Screening Levels for Vapor
Intrusion Contaminants of Concern
Reilly Tar and Chemical Co. Superfund Site
St. Louis Park, Minnesota
February 2011
U.S. Environmental Protection Agency Region 5 is conducting a vapor intrusion investigation at the Reilly site that includes collecting
samples. These sample results, along with other factors and information, are a critical part of assessing health risks from potential
vapor intrusion in the area. In the chart below are screening levels EPA will use to help analyze the sample data.
EPA determines probability of a non-cancer detrimental health effect to occur by calculating a hazard index (HI). The HI is a ratio of a
single substance exposure level during a specified time to a reference dose of the same substance derived from a similar exposure
period. It is recommended the HI of an exposure to a chemical of concern be below or equal to 1. That is the level at which no
adverse human health effects are expected to occur. For cancer risk, EPA recommends a screening level that would equate to a 1 in
1 million (IxlO"6) or greater risk of developing cancer from lifetime exposure to a contaminant. A 1 in 1 million chance means that
for every 1 million people exposed, one extra cancer may occur beyond what would be expected from all other causes. A 1 in ten
thousand risk is the upper limit of US EPA's acceptable range for lifetime cancer risk. Minnesota Pollution Control Agency (MPCA)
has recommended Acute Vapor Intrusion Action Levels at which an immediate action would be recommended to protect residents.
The chart below defines Reilly Tar site-specific screening levels for indoor air and sub-slab soil gas to protect residents from non-
cancer risks equating to a hazard index of 1, and a lifetime cancer risk of 1 in 1 million. The chart also details the MPCA Acute Vapor
Intrusion Screening Level. A screening level based upon a 1 in 10,000 lifetime cancer risk was calculated for the few chemicals of
concern that do not have an Acute Vapor Intrusion Screening Level. These screening levels are denoted by an asterisk.
Chemical of Concern
benzo(b)fluoranthene
benzo(j)fluoranthene
naphthalene
tetrachloroethene
trichloroethene
cis-l,2-dichloroethene
trans-l,2-dichloroethene
vinyl chloride
benzene
ethylbenzene
toluene
xylenes
Residential
Air Interior
ug/m3
2.2E-02
2.2E-02
7.2E-02
4.1E-01
1.2E+00
6.3E+01
6.3E+01
5.5E-01
3.1E-01
9.7E-01
5.2E+03
l.OE+02
Residential
Air Subslab
ug/m3
2.2E-01
2.2E-01
7.2E-01
4.1E+00
1.2E+01
6.3E+02
6.3E+02
5.5E+00
3.1E+00
9.7E+00
5.2E+04
l.OE+03
MPCA Indoor Air
Action Level ug/m3
2.2E+00*
2.2E+00*
7.2E+00*
2.0E+04
2.0E+03
8.3E+02
8.3E+02
1.8E+05
l.OE+03
l.OE+04
3.7E+04
4.3E+04
Sample results from residences near the Reilly site will be compared with screening levels and communicated to property owners
and residents. If results are above screening levels, further testing or mitigation may be necessary, and this will be addressed on a
case-by-case basis. If results are below screening levels, no further action may be necessary.
For more information visit www.epa.gov/oswer/vaporintrusion/ or www.epa.gov/reg3hwmd/risk/human/rb-
concentration table/index.htm or http://www.epa.gov/region5/sites/reillytarmn/index.html. You can also contact EPA Remedial
Project Manager Michelle Kerrat 800-621-8431, Ext. 68961, weekdays 8:30 a.m.-4:30 p.m. or kerr.michelle@epa.gov.
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