milestone environmental contracting...

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SMART Remediation - Ottawa

Milestone Environmental Contracting Inc.

Case Study: Arsenic Groundwater Remediation Using a Zero Valent Iron (ZVI) Permeable Reactive Barrier (PRB)

and ZVI Injection

Jeffrey Burke, P.Eng.February 27, 2014


Overview• Introduction and Background Information• RFP Process and Remedial Approach• ZVI-PRB Theory• Bench Scale Testing• ZVI-PRB Design• ZVI Injection Program• ZVI-PRB Installation• Site Restoration• Monitoring Program• Closing Remarks and Question Period

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Introduction / Background• Former site of tanning and

lead smelting operations• Currently a rowing / canoe

club and public park• Significant soil and

groundwater impacts from arsenic

• Relatively minor chromium, lead, and mercury impacts

• Concern over discharges to the adjacent Cataraqui River and Lake Ontario

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Introduction / Background

• Soils were leachate toxic waste for arsenic

• Soil up to 16,400 ppm arsenic vs. 18 ppm Table 9 SCS

• Groundwater up to 204,000 ppb arsenic vs. 1,500 ppb Table 9 SCS

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Introduction / Background

• Groundwater flow estimated 5 m/year

• Arsenic Impacted groundwater at 2-4 mbgs

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RFP Process and Remedial Approach

• Client – The City of Kingston’s Environment & Sustainable Initiatives Department

• Stakeholders – Kingston Rowing Club, Cataraqui Canoe Club, Utilities Kingston, Cataraqui River Stakeholders Group (Transport Canada, Parks Canada, Environment Canada, Ontario MOE, RMC)

• General Contractor – Milestone Environmental Contracting, Inc.

• Key Subcontrator – Vertex Environmental Inc.

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• Excavate and dispose of over 1,000 mt of soil

• Estimated $500/mtdisposal cost

• Excavation Dewatering• Sub-Grade Cut-Off

Wall Installation• Vertical Groundwater

Extraction Well• Backfill/Restoration

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RFP Process and Remedial ApproachOriginal Scope


RFP Process and Remedial Approach• Client utilized a structured RFP procurement

process including a weighted evaluation of proposals• Value-Added Environmental Solutions and methods

were given higher consideration (reduce soil disposal and water treatment)

• Approx. 30 contractors downloaded the bid package• Milestone teamed with Vertex to develop a

sustainable alternative, cost-saving remedial plan: ZVI PRB with minimal soil excavation and access disruption

• Several meetings with the Client & MOE led to approval for proof-of-concept bench-scale testing

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RFP Process and Remedial Approach

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• Excavate and dispose of only 150 mt of soil (PRB trench spoils)

• Complete Downstream ZVI Injection

• Install ZVI PRB Funnel and Gate Wall

• Backfill/Restoration

Alternative Scope


ZVI and PRB Theory• PRB acts as long-term, passive solution for in-situ

treatment of arsenic contaminated groundwater• Corroding iron (ZVI) creates an environment

supportive for sulphate reducing bacterial growth• The decrease in ORP chemically reduces arsenate

(As5+) to arsenite (As3+)• Some dissolved arsenic passing through the PRB is

sorbed directly onto iron oxide particles• Other dissolved arsenic is removed from solution via

precipitation or co-precipitation as an insoluble sulfide (with or without iron sulfide)

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Bench-Scale Testing• Prepared 4 bench-scale

and 2 control tests• Groundwater control

test (no media)• Media control test

(100% coarse sand)• ZVI design (20% ZVI,

80% coarse sand)• Enhanced ZVI Design

(20% ZVI, 2% EHC-M, 78% coarse sand)

• Benthic sediment (150 g) added to all bench tests due to sulphate reducing properties

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Bench-Scale Testing

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Sampling ports

Assembled test cell

Groundwater from site

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Bench-Scale Testing

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B

A

F

E

C

D

A. HDPE Test CellB. Nitrogen TankC. Primary

Sampling PortD. Secondary

Sampling PortE. Injection PortF. Airlock

SMART Remediation - Ottawa 03/10/2014

Control Samples ZVI Samples

ZVI + EHC-M Samples(Enhanced ZVI test)

