of methods, tools models for assessment of zone enhanced...

Dr. Ian Hers, Golder Associates Ltd.; Dr. Parisa Jourabchi, ARIS; Anne Wozney, Golder; Ehsan Pasha, Golder; Dr. Matthew Lahvis, Shell

Sixth Annual Bettering Environmental Stewardship & Technology (BEST) ConferenceMay 9-10, 2019, Whistler, BC

Development of Methods, Tools and Models for Assessment of Natural Source Zone Depletion and Enhanced Bioremediation at Petroleum Hydrocarbon Impacted Sites [Incorporation of NSZD in Remedial Technology Selection, Transition and Site Closure]

___

2

Outl ine

1. Big Data and CSM

2. NSZD conceptual model

3. NSZD methods

4. NSZD research and rates

5. Remedial technology selection

6. Remedy transitions to natural remediation

Presented in the context of Golder “Toolkits” project and other research programs Golder is conducting

Goal is promote use of new tools/methods

___Remediat ion Toolkits Project

Conceptual Site Model

Multi-Site Database Studies

BC Case Studies

Methods for evaluation of natural attenuation and source depletion

Toolkits 1 & 2 (Golder, 2016)*

Screening criteria for technical feasibility & implementability and comparison to NSZD

Methods & roadmap for implementing green & sustainable remediation (GSR)

In‐progress


In‐progress

https://csapsociety.bc.ca/wp-content/uploads/Monitored-Natural-Attenuation-Toolkit-for-Evaluation-1-and-2_combined-FINAL-.pdf

FUNDED BY SHELL AND CONTAMINATED SITES APPROVED PROFESSIONAL SOCIETY (BC)

___Multi-Site GeoTracker Study – “Big Data” (Garg et al. 2017)

4

T O O L K I T 1

Over 2,000,000 groundwater quality measurements plus notations on remediations performed!

Evaluated effect of LNAPL recovery on groundwater concentrations

No apparent trend for benzene reduction for sites with and without LNAPL recovery (but recovery often

needed to address mobility)

California GeoTracker Database

___Multi-Site GeoTracker Study – “Big Data” (McHugh et al. 2014)

• Data from 4,000 sites with monitoring from 2001-2011 with ≥ 4 years of data

• Increase in source attenuation rate for active remediation compared to NSZD/MNA rate

• Only slightly higher attenuation rate for active remediation

• Estimated median benzene attenuation rates:

• All sites (most with active remediation) = 0.18 yr-1

• NSZD/MNA only (72 sites) = 0.13 yr-1

T O O L K I T 1

Technology Constituent Increase in Source Attenuation Rate (%)

SVE benzene 28MTBE 11

AirSparging

benzene 53MTBE 22

ChemicalOxidation benzene 20

Pump &Treat MTBE 17

Assuming median benzene attenuation rate = 0.13 yr-1 the timeline for attenuation from 10 mg/L to

5 µg/L = 58 years

California GeoTracker DatabaseMostly Retail Gasoline Stations

This database and similar studies suggested the potential for NSZD as site management strategy

___California Low Threat Guidance

6

5 Pathway Scenarios w/ different allowable distances to receptor based on plume length/ strength

key COPCs (benzene, MTBE, TPH)

minimum requirementsgroundwater plume must be stable or decreasingrelease stopped; LNAPL removed to max extent practicable

From Lahvis 2013. Balancing Natural Attenuation, Risk-Based Corrective Action and Sustainable Use of Groundwater Resources. Site Remediation In B.C.:From Policy To Practice” Conference.

___Natural Source Zone Depletion Conceptual ModelT O O L K I T 1

• What is the NSZD rate?• What are the key processes?• What are the effects of NSZD on groundwater and vapour plumes?

vadose zone biodegradation

volatilization (hydrocarbon vapours)

Ground Surface

oxygen diffusion

Dissolved Plume

GroundwaterFlow

sorptiondispersion

biodegradationLNAPLSource Zone

CO2

CO2

___Mass Depletion Processes

B I O D E G R A D AT I O N

D I S S O L U T I O N

V O L AT I L I Z AT I O N

Saturated Zone(ITRC, 2009)

Vadose Zone(ITRC, 2009)

