Woodard & Curran executed a resilient and sustainable remediation strategy at the site of an active manufacturing facility in Connecticut. By instituting water and sediment control measures and exhaustive contingency planning, our team successfully removed 3,300 cubic yards of wetland soil and sediment contaminated with heavy metals without irreparably disrupting an established — and flood-prone — wetland and stream ecosystem.
Under previous operations, nickel and other metals released during manufacturing operations infiltrated the site via stormwater runoff and aerial deposition, accumulating in the wetland area adjacent to the facility. The property was sold to another business in the late 1980s. Years later, state law regarding property transfers changed, retroactively requiring responsible parties to clean up site contamination within 8 years of finalizing the sale. The prior owner selected Woodard & Curran to design and carry out a remediation strategy to meet this obligation.
Despite heavy metal contamination, the impacted wetland continued to support vegetation and wildlife over the decades between release and remediation. Trees and groundcover played a critical role in sediment control, especially in the context of an urban watershed prone to streamflow variability and the site’s position within the 100-Year floodplain. Additionally, environmental investigations revealed the site was home to Eastern Box Turtles (Terrapene carolina carolina), regionally considered a species of special concern.
Permitting the project required coordination with several federal, state, and local agencies. Woodard & Curran’s ecological risk assessment experts reviewed existing toxicology testing results and risk-assessment documentation in support of remedial action plan (RAP) development for the Connecticut Department of Energy & Environmental Protection. We presented this information at public meetings to meet the local Inland Wetlands & Watercourses Commission public outreach requirements.
As part of pre-design activities, we conducted focused additional delineation to update the conceptual site model (CSM) to separate the depth of impact in the stormwater outfall and discharge pathway versus areas that were subject to less frequent overflow from the facility. This allowed for regulatory approval of 6-inch excavations in peripheral lobes and 2-foot excavation in the main stormwater discharge channel. Overall, the excavation volume was reduced by approximately 50 percent. Further, post-excavation sampling was eliminated from the revised excavation approach, representing a decrease in the level of uncertainty for this remediation project.
We conducted a LIDAR assessment of site topography to identify low points. This was critical to design the flooding mitigation measures as well as the post-remediation site restoration features.
Sequencing played a critical role in site protection and remedy resiliency. The project team progressed through site sections, performing excavation and restoration over 13 individual cells. After removing contaminated soil, each area was backfilled with clean fill, secured with straw wattles and erosion control blankets, and replanted with native species of trees and groundcover.
We completed the project in November 2021. In addition to shallow excavation and restoration activities, we also replaced the existing undersized stormwater outfall, improving its capacity and conveyance. The next steps for the site include restoration monitoring and submitting a regulatory closure report.
Throughout the project, our team performed environmental monitoring for Eastern Box Turtles, a species of special concern in Connecticut. We worked with a professional herpetologist and trained all contractors in inspection, identification, and relocation for box turtles inhabiting the site.