Dredging Projects Provided Environmental Remediation and Enhancement
Nine projects were submitted to the Western Dredging Association Environmental Commission for consideration for a 2017 Environmental Dredging award. Three projects won in the categories of Environmental Dredging, Dredging for Navigation, and Mitigation or Adaptation to Climate Change. Described here are four of the six projects submitted but not chosen for awards.
Prepared by Judith Powers
Lower Duwamish Waterway Enhanced Natural Recovery/Activated Carbon Pilot Study
In November 2016, the Lower Duwamish Waterway Group, consisting of King County, Washington, the Port of Seattle, the City of Seattle, and The Boeing Company, with King County as the lead, contracted Pacific Pile & Marine (PPM) to conduct an Enhanced Natural Recovery (ENR) activated carbon pilot study in the Lower Duwamish Waterway Superfund Site.
ENR is the process of covering contaminated sediments (river mud) with a thin layer of sand to speed up the process of natural recovery – the natural deposition of cleaner sediments to cover contaminated sediments. The goal of the study is to determine whether adding activated carbon (AC) to the sand layer can reduce PCB bioavailability in the sediment.
The site is a five-mile section of the Duwamish River, which flows into Elliott Bay in Seattle, Washington. More than 100 years of heavy industrial use left the waterway contaminated with toxic chemicals from commercial operations, stormwater pipes; and runoff from upland activities, streets, and roads. Pollutants include polychlorinated biphenyls (PCBs), dioxins/furans, carcinogenic polycyclic aromatic hydrocarbons (cPAHs), and arsenic. The site was added to USEPA’s National Priorities List in 2001.
In its 2014 Record of Decision (ROD), USEPA announced a cleanup plan for about 177 acres in the waterway. Cleanup will involve dredging, capping, and natural sedimentation at an estimated cost of $342 million.
The study compares the effectiveness of ENR with added AC (ENR+AC) with that of ENR without added AC in three areas, or plots, in the Waterway. These plots are referred to as the Intertidal Plot, the Subtidal Plot, and the Scour Plot. For the purposes of this project, ENR involved the placement of a thin layer of clean material (sand or gravelly sand) over subtidal or intertidal sediments. ENR+AC involved the placement of a thin layer of clean material augmented with AC over subtidal or intertidal sediments.
PPM used a fixed-arm Hitachi 1200-6 hydraulic excavator with RTK-GPS, equipped with a sealed three- to six-cubic-yard clamshell bucket to place the materials. To achieve the minimum four-inch thickness and hit the six to nine-inch overall target thickness, PPM placed the material in two 4.5-inch lifts with an offset bucket pattern.
The overall environmental and economic benefit of this project will be determined by the effectiveness of the pilot study in reducing concentrations of sediment contamination and long-term protectiveness, while limiting short-term adverse effects to water quality during construction. If the results of the study are successful, this application could be used in 48 acres of the overall Duwamish River cleanup.
The study will verify that ENR+AC can be placed uniformly with the prescribed percentage of carbon. It will evaluate the performance of ENR+AC compared to ENR alone in locations with a range of PCB concentrations, assess potential impacts on the benthic community in ENR+AC compared to ENR alone, assess changes in bioavailability of PCBs in ENR+AC compared to ENR alone, and assess the stability of ENR+AC in scour areas (such as berthing areas).
Dredging and Beachfill, Delaware River Main Channel Deepening: Pennsylvania, New Jersey and Delaware, April 2015 through March 2016
Dredging for Navigation
The U.S. Army Corps of Engineers (USACE), Philadelphia District used dredged material from the Delaware River Main Channel deepening beneficially by placing it on the beach facing the small community of Lewes, Delaware, which was struggling to keep its coastline at Broadkill Beach intact.
The contract to complete the initial construction was awarded on June 6, 2014 to Weeks Marine, Inc. (WMI). Construction on the Dredging and Beachfill, Delaware River Main Channel Deepening project started in April 2015 and was expected to provide roughly 1.9 million cubic yards of material to the beach at Broadkill. The work to be completed consisted of dredging new material within the Miah Maull and Brandywine ranges of the Delaware River Main Channel from station 432+200 to station 512+000. Dredging was required to a depth of 45 feet MLLW plus a one-foot allowable overdepth.
