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_." _' '-'Il .... ~,t..;.~'"' works. As future contracts are awarded, the additional landa both for construction and recreation will be acquired. Meanwhile, private landowners in the vicinity of Twin Lakes have been advised that they may improve their sanitation facilities and, should they do so, will be compensated if the Government acquires their property. . 6. Isaue: A further water quality problem may have been overlooked in regard to the "glacial flour" deposited in Twin Lakes. Much of this reportedly waa stirred up during road building and a potential ecological accident may be in the making when two pumping units further atir up the "glacial flour" deposits resulting in potential disruption of natural thermal stratification in the lakes upon which the biological cycles are so critically dependent. Raised by: Name Representing Edwin Herrick National Wildlife Federation Response: The Bureau has conducted a preliainary inveatigation of Twin Lakes pertinent to the construction features, possible turbidity during construction, operation of Mt. Elbert Pumped-Storage Powerplant, and whether the enlargement of Twin Lakes Dam will affect fisheries and spawning areas. Thia report "Preliminary Reaults of Turbidity Studies - Twin Lakes Dam, Ht. Elbert Pumped-Storage Powerplant," dated May 1973, found that the thickness of the unconsolidated silt in the natural channel (between the two lakes) ranged from 5.2 feet to 42.4 feet with the thicker material toward the center of the lake or the deeper portion; ln the tail'd~~ q~~~, th~ ~!1t. thickness ranges from 9.4 feet to 31. 5 feet. . It was found advisable to achedule further investigations to define the extent of the soft material, both in the powerplant tailrace channel as well as other areas of the lake. preaently the Bureau is conducting model studies of Twin Lakes and Mt. Elbert Pumped-Storage Powerplant inlet-outlet channel to determine ita location and proper design. These studies have shown that power- plant operations will cause a fluctuation of 1 to 2 feet in the lake level. When summer stratification is present, the operation will cause a 10 C rise in temperature, resulting in an adjustment in the level of the metalimnion. However, the investigations indicate that destrati- fication will not result from this operation. With the hypolimnion to cushion the powerplant jet, the glacial flour should not be disturbed. . XI-487