Characterizing potential exposure to the public from low-level radioactive waste transportation by truck.

To address public concern about potential exposure to gamma radiation from legal-weight low-level radioactive waste truck shipments to the Nevada Test Site, a stationary, automated array of four pressurized ion chambers was established for trucks to pass through. Data were collected from 1,012 of the 2,260 trucks that transported low-level radioactive waste to the Nevada Test Site from February through December 2003. To avoid perception of biasing a potential exposure low, the maximum reading (muR per hour; muR h(-1)) from the array was assigned as the gross measurement value for each truck. [In this article, exposure measurements are reported as Roentgen (R), as this unit is consistent with the data readings of the measurement instruments and has been historically presented to public stakeholders. Subsequently, dose measurements are reported as Roentgen Equivalent Man (rem).] To calculate the "net exposure" for each truck, the average and standard deviation of the maximum background values during the corresponding 12-h period when the truck arrived were subtracted from the gross value. For 483 trucks (47.7%), calculated net exposure values were equal to or less than zero, indicating that the exposure from the truck was indistinguishable from background. An additional 206 trucks (20.4%) had calculated net exposure values ranging between 0.0 and 1.0 muR h(-1). Cumulative exposure scenarios appropriate for rural transportation routes to the Nevada Test Site were developed; however, these scenarios assumed the unlikely case that the same individual was exposed to all of the trucks on that route. Cumulative exposure values were dominated by a small percentage of the trucks with comparatively high values. In communities along transportation routes, the probability of an individual receiving a potential exposure from a single truck may be a more meaningful perspective.

Community Environmental Monitoring Program: a case study of public education and involvement in radiological monitoring.

The public's trust in the source of information about radiation is a key element of its acceptance. The public tends to trust two groups where risk communication is concerned: (1) scientists with expertise who are viewed as acting independently; and (2) friends, family, and other close associates who are viewed as sharing the same interests and concern, even if they have less knowledge of the subject. The Community Environmental Monitoring Program (CEMP) bridges both of these groups by having members of the public help operate and communicate results of a network of 29 radiation monitoring stations around the Nevada National Security Site (NNSS), formerly known as the Nevada Test Site (NTS), the principal continental location where the United States conducted nuclear tests. The CEMP stations, spread across a 160,000 km area, help provide evidence to the public that no releases of radiation of health concern are occurring from the NNSS to public receptors. The stations provide continuous measurements of gamma radiation and collect air particulate samples that are analyzed for radioactivity and meteorological measurements that aid in interpreting variations in background radiation. A public website (http://cemp.dri.edu) provides data for most instruments. Twenty-three of the 29 stations upload their data in near-real time to a public website as well as to digital readout displays at the stations, both of which are key elements in the CEMP's transparency. The remaining six stations upload their data hourly. Public stakeholders who are direct participants provide the most significant element of the CEMP. The "Community Environmental Monitors," who are residents of towns where the stations are located, are part of the chain-of-custody for the air samples, perform minor station maintenance, and most significantly in terms of trust, serve as lay experts on issues concerning the NNSS and on ionizing radiation and nuclear technologies in general. The CEMP meets nearly all of the principles for stakeholder engagement identified by the International Radiation Protection Association.

Sensitivity of solute advective travel time to porosities of hydrogeologic units.

An integral approach is proposed to quantify uncertainty and sensitivity of advective travel time to the effective porosities of hydrogeologic units (HGUs) along groundwater flow paths. The approach is applicable in situations where a groundwater flow model exists, but a full solute transport model is not available. The approach can be used to: (1) determine HGUs whose porosities are influential to the solute advective travel time; and (2) apportion uncertainties of solute advective travel times to the uncertainty contributions from individual HGU porosities. A simple one-dimensional steady-state flow example is used to illustrate the approach. Advective travel times of solutes are obtained based on the one-dimensional steady-state flow results in conjunction with the HGU porosities. The approach can be easily applicable to more complex multi-dimensional cases where advective solute travel time can be calculated based on simulated flow results from groundwater flow models. This approach is particularly valuable for optimizing limited resources when designing field characterization programs for uncertainty reduction by identifying HGUs that contribute most to the estimation uncertainty of advective travel times of solutes.