Gregory B. Cotten, P.E. and Roland D. Greenwell, P.E.
Parsons Infrastructure & Technology Group Inc.

The Idaho National Engineering and Environmental Laboratory (INEEL) is a 2,305-km² (890-mi²) Department of Energy (DOE) facility located in southeast Idaho in the United States of America. Multiple radionuclide-contaminated soil and debris sites are the result of more than 45 years of nuclear reactor research, development, and failure mode testing. In some cases, the radionuclide-contaminated soils and debris present unacceptable risks to human health and the environment, and require some method of remediation, which usually includes excavation, consolidation, and construction of a long-term engineered barrier for containment.

The INEEL Environmental Restoration Program has implemented the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) process to identify and manage risk to human health and the environment at contaminated sites. For sites requiring remedial action, feasibility studies were performed to develop remedial alternatives to reduce risks to allowable levels. This process is currently underway for multiple waste area groups (WAGs). In addition, current maintenance, decontamination and dismantlement (D&D), and construction activities frequently generate contaminated soils and debris that require management under CERCLA.

A soil strategy to evaluate a Site-wide approach to selecting alternatives for management of the anticipated volumes of soil and debris was developed for the INEEL (see Reference 1). The referenced Operable Unit (OU) 3-13 (WAG 3) Remedial Investigation/Feasibility Study (RI/FS) does not mandate what other WAGs should do with their soils and debris. A Site-wide approach has the advantage of providing one comprehensive evaluation rather than repeating the process for multiple WAGs and associated decision documents. However, each WAG will have its own Record of Decision (ROD) to disposition its own soil and debris. The Site-wide approach merely offers a basis for consistent decisions and potential economies of scale.

The INEEL is evaluating consolidation of soils at an existing CERCLA site capable of accommodating the projected volume and radionuclide content that will be remediated from the various WAGs across the Site. This evaluation is part of the CERCLA process, and any decision regarding the use of a consolidation site (typical) will be documented in a ROD.

A potential site for the soils repository is two existing percolation ponds that currently receive cooling water effluent from the Idaho Chemical Processing Plant (ICPP). These ponds may be replaced pursuant to the remediation ROD for contaminated perched water under the ICPP. The percolation ponds provide a significant hydraulic head to the existing contaminated perched water through lateral comingling along an interbed, and accelerate contaminant transport to the Snake River Plain Aquifer. The percolation ponds would be modified with a natural or synthetic liner system and capped at closure to minimize infiltration.

The INEEL currently operates a DOE Order 5820 low-level waste landfill at the Radioactive Waste Management Complex (RWMC); however, the RWMC has performance assessment and space limitations that factor into the economics of disposal. Therefore, an economic evaluation is being conducted which may justify on-Site disposal at a new facility.

The potential selection of an on-Site soils repository and the use of the existing ICPP percolation ponds as the location for an INEEL soils repository would be the result of an extensive engineering, economic, and political analysis that could provide useful insight to other Sites with similar situations.

Past nuclear research activities at the INEEL have resulted in contamination of soils, structures, process equipment, and other materials with radionuclides and hazardous constituents. The INEEL is currently listed on the National Priority List, and many CERCLA soil cleanup projects are planned or underway at INEEL WAGs. Additionally, D&D activities will generate significant quantities of contaminated building materials, process equipment, and other debris. Previous studies have been prepared at the INEEL, which identified alternatives for disposing INEEL CERCLA and D&D radionuclide-contaminated soils and debris, which include:

• Consolidation of soils and debris from all WAGs and off-Site disposal at a licensed facility
• Consolidation of soils and debris from all WAGs and on-Site disposal in a monofill-type landfill
• Consolidation of soils and debris from all WAGs and on-Site disposal in a Resource Conservation and Recovery Act (RCRA)-type landfill
• Management at the individual WAGs, which is the current approach
• Consolidation of soils and debris from all WAGs and stockpiling for later use in contaminated covers at ICPP.

The report concluded that a centralized radioactive soil and debris management approach would be the most cost-effective approach. Previous studies supported the need for an on-Site disposal option. WAG 3 was selected as the decision vehicle for the following reasons:

• WAG 3 has over 50% of the expected CERCLA contaminated soils and debris
• WAG 3 has a CERCLA site (CPP-67) that could be modified to serve as a soil consolidation facility
• OU 3-13 RI/FS/ROD schedule provide a timely decision

Off site disposal options are viable alternatives, however, cost, transpiration, and facility waste acceptance criteria requirements are issues.

