Electrical Power for Valdez and the Copper River Basin-1981

25. ~e str?ngly recOTmend that an alternate disposal site and methods be1nvest1gated. It appears from the photo on page ii that a benchne~r the portal could serve as a disposal area. Re~egetation ofth1S area would be much easier than the cliff. In addition, if ahaul roa? could safely be constructed down the most gentle slope,the ta111ngs could represent a source of fill or ballast.WATER TEMPERATUR~MITIGATION6. We note that the rationale behind the two tailrace system is todi~ert win~er powerhouse releases directly to Port Valdez, therebynot affect1ng water temperature 1n All1son Creek d~ring salmon egg1ncubat1on. ,However, the most critical months, because of spawningsalmon, are uuly and August. The lake tap would sUbstantially lowerwater Lemperature~ at the time of spawning, thereby delayingdevelopment. It 1S not clear what flow regimes will occur in thestream channel be~ow the powerhouse during these critical months.What proport10n or the total flow would originate from to thepowerhouse ve~sus the natural channel and what temceratures could beexpected? What provisions will be made fort low water years?t;PRESSURE REDUCING TuRBINE i!7.8.The feasibili~y stud~ for the pressure reducing turbine states thatone.of 1ts pr1mary d1sadvantages is that "it would only functionunt1l the 011 runs out." It would appear that once the oil Goes runout, the refinery and most otner economic activity dependent JPonthe oil resource will .also cease. The PRT would then supply energyf?r the 11fe ?f the p1pellne and woula efficiently cease just at thet1me wnen 1t 1S no longer needed. An explanation of why this isseen as a disadvantage should be included ~n future reports.WATER (JUALITYIA lake level fluctuation of 100 feet could ~ause sUDstantial erosionof eX1st1ng Deltas and the lake shore. Tht effects of sedimentreaistribution can be deleterious because of the excessiveresusoension of sediments into the water column. This increasedturbidity could result in adverse fish impacts downstream from thepowerhouse: ~hes;, impacts are briefly mentioned but not adequatelyd1scussed 1n .he C1S sect10n. Future reoorts should discuss :hePOSS1~111ty of clogging the intake with sediment, expected levels ofd1ssolve~ oxyqe~: the cegre~ of fisheries aegradctior: resulting from1ncreas~~ rurD1D1ty anc sed1mentat10n, and possible mitigationr::c-~sti!'es •5. The text has been revised for clarification. Refer to section D.2.a. ofthe FEIS. Alternative disposal sites have been investigated andeliminated mainly due to engineering constraints. Although a bench may beinterpreted from the photo in the Feasibility Report, that area is steepand would require extensive diking to contain the tailings. It is theopinion of the biologists who have visited the site that the proposeddisposal area is the least environmentally damaging alternative.6.7.8.As stated in the DEIS and FEIS, 40C temperature was employed as a worsecase basis because of the lack of specific data at Allison Lake for thistime period. Temperature data from similar Alaskan lakes indicate thattemperatures at the depth of the lake tap would probably be 2 to 30Chigher. Tables 2 Band 3 of Appendix E are calculated flows of bothpowerhouse discharge and the contribution of the watershed below thelake. Estimated percentages of the regulated water from the tailrace are33 percent for July and 40 percent for August of the total Allison Creekflow. When actual intake temperatures are obtained for Allison Lakeduring July and August, provisions to refine the mitigative measures wouldbe employed."Although the stUdy area may enter an economic slump when the ofl isdepleted, the extent and long tenn effects are impossible to assess. Itis probable that if the pipeline did cease to operate for lack of oil, therefinery would remain open and receive oil from elsewhere. Even if loadsdropped significantly. additional energy would be needed above SolomonGulch's output. This would have to come from other sources, most likelydiesel or possibly a railbelt intertie. In either case the cost would behigher than the PRT.Text has been revised fer clarification. The shoreline of Allison Lake iscomposed mainly of large boulders with little fine grain materjal presentexcept for the delta at the head of the lake. Although the erOSionpossibilities of this delta are unknown, the Alaska District believes itwould react similarly to the delta at Long Lake near Juneau. Long Lake isa glacial fed lake of similar configuration to Allison Lake. The lake wastapped for hydroelectric power generation several years ago and the AlaskaDepartment of Fish and G~€ has established a hatchery in its tailrace.Water quality parameters are monitored regularly and no degradation hasoccurred. The shoreline has not experienced erosion and the deltaunderwent a change in slope and stablized after the first year.