PIANC Dredging 2012 Conference. Castro Cove Sediment Remediation Project, Richmond, California

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1 PIANC Dredging 2012 Conference Castro Cove Sediment Remediation Project, Richmond, California Ian Austin PhD PE - URS Corporation Paul Ryan Chevron Environmental Management Company Mark Sutton Dixon Marine Services Why of Interest? Technically challenging mudflat environment Specialty equipment designed to place no-net-fill 20-acre cap Consolidation of hydraulically placed beneficial re-use mud layer Shear stress modeling prior to sheet pile removal

2 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

3 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

4 Engineered 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

5 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

6 Sand 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

7 Sand Placement Automated sand slurry system used to produce accurate slurry concentrations: spreader position only variable

8 Sand Layer Confirmation: Sand barge delivery volumes Bi-weekly bathymetric surveys using purposebuilt, shallow-water, 5-beam sweep system Sand core collection in clear PVC tubes

9 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 dredging Beneficial reuse of 13,000 cy from Point San Pablo Yacht Harbor; 8,000 feet of pipe

10 Mechanical Hydraulic Dredge

11 AOC Confirmation Cross Sections Total sand and sediment volume: 95,500 cy

12 Clay Layer Consolidation Challenge: Dewatered AOC to promote consolidation of mud slurry Extended consolidation time from one month to four months based on shear strengths Measured in-situ shear strength in surrounding mudflats Measured strength of mud in AOC along diagonal transect field shear vane measurements

13 Shear Vane Transect

14 MIKE 21 Shear stress modeling of sheet pile removal Modeled tide-specific sequencing options for reintroducing the tide First: 300-ft pushed down to create 1-foot high weir -> minimize initial tidal prism Second: sheet removal with two barge cranes along north face

15 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)