03/10/2014
1
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
SMART Remediation - Ottawa
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
03/10/2014
03/10/2014
2
SMART Remediation - Ottawa
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
03/10/2014
SMART Remediation - Ottawa
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
03/10/2014
03/10/2014
3
SMART Remediation - Ottawa
Introduction / Background
• Groundwater flow estimated 5 m/year
• Arsenic Impacted groundwater at 2-4 mbgs
03/10/2014
SMART Remediation - Ottawa
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.
03/10/2014
03/10/2014
4
SMART Remediation - Ottawa
• 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
03/10/2014
RFP Process and Remedial ApproachOriginal Scope
SMART Remediation - Ottawa
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
03/10/2014
03/10/2014
5
SMART Remediation - Ottawa
RFP Process and Remedial Approach
03/10/2014
• 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
SMART Remediation - Ottawa
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)
03/10/2014
03/10/2014
6
SMART Remediation - Ottawa
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
03/10/2014
SMART Remediation - Ottawa
Bench-Scale Testing
03/10/2014
Sampling ports
Assembled test cell
Groundwater from site
03/10/2014
7
SMART Remediation - Ottawa
Bench-Scale Testing
03/10/2014
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
03/10/2014
8
SMART Remediation - Ottawa 03/10/2014
Bench-Scale Testing
SMART Remediation - Ottawa 03/10/2014
Bench-Scale Testing
03/10/2014
9
SMART Remediation - Ottawa 03/10/2014
Bench-Scale Testing
SMART Remediation - Ottawa 03/10/2014
Bench-Scale Testing
03/10/2014
10
SMART Remediation - Ottawa 03/10/2014
• 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
SMART Remediation - Ottawa 03/10/2014
• 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
03/10/2014
11
SMART Remediation - Ottawa 03/10/2014
ZVI-PRB Design
SMART Remediation - Ottawa 03/10/2014
ZVI-PRB Design
03/10/2014
12
SMART Remediation - Ottawa 03/10/2014
ZVI-PRB Design
SMART Remediation - Ottawa
ZVI Injection Program
03/10/2014
• 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)
03/10/2014
13
SMART Remediation - Ottawa 03/10/2014
Silty clay till“confining layer”
Upper fill soils
ZVI Injection Program
SMART Remediation - Ottawa 03/10/2014
ZVI-PRB Installation
03/10/2014
14
SMART Remediation - Ottawa 03/10/2014
ZVI-PRB InstallationLine of
temporary points
for injected PRB
Excavation for“cut & fill” PRB
SMART Remediation - Ottawa 03/10/2014
Macro-scale ZVI mixed withconcrete sand in cement truck
Macro-scale ZVI & concrete sandmixture placed into excavation
ZVI-PRB Installation
03/10/2014
15
SMART Remediation - Ottawa 03/10/2014
Geotextile fabric
placed over ZVI PRB
Remaining excavationBackfilled with granular fill
ZVI-PRB Installation
SMART Remediation - Ottawa 03/10/2014
• 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
ZVI-PRB Installation
03/10/2014
16
SMART Remediation - Ottawa 03/10/2014
ZVI-PRB Installation
GCL Base Prep
GCL Liner Install
Asphalt Pad Prep
SMART Remediation - Ottawa
Site Restoration
03/10/2014
03/10/2014
17
SMART Remediation - Ottawa
• City to install monitoring wells surrounding the PRB wall and injected PRB
• City to develop ongoing water quality monitoring program
• Analytical results pending
03/10/2014
Monitoring Program
SMART Remediation - Ottawa 03/10/2014
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
03/10/2014
18
SMART Remediation - Ottawa 03/10/2014
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
SMART Remediation - Ottawa
Questions???
03/10/2014
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
Top Related