Oak Ridge National Laboratory

Waste Area Group 4 – Hazardous Waste Encapsulation

The site located in Oak Ridge, Tennessee was one of the former waste disposal areas for nuclear, toxic and hazardous wastes. Shallow waste trenches were excavated in the rock and contained the wastes. Groundwater migrating through the waste trenches would inevitably transport radioactive isotopes to the nearby waterways. The removal action project initiated was designed to encapsulate the wastes within 4 trenches thereby mitigating radioactive isotope migration into nearby waterways. A combination of the use of both solution and cementitious grouts was specified for the project.

This unique project presented some challenges upfront. The site was considered a hazardous waste site and the extent of the buried wastes was indeterminate. Several proactive safety precautions were incorporated into the production work including the use of semi-remote controlled sleeve-pipe installation equipment. In addition, Industrial Health and Safety personnel played a significant role in the daily work activities. In addition, all personnel at the site were required to complete a 40 Hour HAZWOPER and RadWorker training.

A three step injection process was used to complete the project. First a cementitious grout consisting of type 3 portland cement, bentonite, viscosity modifier, pozzolans, fly ash, grout retarder and silica fume was injected into each zone followed by injection with microfine cement. A final grouting pass in each zone was performed using acrylamide solution grout to ensure maximum encapsulation of the waste mass. Real time computer monitoring of multiple hole grouting operations was completed using electronic flowmeters and pressure transmitters with a xy-recorder and personal computer for data analysis and storage. The average insitu hydraulic conductivity was reduced to a value of 1x10-6cm/s.