Management of PAH and NAPL-Impacted Dredge Residuals—Former Manufactured Gas Plant Site Located in the Portland Harbor Superfund Site
Ryan Barth, Principal Engineer, Anchor QEA, LLC
Co-Authors: Bob Wyatt, NW Natural and Holly Samaha, Anchor QEA, LLC
Monitoring has documented that surface and subsurface sediments remaining after environmental dredging operations have contained elevated concentrations posing a residual risk. The magnitude of these post-dredging residuals often dictates the project’s success. NW Natural is developing a basis of design document for the former manufactured gas plant Gasco Sediments Site (Gasco) located in the Portland Harbor Superfund Site. Development of a site-specific post-dredge/cover residuals management framework is a critical design component. The framework considers the approaches employed at other similar Superfund environmental dredging projects (e.g., Hudson River and Lower Fox River), including dredging equipment selection, controlled operations, and best management practices (BMPs). These projects demonstrated that improvements in equipment and operational BMPs resulted in twofold reductions of generated residuals, but these reductions were insufficient to eliminate elevated residuals. The framework also incorporates innovative, design considerations for site-specific conditions, including the presence of nonaqueous phase liquids (NAPLs). The framework includes an approach to manage measured residuals during construction using design criteria. This approach includes the sequenced placement of three 6 inch layers of clean sand cover immediately following: 1) achievement of design dredge elevations in dredge subareas, 2) completion of all dredging during a dredge season, and 3) completion of all dredging activities after multiple seasons. This sequenced placement will minimize residuals migration from each subarea and following dredging completion. The framework includes the collection of stepwise, multipoint post-dredge/cover verification samples and tiered subsampling to evaluate for missed inventory and residuals concentrations. If elevated residual concentrations or NAPL are identified, the sand cover design will be modified during construction per the design. These modifications will include incorporation of active amendments in the clean cover or additional sand placement.
Ryan Barth is a principal engineer at Anchor QEA, LLC. He holds a BS and M.Eng. in environmental/ecological engineering from the University of California–Berkeley. Mr. Barth has 17 years of experience in environmental engineering with a focus in sediment contamination and remediation, including work at MGP sites in the western United States. His primary work experience includes management of complex remedial investigation/feasibility studies and design projects with multiple objectives, owners, and stakeholders. He has performed a wide variety of source control evaluations, preparation of design and bid package documents, construction monitoring, and management and implementation of field sampling events across a wide range of environmental media. Mr. Barth has worked on multiple multimedia field projects under state and federal programs that included extensive coordination with regulators, the community, stakeholders, insurers, and third-party owners.