Erosion and Sediment Control
Guam Vegetated Landfill Cap
The Guam ORDOT landfill was built in a ravine with a steep slope to the Lonfit River. It started operations in the 1940's as a disposal area during WWII and after the war was used by the U.S. Navy and the local community. In 1983, the 23-acre unlined dump was placed on the list for Superfund, a federal government program designed to fund the cleanup of toxic waste sites.
Site investigations revealed pollutants flowing from the site to the Lonfit River. The landfill ceased operations in 2012 and research began on how to best close the landfill to prevent further contamination to the area.
Severe site conditions made typical cover options of an exposed geomembrane or unconfined soil not possible. The objective was to protect the liner system while providing a vegetated solution. Site conditions included high seismic activity, potential high winds of up to 175 mph, extensive rainfall average of 96 inches per year and extreme UV exposure. An HDPE cellular confinement system was chosen to confine the soils and create a vegetative layer.
A total of 2,100,000 SF (195,096 m2) of 6” (15 cm) and 8” (20 cm) HDPE geocell was used for this project. The HDPE cellular confinement was anchored without the need for stakes that would potentially damage the geomembrane liner. The use of polymeric tendons insured veneer stability and eliminated the need for anchoring stakes. The slopes in some places were in excess of 2.5 to 1. The HDPE cellular confinement filled with concrete was also used to construct the storm water channels and allowed for velocities in excess of 23 fps (7 m/s). The concrete-filled cells also alleviated problems caused by the variance in settlement that would be present on typical large concrete slabs.
The project location in Guam had severe weather conditions throughout the year. This was critical to the scope of not only the installation but also the durability of the system. The HDPE cellular confinement worked well alongside the other geosynthetics materials used - double sided geocomposite and LLDPE single sided textured geomembrane - since it was suspended on the slopes with the tendon system. As each phase of the installation was finished, coral and sand was used to fill the panels with vegetation being added as the final layer.
Since the original installation in 2015, the cellular confinement system is fully vegetated and has protected the geomembrane liner from the harsh UV conditions as well as flying debris during monsoon season. The completed project earned in 2016 the prestigious Construction Management Association of America’s Project Achievement Award.