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Additional Site Assessment Report and Human Health Risk Screening Evaluation www.arcadis.com 9 5.3 Quality Assurance/Quality Control Sample Analytical Results Two field duplicate samples were collected. The field duplicate sample for soil, DUP1, was associated with primary soil sample B-16. The field duplicate sample for soil vapor, DUP-1, was associated with primary soil vapor sample B-16. The primary and duplicate samples for both soil and soil vapor typically showed similar detections. Based on these results, the analytical data are considered acceptable for their intended purposes. 6 Human Health Risk Screening Evaluation Three previous human health risk screening evaluations (HHREs) were performed in 2009, 2012, and 2019. Conclusions from these HHREs are provided below. Additionally, an updated HHRE is provided based on the data collected between 2019 and 2022. 6.1 2009 Science Applications International Corporation Human Health Risk Screening Evaluation Summary Soil analytical data from previous investigations up to 2009 were used to evaluate hypothetical residential and construction worker health risks. Potential on-site residential cancer risks were 1E-06, equivalent to the incremental lifetime cancer risk point of departure, and an excess cancer risk equal to or less than this threshold is considered acceptable by regulatory agencies. The total potential noncancer hazard from oral, dermal, and inhalation exposures to on-site soils was estimated to be 0.4. This level of hazard was less than a hazard index (HI) of 1, and therefore indicated an acceptable noncancer health hazard for exposures to on-site soils for a hypothetical future resident. Groundwater contact was eliminated as an exposure pathway and was not evaluated in this HHRE. Potential on- site construction worker cancer risks were 4E-08, and the noncancer health hazards were estimated at 0.1. SAIC concluded that the HHRE results indicate that the Site does not pose an unacceptable health risk to future construction workers. SAIC concluded that no remedial action was necessary at the Site to protect human health, and that a risk management decision of no further action could be made for on-site affected soils (SAIC 2009). 6.2 2012 Science Applications International Corporation Human Health Risk Screening Evaluation Summary SAIC evaluated cancer risks and noncancer hazards using additional collected analytical data from borings B-1 through B-7. The cancer risks and noncancer hazards were estimated using the same assumptions and methodology as their 2009 HHRE. The estimated excess cancer risks for both residential scenarios evaluated were within, and at the lower end of, the risk management range of 1E-06 to 1E-04 established by the California Environmental Protection Agency (Cal/EPA) and the USEPA. The estimated cancer risk for the construction worker scenario was less than the incremental lifetime cancer risk point of departure, and an excess cancer risk equal to or less than this threshold is considered to be acceptable by the Cal/EPA and USEPA. The noncancer