100-N Area

Active liquid waste disposal operations at 100-N Area did not cease until mid-1992. These disposal operations released millions of gallons per year of reactor cooling water from N Reactor containing high concentrations of strontium-90 into the soil immediately adjacent to the Columbia River. In some parts of the groundwater plume, strontium-90 was thousands of times its drinking water standard, and although no aquatic water quality standard for strontium-90 was available, the shear magnitude of these releases were considered sufficient cause to initiate action.

The effectiveness of the pump-and-treat operations in limiting the discharge of strontium-90 to the Columbia River at N Springs has been questioned throughout its period of operation. The major reason concentrations of strontium-90 in groundwater were reduced occurred as a direct result of ending the discharge of contaminated liquids to the soil column in the early 1990s. Much of the strontium-90 remaining in the groundwater beneath 100-N Area is tightly bound to the aquifer sediments and represents a threat to groundwater quality well into the future, making the return to beneficial use for this portion of the aquifer unrealistic.

A number of technologies other than pump-and-treat have been tested or are planned to be tested to assess their effectiveness for the long-term protection of the Columbia River ecosystem. Previously, technologies including impermeable barriers constructed of steel and sorptive permeable barriers of clay-like materials were evaluated as alternatives to pump-and-treat systems. Investigation determined neither barrier was a suitable replacement for pump-and-treat. Tests are now planned to evaluate two additional technologies that may be candidates to replace the pump-and-treat systems. One alternative under consideration would use deep-rooted vegetation to absorb strontium 90 from the groundwater along the shoreline; then, the contaminated vegetation would be removed and disposed on the Central Plateau. A second method under consideration would be to develop a chemical barrier that would further immobilize strontium-90 in the soil and limit its release to the river through N Springs.

In addition to the evaluation of new and innovative technologies to slow the release of strontium-90 to the Columbia River, studies are underway to evaluate the actual impact of strontium-90 on the aquatic ecosystem. A number of species are now being assessed to determine bioaccumulation rates and the potential impact to organisms exposed to strontium-90. These efforts, in conjunction with the evaluation of new and innovative technologies, should enable the Groundwater Remediation Project to re-evaluate how well the pump-and-treat actions protect the ecosystem and assess the need for additional measures to mitigate the impacts. Evaluation of the technologies, risks, and potential impacts of strontium-90 are expected to be complete in 2006.

For questions or comments, please send a message to Carl Connell.