St. Clair River Area of Concern

Engineering and Design Plan for Management

of Contaminated Sediment

Mike Moroney, Project Manager

St. Clair Region Conservation Authority

Background information on the St. Clair River

Area of Concern

Efforts to date to address mercury contaminated sediment in

the three priority areas of the St. Clair River

Outcome of the assessment of the most recent

sediment, worm, and fish data

Work planned for the engineering and

design plan phase

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Overview

Cooperation on the Great Lakes

International Joint

Commission

Boundary Waters Treaty

(1909)

Great Lakes Water Quality

Agreement

Canada –U.S.

Canada

Federal Great Lakes

Program

Canada-Ontario

Canada-OntarioAgreement

Ontario

Great Lakes

Strategy

3

• The St. Clair River is one

of the Areas of Concern

(AOC) established by the

Great Lakes Water

Agreement (GLWQA)

• Under both the GLWQA

and the Canada-Ontario

Agreement key actions

are identified for the

clean-up of AOCs

• Management of

remaining mercury

contaminated sediments

within the St. Clair River

AOC is one of the key

projects in order to delist

it as a Great Lakes AOC

Great Lakes Areas of Concern

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St. Clair River Area of Concern

Significant Accomplishments to Date:

• Over $75 million has been invested in combined

sewer overflow remediation by the City of Sarnia

• $115 million dollars in ongoing industrial wastewater

improvements over the past 10 years

• $35 million to upgrade the Sarnia, Corunna and

Courtright Sewage Treatment Plants

• On-going shoreline softening effort (approximately

$3 million to date)

• Over 161 hectares (400 acres) of valuable wetland

habitat restored or enhanced within the AOC

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1950s – most of river on shores impaired or degraded

2000 – recovery apparent but three priority areas identified for further study based on benthic community studies

2005 – Initial clean up of three remaining priority areas

History of Sediments in the St. Clair River

1957 1968 1977 1985 2000

This graphic represents

a band of sediment

extending from the

Canadian shoreline.

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St. Clair River Sediment Management Project Overview

• 2005 – A clean-up of contaminated sediment in the river located adjacent to the Dow Canada property was completed. This clean-up was for a number of different contaminants including mercury.

• 2007 - A sediment technical team was established to develop a sediment management strategy for the remaining contaminated sediments. This team included Environment and Climate Change Canada, Ministry of the Environment Conservation and Parks, Sarnia Lambton Environmental Association, St. Clair Region Conservation Authority, Walpole Island First Nation and Aamjiwnaang First Nation.

• 2009 – Sediment assessment of three remaining priority areas completed.

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Remaining Priority Areas for Sediment Management

Priority Area 1

at Suncor Docks

Priority Area 2

at Shell Docks

Priority Area 3

at Guthrie Park

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CorunnaStag Island

St. Clair River Priority Areas Sediment Assessment 2009

• Used the Canada-Ontario Decision-Making

Framework For the Assessment of Great Lakes

Contaminated Sediment.

• Used four lines of evidence:

• Sediment Chemistry

• Sediment Toxicity

• Benthic Community Structure

• Biomagnification Potential

• Results showed high mercury concentrations and

risk of biomagnification in fish

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Sediment Management Goals:• Control this source as it contributes to

downstream sites• Promote local risk reduction• Contaminant mass removal/isolation

St. Clair River Sediment Management Options

2013 – Sediment Management Options report was completed and extensive community engagement conducted on the options.

• Supporting work included Geophysical, Geochemical, and Geotechnical studies.

• Short listed conceptual designs were developed, these included;

o Hydraulic dredging (vacuuming of sediment and

water)

o Blended option (hydraulic dredging and thin-layer

capping)

o Isolation capping

• Endorsement for Hydraulic dredging was received from:

o Technical Team,

o St. Clair River Canadian Remedial Action Plan

Implementation Committee,

o St. Clair River Bi-national Public Advisory Council,

o Aamjiwnaang First Nation and Walpole Island First

Nation.

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2016 – A technical team was formed to review data from three priority areas to review the toxicity reference value to determine risk to fish, and to look at implementation issues based on different management actions

St. Clair River Sediment Management Data Review

Review

existing and

new data for

the priority

areas

Integrate review

findings into

updated

conceptual site

modelsConsensus

on Sediment

management

scope

Technical

working

group formed

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• MECP collected sediment and worm samples in 2010 and 2011 within the priority areas

• MECP/MNRF also collected fish samples in 2015 in the upper, middle, and lower reaches of the St. Clair River

• The new dataset enabled the technical team to recalculate the potential accumulation of mercury from sediment to worms to fish

• And then predict the concentration of mercury in sediment that would result in concentrations in fish below levels of concern in fish residing in the priority areas.

New Data and Analyses

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2015 Fish Sampling Locations In Upper and Middle Reaches of St Clair River

Upper St

Clair River

Middle St Clair River

Priority Areas

1

2

3

Michigan

Ontario

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• Evaluated top 15 cm because surface sediment is more important than deep sediment for biological exposure

• Mercury in deep sediment is not available to biota and unlikely to be disturbed

Sediment Data Water

Surface

Sediment

Deep

Sediment

Mixing

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Area 1

Area 2

Area 3

Mercury Concentrations in Surface Sediment

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• Considered two protective concentrations (i.e., toxicity reference values or TRVs) for mercury in fish– 0.2 mg/kg (Beckvar et al. 2005)– 0.77 mg/kg (Fuchsman et al. 2016)

• The higher value was based on review of the same studies included in Beckvar et al. (2005) as well as more recent studies and data from field investigations

• For purpose of this evaluation, the focus was on 0.2 mg/kg in fish

What Levels of Mercury in Fish are Safe for Fish?

