1. Vapor Intrusion Workgroup July 29, 2010 http://indoorairproject.wordpress.com/ http://indoorairproject.wordpress.com/ 1

2. Agenda Opening Remarks Update on Outstanding Issues –Modeling –MCP Closure –Future Buildings Next Steps –August Meeting on Future Buildings –Data on Vapor Barrier Systems –Issue Draft for Comment Questions? http://indoorairproject.wordpress.com/ 2

3. Vapor Intrusion National Issue High Risk Pathway Technically Challenging to Assess Making Progress on Guidance Add’tl Input Needed to Finalize http://indoorairproject.wordpress.com / Vapor Infiltration Pathway 3

4. Massachusetts Vapor Intrusion Guidance 1990s: Massachusetts developed guidance and standards to protect against VI pathway 2000s: Massachusetts begins to address changes in science and understanding of VI pathway 2006 – MA revised (downward) cleanup standards for several common indoor air contaminants GW-2 PCE now 50 ug/l (was 3000 ug/l) 2008: Massachusetts initiated guidance update discussions 2010: Survey of states/EPA: 18 other states plus EPA updating their VI guidance documents http://indoorairproject.wordpress.com/ 4

5. Vapor Intrusion Guidance Guidance Priorities: Protectiveness Clarity Practicality Certainty http://indoorairproject.wordpress.com/ 5

6. Challenging/Controversial Guidance Topics Role of Modeling MCP Site Closure Future Buildings http://indoorairproject.wordpress.com/ 6

7. Modeling Formerly widely used to predict indoor air concentrations without sampling More recently: –Not predictive of indoor air concentrations –Useful as a screening tool (GW-2) –Useful as a line of evidence 14 states (and EPA) now require indoor air sampling to validate the model http://indoorairproject.wordpress.com/ 7

8. Site Closure Certainty and Protectiveness for sites with Vapor Intrusion (AKA how to RAO if you’ve dealt with CEP) Source eliminated or controlled No Significant Risk Active system not needed to maintain NSR Same as for groundwater Enough data to demonstrate that indoor air really is NSR Multiple rounds over multiple seasons, including winter Two years of data to demonstrate that NSR has been reached AULs as needed to ensure future protectiveness Must be maintained - same as for eliminating exposures to soil Inspections and/or indoor air sampling may be needed under some circumstances (penetration of vapor barrier) http://indoorairproject.wordpress.com/ 8

9. Future Buildings Design and siting –Building situated away from area of contamination –Garage on lowest level –Building elevated above ground Tiered engineering solutions depending on contaminant levels –Vapor barrier with certified installation, +/- subslab system, +/- monitoring http://indoorairproject.wordpress.com/ 9

10. ACB gw < GW-2 gw < “X” x GW-2 gw > “X” x GW-2 “Low” ia sampled ia Not sampled ia Protecting Occupants of Future Buildings: Examples of Possible Off-Ramps MCP Closure: MCP Closure: (assumes all other require- ments are met) A-2 or B-1 RAO No AUL (assumes all other requirements are met) A-3 or B-2 RAO (includes AUL) A-2 or B-1 (with potential future notification obligation) RAO VI (possible future option?) Time “Elevated”“High” Building Construction Unrestricted Use No MCP requirements (assumes unchanged gw conditions) Vapor Barrier & SSDS Building Construction AUL Applies post-RAO RAM with submittals Building Construction AUL Applies post-RAO RAM with submittals VB & SSDS installed meeting Performance Stnds (TBD) Documentation VB & SSDS installed meeting Performance Stnds (TBD) 2 yrs indoor air sampling results (consistent with existing bldg requirements) Documentation MCP Closure: (assumes all other require- ments are met) A-3 or B-2 RAO (includes AUL) A-2 or B-1 (with potential future notification obligation) RAO VI (possible future option?)

11. Recap Issues and Resolutions Modeling – existing buildings –A line of evidence –Validate with Indoor Air sampling Site Closure –Robust sampling effort required to demonstrate NSR over a period of time Future Buildings –Workgroup to develop tiered engineering solutions http://indoorairproject.wordpress.com/ 11

12. Next Steps Explore engineered barrier/future building scenarios –Information sought on vapor barriers –Issue draft proposal early August –Workgroup to meet late August September - issue next draft/solicit comments Finalize guidance! http://indoorairproject.wordpress.com/ 12