Assessment and Closure of a Lime Waste Disposal Site Under Washington State Dangerous Waste Regulations, 1990 Environmental Conference Proceedings

A site characterization investigation of an on-site waste disposal area was completed in 1988 at the Pulp Mill in Everett, Washington. The disposal of lime waste, wood waste, and other debris on-site began in the 1950s and was terminated in 1986. The disposal area covers about 2.4 hectares and overlies a shallow alluvial aquifer. The investigation and closure of the disposal site was mandated by Washington State Department of Ecology (Ecology).

The waste thickness reached 3.7 meters and had a pH greater than 12. Soil samples were collected to define the characteristics of the waste. Monitoring wells were installed to evaluate ground water contamination. Results showed no significant contamination present in the waste. Arsenic and chromium were detected in monitoring wells at the disposal boundary but were attenuated in downgradient wells.

Because of the high pH, Ecology has required closure of the disposal site under the state dangerous waste regulations. Closure options include covering the site with either a membrane

or low permeability soil cover, and installing a collection trench to intercept ground water underflow. The cost to close the disposal site and conduct post-closure monitoring could exceed $1 million. The reuse of the site material was also investigated. There was no contamination present in the waste that would restrict use of the site materials. The lime waste, woodwaste, and sand and gravel, which make up 80 percent Of the waste material, could be used for soil amendment and top soil mix. Considering all costs, the restoration and closure options were equal. Therefore, mill management chose to pursue restoration of the site.