Multiple-Lines-of-Evidence Approaches to Address Complications to - - PowerPoint PPT Presentation

Multiple-Lines-of-Evidence Approaches to Address Complications to Vapour Intrusion Pathway Assessments

Robert Ettinger Geosyntec Consultants October 28, 2014

Challenges to Vapour Intrusion Assessments

• Sensitive subject for many

stakeholders

• The subject of new and

changing regulatory guidance and litigation

• Closed sites reopened to

address vapour intrusion pathway

• Affecting property transactions
• Technically challenging pathway
• Data needs and interpretation for “MLE” assessments
• Evaluation of background contributions to indoor air
• Understanding uncertainties associated with vapour intrusion

modeling

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Managing Uncertainties

• Compounding

conservative assumptions can lead to overly conservative conclusions

• Balance

uncertainties to improve risk-based decision making process

Limited Site Characterization More conservative risk mgmt. decisions Detailed site characterization Less conservative modeling

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Greater understanding

• f contaminant fate

(e.g., bioattenuation) Reduced site characterization requirements

Direction of Regulatory Guidance

• Increased reliance on multiple lines of evidence “MLE”

assessments to address spatial and temporal variability

• Exclusion criteria for petroleum vapour intrusion
• More cautious screening evaluations
• Consideration of short-term action levels
• Less reliance on vapour intrusion modeling /

greater use of indoor air sampling

• Alternate lines of evidence to evaluate

indoor air background sources

• Increased emphasis on engineering controls

and pre-emptive mitigation

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Multiple Lines of Evidence Investigation Approach

Source Top-Down Bottom-Up

Indoor Air Evaluation

• Risk Management Decisions
• Background Contributions
• Mitigation Options

Vapour Intrusion To Building

• Soil Characteristics
• Building Characteristics

Source Characterization

• Groundwater, Soil, Soil

Vapour Concentration Distribution

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Importance of a Conceptual Site Model

• CSM should characterize

potential sources, fate and transport pathways, and receptors (e.g., buildings)

• Use CSM for investigation

planning and identify pros / cons

• f different lines of evidence
• Not all lines of evidence have

equal weight in VI evaluation

• Consider CSM when interpreting

investigation data

• Resolve differences between

data and CSM Develop Initial CSM Conduct Investigation Need Add’l Data? Proceed with Corrective Action Planning / NFA Review/ Update CSM

No Yes

Common Views of Vapour Intrusion Models

• There is a range of opinions about the use of

models for vapour intrusion pathway assessments

• Most modeling questions arise from:
• Different expectations for accuracy of model results

(i.e., typical vs RME estimates)

• Deviation from conceptual model used for vapour

intrusion model development

• Use of inappropriate input parameters
• Uncertainty of significance of model input

parameters

• Some combination of data collection and

modeling is usually appropriate

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Vapour Intrusion Models

• There are many options for VI models available
• Model selection is dependent on what you know about the

site and the level of desired assessment

• Regulatory attenuation factors are simple VI models

Empirical Analytical Numerical

 USEPA Database  Johnson and Ettinger (1991)  VAPOURT (1989)  USEPA VISL

Calculator

 Little et al. (1991)  Sleep & Sykes (1989)  San Diego SAM  RUNSAT (1997)  VOLASOIL (1996)  Abreu & Johnson (2005)  Krylov and Ferguson (1998)  VIM (2007)  DLM - Johnson et al. (1999)  Brown University (2007)  DeVaull (2007)  BioVapor (2010)

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USEPA Empirical Attenuation Factors

• Empirical data from over 900

buildings at over 40 sites from across the country

• Data are predominantly from

residential buildings

• Majority of data from a few

sites

• Used paired data (indoor air and

sub-surface data) to calculate empirical attenuation factors

• Filtered data to screen out poor

data quality and results impacted by background sources

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USEPA Empirical Attenuation Factors

• US regulatory

agencies focus on 95%ile values

• USEPA database

results may be biased by background impacts

• May not be

relevant to non- residential scenarios

• Be careful if simply

using empirical factors

95th percentile J&E Model Prediction

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USEPA Empirical Attenuation Factors Empirical Attenuation Factors

• Always keep limitations of empirical attenuation factors in

mind in risk-based decision making process Source # of Data Pairs Median 95%ile Model Predict

