The following discussion about the erosion-control and flood-control facility features is based on the committee's examination and analyses of (1) available design documentation, including appropriate license application materials; (2) summary reports and materials provided by both opponents and proponents of the project; (3) written information provided during the two NAS/NRC committee meetings in Needles in July and August/September, 1994; (4) field visits to the facility site and to nearby I-40 drainage facilities in July and August, 1994; and (5) other relevant scientific references.


Location and general description of the Ward Valley low-level radioactive waste (LLRW) disposal facility has been presented in Chapter 2. A detailed description of the major elements of the proposed LLRW facility which involve engineered flood and erosion control facilities follows.

Radiological Control Area Facilities

General Trench Area Design

The proposed Radiological Control Area consists of a 5321 m by 532 m (approximately 28 hectares) area surrounded by a 0.9 m to 1.5 m high flood protection berm and an electrified security fence, within which near surface LLRW disposal operations will take place in a series of five progressively developed trenches. Four unlined Class A waste trenches and one unlined Class B/C trench are planned and are illustrated in Figures 7.1, 7.2, and 7.3 (U.S. Ecology, 1990).

A planned buffer zone will extend 122 m around the perimeter of the fenced control area for carrying out environmental monitoring activities, maneuvering construction equipment, and allowing corrective actions to be implemented.

The base of the Class A trenches will be 18 m below the natural surface, and the Class B/C trench will be 13 m deep to eliminate any potential lateral flow from the bottoms of the Class A trenches into the B/C trench. All waste will be buffed up to 6.1 m below the original ground surface and beneath the deepest projected scouting action predicted by a Probable Maximum Flood (PMF).

The four Class A trenches are about 470 m long by 88 m wide at final grade and 34 m wide at the bottom. The interior side slopes of these trenches are a ratio of 1.5 horizontal (H) to 1 vertical (V) (1.5H:1V). A 12 m wide space at the surface separates each completed


All conversions from English system (feet/pounds) to metric (meters/grams) have been rounded to two significant figures. See conversion table in Appendix C.

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