Dissolved Phase Gradients

Vapo

ur P

hase

Gra

dien

tsT O O L K I T 1

Photograph from ITRC LNAPL Guidance (2018)

Direct degassing & ebullition (Amos et al, 2005)

CH4 & CO2bubbles

___NSZD in 2017 and Beyond

2017

2017

March 2018

Key Interest: Use of NSZD rates (baseline and during remediation) as a metric to support when to transition from

active to passive remedies

T O O L K I T 1




BC Case Studies





In‐progress


In‐progress



___NSZD Processes

11

T O O L K I T 2

Unsaturated Zone Processes – Focus of this presentation

Saturated Zone Processes – Requires Hydrocarbon and Geochemistry data

Tools include ITRC Control Volume Method (2009) and GSI Mass Flux Toolkit

After Mackay 2018

___Unsaturated Zone Methods for Estimation of NSZD Rates

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Method Key Data Required Advantages/Disadvantages Tools/Models

Gradient

Chemical diffusion gradient (typically soil gas data), porosity, moisture, water

table, native organic carbon

Uses readily available data/

sensitive to moisture content

(diffusion)

VZBL ModelITRC Control Volume

CO2 Efflux Surface CO2 efflux, 14C of CO2, δ13C of CO2 (optional)

Non-intrusive/requires

correction for natural soil respiration

Dynamic closed chamber LI-CORE-flux static trapEoSense forced

diffusion

Temperature

Temperature profile, soil thermal conductivity

Long-term average

data/background correction complex

GSI Dashboard

Aerobic Vadose

PHC Respiration

Heat

Soil Gas

Thermistors

T O O L K I T 2

Soil gas graphic from API NSZD Guidance (2017)

___CO2 Efflux Measurement Methods

13

LI-COR Instrument: LI-8100A Automated Infrared Detector20 cm dia chamberShort-term measurement (few minutes)

Field Cost ~ $50-$100/location *

E-Flux Sorbent trapSorbent material made from calcium and sodium hydroxidesComposite (1-2 week) measurement

Field Cost ~ $1,000 CDN/location

T O O L K I T 2

Dynamic Closed Chamber (DCC) EoSense Forced Diffusion Sensors E-Flux Low Profile Static Trap Units

EoSense Forced Diffusion SensorInfrared Detector, 10 cm dia. chamber continuous measurements, low power (solar)

Field Cost = variable depending on study duration

* Does not include radiocarbon analyses

___CO2 Efflux Correction for Natural Organic Matter R A D I O C A R B O N C O R R E C T I O N M E T H O D

• Analysis of radiocarbon (14C), a carbon isotope generated by cosmic rays in the atmosphere with half-life of ~ 5,700 yrs, is used to differentiate between CO2 from fossil fuel (contaminant soil respiration, CSR) and natural sources (natural soil respiration, NSR)

• Fraction of 14C content of carbon (F14C) is measured by accelerator mass spectrometry (AMS)

• Assumes F14C associated with fossil fuels (CSR) is zero

• Fraction CSR (FCSR) estimated from 2-component mass balance; Sample A: Ambient air; Sample B: Mixture air and soil gas

Sihota and Mayer (2012); Jourabchi et al. (2017); Wozney (2017)

Key Point: Contemporary (modern) organic carbon is 14C-rich, while fossil fuel carbon is 14C-depleted

___CO2 Efflux Research – Temporal Variability

Site TimeNSZD rate

(as CO2 efflux µmolm-2s-1)

1. Former Refinery Fall 1.24 ± 0.07Eichert et al. 2017 Spring 0.47 ± 0.03

Winter 0.14 ± 0.01Summer 1.2 ± 0.02Seasonal Avg 0.68 ± 0.01

2. Former Refinery Summer 2.0+-0.04Jourabchi et al. 2017 Fall (moist) 0.44Hers et al. (2019) Fall (very wet*) 0.01

Winter 0.133. Bemidi Site (Pipeline)Spring 0.5Sihota et al. 2018 Summer 1.4

Fall 1.7Winter 0.8

* Testing after 211 cm rain in two weeks

Seasonal efflux variability

Site 1: ~ 1 OMSite 2: > 2 OM (<3-1,100 gal/acre/yr!)Site 3: ~ 3X

However, at Site 2 if avoid extreme rainfall events may be closer to 1 OM

Daily efflux variability

Site 2: Up to 2X

___CO2 Efflux – Spatial Variability Examples

Dry & warm summer conditions

1

2

Bemidji Site Sihota et al (2011)

