As part of the design team lead by Fennick McCredie Architects, GZA provided geotechnical and environmental services for an 8-story parking garage. The UMASS Boston campus is located on a peninsula that was formerly a marshland that was subsequently filled with municipal solid waste. Subsurface conditions generally consist of landfill and other random fill materials overlying organic silt and peat, marine sand, marine clay (Boston Blue Clay), glacial till, and bedrock. Because of the presence of the landfill materials and buried organics, landfill gases (methane, hydrogen sulfide, etc.) are produced in the soils underlying most of the UMASS Boston campus. To mitigate landfill gas from migrating into buildings and other subsurface structures, a subslab landfill gas ventilation and barrier system was designed by GZA as part of the building design.
Geotechnical and environmental issues associated with design and construction of the PSAG project included: deep soft clay deposits and consolidation (settlement) of the clay; shallow depth to groundwater; shallow soils consisting of debris-laden soil fill that impact on-site reuse and premium costs for off-site disposal of excess excavated materials; potential residual contamination from the landfill materials, and potential impacts from landfill gas.
GZA assisted the design team in addressing each of these issues. Initial services began with a combined geotechnical and environmental subsurface exploration program to evaluate concept designs of the new Public Safety & Athletics Garage (PSAG), evaluate alternative foundation solutions and to install PVC monitoring wells for landfill gas sampling and testing, as needed to design a sub-slab venting system. Subsequent exploration programs were performed once the footprint location and geometry had been established. GZA provided geotechnical recommendations for design and construction, which included installation of a structural slab supported on deep driven H-piles designed to achieve resistance from side friction in the glacial till and weathered rock and end bearing on bedrock. The upper portions of the pile foundations were epoxy-coated to resist corrosion and to limit downdrag loads on the piles caused by consolidation settlement of the clay and organics under the new site and building loads. GZA was responsible for geotechnical engineering foundation and settlement analyses, preparation of a geotechnical engineering report and development of project specifications. Part of the specification process included development of the pile load testing program. GZA performed construction quality control services during test pile and production pile installation and vibration monitoring to avoid impacts to nearby adjacent structures. GZA provided environmental/LSP support for the project that included a proactive waste management scope of services to sample and classify soils and landfill materials prior to excavation for waste characterization, transport and disposal approval. Pre-characterization of the subsurface soils to be disturbed by construction was critical to achieving the project schedule because volume limits for stockpiled soils on site during construction were set by MADEP. GZA submitted over 850 soil samples for pre-characterization analyses, including asbestos-in-soil (AIS) testing. Utilizing the sampling results, GZA developed soil disposal slice diagrams, which separated the site into approximately 170 waste characterization cells for off-site disposal during construction. Overall, we pre-characterized and drafted disposal diagrams for approximately 100,000 tons of landfill material/soil. During construction GZA provided breathing one air monitoring services in the work areas and perimeter asbestos monitoring services during the handling of potential asbestos-in-soil material. We also provided RAM Plan compliance support and worked directly with the Site project team to reuse excavated material onsite, which substantially reduced the disposal costs for the owner.
The GZA team applied many of the lessons learned from an adjacent project, especially regarding managing environmental issues on the PSAG project. GZA project managers and principals on the projects communicated frequently and the same LSP was assigned to both to maintain continuity and efficiency in addressing compliance with the Massachusetts Contingency Plan under the Special Project Designation issued by MADEP. The facility opened in 2018.