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10/03/19NWEC Tacoma

Urban Sites and Complex Plumes: Importance of HRSC and CSM in Developing Effective In Situ Remedial Systems

Presentation Overview• Importance of CSM Development

• Define Source and larger Plume

• HRSC 

• Urban Sites – Design Considerations

• Technology Selection/Remedial Approach

• Access Restrictions

• Development Timeline

• Question & Answer

• Case Studies

• Thermal and combined remedies at urban Sites – Eureka, Bothell and Schenectady 

• Set Remedial goals/Expectations

• Addressing Critical Data Gaps

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Evaluate Current CSM For Addressing Matrix Back Diffusion Potential

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Fill Data Gaps with HRSC ‐MiHPT

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Estimate Contaminant Mass in Saturated Soil From Source To Plume

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Assess Remedial Options  ‐In Situ design consideration and Technology Selection

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Set Remedial Expectations From % mass reduction to MCLs.

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Remediation Roadmap

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The Matrix Diffusion Challenge To Setting Remediation Expectations

• Low K zones serve as ongoing sources of contamination separate from the initial source and throughout the plume footprint

• This source persists for long time periods

• Concentrations in permeable zones rebound following remediation of those zones using some in situ technologies….. But not all

• Thermal is the only technology that addresses source zones, with no rebound post-remediation

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The Matrix Diffusion Challenge To Setting Remediation Expectations

• Assumption that remediation technologies will either cleanup site to drinking water standards or these technologies will allow the residual contaminants be treated or managed by inexpensive institutional controls and/or MNA.

• Advection-dispersion models are commonly used to predict how quickly plumes dissipate after remediation, however very few sites have considered matrix diffusion in this analysis

• Most are overly optimistic!

The Issue

High mass impacted sites in Urban environments present a unique challenge for In Situ Remediation technologies and approaches

• Spectrum of Contaminant Species Present and associated physio‐chemical properties

• CVOCs• BTEX• TPH‐g• TPH‐mo• 1,4 Dioxane

• Multiple phases exist in the subsurface simultaneously and co‐located

• Aqueous (dissolved phase)• LNAPL• DNAPL• Mass sorbed to the soil matrix  

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Matrix diffusion has the potential to sustain dissolved contaminant concentrations in groundwater after the source has been removed or after removal and isolation of contamination from the transmissive compartment. 

Sustained dissolved contaminant concentrations in groundwater after the source has been removed

Address the Source

• Find the mass• Direct Push Tooling• Advanced Data management and 

Modelling• Make sure source zone boundaries 

are properly delineated

• Address the Source• Address the Plume

Not necessarily independent of each other 

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The Solutions

Combined In Situ Remedial Designs

ISTR Technologies

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Conceptual Model of Typical ISTR System

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Section TitleBothell, WA ERH combined with Bio‐recirculation and Bio‐stimulation 

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Bothell, WA – BSCSS Site – ERH and Bio-Recirculation

Bio‐Recirculation Zone

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ERH TREATMENT AREA 

Bothell, WA – BSCSS Site – ERH and Bio-Recirculation

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Source Zone Identification

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ERH/Heat Enhanced Bio Project

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Design ConsiderationsSubsurface Electrodesin the Street

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Post Thermal Heat Enhanced Bio‐recirculation system

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Design Considerations

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ISTR SOURCE ZONE REMEDIATION – FINAL RESULTS

Pre‐Thermal Soil Sampling – 3,504,000‐ppb avg PCE Post‐Thermal Soil Sampling – 37.9‐ppb avg PCE

99.9989% Reduction

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ERH/Heat Enhanced Bio Project

Source Zone ERH Treatment Dissolved Phase PlumeEnhanced Bio Treatment 

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Section TitleSchenectady, NYHRSC to inform Remedial System Design

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Case Study – Using HRSC to Optimize Design

SVE Wells: 96

DPE Wells: 56

Heaters: 143

AIWs: 286 (nested)

TMPs: 16

TCH Project: Schenectady, NY35⁰C - Heat Enhanced SVE & Biodegredation

Main objective:  Reduce all COCs to below 1,000 mg/kg (from 15,000 mg/kg)

• Thermally enhanced bio and SVE

• BTEX and phenols

• 20‐ft TCH spacing

• WaterlooAPS used to optimize

• 1+ year of heating

• 70% of site met goals after 9 months

• Final polishing steps took project to just over 1 year of operations

• Project goals met 09/05/18

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Section TitleQuestions?

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