It is likely that ICPP will never be fully cleaned up to a "Greenfield" due to technical impracticality and cost. Since the U.S. Government will be managing waste at ICPP for the foreseeable future, it is a good site to consolidate contaminated soil and debris from the many locations across the INEEL reducing "risk footprint" and the number of sites requiring long-term maintenance and monitoring.

Currently constructed/operated waste disposal cells at Hanford (ERDF) have demonstrated extremely cost efficient disposal compared with off-site alternatives and have been shown through extensive analysis to be protective of human health and the environment.

A comparison of the INEEL CERCLA and D&D waste streams versus other typical DOE low-level waste streams is warranted. The Environmental Management (EM)-30 funded low-level waste repositories receive primarily operations generated waste streams that are small in quantity and homogenous in content when compared to the EM-40 CERCLA soils and debris that are usually intermittent in production and large volume and low concentration wastes.

The recent discovery of waste at WAG 3 which may carry hazardous Listed Waste Code(s), further complicates the decision making process. The waste will be handled in one of two ways: (1) a no-longer contained-in determination may facilitate handling of material as nonhazardous waste or as nonlisted waste or (2) the waste will be handled as listed hazardous waste and or mixed (low-level) waste.

Appendix G to the Comprehensive RI/FS for the ICPP OU 3-13 at the INEEL (see Reference 1) proposes a listed-waste strategy which presents a process for making a no-longer contained-in determination for a significant portion of ICPP waste streams. This strategy implements a recent Idaho state policy on contained-in determinations.

The Comprehensive RI/FS for the ICPP OU 3-13, (see Reference 1) Appendix E-Soils Strategy (Soil Repository Conceptual Design) provides a detailed conceptual design for a on-Site soils repository located where two percolation ponds currently receive cooling water effluent from the ICPP. This effluent would have to be redirected to another facility prior to use of the current facility as a contaminated soils repository. In addition, the estimate of soil and debris quantities anticipated to require disposal as identified in Appendix E (see Reference 1) are summarized below in units of cubic meters (yards).

Soil and debris have been classified at the INEEL as follows:

• Type "A" soil refers to soil and debris generated from CERCLA actions that are contaminated with radionuclides of low activity and relatively short half-lives (e.g., cesium-137, strontium-90, etc.), excluding alpha-contaminated soils (i.e., soils with concentrations greater than 10 nCi/g of long-lived alpha emitting radionuclides with atomic numbers greater than 92).
• Type "C" soils refers to soil and debris generated from CERCLA actions that meet the characteristic definition of ignitability, reactivity, corrosivity, or toxicity; and/or contaminated with RCRA-listed waste; and also may be contaminated with low levels of radionuclides requiring RCRA Subtitle C-compliant. Type "C" soil may be treated to remove RCRA characteristics and be converted to Type "D" soil, which requires RCRA Subtitle D-compliant management (similar to a municipal-waste landfill).
• Type "D" soils refers to soils, which require RCRA Subtitle D-compliant management (40 CFR 257).

The preliminary design presented in the Comprehensive RI/FS for the ICPP OU 3-13 (see Reference 1) presents several alternatives combining the various types of cells in various configurations. The final determination of the number and types of cells has not yet been made, but if on-Site disposal is selected as a preferred alternative, additional design work would be required to optimize the economics and configuration of the consolidated disposal facility.

CERCLA disposal cells at the INEEL are designed and constructed to be protective of human health and the environment and are classified as follows:

• Type "A" cells are designed and constructed to be compliant with the substantive portions of DOE Order 5820.2A (Radioactive Waste Management) which are likely to be invoked as applicable or relevant and appropriate requirements (ARARs) in a CERCLA ROD. Key components of the design would include:

• A low-permeability soil bottom liner

• Key components of the closure design would include:

• Clean soil fill to create a sloped foundation for the cap
• A low permeability soil layer constructed to insure protection of groundwater
• A biotic intrusion layer with a capillary break
• A series of filters to prevent the fines in the upper soil cover from migrating into the biotic intrusion layer
• A water balance native soil cover designed for the semi-arid environment to minimize infiltration and maintenance

• Type "C" cells are designed and constructed to be compliant with the substantive portions of 40 CFR 264, Subpart N, and will be prepared for the liner by regrading the bottom to create a slope toward a sump on one side of the cell, and compacting the bottom soil. Key components of the liner system include:

• A low permeability soil bottom liner
• A lower flexible membrane liner
• A leachate collection layer with leak collection pipes routed to the leachate collection sump
• An upper flexible membrane
• A filter membrane of woven geotextile
• A protective layer of soil emplaced as a graded filter.

