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The Mason City Coal Gas site is a former manufactured gas plant (FMGP) located near the centerof Mason City, Iowa. The plant was originally built in the northwestern area of the site between1897 and 1901. Town gas was generated for use in the Mason City area. Following theavailability of natural gas, the gas plant was decommissioned in 1951, and was subsequentlydemolished in 1952. The Interstate Power Company (IPW) and the City of Mason City presentlyown 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 nearthe southeast corner of the site.

Contaminants of concern identified from previous investigations at the site include polycyclicaromatic hydrocarbons (PAHs), volatile organic compounds (VOCs)--primarily benzene, toluene,ethylbenzene, and xylenes (which combined are referred to as BTEX)--phenols, cyanide, andvarious 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 onthree sides by city streets: South Pennsylvania Avenue to the east, 5th Street Southeast (SE) tothe south, and South Delaware Avenue to the west (Figure 1). The northern edge of the site isbounded by Willow Creek which flows easterly past the site and over a low dam at thedownstream end of the site (Figures 1 & 2).

The site was occupied by a manufactured gas plant facility in the early 1900s. The original facilitywas built between 1897 and 1901. The gas plant generated town gas for lighting and heatingpurposes in the Mason City area. At that time, there were several private dwellings located alongthe southern edge of the site on the area that is now 5th Street SE. These residential structureswere removed in 1909 when the gas plant was expanded. During that time, a large capacity gasholder was constructed near the east end of the site for commercial gas storage. This gas storagetank was subsequently cleaned and removed from the site.

Brice Gas and Electric Company operated the original gas plant. Between 1901 and 1906, thecompany was known as Peoples Gas and Electric Company. In 1932, the site was purchased bythe Kansas City Power and Light Company who maintained the gas plant until 1951. Followingthe availability of natural gas, the gas plant was decommissioned in 1951 and was subsequentlydemolished in 1952. After the demolition of the gas plant, a storage building and substation wereconstructed 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 Citypurchased a segment of the site parallel and adjacent to Willow Creek. Currently, the site isessentially vacant, except for the remaining IPW electrical substation and storage building. IPWof Dubuque, Iowa, and Mason City presently own the property.

Soil and groundwater contamination were initially discovered in 1984 during an on-site citysanitary sewer construction project. Contaminated soil and oily sludges were encountered duringa trench excavation. Consequently, the Mason City engineer contacted the Iowa Department ofWater, Air, and Waste Management (IDWAWM), now the Iowa Department of NaturalResources (IDNR), on June 22, 1984. Construction of the sanitary sewer was temporarilysuspended 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 thenexcavated 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 extentof contamination. Potential sources of contaminants were the former gas plant building wherereleases of carburetor oil, tar, or condensate may have occurred, the oil storage tanks, separatingand purifying basins, purifying box, and the tar storage tank (Figure 2). Actual disposal practicesfor waste products during the life of the plant are not known. Typically tar was recovered andsold for use as fuels by other industries, used as wood preservatives, or further refined into usableproducts. The remaining by-products were usually treated as no value and were then disposed onor off-site as fill material or general refuse. No information regarding the generation or disposalof these remaining by-products is available.

The U.S. Environmental Protection Agency (EPA) became the lead agency at some point duringthe initial discovery and removal activities. In June 1986, EPA issued IPW the first ConsentOrder. The order directed IPW to remove all oily sludges containing PAH concentrations above100 parts per million (PPM).

Three previous investigations and other related site work were conducted using a phasedapproach during the initial Consent Order. The preliminary assessment phase was completed inMay 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 werecollected from the site. Four monitoring wells were installed and water and sediment sampleswere 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 geologiccharacter of the underlying bedrock, defined the extent of the vertical and horizontalcontamination, and characterized the waste pile. A local water well inventory was alsoaccomplished in February, 1989, following the Phase II investigation. It was performed toidentify potential receptors of groundwater contaminants from the site.

The third phase, which evaluated the groundwater flow and conditions in the bedrock, wascompleted in March 1989. Test trenching of the waste pile and general site clean-up wereperformed in October, 1988. The trenching was performed to better characterize the waste pilecontents. Three trenches were dug through the pile, and samples were collected from each. Airmonitoring 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 placedover it.

