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<br />\., <br />CD <br />~ <br />o <br />..-:> <br />'::) <br /> <br />Chapter I <br /> <br />INTRODUCTION <br /> <br />Colorado community west of the Continental Divide and serves as-the <br />business and economic center of western Colorado. Other comrnu~ities in the <br />valley are Palisade and Clifton to the east of Grand Junction and Fruita, <br />Lorna, and Mack to the west. <br /> <br />Purnose and Need <br /> <br />The purpose of the Unit is to decrease salt loading to the Colorado River. <br />The Unit was authorized for construction by the Colorado River Basin <br />Salinity Control Act of June 24, 1974 (Public Law 93-320). The Colorado <br />River at its headwaters in the mountains of north-central Colorado has a <br />salinity concentration of about 50 milligrams per liter (mgfL). The <br />concentration progressively increases downstream as a result of water <br />diversions and salt contributions from a variety of sources. In 1987, the <br />total dissolved solids (TDS) concentration averaged about 613 mgfL at <br />Imperial Dam (U.S. Department of the Interior, 1989), the last major <br />diversion point of the Colorado River in the United states. Unless control <br />measures are undertaken, the concentrations are expected to increase as the <br />Colorado River Basin States continue to develop their compact-apportioned <br />waters. 1 <br /> <br />The salt loading to the Colorado River from the Unit area is estimated at <br />approximately 580,000 tons annually, which is 7.0 percent of the average <br />annual load at Imperial Dam. The salt loading is attributed to the Mancos <br />Formation, a local geological formation, which underlies the Grand Valley. <br />This formation consists of a sequence of thick beds of gray calcareous <br />marine shale that contains a high percentage of salt. At the land surface, <br />the Mancos Formation exhibits a thin, weathered, and fractured zone that <br />acts as an aquifer which allows water from irrigation system seepage and <br />irrigation deep percolation to dissolve salts from the shale and convey <br />them to natural drainages and ultimately the Colorado River. <br /> <br />Development of the Unit was planned in stages. Stage One, encompassing <br />about 10 percent of the Unit area and completed in April 1983, consisted of <br />the concrete lining of 6.8 miles of canal, consolidating 34.2 miles of open <br />laterals into 29.7 miles of pipe, and installing an automated moss and <br />debris removal structure. The stage One area is designated by the cross <br />hatching on the Frontispiece Map. The Stage Two area involves most of the <br />remainder of the valley outside the Stage One area. The Price and Stubb <br />Ditches are in the Stage Two area. Stage Two construction began in 1986 <br />and 8 miles of canal and 60 miles of laterals have been improved. <br /> <br />Relationship with Other proiects (SCS) <br /> <br />To accomplish salt reduction, Reclamation and the u.s. Department of <br />Agriculture's Soil Conservation Service (SCS) are conducting a two-segment <br />program. Reclamation is directing the off-farm canal and lateral <br />improvement program, while the SCS is conducting the on-farm improvement <br />segment which consists of upgrading farm irrigation systems and improving <br />irrigation management. The on-farm salinity control program of the u.s. <br />Department of Agriculture is not dependent on the activities of <br />Reclamation. <br /> <br />1 The waters of the Colorado River are divided by the Colorado River <br />Compact of 1922, agreed on by the seven Colorado River 8asin States <br />(Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming). <br /> <br />2 <br />