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RADIOLOGIC HEALTH BRANCH (rhb)            

Parcel A-1 Final Report Frequently Asked Questions

 

1. What was the purpose of the project?

As a result of data falsification elsewhere at Hunters Point Shipyard and public concern regarding Parcel A, the US Environmental Protection Agency (US EPA), the Navy, the Department of Toxic Substances Control (DTSC), and stakeholders from the City of San Francisco requested that CDPH, perform a radiological survey to assess the health and safety of the public and the environment at Parcel A-1. CDPH was selected due to its appropriate expertise and status as an independent department.


2. What were the key findings for Parcel A-1?

Upon completion of the Parcel A-1 project, surveyors discovered a total of 110 radiation anomalies, all except two of which were confirmed to be naturally occurring potassium-40. One was a Navy deck marker discovered at the site boundary, which did not pose a health and safety risk to anyone who happened to be at that spot previously. There was another reading that was barely detectable. When staff went back to re-test the area they did not find an elevated reading. Because the soil was very wet (due to prior rains) when the re-testing occurred – and because heavy water content can shield some radiation - CDPH plans to re-test this area once the soil is dry, out of an abundance of caution. This retesting should occur no later than March 2019.


3. Do the findings of the final A-1 report differ from the preliminary summary that CDPH previously released?

Yes, the final report did identify additional anomalies beyond those identified in the preliminary summary dated November 16, 2018. The preliminary summary identified 89 radiation anomalies in total. After the final quality checks of readings and additional verification were completed, CDPH identified an additional 21 radiation anomalies, bringing the total number to 110 radiation anomalies. (Please see the previous answer for more detail on the anomalies identified.) The conclusion, that no radiological health and safety hazards to the residents of Parcel A-1 were observed, is unchanged.


4. Was there a hazard from the deck marker?

The radium containing deck marker, which was located at the bottom of the hill in an undeveloped area behind a fence and buried under approximately 10 inches of soil, had a radiation reading of 0.09 mrem/hr on soil surface. Radium is a radioactive substance found in nature and is produced by the radioactive decay of uranium. The amount of radiation output by this deck marker would not have resulted in a health or safety hazard to anyone who happened to be at that spot previously. A person would have to be sitting on top of the spot for over 16 hours to receive a radiation dose equal to the amount received from a simple dental x-ray. The Navy remediated the area with CDPH oversight and once the marker was removed the surrounding soil was scanned and was determined to be clear of any residual radioactivity.


5. What is the significance of the low energy peak finding during data quality review?

During the data quality review conducted in November, CDPH noticed an unusual spectrum that had been collected in August. The reading was found on a southwest hillside not considered accessible to the general public. The radiation readings were barely detectible, only slightly above baseline counts. For comparison, the reading on the deck marker (which did not pose a health and safety risk) was about ten times this reading.

On December 3, 2018, CDPH returned to take a supplementary reading on that site. Those readings failed to replicate the original anomaly, indicating that there is no anomalous radiation at this time. However, it had rained prior to the readings, and water can interfere with or dampen an energy signature. To ensure that the wet soil had not interfered with the reading, CDPH will repeat the supplementary readings once the soil is dry. CDPH anticipates that soil will be sufficiently dry by March 2019 for these additional measurements to be taken. However, if the soil dries before March, CDPH will complete these measurements sooner. An addendum to this report will be issued once the additional measurements are completed. (This anomaly is noted as "pending" in Table 1.)


6. Would rain or landscape irrigation have masked other sources of radiation during the CDPH scan of Parcel A-1?

With the exception of the December 3rd follow-up noted above, the entire Parcel A-1 scanning work occurred in clear dry conditions. The average moisture density of soil under normal residential use conditions is very low compared to soils where heavy rains and significant amounts of water seep into soils. Staff found the average residential areas were of low water content, which did not affect the surveying or the survey results.

