treatment using electrical resistance heating (erh) of source
TRANSCRIPT
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Treatment Using Electrical Resistance Heating (ERH) of Source Area CVOCs at a Former Manufacturing Facility, Newtown, CT Art Taddeo
June 13, 2012
Overview
• Site Intro/Conceptual Site Model
• Remedial Approach
• Design and Construction
• Results and Lessons Learned
• Conclusions and Future Activities
• Questions
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Site Intro
• Former metal tubing manufacturing facility operated from
1950’s to 1986
• Site consists of 12 acre former facility and adjacent
undeveloped woodlands/wetlands in suburban area
• Former facility parcel abuts an active railroad line
• Groundwater classification GA/GAA
• Chlorinated solvents from manufacturing process released
to subsurface (TCE, other related compounds)
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Conceptual Site Model
• Residual NAPL observed in former facility building slab
area
• Source impacts observed in fine grained saturated soils
(till), minor permeable drift zones and in weathered bedrock
• Two dissolved plumes: one smaller one to the northwest of
the slab and a larger one northeast of the slab (off-site
plume)
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Conceptual Site Model – Plan View
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Upland
Source Area
Wetland Wetland
Stream
2 mg/L
750 mg/L
20 mg/L
2 mg/L
TCE Plume
RR Track
GW Flow
Conceptual Site Model – Cross Sectional Views
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Source Area
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Remedial Approach
• Targeted soil removal performed to achieve residential
direct exposure criteria (RDEC) in slab area
• SVE was performed on-site in the past with limited success
• A focused feasibility evaluation was performed as well as
an in situ bioremediation pilot study for the on-site slab area
• Remedial strategy: in situ thermal for treatment of slab
source area and in situ bioremediation (ERD) for the west
of slab and off-site plumes
• Slab area treatment goal (760 ppb) modeled TCE levels
that will not exceed surface water criteria off-site
• Technical Impracticability (TI) Waiver permit for the site and
adjacent properties will be pursued
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Permitting / Approvals
• Remedial action plan (off-site thermal impacts a concern)
• CTDEP Wastewater Discharge/UIC Permit
• General Permits for Discharge of Wastewater to Surface
Waters and Sanitary Sewer
• CT DEP air emissions permit applicability (permit
exemption and non-applicability)
• Local inland wetlands and building permits
• Local and State noise ordinances
• Access agreements – railroad and utility company
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Remediation Project Overview
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Staging
Area
Access
Road
Biobarriers
Thermal
Treatment Area Railroad Line
Bioremediation Area
High Voltage Electric
Transmission Lines
Design-Construction
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ERH Design
• Grid (20 ft on center) of 89 steel electrodes to weathered
bedrock (21 to 42 ft bgs)
• Co-located vapor recovery wells screened from 3 to 6 ft bgs
• 8 multi-depth temperature monitoring points (TMPs) with
thermocouples every 5 feet in depth
• Design treatment duration of a minimum of 4 months with
at least 30 days at 100 C to reach 760 ppb or less TCE
(reduction of 99.9% or greater)
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ERH Design
• Design of 4,330,000 kWh energy input
• 600 lbs TCE mass in subsurface slab area
• Thermal oxidizer with four backup 2,000 lb vapor carbon
filters
• Three 2,000 lb liquid carbon filters for condensate/scrubber
wastes
• Recyling of condensate for electrode re-wetting drip, if
necessary
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Power control Unit (PCU)
Condenser and Cooling Tower
Stack,
Scrubber,
Caustic
feed
Electrode field and vapor recovery piping
Vacuum
blower
Thermox
Unit
Vapor
GAC
vessels
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Safety Procedures
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Hot Media Sampling Procedures
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Results/Conclusions
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Thermal Remediation - Heating
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Thermal Remediation – TCE (ug/L) 3 Month post-treat
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11/09: 5,800
5/11: 5
12/09: 12,000
1/11: 140,000
5/11: 4 11/10: 14
1/11: 14,000
5/11: 2
2/10: 30,000
5/11: 2
2/10: 3,100
5/11: 8
6/10: 1,300
11/10: 11,000
5/11: 10
6/10: 1,600
8/11: 19
1/10: 2,200
5/11: 16,000
8/11: 1,400
6/10: 47,000
1/11: 22,000
10/11: 460
6/10: 1
2/11: 88,000
5/11: 39
2/10: 27,000
1/11: 50,000
8/11: 1,600
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Thermal Remediation
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Conclusions
• Temperatures rose above the boiling point of TCE and
water throughout most of the treatment area (exception of
the weathered bedrock where temperatures rose to 80 C
• Very little heat appears to have migrated in groundwater
off-site to the wetlands area (only MW-210WB reached
110 F for 1-2 months)
• TCE concentrations have significantly decreased in
groundwater to date. 19 of 22 wells are now below the TCE
cleanup goal
• The residual TCE mass is very low and the TCE mass flux
has been reduced significantly and is below the TCE mass
flux associated with the cleanup goal for the site
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Lessons Learned
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Conclusions and Future Activities
• Thermal remediation
– Fully heated zones were established
– Treatment of weathered bedrock is
challenging
– Treatment of aqueous and soil phase
CVOCs & residual DNAPL is being
achieved and mass flux reduced
– Stray voltage mitigated cost-effectively
– “All-Inclusive” Cost: $120/CY
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Conclusions and Future Activities
• Thermal remediation
– Future activities include:
• Continued monitoring for rebound and
migration of heated groundwater
• Abandonment of electrodes and TMPs
• Post-remediation monitoring
• Polishing with bio if necessary
• Technical impracticability waiver zone permit
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Acknowledgements
• John Albrecht, L.E.P. (AECOM, Rocky Hill, CT)
• Lucas Hellerich, Ph.D., P.E., L.E.P. (AECOM, Rocky Hill,
CT)
• Paul Dombrowski, P.E. (AECOM, Wakefield, MA)
• Brian Finnell, P.G., C.E.G. (AECOM, Chelmsford, MA)
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