Mary Ann Parcher ES&T, a Division of GES

Transcription

1 Applying the LNAPL Conceptual Site Model (LCSM) Approach for Remedial Selection and Design, Determining Remedial Endpoints, and Negotiating Site Closure Mary Ann Parcher ES&T, a Division of GES mparcher@esnt.com

2 ES&T/GES Recognized Leaders American Petroleum Institute Developed Interactive LNAPL Guide Taught Workshops ASTM E 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

3 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

4 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

5 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

6 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

7 National Initiatives for Change American Petroleum Institute Guidance USEPA/RTDF Initiative ASTM Guidance for LNAPL Conceptual Site Model Development for Risk-Based Decision Making

8 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

9 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?

10 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

11 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

12 LNAPL Characterization LNAPL Understanding is an Iterative Process 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 Source: ITRC 2009

13 Concerns and Drivers

14 Exposure Scenarios at an LNAPL Site a 3b 2 Drinking Water Well LNAPL Emergency issues When LNAPL in the Ground LNAPL Risk Scenarios When LNAPL in the Ground Additional considerations When LNAPL in Wells 1 Not shown Vapor accumulation in confined spaces causing explosive conditions Direct LNAPL migration to surface water Direct LNAPL migration to underground spaces 2 Groundwater (dissolved phase) 3a 3b Not Shown LNAPL to vapor Groundwater to vapor Direct Skin Contact 4 LNAPL migration (offsite migration, e.g. to surface water, under houses) 5 LNAPL in well (aesthetic, reputation, regulatory) Garg, 2009

15 Three LNAPL Plume Scenarios 1 LNAPL in wells and still migrating (early stage) Condition: LNAPL in wells, mobile Driver: LNAPL saturation 2 LNAPL in wells but stable (later stage) Condition: LNAPL in wells, immobile Driver: LNAPL composition, saturation 3 No LNAPL in wells and stable plume Condition: No LNAPL in wells Driver: LNAPL composition May apply RBCA for risk-analyses Adapted from ITRC 2009 We don t always differentiate between Scenarios 1 and 2

16 Oil Saturation vs. Composition A Lowering COC concentration in LNAPL reduces risks Similar behavior for soil gas B < Typical Residual Saturation C 16 Garg, 2009

17 ITRC 2009 LNAPL Management Overview

18 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

19 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

20 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

21 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

22 Site-Specific Remedial Endpoints Oil Transmissivity, ft 2 /day a) OIL TRANSMISSIVITY Transmissivity Oil Thickness, ft

23 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

24 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

25 Tools for LCSM Development

26 Overview Field and laboratory methods Information management and Geographic Information Systems (GIS) Visual imagery analyses Lines of evidence Modeling and software applications Protocol documents

27 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

28 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) Carrier Gas Supply Gas Return Tube Permeable Membrane VOCs in Soil 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

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

30 Combined CPT-ROST Log

31 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

32 Core Photography Sawed vertically in lab High resolution photo White light photo shows details of texture UV light shows presence of LNAPL

33 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

34 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

35 API Recommended Methods of Baildown Test Analysis Modified Slug Test Solutions for K o Estimate Bouwer & Rice, Cooper et al., etc. Lundy and Zimmerman (1996) K o estimated from changes in oil thickness K w estimated from rising water table (Z aw ) Huntley (2000) K o estimated from recovery of the oil table, Z ao Change in Oil Thickness, feet Oil Transmissivity, ft 2 /day Elapsed Time, minutes Field Data Best-Fit Line Change in Water Table, feet Calculated with Average Parameters Baildown Results Field Data Best-Fit Line Elapsed Time, minutes Free Oil Thickness, feet

36 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

37 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

38 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

39 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

40 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

41 MIPs FID Response Visual Response at 880 ft MSL Existing Recovery System FID Response 1.0e 9 1.0e 8 1.0e 7 1.0e 6 1.0e 5 1.0e 4 1.0e 3 1.0e 2 1.0e 1 0 Minimum Level Displayed = 1.0 e 5 Historical High and Low Water Tables

42 Effect of Water Table Changes Changes in Observed Well Product Thickness Due to Water Table Changes

43 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 K w 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

44 Modeling Applications Groundwater and LNAPL flow Contaminant fate and transport Source assessment Impacts of hydrologic changes Remedial selection and design optimization

45 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

46 API - LDRM

47 Mobility of a LNAPL Plume Inherent Mobility Curve Spatial Distribution of Mobility across a Plume 2.0 Inherent Mobility (m/day) Well Product Thickness (m) 0 25 Scale (m) 50 Contour Interval = 0.5 m/d

48 Site-Specific Remedial Endpoints Specific Volume, ft b) SPECIFIC VOLUME Specific Volume Transoil/Voloil, ft/day Oil Thickness, ft Mobility c) INHERENT MOBILITY Oil Thickness, feet Oil Transmissivity, ft 2 /day a) OIL TRANSMISSIVITY Transmissivity Oil Thickness, ft

49 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

50 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

51 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

52 Predictive Models for LNAPL Recovery 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

53 LDRM Modeling Example Match historical recovery data Estimate LNAPL transmissivity Predict future recovery Estimate area of influence of recovery well Cumulative Volume, Barrels API Model Observed Elapsed Time, days

54 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

55 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 groundwater/lnapl/ lnapl-guide.cfm

56 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

57 API Calculation Tools

58 Soil properties Porosity Conductivity Capillary properties Residual water content Hydrocarbon properties Specific gravity (density) Viscosity NAPL / Water interfacial tension NAPL / Air interfacial tension Tools: API Databases

59 API - Interactive LNAPL Guide

60 EPA RTDF Guidance US EPA Remediation Technology Development Forum NAPL Cleanup Alliance 2001 to 2006 Identifying technically practicable, costeffective 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

61 EPA RTDF Guidance Developed and published A Decision Framework for Cleanup of Sites Impacted by Light Non-Aqueous Phase Liquids (LNAPLs) (EPA 542-R ) March 2004 Classroom training module The Basics Understanding the Behavior of LNAPLs in the Subsurface Available in API Interactive LNAPL Guide

62 EPA Guidance: Management Approach

63 ASTM Guidance Guide Components Scope Referenced standards Terminology Summary of guide Significance and use Components of the LNAPL CSM Procedure Keywords Appendices ASTM Designation E

64 Appendices Additional LNAPL reading ASTM Guidance 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

65 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

66 Guidance documents ITRC LNAPL Team 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)