Bench-Scale Testing

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Bench-Scale Testing


Bench-Scale Testing

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Bench-Scale Testing


Bench-Scale Testing

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• Within three (3) weeks arsenic concentrations in groundwater dropped from 23,100 ppb to average of 87 ppb in test cells (99.6% reduction) and to average of 3.6 ppb after four (4) weeks (99.98% reduction)

• MOE Table 9 site condition standard = 1,500 ppb• ZVI PRB concept proven decisively• Arsenic removal half-life estimated at 2.5 days• Noting substantial cost-savings and enhanced

environmental sustainability, contract was awarded to Milestone for ZVI-PRB installation

Bench-Scale Testing


• Client requested ZVI-PRB wall installation combined with secondary ZVI injection program

• Traditional PRB (cut & fill): “funnel and gate” design with concrete wing walls and central PRB section

• Injected PRB: based on an in-situ ZVI concentration of 1.5% by weight soil mass (Slurry = 30% ZVI by weight)

• Design contact time of groundwater within PRB was approx. 40 days, more than sufficient to achieve required treatment based on bench and site data (i.e., 6.5–14 days)

• Traditional PRB lifespan estimated at >20 years• Both “keyed” into silty clay till

ZVI-PRB Design

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ZVI-PRB Design


ZVI-PRB Design

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ZVI-PRB Design


ZVI Injection Program

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• Injected PRB installed first near shoreline (3 day program)

• Two (2) test boreholes advanced & sampled to confirm depth of “confining layer”

• Total of eleven (11) temporary injection points on a 1.5 m spacing from 1.5 to 3.5 mbgs

• Total of 2,450 kg micro-scale ZVI in a 30% slurry (8,100 L total)

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Silty clay till“confining layer”

Upper fill soils

ZVI Injection Program


ZVI-PRB Installation

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ZVI-PRB InstallationLine of

temporary points

for injected PRB

Excavation for“cut & fill” PRB


Macro-scale ZVI mixed withconcrete sand in cement truck

Macro-scale ZVI & concrete sandmixture placed into excavation


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Geotextile fabric

placed over ZVI PRB

Remaining excavationBackfilled with granular fill



• Traditional PRB was 5.2 m long, 1.0 m wide and from 2.0 to 3.8 mbgs “keyed” 0.5 m into silty clay till

• Total of 9,000 kg macro-scale ZVI mixed with 12,600 kg “concrete sand”

• One (1) day to direct place in two (2) loads• Vertex completed QC/QC testing on batches

of ZVI/sand mixture (magnetic separation)• Target minimum 30% ZVI by weight; results

were 40.5% & 43.2%, averaging 41.9% ZVI


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GCL Base Prep

GCL Liner Install

Asphalt Pad Prep


Site Restoration

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• City to install monitoring wells surrounding the PRB wall and injected PRB

• City to develop ongoing water quality monitoring program

• Analytical results pending

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Monitoring Program


Closing Remarks

• Milestone teamed with Vertex to offer a value-added and non-traditional solution to a significant environmental problem

• Bench-scale testing completed as “proof of concept” (very successful: 99.98% reduction of arsenic in groundwater)

• Full-scale project awarded to Milestone and Vertex by City of Kingston

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Closing Remarks

• Project benefits to client:▫ Significant cost savings over soil excavation

and disposal as hazardous waste at $500/tonne

▫ Much less physically disruptive to site and users

▫ Environmentally sustainable solution to problem

▫ No on-going pump and treat requirements for groundwater


Questions???

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Kevin French, P.Eng.Vertex Environmental Inc.(519) 653-8444 x304 office

(519) 404-5442 [email protected]

www.vertexenvironmental.ca

Jeffrey Burke, P.Eng.Milestone Environmental Contracting Inc.

(416) 214-4197 office(647) 389-4173 [email protected]

www.milestoneenv.ca

Thank You For Your Time and Attention

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