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Appendix G - Detailed Description of Alternative 4: Do>mt-2001-1I
^ Entombment with Internal and Eicternal Waste Disposal Rev. i Draft-B
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2 After placing, grouting, and pouring the topping grout or concrete layer on the third layer of
3 cargo containers, the height from the grout layer to the underside of the canyon roof would be
4 approximately 2 an. This would be too short to allow placement of cargo containers. Rather than
5 fill this large void with grout, placement of waste-filled burial boxes (1.2 an by 1.2 an by 2.4 an
6 long [4 ft by 4 ft by 8 ftj) would be performed. For this final FS report, it is assumed that
7 960 boxes of this size could be placed into a fourth and final layer of waste within the canyon.
8 With tighter packing, the number of boxes placed could be increased to 1,500. Void spaces on
9 the interior of the boxes would be filled with grout prior to placement. As a 6na1 step in
10 placement of waste inside the canyon, holes would be drilled through the canyon roof. Flowable
11 grout would be delivered into the canyon through these holes to fill around the boxes. Pressure
12 grouting would be used to ensure that voids not reached by the flowable grout are filled.
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14 Upon completion of waste placement within 221-U, available space within the facility would be
15 filled with waste and/or grout. The containment provided by grouting the waste inside openings
16 in the canyon would eliminate all large voids. These steps would stabilize 221-U and ready it for
17 placement of the environmental cap.
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19 G.2.23 Install Engineered Fill. As the canyon is filled with waste, engineered fill would be
20 compacted in lifts around the exterior of 221-U. The engineered fill elevation would be
21 maintained within a few mcters of the same level as the grouted wastes within 221-U. This
22 would prevent an excessive load across the canyon walls, including the end walls. The
23 engineered fill would also provide an access ramp to the south end of 221-U for container
24 delivery.
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26 The engineered fill would be clean, compacted granular material, which would be placed in lifts.
27 Its source is assumed to be a Hanford Site borrow pit within 24 km of 221-U. The actual source
28 location has not been identiGed. The volume of engineered Gll for Alternative 4 is approximately
29 1,115,400 m3 (1,458,850 yd3). The extent of the engineered fill and environmental cap is shown
30 in Figure G-1.
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32 The fill would be compacted to a density in the range of 95% to 98% relative compaction where
33 relative compaction is determined by standard proctor (ASTM D698). Final design of the
34 engineered fill would determine the compaction requirements and the material specifications.
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36 G.2.3 Placement of External Waste at 22I-U
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38 Alternative 4 would include an external waste disposal area within the engineered fill that
39 surrounds 221-U. The overall size of the environmental cap for Alternative 4 is assumed to be
40 the same size for Alternative 3 to allow for an equitable comparison of these two alternatives.
41 The waste disposal area is limited to that area of the engineered fill cross section that is protected
42 by the environmental barrier. Further, the size of the disposal area is restricted by constructability.
43 The disposal area would have a dual-liner leachate collection system. For Alternative 4, this
44 liner system Is assumed to have a 3 horizontal to I vertical slope. The cross section shown for
45 the bottom liner (see Figure D-5 in Appendix D) is identical to the dual liner that has been used
Final Feasibility Snidy for the Canyon Disposition lniriarive (22i-U Facility)
1ine 100.1
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