OWNER:
Dow Chemical Company

CONTRACTOR:
Radion International, LLC

ENGINEER:
AWD Technologies, Inc.
Freeport, Texas

The owner proposed to place a final soil cap over two industrial waste sludge ponds at their Freeport, Texas facility. The surface area of the two ponds was approximately 8 and 11 acres, with a sludge depth of nearly 18 feet. In-situ shear strength measurements indicated that the shear strength of the soft sludge gradually increased from about 5 psf near the surface to about 35 psf near the bottom of the pond. A study was conducted that suggested several options including: excavation, incineration and disposal, sludge press and landfill, and solidification. The time and costs associated with these alternatives, along with the extremely soft nature of the sludge, resulted in Dow searching for alternatives. The owner’s previous experience using geosynthetics to cap sludge led to development of a plan to utilize biaxial geogrid and geotextile to construct an initial working platform over the sludge. A lightweight fill consisting of tree bark was spread over the geosynthetics using a prescribed construction technique and lightweight equipment. A drainage system consisting of perforated pipes was installed to collect and remove water expelled from the sludge during the consolidation process. Once the initial lift of bark was completed, the final soil layer was placed and graded to the desired contours using lightweight dozers. The final soil cap was successfully completed and the project received an “Outstanding Achievement” award from the Industrial Fabrics Association International (IFAI) in 1996. The completed cap reduced the construction schedule by 80%, while reducing costs by 25%, as compared to other alternatives considered.