ebc seminar the iaq/mold assessment – getting it right...
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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.
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
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
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
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