Applying the LNAPL Conceptual Site Model (LCSM)

Approach for Remedial Selection and Design, Determining Remedial

Endpoints, and Negotiating Site Closure

Mary Ann ParcherES&T, a Division of GES

mparcher@esnt.com

ES&T/GES – Recognized Leaders

• American Petroleum Institute– Developed Interactive LNAPL Guide– Taught Workshops

• ASTM E-50.04 LNAPL Task Group

• Presentations at Conferences

• Short Courses for EPA, NGWA and MA LSPA

• Remediation Technologies Development Forum

• Participation with Regulatory Community– TRRP, MA LSP, Bahamas

• Developed various analytical and numerical models associated with multiphase flow

Importance of Understanding the “Basics”

• Fundamentals of LNAPL behavior in subsurface media– Concepts such as wettability, capillary forces, saturation, and

relative permeability

• Predicting LNAPL behavior in the subsurface– More accurate estimate of oil volume– A way to quantify oil mobility, transmissivity, and recoverability

• Relationship with the dissolved and vapor phases

• Using the knowledge to know why a specific remedial technology may, or may not, be appropriate

• For establishing achievable remedial objectives

• Building adequate LCSMs

Conceptual Site Model Development

• Backbone of the decision making process

• Incorporates site history, site conditions, subsurface conditions and all risk based and non-risk based remediation factors

• Key is the balance between too much and too little

Approach to Managing Site with LNAPL

• LCSM Development– LNAPL mobility and stability assessment (saturation)– LNAPL source strength assessment (composition)

• LNAPL Remediation Endpoints– Defines “remove to degree practicable”– Endpoint-closure provides evidence for:

• Practical hydraulic recovery limit • LNAPL plume stability• Acceptable environmental risks -- no exposure pathway

completions• Long-term natural attenuation

Why This Approach?

• Disproportionate spending on LNAPL sites

• Practicability limits on LNAPL don’t work

• RBCA’s inadequate treatment of LNAPL

• Need to connect LNAPL to other phases that drive environmental risks (holistic approach)

• New conceptual models for LNAPL available that can more quantitatively define volumes, transmissivity, and recoverability

• American Petroleum Institute Guidance

• USEPA/RTDF Initiative

• ASTM Guidance for LNAPL Conceptual Site Model Development for Risk-Based Decision Making

National Initiatives for Change

LCSM Defined (ASTM) and Importance

• Describes the physical properties, chemical composition, occurrence, and geologic setting of the LNAPL body from which estimates of flux, risk, and potential remedial action can be generated

• Dynamic and updated with new site data or changes due to remedial activities

• Includes data on dissolved and vapor phase conditions

• Tiered approach

• Use to determine practical remedial endpoints and effectively design remediation systems

• Part of the overall corrective-action process for a site

LCSM Components

• Delineate LNAPL in the subsurface– Vertical and lateral distribution/geometry

• Define properties of the subsurface media containing the LNAPL (groundwater and hydrogeologic conditions)

• Define LNAPL physical properties and composition (COCs)

• Release source and timing?

LCSM Components

• Define receptors and exposure pathways

• Calculate LNAPL volume/mass

• Define mobility or stability conditions of the LNAPL, groundwater and vapor plumes

• Estimate chemical fluxes or concentrations in all phases at points of compliance

LCSM Overview (ITRC)

• Link between site characterization and management

• Description and interpretation of physical and chemical state of the LNAPL body

• Facilitates understanding of the LNAPL conditions, site risks, and how best to remediate

• Scaled to the LNAPL impacts and associated issues that require management

• Iterative process to increase the understanding of the LNAPL body and site risks

• Sufficient when additional information likely would not lead to a different decision

LNAPL Characterization LNAPL composition LNAPL saturation LNAPL location

LNAPL Conceptual Site Model

LNAPL Management Maximum extent practicable? Drivers: mobility and future risk Remedial objectives and end

points Remedial action selection

LNAPL Understanding is an Iterative Process

Source: ITRC 2009

Concerns and Drivers

Exposure Scenarios at an LNAPL Site

3a

2

3b

45

Drin

king

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ell

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LNAPL Risk ScenariosWhen LNAPL in the Ground

