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SAP/QAPP Addendum Lodi-125 N Stockton Final March 24,2025 4.0 SAMPLING RATIONALE The purpose of this TBA is to identify and characterize potential hazards at the Site and to assess whether further investigation or cleanup is warranted based on the planned land use.The scope of this SAP includes: (1) a geophysical survey; (2) soil sampling; (3) soil gas sampling;and (4) indoor air sampling.Three Toeroek Team members will conduct the field activities.Any person in the field who discovers a cultural resource during the course of sampling will follow the unanticipated discovery plan in Appendix B. 4.1 Geophysical Survey A geophysical survey will be performed to assess the presence of a UST or backfill materials consistent with a former UST excavation within an area approximately 10 feet by 10 feet.The geophysical survey will be performed using a Geonics EM61 MK2 time-domain metal detector and a GSSI SIR4000 GPR with a 350- megaHertz transducer antenna.The purpose of the EM61 survey will be to detect and map possible USTs, vaults, sumps,metallic underground lines,and buried metal within the survey area.The purpose of the GPR survey will be to detect and map possible former backfilled excavations,and buried pipelines and utility lines. The EM61 data will be conducted along transects nominally spaced 2 feet apart across the survey area. GPR transects will also be conducted along transects nominally spaced 2 feet apart and over detected EM61 anomalies of interest.The recorded EM61 data will be downloaded to a portable computer in the field for preliminary analysis and quality control review in the field. EM61 data will be processed and gridded using Geosoft Oasis montaj software. Seequent Oasis montaj software will be used for overlaying and comparing EM61 and GPR data,mapping interpretations of anomalous features,and creation of final maps.In addition, detectable underground utilities and pertinent surface features will be mapped using differential global positioning system (DGPS).The geophysical survey area is shown on Figure 3. 4.2 Hazardous Building Materials Survey A hazardous building materials survey will be conducted at the unoccupied office building on the Site. Samples will be collected as needed to identify any ACM,LBP,and PCBs in building materials.Bulk building material samples will be collected by an inspector certified to conduct ACM and LBP building inspections by respective EPA-accredited training providers. Bulk samples will be collected from building materials suspected to be ACM that may be disturbed during future repairs or renovations at each building. Sampling locations will be based on results of an asbestos inspection by the Toeroek Team.The asbestos inspection will include a room-by-room assessment of the 39