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Revised Workplan-Additional Site Investigation for PFAS BSK Project E20-016-01F Stockton Metropolitan Airport(SCK) March 1, 2023 Stockton, California Page 22 4. As required by California regulations, a hand auger will be used to explore the upper 5 ft of each boring. If deemed necessary by SCK, an air knife rig will be used to excavate a 10-foot deep pilot boring next to or within any proposed boring locations that may be located in the vicinity of deep underground utilities. 6.3.1.3 Site Access and Restrictions Prior to Site mobilization,a list of BSK field personnel,subcontractor,and vehicles will be provided to SCK for security and access coordination. Upon arrival each day,the field staff will check in with the SCK Point of Command (POC) person. Anticipated work hours are between 7:00 AM and 6:00 PM during the work week. Site personnel will be accompanied by a SCK-approved escort. 6.3.2 ADVANCEMENT OF BORINGS AND SAMPLE COLLECTION Drilling activities will be performed by a California C-57 licensed drilling contractor subcontracted by BSK. Soil borings include deep borings for monitoring well installation and vertical groundwater sampling (estimated to be up to 90 ft depth based on BSK's 2020 Preliminary Investigation). Borings advanced for subsequent monitoring well installation,orvertical groundwater sampling,will have soil samples collected for chemical analysis in the upper 10 ft of the boring (i.e., 1 ft, 5 ft, and 10 ft bgs). Monitoring well borings will be advanced using a Hollow Stem Auger(HSA)drilling rig. A Global Positioning Satellite (GPS) device (e.g., cellular phone with internet access) will be used to record locations of each boring. 6.3.2.1 Soil Sampling Subsurface soil samples for chemical analysis will be collected during advancement of the monitoring well and vertical groundwater definition borings with a HSA drilling rig using a Modified California or Standard Penetration Test (SPT) split-barrel sampler. Soil from the monitoring well borings, and borings advanced for vertical groundwater sampling will be collected continuously for the entire depth of the boring using a Modified California or SPT split-barrel sampler. Subsurface soil samples from the monitoring well borings will also be logged according to the USCS. Lithologic classifications and observations will be recorded on a drilling log and a monitoring well construction log (see Appendix A-A of the SAP). The following information will generally be recorded on the soil sampling logs: • Depth (total and any other relevant depth information). • USCS classification (ASTM D2487-17). • Color. • Moisture content(i.e., dry, moist, wet, saturated). • Density(relative to soils found on site). • Depth to groundwater, if encountered.