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4 Acoustics <br /> The site is a relatively flat valley floor. Where the rural <br /> character predominates, the ambient sound pressure level <br /> ranges between 40 and 45 dB (A) , equivalent to that expected <br /> in an average residence with minimum street noise. <br /> The ambient sound pressure level increases near U.S . 36 , <br /> near the residential area to the west, and near Colorado 93 <br /> at the southwest, where the influence of traffic, an elementary <br /> school and residential sounds create an ambient level of <br /> 50 to 55 dB (A) . <br /> • A berm constructed east of the Tantra subdivision acts as <br /> a noise and visual barrier between these residences and the <br /> proposed mining area. <br /> History and Archaeology <br /> Before settlement occurred in the Boulder area, the Arapahoe <br /> and Ute Indians lived in the region. Kiowa, Comanches , <br /> Cheyennes and Sioux passed through what is now Boulder County <br /> on hunting and trading expeditions. Deer, antelope and <br /> elk were plentiful and the Arapahoes shared their hunting <br /> lands, and techniques, with the white settlers who came to <br /> the territory in the 1850 ' s. Most of this activity took <br /> place north and east of what is now the City of Boulder, <br /> although wandering bands of hunters and trappers likely <br /> A-11: <br />