Water Diversion at Low‐Level Waste Disposal Sites

Shallow depth to groundwater, surface drainage, and subsurface flow during storm events can cause major environmental problems in low‐level radioactive waste management operations in humid regions. These three problems were encountered at two waste disposal sites on the Oak Ridge Reservation. In September 1983, two similarly designed, engineered drainage projects were initiated at the disposal sites. The SWSA 4 (solid waste storage area four) project was designed to divert surface runoff and shallow subsurface flow originating upslope of the site away from the disposal area. The second project, a passive French drain constructed in SWSA 6, was directed strictly toward suppressing the site water table, thus preventing its intersection with the bottoms of disposal trenches. Postconstruction monitoring for performance evaluation showed that the water table in the SWSA‐6 area is suppressed to a depth $>4.9m$ below the ground surface over 50% of the site, as compared to a depth of only 2.1m for certain parts of the same area observed during seasonally wet months. The SWSA 4 project evaluation indicates that 56% of the winter‐spring 1984 runoff was diverted around SWSA 4 via the drainage system. As a result of the reduced flow in the SWSA 4 tributary to White Oak Creek, a 44% reduction in ${}^{90}\mathrm{Sr}$ flux from SWSA 4 was calculated.