Crawl Space 41 0.39 0.90 NC Sub-Slab Soil Gas 411 0.0027 0.026 0.0024 Soil Gas 106 0.0038 0.25 0.0013 Groundwater 743 0.000074 0.0012 0.00041

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Vapor Intrusion Attenuation Factor

• USEPA VI database study is commonly referenced to estimate VI

attenuation factor, but limitations of study should be recognized

• Data predominantly from single family homes
• Difficult to completely address background effects
• Natural vadose-zone biodegradation effects not captured
• Use of 95%ile empirical factors will over-state potential risks
• Ability for site-specific modeling/assessment is important

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Site-Specific Modeling

• Site-specific modeling can be useful tool to characterize

uncertainty in preliminary screening vapour intrusion assessments

• Consider differences in site conceptual model from

default assumptions

• Focus site-specific inputs for “critical” parameters that

can be well characterized (see Johnson, 2003)

• Additional support may be needed if calculated results

are significantly different from expected range

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Vapour Intrusion Critical Processes for Modeling Evaluation

Process

Key Considerations Sensitivity Measurements

Diffusive Transport (Diffusive Flux)

Soil type, moisture content, presence of groundwater VI decreases when higher moisture content soils are present Continuous boring logs, soil property data, in-situ diffusivity test, VOC soil gas profile

Building Ventilation

Varies by building use/design Increasing ventilation reduces indoor air concentrations Building ventilation rate

Soil Gas Convection

Default values typically used Key parameter for sub-slab data or pos. press. Cross-slab pressure

Partitioning

Groundwater to soil gas relationship Uncertainty reduced by collection of soil gas samples Soil gas samples for source characterization

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Evaluation Framework for Petroleum Hydrocarbons

• PVI is different than VI for chlorinated compounds
• PVI rarely shown to be a complete

pathway due to natural biodegradation in vadose-zone soils

• Investigation strategies for chlorinated

sources are not well-suited for many petroleum release sites

• PVI guidance focuses on identifying site conditions where PVI

is not of concern (exclusion criteria)

• USEPA OUST and ITRC developed guidance on parallel

tracks

From API, 2004

PVI Conceptual Model 15

USEPA PVI Database

• Data from 74 sites
• Predominantly UST sites, but data from terminals,

refineries, and petrochemical sites included

• Data analysis focuses on paired soil vapour and

groundwater data to identify distance for vertical attenuation in vadose zone

• Distance to attenuate to 50 – 100 µg/m3
• Different from analysis for CVOCs due to

background sources of petroleum compounds

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USEPA PVI Database Dissolved-Phase Source

From USEPA, 2013. Evaluation of Empirical Data to Support Soil Vapor Intrusion Screening Criteria for Petroleum Hydrocarbon Compounds, EPA 510-R-13-001.

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USEPA PVI Database LNAPL Source

From USEPA, 2013. Evaluation of Empirical Data to Support Soil Vapor Intrusion Screening Criteria for Petroleum Hydrocarbon Compounds, EPA 510-R-13-001.

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Considerations for Sites That Do Not Meet Exclusion Criteria

• Petroleum hydrocarbons degradation occurs for

wide range of petroleum contaminated sites

• Typically re-visit multiple-lines-of-evidence

approach

• Data collection to assess biodegradation (soil vapour
• r sub-slab soil vapour probes)
• Modeling
• Indoor air sampling is challenging for petroleum

hydrocarbons

• Consider whether remediation and/or mitigation

is warranted

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Indoor Air Sampling

• Indoor air concentration measurements are used to make

decisions about potential health risks, but there are difficulties with sampling and interpretation.

• Challenges to indoor air sampling
• VOCs frequently detected
• Occupant disruption
• Temporal and spatial variability
• Interpretation for future

land development scenarios

• Background effects

WMS Sampler

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10 20 30 40 50 60 70 80 90 100 Toluene (0.03 - 1.9) m/p-Xylene (0.4 - 2.2) Benzene (0.05 - 1.6)

• -Xylene (0.11 - 2.2)

