What is Vapor Intrusion (and Why Does it Matter)? · What is Vapor Intrusion (and Why Does it...

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What is Vapor Intrusion (and Why Does it Matter)?

Webinar for EPA Staffby

Richard Kapuscinski

Office of Land & Emergency Management (OLEM)

September 2017 1

Briefing Organization & Scope

• What is vapor intrusion (VI)?

• How and why does it occur? What are the principal processes underlying VI?

• Where can VI occur?

• Why is VI of interest to EPA/OLEM?

• What makes VI so complicated?

• Risk communicationSeptember 2017 U.S. Environmental Protection Agency 2

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I(A). What is Vapor Intrusion?

• Vapor intrusion “is the general term given to migration of hazardous vapors from any subsurface vapor source, such as contaminated soil or groundwater, through the soil and into an overlying building or structure.”

September 2017 U.S. Environmental Protection Agency 3

I(B). How Does Vapor Intrusion Occur?

September 2017 Source: EPA [2002], Figure 1 4

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I(B). How Does Vapor Intrusion Occur? (continued)

– Vapor-forming chemicals can also enter buildings via ‘conduit gas intrusion’ if and when present in sewer or drain lines, utility tunnels, or other conduits

September 2017 5Image Source: McHugh & Beckley [2015]

I(B). Why Does Vapor Intrusion Occur?(continued)

• Driving “forces”

– Pressure differences between the building air and subsurface soil or conduits (facilitate flux via advection)

– Vapor concentration differences (facilitate net flux via diffusion)


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I(B). Why Does Vapor Intrusion Occur? (continued)

• Openings in buildings

– Cracks, seams, interstices and gaps in basement floors, walls, or foundations

– Intentional openings (e.g., for utility conduits, including sewers, sump pits, and drainlines)

September 2017 7Image Source: USEPA [2008], Figure 1; USEPA [1993], Figure 2-2

I(B). Why Does Vapor Intrusion Occur?(continued)

• A broad range of hazardous substances, contaminants, and pollutants in the subsurface environment have sufficient volatility and toxicity, including

– Chlorinated solvents (e.g., PCE, TCE)

– Petroleum hydrocarbons (e.g., BTEX, naphthalene)

– Hydrophobic compounds that also meet criteria (e.g., some PCBs, some pesticides)

September 2017

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U.S. Environmental Protection Agency

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Q&A

September 2017 Vapor Intrusion Physics 9

I(C). Where Can Vapor Intrusion Occur?

• Any site with “vapor-forming chemicals” in the subsurface and a building or structure nearby

– Hundreds of sites on the National Priorities List (NPL) have TCE, only one of the vapor-forming chemicals of potential concern

– Hundreds of additional sites with subsurface contamination with TCE are subject to the corrective action provisions of the Resource Conservation and Recovery Act (RCRA)


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I(C). Where Can Vapor Intrusion Occur? (continued)

• Can occur in a broad range of land use settings and buildings

– Residential (e.g., detached single-family homes, multi-unit apartments and condominiums)

– Commercial (e.g., office buildings, hotels, retail establishments)

– Institutional (e.g., hospitals, schools, and gyms)

– Industrial (e.g., manufacturing plants)

September 2017 11U.S. Environmental Protection Agency

I(D). Why is Vapor Intrusion of Interest?

• It’s a potential human exposure pathway -- a way that people may come into contact with hazardous vapors while performing their day-to-day indoor activities.

– Can pose health or safety threats


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I(D). Why is Vapor Intrusion of Interest? (continued)

• There is evidence suggesting adverse health effects in at least one community subject to vapor intrusion exposures posed by PCE and TCE [Forand et al. 2012]

– Maternal residence in both areas was associated with cardiac defects.

– Residence in the TCE area was also associated with low birth weight and fetal growth restriction.


Comparing Human Exposure Scenarios

Feature Occupancy of Building Subject to Vapor Intrusion

Use of Contaminated Groundwater

Human Exposure Route(s)

Inhalation of contaminated indoor air

Ingestion of and dermal contact with groundwater; inhalation of chemicals volatilized during gw use

Can Behavior be Changed to Avoid Exposure?

Breathing unavoidable;supplying a self-contained breathing apparatus isn’t a practical response action

Groundwater use avoidable;alternate water supply for drinking (e.g., bottled water) is feasible

Location(s) of Investigation

Generally, “interior” (inside building), as well as “exterior”

Almost exclusively “exterior” (outside of building)

September 2017

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I(E). Risk Communication & Stakeholder

Engagement

• Informing people about potential health hazards posed by vapor intrusion is a key responsibility of the Agency

• Specialty expertise is warranted, because there are personal, cultural, and societal dimensions of risk perception.

