- Manufactured Gas Plant Removal
Burns & McDonnell was retained by Ameren Services to complete a human health risk assessment, an engineering evaluation/cost analysis, a removal action work plan and construction specifications for the manufactured gas plant site in Moberly, Mo. In addition, Burns & McDonnell performed construction oversight and perimeter air monitoring during the removal action. This work was completed under Administrative Settlement Agreement on Consent (AOC) with the U.S. Environmental Protection Agency (EPA) Region 7. The removal action was substantially completed in July 2008.
- Risk assessment
- Engineering evaluation/cost analysis
- Removal action work plan
- Implementation and oversight of the removal action
- Ambient air monitoring
The site is part of the Ameren Works headquarters (AWH) and is used primarily for the storage of equipment and materials. The AWH is also used as a base of operations for field crews and customer service. Three aboveground manufactured gas plant (MGP)-era structures remain on the property. These structures include the former electric plant building, the governor house and a concrete containment structure that previously contained two aboveground fuel oil tanks. The gas plant building was demolished in 2001. An electrical substation and office/garage/warehouse building occupy the western half of the AWH, west of the former manufactured gas plant (FMGP) site. There is no indication that MGP operations were conducted on the western half of the AWH, which appears to have been used for residential purposes and separated from the MGP by an alley during the years of MGP operation.
The Moberly MGP manufactured gas using the coal gas and Lowe processes as early as 1875 through 1935. It began operations in 1875 as Moberly Gas Light & Coke using the coal gas process, and added the Lowe process (carbureted water gas) in 1911. Gas production ranged from 6.5 million cubic feet (Mcf) in 1886 to 61 Mcf in 1929.
A site assessment/characterization field investigation was performed in two phases by others. Site investigation activities were conducted at a time when the site was enrolled in the Missouri Department of Natural Resources Voluntary Cleanup Program. The first phase was conducted in February 2000 and the second phase was conducted in July 2000. Site investigation activities consisted of the completion of 55 probeholes, the installation of five monitoring wells and the excavation of 11 test trenches. Below-grade and at-grade portions of some of the FMGP structures were identified in test trenches in the general areas indicated on historical drawings. The subsurface masonry tank of the relief gas holder, the concrete foundation for the tank for the 100,000-cubic-foot gas holder, the concrete base for a purifier, the rectangular tar well, and the circular tar well were the FMGP structures encountered in test trenches excavated during the site assessment/characterization. The subsurface masonry tank of the relief gas holder, the rectangular tar well and the circular tar well contained source materials (tar or other non-aqueous phase liquids).
A human health risk assessment (HHRA) was conducted in 2006 using data collected during the site assessment/characterization. The risk assessment identified four potentially exposed populations: current and future indoor workers, future groundskeeper, future construction worker and future resident. Potentially completed exposure pathways included incidental ingestion of soil, absorption through dermal contact with soil and groundwater, inhalation of fugitive dusts, inhalation of outdoor vapors from air, and inhalation of indoor vapors from soil and groundwater. The assessment concluded that both cancer and noncancer risks exceeded U.S. EPA-accepted levels. The HHRA was approved by the U.S. EPA in August 2007.
An engineering evaluation/cost analysis (EE/CA) report was prepared to assess potential removal options. The EE/CA was prepared using site data obtained during the site assessment/characterization and from the HHRA. The recommended removal action alternatives were a combination of Alternatives 2 and 3, which consist of source (tarry or tar-coated) material excavation, removal of contaminated soil off-site, installation of an engineered barrier (asphalt cap) on-site and institutional controls (i.e. land use restrictions and dig policy). The EE/CA was approved by the U.S. EPA in August 2007, and the recommended removal action alternatives were accepted.
A removal action work plan (RAWP) was prepared as required by the AOC based on the HHRA and EE/CA. The RAWP included site-specific preliminary remediation goals (PRGs) based on the results of the HHRA. The RAWP was completed in February 2008 and approved by the U.S. EPA.
In addition, Burns & McDonnell prepared an ambient air monitoring plan for the removal action. Construction specifications provided requirements to Ameren’s excavation subcontractor.
The removal action activities began in January 2008 and were substantially completed in July 2008. A temporary building was constructed over the area of the site expected to contain to vast majority of the source materials to protect against adverse weather and to mitigate possible off-site odor and dust migration during critical portions of the work. The universal fabric structure building was 131 feet wide by 115 feet long and 49 feet high at the peak. An air handling system with carbon filtration was designed to provide for 3 to 3.5 air changes per hour inside the temporary building. Some open excavation was conducted after the maximum amount of soil removal was completed inside the temporary building and the building was dismantled. Excavated source materials were solidified and transported to a Subtitle C solid waste landfill for disposal. Contaminated soil and debris was transported to a Subtitle D landfill for disposal. Approximately 8,000 tons of Subtitle C waste and 10,000 tons of Subtitle D waste was generated during the removal action. Approximately 160,000 gallons of wastewater was generated, treated on-site and discharged to the sanitary sewer with approval from the City of Moberly. Confirmation soil samples were collected from excavation side walls and floor for comparison the site-specific PRGs, per the RAWP and AOC.
An asphalt pavement (engineered barrier) was designed and installed in spring 2009. Burns & McDonnell developed specifications and contract documents for the pavement work. Burns & McDonnell prepared a removal action completion report for submittal to U.S. EPA. Land use restrictions were filed with the property deed to prohibit residential use, safety requirements for construction work that requires on-site excavation and requirements for maintenance of the engineered barrier.
Burns & McDonnell performed perimeter air monitoring during the removal action to monitor the concentration of volatile organic compounds (VOCs), polynuclear aromatic hydrocarbons and particulate generated by removal action activities to allow for the implementation of engineering controls when necessary to reduce emissions that could have deleterious effects on surrounding community. During the removal action 72-hour time-averaged sampling was conducted at selected locations on the site perimeter utilizing high-volume samplers for collection of polycyclic aromatic hydrocarbons (PAHs — TO-13A), and PM10 particulate matter. In addition, Summa canisters (TO-15) were used for VOC analysis. Real-time monitoring of benzene, VOCs and particulate was conducted at the site perimeter hourly using a Photovac Voyager gas chromatograph, a photoionization detector and a MIE DataRAM (PM10), respectively. Meteorological monitoring was conducted to capture weather conditions during the removal action.
- U.S. EPA Region 7 oversight under an AOC
- Active Ameren Works headquarters
- Removal action
- Remediation inside a temporary building
- Perimeter ambient air monitoring
- Design and installation of an engineered barrier
- Institutional controls