Oil

Former Refinery SiteJourabchi et al (2017)

___CO2 Efflux ProtocolKey factors (conceptual site model)1. Surface cover2. Native soil organic content3. Soil moisture4. Soil temperature5. Barometric pressure?6. Water table7. PHC distribution

Challenging Sites (possible precluding conditions)1. Paved surface – gas channeling?2. Peat – old carbon3. Carbonate – may remove or produce carbon4. Very shallow source – methane efflux?5. Fractured bedrock – high variability

Key lessons/emerging protocol1. Can be significant spatial variability –

DCC method better suited than E-flux method to obtain high frequency data

2. Can be significant temporal variability –do not test after heavy rain (wait several days) and conduct daily repeat and seasonal sampling (minimum 2 events)

3. Must correct for native soil matter respiration – recommend radiocarbon tests at 10-20% of sample locations

4. Consider continuous efflux monitoring some sites

5. Some sites not conducive to efflux monitoring – consider other methods e.g., gradient

___Unsaturated Zone Biodegradation RatesT O O L K I T 2 – L I T E R AT U R E R E V I E W

0

500

1000

1500

2000

2500

Gal/a

cre/yr

Dynamic Static Model

C

CC

W

W

W

WD

• 500-1500 Gal/acre/yr

• From estimate of TPH mass can predict depletion times

• Uncertainty in long term rates

• Recent emphasis on prediction of compositional change (not just bulk TPH rates)

C = cold climate W = warm climate D = deep source (confined)




BC Case Studies





In‐progress


In‐progress



___LNAPL Site Assessment and Remediat ion Framework

Evaluate LNAPL

Concern

Conduct Remedial Options

Evaluation

Select and Implement

Remediation

Adjust or transition to alternative technology

Continue with

technology

Goals Met?

No

YesSite

Closure

Develop CSM in Tiered Framework – Increasing data needs with respect toInvestigation → Remediation Options Screening → Design

Performance Acceptable?

Yes

No

See LNAPL Concerns and Remedial Options Evaluation Figure 2

T O O L K I T 3

Optimization & Transitions is Key!

Engage Stakeholders throughout the Process

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21

LNAPL Concern Assessment Framework

Potential Concern Evaluation Criteria Guidance/Tools

Migrating LNAPLMLE evaluation- Measurement- Modeling

ITRC LNAPL Guidance (2018)ASTM E2856-13API 4760 (LDRM Model)CL:AIRE LNAPL Handbook (2014)NSZD Guidance: BC Toolkits, API NSZD Guidance (2017)

Presence of Mobile LNAPL

Example criteria is thickness above a regulatory threshold

Regulatory specificITRC LNAPL Guidance (2018)CL:AIRE LNAPL Handbook (2014)

Health Risk or Safety (soil, groundwater, soil vapour, biogenic gases)

Comparison to regulatory criteria or thresholdRisk assessmentSafety assessment

Regulatory specificASTM E2993-1 (methane focus)

Aesthetics Odour and tasteSheen in water

Regulatory specificProject specific

T O O L K I T 3 ( A D A P T E D F R O M I T R C 2 0 1 8 )

Geotechnical stability is an additional potential concern not addressed in guidance

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22

Connection between LNAPL Concern, Remedial Goal and Primary Mechanism

Primary Mechanism

Key point: Select the right tool for the job!

Concern or Risk Remedial Goal

Migrating LNAPL Saturation or Containment

Presence of Mobile LNAPL Saturation

Health Risk or Safety (soil, groundwater, soil vapourabove risk-based criteria)

Composition or Containment

Aesthetics (sheens, taste, odour above thresholds) Aesthetic

Remedial Goal Primary Mechanism

Saturation Mass Recovery - reduce LNAPL saturation

Composition Phase Change - change LNAPL characteristics

Containment Control Measures - stop LNAPL and associated plumes

Aesthetic Phase Change - change LNAPL characteristics

An additional Primary Mechanism is a combination of Mass Recovery and Phase Change address saturation or composition

concern (less common)

