EBC Seminar

The IAQ/Mold Assessment

– Getting it Right! –Controlling Your Risk

Next Speaker

Rosemary McCafferty

Haley & Aldrich, Inc.

Outline

• Vapor Intrusion Overview

• Vapor Intrusion Sampling

• Vapor Intrusion Evaluation Consideration

• Remediation

• Case Study

• Questions

Vapor Intrusion Overview:

Vapor Intrusion to Indoor Air

Vapor intrusion is the migration of volatile chemicals from the subsurface (soil gas) through cracks in the foundation and into indoor air. Sources can be soil, groundwater or free product (LNAPL).

Soil Gas Properties And Factors

Affecting Its Behavior• Soil gas enters structures through the openings in

the foundation. The concentration found in any building is determined by several factors, including:

– the concentration of gas in the soil– the permeability of the soil– the pressure differential between the soil and the

building– other preferential pathways

• Most buildings exert a negative pressure on the soil because of the natural stack effect and exhaust devices that exist in all buildings. This “stack effect”can bring in soil gas.

State Vapor Intrusion Guidance

Not evaluated

Defers to federal program

Developed/developing program with varied flexibility

Developed program with varied flexibility, including numerical standards/screening criteria

Conservative program with substantial regulatory oversight

Currently developing guidance

No guidance; pathway not evaluated currently

Attributes of MA, NY, and NJ

Guidance

YesYesNoHypothetical future

use?

YesYesYesOutdoor air

sampling?

Full suite

TO-15

SV: “wide range”

IA: site-related

Site-

related

Analyte list

NoYesYesBackground #s

incorporated?

IA, possibly SV and

GW

IA

(5

compounds)

GWNumerical criteria

Measurem

ent

Measurem

ent

Measurem

ent

Modeling

vs. Measurem

ent

100H;

30V?

100GW: 30H;

15V

Soil: 6H;

10V

Trigger

distance (feet)

NJNYMA

Massachusetts DEP VI

Regulatory Guidance• GW-2 Groundwater-to-Indoor Air

Standards

• Indoor Air Sampling & Evaluation

Guide, April 2002

• Tiered, risk-based approach:

– Generic cleanup standards,

– Site-specific standards using modeling,

– Site-specific risk assessment

• Background included quantitatively in

standards and evaluation (75th - 90th

percentile literature value)

Vapor Intrusion Sampling:

When VI would be evaluated (in

MA)• Presence of occupied building

• Groundwater concentrations (MA trigger distances) exceed GW-2 standards

• Volatile compounds detected in soil (no screening levels provided)

• Presence of LNAPL/free product (MA trigger distances)

• Soil gas concentrations above screening values (petroleum sites only)

• Known or suspect source beneath

Definitions Of Soil Gas• Gaseous compounds (and/or

elements) in the spaces between

particles of the earth and soil. These gases can be moved or driven out

under pressure.

• Soil gas is vapor that can be

extracted from the subsurface, from pores in unconsolidated material

above the water table.

Bang Bar Installation

source: Solinst

Soil Gas from Permanent Well

Indoor Air Sampling

Considerations• Conceptual

Site Model

• Site-Specific

Compounds

of Concern

• Building

Survey

• Preferential

Pathways

• Background*

• Individual or

When to Collect Indoor Air

Samples?Parameter Most Conservative Least Conservative

Season Late winter/early spring Summer

Temperature Indoor 10°F > Outdoor Indoor < Outdoor

Wind Steady > 5 mph Calm

Soil Saturated with rain Dry

Doors/Windows Closed Open

Mechanical HeatingSystem

Operating Off

Mechanical Fans Off On

(Indoor Air Sampling and Evaluation Guide, MADEP, April 2002)

Indoor Air Background

• Things that are present at a site in the absence of a release

• May be naturally occurring or anthropogenic• Mold, Moisture, Radon, Pet allergens

• Carbon dioxide and Carbon monoxide

• Asbestos and Particulates

• VOCs/SVOCs

• Can differ from residence to residence & from night to day

• Background sources/studies• EPA VOC Database/Shah and Singh – 1988

• Stolwijk – 1990

• MA DEP IA Hydrocarbon Study – 1997

Vapor Intrusion Evaluation

Considerations

(in Massachusetts)

Evaluation of Potential

Indoor Air Impacts from

Subsurface Source1. Compare groundwater, soil

and/or soil gas concentrations to screening levels

If groundwater or soil gas concentrations do not exceed screening levels AND no precluding factors exist, then no further action is necessary.

Precluding factors include:

– Preferential migration pathways (e.g.,

utilities, sumps, openings to the

subsurface)

Evaluation of Potential Indoor Air

Impacts from Subsurface Source2. Compare list of indoor

air contaminants to

subsurface

contaminants

– Chemicals detected in

both subsurface media and indoor air are more

likely to be site-related

– Indicator compounds not

commonly found in household products (e.g., 1,1-DCE, radon)

– Potential for reverse migration of vapors to

Evaluation of Potential

Indoor Air Impacts from Subsurface Source

4. Compare indoor air concentrations from different levels (or areas) to evaluate presence of concentration gradients.

basement

1st floor

2nd floor

soil gas

groundwater

Remediation:

Setting Cleanup Standards

• Risk Based Targets

• Background Values

• Non-Detect (CEP)

Consider Vapor Mitigation

Options• Engineering

Controls– Floor slab sealing– Vapor barriers– Increased

ventilation– Sub-slab

depressurization

• Institutional Controls– Deed restrictions

• Active Remediation– SVE

• Monitoring– Long-term costs– Ownership– Liability

(USEPA-TIO Internet Seminar, February 11-12, 2003.

Summary

• Management of VI sites differs between states

• Sampling should be guided by historic information, site conditions, and available data

• Cleanup standards will depend on site use

• VI mitigation is often a cost-effective solution, especially when implemented during

Case Study

Site: 6 Family Residence• Conditions: adjacent dry cleaner potential

source of legacy chlorinated solvents; groundwater < GW-2, however, elevated soil gas

• Identified: Substantial Release Migration “releases to the groundwater that have resulted or are within one year likely to result in the discharge of vapors into school buildings or occupied residential dwellings.”

• Installed and are operating of a subslabdepressurization/ventilation to mitigate the volatilization of VOCs into the building

Thank You

• State and federal vapor intrusion guidance and references can be found at: http://www.haleyaldrich.com/vi%20services.html

• Searchable, indexed database for household products: http://householdproducts.nlm.nih.gov/

• Questions?