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Additional Site Assessment Report and Human Health Risk Screening Evaluation www.arcadis.com 4 • 2532 Dorset Lane. Originally, one boring (tentatively designated as B-14 Alternate) was proposed at 2532 Dorset Lane. This boring was completed in 2019, but it was redesignated as B-12 to maintain the numbering sequence with previous borings. A second boring, designated as B-13, was added at 2532 Dorset Lane in 2019. A third boring, designated as B-16, was then added at this property in 2022. • 2502 Dorset Lane. Originally, one boring (tentatively designated as B-13) was proposed at 2502 Dorset Lane. This boring was completed in 2020, but it was redesignated as B-14 to maintain the numbering sequence with previous borings. A second boring, designated as B-15 was added at this property during 2020. In addition to soil vapor probe installation activities, the Work Plan (Arcadis 2019a) proposed a comprehensive soil vapor sampling event, which would include the existing soil vapor probes B-8 through B-11, if accessible and feasible, and any newly installed soil vapor probes on the residential properties. 3.2.2 Soil Assessment Penecore Drilling, Inc., located in Woodland, California, advanced five soil borings (B-12 through B-16) under Arcadis’ supervision between 2019 and 2022. The boring locations are shown on Figure 2. On December 30, 2019, two borings (B-12 and B-13) were advanced at 2532 Dorset Lane. Boring B-12 was advanced and sampled to a total depth of 10 feet bgs on the eastern side of the property. After reaching total depth, approximately 14 inches of water entered the borehole. The boring was abandoned and a step-out boring (B-13) was advanced to approximately 8.25 feet bgs on the eastern side of the residential property. No groundwater was observed at B-13. On October 6, 2020, two borings (B-14 and B-15) were advanced at 2502 Dorset Lane. Boring B-15 was advanced on the western side of the property to a total depth of 4 feet bgs where shallow water was encountered, which may be the result of an irrigation system. As a result, the boring was abandoned, and a second boring (B- 14) was advanced to 8.25 feet bgs on the eastern side of the residential property to avoid the potential of shallow water from an irrigation system. No water was observed at B-14. On February 23, 2022, one boring (B-16) was advanced at 2532 Dorset Lane. The boring was advanced on the western side of the property as a stepout for previous borings B-12 and B-13 on the eastern side of the property. No water was observed at B-16. The soil borings were continuously logged using the Unified Soil Classification System and a Munsell color chart. The soils logged in the borings consisted predominantly of silty sand and sandy silt. Boring logs are provided in Appendix C. Soil cuttings were screened in the field using a calibrated photo ionization detector (PID) with a 10.6 electron volt lamp to monitor the presence and approximate concentration of organic vapors in soil headspace samples. The PID was calibrated to the manufacturer’s specifications a minimum of once per day and more often if field personnel deemed it necessary. The headspace samples were prepared by disaggregating a portion of soil sample in a resealable plastic bag, letting the headspace equilibrate within the bag for 5 to 10 minutes, and measuring the organic vapor concentration within the headspace using the PID. Soil sampling was conducted at borings B-12, B-13, B-14, and B-16; boring B-15 was terminated at a shallow depth and was not sampled. At each of the four sampled locations, two soil samples were collected using a slide hammer: a shallow sample at a depth of approximately 4.5 to 5.0 feet bgs, and a deeper sample at depths ranging from 5.5 to 10 feet bgs. A total of eight primary soil samples (plus one duplicate soil sample from boring B-16) were analyzed. Soil sample depths are presented in Table 1, and in boring logs provided in Appendix C.