Presentation on theme: "EBC Seminar The IAQ/Mold Assessment – Getting it Right! – Controlling Your Risk Next Speaker Rosemary McCafferty Haley & Aldrich, Inc."— Presentation transcript:
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 MANYNJ Trigger distance (feet) GW: 30H; 15V Soil: 6H; 10V 100100H; 30V? Modeling vs. Measurem ent Measurem ent Numerical criteria GWIA (5 compound s) IA, possibly SV and GW Backgroun d #s incorporate d? Yes No Analyte listSite- related SV: “wide range” IA: site- related Full suite TO-15 Outdoor air sampling? Yes Hypothetic al future use? NoYes
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 (75 th - 90 th 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.
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? (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 Source 1.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) –Very shallow vapor sources or wet basements –Very “tight” buildings with low air exchange rates or high indoor/outdoor pressure differentials 2.Groundwater, Soil, Soil Gas Modeling
Evaluation of Potential Indoor Air Impacts from Subsurface Source 2.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 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
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 http://www.haleyaldrich.com/vi%20services. html Searchable, indexed database for household products: http://householdproducts.nlm.nih.gov/ http://householdproducts.nlm.nih.gov/ Questions?