Former MGP Site: Cutoff Wall & Jet Grouted Bottom - Wetlands Design

Challenge

Three independent remediation contractors had already been retained by the Owner on this complex former MGP site when GZA was contracted as Construction Manager as Agent. The contractors’ scopes of work included demolishing buildings; relocating an active rail line; re-routing subsurface utilities; relocating a non-interruptible high-voltage power distribution lines to a local hospital; reclaiming a two-acre wetlands; installing a 50-foot-deep slurry wall by conventional means; jet grouting a five-foot-thick bottom to encapsulate the two-acre Site; managing removal and disposal of 25,000+ tons of impacted material; and installing new roads and sidewalks adjacent to a residential neighborhood.

Solution

GZA coordinated the efforts of the three primary contractors (remediation, slurry wall/jet grouting, and transportation/treatment/disposal); enforced all scope, schedule, and contract compliance issues; and reviewed and approved all invoices for direct payment by the Owner. GZA also developed and permitted wetlands removal, reclamation, and restoration design in/around the site.

Slurry wall construction included both cement-bentonite and soil-bentonite sections to accommodate vehicular and train traffic. More than 1,200, 45-foot-deep jet grouted columns were completed for the installation of a sealed bottom. Several full-length columns were installed below the active freight rail line and below the footprint of a proposed building.

Benefit

By proactively identifying scheduling constraints, understanding the level of effort required for the independent contractors to complete their work, and recognizing the logistical challenges, GZA kept this project on schedule with no down-time claims from contractors and no complaints from the adjacent residents or the manufacturing facility that depended upon rail delivery of their raw materials.