Performance Assessment for the E-Area Low-Level Radioactive Waste Disposal Facility at the Savannah River Site: Appendix A

Abstract

SWM commissioned this SA to determine the effects of placing operational stormwater runoff covers over ST DUs ST01 through ST07 at about years 5, 10, and 15 of the 30-year operational period. Covering changed the movement of contaminants to the water table and the hypothetical well. Early movements typically decreased because the cover decreased the flow of water from the surface through the contaminants. Later movements typically increased because less of the inventory had been released than for the uncovered cases analyzed in the PA. These effects on contaminant movement translated into higher SA-calculated limits relative to PA limits in the early years and some lower SA-calculated limits relative to PA limits in the later years. Because the lower of the two sets of limits was always selected as the operational limit, the net effect was to lower limits in the later years (typically 100 years and later). Earlier covers at 5 years magnified the changes.