This project was a contender for the Dredging for Navigation environmental award at the Western Dredging Association 2017 Annual Meeting.
By Judith Powers
The Port of Long Beach coordinated its West Basin Navigation Dredging Project with the Middle Harbor Terminal (MHT) Redevelopment project to use all 1.6 million cubic yards of material from the deepening to create 55 acres of new land at the MHT.
Dredging contractor Manson Construction Company is deepening the shipping channel that accesses Pier T the largest terminal in the Port to -55 feet MLLW from the existing -50 feet MLLW.
After geotechnical and chemical sampling showed that the material in the Pier T/West Basin dredge footprint was suitable for the MHT fill the project team worked with different port divisions (engineering environmental and construction) consultants and regulatory agencies to align the two projects quickly and efficiently and to obtain the necessary permits. Advanced planning among multiple groups was important to successfully implement and complete the project and to ensure it addressed the areas that needed to be dredged for navigation and that the sediment was placed in the appropriate level of the fill site.
As of April 2017 the Pier T/West Basin Navigational dredging project was about 60 percent complete and estimated to be finished toward the end of the year.
The West Basin and the Pier T Terminal were part of the former Long Beach Naval Complex. After 50 years of naval operations areas of the West Basin contained contaminated sediments and the port inherited the responsibility of remediation. It contracted several dredging projects which left trace residuals of contaminated sediments and the West Basin dredging project presented a great opportunity to further remove contaminated sediment exposing uncontaminated native material.
Sampling and Analysis
The West Basin was sectioned into multiple dredge units for the purposes of sampling and analysis. Sampling showed that the dredge footprint contained a mixture of clean and contaminated sediment and the engineering team designed the dredge and fill plan so that areas not found to be open-ocean suitable would be dredged first and placed lower in the fill site (below elevation 0 feet MLLW). Placing the unsuitable material in the fill site eliminated 23000 truck trips to an upland site along with the resulting traffic and air quality impacts.
When mining material for land reclamation it is common practice to dredge a deep hole possibly 80 feet deep which can result in anoxic conditions detrimental to the benthic community. The port reduced these impacts by dredging across a larger area to a depth of -55 feet MLLW where navigational dredging would occur in the future. Although the port needed to dredge to -70 feet in one portion to access better quality geotechnical material that area was designed not as a deep hole but as a gradual slope from the West Basin into the port’s Main Channel which is already -76 feet deep.
Additional environmental benefits include using an electric dredge and Tier 2 tugs to mitigate air quality impacts.
In the design phase of the project creosote pile remnants from the old Navy piers were discovered and removed during the construction phase. Also the geotechnical and environmental sediment sampling was performed simultaneously using the same vessels which minimized vessel mobilization and working time.
Only three of the 18 dredge units were not suitable for open-ocean placement and were slated to be placed low in the fill site. When the sampling results were presented to the regulatory agency members some had concerns over total polychlorinated biphenyl (PCB) levels in four additional areas and requested that those areas also be placed low in the fill site. A total of 400000 cubic yards of sediment were judged to be contaminated enough for placement in low areas.
The port’s engineering design team had to sequence the dredging to place the unsuitable material from the West Basin along with unsuitable material from other sources in the port below 0 feet MLLW in the fill site. These sediments also had to meet the right geotechnical characteristics at each elevation for constructability. This process was a beneficial use of these contaminated materials.
Economic Benefits of Beneficial Use
The Port of Long Beach saved more than $35 million in contaminated sediment treatment costs by using this material in the reclamation project. Open water disposal of the clean sediments from the West Basin would have cost an additional 20 to 30 percent more per cubic yard so their beneficial use in the reclamation also saved the port considerable cost.
The proximity of the West Basin site to the MHT fill site as a source of borrow material provided cost savings as it allowed for the use of both mechanical and hydraulic dredging. Hydraulic dredging is more efficient and less expensive than mechanical dredging and is better for air quality since it eliminates barge trips to the placement site.
This approach could be utilized by other seaports if a similar opportunity presents itself – i.e. a need to perform navigational dredging along with a disposal site available for clean and contaminated material. This project can serve as a model to think strategically and coordinate between different divisions/departments to determine if any projects can be paired up on the same time schedule and whether work can be performed under existing permits. Also it may be worth the effort to perform both geotechnical and chemical sampling of a navigational dredge area to determine whether it can provide structural material for a future fill site.
The port coordinated with the regulatory agencies and presented several updates on this project to the Los Angeles Contaminated Sediments Task Force (CSTF) which focuses on the management of contaminated sediments in the Los Angeles area. It includes representatives from the U.S. Army Corps of Engineers U.S. Environmental Protection Agency California Coastal Commission Los Angeles Regional Water Quality Control Board California Department of Fish and Game Port of Long Beach Port of Los Angeles City of Long Beach Los Angeles County Beaches and Harbors Heal the Bay and other interested parties. Using the CSTF helped to involve all the key agencies that regulate dredging and fill activities environmental groups and organizations involved in dredging which helped to keep all parties informed and make the approval process more efficient.
The port and construction contractor worked closely with the terminal operator to work around shipping schedules and avoid impacts to the Pier T Terminal ensuring that dredging could be completed as planned to line up with the MHT fill site schedule.
Papers on this project were presented at the 2015 WEDA Pacific Chapter Conference and the 2016 Coasts Oceans Ports and Rivers Institute (COPRI) and World Association for Waterborne Transport Infrastructure (PIANC) Ports conference.