Navy VI Web Tool: A Systematic Approach for Assessing Strength of Evidence

Navy VI Web Tool: A Systematic Approach for Assessing Strength of Evidence EPA Workshop 2012 Donna Caldwell / NAVFAC Atlantic Dr. Loren Lund / CH2M HILL

Why Navy Developed VI Evaluation Tool 116 potential VI sites across Navy ~ 85% chlorinated groundwater plumes ~ 28% NAPL present ~ 75% of the sites for current buildings Consistent and efficient VI evaluations in Restoration Program VI information overload and variability in VI guidance Break information into manageable components Customize the information for conceptual site model (CSM) EPA Web Site, Workshops, Presentations 2002 2008 OSWER Draft Guidance for Evaluating the VI 2010 R5 2010 Review of EPA Draft VI Guidance U.S. EPA's Vapor Intrusion Database EPA/NOAA VI Guidebook ITRC, DoD, State, VI Conferences, Literature ITRC VI Pathway: A Practical Guideline VI Guidance, New Jersey Oct. 2006 DoD Vapor Intrusion Handbook Jan. 2009 AWMA VI Conference, Sep. 2010 2012 Conceptual Model Scenarios for the Vapor Intrusion Pathway Guidance Evaluating VI New York Oct. 2006 NAVFAC Background Guidance VI 2

Why Navy Developed VI Evaluation Tool Need for systematic decision framework to manage VI challenges Spatial/temporal variability of data Background sources (indoor and outdoor) Determining the significance of the evidence More indoor air sampling New techniques Real-time GC/MS Passive samplers Document VI decision process Provide one-stop shopping VI resource Track magnitude of Navy VI impacts & costs GW VI Occurring Near Primary Release Vadose Zone Capillary Fringe Groundwater IA VI Not Occurring Distant from Primary Release Groundwater Flow 3

Evolution of the VI Practice Ahead of Guidance Typical Guidance 2002 Linear (flow chart) Approach Sequentially Evaluate Single Lines of Evidence Screening Evaluation [GW] > VI Screening Levels (SLs) Exterior Soil Gas (SG) [SG] > VI SLs Subslab Soil Gas (SSV) [SSV] > VI SLs Interior Concurrent SSV, Indoor Air (Outdoor Air) 4

Evolution of the VI Practice Ahead of Guidance Subslab Soil Gas Data Exterior Groundwater and Soil Gas Data Non-Linear Approach 2012 Simultaneously Weigh Multiple Lines of Evidence Understand Evidence Strengths/Limitations Strong Focus on Conceptual Site Model Navy VI Tool Building Characteristics, Occupancy and Use Indoor Air Data Site/Building History Background Sources Subsurface Characteristics GW VI Occurring and Significant IA VI Not Occurring or Insignificant Other considerations Intrusiveness Ownership/Access Mission Needs Sustainability Schedule, Cost 5

Systematic Approach for Assessing Strength of Evidence Develop VI Conceptual Site Model (CSM) Scenario Define Goal Select optimal investigative strategy; or Evaluate data to determine if VI is occurring and significant Consider VI Strategies / Lines of Evidence e.g., Groundwater, subslab, or indoor sampling Evaluate Strength of Each Line of Evidence Depends on CSM scenario and critical VI factors Assess Cumulative Strength of Evidence Key Points Approach based on Fundamental Truths of VI Systematic approach forms basis of Navy VI Web Tool 6

Vapor Intrusion Fundamental Truths Multiple lines of evidence are typically required Identify best lines and combine pieces of puzzle Not all lines of evidence are created equal Near Primary Release Vadose Zone Capillary Fringe Groundwater Groundwater Flow Distant from Primary Release Groundwater Indoor Air Example Individual Lines of Evidence Definitive VI Occurring Inconclusive Definitive VI Not Occurring 7

Vapor Intrusion Fundamental Truths (cont.) Strength of Evidence Depends on CSM scenario Near Primary Release Distant from Primary Release Free Phase TCE Sorbed TCE Dissolved TCE Groundwater Flow GW D GW VI Occurring and Significant VI Not Occurring or Insignificant VI Occurring and Significant VI Not Occurring or Insignificant 8

Vapor Intrusion CSM Scenario VI CSM Elements Near Release Distant from Release Office Warehouse Shop Hanger Residence Barracks School Daycare Hospital Current or future building? Small, medium, or large building? Near or distant to vadose zone release? Slab-on-grade, basement, crawlspace? Tight or leaky building envelope? Heating and air conditioning unit? 9

Consider VI Strategies and Lines of Evidence Categories of Strategies: Above-ground (indoor air) Below-ground Building and vadose zone characteristics Combinations of above VI Occurring & Significant VI Not Occurring or Insignificant Other considerations Regulatory acceptance Intrusiveness Cost 1) Not all lines of evidence created equal 2) Strength of evidence depends on CSM 10