2 Groundwater (dissolved phase)

3a

Groundwater to vapor3b

LNAPL to vapor

Direct Skin ContactNot Shown

Additional considerations When LNAPL in Wells

4 LNAPL migration (offsite migration, e.g. to surface water, under houses)

5 LNAPL in well (aesthetic, reputation, regulatory)

LNAPL Emergency issuesWhen LNAPL in the Ground

Vapor accumulation in confined spaces causing explosive conditions

1

Direct LNAPL migration to surface water

Direct LNAPL migration to underground spaces

Not shown

Garg, 2009

Three LNAPL Plume Scenarios

LNAPL in wells and still migrating (early stage)

Condition: LNAPL in wells, mobile

Driver: LNAPL saturation

1

2

3

LNAPL in wells but stable (later stage)Condition: LNAPL in wells, immobile

Driver: LNAPL composition, saturation

No LNAPL in wells and stable plumeCondition: No LNAPL in wells

Driver: LNAPL composition

May apply RBCA for risk-analyses

We don’t always differentiate between Scenarios 1 and 2Adapted from ITRC 2009

Oil Saturation vs. Composition

•Lowering COC concentration in LNAPL reduces risks•Similar behavior for soil gasA

B

C

16

Garg, 2009

< Typical Residual Saturation

LNAPL Management Overview

ITRC 2009

General Approach

• Stop on-going releases

• Address safety and risk issues

• Evaluate LNAPL plume stability– If plume is migrating, take measures (e.g., hydraulic

recovery, barriers)

• Perform risk assessment– Mitigate or manage risks– Conventional remediation methods

• Consider institutional controls

Establish a Long-term Vision

• Get stakeholders on the same page

• Begin to understand what is achievable

• Set the stage for discussing objectives and goals– Objective: Specific set of outcomes that serve as basis for

remedial action

– Goals: Metrics for achievement of specific LNAPL management / remediation objectives

• Long-term vision may be revised if goals are later found to be not achievable

• A long-term vision can be developed for operating or inactive sites

LNAPL Remediation Objectives• Risk-based objectives

– Reduce risk-level or hazard– Exposure pathway/LNAPL specific

• Non-risk objectives (examples)– Reduce LNAPL flux– Reduce source longevity– Reduce LNAPL mass or well thickness– Reduce LNAPL transmissivity– Abate LNAPL mobility

• Evaluate whether applicable objective(s) are best addressed by reducing LNAPL saturation or by modifying the LNAPL composition

Goals Provide Measure of Performance

• Provide metrics to measure achievement of specific LNAPL management/ remediation goals

• Goals are highly site and project specific

• Goals quantify the point at which active systems can be shut down

• Goals can be phased or tiered

Site-Specific Remedial Endpoints

a) OIL TRANSMISSIVITY

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Transmissivity

Why Use LNAPL Transmissivity?

• Observed LNAPL well thickness– Not always in equilibrium– Inconsistent between soil types– Changes with water elevation fluctuations– Impacted by hydraulic scenarios (unconfined, confined, perched)– Poor indicator of LNAPL recoverability

• Transmissivity– Since depends on soil type, LNAPL properties, saturation, and

thickness of mobile layer, better indicator of LNAPL recoverability– Higher the transmissivity, the higher the LNAPL recoverability– Quantifies mobility of the entire LNAPL interval– Consistent across hydraulic scenarios (unconfined, confined,

perched) and soil types– Estimated with field testing or existing recovery data

Summary• Understanding of the science is critical

• Use of comprehensive risk-based LCSMs– Better understand sites– Link between site characterization and management– Define realistic remedial goals and select appropriate

remedial approach– Helps with stakeholder and regulatory involvement– Facilitate site redevelopment and case closures– Means to balance being protective of human health

and the environment with allocation of resources

• Numerous available resources and guidance documents

Tools for LCSM Development

Overview

• Field and laboratory methods

• Information management and Geographic Information Systems (GIS)

