HEALTH CONSULTATION
RIPON MANUFACTURED GAS PLANT
RIPON, FOND du LAC COUNTY, WISCONSIN
The Wisconsin Department of Natural Resources asked the Wisconsin Bureau of Environmental Health, Department of Health and Family Services (BEH), to review preliminary environmental assessment data collected at a former manufactured gas plant (MGP) site (now a public park) in Ripon Wisconsin. BEH was to evaluate any health hazard associated with contamination in surface soil and identify other areas where health hazards might exist. BEH determined that elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) are present in surface soils. Still, BEH concluded that even while site remediation is pending, the high-quality groundcover within the site will prevent any immediate health hazard—the groundcover provides protection from direct contact with or exposure to the soil PAHs. But the total health effects of petroleum-like contaminants in groundwater and soil more than 3 feet below ground surface await a complete environmental assessment. Similarly, more information is needed to determine if sediments in adjacent Gothic Mill Pond are contaminated, and whether such contamination is a public health hazard.
BACKGROUND AND STATEMENT OF ISSUES
Selfridge Park, in the city of Ripon, Fond du Lac County, Wisconsin, is the site of a former manufactured gas plant (MGP) which operated from 1873 to about 1929. Prior to the commercial availability of natural gas, many towns and cities nationwide operated MGPs for the production of fuel gas from oven-heated coal or carburetted oil. Wastes from these operations were often deposited on or near the gas plant site. In recent years the resulting soil and groundwater pollution at MGPs has become a focus of environmental remediation. The contaminants expected around the former MGP in Ripon relate to its use of naphtha as feedstock. Naphtha is a clear, low-viscosity, low-density petroleum mixture. Preliminary investigations of the site (1,2,3) revealed some surface layer (0-0.5 feet) soil samples that exceeded—albeit by a small amount—the U.S. EPA standards for polycyclic aromatic hydrocarbons (PAHs). In addition, concentrated amounts of an oily, petroleum-like material were detected several feet below the soil surface. The site is currently undergoing an environmental investigation to determine the degree and extent of soil, sediment, and groundwater contamination remaining from the gas plant operation (4). At the request of the Wisconsin Department of Natural Resources (WDNR), Alliant-Wisconsin Power & Light (Alliant-WPL) is conducting that investigation.
Selfridge Park is an open, roughly 2-acre grass-covered peninsula, bounded on three sides by Gothic Mill Pond—a stream reservoir. The pond is used for fishing and, possibly, occasional swimming, although the park does not currently have a defined swimming area. The west side of the park is bounded by a residential area consisting mostly of houses built in the 1940s. In September 2002, over concerns that its environmental contamination might threaten the public, Ripon city officials closed Selfridge Park. This has led to public interest in the current safety, as well as the future, of Selfridge Park. Since spring 2002 the Wisconsin Bureau of Environmental Health (BEH), in cooperation with the WDNR, has reviewed the environmental assessment data Alliant-WPL has collected to date. It should be noted also that contaminated groundwater is not a focus of this health consultation—area residents are served by municipal water supplies, which are not affected by the site. The sources of potential exposure to contaminants in the park are through direct contact with affected soil, particularly under play structures, and with sediments of Gothic Mill Pond surrounding Selfridge Park.
PROPERTIES OF POLYCYCLIC AROMATIC HYDROCARBONS
Polycyclic aromatic hydrocarbons (PAHs), are a large, structurally diverse group of organic compounds formed during incomplete combustion, which makes PAHs a primary constituent of soot. The diverse structures, health effects, and wide environmental distribution of PAHs is a complex topic that has been reviewed in detail elsewhere (5,6). Humans are able to metabolize small amounts of PAHs, although with excessive chronic exposure some PAH structures are carcinogenic. Carcinogenesis can occur when certain PAH structures are metabolized in the body to harmful diol epoxides. Those PAHs with a well-characterized potential for metabolizing into reactive structures are benzo(a)pyrene, dibenz(a,h)anthracene, benz(a)anthracene, benzo(b)fluoranthene, and benzo(k)fluoranthene. The major release mechanisms of PAHs into the environment are wood burning and vehicle fuel combustion. Industrial sources are a third major category.
PAHs, dispersed in air as soot or sorbed to fine soil particles, can be deposited on surfaces people encounter while playing or eating outdoors. And incidental ingestion of soil would be the way people would be exposed to PAHs while playing or eating. In that regard, it is important for anyone, including casual visitors to a PAH site, to know that most exposure to PAHs from the incidental ingestion of soil can be avoided by normal hand washing prior to eating. Also, PAHs in soil are not water soluble; they tend to bind tightly to soil particles where they become relatively immobile. They do not move appreciably in the soil by precipitation or groundwater—they are primarily dispersed as windblown soil. When they are dissolved by high concentrations of organic solvents in soil, PAH movement through soil and groundwater becomes more important.