7. What were the major elements of the project?


The CDPH survey included the scanning of all outdoor areas of Parcel A-1 accessible to CDPH staff in order to assess the radiological health and safety of the public and the environment. Broadly, this survey included the use of instruments that were towed along such areas as roads and sidewalks (‘towed array’), as well as handheld instruments that were used to cover less accessible areas (‘walk over’).

The walkover component employed the use of highly sensitive handheld radiation survey detectors with trained and experienced CDPH health physicists performing gamma walkover surveys of soils, vegetation and hardscaped areas around the existing buildings and in accessible areas. This included areas that were not in the original work plan, but which had been added in response to resident requests (e.g., most of the slopes, large dirt pile to south of residence area, private/semi-private outdoor areas).

For the towed array component, CDPH used a Radiation Solutions RS-700 system that consists of two large volume, highly sensitive gamma mapping detectors to perform gamma scans of roads, sidewalks, accessible hardscaped areas and areas where vegetation was absent or less than four inches in height.


Any anomalies that were detected were subsequently investigated by using gamma spectroscopy radioisotope identifiers, Model-Canberra Inspector 1000, that measure the energy range of the suspected anomaly and therefore exactly identify the radioisotope causing the anomalous reading. CDPH employed this instrument 110 times for this purpose over the course of the project and conducted an additional 55 supplemental readings that did not have anomalies but were used for data validation.


8. Why didn’t you test the soil?

As part of the redevelopment, considerable excavation and grading of soil, use of some of that soil as fill, and import of clean soil has occurred throughout Parcel A-1. Other new materials such as sidewalks, streets and landscaping have been added, such that the area available to survey in Parcel A-1 is mostly developed and covered with concrete, asphalt, or landscaping soils brought in subsequently as part of the redevelopment. Scanning is the most effective method for detecting discrete (i.e., not uniformly distributed) radiation sources. However, when the gamma radiation survey detected radiation anomalies above the work plan trigger levels, or radiation that could be a potential concern to public health, additional testing was conducted. In addition, large volumes of excavated original A-1 soil had been transferred and laid onto Parcel A-2. The A-2 scan will provide further information regarding anything that may have been present on A-1 historically.

 
9. What is potassium-40?

Potasium-40 is a naturally occurring radioisotope of potassium, omnipresent in the biological world. It is a substance found throughout nature, including in plants, animals, various foods, and our bodies. Detection of potassium-40 is not unusual for a radiation scan of this type and is not a health or safety concern for people or the environment.


10. Why wasn’t indoor scanning included?

Because the soil material under residences is likely to be similar to what is present in the outdoor areas, and because there is less shielding outdoors, scanning outdoor surface areas was representative of Parcel A-1 and provided the best opportunity to identify any radiation of concern in the material present there. Considerable excavation, grading, mixing and addition of clean fill occurred as part of the development prior to construction of the residential units. And the installation of building foundations, including at least 4" to 6" concrete slabs, resulted in additional shielding from anything in the soil below.


11. How did you determine background?

A developed area such as Hunters Point contains dozens of different regions of material composition, construction materials choices, and landscaping. For this reason, this survey evaluated every identifiable material mix against itself to look for statistically excessive measurements. For example, if samples are taken in a grassy field and compared to samples from an asphalt parking lot, the averages and standard deviations of the regions are unlikely to be similar because the elemental composition is different. This approach, comparing readings to what is expected for the material and location, helps to distinguish between normal and anomalous readings.


12. Why were the instruments you used the appropriate type?

The detection instruments that were used are state-of-the-art, highly-sensitive, calibrated, instruments that are appropriate for performing sensitive gamma ray scans. Sodium iodide detectors were used due to their high sensitivity to gamma radiation. Radiation may have alpha, beta or gamma activity, but only gamma radiation may penetrate soil and other materials now present at Parcel A.

13. How many total static measurements did you perform?

Over the course of the project surveys completed 4,327 total static counts using highly sensitive sodium-iodide 2"x 2" detectors. Static counts, or measurements, are when surveyors, who used handheld radiation survey detectors, stopped about every 50 feet to take one minute static counts, which are used to further validate walkover readings. ​​

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