In June 1989, a Risk Evaluation was prepared by EAH to examine the potential receptor risksrelated to the site. A Feasibility Study (FS) was performed in August 1990, pursuant to the June1986 Consent Order. The FS explored the treatment and remediation options for the site. Abiological treatability study was also undertaken in late 1990 to determine the applicability ofbiological treatment for the contaminants of concern. Although the result of the study wasinconclusive with respect to the type of microorganism responsible for reduction of PAHs, it didindicate that this treatment may be made applicable as a remedial option for some contaminants atthe site.

Investigations carried out under the initial Consent Order did not fully characterize all potentialsources of contamination. The vertical and horizontal extent of contamination was not fullydefined. 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 wascompleted in January 1993, and revised in August 1993. Addendum reports for the RI (VolumesI,II, and III) were issued in April 1994 (3, 4). An Interim Baseline Risk Assessment wascompleted 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. TheRADD 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 negotiatedand finalized between the primary responsible parties and EPA. The proposed action involves theexcavation of contaminated soils and wastes and the treatment of these materials at an off-sitethermal treatment facility. The removal of the contaminated materials which are in contact withgroundwater will eliminate on-going sources of contamination and should have a positive impacton any future action concerning groundwater (5).

C. Site Visit

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 thedirector and the coordinator of environmental health of the Cerro Gordo County HealthDepartment prior to the actual site visit.

Access to the site was fully restricted by a chain-link fence. A six-foot chain-link fence borderedthe streets, and a three-foot chain-link fence was on the retaining wall that separates WillowCreek and the site. No one can easily enter the site. The area within the fence was covered witha mixture of dirt and gravel which was sparsely vegetated (this area is used as an access road inand out of the site). Although the fence restricted access, no signs were posted to warn that ahazardous waste site was in the area. The entrance was restricted with a chain-link gate that waspadlocked.

D. Demographics

The population within a mile radius of the Mason City Coal Gas site, according to the 1990census, is 20,014. There are nine schools within a mile of the site. They are: Hamilton BusinessCollege; 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 thesame area: North Iowa Mercy Center, Good Shepherd Health Center, and the Heritage HealthCenter (Figure 1-A).

The population density of Mason City within a mile radius of the site, when compared to othercities of comparable size in the county and the state, is similar. Population data is listed toprovide 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 thefollowing 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

E. Land Use

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 singleresidential homes and northeast of the site are multiple dwelling units. The property west of thesite 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 ofWillow Creek is used for commercial purposes that include an exercise club, an automotive bodyshop, and an antique shop. The property west of the site is currently vacant and is being used as aparking lot. City streets surround the site except on the north side, which is adjacent to WillowCreek.

F. Natural Resource Use

Willow Creek is the most prominent surface water feature near the site. Surface water runofffrom the site flows to Willow Creek. The creek originates north of Clear Lake and receives waterfrom Clear Lake via Clear Creek. Several other tributaries join Willow Creek upstream of thesite. That portion of Willow Creek in proximity to the site is not used for recreational fishingpurposes. 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 thecommunity water supply system. Results of the previous Mason City Well Inventory concludedthat no domestic wells are currently being impacted because of their distance from the site.

G. Health Outcome Data

The state maintains health databases on several registries: Cancer Registry, Birth DefectsRegistry, Infant Mortality Database, and Tuberculosis (TB) Registry. Disability PreventionPrograms (case evaluation for low birth weights, infant deaths, etc.) are also maintained by thestate. The state cancer registry has collected data since 1969. The birth defects registry hascollected 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 ispresented in the Public Health Implications section. The county and local health departments donot have relevant or appropriate health data pertinent to this site.


Based on conversations with the Cerro Gordo County Health Department Director, and theCoordinator of Environmental Health during the site visit on October 6, 1994, IDPH hasdetermined that there are no community health concerns related to the site. IDPH is not aware ofany other complaints or public health concerns at this time.

This public health assessment was released for public comment on August 15, 1995, throughSeptember 14, 1995. During that period, IDPH sought written and oral comments regarding thehealth assessment's findings, conclusions, and recommendations. No comments were receivedand the county sanitarian did not report any other complaints or community health concernsduring the public comment period. Though the official comment period has ended, anysubsequent comments or information pertinent to the site and the public health assessment will beconsidered for future assessments, consultations, or site reviews and up-dates. Any informationsuggesting that adverse health effects are related to exposure from contaminants at the site will befurther evaluated for any indicated follow-up. Area residents will be notified of any health riskidentified during subsequent investigation.

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