Los Angeles Basin Contaminated Sediments Task Force
Summary of Aquatic Disposal and
Dredge Operations
Committee Meeting
February 25, 1999
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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.
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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
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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:
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Physical Characterization
of the Marina del Rey (dredged material) and Queens Gate
(capping material) sediments.
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Chemical Characterization
of the Marina del Rey (dredged material) and Queens Gate
(capping material) sediments.
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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.
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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:
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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.
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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.
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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.
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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.
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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.
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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.
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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).
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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).
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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.
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List of Aquatic Disposal Subcommittee members that attended the February 25, 1999
meeting:
Tony Risko |
Corps of Engineers (Coastal) |
Noel Davis |
Chambers Group |
Russ Boudreau |
Moffatt & Nichol Engineers |
Michael Lyons |
Los Angeles RWQCB |
Lauma Jurkevics |
California Coastal Commission |
Terri Ely |
Corps of Engineers (Regulatory) |
Mitzy Taggart |
Heal the Bay |
Andrew Kadib |
Corps of Engineers (Coastal) |
Joseph Johnson |
Corps of Engineers (Coastal) |
Mo Chang |
Corps of Engineers (Operations) |
Larry Smith |
Port of Los Angeles |
Susie Ming |
Moffatt & Nichol Engineers |
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