Funnel & Gate
Andres AFB, MD: Soil-Bentonite Barriers with Permeable Reactive Barrier Gates, Funnel and Gate Groundwater Control System
This site is located on Andrews AFB (AAFB) in Northern Maryland, just outside Washington, DC. AAFB is home to the 89th Airlift Wing as well as the 79th Medical Wing of the United States Air Force (USAF). The USAF contracted URS Corporation (URS) through The Air Force Center of Engineering Excellence (AFCEE) to support a remedial action at the LF-05 site, a former landfill on base also known as the Leroy's Lane Landfill. URS contracted with Geo-Solutions Inc. in 2009 to perform the underground barrier and PRB installation. Geo-Solutions worked with URS engineers and personnel in Herndon, VA, Pittsburgh, PA and Salt Lake City, UT to bring this project to the field.
The funnel and gate system at Andrews Air Force Base (AAFB) was designed to be installed to an invert elevation of 224 feet above mean sea level, approximately 37 feet below most of the prepared work platform. The three funnel portions of the application were designed to be installed as low permeability soil-bentonite (SB) slurry walls. Two gate sections are to be installed as permeable reactive barriers (PRBs) utilizing the bio-polymer slurry wall method. Excavation depths of up to 41 feet below the ground surface (bgs) are expected to account for deviations in the final elevation of the work pad prepared by URS. Geo-Solutions executed excavation of both the funnel and gate portions of the project to the designed depths using a long-reach hydraulic excavator. The overall construction approach consists of the following definable features of work:
- Site Preparation - Includes the installation of water handling as well as slurry batching and delivery systems.
- SB Trench Installation - Includes excavation, spoil handling, preparation and placement of bentonite slurry as well as backfill mixing and placement.
- Trench Delineation - Includes the temporary placement of delineating beams between the SB and PRB portions of the trench.
- PRB Trench Gate Installation - Includes excavation, spoil handling, placement of imported sand and gravel fill, degradation of bio-polymer slurry, trench development, removal of the delineation beams and installation of the specified injection wells.
- General Cleanup - Includes the cleanup of Geo-Solutions' operation.