It is likely that additives and special placement methods will be needed to achieve this low conductivity with INEEL borrow soil. There are also questions as to the ability of a compacted clay liner to maintain a low hydraulic conductivity in an arid environment like the INEEL for any length of time due to desiccation cracking as the liner clay gives up moisture to the very dry surrounding soil and atmosphere. Asphaltic concrete mixtures have also been considered for use as liners in arid areas. In this case, a high asphalt ratio (>8%) and special placement methods would have to be used. These issues will be evaluated during final design. Closure for this type of cell would include the following:

• Clean soil fill to create a sloped foundation for the cap:

• A low permeability native soil layer possibly enhancing the natural materials with additives
• A flexible membrane liner
• A drainage layer of sand
• A biotic intrusion barrier
• A series of filters consisting of graded sand
• A cover layer of clean soil to limit infiltration of water to the filter layer and provide freeze protection for the low permeability layer
• A human intrusion and erosion barrier

Geosynthetic materials are available for many applications in the liner and cap, such as the leachate collection, leak detection, drainage layers, and the graded filters. However, because this cell may also contain mixed and low-level waste, natural materials in place of geosynthetics were selected because of the longer service life of natural materials.

• Type "D" cells are designed and constructed to be compliant with the substantive portions of 40 CFR 257 and portions of 40 CFR 258 for added protection. The liner and cap for the Type D cell are similar to the Type C cell, except that the Type D liner does not have a leak detection layer and piping, and the compacted clay layers in the Type D cell are not as thick. Also, the hydraulic conductivity requirement that the clay liner must achieve is less rigorous under Subtitle D than under Subtitle C, so it is possible that this conductivity could be achieved without additives for the Type D cell.

Design considerations unique to the INEEL include:

• Retrofitting a percolation pond to a repository which maximizes available space in a pre-defined facility
• Placement over a sole source aquifer near a seasonal flow river

• will severely limit waste acceptance criteria to insure protection of groundwater
• evaluating of innovative filter media to trap incidental metals and long-lived radionuclides
• Appropriateness of a RCRA Subtitle "C" disposal cell

• Must provide ability to expand or place new cell(s) due to high inventory uncertainty

Previous studies at the INEEL have also addressed treatment alternatives for the CERCLA soils and debris concluding in the following:

• RCRA characteristic treatment will be required which is large cost driver
• Radioactive soil physical separation may be effective, cost effectiveness has not been demonstrated at the INEEL. Currently the INEEL is participating in an Technology Deployment Initiative (TDI) to determine this.
• Appears to be more cost effective to provide more disposal space than to treat radionuclide contaminated soil based on life cycle analysis. However, TDI is needed to verify this.

The proposed operational cycle for the consolidated soil repository is somewhat unique at the INEEL, specifically:

• Semi-active for four years, but will remain open for more than ten years as remediation progresses
• Various operational campaigns will be required to coincide with the various WAG remediation schedules and facility operation interfaces
• Operation of the disposal facility may be appropriate for "self operated" remediation contracts at various point in the life cycle.

The use of these new consolidated disposal facilities would offer the following advantages:

• Reduced overall footprint of disposal facilities when compared to the WAG specific option
• Decreased O&M costs associated with a single contiguous disposal facility when compared to the WAG specific option
• Significant cost reduction by economies of scale (i.e., large disposal operation instead of small individual site actions)
• Accelerate clean up by providing ready disposal capacity when funds are available

1. Lockheed Martin Idaho Technologies Company, "Comprehensive Remedial Investigation/Feasibility Study for the Idaho Chemical Processing Plant Operable Unit 3-13 at the INEEL-Part B, Feasibility Report," U.S. Department of Energy-Idaho Operations Office, DOE/ID-10572, (1997).
2. United States National Defense Authorization Act for Fiscal Year 1993, Section 3161, Department of Energy's Worker and Community Transition Program, Public Law 102-484, October 23, 1992.

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