57    AN INTEGRATED APPROACH TO THE CLOSURE OF PULP
AND PAPER SLUDGE LANDFILLS AND LAGOONS
Victor C. Jones, Civil Engineer
Kent Nilsson, Geotechnical Engineer
RMT, Inc., Greenville, South Carolina 29606
INTRODUCTION
Closure of pulp and paper sludge landfills and impoundments in compliance with applicable
regulations is often problematic due to the saturated, weak and compressible nature of the waste
materials they contain. In many cases, the characteristics of the waste make it impossible to use
construction equipment on the landfill to shape the surface and place an approved cap. This condition
affects not only closure procedures, but also restricts facility operation to placing sludge by perimeter
dumping or sluicing.
These placement methods of sluicing or perimeter dumping prevent an engineered surface which
would allow for efficient storm water management. This tends to reduce the sludge storage capacity
by increasing the amount of water stored. This increased amount of water stored directly impacts the
difficulties in closing the landfill or lagoon. Improvement of the waste surface not only allows more
efficient operation of the landfill but facilitates its ultimate closure. Therefore, where possible,
landfill operation should be integrated with plans or intentions for closure.
BACKGROUND
Pulp and paper mill sludges are composed of fibrous organic matter that characteristically feature:
• high moisture content,
• potential for leachate and gas production (gas may be highly odorous),
• low shear strength and bearing capacity, and
• high compressibility.
Research indicates that the undrained shear strength of the sludge increases as the water content
decreases. The undrained strength is also directly related to consolidation potential. Significant
increases in shear strength have been observed where water is allowed to drain and sludge to
consolidate.'
Although the vertical permeability of the sludge has been shown to range from 10"8 cm/s to 10"6
cm/s,2,3 field observations and measurements indicate that the lateral permeability can be as much as
one to three orders of magnitude greater.
These characteristics can make it difficult to meet the regulatory requirements for closure. The goal
of a landfill or lagoon closure is to construct a cap that will minimize infiltration; promote storm
water runoff; support a vegetative cover to control erosion and enhance evapotranspiration; control
odor generation; control vector penetration, and provide gas management.
While regulations may vary on a state or regional basis, generally speaking, closure requirements
include:
• 4% minimum slopes,
• 24-inch barrier layer with a permeability of less than 10"7 cm/s,
• 6-inch vegetation layer, and
• gas management/odor controls.
In order to meet these requirements, the basin must be stabilized to preserve the integrity of the cap
and to create a working surface for low-pressure earth-moving equipment. Several alternatives for
creating a working surface have been implemented by pulp and paper mills with varying degrees of
success.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.