During remediation of any PAH-contaminated site, site management—including dust suppression and containment, and air monitoring—must be sufficient to detect unsafe PAH dispersal and deposition. Should air monitoring indicate that PAHs have not been sufficiently contained, additional cleanup of nearby sensitive areas (e.g. playgrounds) might be needed.
To date, BEH has reviewed preliminary surface soils analyses from several samples taken several feet below surface, as well as some very limited information from the sediments of Gothic Pond (1,2,3). The investigation by Alliant-WPL is still in progress (4). From the preliminary information, BEH has concluded that the materials remaining in the soil from the MGP are not a health risk to anyone using the grass-covered areas and play structures in the park. The sample data reveal that the PAH contaminants present in the surface soils are somewhat elevated over U.S. EPA risk-based concentration levels for residential soils (table 1). These soil PAHs were detected in highest concentration (e.g. up to 16 mg benzo(a)pyrene/kg soil) at the location of former MGP structures, notably the refuse tank, tar tank, and gas holder. Nevertheless, the thick sod and other ground cover in the park, if properly maintained, will prevent direct contact with the surface soil.
BEH visited Selfridge Park during the placement of seven temporary wells in saturated soils (2,3). Overall, these test wells contained total groundwater concentrations of volatile organic compounds (VOCs) of 3-43 milligrams per liter (mg/L) and total PAHs ranging from 5-1,564 mg/L. The specific contaminants will be reviewed when complete sediment data are available. Organic contaminants present in deeper (>3 feet below surface) soils in Selfridge Park present a potential health hazard through migration to nearby structures and pond sediments. At this time, however, no specific remedy has been proposed for the removal of these organic contaminants. But to prevent health hazards from potentially released air contaminants, the removal of organic contaminants present in deeper Selfridge Park soils (>3 feet below surface) will require carefully applied contaminant removal and air mitigation measures.
Another area of concern in the park is contact with sediments on the north side of Gothic Pond, such as might occur during wading. More information is needed to form conclusions regarding the health risk from contact with Gothic Mill Pond sediments. At this time BEH does not have information to form any conclusion about contact with pond sediments. Because, however, there is a possibility of a health concern from contact with these sediments, a conservative recommendation would be to prevent park users from wading in the area near the former MGP. At similar sites elsewhere in Wisconsin, posting the shoreline with warning signs has served this purpose. This recommendation, although conservative from a health perspective, would still permit normal use of most of the park.
Selfridge Park is a playground for children, but has surface soils contaminated with PAHs. Still, these soils do not represent a current public health risk for children. The park has a well-maintained ground cover consisting primarily of sod, as well as wood chips around play structures. This ground cover prevents direct contact with the surface soil. It also prevents a health hazard from any PAHs detected at concentrations exceeding U.S. EPA risk-based concentration levels for direct contact (Table 1).
Robert Thiboldeaux, Ph.D.
Toxicologist
Health Hazard Evaluation Unit
Bureau of Environmental Health
Division of Public Health
Wisconsin Department of Health and Family Services.
Table 1. Hydrocarbons detected in surface soils within Selfridge Park, Ripon WI
April 2002 survey.*
|
Substance |
Mean Concentration† (mg/kg±Std.Error, n=7) |
Maximum conc. detected (mg/kg) |
Risk-based concentration‡ (mg/kg) |
| benzo(k)fluoranthene | 1.6±0.8 | 5.0 | 8.8 |
| Benzo(a)anthracene | 1.3±0.5 | 3.5 | 0.88 |
| Indeno(1,2,3-cd)pyrene | 4.5±2.4 | 16 | 0.88 |
| benzo(b)fluoranthene | 2.4±1.1 | 6.8 | 0.88 |
| benzo(a)pyrene | 13.5±9.5 | 16 | 0.088 |
*Mongomery Watson Harza, Inc. April 2002. Initial Phase II Site Investigation Report, Ripon Manufactured Gas Plant Site.
†Depth of soil sample: 0-0.5 feet.
‡U.S. EPA Region III Risk-based concentration, carcinogenic effects, residential soil, ingestion. Note that these values are similar to those suggested by the federal Agency for Toxic Substances and Disease Registry, and by the Wisconsin Administrative Code ch. NR 720. Exposure to soil contaminants below these levels are is not likely to result in greater than a 1-in-1 million increased cancer risk.
mg/kg = milligrams per kilogram
This public health consultation for the Ripon Manufactured Gas Plant Site in Ripon, Wisconsin, 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 D. 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.
Sven E. Rodenbeck
for Richard Gillig
Chief, State Programs Section, DHAC, ATSDR
