Interception of a Groundwater Plume Containing Strontium-90

Abstract

In December 1998, a vertical, permeable "barrier" of granular zeolite (clinoptilolite) was emplaced underground in the path of groundwater that was transporting strontium-90 (⁹⁰Sr) toward a wetland on the property of Atomic Energy of Canada Limited;s Chalk River Laboratories (CRL). The primary components of the barrier were a 30-m long, steel-sheet piling cut-off wall and a 130 m³ volume of granular clinoptilolite. The granular clinoptilolite was to act as an ion exchange permeable reactive barrier (PRB) to intercept the ⁹⁰Sr groundwater plume. It was 2-m thick in the direction of groundwater flow, 11-m wide and 6-m deep. It was not emplaced at the depth of groundwater contamination. Instead, the clinoptilolite was "hung" like a "curtain" with its base at an elevation 3 to 4 m above the natural pathway of the groundwater. A locally reduced elevation head in the curtain was intended to cause the groundwater plume to angle upward and to flow through the curtain.

The concentration of ⁹⁰Sr in the influent groundwater has been about 400 Bq/L and the 12-year record of gross beta measurements has shown no sign of ⁹⁰Sr breakthrough. Attempts to measure 90Sr radiochemically revealed less than 0.1 Bq/L ⁹⁰Sr in the effluent. Hydraulic controls on the incoming groundwater have performed as intended. As of this writing, the groundwater plume continued to be intercepted and the reactive barrier had been effective for long-term subsurface control and mitigation of groundwater contaminated with ⁹⁰Sr.