Water treatment technologies for a mixed waste remedial action

Water treatment is an important element of the Weldon Spring Site Remedial Action Project (WSSRAP), which is cleaning up a former uranium processing plant near St. Louis, Missouri. This project, under the management of the U.S. Department of Energy (DOE), includes treatment and release of contaminated surface water and possibly groundwater at the plant site and a nearby quarry, which was once used for waste disposal. The contaminants include uranium, thorium, radium, nitroaromatics, nitrates, and metals. Three water treatment plants will be used to treat contaminated water prior to its release to the Missouri River. The first, construction of which is nearly complete, will treat contaminated surface water and interstitial water in and around the quarry. A stepwise process of sedimentation, clarification, filtration, adsorption, and ion exchange will be used to remove the contaminants. A similar sequence will be used for the first train of the water treatment plant at the plant site, although process details have been adjusted to address the different contaminant concentrations. The site water treatment plant will also have a second train consisting of a vapor compression/ distillation (VCD) system. Train 2 is necessary to treat waters primarily from four raffinate pits containing high concentrations of inorganics (e.g., nitrates, sulfates, and chlorides) in addition to radionuclides, nitroaromatics, and metals contamination that are common in most of the waters at the site. Construction is under way on the First train of this facility. After it is treated, all water will be impounded and batch tested for compliance with the project's National Pollution Discharge Elimination System (NPDES) permits prior to release to the Missouri River. The third water treatment plant is a mobile system that will be used to treat waters in some of the building sumps. (author)