Closure of a Paper Mill Sludge Lagoon: A Comparison of Design vs. Performance, 1993 Environmental Conference Proceedings

Simpson Paper Company prepared a closure plan for their 2.5-acre lagoon used between 1969 and 1988 to dispose of primary paper mill sludge generated in their paper making process. The closure plan was prepared in accordance with the applicable state regulations for the closure of a residual waste impoundment. Special engineering considerations were required for the closure of this facility due to the soft, highly compressible nature of the sludge. These considerations included the potential for a substantial volume of water, referred to as “squeezate”, contained within the lagoon to be expressed out of the sludge during closure, andstability issues associated with a dike which was built to contain the sludge.

Borings were drilled within the lagoon to collect samples of the sludge for laboratory analyses. The analyses included consolidation testing, moisture content, and organic content and were performed to measure the physical and engineering characteristics of the sludge. The test results were used to evaluate the amount of settlement, and the rate and volume of squeezate that would potentially be generated during construction of the final cover system. The proposed design included grading the landfill in stages with varying thickness of cover and drainage material to account for the expected settlements. A geogrid was specified to provide strength and a drainage system was designed to contain and collect the squeezate produced as a result of the sludge consolidation. A squeezate

transport pipeline from the lagoon to Simpson’s wastewater treatment plant, was designed to convey the expected volume of squeezate during peak consolidation periods.

Measurements of the actual amount of settlement and the rate and volume of squeezate generated and collected in the cover drainage system will be obtained during construction. The measured settlement and leachate volumes will be compared to predicted values used to design the final cover system. This data will provide beneficial information to design future cover systems for paper mill sludge lagoons or other impoundments that contain similar waste.