Barrier Technologies for Environmental Management Summary of a Workshop (1997) / Chapter Skim
Currently Skimming:
Ecology, Design, and Long-Term Performance of Surface Barriers: Applications at a Uranium Mill Tailings Site
Ecology, Design, and Long-Term Performance of Surface Barriers: Applications at a Uranium Mill Tailings Site
Pages 54-67
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 54... ...
. Engineered surface barriers or covers for tailings repositories typically consist of compacted soil layers, sand drains, and rock riprap intended to function as physical barriers to radon releases, water infiltration, and erosion (USDOE, 1989)
|
From page 55... ...
Our goal was to design a cover that will improve rather than degrade over the long term as inevitable natural processes act on the repository. We summarize contaminant release mechanisms at uranium mill tailings repositories and then compare the design and intended functional performance of the Monticello cover with conventional RCRA and UMTRCA covers.
|
From page 56... ...
Desiccation and frost cracking may lead to increased permeability and gas diffusion in compacted soil layers within the frost zone (Kim and Daniel, 19921. Frost heaving may also cause distinct engineered soil layers to become mixed, thereby disrupting the integrity of critical layer interfaces (Bjornstad and Teel, 19931.
|
From page 57... ...
The Monticello cover design for controlling water infiltration is essentially an MTG RCRA design (sand drainage layer, geomembrane, and compacted soil layer) but with a thicker topsoil layer.
|
From page 58... ...
, the capillary barrier limits downward water movement and increases the water storage capacity of the topsoil layer because high tensions (suction) in the small pores of the topsoil impede movement of water into the larger pores of the underlying sand layer.
|
From page 59... ...
Preliminary results corroborate results of the previous studies. For the next generation of DOE cover designs, a water-balance system without redundant geomembranes and compacted soil layers may be adequate to control water infiltration at arid and semiarid sites.
|
From page 60... ...
Frost Protection The 170-cm composite topsoil layer (Figure 1) provides more than adequate depth to isolate the capillary break layer, drainage layer, geomembrane, and compacted soil layer (radon/infiltration barrier)
|
From page 61... ...
The composite topsoil layer thickness is also the primary barrier to burrowing; it exceeds the maximum burrow depths of most vertebrates at Monticello. The 30-cm layer of native pediment gravel within the composite topsoil layer is an added deterrent.
|
From page 62... ...
In contrast, the DOE design for the Monticello cover relies on natural processes to isolate tailings and to control the release of contaminants and is expected to improve over time. The Monticello design should be considered as an alternative to RCRA Subtitle C and UMTRCA designs at other arid and semiarid sites: - Compacted soil layers, as required for RCRA and UMTRCA designs to control water infiltration, are vulnerable to damage by desiccation and biointrusion.
|
From page 63... ...
Results of small-scale field tests and numerical modeling suggest that the water-balance cover will satisfy perfo~ance standards for water infiltration and radon releases without the engineered barriers. · Field monitoring of water balance, erosion, and biointrusion are needed to evaluate the performance of the Monticello design under realistic conditions, before the design is used at other sites without the redundant engineered barriers.
|
From page 64... ...
Pp. 273-282 in Proceedings of Seventh Symposium on Management of Uranium Mill Tailings, Low-Level Waste, and Hazardous Waste, Colorado State University, Ft.
|
From page 65... ...
In Proceedings of the Seventh Symposium on Management of Uranium Mill Tailings, Low-Level Waste, and Hazardous Waste, Colorado State University, Ft. Collins.
|
From page 66... ...
1989. Calculation of Radon Flux Attenuation by Earthen Uranium Mill Tailings Covers, Regulatory Guide 3.64 (Task WM 503-4~.
|
From page 67... ...
1993. The Development of Permanent isolation Surface Barriers: Hanford Site, Richiand, Washington, U.S.A., WHC-SA-1799-FP, Westinghouse Hanford Company, RichIand, Wash.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.