MASON CITY COAL GASIFICATION PLANT
MASON CITY, CERRO GORDO COUNTY, IOWA
The Mason City Coal Gas site is a former manufactured gas plant (FMGP) located near the center of Mason City, Iowa. The plant was originally built in the northwestern area of the site between 1897 and 1901. Town gas was generated for use in the Mason City area. Following the availability of natural gas, the gas plant was decommissioned in 1951, and was subsequently demolished in 1952. The Interstate Power Company (IPW) and the City of Mason City presently own the site. The site is essentially vacant, except for the existing IPW electrical substation, storage building, and the waste pile covered with a synthetic cap. The waste pile consists of tars, soils, sludges, and remnants of buried structures that were excavated in 1984 and stockpiled near the southeast corner of the site.
Contaminants of concern identified from previous investigations at the site include polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs)--primarily benzene, toluene, ethylbenzene, and xylenes (which combined are referred to as BTEX)--phenols, cyanide, and various heavy metals that also occur naturally in soils.
No community concerns have been identified regarding the site.
The Agency for Toxic Substances and Disease Registry (ATSDR) and the Iowa Department of Public Health (IDPH) conclude, based on review of available data, that the Mason City Coal Gas site poses no apparent public health hazard. No completed exposure pathways to site contaminants leading to adverse health effects have been identified. Potential exposure pathways, however, exist under current site conditions. The shallow aquifer on-site and off-site is contaminated with PAHs, benzene, arsenic, and lead. If contaminants migrate to off-site domestic wells or if contaminated groundwater is used for domestic consumption, exposure to site-related contaminants would occur. The waste pile contains contaminated materials excavated from previous source areas. During remedial activities, exposure to those contaminants can be avoided if workers adhere to current occupational safety standards. Possible exposure to nearby community members can also be avoided or minimized if the community is provided with the information needed to do so.
The data and information developed in the Mason City Coal Gas site public health assessment have been evaluated by the ATSDR Health Activities Recommendation Panel (HARP) for follow-up health actions. HARP has determined that people in the community near the site should be informed about their potential for exposure to site contaminants. A community health education program designed to assist the community in understanding the potential for exposure, how to prevent or mitigate the effects of exposure, and how to assess adverse health occurrences in the community, is indicated. IDPH will provide workers and local residents that information. ATSDR/IDPH will reevaluate this site for additional follow-up public health actions if new data become available that indicate a need.
A. Site Description and History
The Mason City Coal Gas Site is located near the center of Mason City, Iowa. It is bounded on three sides by city streets: South Pennsylvania Avenue to the east, 5th Street Southeast (SE) to the south, and South Delaware Avenue to the west (Figure 1). The northern edge of the site is bounded by Willow Creek which flows easterly past the site and over a low dam at the downstream end of the site (Figures 1 & 2).
The site was occupied by a manufactured gas plant facility in the early 1900s. The original facility was built between 1897 and 1901. The gas plant generated town gas for lighting and heating purposes in the Mason City area. At that time, there were several private dwellings located along the southern edge of the site on the area that is now 5th Street SE. These residential structures were removed in 1909 when the gas plant was expanded. During that time, a large capacity gas holder was constructed near the east end of the site for commercial gas storage. This gas storage tank was subsequently cleaned and removed from the site.
Brice Gas and Electric Company operated the original gas plant. Between 1901 and 1906, the company was known as Peoples Gas and Electric Company. In 1932, the site was purchased by the Kansas City Power and Light Company who maintained the gas plant until 1951. Following the availability of natural gas, the gas plant was decommissioned in 1951 and was subsequently demolished in 1952. After the demolition of the gas plant, a storage building and substation were constructed at the site. The storage building and substation currently remain on-site.
IPW acquired the site in 1957 and remained the sole owner until 1982, when Mason City purchased a segment of the site parallel and adjacent to Willow Creek. Currently, the site is essentially vacant, except for the remaining IPW electrical substation and storage building. IPW of Dubuque, Iowa, and Mason City presently own the property.
Soil and groundwater contamination were initially discovered in 1984 during an on-site city sanitary sewer construction project. Contaminated soil and oily sludges were encountered during a trench excavation. Consequently, the Mason City engineer contacted the Iowa Department of Water, Air, and Waste Management (IDWAWM), now the Iowa Department of Natural Resources (IDNR), on June 22, 1984. Construction of the sanitary sewer was temporarily suspended until the contamination was assessed. The initial investigation identified coal tar-contaminated soils in the vicinity of the former purifying box, separating basin, purifying cistern, and raw gas holder. Tars, soils, sludges, and remnants of the buried structures were then excavated and stockpiled near the southeast corner of the site and covered with plastic sheeting. Final excavation and construction of the city sanitary sewer then proceeded across the site.
