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.
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.