Importance of Understanding Potential Background Sources in VI EvaluationsGina PlantzRich Rago

Collecting Field Data- you may only get one shot

• Take opportunity to collect as much information as possible

• Document procedures and keep records

• Include shut-in tests for soil gas sampling

• Collect pressure differential data and review with concurrent data for barometric pressure

• Make careful observations of building slabs, especially when locating sub-slab samples

• Do thorough building surveys

• Take lots of photographs

Data Reduction and Multiple Lines of Evidence (MLE)

• Simple comparison of data to screening levels may result in complicated matters and incorrect decision-making

• Consider the Conceptual Site Model for VI in planning investigations

• Consider MLEs• Contaminant ratios

• Modeled concentrations

• Building pressure differentials and meteorological data

• Contaminant trends

• Background sources identified

EPA Region 9 Guidelines, Item #1(30 June 2014 Clarification)

“[T]he health protective risk range for both accelerated response actions and long-term exposures become truncated to: • 0.5 – 2 µg/m3 for residential exposures and • 3 – 8 µg/m3 for 8-hour/day commercial/industrial exposures.”

Implementation of Interim Measures to Mitigate TCE Short-term Exposure

• Increasing building pressurization and/or ventilation • Sealing potential conduits where vapors may be entering the

building• Treating indoor air (carbon filtration, air purifiers)• Installing and operating engineered exposure controls (sub-

slab/crawlspace, depressurization systems)• Temporarily relocating occupants

Indoor Air Background

• “One of the most difficult facets of investigating VI is the interpretation of the available information and the subsequent conclusions reached on the completeness of the pathway. This task is complicated by the impact of background contaminant sources on the overall indoor air quality.”

• “…..the most critical point is in the assessment of indoor air data as it relates to background contamination.” - NJDEP 2012

Relevance of Indoor Air Background• Potential overlap of site contaminants from subsurface sources and personal,

indoor, and ambient sources

• Requires careful consideration in VI assessments

• VOCs are very common to personal, indoor air (Gordon, et al, 1999; Clayton, et al, 1999; Kinney, et al, 2002; Sexton, et al, 2004; Bradley, et al, 2004, RIOPA, 2005, Rago, et al, 2007; EPRI, 2007; MT DEQ, 2012), and ambient sources (EPA, 1988; EPA, 2000)

• USEPA has developed a database and technical paper on national indoor air background levels.

• For more information:• “The Inside Story: A Guide to Indoor Air Quality”

http://www.epa.gov/iaq/pubs/insidest.html

• Background paper, Dawson et al, June 2011

• Summaries of recent studies

Relevance of Indoor Air Background (continued)

• Common VOCs identified in new (finished and operational, but unoccupied) pre-fabricated and site-built houses (Hodgson, et al, 2000)

• Higher background levels of VOCs have been observed in homes with attached garages (Kurtz, 2004; Graham, et al, 2004; McCafferty, 2006)

• VOCs are also commonly encountered in commercial buildings (Daisey, et al, 1994; Girman, et al, 1999) and schools (Adgate, et al, 2004)

Limitations of Existing Literature Data for Non-residential Buildings

• Older data sets

• Inconsistent sampling and analytical methods

• Higher detection limits

• Varying objectives, methodologies, geographies, statistics

• Consumer products and ambient air quality have changed over time (e.g., 1,2-dichloroethane)

• No data on petroleum “hydrocarbon ranges”

Importance of New Study• Information on indoor air background is critical in VI

investigations

• Little recent literature data exists on office buildings and schools

• Practitioners and Regulators may default to residential criteria which may or may not be appropriate

• Compare TO-15 and TO-17 data for canisters and passive samplers

Summary of Selected VOCs (µg/m3)

Preliminary data; N=60

CompoundFrequency of

DetectionMinimum (ug/m3)

Maximum (ug/m3)

1,2-Dichloroethane 70% 0.081 0.498Trichloroethene 15% 0.107 115

Tetrachloroethene 75% 0.136 9.02Benzene 90% 0.319 24.8Toluene 98% 1.01 242

Ethylbenzene 98% 0.109 45.6p/m-Xylene 98% 0.243 157

o-Xylene 98% 0.104 51.3C5-C8 Aliphatics 95% 2 3000

C9-C12 Aliphatics 85% 14 990C9-C10 Aromatics 12% 10 120

Trichloroethylene

N=100Preliminary data; N=37

Some Observations of Preliminary Results

• Tetrachloroethylene detected in 75% of office/school samples• Concentrations ranging from 0.136 ug/m3 to 9.02 ug/m3

• Benzene detected in 90% of office/school samples• Concentrations ranging from 0.319 ug/m3 to 24.8 ug/m3

• Trichloroethylene detected in 9 office samples• Ranging to 115 ug/m3

• 1,2-dichloroethane detected in 70% of office samples and 60% of school samples• Concentrations ranging from 0.081 ug/m3 to 0.498 ug/m3

Summary

• Indoor air background is building-specific and commercial product formulations can and do change

• Carefully review background studies for focus, relationships, and ranges

• Understanding background data can be of strategic importance in vapor intrusion data review, focusing investigations, mitigation decision making, and risk communication