Complex Remedial Design in a River Estuary

OUR CHALLENGE

Mercury contamination from decades of industrial operations on the Penobscot River estuary have impacted wildlife and impaired resources.  A consent decree for the estuary identified actions and associated funding for multiple categories of remediation, but site conditions, such as high currents, significant tidal shifts, winter ice, and privately owned intertidal areas, create a challenging setting in which to permit and implement the work. Integral is leading the design of a capping remedy for 130 acres of intertidal flats to accelerate natural recovery of the estuary.  The goal is to maximize remedy benefits while minimizing impacts to the ecological function of the flats. 

OUR APPROACH

Integral is working with the Trustee overseeing the project to cap the most contaminated intertidal areas and achieve the greatest reductions in sediment mercury concentrations.  This strategy includes a series of investigations and modeling efforts to refine the conceptual site model and identify constraints to remedy implementation.  This includes a river velocity study and bathymetric survey integrated with light detection and ranging (LiDAR) data to develop a detailed hydrodynamic model to evaluate stable areas for cap placement.  Integral will also complete investigations to evaluate areas to be capped, maintenance of slope stability, impacts of ice scour, and state of the benthic community. Integral’s design strategy recognizes the uncertainty inherent to executing a large remedial action within a complex system such as the Penobscot River estuary and incorporates an adaptive management strategy to allow for adjustments to the remedy design and implementation as more information is available to maximize overall benefit. 

OUR IMPACT

Integral’s early identification of key concerns along with approaches to mitigate potential impacts to the community, evaluate constructability, and engage permitting agencies, is providing the client with an acceptable remedial program that maximizes environmental benefit given available funds.