Radiological risk assessment of the Hunters Point Naval Shipyard (HPNS)

Hunters Point Naval Shipyard in San Francisco, California was deemed a Superfund site by the USEPA in 1989 due to chemical and radiological contamination resulting from U.S. Navy operations from 1939 to 1974. During characterization and remediation efforts, over 50,000 radiological soil samples and 19,000 air samples were collected. This risk assessment, conducted in accordance with federal guidelines, represents the first comprehensive evaluation of past, present, and future health risks associated with radionuclides present at the site. The assessment indicated that before site remediation, most radionuclide soil concentrations were at or near local background concentrations. Had such low remedial goals not been established, significant remediation of surface soils would not have been necessary to protect human health. The pre-remediation lifetime incremental cancer morbidity risks for on-site workers and theoretical on-site residents due to radionuclide contamination were found to be 1.3 × 10^-6 and 3.2 × 10^-6, respectively. The post-remediation risks to future on-site residents were found to be 6.3 × 10^-8 (without durable cover) and 3.7 × 10^-8 (with durable cover), while post-remediation risks to on-site workers were found to be 2.6 × 10^-8 (without durable cover) and 1.6 × 10^-8 (with durable cover). Risk estimates for all scenarios were found to be significantly below the acceptable risk of 3 × 10^-4 approved by regulatory agencies. Upwind and downwind air samples collected during remediation indicate that remediation activities never posed a measurable risk to off-site residents. This risk assessment emphasizes the importance of establishing clear and scientifically rigorous soil remedial goals at sites as well as understanding local radionuclide background concentrations.