Scientific basis for establishing dry-well-monitoring frequencies

A scientific basis has been developed for establishing the frequency of monitoring dry wells. Dry wells are used to detect radioactivity from a leaking underground high-level radioactive waste-storage tank. The frequency of monitoring a dry well is dependent on the response characteristics of the radiation-detection system periodically used to monitor dry wells for encroaching radioactivity. The response characteristics have been combined in the Dry Well Radioactivity Response Equation, which is derived from: variation in dose rate (roentgen per hour) as a function of source strength; variations in dose attenuation by the soil as the radioactive waste front approaches the dry well; response of radiation detector, in counts per second, as dose rate changes (instrument calibration); distance of dry well from tank leak source; leak rate; geometry of soil wetted by leaking waste; and hydrologic properties of the soil. These variables are used with the current status of tank contents and available liquid-level-monitoring system information to generate a monitoring schedule for individual dry wells and horizontal laterals associated with single-shell, high-level waste-storage tanks on the Hanford Site