• Technical complexity complicates communicationsSeptember 2017 15

Q&A

September 2017 Vapor Intrusion: Agency and Public Interests 16

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I(F). Vapor Intrusion: Why So

Complicated?

• Process rates and vapor concentrations that can vary over time and space

• Variety of buildings with unobservable features/conditions that influence VI

• Vapor sources other than vapor intrusion (e.g., indoor and community sources)


September 2017 Conceptual Diagram of Soil Gas Intrusion ProcessesSOURCE: Reichman et al. [2017], Figure 1

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September 2017

Building Under-pressurization in an Intensively Monitored Building SOURCE: EPA [2012], Figure 10-1

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I(F). Complications: Contributors to Spatial

Variability (continued)

– Source and building geometry

– Incomplete mixing of indoor air within building

September 2017 20Image Source: EPA [2010], Figure 4-6

Isoconcentration Contours for Vapors in Soil Gas

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I(F). Complications: Spatial Variability (continued)

– Heterogeneity in vadose zone conditions that influence vapor migration

– Preferential (i.e., high-flux) migration routes for vapors, when present

September 2017 21Results of Monitoring Soil Gas at Test House in Utah

Source: Guo [2015]

I(F). Complications: May Not Be Readily

Observable (continued)

September 2017 Images’ Source: Paul Johnson (ASU & CSM) 22

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I(F). Implications of VI Complexity [continued]

• “The ability of human experts to effectively predict such a complex multivariable process [i.e., vapor intrusion] is expected to be limited” [USEPA-ORD, 2015].


I(F). Implications of VI Complexity [continued]

• Our collective understanding may not (yet) be sufficient for purposes of

• Anticipating time periods that represent a reasonable maximum exposure (“RME”) condition

• Predicting spatial and temporal patterns of vapor concentrations; for example, due to– Time-variable gas entry

– Fluctuating groundwater tables

• Predicting cleanup/remediation timeframes


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I(F). Manifestations of VI Complexity (continued)

– Impacts of soil gas intrusion are not necessarily worse in the winter in every climate and geographic area, or contamination scenario

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Example Showing Greater Soil Gas

Intrusion in Summer Months

Image Source: Barnes & McRae [2017,

Figure 1]

September 2017 26

Vapor Intrusion Conditions in Contiguous Structures SOURCE: MassDEP [2016], Report Figure 8

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I(F). Manifestations of VI Complexity (continued)

September 2017 DATA SOURCE: Gorder and Dettenmaier [2011] 27

0 20 40 60 80 100 120 140 160

Storage Area

Bathroom

Living Room

Vapor Concentrations in Indoor Air (µg/m3),

Residence 40, Hill AFB

PCE 1,1-DCE TCE

I(F). Complications: Vapor Sources Other

Than VI (continued)

– Indoor sources may include products stored or used within building.• Consumer products in homes

• Industrial processes and operations

– Air exchange will introduce vapors into a building from ambient air.

September 2017 28

Examples of Indoor Sources of Vapors

Image Source: Tom McHugh

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Q&A

September 2017 Vapor Intrusion: It’s Complicated 29

1(G). Additional Information About VI

• Conceptual Model Scenarios for the Vapor Intrusion

Pathway (EPA-530-R-10-003). Office of Solid Waste and Emergency Response. February 2012.

• OSWER Technical Guide For Assessing And

Mitigating The Vapor Intrusion Pathway From

Subsurface Vapor Sources To Indoor Air (OSWER Publication 9200.2-154. Office of Solid Waste and Emergency Response. June 2015

– see Section 2, in particular


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1(G). Additional Information About VI (continued)

• Simple, Efficient, and Rapid Methods to Determine

the Potential for Vapor Intrusion into the Home:

Temporal Trends, Vapor Intrusion Forecasting,

Sampling Strategies, and Contaminant Migration

Routes (EPA/600/R-15/070). Office of Research and Development. October 2015.


Additional Introductory Presentations

• OSWER Vapor Intrusion Guide (October 18)

• VI Investigations (October 31)

• Cleanup Plans for Vapor Intrusion (November 2)


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OSWER Technical Guide For Assessing And Mitigating The Vapor Intrusion Pathway From Subsurface Vapor Sources To Indoor Air

OSWER Publication 9200.2-154

June 2015

This document is intended for

use at any site being

evaluated pursuant to

CERCLA or the corrective

action provisions of RCRA,

where vapor intrusion may be

of potential concern

(“OSWER VI Guide”).

It is also intended for use by

EPA’s brownfield grantees,

where vapor intrusion may be

of potential concern.

It is applicable to both

residential and non-residential

settings (e.g., commercial and

industrial). 33

Contact Information for Speaker

• Rich Kapuscinski

– [email protected]

– (703) 305-7411


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