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Vapor Intrusion Monitoring

Vapor Intrusion Defined
Vapor intrusion (VI) occurs when volatile chemicals in buried wastes and/or contaminated groundwater emit vapors that migrate through subsurface soils and into indoor air spaces of overlying buildings. This can result in an indoor air quality problem.

Sampling at the Source - Soil
Soil Gas Sampling — U.S. EPA SOP#2042
Because soil is the pollutant pathway, many vapor intrusion studies include a soil study. Soil gas sampling results can identify underground contamination and trace the source, extent, and movement of pollutants.

Typical soil gas sampling includes driving a hole into the ground and inserting a probe into the hole. The air sample is pulled through the probe and collected into a container. U.S. EPA Standard Operating Procedure (SOP) # 2042 for Soil Gas Sampling specifies Tedlar® sample bags as containers and the use of negative-pressure sampling for soil gas collection. A sample bag is placed in an airtight chamber (e.g. Vac-U-Chamber) and a sample pump is used to create a vacuum in the chamber. This causes the air sample to enter into the bag without going through the pump; this method eliminates contamination of the sample and the pump. Stainless steel canisters may also be used as containers. Samples are analyzed in the field using direct-reading instruments and/or sent to a qualified laboratory for analysis.

SKC Sampling Equipment for EPA SOP 2042

SKC Vac-U-Chamber
for Negative Pressure Soil Gas Sampling

Canisters

Soil Gas Sampling — ASTM D5314-92 (2006)
ASTM D5314-92 Standard Guide for Soil Gas Monitoring in the Vadose Zone recommends collection by a whole air/sorbent method or a bulk soil/water sample for sampling headspace. Per the standard, the whole air/sorbent method is preferable because headspace sampling has significant disadvantages.

Sampling in the Overlying Structure

Vapor Intrusion Monitoring
Indoor air sampling in vapor intrusion studies has been performed typically with 6-liter stainless steel canisters to collect ppb-level VOCs. U.S. EPA validated sampling and analytical methods TO-14A and TO-15 specify stainless steel canisters. However, passive samplers are emerging as a cost-effective alternative to canisters. A side-by-side study shows SKC Ultra Passive Samplers to have good correlation with canisters. Ultra Passive Samplers are smaller, less expensive to ship, and their lower cost allows more samples to be collected. Ultra samples are thermally desorbed for sub-ppb level detection of many VOCs.

Stainless Steel Canisters: The Traditional Approach

Ultra Passive Samplers: The New Approach

Canister vacuum pulls the air sample without use of batteries or AC power
Flow restrictors maintain flow stability over the desired time period from < 1 minute to 12 hours

Collect samples for low ppb to ppt-level measurements
Easy, cost-effective alternative to canisters
Side-by-side study with canisters shows good correlation

SKC Ultra I Passive Samplers		SKC Ultra II Passive Samplers

Internal funnel for direct transfer to thermal desorption tube SKC Ultra I Passive Samplers contain thermally purged sorbent that is ready for immediate use within 30 days for low ppb-level measurements.		Internal funnel and built in vial adapter for easy filling and emptying SKC Ultra II Passive Samplers are sold empty and are filled by the user with purged sorbent (supplied in vials) for ppt-level measurements. See SKC update to U.S. EPA Method TO-17 (PDF)

Current Initiatives in Vapor Intrusion

ASTM International
ASTM E2600-08 Standard Practice for Assessment of Vapor Intrusion into Structures on Property Involved in Real Estate Transactions is a new standard to be used to perform vapor intrusion assessments on properties involved in real estate transactions. ASTM E2600-08 can also be used as a voluntary supplement to Standard Practice E 1527 Phase 1 Environmental Assessment. This standard complements existing state and federal vapor intrusion policy and guidance.

AIHA Task Force
A February 2007 Synergist article reported that the AIHA® Environmental Issues Committee has begun a vapor intrusion project to monitor this focus area for industrial hygienists.

Laboratories
Laboratories for Analysis of Ultra Passive Samplers

Related Links
U.S. EPA OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance, EPA530-D-02-004, Nov. 2002 )

U.S. EPA Fact Sheet: Evaluating the Vapor Intrusion into Indoor Air, EPA530-F-02-052, Nov. 2002

New York State Department of Health - Guidance for Evaluating Soil Vapor Intrusion in the State of New York, Oct. 2006