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Record of Decision System (RODS)

MOUND PLANT (USDOE)

Abstract

Site Name:  MOUND PLANT (USDOE)
Address:  MOUND RD 
City & State:  MIAMISBURG  OH  45342
County:  MONTGOMERY
 
EPA ID:  OH6890008984
EPA Region:  05
 
NPL Status:  Currently on the Final NPL
 
ROD Type:  Record of Decision
ROD ID:  EPA/ROD/R05-95/292
ROD Date:  06/12/1995
Operable Unit(s):  01
 
Media:  groundwater, waste materials, soil
 
Contaminant:  VOCs, vinyl chloride, trichloromethane, 1,2-cis-dichloroethene, TCE, tetrachlorethene, 1,1,1-trichloroethane, radium-226, 2,3,7,8-TCDD, arochlor-1248, benzo(a)pyrene, benzo(b)flouranthene, plutonium-238, strontium-90
 
Abstract:  Please note that the text in this document summarizes the Record of Decision for the purposes of facilitating searching and retrieving key text on the ROD. It is not the officially approved abstract drafted by the EPA Regional offices. Once EPA Headquarters receives the official abstract, this text will be replaced.

The U.S. Department of Energy (DOE) Mound Plant site is located within the southern city limits of Miamisburg, Ohio. The site is approximately 10 miles south-southwest of Dayton and 45 miles north of Cincinnati. Miamisburg is predominantly a residential community with some supportive commercial facilities and limited industrial development. Much of the residential, commercial, and industrial development within a 5-mile radius of the site is concentrated on the Great Miami River floodplain. The adjacent upland areas are used primarily for residences and agriculture or are unused open spaces.

Mound Golf Course and Miamisburg Mound State Memorial Park, both directly east of the facility across Mound road, are heavily used during favorable weather. The park is the site of a 68-foot high ancient Indian Mound, located 380 feet east of the Mound Plant boundary. Other recreational areas within 1 mile of the facility include the Miamisburg municipal park and swimming pool, located immediately west of Mound Plant, Harmon Athletic Field, and Library Park. These areas are used extensively during the summer.

There are no large lakes within a 5-mile radius of the site. Some vestiges of the old Miami-Erie Canal lie between the Conrail Railroad and the Dayton-Cincinnati Pike west of the site. The remnant of the old Miami-Erie Canal is designated as Operable Unit (OU4). The major water body in the vicinity of the Mound Plant is the Great Miami River. It is approximately 150 to 200 feet wide in this area.

Agricultural land within a 5-mile radius area around the site is primarily used for corn and soybean production and for livestock grazing.

The population of Miamisburg is 17,834, Dayton is 182,044, and Montgomery County is 573,809. The only historic landmark in the vicinity of Mound Plantis the Miamisburg Mound, an ancient Indian mound located 280 feet east-southeast of Mound Plant in Miamisburg Mound State Memorial park. The mound - a symmetrical, conical earthwork 68 feet high and 800 feet in perimeter - is one of the largest of its type. It is believed to be the sepulcher of a chief of the Adena culture of Mound Builders, who inhabited the Ohio region as early as 800 B.C.

OU1 also includes the three plant production wells located along the southern plant boundary. An extended discussion of OU1 history, including waste disposal and construction activities, is provided in the Remedial Investigation (RI) report.

The former waste disposal sites within OU1 (the historic landfill and associated features) are concentrated within, beneath, and immediately adjacent to the current site sanitary landfill. These waste disposal sites are the result of a long history of dumping, burning, moving, reworking, burying, and partially removing wastes and placing them into the engineered structure (the site sanitary landfill). Currently, the area bounded by the overflow pond to the north, the paved roads to the west and south, and the bunker area to the east can be considered a single entity. It is internally heterogeneous; not all portions are contaminated. However, subdividing the area does not increase understanding of the transport phenomena that are occurring, nor does it facilitate developing remedial alternatives.

Mound Plant was established at its present location in 1948. Currently, the facility is operated by EG&G Mound Applied Technologies for DOE as an integrated research, development, and production facility that supports the DOE weapons and energy programs. To reconfigure and consolidate the nuclear complex, DOE has decided to phase out the future defense mission. As a result, the Mound site has been designated an environmental management site and the plant is in the process of being converted into a commercial and industrial site.