Ethylbenzene (0.01 - 2.2) Methylene chloride (0.12 - 3.5) Carbon Tetrachloride (0.12 - 0.25) Chloroform (0.02 - 2.4) Tetrachloroethylene (0.03 - 3.4) 1,1,2-Trichloro-1,2,2-trifluoroethane (0.25) Methyl tert-butyl ether (MTBE) (0.05 - 1.8) 1,1,1-Trichloroethane (0.12 - 2.7) Trichloroethylene (0.02 - 2.7) 1,2-Dichloroethane (0.02 - 0.25) Vinyl chloride (0.01 - 0.25) 1,1-Dichloroethylene (0.01 - 2.0) cis 1,2-Dichloroethylene (0.25 - 2.0) 1,1-Dichloroethane (0.08 - 2.0) trans 1,2-Dichloroethylene (0.8 -2.0)

Total Percent Detections

Chemical (Reporting Limits in ug/m

3)

Dawson and McAlary, 2009, “Background Indoor Air,” Ground Water Monitoring & Remediation 29, No. 1

VOCs Commonly Detected in Indoor Air

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Detection of VOC in indoor air is not a useful single line of evidence to assess vapour intrusion pathway

Indoor Petroleum Hydrocarbon Sources

20:50 Richard Wilson Saatchi Gallery Permanent Exhibit

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Indoor Air Concentrations Are Greater Than Outdoor Air Concentrations

From Sexton, et al., 2004. Comparison of Personal, Indoor, and Outdoor Exposures to Hazardous Air Pollutants in Three Urban Communities

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Approaches for Indoor Air Background Assessment

• Various approaches available to evaluate background

contributions to indoor air quality measurements

• Traditional approach - chemical inventory

and comparison to literature values

• Real-time monitoring with portable GC/MS
• Compound ratio analysis / tracers
• Building pressure control
• Compound-specific stable isotope analysis (CSIA)
• Detailed data analysis
• Pros and cons to each of these methods
• Risk management considerations should be used to

assess need for detailed background evaluation

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Indoor Air Sources

Latex Paints X X X Alkyl Paints X X Carpets X X X X Glued Carpets X X X X X X Wood Burning X X X X X Foam Board X Paint Removers X Spray Products X Adhesives/Tapes X X X X Room Deodorants X Tobacco Smoke X X X X X Gasoline/driving X X X X X Solvents X X Dry Cleaning X

Source

From Hers et al., 2001. The use of indoor air measurements to evaluate intrusion of subsurface VOC vapors into buildings, J. Air & Waste Manage. Assoc. 51:1318-1331.

Expect detections of VOCs in any indoor air sample

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Example Background Indoor Air Concentrations

Consider background range as well as typical values

From D Dawson and M McAlary, 2009 2009

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0 .0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1 .0 2 0 0 4 2 0 0 5 2 0 0 6 2 0 0 7 2 0 0 8

Note: 1) 1,2-DCA = 1,2-dichloroethane From McHugh et al., 2009. Also see Doucette et al., GWMR, 2010

CONCENTRATION DETECTION FREQUENCY

1,2-DCA Detect. Freq. (%) 1,2-DCA Conc. (ug/m3)

USEPA INDOOR AIR LIMIT

0 % 1 0 % 2 0 % 3 0 % 4 0 % 5 0 % 6 0 % 7 0 % 8 0 % 9 0 % 1 0 0 % 2 0 0 4 2 0 0 5 2 0 0 6 2 0 0 7 2 0 0 8

<0.08 <0.08 <0.08

Median 1,2-DCA Conc. 90%ile 1,2-DCA Conc.

1,2 DCA Background Source: Detailed study by Hill AFB identified molded plastic

• rnaments manufactured in China as source for 1,2 DCA.

Background Concentration of 1,2-DCA

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Real Time Monitoring with Portable GC/MS

• Building survey to sub-ppbv levels
• Use to identify preferential pathways or indoor sources
• HAPSITE GC/MS
• Analyze for target VOCs in SIM mode
• ~10 minute sample time
• Can also be run in scan mode

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Building Pressure Control

• Negative pressure

= induced vapour intrusion

• Positive pressure =

inhibited vapour intrusion

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Building Pressure Cycling Concept

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Short-Term EPA TCE Response Action Levels (RAL)

• USEPA issued TCE toxicity reassessment Sept. 2011
• Strengthened confidence “that TCE is a human carcinogen”
• Identified non-cancer effects
• Decreased thymic weights

(immune system)

