Raleigh, NC: North Wake Co. Landfill Gas Collection Trench

Raleigh, NC: North Wake Co. Landfill Gas Collection Trench

Project Description

Description of Work:

Geo-Solutions was subcontracted to perform the construction of a gas collection trench for collection and extraction of methane gas.  This collection trench was constructed using the bio-polymer slurry trenching technique.  The collection trench, installed as part of a landfill-wide gas collection system, was designed to capture the methane gas generated by the capped and closed portion of the landfill to be used for the off-site generation of electricity.

The 22,700 square foot collection trench, with a maximum depth of 34 feet and length of 1,000 feet, consists of crushed rock and seven separate one-hundred-foot-sections of four-inch diameter perforated collection pipe.  In addition, the collection trench included a down gradient 60 mil HDPE vapor barrier to prevent any un-extracted gas from migrating offsite.   The trench was also separated into seven subsections by the installation of HDPE “diaphragms” within the trench alignment.  Real-Time air monitoring was performed during all intrusive activities.   This project was performed at the base and property boundary of a closed landfill, due to the topography Geo-Solutions had to install the collection trench in an extremely limited workspace.  Extreme care had to be taken so as not to disturb the existing cap and waste footprint.  Despite these constraints the project was completed ahead of schedule and with zero incidents.



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