The 32-acre property on the Mystic River selected for the Encore Boston Harbor resort and casino had been impacted by historic chemical manufacturing use; much of the site was on salt marsh that had been filled with waste materials from operations at the site and/or nearby facilities. The buildings on the property were razed in the 1970s and the property had been used primarily as a material storage and staging yard since the mid-1990s, when rock and fine-grained material (“tunnel muck”) from the construction of the Deer Island Outfall project were stockpiled on it and later spread out. In addition, the geologic conditions varied greatly within the site. The combination of complex environmental and geologic conditions, coastal flood vulnerability, the waterfront setting, and the fast-paced nature of this mega-development project required a focused project team with a diverse set of technical skills.


During initial phases of the project, GZA participated in negotiations with the former owner regarding the extent of remediation warranted by site conditions. GZA also prepared several sections of the reports required by the Massachusetts Environmental Policy Act (MEPA), and developed cost estimates for reaching regulatory closure under the Massachusetts Contingency Plan (MCP) and for dealing with contamination encountered during construction. To meet the growing needs of the project, GZA’s involvement quickly grew to include geotechnical and marine engineering as well as comprehensive natural resources and permitting services.

Ecological Services and Resilient Design: GZA’s natural resources team conducted topographic and hydrographic surveys; performed biological surveys of the shoreline, intertidal, and sub-tidal zones; conducted extensive sediment sampling and analysis to further define the nature and extent of sediment impacts from historic operations; characterized sediments within a former ship channel to identify costs associated with dredging and reopening the channel for the project’s use; and developed plans for a Living Shoreline to return the native salt marsh and native coastal bank plant species to the fringe of the site as part of the environmental impact mitigation for the project.

Geotechnical Engineering: GZA developed geotechnical foundation design recommendations to support the 29-story tower as well as the low-rise portions of the project. With a large portion of the building footprint constructed over a multilevel garage, groundwater control was an important issue for both construction and building design. GZA evaluated foundation, groundwater control, and lateral earth support options, taking into account both the extent and depth of the basement, and both geotechnical and environmental considerations. Given the variety of building loads and subsurface conditions, multiple foundation types were utilized: slurry walls for excavation support and the support of building loads; load-bearing elements to support the tower; precast prestressed concrete piles and drilled mini piles to support low rise portions of the building; a mat foundation for the majority of the below-grade garage; and rock tiedowns to help resist hydrostatic uplift pressures.

Environmental Services: GZA designed and implemented remedial activities to address three highly contaminated areas of the site prior to building construction. In one area, in-situ stabilization was used to help neutralize low-pH groundwater. In two other areas with elevated concentrations of metals, soils were excavated and replaced. While providing Licensed Site Professional (LSP) services for the project, GZA pre-characterized and drafted disposal documentation for over 800,000 tons of soil removed from the site during building and site construction.

Waterfront Engineering: GZA was also responsible for the resilient design of the project’s waterfront marina, with over 600 linear feet of bulkhead and a 300-foot-long floating dock. Due to the soft soils at the site, a load-transfer platform was designed to support new loads and mitigate settlement concerns.


At a total estimated design and construction value of $2.6 billion, the Encore Boston Harbor resort and casino is the largest single-phase private development in Massachusetts history. By nimbly responding to changes to the proposed project during construction, GZA was able to provide the multidisciplinary services and management skill required to help move this high-profile, technically-challenging project forward to an on-time completion date.