Remediation of contaminated sediments in open water is a complex and inten-
sive operation. The presence of adjacent industrial activities on land, varied
dockwall and pier design, utility entries into slips, and aging infrastructure,
each complicate the design of an effective remediation strategy. Slip 2 is one
of eight slips in the St. Louis River Area of Concern (AOC) impaired by legacy
contamination from industrial and municipal wastes and harmful land use prac-
tices. Soil samples taken from behind the dockwall of the adjacent Pier B site
contained asbestos and exceeded MPCA recreational soil reference values for
arsenic, mercury, semi-volatile organic compounds (SVOCs), and diesel range
organics (DRO). Dive inspections revealed extensive failures in the existing
dock walls, leaving voids where contaminated site soils leeched into Slip 2 and
out into Lake Superior. The conventional method of slip remediation by dredg-
ing to remove contaminated sediment would have further deepened the slip,
causing complete failure of the adjacent dockwalls and accelerated leeching of
contaminated soil into Slip 2.
AMI consulting Engineers developed a phased approach for the remediation of
Slip 2, coupling the remediation of the slip with that of the adjacent pier. Exca-
vation and removal of contaminated soil from along the dock wall, and repairs
to the dock wall system were critical to the long term success of the Slip 2 sed-
iment remediation. The remediation strategy and lessons learns from Slip 2
should serve as a model for future slip remediation efforts in the St. Louis Riv-
er Area of Concern.
Variable structural designs and failed dock wall conditions
Adjacent contaminated site soil migrates through failed dock walls;
potential recontamination if not properly contained prior to remediation
Sediments below dock walls have typically not been characterized
Adjacent land is often privately owned and dock wall repairs are cost prohibitive
Unknown future land use complicates overall project design
Multi-agency permitting, approvals, and consultations
Historic preservation of dock walls may limit repair options and complicate project timing
Coordination of dredged materials and USACE hired dredging contractor
Pre-project testing of dredge materials may be insufficient
Contaminated sediment containment and/or disposal during remediation
Conflicting property interests due to multiple property owners
The complexities of slip remediation
Assess the condition and design of the terrestrial and water portions of the dock walls
Characterize sediment contours and contamination below dock walls
Perform comprehensive feasibility study, identify alternatives, and prepare cost estimates
Obtain agency permits and perform consultations (RAPs, EAW, Section 106, etc.)
Secure funding, capping material, and establish remediation credits
Execute a project partnership agreement between land owners and agencies
Design the remediation
91 MAIN STREET SUPERIOR, WI 54880 715.718.2193 AMIengineers.com
Authors: LaRae Lehto, Bryan Murdock, Ted Smith, Doug Olson, Seth Johnson, Chad Scott
Abstract
Pre-Remediation Planning
The complexities of sediment remediation of Duluth Superior harbor slips
CONCRETE SLAB CONCRETE RELIEVING
PLATFORM FILL OF UNKNOWN ORIGIN
WOOD RETAINING WALL ROUND WOOD PILE
MIGRATING FILL
IMPACTED WITH
CONTAMINANTS
DAMAGED RELIEVING
PLATFORM
BROKEN UNSUPORTED CONCRETE SLAB
HEAVILY DETERIORATED
FORM LUMBER UPPER SECTIONS OF
RETAINING WALL
CLEAN SOIL FILL EXISTING CAP
CUT DOWN
NEW CONCRETE BOARDWALK
SLIP SHALLOWED TO SUPPORT PILES STRUCTURES AND CAP CONTAMINANTS
STONE FILL
GEOTEXTILE FABRIC
CONCRETE SLAB CONCRETE RELIEVING PLATFORM
FILL OF UNKNOWN ORIGIN
WOOD RETAINING WALL ROUND WOOD PILE
MIGRATING FILL
IMPACTED WITH
CONTAMINANTS
DAMAGED RELIEVING
PLATFORM
BROKEN UNSUPPORTED CONCRETE SLAB
HEAVILY DETERIORATED
FORM LUMBER UPPER SECTIONS OF RETAINING
WALL ROTTED AND MISSING
CLEAN SOIL FILL TO SUPPORT PILES
CLEAN SOIL FILL
NEW CONCRETE BOARDWALK
NEW SHEET PILE
CONTAINMENT WALL
NEW STEEL CAP
STONE FILL
GEOTEXTILE FABRIC
TIMBER FENDER
ROUND WOOD PILE
CONCRETE CAP
TIMBER CRIB
CONCRETE SLAB
FILL OF UNKNOWN
ORIGIN
TIMBER FENDER MISSING
MIGRATING FILL WITH
CONTAMINANTS
DAMAGED CAP
UPPER REGIONS OF CRIB
HEAVILY DETERIORATED
DAMAGED
FOUNDATION
UNSUPPORTED BROKEN
SLAB
SLIP SHALLOWED TO SUPPORT PILES AND CAP CONTAMIANANTS
DETERIORATED SECTIONS REMOVED
STONE RIP RAP
OR
IGIN
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ON
ST
RU
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ION
D
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ER
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AT
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CO
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ITIO
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DIA
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WOOD PILE / SUPPORTIVE CAP CRIB / CAP REMOVAL & SUPPORTIVE CAP WOOD PILE / SHEETPILE WALL
Arsenic impacts adjacent to Slip 2