Los Angeles Basin Contaminated Sediments Task Force

Summary of Aquatic Disposal and Dredge Operations
Committee Meeting
February 25, 1999

1. The Aquatic Disposal subcommittee met on February 25, 1999 at the Los Angeles District office. The U.S. Army Corps of Engineers Waterways Experiment Station (WES) briefed the subcommittee members on the status of their effort to analyze the North Energy Island Borrow Pit as a potential subaqueous capping site for contaminated dredged sediments.
2. Representatives from WES included the following:
   

Dr. Joseph Galiani (Coastal and Hydraulics Laboratory)
Mr. Jim Clausner (Coastal and Hydraulics Laboratory), Telephone Conference
Ms. Barbara Tardy (Environmental Laboratory)
Dr. Michael Palermo (Environmental Laboratory), Telephone Conference

3. Ms. Tardy presented the subcommittee members with the status of the contaminant flux analysis currently being conducted by the Environmental Laboratory. To date, the following contaminant flux work has been accomplished by the Environmental Laboratory:

• Physical Characterization of the Marina del Rey (dredged material) and Queens Gate (capping material) sediments.
• Chemical Characterization of the Marina del Rey (dredged material) and Queens Gate (capping material) sediments.
• Batch Adsorption tests were accomplished with aqueous contaminants on the capping material to obtain adsorption coefficients for metals. The sorption coefficients obtained by the batch adsorption tests will be used in contaminant transport models to predict advective and diffusive transport of contaminants.

4. Ms. Tardy informed the subcommittee members that the Environmental Laboratory was awaiting NRC approval to utilize Nickel-63 as a tracer to continue with the contaminant flux analysis. The additional contaminant flux work would include the following:

• Conduct Centrifuge Testing of the contaminated and cap material to physically model pore water advection due to consolidation of dredged material after cap placement, advective transport of contaminants, and sorption by cap material. Results of the centrifuge tests will be used to validate the results of the contaminant transport model.
• The Capping Analysis Program (CAP) is a numeric contaminant transport model that will be used by the Environmental Laboratory to predict contaminant flux by diffusion, bioturbation, and advection induced by consolidation.

5. The second half of the meeting was dedicated to receive a status report from WES's Coastal and Hydraulics Laboratory (CHL) on their work effort to develop dredged material placement scenarios to obtain the optimal mound geometry and to analyze potential storm-induced erosion of the capped mound.
6. Mr. Jim Clausner (CHL) reported (via telephone conference call) the status and results of the dredged material placement and mound geometry work. In summary, Mr. Clausner utilized the multiple dump FATE (MDFATE) model developed by WES to simulate three placement scenarios within the east end of the North Energy Island Borrow Pit. These scenarios included placement within the Borrow Pit of: 1) 190,000 cubic meters of Marina del Rey sediments; and, 2) 230,000 cubic meters of Marina del Rey sediments followed by an additional 230,000 cubic meters of Los Angeles River Estuary sediments. The design goal for placement of the contaminated material was to achieve a level surface for the disposal mound with minimal material spilling outside the rim.
7. Mr. Clausner presented a placement scenario that resulted in a near flat mound surface within the borrow pit, with minimal loss of sediments outside the disposal area. Mr. Clausner stated that there would be small loss outside of the intended disposal area, but could not quantify the extent and volume with the MDFATE model. Mr. Clausner recommended various monitoring techniques that could identify the losses outside of the target area. Decisions on whether or not corrective actions would be required for the losses could be made based on the monitoring results. Mr. Clausner recommended an overall project monitoring program that includes: 1) bathymetric surveys; 2) sub-bottom profiling; 3) sediment profile imaging surveys; 4) core and grab sampling; 5) real-time current monitoring; and, 5) water quality monitoring.
8. Dr. Joseph Galiani (CHL) reported on his work to analyze the potential for storm-induced and long-term erosion of the capped mound utilizing the Long-Term FATE (LTFATE) numeric model. Erosion scenarios for five mound configurations within the borrow pit were run by Dr. Galiani. These configurations included: 1) a disposal mound containing 190,000 cubic meters of contaminated dredge material with a 1.2 meter cap; 2) a disposal mound containing 465,000 cubic meters of contaminated dredged material with a 1.4 meter cap; and, 3) hypothetical mounds with crests depths of -13.7 meters, -11.9 meters, and -9.1 meters.
9. Dr. Galiani discussed the data collected prior to running the LTFATE model, which included: 1) obtaining the Borrow Pit's bathymetry (Los Angeles District); 2) physically characterizing the dredged and cap material (WES); 3) establishing the erosion rate coefficients for the cap material (UC Santa Barbara); 4) collecting tidal and LA River discharge currents (Los Angeles District); 4) obtaining historic storm wave and LA River storm runoff parameters (Los Angeles District); and, 5) simulate near bottom currents using the CH3D Hydrodynamic Model (WES).
10. Dr. Galiani reported that for the worst case storm event (return period of 200 years) LTFATE simulations predicted a maximum cap erosion of 34 centimeters (approximately 1 ft) for a mound with a crest elevation of -9.1 meters. For the mound configuration containing 190,000 cubic meters of contaminated dredged material with a 1.2 meter cap, LTFATE simulated a maximum vertical erosion of 22 cm (approximately 8.5 inches).
11. Dr. Galiani was asked to comment on what the extent of the vertical erosion would be if the North Energy Island Borrow Pit were to experience a series of 200 year storm events. Dr. Galiani responded that he believed subsequent cap erosion rates would be greatly reduced because of cap material consolidation at the mid to lower layers. Dr. Galiani also commented that bathymetric surveys of the capped mound should take place after any significant storm event to assess the need for replacement of any cap material loss.
12. List of Aquatic Disposal Subcommittee members that attended the February 25, 1999 meeting:

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