Geology 



Libby Dam and the proposed reregulating dainsite are located on a geologic area 

 known as the Wallace Formation. The main constituents of this formation are calcar- 

 eous and dolomitic limestone. 



Pleistocene ice was up to 4,000 feet thick in this region and today glacial 

 sediments form the bulk of soil overburden. The Corps believes that these glacial 

 deposits are rather constant and undisturbed and has stated that there has been 

 little tectonic activity since the last glacial advance, some 10,000 years ago. The 

 Corps has concluded that major faults in the area are inactive. 



One of the major faults, the Thompson Lakes Fault, is under the west side of the 

 proposed reregulating damsite, according to one reconnaissance level study. However, 

 according to the Corps, the fault lies 1,500 feet east of the east riverbank, but has 

 two branches under the proposed damsite. 



The U.S. Department of Commerce has categorized the area as a "moderate damage 

 earthquake potential zone", but much of the western United States is similarly cate- 

 gorized. 



Dr. Richard Konizeski of the University of Montana contends that the Corps 

 should have collected microearthquake data for one year before filling Lake Koocanusa 

 (a microearthquake is one that registers less than 3.5 on the Richter scale). He 

 further contends that a strong correlation exists between the filling of certain large 

 reservoirs and the increased potential for earthquakes. While seismologist are gen- 

 erally not willing to accept the latter contention, they agree that seismologic data 

 should be gathered before, during and after a large reservoir is formed. 



The Corps has recently installed three stations that record microseismic activity 

 in the Libby area. The greatest earthquake recorded within a seismologically signif- 

 icant radius of the proposed damsite registered 5.4 and was 20 to 30 miles southeast 

 of Libby Dam. For this reason, the proposed reregulating dam has been designed to 

 withstand a probable maximum earthquake of 5.5, within I'i to 14 miles of the damsite. 



Reserving Power Generated From Libby Dam for Montana 



Two major hydroelectric dams have been federally funded and constructed in 

 Montana--Hungry Horse Dam on the South Fork of the Flathead River and Libby Dam. 



The records are clear and it has been established tfirough both public law and 

 Congressional intent that Montana should receive geographical power preference for 

 the sale and distribution of energy produced by federal hydroelectric projects with- 

 in Montana. 



The preference to which Montana consumers are entitled in the sale of energy 

 produced by the Hungry Horse Project was clearly implied in legislation which author- 

 ized the construction of the project. That legislation (Public Law 329) declared 

 the purpose of the Hungry Horse Project to be: 



...irrigation and reclamation of arid lands, for controlling floods, 

 improving navigation, regulating the flow of the South Fork of the 

 Flathead River, for the generation of electric energy, and for other 

 beneficial uses, primarily in Montana but also in downstream areas 

 ..." (emphasis added) 



Other BPA and Congressional records are replete with reference to Montana's pre- 



11 



