HEALTH CONSULTATION
TRI-PAR OIL
CEDARBURG, OZAUKEE COUNTY, WISCONSIN
Representatives of the Tri-Par Oil Company and the Immanuel Lutheran Church in Cedarburg requested the assistance of the Wisconsin Department of Health and Family Services (DHFS) in reviewing the potential for indoor air impacts from chemical vapor intrusion at the church. On the basis of DHFS review of the available site information, currently there does not appear to be an indoor air impact at the church and it is unlikely that an indoor air impact has existed in the past. The site does not currently pose a public health hazard from vapor intrusion exposure at the church. Although the potential for future impact decreases as clean-up efforts continue to reduce the contamination, it is not possible to completely rule out that potential in the future. Therefore, the site poses an indeterminate public health hazard in the future. DHFS recommends some additional actions to minimize concerns related to this potential.
The Tri-Par Oil Company site is located at W61 N505 Washington Avenue, Cedarburg, Wisconsin, at the northwest corner of the intersection with Western Avenue. The business operated from the 1950s until 1998. Contamination was first found on the property in 1993. Following initial investigation of the degree and extent of the contamination, the business closed and began the clean-up process. The cleanup has included the removal of 1,300 tons of contaminated soil in the impacted area around former storage tanks and the removal of petroleum floating above the groundwater table. As much as 5 feet of petroleum was found on the water table in the source area on the site in 1999. Currently, that level has decreased to less than a foot. In addition to the petroleum contamination floating on the surface of the water table, some petroleum-related chemicals have dissolved into the groundwater and have moved with groundwater away from the site. (C. Warzecha. Personal communication with D. Bauer, Sigma Environmental Services, Inc., June 16, 2003.)
This area is served by a municipal water supply, and the wells for that system are located outside the area of impact from this site contamination. Bedrock in this area is less than 10 feet from the surface. This bedrock is known to be fractured, and groundwater in this area moves through the fractures. At this time, the owner of the Tri-Par Oil Company site is planning to continue investigating and cleaning up the property for redevelopment. Redevelopment is expected to begin in the summer of 2004, and accommodations are being made in the development plans to ensure that clean-up activities will not be affected. The redeveloped property will be used for small businesses and residences, with slab-on-grade construction. (C. Warzecha. Personal communication with D. Bauer, Sigma Environmental Services, Inc., June 16, 2003.)
Many of the chemicals in petroleum products (such as gasoline and diesel fuel) evaporate readily from liquids into the air. For this reason there is potential for chemicals to move from a site in groundwater or soil vapor and enter the indoor air of nearby buildings. In this case, the Immanuel Lutheran Church building is across Washington Avenue to the east. Contaminated groundwater has been found on church property, though it is not known if it extends to or under the building itself. The church and Tri-Par would like to ensure that site contamination does not impact the indoor air of the church. The church basement is used for childcare services and other functions. There have been no reports of petroleum odors in the church basement in the past. Additionally, the basements of a residence and a business adjacent to the Tri-Par property have been inspected for air impacts in the past. The occupants of these properties have not reported petroleum odors in the past. (C. Warzecha. Personal communication with M Larson, Immanuel Lutheran Church; June 23, 2003. C. Warzecha. Personal communication with D. Bauer, Sigma Environmental Services, Inc.; June 16, 2003.)
The concept of vapor intrusion involves the movement of volatile contaminants (those that evaporate from a liquid to the air) from contaminated soil or groundwater to the indoor air of nearby buildings. This can happen when one or more of the following things take place: contaminants evaporate at the source and move to buildings with soil gas; contaminants which are dissolved in groundwater move near buildings where they then evaporate into soil vapor and then move into buildings in the vapor; contaminants which are dissolved in groundwater move directly into buildings when contaminated groundwater comes into contact with the foundation; and the contaminant source itself moves independently or with groundwater into proximity to buildings.
Petroleum-related contaminants break down relatively well when low-to-moderate concentrations are found in soil, groundwater, or soil vapor. The degradation properties of petroleum contaminants severely limit their ability to migrate significant distances with soil gas. For this reason, intrusion of petroleum vapors into indoor air is unlikely in the absence of the two conditions listed last in the previous paragraph [1]
Results from a monitoring well located in the driveway north of the church building show that dissolved contamination is present in groundwater close to the building. Benzene in this well is at 240 parts per billion (ppb). For comparison purposes, the health-based drinking water standard for benzene is 5.0 ppb. Groundwater at this location is about 14 feet below the ground surface. The fractured bedrock is 7 feet below ground at the site and about 9 feet below ground near the church. The orientation and random distribution of fractures within the bedrock can make it difficult to investigate and predict the movement of both groundwater and petroleum contamination. The water table and the measured levels of petroleum floating above it fluctuate in a way that indicates some product is still held in the rock and soil above the water table. As rainwater infiltrates and the water table cycles from high to low in the future, more of the remaining contamination will be flushed down to the water table. [2]
Although no evidence of vapor intrusion has been found to date, because of the fractured bedrock, it is not possible to predict how the remaining contamination will move with unusual or extreme weather events, major work in the subsurface, or changes in surface features affecting runoff. Additional investigation may give us more confidence that contaminated groundwater does not extend below the church at this time. However, it is likely that the free product at and near the site must be gone before we can be assured that vapor intrusion is not a viable exposure pathway in the future.