• Toxic nephropathy

(kidney)

• Conotruncal cardiac defects

(developmental)

• USEPA Region 9 recently

proposed short-term action levels

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USEPA Region 9 TCE Indoor Air Screening Levels

Exposure Scenario Urgent RAL (µg/m3) Accelerated RAL (µg/m3) Chronic RSL (µg/m3) Residential 6 2 0.48 Commercial (8 hr/day) 24 8 3.0 Commercial (10 hr/day) 21 7 2.4

• Accelerated RAL – Accelerated Response Action Level based on Hazard Quotient =1

Implement corrective action within a few weeks

• Urgent RAL – Urgent Response Action Level based on Hazard Quotient =3

Implement corrective action immediately

• Chronic RSL – Chronic Regional Screening Level based on 1x10-6 target risk level.

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TCE Response Action Levels

• Technical questions have been raised regarding the

development of the response action level for TCE

• Laboratory test procedures
• Reproducibility of laboratory tests
• Calculation of acute reference concentration
• Expect further questions/

comments regarding the TCE Response Action Level

From: Symposium on New Scientific Research Related to the Health Effects of Trichloroethylene, Washington, DC. February 26-27, 2004. (http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=75934)

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Considerations for Indoor Air Monitoring

Focus on short-term action levels and need for expedient response may affect indoor air sampling strategies

• More difficult to address data with quality control issues

(e.g., false positives)

• Temporal variability in indoor air concentrations may

lead to requests for more frequent monitoring

• Consider longer duration sampling

(i.e., passive sampling)

• Allows for 2-3 week time-average samples
• Impractical to implement if sampling with HVAC off is required
• Expedited decisions require planning before sample collection
• Develop decision tree for contingent actions
• Consider whether expedited laboratory analysis provides value

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Response Process

• Occupant relocation or indoor air

purification (if expedited action needed)

• Source removal and/or mitigation (e.g.,

excavation, soil vapour extraction)

• Local regulatory or building code

requirements

• Barriers to chemical entry
• Pathway sealing
• Sub-slab depressurization
• Sub-slab venting
• Aerated Flooring
• HVAC modifications to increase

ventilation or change building pressure

• Consider VI pathway in redevelopment

plan

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Active Remediation vs Engineering Controls

• Site-specific determinations are needed at balance short-

term and long-term vapor intrusion concerns

• Engineering controls can provide a short-term solution to

address vapor intrusion concerns

• Remediation may be better suited to address long-term

concerns

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Sub-Slab Depressurization

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Novel Mitigation Technique: Aerated Flooring

A plastic form used to create a continuous void below concrete slabs

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Concrete is poured over the forms

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Vapour Intrusion Mitigation System Considerations

• Design
• Implementability

(e.g., new vs existing structure)

• Effectiveness
• O&M Requirements
• Electrical costs
• Equipment upkeep
• Monitoring Requirements
• Requirements to demonstrate

effectiveness

• Cost Considerations
• Installation costs may be much less than monitoring costs
• Other Issues
• Impacts to building occupants

(i.e., aesthetics, costs)

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Parameter 1 Parameter 2

Risk-Management Decision Matrix

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Increasing VI Risk Increasing VI Risk

Risk Management Assessment Risk management in mitigation decision process

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< RBSL and < Background > RBSL and < Background > RBSL and > Background <100 x RBSL Pre-emptive Mitigation / Remediation Pre-emptive Mitigation / Remediation Mitigate / Remediation <10 x RBSL Confirmation Monitoring Monitor/ Pre-emptive Mitigation Mitigate / Remediation <RBSL No Further Action Confirmation Monitoring Monitor/ Background Assessment

Increasing Indoor Air Concentration Increasing Sub-Slab Concentration

Summary

• Regulatory approaches for the vapour intrusion pathway

are continuing to change.

• Vapour intrusion evaluation methods continue to be

developed and improved, including methods for:

• Site investigation
• Site-specific modeling
• Identification of background sources
• Consider risk management, risk communication, and

long-term liabilities to address uncertainties associated with vapour intrusion pathway assessments

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Acknowledgements

• Special thanks to colleagues at Geosyntec who

contributed to this presentation:

• Nancy Bice
• Todd Creamer
• Helen Dawson
• David Folkes
• Todd McAlary
• Bill Wertz

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