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During routine soil remedial activities, the Navy excavated approximately a basketball-sized amount of soil beneath 10 inches of concrete at the entrance of a residential unit within the former Naval Station Treasure Island (NSTI) Site 12 Housing Area.
Because the Navy’s first priority in the cleanup at NSTI is public health and safety, the Navy has standard procedures in place to conduct radiological scans before, during, and after chemical cleanup work to determine whether any radiological materials are present during the soil excavation.
After removing the concrete, the Navy detected radiation above the background range in degraded material contained in the soil beneath the removed concrete. The Navy then excavated an area roughly 21 inches deep to ensure any contaminated material was safely removed.
Following the excavation, the Navy scanned the excavated area again and confirmed that all contaminated material was removed. The hole was refilled with clean soil and the concrete entrance was repaired.
Based on the results of the pre-excavation scan, which found no elevated radiation levels, and the scan results during the excavation work, Navy radiological health experts are confident there was no health risk to local residents or the public while the impacted material was in place or during its removal.
Supplemental information added October 4, 2019:
This means if a person was directly exposed to this unearthed degraded material for one hour per day for one year, the total accumulated dose over that year would be 4.7 millirem (mrem) which is about the average dose (4 mrem) a person receives from a cross-country flight from San Francisco to Washington, D.C.
It’s important to note that the 10 inches of concrete in place prior to excavation provided enough shielding such that radiation readings were indistinguishable from background prior to removal of the concrete.
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