• Visual imagery analyses

• Lines of evidence

• Modeling and software applications

• Protocol documents

Field and Laboratory Analyses

• Geophysical Tools (Direct Push)– LIF/ROST/MIP/CPT/HPT

• Soil and Fluid Characterization– Undisturbed soil cores

• Core photography• Saturation and porosity measurements • Capillary properties

– Fluid physical properties

• Baildown Tests– LNAPL and water conductivity– Estimate capillary properties

Geophysical Tools

• Map the horizontal and vertical extent of LNAPL (free and residual phases) in the subsurface– MIPs (Membrane Interface Probe)

• Measures vapor stream with on-site GC (PID, FID, ECD)

• Detects all phases of hydrocarbon (LNAPL, dissolved, vapor)

– LIF/ROST (Laser Induced Fluorescence/ Rapid Optical Screening Tool)

• UV light will cause LNAPL to fluoresce• Fluorescence signal (wavelength)

is recorded as the sonde is pushed through soil

Gas Return Tube

Permeable Membrane

VOCs in Soil

Carrier Gas Supply

Geophysical Tools

• Characterize lithology and permeability– CPT (Cone Penetrometer Testing)

• Physical properties of the lithology• Estimate soil type

– HPT (Hydraulic Profiling Tool)

• Estimate hydraulic conductivity

Flow

K ~ Q/P or K~1/P, where Q is constant.

Water

Combined CPT-ROST Log

Benefits/Limitations of Geophysics

• Fastest way to map the extent of LNAPL

• But geophysical data are qualitative –for screening purposes only

• Data collection is limited to poorly consolidated earth materials

Core Photography

• Sawed vertically in lab• High resolution photo• White light photo shows

details of texture• UV light shows presence of

LNAPL

Core Sampling

WALL DAMAGE and/or FLUID INVASION: May occur during coring.

VERTICAL SAMPLE: Sample diameter is limited by core diameter.

HORIZONTAL SAMPLE: Sample must be long enough to meet Darcy flow requirements.

Source: PTS Laboratories

Lab Analyses of Core Samples

• Fluid saturations – air, oil, water• Capillary properties – air-water drainage test• Hydraulic conductivity• Effective and total porosity• Residual LNAPL saturations for vadose or

saturated zones• Dual porosity assessment of fractured porous

media• Grain-size analyses, moisture content, bulk

density

API Recommended Methodsof Baildown Test Analysis

• Modified Slug Test Solutions for Ko Estimate– Bouwer & Rice, Cooper et al.,

etc.

• Lundy and Zimmerman (1996)– Ko estimated from changes in oil

thickness– Kw estimated from rising water

table (Zaw)

• Huntley (2000)– Ko estimated from recovery of

the oil table, Zao

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Calculatedwith AverageParametersBaildownResults

Importance of Information Mngt

• Vast quantities of site data and information

• If data are not organized efficiently: – Difficult to understand temporal and spatial trends– Difficult to perform statistical analyses– Regulatory reporting inefficient

• If data are not analyzed and understood: – Money and time are wasted– Inappropriate/ineffective decisions

Information Management

• Store information in relational database– Direct EDD database entry– Link information to a GIS – Facilitates analysis and presentation of data– Optimizes investment in site characterization data;

translates into cost savings

• Enables multiple parties to effectively and efficiently interact

• Produces positive results in regulatory and public interaction

GIS Applications

• Use to display/contour water table gradients and LNAPL plume distributions

• Examine spatial and temporal trends

• Perform geostatistical analyses for monitoring well network design or soil sample locations

• Perform technical analyses– Defined spatial distributions as thematic

layers for soil properties, hydrocarbon properties, oil saturation volume, and oil gradients

– Calculate LNAPL plume volume and migration estimates

Visual Imagery Analyses

• Facilitate understanding; development of site conceptual models– Still or interactive 3D images of subsurface conditions– Animations of NAPL or dissolved plumes over time– Presentations for discussions with regulators, third

parties or technical team members• Computer-aided visualization assists with

characterizing LNAPL plume distributions– permeable zones– stratigraphic traps– transient conditions

