soil impacts groundwater impacts vapor intrusion
TRANSCRIPT
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Steven P. Sittler, P.G. Patriot Engineering and Environmental Inc. 6150 E. 75th Street, Indianapolis, IN 46250
(574) 876-9835 [email protected]
Soil Impacts
Groundwater impacts
Vapor Intrusion
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Identify preferential pathways –may need to sample
Perform paired sub-slab (SS)/indoor air (IA) sampling (or soil gas sampling in certain situations)
Samples to be collected winter (heating) & summer (cooling) seasons – “worst case”
SS samples to be collected 3 per 5,000 ft2 plus 1 for each additional 2,000 ft2
IA samples – minimum of 3, more for larger buildings
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IDEM Definition: Pathway extends through both a soil or GW source area AND a building
Investigations typically involve soil gas sampling of backfill surrounding utility corridors
A recent study in Indiana found that while 88% of identified preferential pathways were complete, only 8% resulted in subsequent IA issues!
“The relationship between the presence of elevated PCE/TCE concentrations in utility corridor backfill leading to an indoor air problem may be overstated”
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Sub-Slab Indoor Air
Soil Gas
How long should the sampling period be?
When should I sample?
Where should I sample?
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8-Hour Samples for Commercial/Industrial Sites
24-Hour Samples for Residential Sites
What about background chemicals?
What if someone tampers with the sampling device?
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Figure from Blayne Hartman presentation – Battelle 2016
8-Hour or 24-Hour Sampling may not give you an accurate representation of exposure!!!
Summa canisters
Passive samplers
Continuous samplers
Educate yourself on the benefits and
limitations of sampling options
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Additional Sampling
Positive Pressure HVAC System
Vapor Mitigation System
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Passive or active systems
PASSIVE
Sealing Vapor barriers (pre- and post-
construction) Passive venting
ACTIVE
Sub-slab depressurization systems Building overpressurization (HVAC)
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So what does that involve?
“Routine long term operation, maintenance & monitoring (OMM) of the vapor mitigation system will be necessary for as long as it is used to interrupt the VI pathway” – IDEM Vapor Remedy & Implementation Guidance document – February 2014
You are here
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Schedule 1
1. Perform activities specified in Section 3.3, generally on an annual basis.
2. Annual sampling of lAduring the winter worst case season during the first, second, and fifth year, and every fifth year thereafter.
Schedule 2
l. Perform activities specified in Section 3.3, generally on an annual basis.
2. Annual sampling of IA during the winterworst case season during t.ie first, second, and fourth year, and every other year thereafter.
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VAPOR MITIGATION IS A TREATMENT, NOT A CURE!!
=“It’s a Vicious Circle”
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Fully quantitative
Low detection levels
Short analysis time
Multiple locations
Low operating costs
Very stable
Real-time data
Summary from Blayne Hartman presentation – Battelle 2016
Identify fluctuations in target constituent concentrations
Pinpoint sub-slab source areas
Avoid unnecessary VI mitigation
Save $$$
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HOW MUCH FARTHER IS IT?”
MUST know source areas and distribution of impacts
MUST understand site biogeochemical conditions
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Focused Soil Excavation
Remedial Injections
ISCO - In-Situ Chemical Oxidation (ISCO)
Injection of aggressive chemicals to promote
oxidation of contaminants
Rapid remediation
Limitation: contact-based approach – injection
materials must physically contact contaminants
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ENHANCED BIO
Adding oxygen (aerobic) or electron
donors/bacteria (anaerobic) to
accelerate degradation
Not diffusion limited because bacteria move with groundwater flow
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Off-Site plume impacting unknown portion of Site
VI mitigation system installed during construction
8 buildings – most with little or no indoor air issues
Sub-slab ports installed in all buildings – sampled with VI systems off
Results – only 1 of 8 buildings will need continued VI mitigation &
long-term sampling
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Would operate indefinitely without
remediation of backfill, soil, &
groundwater impacts
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ISCO injection in backfill immediately below slab in source area
ERD injection in groundwater in source area and vicinity
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30 Sites
30 of 30 (100%) rec’d NFA
Average time to closure: 3 years
Average cost to closure: $70,000
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Vapor intrusion is a (perhaps THE) primary driver of environmental projects today
Current commonly-accepted VI sampling methodologies may give false or misleading results
Vapor intrusion does not always require vapor mitigation
Vapor mitigation is a treatment not a cure – and long-term stewardship applies!
Focused remediation can eliminate long-term stewardship requirements (and save $$$$).
Closures CAN BE ACHIEVED!!!