The Melton Valley watershed is a 1,000-acre area bounded on the north by the Bethel Valley watershed and on the west by the Clinch River (see Figure 4.3). It is separated from Bethel Valley by Haw Ridge.

Melton Valley contains more than 1000 acres of burial grounds, seepage pits, contaminated floodplains and hydrofracture wastes. These wastes originated both from local operations and from other sites. The bulk of disposal activities involved shallow land burial. In some cases, wastes are in constant contact with groundwater, resulting in shallow groundwater contamination.

From 1955 to 1963, ORNL’s solid waste storage areas were designated by the Atomic Energy Commission as the Southern Regional Burial Ground. About one million cubic feet of solid waste from various off-site installations was buried in Solid Waste Storage Areas 4 and 5. During this period, ORNL served as a major disposal site for wastes from such facilities as Argonne National Laboratory, Knolls Atomic Power Laboratory, Mound Laboratories, Battelle Memorial Institute, General Electric Company in Evendale, Ohio, and about 50 other off-site installations.

The major areas of contamination in Melton Valley are described below:

Waste Area Grouping 2 includes White Oak Creek, White Oak Lake, their tributaries and adjacent lands. In this area, sediments are contaminated with cesium-137 and cobalt-60.

Waste Area Grouping 4 was used for disposal of solid low-level wastes in trenches and auger holes. This area is a significant source of strontium 90 levels at White Oak dam where surface water from Melton Valley is released toward the Clinch River from White Oak Lake. Groundwater contaminants are strontium-90, tritium and transuranic elements.

Waste Area Grouping 5 was used for disposal of low-level radioactive wastes in trenches and auger holes. Approximately 1800 curies of tritium are released annually from this area to the Clinch River via the White Oak Dam. The most heavily contaminated groundwater wells in Melton Valley are located in this area. Groundwater contaminants are transuranic elements, strontium-90, tritium, and volatile organic compounds.

Waste Area Grouping 6 was used for low-level waste disposal into trenches, auger holes and silos. Groundwater contaminants are organic solvents and tritium.

Waste Area Grouping 7 contains seven waste pits and trenches used from 1951 to 1966 for disposal of liquid low-level radioactive wastes. Wastes were piped into these seepage pits, resulting in extensive soil contamination. Seven Homogeneous Reactor Experiment fuel wells are also located in this area. Groundwater contaminants are strontium-90, cobalt-60, and transuranic elements.

Waste Area Grouping 8 includes both active facilities and CERCLA sites. Active facilities are the High Flux Isotope Reactor, Transuranium Processing Plant, and the Transuranium Research Facility. CERCLA sites include surface impoundments, low-level waste storage tanks, waste storage facilities, a backfilled impoundment, and the Molten Salt Reactor Experiment facility. (These reactors were not discussed in detail by the EUWG and are not included in the recommendation for Melton Valley. They are discussed in the recommendations for sites outside the existing administrative watersheds in Section 4.8.)

Waste Area Grouping 9 contains the Homogeneous Reactor Experiment and support facilities. The primary releases are associated with the Homogeneous Reactor Experiment ponds, leaks from tanks, pits and/or pipelines, and leachate from decontamination ponds. (The Homogeneous Reactor Experiment was not discussed in detail by the EUWG and is not included in the recommendation for Melton Valley. It is discussed in the recommendations for sites outside the existing administrative watersheds in Section 4.8.)

Waste Area Grouping 10 consists of hydrofracture injection sites. In the hydrofracture process, waste containing up to one million curies was mixed with cement grout. This mixture was pumped under pressure via injection wells into the Pumpkin Valley Shale geologic formation, located 700 to 1000 feet below the surface, where groundwater is 10 times more saline than seawater and is not part of an active groundwater flow system. There are no known releases to surface water, sediments, or surface soils from the hydrofracture process. There is some speculation that pressure below the hydrofracture zone may cause water to flow up boreholes or wells. Hydrofracture material is not believed to be migrating from the injection sites, and no practical way exists to remediate this material.

Waste Area Grouping 13 includes the former experimental cesium plots. This site was not included in the Melton Valley recommendation because some remediation had already occurred. This site is addressed in the recommendation for sites outside existing watersheds in section 4.8.

The DOE provided the Group with information on two end uses:

• an unrestricted end use with complete removal of contaminated material (except for the grout sheets) but without groundwater use (estimated costs of $3 to $6 billion); and
• a restricted waste disposal end use with a focus on in-place management and removal of some "hot spots" (estimated costs of $200 to $700 million).

Because this area contains some of the most highly radioactive waste materials (though with half lives of only 7 to 30 years) on the Reservation, near-term excavation would be risky and expensive, and because better technology might someday become available, members believed that Melton Valley should have a restricted waste disposal end use and that stewardship requirements for the area should be addressed.

The contamination in Melton Valley is extensive and complex. The Group was evaluated a great deal of information about the waste present throughout the valley and how some of it is migrating toward the Clinch River. In much of this information, the White Oak Dam was used as an integration point where to show how waste leakage from each disposal area contributed to the entire problem. The White Oak Dam was ultimately used by the group as an integration point in framing its recommendation to ensure that waste would be contained within Melton Valley. It was not intended to be a point of compliance for groundwater and surface water requirements.

Most members believed that, while only limited excavation of wastes is feasible at this time, many contaminants will decay to manageable levels over the next two to three centuries. EUWG members preferred that remediation occur eventually.

• concern that end use recommendations for Melton Valley are premature, since disposal areas have not yet been fully characterized;
• concern over vague meaning of restricted end use;
• concern about the spread of contamination by animals; and
• concern about the ecological health of the valley.