Authors: Dave Forse, CPG, FPM Remediations, Inc. and Kyle Carlton, PG, Directional Technologies, Inc.
Introduction:
How do you remediate beneath an active airport taxiway without interfering with commercial airliners and
To solve the problem, our long-time client, FPM Remediations, Inc., used their knowledge of horizontal
Background/Challenge:
Active remediation of jet fuel plumes at a joint international airport and Air Force base in the Southeast have been ongoing since 1992. A free product recovery system consisting of recovery trenches and vertical recovery wells successfully removed the majority of non-aqueous phase liquid (NAPL) from the subsurface. Residual contamination resulting in dissolved concentrations of jet fuel chemicals above the state regulator’s cleanup criteria were still present beneath the taxiway and aircraft parking areas. To address the remaining dissolved hydrocarbon concentrations, installation of an ozone/air sparge system was suggested with vertical sparging points; however, the proposed vertical system would unacceptably limit the use of the airport taxiway and aircraft parking areas. FPM Remediations, Inc. proposed an alternative plan horizontal
Site Geology:
The site is underlain by primarily fine to medium grained sands with some clay and silt. This fine sand overlies a dense grey-green clay present beginning approximately 17 feet below ground surface (
Horizontal Bio-sparge Well System Design:
To effectively treat the target area, a total of three horizontal
The three horizontal wells are constructed with 180 feet to 320 feet of 3-inch diameter HDPE well screen designed with 0.010-inch longitudinal slotting at custom spacing. The customized slotting allows for air delivery rates of 0.1 cubic feet per minute (
Horizontal Well Installation with Horizontal Directional Drilling:
Directional Technologies was selected by FPM to provide horizontal environmental directional drilling and horizontal bio-sparge well installation based on previous experience with FPM at similar sites. The horizontal well paths traversed beneath the active taxiway and aircraft parking area to the target air delivery locations.
To conduct work at the site, FPM performed months of coordination with the DoD and FAA prior to mobilization. Site access permits, worker security clearances, along with specialized worker training and certifications were required to access the aircraft taxiway and other secured areas.
Minimal Site Interruption:
While the environmental directional drilling was being performed, the taxiway was never shut down for installation of the horizontal wells. Air traffic continued to move freely at the site, satisfying the requirements of the DoD.