Three-mile long Broadkill Beach is located on the DE Bay north of Cape Henlopen and adjacent to Prime Hook NWR. It is known as the official sanctuary for horseshoe crabs. The DE River Main Channel is used by various types of marine vessels, including commercial vessels sailing to the ports in Philadelphia, Pennsylvania. The Broadkill Beach, Delaware project was authorized for construction by Title I, Section 101 (a) (11) of WRDA 1999 under the House Committee Resolution dated October 1st, 1986. The Delaware Department of Natural Resources and Environmental Control was the sponsor for this project.
A Pacific Pile & Marine crew uses the company’s Hitachi 1200-6 long reach excavator with Jewell boom to place ENR + AC (enhanced natural recovery plus activated charcoal) in a scour area in the Lower Duwamish Waterway. The project had a target thickness of six to nine inches over a minimum of 80 percent of the area, and four inches or more over 100 percent of the area. PP&M used a sealed three to six cubic yard clamshell bucket to place the material, with the aid of RTK-GPS. The activated charcoal is intended to reduce the bioavailability of PCBs.
The majority of the funding was provided by the federal government and 25 percent of the project was funded by the Philadelphia Port Authority.
The main purpose of this project was to increase the navigable channel depth from 40 feet to 45 feet MLLW to allow for larger commercial vessels to travel safely through Delaware Bay.
Other objectives for this project included provisions for hurricane and coastal storm damage reduction at Broadkill Beach.
WMI successfully completed the dredging portion using two hopper dredges, the RN Weeks and the BE Lindholm, transporting the material to Broadkill Beach, and providing the community with a 150-foot-wide berm and a new dune by March 2016.
Seal Beach/Huntington Harbor Maintenance Dredging and Waterline Installation Project
Mitigation or Adaption to Climate Change
Curtin Maritime was the contractor on a project to maintenance dredge Seal Beach and Huntington Harbors in Southern California, using the dredged material to raise the level of the salt marsh at the Seal Beach National Wildlife Refuge (SBNWR), and to nourish the beach at Seal Beach.
The sediment augmentation was the first-ever thin-layer salt marsh sediment augmentation project on the west coast of the United States, and was accomplished using a spray nozzle developed by the project team.
Salt marsh habitat within the project site had been degraded by excessive tidal inundation, due to the combination of subsidence, gradual sea level rise, and the historical alteration of natural sediment inputs. Raising the elevation of the site by applying 10 inches of clean sediment over the 10-acre low salt marsh project site enhanced the quality of the cordgrass-dominated salt marsh habitat and improved nesting opportunities for the federally endangered lightfooted Ridgway’s rail. Improving the quality of the cordgrass vegetation is also expected to maintain carbon sequestration within the marsh over time (USFWS 2016).
The SBNWR is one of the most sensitive wetland habitats in Southern California. As home to thousands of marine and estuarine species, including many that maintain special protection status (eelgrass, sea turtles, marine mammals, and hundreds of avian species), impacting habitat to create new habitat was unacceptable both for the project proponents and the Curtin Team.
To ensure environmental protections, National Marine Fisheries Service (NMFS) and CDFW-certified biologists were onsite during all construction times to observe, alert, and report on possible biological concerns. Daily inspection of all pipelines crossing estuary channels, and water quality monitoring were also part of the environmental protections in place for the project.
Small-vessel escorts were required for dump scow movements into and out of the harbor. In this way, the Curtin Team ensured that animals who spend part of their time at the surface, like sea turtles and sea lions, could be identified and avoided, protecting them from collision with a scow.
The project demonstrates how dredging can become the conduit for enhancing the environment through stakeholder involvement and identifying regionally beneficial opportunities. Traditionally, a maintenance program such as the Seal Beach/Huntington effort would have likely disposed of the material offshore. However, through cooperative planning and funding, greater ecological benefit could be realized through the reuse of sediments for beach nourishment and sediment augmentation purposes.
The project leveraged the dredge mobilization costs and permitting efforts to help meet one of the City of Huntington Beach’s infrastructure priorities.