T O O L K I T 3

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23

Mobile and Migrat ing LNAPLA D A P T E D F R O M I T R C 2 0 0 9

LNAPL Saturation (% Pore Space)0

0100

Res

idua

lSa

tura

tion

Mobile LNAPL, Potentially Recoverable, Potentially able to Migrate

Saturation goal – Reduce mass – e.g., LNAPL recovery by pumping

Composition goal – Change the phase (with some mass reduction) – e.g., Soil Vapour Extraction to remove lighter VOCs (benzene)

___Remediat ion Select ion Process - Saturat ion and Mass Removal /Recovery Example

Primary Mechanism

RemediationObjective

Reduce SaturationAbate LNAPL Body MigrationReduce Mobile LNAPL

LNAPL Concern

Migration

LNAPL Remedial

Goal

SaturationRemoval

or Recovery

Key point: Framework includes NSZD and sustainability metrics

System Performance

Metrics

LNAPL Recovery vs. time / cost / GHG emissionsLNAPL:water: vapour ratio recovery

Hydraulic Recovery NSZD (emerging)

Select Technology (partial list)Subsurface

Performance Metrics

(baseline & transition)

LNAPL presencecomposition, saturation & thicknessNSZD (TPH) RateTransmissivityLNAPL velocity

Technology limits/ performanceCompare passive & active ratesConsider sustain-ability/ cost

Transition/Optimize

Exit (when complete)

Tools

___Remediat ion Select ion Process – Composit ion and Phase Change Example

Primary Mechanism

RemediationObjective

Reduce concentration/flux to below risk-based threshold

LNAPL Concern

Health Risk

(above standard)

LNAPL Remedial

Goal

CompositionPhase

Change (+ some mass reduction)

Key point: Framework includes NSZD and sustainability metrics

System Performance

Metrics

COPC Recovery vs. time / cost / GHG emissionsCOPC water: vapour ratioRound test

SVE/BioventingSpargingEnhanced bioPhytoNSZD

Select Technology (partial list)Subsurface

Performance Metrics

(baseline & transition)

COPC concentrationCOPC fluxNSZD (COPC) rateRespiration TestRebound Test

Technology limits/ performanceCompare passive & active ratesConsider sustain-ability/ cost

Transition/ Optimize

Exit (when complete)

Tools

___

26

Remedy Transit ion Evaluation Framework

Review Goals and

Objectives

Evaluate Regulatory Status: LNAPL & plumes stable/shrinking? Assess progress

to meeting applicable criteria

II. Compare Relative

Performance of Technologies

Determine Appropriate Transition Strategy

III. Evaluate Sustainability

for Project Lifecycle (Toolkit 4)

I. Evaluate Technology

Limits & Performance

T O O L K I T 3

Key point: Follow structured MLE approach to optimize decisions

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27

Remediat ion Transit ion Rationale

• NSZD results in longer-term mass depletion and compositional change

• Case studies indicate NSZD rates are typically 500-1,500 Gal/Acre/yr – these are significant depletion rates (Toolkit 2)

• There remain questions for longer-term rates and kinetics (quasi zero-order?) and compositional change

• Case studies show later stage active LNAPL recovery rates for technologies such as LNAPL pumping, SVE, and MPE can be comparable to or less than NSZD depletion rates

T O O L K I T 3

Key point: Baseline and subsequently measured NSZD rates can support decisions for technology transition over the project life-cycle as a more sustainable approach

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28

Threshold and Transit ion Metr icsT O O L K I T 3

Time

Subs

urfa

ce M

edia

C

once

ntra

tion

Threshold

Conventional Paradigm – Compare to regulatory standard

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29

Threshold and Transit ion Metr ics

LNA

PL M

ass

Dep

letio

n R

ate

Active Remedy

NSZD

Time

Subs

urfa

ce M

edia

C

once

ntra

tion

Time

Mas

s Fl

ux

Time

Con

tam

inan

t Mas

s R

emov

al R

ate

Kg

GH

G/k

g m

ass

rem

oved

Time

Log

(Sur

face

Med

ia

Con

cent

ratio

n)

