Gene Revelas and David Schuchardt recently presented at the 2005 Sediments Conference held in New Orleans, Lousiana, January 24-27, 2005. Below are abstracts of Mr. Revelas’ and Mr. Schuchardt’s talks.
Assessing Sediment Stability in a Riverine Environment for the Portland Harbor RI/FS
Eugene C. Revelas, Susan M. Fitzgerald (Integral Consulting, Olympia, WA, USA), and Jon L. Dasler (David Evans and Associates, Portland, OR, USA)
The Lower Willamette River/Portland Harbor (Oregon) was listed as an NPL (Superfund) site in December 2000 because of sediment contamination within this segment of the river. A remedial investigation/feasibility study (RI/FS) was initiated in October 2001. In order to develop an effective RI/FS sampling program, physical system investigations were performed to gain an understanding of the complex sediment dynamics in this large riverine environment. In addition to the compilation of existing information, such as hydrologic data and dredging records, two site-specific studies were conducted, a sediment-profile image (SPI) survey and time-series precision bathymetry measurements. The SPI survey allowed gradients in near-surface sediment texture and stratigraphy, geochemical features (e.g., apparent redox depths, sedimentary methane), and animal-sediment interactions (e.g., biogenic mixing depths) to be mapped. The bathymetric measurements delineated large-scale topographic features (e.g., sand waves, scour holes). Overlays of bathymetric data from four surveys documented temporal changes in riverbed elevations caused by both scour and accretion, and defined the predominant depth of the physical mixing of surface sediments under a range of hydrologic conditions. In combination, these data were used to develop a preliminary physical conceptual site model of large-scale sediment dynamics and benthic processes throughout Portland Harbor. This model was used to define the surface mixed layer for RI sediment sampling and to help optimize station placement for an extensive surface and subsurface sediment-sampling program. Over the course of the RI/FS, the understanding of the site’s physical system gained through these investigations will support the evaluation of the nature and extent of contamination, source evaluations, the baseline risk assessments, and the identification of remedial alternatives.
Beneficial Use of Dredged Material for Capping: Design and Implementation
David Schuchardt, P.E. (Integral Consulting, Inc., Seattle, Washington, USA)
Construction of a 58-acre marine sediment cap at the Pacific Sound Resources (PSR) Superfund site is nearing completion. The cap has been designed to address a unique and complex set of site conditions and remedy requirements. Significant engineering challenges were posed by steep slopes, deep water, the need to restore critical habitat, and the desire to use dredged material for cap construction.
The PSR site is located on the south shore of Elliott Bay in Puget Sound, in Seattle, Washington. The site sediments are highly contaminated with PAHs, PCBs, and mercury. The 58-acre cap extends from upper intertidal elevations to water depths of 240 feet, including 2,000 feet of shoreline, and requires approximately 550,000 cy of cap material. To successfully isolate the contamination in the various regions of the site, five distinct cap designs were developed. A key challenge during the design was maximizing the beneficial use of clean dredged material for cap construction, considering the nature and availability of dredged material, engineering constraints, logistics, and contracting.
The final design specifies the use of approximately 200,000 cy of dredged material from other local projects to construct the deepwater portion of the cap (approximately 22 acres). The dredged material is being placed by bottom-dumping from split-hulled barges. During construction of nearshore areas, an additional 50,000 cy of dredged material was opportunistically used as a substitute cap material and placed with a bucket. By designing and contracting for beneficial re-use of dredged material, cap construction costs are reduced by about three million dollars. This presentation focuses on the design, logistical, contracting, and regulatory approaches to successfully construct the cap using dredged material.