Potential Radiation Doses from 1994 Hanford Operations

Present and past operations at Hanford have resulted in the release of radionuclides into the surrounding environment. Members of the public are potentially exposed to low levels of radiation from these effluents through a variety of pathways. The potential radiation doses(a) to the public in 1994 from Hanford operations were calculated for the hypothetical MEI and for the general public residing within 80 km (50 mi) of the Hanford Site. These doses were calculated from effluent releases reported by the operating contractors, and radionuclide measurements in environmental media, using Version 1.485 of the GENII code (Napier et al. 1988a, 1988b, 1988c) and Hanford Site-specific parameters listed in Appendix D and by Bisping (1995).

The potential dose to the MEI in 1994 from Hanford operations was 0.05 mrem () compared to 0.03 mrem () reported for 1993. The potential dose to the local population of 380,000 persons (Beck et al. 1991) from 1994 operations was 0.6 person-rem (0.006 person-Sv), compared to 0.4 person-rem (0.004 person-Sv) reported for 1993. The 1994 average dose to the population was 0.002 mrem () per person. The current DOE radiation dose limit for an individual member of the public is 100 mrem/yr (1 mSv/yr), and the national average dose from natural sources is 300 mrem/yr (3 mSv/yr). During 1994, the MEI potentially received 0.05% of the DOE dose limit and 0.02% of the natural background average dose. The average individual potentially received 0.002% of the standard and of the 300 mrem/yr received from typical natural sources.

The small additional dose to the MEI in 1994 was a result of increased concentrations of uranium isotopes measured in Columbia River water collected downstream of the Hanford site and of continued experimental work in the 300 Area. This work entailed the release of radon isotopes (160 Ci of radon-220 and 1.2 Ci of radon-222) to the atmosphere from the 327 Building ventilation system (see Table 3.1.1). The new MEI location chosen for the 1993 dose calculations [1.5 km across the river (east) from the 300 Area] was retained for 1994.

During 1994, radionuclides reached the environment in gaseous and liquid effluents from present and past Hanford operations. Gaseous effluents were released from operating stacks and ventilation exhausts. Liquid effluents were released from operating waste-water treatment facilities and in seepage of contaminated ground water into the Columbia River. These radioactive materials were then transported throughout the environment by wind and the Columbia River. Eventually, animals and people can be exposed to these radionuclides through external exposure and inhalation and ingestion of contaminated air, water, and foodstuffs. Because of the many variables involved in the transport of the radionuclides in the environment and differing living habits of people, the assumptions used to describe the exposure scenarios are conservative (i.e., the doses are likely to be overestimated).

Potential radiation doses to the public from these releases were evaluated in detail to determine compliance with pertinent regulations and limits. The potential radiological impacts of 1994 Hanford operations were assessed in terms of the following:

• dose to a hypothetical MEI at an offsite location
• maximum dose rate from external radiation at a publicly accessible location on or within the Site boundary
• dose to an avid sportsman who consumes wildlife exposed to radionuclides onsite
• dose to the population residing within 80 km (50 mi) of the operating areas
• absorbed dose rate (rad/d) potentially received by animals associated with contaminant releases to the Columbia River.

As in the past, the differences in measured concentrations of certain radionuclides in samples of Columbia River water collected upstream and downstream of the Hanford Reach were used to estimate the doses to the public from these radionuclides entering the river with riverbank seepage of ground water. During 1994, iodine-129, tritium, and isotopes of uranium were found in the Columbia River downstream of Hanford at greater concentrations than predicted from direct discharge from the 100 and 300 Areas.

Although the uncertainty associated with the radiation dose calculations has not been quantified, whenever Hanford-specific data were not available for parameter values (for example, vegetation uptake and consumption factors), conservative values were selected from the literature for use in environmental transport models. Thus, radiation doses calculated using environmental models should be viewed as maximum estimates of potential doses resulting from Hanford operations.

Maximally Exposed Individual Dose

The location selected for the MEI can vary from year to year depending on the relative importance of the several sources of radioactive effluents released to the air and to the Columbia River from Hanford facilities. Historically, two separate locations in the Hanford environs have been identified as potential sites for the MEI: the Ringold area, 26 km (16 mi) east of the 200 Areas separation facilities, and the Riverview irrigation district across the river from Richland (Figure 6.0.1). The principal differences between the two MEI locations are that Ringold is closer than Riverview to the Hanford facilities, which had been the major contributors of airborne effluents in the past, but the MEI at Ringold does not drink water derived from the Columbia River. The MEI at Riverview, although farther from the Hanford sources of airborne radionuclides, can be exposed to the one additional pathway of irrigation water derived from the Columbia River.

During 1994, the hypothetical MEI (assumed to be located 1.5 km [1 mi] directly across the Columbia River from the 300 Area) was calculated to have received a slightly higher dose in 1994 than an MEI located at either Ringold or Riverview. The farms located across from the 300 Area use water obtained from the Columbia Irrigation System far upstream of the Hanford Site for irrigation and well water for sanitary purposes. Foods grown there would only contain radionuclides released with airborne effluents of Hanford origin. Therefore, the conservative assumption was made that the diet of the MEI residing across from the 300 Area consisted totally of foods purchased from the Riverview area, which could contain radionuclides present in both liquid and gaseous effluents from Hanford. The added contribution of the radionuclides in the Riverview irrigation water maximizes the calculated dose from all air and water pathways combined.

The following exposure pathways were included in the calculation of doses potentially received by the hypothetical MEI for 1994: inhalation of and submersion in air downwind of the Site, consumption of foods contaminated by radionuclides deposited from the air and by irrigation with water from the Columbia River, direct exposure to radionuclides deposited on the ground, consumption of fish taken from the Columbia River, and external radiation during recreation activities on the Columbia River and its shoreline. The MEI for 1994 was postulated to be an individual who:

• was a resident of the closest farm 1.5 km (1 mi) across the Columbia River from the 300 Area
• consumed foodstuffs irrigated with Columbia River water grown in the Riverview Irrigation District
• used the Columbia River extensively for boating, swimming, and fishing and consumed the fish caught
• drank well water that did not contain radionuclides of Hanford origin
• was exposed via inhalation and external exposure to the airborne radionuclides released from Hanford facilities.

The total potential radiation dose to the hypothetical MEI in 1994 was calculated to be 0.05 mrem () compared to 0.03 mrem () calculated for in 1993. The primary pathways contributing to this dose as determined by the computer calculations were

• consumption of fish containing radionuclides, principally isotopes of uranium, from the Columbia River (33%)
• consumption of food irrigated with Columbia River water containing radionuclides, principally tritium and uranium (27%)
• inhalation of airborne radionuclides, principally the iodine-129 released from the 200 Area (20%).

The doses from Hanford operations for the MEI for 1990 through 1994 are illustrated in Figure 6.0.2.

During each year the doses were estimated using methods and computer codes that were state-of-the-art at the time. During the period of 1990 through 1992, the MEI was located at either Ringold or Riverview, whichever location represented the maximum hypothetical dose. For 1993 and 1994, the hypothetical MEI was located across the Columbia River from the 300 Area.

Figure 6.0.1

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