Corps Base Camp Lejeune: Utilizing the DoD Phased Approach to Prioritize Building Investigations

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1 A Base-Wide Vapor Intrusion Evaluation at Marine Corps Base Camp Lejeune: Utilizing the DoD Phased Approach to Prioritize Building Investigations Jennifer Simms, Loren Lund, and Keri Hallberg, CH2M HILL, Inc. Robert Lowder, US Marine Corps, Camp Lejeune Bryan Beck, NAVFAC Mid-Atlantic AWMA 2010 Vapor Intrusion Specialty Meeting

2 MCB, Camp Lejeune Jacksonville, North Carolina 236 square miles 150,000+ military personnel, dependants, retirees and civilians Environmental investigations began in IR/RCRA/UST active sites Predominantly sands and silty sands with some clay lenses Shallow GW (0-20 ft bgs) ~7,000 structures Base-wide vapor intrusion investigation began in 2007

3 Phased Vapor Intrusion Assessment Generic screening to identify potential buildings of interest Site-specific screening to refine the list of buildings of interest Phase 1 sampling (exterior/structure sampling) Multiple lines of evidence (MLE) evaluation of Phase 1 data Phase 2 sampling (structure sampling) MLE evaluation Phase 2 data

4 Investigation Areas

5 Generic Screening: Identify Potential VI Buildings of Interest Began with ~ 7,000 structures Objective: Prioritize buildings relative to VI potential Identified 25 IR/RCRA/UST sites with VOC-impacted GW Excluded NFA sites or those without GW data Compiled GW data into a database Screened data to identify COPCs for each investigation area North Carolina GW Quality Standards or USEPA 2002 VI GW screening levels (GWSLs) Identified buildings within 100 ft of monitoring wells with COPC exceedances of generic VI GWSLs (used GIS) Included buildings 100 ft of free product or active remediation systems G i i id tifi d 168 Generic screening identified 168 potential buildings of interest

6 Example Figure Showing Buildings 100 ft of Generic GWSL Exceedances

7 Site-Specific Screening: Identify VI Buildings of Interest for Phase 1 Sampling Developed site-specificspecific GWSLs for each investigation area using the J&E model. Site-specific inputs: Depth-to-groundwater and soil type Building dimensions for three size categories (residential, small industrial, and large industrial) Identified buildings 100 ft of shallow monitoring wells with COPC site-specific GWSL exceedances Included buildings 100 ft of free product or active remediation systems Eliminated buildings which were not occupied or enclosed Site-specific screening identified 50 buildings of interest for Phase I sampling

8 Example Figure Showing Buildings 100 ft of Site-Specific GWSL Exceedances

9 Phase 1 Sampling Event Exterior sampling Co-located/concurrent soil gas and grab water table samples Soil gas samples collected near water table and adjacent to buildings reduced vadose zone transport uncertainties Practical constraints (access/security/disruption) were also a factor in selecting an exterior sampling strategy Structure sampling at select buildings Buildings 100 feet from NAPL or active remediation systems Buildings where GW < 5 ft bgs Concurrent subslab and indoor/outdoor air sampling strategy Conducted building surveys Total Phase 1 Samples (44 buildings) 54 GW, 40 exterior soil gas, 21 subslab soil gas, 15 indoor air, and 6 outdoor air samples

10 Phase 1 Data Evaluation Assessed validity of site-specific screening levels Compared measured vs. modeled SG levels using co-located GW/SG results Modeled soil gas levels over- & under-estimated measured concentrations Used generic screening levels to minimize fate-and-transport uncertainties Multiple Lines of Evidence Evaluation Fundamental Truths Not all lines of evidence are created equal Consider strength of evidence in the context of the CSM

11 Selection of Buildings for Phase 2 Sampling Lines of evidence considered d Magnitude, correlation, and spatial distribution of GW, exterior SG, subslab SG, and/or indoor-outdoor air data Building construction and use/occupancy Chemical ratios 23 buildings selected Retained if exterior groundwater or soil gas concentrations exceeded screening level Greater weight placed on soil gas vs. GW data Decisions to retain other buildings were made on a case-by-case basis

12 Phase 2 Sampling Event Structure sampling subslab soil gas and/or indoor/outdoor air Indoor air samples collected if exterior SG levels >100-times screening level (unless significant indoor VOC source) Subslab sampling at all other buildings Conducted building surveys Pressure differential monitoring conducted at select buildings

13 Phase 2 Data Evaluation Multiple lines of evidence considered Site history Potential presence of NAPL Existing remediation and/or vapor mitigation systems Building construction / conditions (e.g., air pressure) Building activities & occupancy Chemical product and use inventory Potential ti preferential pathways The magnitude, correlation, and spatial (horizontal and vertical) distribution of historical and Phase 1 & 2 groundwater Exterior soil gas, interior subslab blbsoil gas, id indoor, and/or outdoor air data Chemical ratios Pressure differential measurements Calculated base-specific empirical soil gas-to-indoor air attenuation factor (AF) Created building-specific VI conceptual site models

14 Calculation of Empirical Soil Gas-to- Indoor Air Attenuation Factor Phase 1 and 2 concurrent indoor air and subslab data from 20 buildings Representative range of industrial building types and ages Eliminated results with low subslab source strength from analysis Subslab levels <100-times reporting limit Eliminating low source strength results reduced likelihood of biasing AFs Empirical AFs calculated for 88 paired data sets Identified AFs where indoor air levels were at least 2-times outdoor air levels Reduced likelihood AFs will be biased by above-ground source(s)

15 Base-specific AF of 1E-03 used during Phase 2 data evaluation

16 Example Vapor Intrusion 3-D Conceptual Site Model

17 Overall Conclusions/Take-Home Points for Phases 1 and 2 Effectively prioritized and identified buildings with highest VI potential ~7, buildings VI is not currently significant at Phase 1 & 2 buildings, even those with high subslab concentrations Indoor air detections potentially related to VI were below 1E-04 risk Slabs (as barriers) and building characteristics (e.g., air mixing/exchange) likely minimizing impacts at buildings with high subslab VOCs Base is proactively installing mitigation systems at select buildings to address future VI concerns Phase 3 draft assessment/report nearly complete. Primary objectives: Assess temporal and spatial variability Evaluate preferential vapor transport via utility conduits Assess need for existing subslab depressurizations systems

18 Overall Conclusions/Take-Home Points for Phases 1 and 2 (cont d) Generic AF and Phase 1 exterior sampling strategy t (co-located GW and SG): Minimized GW volatilization and vadose zone transport uncertainties Helped identify near-building vadose zone sources Minimized premature elimination of buildings It is important to reality-check site-specific modeled VI screening levels Vadose zone or subslab sources can contribute to subsurface vapors Review site history; conduct thorough building surveys; talk with knowledgeable individuals When feasible, calculate site-specific attenuation factors Two orders of magnitude less conservative at Camp Lejeune than generic value Feasible due to number of buildings sampled and the measured levels Address future VI concerns at buildings with elevated subslab VOCs: Consider remediating subsurface source Implement building/land-use d restrictions ti ti and re-assess in future

19 Success Story - Phase 1 & 2 Report an excellent evaluation of the potential vapor intrusion and indoor air impacts to human health. The State concurs with the conclusions and recommendations of each area building evaluated. NCDENR The documents present a clear evaluation of buildings that may be impacted by vapor intrusion and is an excellent data source that should be included in the appropriate remedial investigations. USEPA EMD [Environmental Management Division] has been at the forefront at evaluating the emerging environmental issue of vapor intrusion