PIANC Dredging 2012 Conference Castro Cove Sediment Remediation Project, Richmond, California Ian...
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Transcript of PIANC Dredging 2012 Conference Castro Cove Sediment Remediation Project, Richmond, California Ian...
PIANC Dredging 2012 Conference
Castro Cove Sediment Remediation Project, Richmond,
CaliforniaIan Austin PhD PE - URS Corporation
Paul Ryan – Chevron Environmental Management CompanyMark Sutton – Dixon Marine Services
Why of Interest?Technically challenging mudflat environmentSpecialty equipment designed to place “no-net-fill” 20-
acre capConsolidation of hydraulically placed beneficial re-use
mud layerShear stress modeling prior to sheet pile removal
Castro Cove Sediment Remediation Project Site Location
• Embayment of San Pablo Bay in north San Francisco Bay
• Adjacent to active refinery• Mudflats at +2 to +3 feet MLLW• Shear strengths; 50, 150 psf at 1, 2 foot depths
Castro Cove Sediment Remediation Project AOC
• Effluent discharged into Cove from early 1900s until 1987
• ERA: 20-acre AOC based on PAHs, mercury, benthic risk
• 2007: Dredged 97,000 cy sediment, placed upland • Approximately 6-inch thick layer of residual
contamination remained in AOC after dredging
Castro Cove Sediment Remediation ProjectEngineered Cap Design
• Cap designed using lab tests and chemical flux modeling, expert peer review (Danny Reible)
• Sequential Batch Leach, Thin Column Leach, and cap-loading tests used to develop partition coefficients and sorption capacities
• Design includes; • “No-net-fill” requirement, < 97,000 cy• 1.5 acres of Reactive Core Mats
(RCM), • 6-inch+ sand layer for chemical
isolation and containment, • 18-inch+ clean Bay mud layer to
restore biological viability for benthic communities
Castro Cove Sediment Remediation Project
Sand Placement Challenge• Performed “in-the-wet” with 3 to 5 feet
of water inside 2,700 foot sheet pile enclosure
• Adjacent to an operating refinery• Place a nominal 6-inch layer of sand over
20-acres (45,000 cy maximum) • Could not disturb or re-suspension
residual contamination• RWQCB Order only allowed discharge of
water inside sheet-pile after sand placement and WQ confirmation testing: closed loop system
• Required finesse, rather than bulk production
Castro Cove Sediment Remediation ProjectSand Placement
thr
Specialized Equipment Design: • Worked with DMS on hydrodynamic design of
spreader• Hydraulic placement of sand pumped 5,000 feet,
needed to reduce velocities from 14 fps to 2 –> 3 fps• Used computer model (HEC-RAS) to design spreader
plate, flare width and slope• Modular construction based on two 10-ft by 40-ft
pontoons
Sand Placement
Automated sand slurry system used to produce accurate slurry concentrations: spreader position only variable
Castro Cove Sediment Remediation Project
Sand Layer Confirmation: Sand barge delivery volumes
Bi-weekly bathymetric surveys using purpose-built, shallow-water, 5-beam
“sweep” systemSand core collection in clear PVC tubes
Castro Cove Sediment Remediation Project
Mud Layer Placement Challenge: Two weeks prior to start-up, required to change from hydraulic to mechanical dredging due to post-permit (DF&G)
change in position regarding impacts to long-fin smelt
Beneficial reuse of 37,500 cy of dredge sediment from Richmond Rod & Gun Club
Yacht Harbor dredgingBeneficial reuse of 13,000 cy from Point
San Pablo Yacht Harbor; 8,000 feet of pipe
Castro Cove Sediment Remediation Project Mechanical Hydraulic Dredge
Castro Cove Sediment Remediation Project AOC Confirmation Cross
Sections
Total sand and sediment volume: 95,500 cy
Castro Cove Sediment Remediation Project
Clay Layer Consolidation Challenge: Dewatered AOC to promote consolidation of mud
slurryExtended consolidation time from one month to
four months based on shear strengthsMeasured in-situ shear strength in surrounding
mudflatsMeasured strength of mud in AOC along diagonal
transect – field shear vane measurements
Castro Cove Sediment Remediation ProjectShear Vane Transect
Castro Cove Sediment Remediation ProjectMIKE 21 Shear stress modeling of sheet pile removal
Modeled tide-specific sequencing options for reintroducing the tideFirst: 300-ft pushed down to create 1-foot high weir -> minimize initial tidal prismSecond: sheet removal with two barge cranes along north face
Castro Cove Sediment Remediation Project Conclusions
• Cooperation between regulatory agency, owner, engineer, contractor needed to complete the project (from 1997 to 2012)
• Integration of science, engineering, construction needed to meet technical challenges (material delivery, mud consolidation, sheet pile removal)