Visual Imagery – Key Benefits

• Clarifies physical and chemical interrelationships of the subsurface environment – Stratigraphy– Water levels– Contaminant distributions– Facility features

• Quantifies data uncertainty and identifies data gaps• Significant cost savings result from improved

communication, decreased time of analysis, and improved technical understanding

• Project managers and consultants can easily understand site conceptualization; time can be invested on remedial strategies rather than learning site information

MIPs FID Response Visual

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Minimum Level Displayed = 1.0 e5

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Minimum Level Displayed = 1.0 e5

Historical High and Low Water Tables

Existing Recovery System

Existing Recovery System

Response at 880 ft MSL

Effect of Water Table ChangesChanges in Observed Well Product Thickness

Due to Water Table Changes

Lines of Evidence of LNAPL Footprint Stability

• Monitoring Results– No appearance of LNAPL in perimeter wells used to delineate plume – No increase in LNAPL thickness at edge of plume

• Ensure increasing thickness not because a well is new and not reached equilibrium or related to water table fluctuations

– Stable or shrinking dissolved phase plume

• Calculated Velocity– Perform baildown test or estimate from Kw

– Measure LNAPL gradient

• Age of the Release– Weathering indicators

• Decreasing LNAPL Recovery Rates

• Petrophysical laboratory data– Measured native state saturations less than or slightly greater than residual

saturations

Modeling Applications

• Groundwater and LNAPL flow

• Contaminant fate and transport

• Source assessment

• Impacts of hydrologic changes

• Remedial selection and design optimization

LNAPL Modeling

• Saturation Profiles• Volume Estimates

– Mobile / Residual• Inherent Mobility

– Inherent Mobility Curve – Spatial Distribution of Mobility– Establishment of Practical Limit of Mobility (PLM)

• Plume Migration• Transmissivity• Recoverability

API - LDRM

Mobility of a LNAPL Plume

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Inherent Mobility CurveSpatial Distribution of

Mobility across a Plume

Site-Specific Remedial Endpointsb) SPECIFIC VOLUME

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Transmissivity

Why Use LNAPL Transmissivity?

• Observed LNAPL well thickness– Not always in equilibrium– Inconsistent between soil types– Changes with water elevation fluctuations– Impacted by hydraulic scenarios (unconfined, confined, perched)– Poor indicator of LNAPL recoverability

• Transmissivity– Since depends on soil type, LNAPL properties, saturation, and

thickness of mobile layer, better indicator of LNAPL recoverability– Higher the transmissivity, the higher the LNAPL recoverability– Quantifies mobility of the entire LNAPL interval– Consistent across hydraulic scenarios (unconfined, confined,

perched) and soil types– Estimated with field testing or existing recovery data

Objectives of Recovery Predictions

• Design of efficient (realistic) free-product recovery systems

• Provide estimates of recovery performance

• Provide estimates of recovery time

• Provide a means of establishing practical goals

Predictive Models for LNAPL Recovery

• Analytical models(e.g., API LNAPL Distribution and Recovery Model, and API Interactive LNAPL Guide)– 1-D analytical– Relatively easy to use and inexpensive– Good estimates (if properly applied)– API LNAPL parameters database

• Numerical models(e.g., ARMOS, BIOSLURP, MAGNAS3, MARS, MOVER)– 2-D, 3-D; consider need!– Can be headaches and expensive– May be, but not necessarily, more accurate

• Typically, models are based on vertical equilibrium (VEQ) model and utilize observed LNAPL well thicknesses

• If there is recovery or transmissivity measurement data, can try to “calibrate” model to match recoveries

• Modeling may be appropriate on more complex sites, may be useful as what-if predictor to evaluate different scenarios

• Additional site-specific data generally required as complexity of model increases

