Figure 13. Calculated Effective Dose Equivalent to the Hypothetical Maximally
Exposed Individual, 1991-1995.
In 1995, potential public doses resulting from exposure to Hanford liquid and gaseous effluents were evaluated to determine compliance with pertinent regulations and limits. These doses were calculated from reported effluent releases and environmental surveillance data and Hanford site-specific parameters.
The potential dose to the maximally exposed individual in 1995 from Hanford operations was 0.02 millirem (2 x 10-4 milliseivert), compared to 0.04 millirem (4 x 10-4 milliseivert) calculated for 1994 (Figure 13). The radiological dose to the local population of 380,000 from 1995 operations was 0.3 person-rem (0.003 person-seivert), compared with the dose of 0.6 person-rem (0.006 person-seivert) calculated for 1994 operations. The average per capita dose from 1995 Hanford operations was 0.0009 millirem (9 x 10-6 milliseivert). The current DOE radiological dose limit for an individual member of the public is 100 millirem per year (1 milliseivert per year), and the national average dose from natural background sources is 300 millirem per year (3 milliseivert per year) (Figure 14). The average individual potentially received 0.001% of the standard and 0.0003% of the 300 millirem per year received from typical natural sources.
Figure 13. Calculated Effective Dose Equivalent to the Hypothetical Maximally
Exposed Individual, 1991-1995.
Figure 14. National Annual Average Radiation Doses from Various
Sources.
Special exposure scenarios not in the above dose estimates include the potential consumption of game residing on the Hanford Site and exposure to radiation at a publicly accessible location with the maximum exposure rate. Doses from these sources also would have been small compared to the dose limit.
Dose through the air pathway was 0.06% of the EPA limit of 10 millirem per year.
The "boundary" radiation dose rate is the external radiation dose rate measured at publicly accessible locations on or near the Site. The "boundary" dose rate was determined from radiation exposure measurements using thermoluminescent dosimeters at locations of expected elevated dose rates onsite and at representative locations offsite. These boundary dose rates should not be used to calculate annual doses to the general public because no one can actually reside at any of these boundary locations. However, these rates can be used to determine the dose to a specific individual who might spend some time at that location.
The annual average dose rate at the location with the highest exposure rate along the 100-N shoreline (Figure 15) during 1995 was 0.02 millirem per hour (2 x 10-4 milliseivert per hour), or about twice the average background dose rate of 0.01 millirem per hour (1 x 10-4 milliseivert per hour) normally observed at offsite shoreline locations. Therefore, for every hour someone spent at the 100-N Area shore-line during 1995, the external radiation dose received from Hanford operations would be about 0.01 millirem (1 x 10-4 milliseivert) above the natural background dose. If an individual spent 2 hours at this location they would receive a dose similar to the annual dose calculated for the hypothetical maximally exposed individual at Sagemoor. The public can approach the shoreline by boat, but are legally restricted from stepping onto the shoreline. Therefore, an individual is unlikely to remain on or near the shoreline for an extended period of time.
Figure 15. The N Reactor Complex Located Along the Columbia River
Shoreline.
Wildlife have access to areas of the Site that contain radioactive materials and some do become contaminated. Sometimes contaminated wildlife travel offsite. For this reason, sampling is conducted onsite to estimate maximum contamination levels that might possibly exist in animals hunted offsite. Since this scenario has a relatively low probability of occurring, these doses are not included in the maximally exposed individual calculation.
Listed below are estimates of the radiation doses that could have resulted if wildlife containing the maximum concentrations measured in onsite wildlife in 1995 migrated offsite, were hunted, and were eaten. These are very low doses, and qualitative observations suggest that the significance of this pathway is further reduced because of the relatively low migration offsite and the inaccessibility of onsite wildlife to hunters. The methodology used to calculate doses from consumption of wildlife was to multiply the maximum concentration measured in edible tissue by a dose conversion factor for ingestion of that tissue. The dose from eating 1 kilogram (2.2 pounds) of deer meat containing the maximum concentration of cesium-137 (0.037 picocuries per gram) measured in a deer collected onsite is estimated to be 2 x 10-3 millirem (2 x 10-5 milliseivert). The dose from eating 1 kilogram (2.2 pounds) of whitefish or sucker meat containing the maximum concentrations of cesium-137 (0.04 picocuries per gram) measured in whitefish or suckers collected from the Hanford Reach of the Columbia River is estimated to be 2 x 10-3 millirem (2 x 10-5 milliseivert). The dose from eating 1 kilogram (2.2 pounds) of goose meat containing the maximum concentration of cesium-137 (0.007 picocuries per gram) measured in a Canada goose collected onsite is estimated to be 4 x 10-4 millirem (4 x 10-6 milliseivert).
