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EPA Region 7 Dan Nicoski } EPA Region 7 approach to evaluating the - - PowerPoint PPT Presentation
EPA Region 7 Dan Nicoski } EPA Region 7 approach to evaluating the - - PowerPoint PPT Presentation
EPA Region 7 Dan Nicoski } EPA Region 7 approach to evaluating the VI Pathway } Using the VISL Calculator } Why Pre-emptive Mitigation? } New ORD VI Documents } EP EPA R7 recommended approach Sub-slab/Indoor Air/Ambient t Air/Survey }
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} EP
EPA R7 recommended approach… … Sub-slab/Indoor Air/Ambient t Air/Survey
} Sub-slab only
- Indicator of potential VI concerns
- Can’t fully evaluate the VI pathway
} Indoor Air only
- Must assume any detects are from the subsurface
- Evaluate potential indoor sources
- Contributions from outdoor air?
} Sub-slab/Indoor Air – VI pathway evaluated;
what about outdoor contributions?
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} Exterior Soil Gas
- Provides an additional line of evidence
- Collect samples at depth of foundation or 5 ft
whichever is deeper & on multiple sides of structure
- Evaluate attenuation; collect soil vapor samples
from various interval(s)
- Near source/exterior soil vapor concentrations
may not represent concentrations under structure
- Due to this potential effect, any detections above
the 1E-06 cancer risk value will warrant IA/SS sampling
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} Typically recommend 4 quarterly sampling
events; co-located/concurrent SS/IA
} Spatial & temporal variability } Active sampling - Summa or sorbent tubes } Industrial
- Greater slab thickness than residential
- Higher air exchange rates
- Building construction – OH doors, vents & fans, HVAC
systems, more open areas
- Building use – sensitive populations, office settings,
chemical use or storage
- Provides RPs with data to evaluate work place
exposures
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2002 Draft VI Guidance 2015 VI Guidance
} Groundwater – 0.001 } Sub-slab/soil gas
- shallow - 0.1
- deep – 0.01
} Exterior Soil Gas – SAA } Crawl Space = soil gas } Groundwater
- generic - 0.001
- fine grained - 0.0005
} Sub-slab – 0.03 } Exterior Soil Gas – 0.03 } Crawl Space – 1
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} Identifies chemicals of sufficient volatility &
toxicity
} Provides updated RSL concentrations } Facilitates calculation of site-specific
screening levels
} Ensure use of the appropriate exposure
scenario, risk value, SS-IA, GW-IA, groundwater temperature & attenuation factor
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} Subsurface contaminants may indicate
potential vapor intrusion concerns
} Sensitive populations – daycare, senior
living center, elementary school
} Cost-effective means of protecting human
health
} Reduce potential risks of indoor air
exposure due to prolonged study periods
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} Monitoring the VMS
- Collect indoor air samples after installation
- Evaluate pressure measurements
} Operation and maintenance of VMS
- Periodic routine inspections/repair/
replacement
- Fans, piping, seals & membranes
} Termination/Exit Strategy
- Operates until source remediated to clean-up
levels
- Sample sub-slab/indoor air to verify above
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} Assessment of Mitigation Systems on VI:
Temporal trends, Attenuation Factors, and Contaminant Routes under Mitigated & Non- Mitigated Conditions; EP EPA/600/R-13/241, June 2015.
} Simple, Efficient, & Rapid Methods to
determine the Potential for VI into the Home: Temporal Trends, VI Forecasting, Sampling Strategies, & Contaminant Routes; EP EPA/600/ R- R-15/070 15/070, October 2015.
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} No apparent effects of rain on VI sampling;
snowfall & snow/ice accumulation can increase VOC VI.
} VMS are highly effective on radon (>90%) but not
as effective on VOCs (~60%).
} Interactive effect of cold temps, snowfall/ice,
barometric pressure and wind load on VOC VI; perhaps up to 10 factors (build construction, geology, DTW, preferential pathways, etc.).
} Tracer studies suggest horizontal migration from
up to 20 ft; vertical migration from 13 ft to 6 ft.
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} Reasonable agreement between observed
deep soil gas concentrations and those predicted by Henry’s Law from groundwater.
} Collection of two VI samples in winter (one
early, one late) may provide a reasonable prediction of near-term/worst-case VI.
} The ability of human experts to effectively
predict such a complex multivariable process is expected to be limited.
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