Point of diminishing returns – adverse impact outweighs benefit

Threshold

Time

Threshold

Concentration attenuation statistically demonstrated, progressing to threshold

Other metrics• Cost per kg

removed• Risk reduction• Time frameThreshold

Transition Metric

ITRC Mass Flux GuidanceGSI Mass Flux Toolkit

Toolkit 3

Toolkit 2Regression tool

Toolkit 4

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30

Sequenced Technology Deployment (“Treatment Train”)F R O M I T R C 2 0 1 8

LNAPL State Residual Mobile Migrating

LNAPL Concern Linked to Goal

Health Risk and Safety – Composition*Migrating LNAPL - Saturation

Mobile LNAPL - Saturation

MechanismPhase Change

Containment **Recovery or Phase Change/Recovery

RecoverabilityRecovery is ineffective

0.1-0.8 ft2/day

Transmissive

1. Containment 2. Recovery (+ NSZD)

3. Phase Change (+ NSZD & MNA) 4. MNA & NSZD

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31

Remedy Transit ions – Technology Limits & Performance - Tools

• TPH • COPC • API NSZD Guide• BC Toolkits

NSZD Rate

• LNAPL transmissivity• LNAPL decline curve

analysis• ASTM E2856-13

LNAPL Recovery Rate

• Respiration test• US EPA 1995 Bioventing

Principles and Practices

Enhanced Biodegradation

Rate (Bioventing)

Volatilization Rate (SVE)

• Measure VOCs in exhaust• Rebound test• US Corp Eng 2002 SVE &

Bioventing Design

0

900

1800

2700

3600

0 5000 10000

LNAP

L Re

covery Rate

(L/year)

Cumulative Recovery (L)

LNAPL Recovery

Respiration Test

T O O L K I T 3 – E X A M P L E F O R A I R - P H A S E T E C H N O L O G I E S A N D AV A I L A B L E T O O L S

Key point: Importantto collect and evaluate

data on remedial performance

(for all phases, LNAPL, water,

vapor), for comparisonto NSZD rates




BC Case Studies





In‐progress


In‐progress



___Sustainabi l i ty - Environment Footprint Analysis

Examples of on-site and off-site inputsKey StepsIdentify GoalsIdentify IndicatorsEstablish System Boundaries Conduct Environmental InventoryFootprint CalculationDocumentation

Simplified life cycle analysis (LCA) can be used to guide the analysis – Critical to

establish consistent boundaries (time, space)

T O O L K I T 4

Key Environmental IndicatorsGHG emissions & air pollutantsEnergy useWaste generationMaterials useLand use and ecosystem

Select Tools:SiteWiseSimaProUS SEFAGoldSET

SR Dashboard (developed for Toolkits project)

___Enhanced Bioremediation Research

Previous study by GSI indicated plastic increases temperature as much as 10°C below plastic and 2.2°C at 3.3 m

Research planned

Promotes aerobic biodegradation, which also increases temperature (Shell Carson study indicated temperature increased by up to 8°C when air added)

Research planned

Solar-heating of water, inject water into well with closed loop heat exchanger

Previous study by Pennington et al. 2018 indicates elevates groundwater temperature to 20-60°C

Patent pending process (TISRTM)

Solar-Powered Bioventing

Solarization

North Carolina Statettps://content.ces.ncsu.edu/extension-gardener-handbook/6-weeds

Hot-water Injection

Q10 rule – 10°C increase temperature results in 2-3X increase in biodegradation rate

https://techportal.eere.energy.gov/techpdfs/SRNL_MicroBlower_Success.pdf

Digital temperature sensor

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35

Summary

• Big Data evaluations provide inform on relative performance of technologies and possible use of NSZD as site management strategy

• New methods have been developed for estimation of NSZD rates

• Recent case studies indicate that NSZD rates, though seasonally variable, can be significant and exceed rates for later stage active remediation

• NSZD rate measurements serve as basis for assessing NSZD as a remedy and can be compared to measured or estimated rates for other technologies

• Typically NSZD should be considered as a secondary remedy after primary active remediation is no longer effective or sustainable

• More research needed on long-term NSZD rates and compositional change, detailed tools being developed

___Thank you!

Toolkits 1 and 2 available at link

Toolkits 3 and 4 completion in 2019

Please contact Ian Hers if you would like to receive these tools

[email protected]


___Effect of Precipitation

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