As a continuing part of this effort, the USFWS will monitor the sediment augmentation area for the next five years. Through a partnership with local, State, and Federal agencies, USFWS has secured the funding necessary to support post-sediment augmentation monitoring on the project site and a nearby control site. As of January 2017, the augmented area was starting to show signs of recolonization by cordgrass, an intended consequence of the augmentation. A sediment application guidance document will also be prepared to describe the process and lessons learned. To date, the USFWS has presented information relating to this project at the several conferences, and produced a series of informational presentations relating to the augmentation effort.
The project was funded jointly through the County of Orange ($7.2M), and the cities of Huntington Beach and Seal Beach ($800K), and supplemented with additional grant funding through the U.S. Fish and Wildlife Service (USFWS) Cooperative Recovery Initiative ($500K) and the California Department of Fish and Wildlife (CDFW) Wetland Restoration for Greenhouse Gas Reduction Grant Program ($1.1M), the California Coastal Conservancy ($633K), and the US Army Corps of Engineers Los Angeles District ($50K).
In all, more than 190,000 cubic yards (cy) were dredged. One hundred and thirty thousand cubic yards were transported through the congested and ecologically sensitive waters of the SBNWR to the ODMDS LA-2 shore disposal. Approximately 47,000 cy of suitable material was placed in the nearshore environment near Seal Beach for beach replenishment purposes, and over 18,000 cy of material were hydraulically pumped to the SBNWR for existing wetland augmentation.
In addition to the dredging and augmentation, the Curtin team installed a 16-inch diameter emergency waterline to carry water to Trinidad Island in Huntington Harbor. Prior to this effort, an older 12-inch ductile iron pipe was the only primary feed to provide adequate fire flow protection to the island. The new pipeline provides redundancy, allowing the city ample time in the future to replace the 12-inch pipe when it has reached the end of its useful life.
Weeks Marine’s 320 Unloader pumps material from a hopper barge onto Caminada Headland. The barges were
used to transport sand mined from Ship Shoal for project to restore the beach and dune system Caminada Headland
near the Port Fourchon entrance. Since the project was completed, the dune system has been performing
better than expected. At press time it was undergoing a further test as Hurricane Harvey hit the Gulf Coast.
Caminada Headland Beach and Dune Restoration Project, Increments 1 and 2 Lafourche and Jefferson Parishes, Louisiana
The Caminada Headland Restoration Project is the largest coastal restoration project completed in Louisiana by the Coastal Protection and Restoration Authority (CPRA).
Construction included the placement of over 8.8 million cubic yards of sand from the Ship Shoal Borrow Area offshore, which ranged from 27 to 41 nautical miles from the project site, and adding new sediment to the barrier island chain from outside of the active littoral system.
The project created 792 acres of critical beach and dunes, which provide habitat for migratory, threatened, and endangered species. There were over 13 miles of sand fence installed, to promote deposition of windblown sand to create dune features and conserve sediment placed on the Headland. The contractor planted 275,976 native plants on the dune to accelerate colonization of vegetation on the dune to conserve sediment.
Over the last century, the Caminada Headland shoreline has experienced some of the highest shifts of the Louisiana coastline. The Headland has experienced significant shoreline erosion and land loss because of storm overtopping and breaching, saltwater intrusion, wind, and wave-induced erosion, and relative sea level rise.
Restoring barrier shorelines is a top priority of the “multiple line of defense” restoration strategy, which is a key tenet of Louisiana’s Coastal Master Plan. The goal of the Caminida Project is to protect and preserve the structural integrity of the barrier shoreline of the Caminada Headland which will reduce wave energy and salt-water intrusion from the Gulf of Mexico into back-barrier environments, consisting of Chenier ridges, intertidal marshes, and bays. Restoration of these fragile habitats will protect and sustain significant and unique foraging and nesting areas for threatened and endangered species.
The project also provides storm protection to Port Fourchon, which services over 90 percent of the Gulf of Mexico deep water oil production and supports production of approximately 18 percent of the nation’s oil supply.
The project was nominated by Coastal Engineering Consultants, Inc. Weeks Marine, Inc. performed the project for the Louisiana Coastal Protection and Restoration Authority. Project team members numbered more than 30 organizations, including government organizations, county and municipal governments, contractors, consultants, surveyors, and other involved parties.