The lack of any past observations of petroleum odors in the indoor air of the church basement is a strong indication that a vapor intrusion-related health concern is not present. Benzene is often the chemical of greatest health interest from petroleum contamination. The odor threshold for benzene alone does not provide adequate protection against exposures of public health concern. However, benzene from petroleum contamination is generally present with a complex mixture of other petroleum compounds with very low odor thresholds (as is the case with contamination from the Tri-Par site). As a result, the odor thresholds of these other petroleum volatile organic compounds serve as a surrogate odor that indicates potential unsafe benzene exposures for gasoline and diesel fuel spills. [1]
There are a number of reasons why air sampling for petroleum cases is not generally recommended. Soil vapor migration into a home varies from day to day and throughout the day. This is affected by wind speed and direction, temperature, barometric pressure, humidity, opening and closing doors and windows, and seasonal variation (such as frost and precipitation). An air sample will only tell the air quality at the time that it is collected. However, people are in the church much of the time, and any odors would be detected by the people who are in the building. There are hundreds of different chemicals found in gasoline and the various fuel oils. Many of these contribute to odor but are not specifically identified by most analytical methods.
A variety of petroleum distillates, including benzene, can be found in indoor air from a number of sources within and outside a typical home. Without a characteristic petroleum odor (at least occasionally), it is difficult to link the presence of low-level petroleum chemicals to a vapor intrusion source. In addition, outdoor ambient air commonly contains detectable concentrations of these same chemicals (particularly near gasoline stations). These potential background concentrations generally fall below the odor thresholds for these chemicals.
The proposed redevelopment of the site with a slab-on-grade constructed building presents a low but still possible vapor intrusion risk for the future. However, because vapor intrusion can still occur in a slab-on-grade building and some free product remains on the site, the potential for vapor intrusion remains. Construction practices and techniques now allow developers to minimize the potential for vapor intrusion. These techniques have been developed to prevent radon gas from entering buildings. Scientists have found that radon gas, which occurs naturally in soil in some areas, can move into buildings in much the same way chemical vapors do. Information on some of these construction practices, including a document called "Building Radon Out," can be found on the U.S. Environmental Protection Agency's Web site on radon[3].
Because extreme weather events are the most likely periods that could create a vapor intrusion potential at the church, church officials should make it a point to check the basement for odors after heavy rainfalls or periods of snow melt. Odors may also be most pronounced in small, closed areas in the basement, such as closets, so these are areas to check. If characteristic petroleum odors are noticed, contact John Feeney at the Wisconsin Department of Natural Resources (920-892-8756). For severe odors after hours or on weekends, you may call the department's spills hotline (1-800-943-0003).
The two situations in which we are concerned about exposure to petroleum vapors include short-term exposures to levels much higher than the odor threshold, and long-term daily exposures to lower levels of chemicals in indoor air. Short-term exposures to high concentrations can cause common irritation symptoms, including eye and respiratory irritation, nausea, neurological effects, and headaches. These symptoms are not permanent effects and should subside shortly after the individual moves to an area with fresh air. Daily exposures to high concentrations of benzene for many years were found to pose an increased risk of developing some types of cancer in workers. Therefore, to be prudent, we want to prevent long-term exposures to even very low concentrations of benzene. [4]
Because the church basement is used for childcare services and other activities involving children, there is a higher level of concern about indoor air quality in the basement. To be able to provide assurances to the church members that impacts are not present, it may be necessary to conduct additional testing. A sample of the soil vapor beneath the slab and a sample of indoor air could be a potential substitute for additional soil gas or groundwater monitoring for this pathway. Results of analysis of these samples could also serve to provide additional assurances to church members.
Chuck Warzecha
Health Hazard Evaluation Program
Bureau of Environmental Health
Wisconsin Department of Health and Family Services
This public health consultation on the Former Tri-Par Oil property 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), an agency in the U.S. Department of Health and Human Services. It is in accordance with approved methodology and procedures existing at the time the public health consultation was begun.
Gail Godfrey
Technical Project Officer, SPS, SSAB, DHAC
The Division of Health Assessment and Consultation, ATSDR, has reviewed this public health consultation and concurs with the findings.
Roberta Erlwein
Chief, SPS, SSAB, DHAC, ATSDR
