Geo-Con was engaged to construct a groundwater barrier wall around a former ConEd coal gasification plant site with groundwater contaminated with phenols and other compounds typical of that process. A tributary to Long Island Sound borders the site. The groundwater barrier included a sheet pile wall, a jet grout wall, and a cement-bentonite slurry wall that surrounded the site. Plans included excavation of the contaminated soil inside the barrier wall as part of the site remediation.

McMahon & Mann analyzed the stability of the slurry trench and ground water conditions since the plans called for it to be constructed close to existing buildings, and provided recommendations for constructing the barrier wall. The trench stability was affected by a groundwater level a few feet below ground surface and a loose sand deposit. Construction was complicated by the close buildings and a network of buried utilities that paralleled the trench in some locations and crossed it in other locations.