Several investigations have subsequently been performed to characterize and determine the extent of contamination. Potential sources of contaminants were the former gas plant building where releases of carburetor oil, tar, or condensate may have occurred, the oil storage tanks, separating and purifying basins, purifying box, and the tar storage tank (Figure 2). Actual disposal practices for waste products during the life of the plant are not known. Typically tar was recovered and sold for use as fuels by other industries, used as wood preservatives, or further refined into usable products. The remaining by-products were usually treated as no value and were then disposed on or off-site as fill material or general refuse. No information regarding the generation or disposal of these remaining by-products is available.
The U.S. Environmental Protection Agency (EPA) became the lead agency at some point during the initial discovery and removal activities. In June 1986, EPA issued IPW the first Consent Order. The order directed IPW to remove all oily sludges containing PAH concentrations above 100 parts per million (PPM).
Three previous investigations and other related site work were conducted using a phased approach during the initial Consent Order. The preliminary assessment phase was completed in May 1987, by Eugene A. Hickok and Associates (EAH), now part of James M. Montgomery, Consulting Engineers, Inc. (Montgomery). Nine soil borings and five shallow soil samples were collected from the site. Four monitoring wells were installed and water and sediment samples were collected from Willow Creek to determine if the site had impacted the creek.
The second phase of investigation was completed in April, 1988. It further defined the geologic character of the underlying bedrock, defined the extent of the vertical and horizontal contamination, and characterized the waste pile. A local water well inventory was also accomplished in February, 1989, following the Phase II investigation. It was performed to identify potential receptors of groundwater contaminants from the site.
The third phase, which evaluated the groundwater flow and conditions in the bedrock, was completed in March 1989. Test trenching of the waste pile and general site clean-up were performed in October, 1988. The trenching was performed to better characterize the waste pile contents. Three trenches were dug through the pile, and samples were collected from each. Air monitoring was performed during the trenching activities. Following these activities, contaminated wastes were placed on the waste pile on-site and a new synthetic cap was placed over it.
In June 1989, a Risk Evaluation was prepared by EAH to examine the potential receptor risks related to the site. A Feasibility Study (FS) was performed in August 1990, pursuant to the June 1986 Consent Order. The FS explored the treatment and remediation options for the site. A biological treatability study was also undertaken in late 1990 to determine the applicability of biological treatment for the contaminants of concern. Although the result of the study was inconclusive with respect to the type of microorganism responsible for reduction of PAHs, it did indicate that this treatment may be made applicable as a remedial option for some contaminants at the site.
Investigations carried out under the initial Consent Order did not fully characterize all potential sources of contamination. The vertical and horizontal extent of contamination was not fully defined. Consequently, the EPA and IPW entered into another Consent Order on October 1, 1991. Remedial Investigation and Feasibility Studies (RI/FS) were instituted. The RI report was completed in January 1993, and revised in August 1993. Addendum reports for the RI (Volumes I,II, and III) were issued in April 1994 (3, 4). An Interim Baseline Risk Assessment was completed for the site in September 1993, with addendum issued on June 21, 1994 (1, 2).
B. Actions Implemented During the Health Assessment Process
A Removal Action Decision Document (RADD) was approved by EPA on March 20, 1995. The RADD contained the selected non-time critical removal action for soil and wastes at the site. The removal action will be implemented after the Administrative Order on Consent is negotiated and finalized between the primary responsible parties and EPA. The proposed action involves the excavation of contaminated soils and wastes and the treatment of these materials at an off-site thermal treatment facility. The removal of the contaminated materials which are in contact with groundwater will eliminate on-going sources of contamination and should have a positive impact on any future action concerning groundwater (5).
On October 6, 1994, Brad Cudal and Rick Welke from the Iowa Department of Public Health, Toxic Substance Evaluation Program (IDPH/TSEP) visited the site. IDPH staff visited with the director and the coordinator of environmental health of the Cerro Gordo County Health Department prior to the actual site visit.