During 1995, ground water was used as drinking water by workers at the Fast Flux Test Facility. Therefore, this water was sampled and analyzed throughout the year in accordance with applicable drinking water regulations. All annual average radionuclide concentrations measured during 1995 were well below applicable drinking water standards, but concentrations of tritium were detected at levels greater than typical background values. Based on the measured concentrations, the potential dose to Fast Flux Test Facility workers (an estimate derived by assuming a consumption of 1 liter per day for 240 working days), the worker would receive a dose of 0.2 millirem (0.002 milliseivert). Of this total, drinking water obtained from the emergency backup ground-water well during June and July 1995 accounted for 0.05 millirem.
The regulations controlling radiation dose to the public from airborne emissions from DOE facilities specify that no member of the public shall receive a dose of more than 10 millirem per year (0.1 milliseivert per year) from exposure to airborne radionuclide effluents (other than radon) released at DOE facilities. Each DOE facility is required to submit an annual report that supplies information about atmospheric emissions for the preceding year and their potential offsite impacts.
The 1995 air emissions from monitored Hanford facilities, including radon-220 and radon-222 releases from the 327 building in the 300 Area, resulted in a potential dose to a maximally exposed individual across from the 300 Area of 0.006 millirem (6 x 10-5 milliseivert), which is 0.06% of the limit. Of this total, radon emissions from the 327 building contributed 0.0035 millirem, and non-radon emissions from all stack sources contributed 0.0028 millirem. Therefore, the estimated annual dose from monitored stack releases at the Hanford Site during 1995 was well below the Clean Air Act standard.
During 1995, the estimated dose from diffuse sources to the maximally exposed individual across the river from the 300 Area was 0.02 millirem (2 x 10-4 milliseivert), which was greater than the estimated dose at that location from stack emissions (0.006 millirem or 6 x 10-5 milliseivert). Doses at other locations around the Hanford Site perimeter ranged from 0.02 to 0.03 millirem (2 x 10-4 to 3 x 10-4 milliseivert). Based on these results, the combined dose from stack emissions and diffuse and unmonitored sources during 1995 was much less than the EPA standard.
Although no increase in the incidence of health effects from low doses of radiation has actually been confirmed by the scientific community, most scientists accept the hypothesis that low-level doses might increase the probability of certain types of effects, such as cancer. Regulatory agencies conservatively (cautiously) assume that the probability of these types of health effects at low doses (down to zero) is proportional to the probability per unit dose of these same health effects observed historically at much higher doses (in atomic bomb victims, radium dial painters, etc.). Under this assumption, even natural background radiation (which is hundreds of times greater than radiation from current Hanford releases) increases each personŐs probability or chance of developing a detrimental health effect.
Scientists do not agree on how to translate the available data on health effects into the numerical probability (risk) of detrimental effects from low-level radiation doses. Some scientific studies have indicated that low radiation doses may cause beneficial effects. Because cancer and hereditary diseases in the general population may be caused by many sources (e.g., genetic defects, sunlight, chemicals, and background radiation), some scientists doubt that the risk from low-level radiation exposure can ever be conclusively proved. In developing Clean Air Act regulations, EPA uses a probability value of approximately 4 per 10 million (4 x 10-7) for the risk of developing a fatal cancer after receiving a dose of 1 millirem (0.01 milliseivert). Recent data support the reduction of even this small risk value, possibly to zero, for certain types of radiation when the dose is spread over an extended time.
Government agencies are trying to determine what level of risk is safe for members of the public exposed to pollutants from industrial activities (for example, DOE facilities, nuclear power plants, chemical plants, and hazardous waste sites). All of these industrial activities are considered beneficial to people in some way, such as providing electricity, national defense, waste disposal, and consumer products. Establishing environmental regulations that control levels of risk to the public without unnecessarily reducing needed benefits from industry is a complex task.
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