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The Wisconsin Department of Natural Resources (WDNR), the Wisconsin Department ofCommerce, and the Wood County Public Health Department asked the Wisconsin Department ofHealth and Family Services (DHFS) to assess the potential for vapor intrusion of petroleum fuelswithin a railroad corridor into the basement of a private residence and to determine if this is apathway of concern. Based on groundwater monitoring and soil sampling conducted onCanadian National property and an adjacent private residence in Marshfield, Wisconsin, thepotential for vapor intrusion of volatile organic compounds (VOCs) cannot be ruled out. Therefore, volatile organic compounds (VOCs) on this site are an indeterminate public health hazard. The remediation of this property is currently being planned. The vapor intrusionpathway should be formally investigated and addressed as part of the scope of work at this site.


Petroleum from a former petroleum storage area within a railroad industrial corridorcontaminates the soil of an adjacent residential property in Marshfield, Wisconsin. The site isundergoing remediation as part of a road construction project. Percent levels ("free product") ofpetroleum-related compounds, including benzene, xylenes, 1,2,4-trimethylbenzene,ethylbenzene, and 1,3,5-trimethylbenzene have been detected in soil 75 feet from the residence,with somewhat lower concentrations detected at other locations 10-100 feet from the building(Table 1; Envirogen 2002). Of these, benzene is addressed as the contaminant of greatestconcern for affecting indoor air because of its high volatility and status as an EnvironmentalProtection Agency (EPA) Class A carcinogen. The risk of chronic exposure of benzene topeople living in an adjacent residence was investigated, at the request of WDNR, the Wisconsin Department of Commerce, and the Wood County Health Department.

Table 1.

Concentration of benzene in soil and groundwater near the former Mobile Oil lease site, Marshfield, Wisconsin1
Location1 Concentration in soil
Concentration in groundwater
Distance to house
(feet below surface)
SB-8356Not avail.502-4
SB-9565Not avail.502-4
MW-2Not avail.Free product7510

1Sample locations and results reported by Envirogen (2002).


Site visit. The residence was visited on February 27, 2003, by representatives of the WDNR,Wood County Public Health, and DHFS. Prior to the home visit, fuel odors were expected at theresidence based on the close proximity of fuel-contaminated soil and groundwater, the relativelyshallow local water table, and the high porosity of the century-old stone-and-mortar foundationat the residence. At the time of the February 27 visit, petroleum odors were not detectedindoors, nor were there anecdotal reports of odors from the residents.

Evidence of occasional groundwater infiltration into the basement was noted. Water infiltrationfrom a source contaminated with VOCs is a condition that could cause vapor intrusion. Lightercomponents of petroleum compounds such as benzene might be expected to intrude intobuildings before the heavier components. It cannot be determined solely on the lack of petroleumodors in the residence whether there is an ongoing exposure to fuel contaminants in soils outsidethe house. Ultimately, eliminating the potential for vapor intrusion is dependent uponeliminating or reducing the source of soil vapor contaminants. Exposure to petroleum viadrinking water is not a concern at this property because the residence is served by municipalwater supplies unaffected by this contaminant source.

Interpretation of Environmental Investigation. Contamination in soils from the 0-3 foot depth,and at distances from 8-100 feet from the house, exceeds Wisconsin Administrative Code Ch.NR 720 and 746 standards (below screening values) for several fuel-related compounds (seeEnvirogen 2002, table 1). However, these concentrations are not a public health threat for eitherincidental ingestion, direct contact with contaminated soils, or from transfer of contaminantsfrom surface soils to air. This conclusion is based on comparison to health-based values from thefederal Agency for Toxic Substances and Disease Registry (ATSDR soil comparison values) andEPA (Region III risk-based concentrations).

In contrast, the potential for a health threat from organic vapor migration from soil orgroundwater to building foundations cannot be excluded based on the Envirogen (2002) report.EPA (2002) has published model-based guidance and screening values for evaluating VOCmigration and vapor entry into buildings. A strict application of these screening values to thebenzene measured at this site (Appended) quantitatively predicts a strong potential for vaporentry into buildings at this site. However, EPA acknowledges that at petroleum-contaminatedlocations, site-specific features dominate, making modeling less predictive. DHFS guidance(2003) agrees with this position. Site-specific features would include microbial degradation,preferential pathways and other subsurface features, and the response of the source to high-waterevents. The lack of odors within the basement suggests that fuel contaminants are notcontinually migrating into the building. However, the presence of this contaminant source insoil and groundwater very near the home is cause for concern for future exposures. Underchanging environmental conditions such as heavy rainfall, high water table, or excavation workon the property, contaminants could easily move the short distance to the home. Consequently,the vapor intrusion pathway should be formally investigated and addressed as part of the scopeof work at this site.

