GZA delineated MGP constituents at this former MGP site, identifying contaminants in soil between layers of silt that extended very deep into the groundwater in the Site’s residential neighborhood.


To isolate this residual product and prevent it from acting as a continued source to impact groundwater, GZA designed and installed a groundwater cutoff wall as deep as 60 feet below grade. The cutoff wall surrounded the Site and traversed an active rail line. The depth of the installation, constrained site configuration which limited construction options, and restrictions required by the railroad added complexity.


Multiple cutoff wall construction methods were explored and GZA ultimately recommended using a DSM rig which offered a superior level of accuracy and the ability to conform to the non-linear wall alignment. During construction, quality control measures were implemented to verify compliance with the permeability in strength performance specifications for the 2,500-foot-long cutoff wall. Close coordination with the railroad was maintained to remove and re-install track sections during weekends to minimize shutdowns.


GZA’s solution produced less impacted soil and spent grout, which resulted in less off-site disposal and a smaller footprint compared to other construction techniques to reduce project cost and time.