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<br />... <br />00 <br />c;o <br />N <br />c <br />c were taken. First, the number of known sites within the Phase B study area <br />were identified. .This information was compared with data from other nearby <br />CAP-related studies. Based on the number of sites known, an estimate was <br />made to determine the total number of archeological sites that could be <br />affected. Using this process it is estimated that five sites per square <br />mile would be affected. The East Side Plan is predicted to impact a fewer <br />number of cultural resource sites than the West Side Plan based on the <br />number of acres disturbed. However, while the number of sites on the east <br />side of the Tucson Mountains is expected to be less than on the west side, <br />individual sites may be of greater size and significance. <br /> <br />A cultural resource mitigation plan will be developed for the proposed ac- <br />tion, The Bureau will consult with the Advisory Council on Historic Preser- <br />vat i on and the Arizona State Hi storic Preservation Officer regardi ng the <br />disposition of significant properties that may be affected by construction. <br />This consultation will meet the requirements of the National Historic Pres- <br />ervation Act as aMmended (Public Law 89-665). <br /> <br />Geology <br /> <br />The Avra Valley and Tucson Basins contain ground-water reserves which pro- <br />vide all of the available water supplies in the study area. These ground- <br />water supplies have been used in excess of the available recharge causing <br />a drop in ground-water levels. As ground-water levels drop, the sediments <br />of the alluvial basins subside and cracks called earth fissures form in the <br />sediments along the basin margins. The potential exists for subsidence and <br />earth fissures along the Santa Cruz River northwest and south of Tucson. <br />Earth fissures have been reported in Avra Valley and subsidence is suspect- <br />ed. <br /> <br />Where the Tucson Aqueduct must cross these areas, appropri ate means wi 11 <br />be taken to insure aqueduct integrity. These means may include special <br />aqueduct designs, reinforced canal linings, additional water control struc- <br />tures, and water level monitors to indicate an unexpected change in water <br /> <br />10 <br />