Toxicology of benzene. The petroleum fuels found in soil at this site contain a mixture ofchemicals, each having individual properties of toxicity, metabolic fate, and environmental fate. Of this mixture, benzene is the chemical with perhaps the most characterized toxicity to humans.It is also among the most volatile chemicals in the fuel mixture. Consequently, benzene receives focal attention in the public health evaluation of petroleum-contaminated property.

EPA classifies benzene a class A carcinogen, which means that benzene is known to causecancer in humans. Much evidence supports benzene as a leukemogen in humans, where reactiveintermediates formed during the metabolism of benzene preferentially affect the bone marrow.Over the long-term in a residential exposure situation, benzene levels at the odor threshold,roughly 5 parts per million (ppm), are an increased cancer risk. This exposure is more than onethousand times greater than health officials would permit in drinking water. Although benzene israrely present above the odor threshold, its presence at harmful concentrations may still besuspected when the odors from other petroleum chemicals are noticed. When faint butperceptible gasoline odors are noticed, benzene levels can still be ten-to-one hundred-fold higherthan levels considered safe and appropriate for residential indoor air. Other components ofpetroleum, such as toluene, xylenes, and naphthalene, can be smelled at very low concentrationsthat signal the presence of benzene. Long-term exposures to these and related VOCs pose a riskof non-cancer health effects including damage to the liver, kidneys, and nervous system. Thesenon-cancer health effects can be addressed by addressing unnecessary cancer risks (DHFS,2003). Although the odor of petroleum indoors is usually enough to conclude there is a problemwithout analyzing the air, the absence of odor may not rule out potential health effects when there is a known source of volatile compounds in soil or groundwater near a building.


The inhalation of petroleum-related chemicals, where present in indoor air, is a risk to childhealth. Although there are children living in the house, there is no known current exposure of health concern to petroleum from contaminated soils and groundwater.


  • Benzene concentrations in soil and groundwater indicate that vapor migration into homes is a possible pathway of concern. The possible vapor intrusion poses an indeterminate public health hazard to buildings adjacent to the contaminant source.

  • Although an inspection of the residence in question did not reveal the presence of physical evidence that vapors were entering the home, no indoor air data were available to eliminate the possibility.

  • No conclusions can be drawn at this time whether future high water events will carry volatile contaminants into the house.

  • There is no public health hazard from direct contact with surface soils at this site, based on comparison with ATSDR and EPA values.


  • Vapor migration into the residence should be investigated and characterized as part of the scope of work for this site.

  • If an environmental investigation concludes that vapor intrusion is occurring or could occur at levels of health concern, actions should be taken to prevent or mitigate possible exposures.


  • The Responsible Party has contracted, under the authority of the WDNR and the Wisconsin Department of Commerce, to remove part of the petroleum-contaminated soil.

  • The Environmental Consultant representing the Responsible Party has agreed to investigate the vapor migration pathway from the petroleum source to the residence.

  • When the results of the investigation are available, the Wood County Health Officer will discuss them with residents.


Robert Thiboldeaux, Ph.D.
Health Hazard Evaluation Unit
Bureau of Environmental Health
Division of Public Health
Wisconsin Department of Health and Family Services


American Industrial Hygiene Association. Odor Thresholds of Chemicals with EstablishedOccupational Health Standards. Akron, OH: AIHA. 1989.

Envirogen, Inc. Site Investigation Report, Former Mobile Oil Lease Site, Marshfield, WI. PIN5662443. September 2002.

U.S. EPA. 2002. Draft guidance for evaluating the vapor intrusion to indoor air pathway fromgroundwater and soils.

Wisconsin Department of Health and Family Services. 2003. Chemical vapor intrusion andindoor air: Guidance for environmental consultants and contractors.


Environmental fate of benzene. Using guidance developed by EPA (2002), a screening value (based on predictions of the Johnson and Ettinger model) of 14 micrograms/liter (µg/L) for benzene in groundwater is estimated for this site. This is based on a vapor attenuation factor of 1x10-4 (EPA, fig. 3b, loam) and a cancer risk factor of 1x10-6. The corresponding generic screening value for groundwater, where soil information is absent, is 5.0 µg/L. In addition, the EPA recommends that these screening values not be used when actual groundwater concentrations exceed 20-times the screening value (in this case, 280 µg/L). At concentrations this high, the predictive value of the Johnson and Ettinger model (U.S. EPA, 2000) diminishes, and must be supplemented with target-specific information. According to the Envirogen report, benzene exceeds 280 µg/L at several sample locations within 100 feet of the residence.


This public health consultation for the former Mobile Oil facility was prepared by the Wisconsin Department of Health and Family Services under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the Public Health Consultation was begun.

Gail Godfrey
Technical Project Officer, S.P.S., SAAB, DHAC

The Division of Health Assessment and Consultation, ATSDR, has reviewed this Public Health Consultation and concurs with the findings.

Roberta Erlwein
Chief, State Program Section, DHAC, ATSDR

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
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