EBC SeminarThe IAQ/Mold Assessment

– Getting it Right! – Controlling Your Risk

Next Speaker

Rosemary McCaffertyHaley & 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 GuidanceMA NY NJ

Trigger distance (feet)

GW: 30H; 15VSoil: 6H; 10V

100 100H; 30V?

Modeling vs. Measurement

Measurement

Measurement

Measurement

Numerical criteria

GW IA (5 compounds)

IA, possibly SV and GW

Background #s incorporated?

Yes Yes No

Analyte list Site-related SV: “wide range”IA: site-related

Full suite TO-15

Outdoor air sampling?

Yes Yes Yes

Hypothetical future use?

No Yes Yes

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)

• **Critical Exposure Pathways – “measurable concentrations of OHM into the living or working space of a pre-school, daycare, school or occupied residential dwelling…” – Experience says that “background” is not always sufficient. Individual

case managers may require non-detects.

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 structure

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 Batch Cleaned

Canisters• Sample Collection• Method TO-15/-14/-17,

APH• Certified Laboratories

When to Collect Indoor Air Samples?

Parameter Most Conservative Least Conservative

Season Late winter/early spring Summer

Temperature Indoor 10F > 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• H&A/Alpha Labs MA Residential IA Study-2004/2005

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 levelsIf 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)

– Very shallow vapor sources or wet basements– Very “tight” buildings with low air exchange rates or high

indoor/outdoor pressure differentials2. Groundwater, Soil, Soil Gas Modeling

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 occur (from building interior to sub-slab)

3. Compare indoor air concentrations to literature or site-specific background values and outdoor air concentrations

Evaluation of Potential Indoor Air Impacts from

Subsurface Source4. 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– Public perception

(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 construction or redevelopment

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 subslab depressurization/ventilation to mitigate the volatilization of VOCs into the building from the underlying groundwater.

• Assessed indoor air quality to evaluate the effectiveness of the subslab system

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?