Access to the site was fully restricted by a chain-link fence. A six-foot chain-link fence bordered the streets, and a three-foot chain-link fence was on the retaining wall that separates Willow Creek and the site. No one can easily enter the site. The area within the fence was covered with a mixture of dirt and gravel which was sparsely vegetated (this area is used as an access road in and out of the site). Although the fence restricted access, no signs were posted to warn that a hazardous waste site was in the area. The entrance was restricted with a chain-link gate that was padlocked.
The population within a mile radius of the Mason City Coal Gas site, according to the 1990 census, is 20,014. There are nine schools within a mile of the site. They are: Hamilton Business College; Discovery Time Pre-school; Newman Catholic Elementary School; Sugar Plum Pre-school; Sunbeam Pre-school; Newman Catholic Elementary School; Roosevelt Middle School, and the Washington Elementary School. Three health care facilities are also located within the same area: North Iowa Mercy Center, Good Shepherd Health Center, and the Heritage Health Center (Figure 1-A).
The population density of Mason City within a mile radius of the site, when compared to other cities of comparable size in the county and the state, is similar. Population data is listed to provide an estimate of potential subpopulations at risk, i.e., the very young and elderly.
Population and housing information for a one mile radius around the site are listed in the following tables:
| Total Area: One block group mile | |
| Total Persons: 20,014 | |
| % Male (9,213) = 46% | % Under age 5 = 6.8% |
| % Female (10,801) = 54% | % Age 65 & older = 18.61% |
| % White = 91.74% | % Asian/Pacific Islander = .07% |
| % Black = 1.6% | % Hispanic = 4.6% |
| % American Indian, Eskimo, or Aleut. = 0.09% |
% Other races = 1.9% |
| Total Area: One block group mile | |
| Occupied Households: 8,622 | |
| % Owner Occupied: 62% | Median Value: $45,184 |
| % Renter Occupied: 38% | Median Rent: $269/month |
| Household Mobile Homes: 127 | |
| Persons Living in Group Quarters: 586 | |
Residential and commercial areas surround the site. Several light commercial establishments, including a fast-food restaurant, are located south of the site. Southeast of the site are single residential homes and northeast of the site are multiple dwelling units. The property west of the site is currently being used as a parking lot. Willow Creek is immediately north of the site, separated only by a concrete wall with a 3-foot, chain-link fence on top. The area north of Willow Creek is used for commercial purposes that include an exercise club, an automotive body shop, and an antique shop. The property west of the site is currently vacant and is being used as a parking lot. City streets surround the site except on the north side, which is adjacent to Willow Creek.
Willow Creek is the most prominent surface water feature near the site. Surface water runoff from the site flows to Willow Creek. The creek originates north of Clear Lake and receives water from Clear Lake via Clear Creek. Several other tributaries join Willow Creek upstream of the site. That portion of Willow Creek in proximity to the site is not used for recreational fishing purposes. There are no private wells close to the site. Most of the private residences, schools, and other commercial establishments within a mile radius of the site are connected to the community water supply system. Results of the previous Mason City Well Inventory concluded that no domestic wells are currently being impacted because of their distance from the site.
The state maintains health databases on several registries: Cancer Registry, Birth Defects Registry, Infant Mortality Database, and Tuberculosis (TB) Registry. Disability Prevention Programs (case evaluation for low birth weights, infant deaths, etc.) are also maintained by the state. The state cancer registry has collected data since 1969. The birth defects registry has collected data since 1985.
Because of the possibility of exposure to site contaminants by receptor populations near the site, available state data from the Iowa Cancer Registry for the period of 1973-1992 was reviewed. An evaluation of the usefulness of that health data in relation to the Mason City Coal Gas site is presented in the Public Health Implications section. The county and local health departments do not have relevant or appropriate health data pertinent to this site.
Based on conversations with the Cerro Gordo County Health Department Director, and the Coordinator of Environmental Health during the site visit on October 6, 1994, IDPH has determined that there are no community health concerns related to the site. IDPH is not aware of any other complaints or public health concerns at this time.
This public health assessment was released for public comment on August 15, 1995, through September 14, 1995. During that period, IDPH sought written and oral comments regarding the health assessment's findings, conclusions, and recommendations. No comments were received and the county sanitarian did not report any other complaints or community health concerns during the public comment period. Though the official comment period has ended, any subsequent comments or information pertinent to the site and the public health assessment will be considered for future assessments, consultations, or site reviews and up-dates. Any information suggesting that adverse health effects are related to exposure from contaminants at the site will be further evaluated for any indicated follow-up. Area residents will be notified of any health risk identified during subsequent investigation.
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