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. , 014:) material is satisfactory from permeability and strength standpoints, and that adequate supplies exist. As regards the proposed sandy soil to be used in the shells of the dam, it ap- pears to be satisfactory from general strength and permeability standpoints, but, be- cause it is probably brittle when compacted and easily eroded by seepage, it should be isolated from any seepage exiting from the core or the foundation, by provision of a multi-layered filter and drain zone. Tn particular, the drain layer should be specified to be washed, highly pervious gravel. We understand that USBR favors this modifica- tion of the feasibility design, but it places a further burden on locating a suitable and economic source of gravel. As further regards the sandy soil borrow, we would be strongly opposed, as a policy matter, to lltilizing any portion of proposed Borrow Area X, because it lies im- mediately upstream from the right abutment area of the dam which has been questioned regarding safety and stability under flood level seepage conditions. It would seem to be inviting underseepage problems if existing, semi-pervious, soil deposits were allowed to be stripped from Area X. Tn regard to the search for gravels, we have examined the available data on test pits in the broad river bottom area upstream from the dam. Those data, showing a gravel content in the river alluvium of 5 to 28% suggest that dredging and processing the river sands may be feasible and economical. It seems possible that about 1,000,000 cy of clean gravel ranging between! in. and I! in. in diameter could be obtained by dredging about 5, ODD, 000 cy of alluvium. The minus! in. would be used as compacted shell fill. Coarse gravels, probably desired for both drain material and concrete ag- gregate, would stilI have to be imported. 6. Embankment Design . a. Left Abutment and Riverbed. The feasibility design, with the pro- posed modification which would incorporate an inclined, multi-layer, filtered drain, located between core and downstream shell and between downstream shell and founda- tion, is acceptable. b. Ri!l:ht Abutment - Slurrv Trench Reach. The feasibility design, 15.