OU1, also identified as Area B, occupies approximately 4 acres in the southwestern portion of the Mound Plant. OU1 includes a historic landfill site that was used by the Mound Plant from 1948 to 1974. Plant waste materials that were disposed of in OU1 included general trash and liquid waste. Much of this waste was later relocated and encapsuled in a site sanitary landfill constructed in 1977. An overflow pond was constructed at the same time, partially covering the historic landfill site. After 1974, waste was no longer disposed of in OU1. There are known releases of volatile organic compounds (VOCs) from OU1 into the adjacent Buried Vallet aquifer (BVA). In addition, tritium was detected in water samples taken from wells in OU1, although the concentration was below the drinking water maximum contaminant level.

Cut and fill activities and refuse and waste disposal occurred within OU1 from 1948 to 1974. No written manifests of the waste types and quantities exist, and uniform disposal practices were not followed.

Before 1947, OU1 was a residential area with two or three small houses and storage buildings. During plant construction, the area was exploited for its gravel deposits. Removal of gravel was routine until 1977.

The old gravel excavation and the disturbed area just north of the excavation were used for a landfill, including open burning of trash and garbage from plant operations. A burn cage, consisting of a wire mesh structure that caught ashes from burning wood, paper, and other materials, was used. Solid waste, mostly paper, office, and kitchen garbage, was placed in the burn cage and ignited to reduce its volume.

In 1954, the first burial at OU1 occurred along the southern boundary of the old gravel quarry, just north of and parallel to the east-west road that climbs the SM/PP Hill. A backhoe was used to excavate an irregularly shaped trench to the maximum depth possible. Residual steel and metal debris were progressively buried in the trench. The debris and backfill were regraded to just below the road level.

During 1955 and 1956, empty drums that had contained thorium were buried in the southwest corner of OU1. A shallow excavation was made, and about 2,500 55-gallon drums were crushed and then covered with a thin layer of soil cover. The buried drums and backfill were regraded to just below the level of the road. In 1969, the state of Ohio banned open burning, and Mound Plant prohibited open burning of solid and liquid waste in OU1. Hazardous liquid waste was collected and disposed of off site. Solid waste was placed in east-west trending trenches cut by a bulldozer.

In 1977 and 1978, the overflow pond and site sanitary landfill were constructed on the site of OU1. The overflow pond was built to complement the low-flow retention basins, which were constructed in 1976 on the lower reach of the plant drainage ditch. Much of the solid waste in the historic landfill was excavated and moved to the site sanitary landfill. Generally, debris from the Dayton Unit fire in the first trench and empty, crushed drums that had contained thorium in the second trench were not excavated and remained under the landfill. The volume excavated was limited by the volume required for the pond construction.

The pond was built with a natural clay-bearing compacted glacial till liner and earthen dikes. It has a 5,000,000 gallon capacity. Effluent in the overflow pond is discharged through a standpipe in the northwest corner of the pond to the stilling basin below the low flow retention basins. It then goes to the Miami-Erie Canal and to the Great Miami River through National Pollutants Discharge Elimination System (NPDES) Outfall 002 at a rate of approximately 660,000 gallons per day.

As of 1995, OU1 remains much as it did in 1978 after the overflow pond and site sanitary landfill were constructed. The road along the north and west boundary had been paved and, in the 1980s, a bridge was built over the overflow channel from the plant drainage ditch to the overflow pond.
 
Remedy:  This remedial action is the first of several actions planned as part of the overall remedial action for the Mound Plant site. The function of this remedial action is to control groundwater contamination to prevent migration of contamination toward the Mound Plant production wells and to minimize exposure to potential receptors. The pathway of concern consists of leaching of contaminants from site soils or disposed waste; entrainment in the groundwater flow; and withdrawl by the Mound Plant production wells or by other future wells.
The selected remedy for OU1 is collection and treatment of contaminated groundwater and disposal of treated water. The precise method for treating the contaminated water will be determined during the remedial design phase of the project. All extracted groundwater will be treated to levels that comply with the requirements of the Mound Plant NPDES Permit.

The major components of the selected remedy include: installing two groundwater extraction wells within OU1, using standard equipment and procedures; treating the extracted groundwater to remove VOCs and other constituents, as required, using cascade aeration, UV oxidation, conventional air stripping, or other suitable treatment units; discharging the treated groundwater to the Great Miami River through the existing plant NPDES outfall or a new outfall. Following installation and operation of the groundwater extraction wells, the chemical properties and hydraulic behavior of the groundwater system will be monitored to verify the adequacy of the remedy.
 
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