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. ,e 0415 pump-turhin~-motor-generator unit and preparatory work necessary to accommodat~ the second unit at a later date will be accomplished dur- ing initial construction. Congressional authorization for the sccond unit' is required before it can be purchased and installed. The powerplant structure will be the equivalent of a 15-stcry concrete building in height with only the top floor exposed above ground level as seen from the relocated Highway 82. About 1,550,000 cubic yards of material will be excavated for the powerplant structure, tailrace and lower penstocko All of these materials will be utilized later for backfill around the powerplant, lower penstock and for landscaping and leveling the construction and aggregate borrow areas. In addition, about 1,160,000 cubic yards of material will be excavated from the inlet channel, gate shaft and upper portion of thf' penstock. It is anticipated that these material~ will be utilized in the subsequent construction of the forebay dam and blanket for the forebay reservoir. Operation of Mt. Elbert Pumped-Storage Powerplant Hours of Operation.--The Mto Elbert Pumped-Storage Powerplant will normally generate power during the hours from 8:00 a.m. to 10:00 p.rr., but may generate at any time when there is a need for reserve capacity on the inter- connected power system. Pumping will ge"erally occur' from 10: 00 p. m to 8:00 a.m. and on the weekend" Fluctuation of Twin Lakes from Powerplant Oper~tion.--The existing Twin Lakes is an irrigation storage reservoir subject to ~ec:.sonal operational fluctuations with a maximuffi variation of 30 feet. With the proposed project, seasonal fluctuations \o1ill be somewhat modified with a maximum variation of 40 feet. However, fluctuation of the water' surface in any one year will usually be considerably less than this with the a,-"rage of annual fluctuations estimated to be about 18 feet, The highest water levels will usually oCCUr following spring runofi in June, July or August. The water level will usually d8cline from August to December; then remain fairly steady at a lOH lev'?: lll1til the next spring runoff in April or May. In very wet or dry years, the water surface may remain near the maximum or minir.um levels for all or most of the year. Intermi ttent pOllfr production and pumping will aiso cause daily and weekly fluctuatiolis. The mos t pronounced changes due to powerplant operation \01 ill occur when Twin Lakes is near the minimum storage level 'Illere t,,~ '-',',ipaci ty per foot of water level is lO\o1esto Weekly c~;dnges of 'later surface of up to 4 or 5 feet would be norma} ,lith daily changes of 2 to 4 feet super- imposed on this fluctuation 0 Also releases of water for downstream use may cause fluctuations in excess of the above described fluctuations due to powerp!.ant operation. 2