Predictive Models for LNAPL Recovery

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Observed1998-2004

LDRM Modeling Example

• Match historical recovery data

• Estimate LNAPL transmissivity

• Predict future recovery

• Estimate area of influence of recovery well

Predictive Models – Caution Warning

• What is the uncertainty in the predictive models?– Vertical equilibrium?– Hydrogeologic properties– Spatial and vertical heterogeneity

• Geologic• Texture/capillary properties• Fluid properties

– Residual saturation– Radii of capture and influence– Ideal versus real wells

• Many of these lead to overestimating volume and recovery rate, and underestimating time of recovery

API - Interactive LNAPL Guide• Interactive, browser-based,

multi-media tool

• Contains educational information, assessment tools, LNAPL management strategies, regulatory perspectives, and other useful information

• Incorporates videos, computer generated animations, and interactive graphics to facilitate easier understanding of LNAPL concepts

• Hyperlinks between assessment tools, parameter tables, and relevant information

http://www.api.org/ehs/groundwater/lnapl/

lnapl-guide.cfm

API - Interactive LNAPL Guide

• Provides technical information, quantitative tools, and methods to evaluate the management of LNAPL

• Designed to provide an overall approach for evaluating LNAPL:– assessing its potential risk– quantitatively defining mobility

and recoverability– developing remedial strategies– examining methods to enhance

site closure opportunities

API – Calculation Tools

Tools: API Databases

• Soil properties– Porosity– Conductivity– Capillary properties– Residual water content

• Hydrocarbon properties– Specific gravity (density)– Viscosity– NAPL / Water interfacial

tension– NAPL / Air interfacial

tension

API - Interactive LNAPL Guide

EPA RTDF Guidance

• US EPA Remediation Technology Development Forum “NAPL Cleanup Alliance”

• 2001 to 2006

• Identifying technically practicable, cost-effective solutions to petroleum hydrocarbon contamination problems at larger sites

• Develop a better understanding of the cost and effectiveness of existing, innovative, or aggressive LNAPLs removal technologies

EPA RTDF Guidance

Available in API Interactive LNAPL Guide

• Developed and published – A Decision Framework for

Cleanup of Sites Impacted by Light Non-Aqueous Phase Liquids (LNAPLs) (EPA 542-R-04-011)March 2004

– Classroom training module The Basics –Understanding the Behavior of LNAPLs in the Subsurface

• www.rtdf.org/public/napl

EPA Guidance: Management Approach

ASTM Guidance

• Guide Components– Scope– Referenced standards– Terminology– Summary of guide– Significance and use– Components of the

LNAPL CSM– Procedure– Keywords– Appendices

ASTM DesignationE2531-06

ASTM Guidance

• Appendices– Additional LNAPL reading

– Overview of multiphase modeling

– Example calculations

– Data collection considerations and resources

– Remediation metrics

– Example use of the LNAPL guide

– Glossary of technical terms for characterizing immiscible fluids in soil and geologic media

– Glossary of technical terms for characterizing the nature and migration of chemicals derived from LNAPL in soil and geologic media

ITRC Overview

• Interstate Regulatory & Technology Council

• A coalition of state environmental regulators working with federal partners, industry, and stakeholders to streamline regulatory acceptance of innovative environmental technologies

• Consists of 50 states, DC, multiple federal partners (EPA, DOE, DOD), industry participants, and other stakeholders– Cooperating to break down barriers and reduce compliance costs– Making it easier to use new technologies– Helping states maximize resources

• Develops guidance documents and training courses

• Various technical teams – LNAPL team

ITRC – LNAPL Team• Guidance documents

– Evaluating Natural Source Zone Depletion at Sites with LNAPL(April 2009)

– Evaluating LNAPL Remedial Technologies for Achieving Project Goals (December 2009)

• Internet training– An Improved Understanding of LNAPL Behavior in the Subsurface

- State of Science vs. State of Practice (LNAPL Part 1)– LNAPL Characterization and Recoverability – Improved Analysis

- Do you know where the LNAPL is and can you recover it? (LNAPL Part 2)

– Evaluating LNAPL Remedial Technologies for Achieving Project Goals (LNAPL Part 3)

• www.itrcweb.org• www.clu-in.org