Evaluating the Strength of the Evidence Performed after defining VI CSM scenario, selecting strategy, and collecting data Strength of each line of evidence Depends on CSM scenario and critical VI elements Determined through (1) a series of questions and answers; and (2) an understanding of the implications Do groundwater VOC levels exceed VI screening values Yes No Uncertain Implications within 100 ft of building? NO VI VI No VI Strength of Evidence Bar 11

") Case Study Background Information Industrial area with multiple chlorinated-voc sources and groundwater plumes Large compartmentalized single-story industrial building (slab-on-grade) Manufacturing, maintenance, storage, and administrative Depth to GW is 5 to 9 ft bgs Fine sand (0-9 ft bgs) with sandy-clay lenses TCE (µg/l) 3 30 30 300 300 3,000 3,000 11,000 >11,000 133 12

Case Study Investigative Strategy Portion of building overlies a soil source (former plating shop area) Lines of evidence Historical shallow GW data Subslab soil gas, exterior soil gas, and water table data Building TCE (µg/l) 3 30 30 300 300 3,000 3,000 11,000 >11,000 Subslab Soil Gas Location Water Table and Soil Gas Above Capillary Fringe Location 13

Case Study Subslab, Soil Gas, and Water Table Results Soil Gas Location Above Capillary Fringe Subslab Soil Gas Location Water Table Temporary Well Location Concentrations in shaded cells exceed VI screening levels 14

Case Study Evaluation of Subslab Data Do subslab VOC levels exceed VI screening values? What is the magnitude of exceedance? Do building characteristics (e.g., occupancy/air exchange) strongly indicate no VI? 15

Case Study Evaluation of Subslab Data Do subslab VOC levels exceed VI screening values? What is the magnitude of exceedance? VI not expected to be significant in buildings with large volumes / high air exchanges / positively pressurized Do building characteristics (e.g., occupancy/air exchange) strongly indicate no VI? e.g., buildings not fully enclosed; large warehouses / hangers; structures with bay doors that are constantly open Range of evidence is from slightly suggestive-to-definitive Shed that is not fully enclosed would provide definitive evidence Older, leaky building slightly suggestive unless more evidence obtained to support high exchange / mixing 16

Case Study Evaluation of Subslab Data Do subslab VOC levels exceed VI screening values? What is the magnitude of exceedance? Do building characteristics (e.g., occupancy/air exchange) strongly indicate no VI? 17

Case Study Evaluation of Subslab Data Do subslab VOC levels exceed VI screening values? What is the magnitude of exceedance? Do building characteristics (e.g., occupancy/air exchange) strongly indicate no VI? Summary Subslab data provide inclusive-tosuggestive evidence VI may be significant Further investigation (e.g., indoor air sampling) warranted 18

Case Study What if assessment had been based on exterior soil gas and water table results? Building TCE (µg/l) 3 30 30 300 300 3,000 3,000 11,000 >11,000 Subslab Soil Gas Location Water Table/Deep Soil Gas Location 19

Case Study Evaluation of Water Table Data Do groundwater VOC levels exceed VI screening values? Do the groundwater data characterize the water table? Is there sufficient spatial and temporal coverage? Summary May have concluded water table data provide suggestive-to-definitive evidence VI not occurring or insignificant 20

Case Study Evaluation of Soil Gas Data Above Capillary Fringe Do soil gas levels above capillary fringe exceed VI screening values? Is there sufficient spatial and temporal coverage? Summary May have concluded soil gas data above capillary fringe provide suggestive-to-definitive evidence VI not occurring or insignificant 21

Cumulative Strength of the Evidence Assume groundwater, deep soil gas, subslab, and indoor concentrations exceed screening levels Is VI significant? 22

Background Indoor / Outdoor Air Evaluation Comparison of Multiple Constituent Ratios (Fingerprinting) Real-time Sampling and Analysis (e.g., portable HAPSITE GC/MS) Background Indoor Air Source Identification and/or Removal Conclusion Indoor air concentrations due to background indoor VOC source(s) 23

Cumulative Strength of the Evidence Key Points Subsurface / subslab data suggest VI may be significant Indoor air data / background evaluation provide more definitive evidence that VI is not occurring or significant Multiple lines of evidence evaluation is critical 24

Systematic Approach for Assessing VI Summary and Take Home Points Approach is an explicit process for selecting optimal VI strategies and evaluating strength of evidence Captures degree of uncertainty and increases defensibility Based on VI Fundamental Truths Multiple lines of evidence are typically required Not all lines of evidence are created equal Strength of the evidence depends on the VI CSM scenario Breaks information into manageable components Systematically considers range of possibilities (without being expert) Helps manage technical challenges (e.g., variability, background) Strategies, evaluations and decisions are more transparent Increases consistency in assessments and helps control costs 25

26 Questions?