attached to a flow regulator set to sample at a rate less than 200 milliliters per minute(mL/minute). Leak detection testing was performed to evaluate whether there was intrusion of ambient air into the vapor samples.During the collection of each vapor sample, 1,1-difluoroethane(DFA)was applied within a shroud placed directly around the sampling interface at the surface.DFA was included in the laboratory analyses. 3.3 SUB-SLAB SOIL GAS SAMPLING PROCEDURES TEG Norcal, under Condor's oversight, installed sub-slab vapor sampling points by drilling into the concrete slab at two locations (Sub-1 and Sub-2) using a rotary hammer drill with a 5/8-inch drill bit and inserted 1/8-inch Nylaflow tubing with plastic air diffuser tips set at approximately 6 inches bgs,which was 2 inches beneath a 4-inch concrete slab. The hole around the tubing was sealed at the surface with hydrated bentonite. Sub-1 was installed near the southeast corner of the apartment building and Sub-2 was installed near the center-west corner of the apartment building(Figure 3,Appendix A). Shut-in tests were performed to confirm that no leaks were present in the sample train. The tubing was then purged of approximately 100 mL and sampled using a 1,000-mL Summa canister and flow regulator set at a flow rate no greater than 200 mL/minute. Leak detection testing utilizing DFA was performed to evaluate whether there was intrusion of ambient air into the vapor samples following the same protocol as for the active soil gas sampling procedures, above. i,i CONDOR