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• Mercury concentrations in fish were generally low

• All but two species had average concentrations < 0.2 mg/kg on a whole body basis

• Freshwater Drum and Yellow Perch had slightly higher average concentrations but they are migratory fish with other potential sources of mercury exposure

2015 Fish Data from Upper and Middle Reaches

Yellow Perch

Freshwater Drum

Redhorse Sucker

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• Objective = Identify the mercury concentration in sediment that is protective of fish

• Calculated mathematical relationship between– Sediment and worms– Worms and fish

• Based on new and historical data

Predicting Fish Mercury from Sediment Mercury

Redhorse suckerWormsSediment

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• First, the technical team predicted mercury in worms based on mercury concentration in sediment

• Based on the mathematical relationship within the 2010/2011 paired worm and sediment data

Sediment to Worms

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• Then, the team predicted

mercury in fish based on

predicted mercury

concentration in worms

• Calculated two biomagnification

factors (BMFs) based on new

data and on new + historical

data

• Results were similar and both

BMFs were used in the analysis

Worms to Fish = Biomagnification Factor

= BMF

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• The team’s analyses predict that an average mercury concentration in sediment of 3 mg/kg will result in an average concentration in fish of 0.1 – 0.2 mg/kg

• Fish are exposed to average concentrations in worms and sediment because they feed over a large area

Fish Mercury

0.1 – 0.2 mg/kg

BMF

Redhorse suckerWormsSediment

3 mg/kg

Sediment to Fish

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• Action level is the concentration above which remediation will take place

• The technical team evaluated a range of action levels and calculated what the average mercury concentration would be after remediating sediment greater than the action level and replacing with a layer of clean backfill

• An action level of 10 mg/kg was selected because it results in an average mercury concentration in sediment that is protective of fish

Identification of Action Level in Sediment

Sediment Mercury

Action Level

10 mg/kg

3 mg/kg

Sediment

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Area 1

Area 2

Area 3

CurrentMercury Concentrations in Surface Sediment

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Remove Sediment with Mercury > 10 mg/kgReplace with Clean Backfill

Area 1

Area 2

Area 3

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Action Level of 10 mg/kg in Sediment Predicted to Result in Fish Mercury of 0.1 – 0.2 mg/kg

Fish Mercury

0.1 – 0.2 mg/kg

BMF

Redhorse suckerWorms

Sediment Mercury

Action Level

10 mg/kg

Sediment

3 mg/kg

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• Remove sediment via hydraulic dredging or, in targeted areas, mechanical dredging where mercury concentrations in surface sediment exceed 10 mg/kg

• Replace with a layer of clean backfill so average mercury in each priority area is 3 mg/kg

• In areas inaccessible for dredging, consider capping to cover contamination

• Details will be refined based on additional data collection during detailed engineering design of the remedy

Outcome of Re-evaluation

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Detailed Engineering and Design Project

• December 2018 - Announced that the St. Clair Region Conservation Authority had been granted funding from Environment and Climate Change Canada, the Ontario Ministry of the Environment, Conservation and Parks, and Dow for this phase of the project.

• St. Clair Region Conservation Authority took the lead in the management of the detailed engineering and design plan work to further refine an implementation plan, and costs for remediation of contaminated sediment.

• Information sessions began in April 2019 to engage the public, Indigenous communities, stakeholders and others on the project work, key tasks, and timelines.

• Parsons Inc. was hired in August 2019 to begin the technical work.

• Design work will take up to two years to complete, and is scheduled to be completed by spring 2021.

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Detailed Engineering and Design ProjectScope of Work

Work to be undertaken by the consulting firm will include:

• Collecting sediment samples in each of the three priority areas to better define the area of contaminated sediment to be dredged

• Assessing the potential for erosion by conducting water velocity measurements and assessing surface sediment

• Assessing the condition of structures in the vicinity of the areas to be dredged (e.g. docks, containment walls)

• Identifying staging areas that can be used along the shoreline during the implementation phase of the sediment remediation work.

• Preparing detailed design drawings and specifications for remediating the mercury contaminated sediment in each of the three priority areas, using hydraulic dredging and a backfill approach, or alternative, if required, due to site specific conditions.

• Providing details on how contaminated sediment that is removed will be managed, and how downstream water quality will be protected during sediment remediation work.

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Hydraulic Dredging

Hydraulic Dredge

Existing Mudline

Cutter HeadDredging Position

Cutter HeadMaintenance Position

FloatingPipeline

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Hydraulic Dredging Example

Cutterhead dredge

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Mechanical Dredging

Existing Mudline

Clam ShellDigging Position

Clam ShellClosed Position

Transport Barge

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Mechanical Dredging Example

Derrick dredge with CableArm

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Broadcast spreader

Hydraulic slurry

Cap Placement Techniques

Conveyor belt

Mechanical bucket

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(7) Post Construction

(6) Implementation\Construction

(5) Tender Award

(4) Detailed Engineering and Design Plan

(3) Sediment Management Options Conceptual Engineering Design

(2) Conceptual Design

(1) Sediment Assessment

Increasing Certainty

in Cost Estimate

Certainty of Project Cost Estimate

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Stages of Sediment Projects

Next Steps

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Activity Timing

Conduct field work to gather additional

information to address data gapsFall 2019

Submit draft Engineering and Design Plan Spring 2020

Meetings on proposed measures to protect

water quality during dredging and backfilling

activities

Spring 2020

Conduct additional field work if necessary to

address any remaining data gaps Spring/Summer 2020

Submit second draft Engineering and

Design PlanWinter 2020

Submit final Engineering and Design Plan May 2021

Questions?

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