Development of a passive-flow treatment system for {sup 90}Sr-contaminated seep water at Waste Area Grouping 5 at Oak Ridge National Laboratory

Abstract

Seep C is a free-flowing stream of groundwater (typical flow of 0.2 to 2 L/min) that emerges in a narrow valley below the old low-level waste disposal trenches in Solid Waste Storage Area 5 (SWSA 5), which is part of Waste Area Grouping 5 (WAG 5). The seep water contains high concentrations of Sr-90 (10,000 to 20,000 Bq/L) and contributes about 25% of all the Sr-90 leaving Oak Ridge National Laboratory. Seep C was identified as a primary source of off-site contaminant transport and was designated for an early removal action under the Comprehensive Environmental Response and Liability Act (CERCLA). A passive-flow treatment system was chosen as the most cost-effective method for treating the seep water. The goal of the removal action is to have a system operational by November 1, 1994, that reduces the Sr-90 concentration in the water collected and treated by at least 90%. In order to provide design and operating data for the full-scale system, a pilot-scale system, consisting of a 5-gal bucket with an inlet connection in the lid and a screened outlet on the bottom filled with 16 L of chabazite zeolite, was used to treat the seep water. The test was started onmore » March 17, 1994, and concluded on June 15, 1994. The system treated 63,470 L (3967 bed volumes) of water and 22.7 mCi of Sr-90 from the seep water. The system removed over 99.5% of the Sr-90 from the first 43,000 L of water treated, after which the removal efficiency slowly decreased as the zeolite became loaded until it reached 84% for the final sample. The passive system performed at least as well as comparable pumped zeolite systems in terms of removal efficiency and zeolite utilization. The test was terminated just before the construction crew mobilized at Seep C to build the full-scale system.« less