Pre- and Post-Assessments (Performance, Progress, and Risk) for Radiological Impact at Uranium Mine Facilities (Case Study Coles Hill) for a 100-y Rainfall Event Including Surface Water Transport and Fate Modeling

The general guidance for a radiological impact using pre- and post-assessments for legacy, new, and planned uranium mining facilities are presented. Specific items to consider during the process and the rationale such as mitigation, order of model, loading functions and approaches, hydrographs, pollutographs, water quality modeling, and health physics are provided. A case study using a conventional Coles Hill proposed uranium mine in Virginia demonstrates typical pollutograph construction processes for a worst-case scenario 100-y intense rainfall pre-assessment. For the case study, an intense 3-h duration, 100-y synthetic rain event overlapping a sudden rupture of a full 5.00 × 104 m3 leachate (= 2.78 × 105 Bq m-3) storage tank over a 3-h duration was considered. Having similar characteristics, a surrogate Rio Road Watershed hydrograph was used to emulate the local watershed at White Horn Creek, Coles Hill. The uranium mine waste (leachate, slime, sand) was transported over the local land area and river embankment into the nearby Banister River as it mixed with a spatial temporal runoff rate (q-Series). A Continuous Spill/Step Loading Runkel water quality model determined the concentrations in 15-min increments the entire length of the Banister River downstream to the Kerr Dam. There was insignificant evidence that there would be an exceedance of the MCL for 226Ra/228Ra (= 1.85 × 10-2 Bq m-3), total alpha (= 5.55 × 10-2 Bq m-3), or uranium (= 3.00 × 10-6 Kg m-3) at the Town of Halifax's drinking water intakes (approximately 50 km). Therefore, it is highly unlikely that there would be an exceedance of 226Ra/228Ra, total alpha, or uranium near the drinking water intakes of the Town of Halifax, Virginia, or further downstream at Clarkesville's and Kerr Dam's drinking water intakes. Furthermore, there would be a need for post-disaster data collection and potential remedial action of radioactive contamination in water, soil, sediment, building structure, and the ecosystem.