Project Profile: Reshaping a Lexington, MA, Brownfield

Sept. 1, 2010

The Samuel Hadley Public Services Building in Lexington, MA, demonstrates the value of project delivery placing civil engineering and landscape design on par with building design and construction. Implemented in response to strict municipal resource conservation mandates, this approach fueled comprehensive stormwater control measures that transformed a brownfield into a sustainable site replicating predevelopment stormwater runoff conditions.

Environmental Challenges Inspire Innovative Team Structure
A mounting ecological crisis in Lexington created the backdrop for progressive solutions. Ever-larger homes and commercial buildings in the historic Boston suburb had pushed stormwater levels to a breaking point, leading to the 2007 adoption of a Conservation Commission mandate that required predevelopment-level stormwater control on all projects. Beyond meeting the stormwater control thresholds of past developments, the bylaw stipulated that projects match the runoff levels of a virgin landscape–a significant challenge amplified by a preexisting townwide requirement for Leadership in Energy and Environmental Design (LEED) Silver sustainable design on public projects.

The dual building and site sustainability requirements led building architect HKT Associates to look beyond a typical design-subconsultant partnership. Instead, the company turned to Bioengineering Group, an interdisciplinary sustainable engineering and design firm, to provide lockstep site planning, civil engineering, and landscape design services. The partnership allowed HKT to design the building for maximum LEED points while Bioengineering Group simultaneously tackled site and stormwater challenges through a robust in-house platform and team of subconsultants.

It was a crucial strategy–generating effective technical solutions, permitting the project, and creating budget and schedule efficiencies. Duke Bitsko, director of interdisciplinary design at Bioengineering Group, says, “When stormwater concerns and site ecology aren’t properly emphasized in project delivery, we’re often brought in at the end to fix problems. Lexington went way beyond that. Its challenges created its opportunities: holistic design, simultaneously tackling permitting issues, aesthetics, technical systems, and so on. It saved time, and cost, at the back end.”

Site Analysis Drives Solutions
Analysis of the building’s site, a 9.6-acre brownfield within a residential neighborhood and adjacent to a public wetland, kick-started Bioengineering Group’s approach by exposing the project’s daunting preconditions as only the tip of the iceberg. Functional requirements for the Hadley Building–including material storage for sand and salt and vehicle storage, fueling facilities, maintenance bays, and some 100 parking spaces–needed to be balanced with aesthetics and ecological sensitivity fit for the site’s context: a residential area and natural habitat. Moreover, the town of Lexington hoped to implement educational signage promoting the site’s transformation from contaminated brownfield to sustainable, nonpolluting facility, a vision that called for a heightened degree of visibility for the project’s stormwater control solutions.

Based on analysis revealing suitable existing soil, and given the town’s challenge to infiltrate as much runoff as possible, Bioengineering Group opted to implement several localized technologies that worked in concert with existing hydrology while redesigning the site to mimic natural hydrological conditions.

“On such a complicated site, we used hydrology as the connecting factor to achieve water-quality goals, stormwater requirements, and enhanced landscape and habitat values,” explains water resources engineer Siva Sangameswaran. “The approach was to capture runoff almost at source, and treat it locally and cumulatively before it infiltrated the ground or the town storm drains. Designing multiple systems in series allowed water benefits to accrue.”

This collection of solutions is highlighted by two green roof segments accounting for a 12.25% reduction in runoff, an emergent wetland, extended detention ponds, sediment forebays, and a rain garden or biobasin that uses native vegetation and engineering soils to treat and infiltrate stormwater runoff for use in an onsite municipal vehicle wash. Notably, in areas of high pollutant loading potential like the vehicle fueling station, the team also implemented water-quality inlets and other manufactured treatment devices per Massachusetts Department of Environmental Protection regulations.

In addition, predevelopment runoff requirements led the team to engineer subsurface infiltration chambers capable of holding and infiltrating the 100-year, 24-hour runoff volume from the building roof (excluding the “green” segments), and located them adjacent to the runoff sources to capture, treat, and infiltrate water at or near the source.

Similarly, the constructed wetland is strategically located to capture runoff from an adjacent drainage area.

Sustainable site design complements all these technical solutions. The team recycled soil and building materials, minimized paved surface, and, where paving was necessary, used porous pavement. According to Sangameswaran, “Relying on native vegetation and natural systems-based processes helped us keep costs low. Porous pavement was an ideal solution to convert paved surfaces to infiltrating surfaces, given the suitability of the soils beneath.”

Historic Rainfall Tests Results
The building opened, on schedule, in 2009 and was certified as the first LEED Silver public works facility in the state that winter. Not long afterward, historic rainfall flooded the region–a significant performance test for the Hadley Building’s new stormwater solutions. While most systems performed admirably and as designed, some interior flooding, traceable to an unopened drainage grate, underscored the difficulties associated with even the most effective new stormwater technologies. “The systems work, but they’re vulnerable,” points out Bitsko. “Drains need to be cleared, for example, and the stormwater systems need to be
maintained.”

The March storm brought the promise and challenge of modern storm-water treatment technologies into stark relief. “Towns like Lexington are steadily embracing smaller, localized water treatment options,” says Bitsko. “It’s a great step and essential in areas where development has given stormwater, essentially, nowhere to go.” But the systems, he notes, require collective expertise. “Success isn’t measured by a LEED rating. It’s measured over the life of a building and ecosystem, storm after storm. Designing for that type of performance requires ongoing commitment from everyone, from the architect and engineers to the end users.”