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<br />,1~ <br />":::j~/j <br /> <br />-., <br />. /-';' :.~;: <br />....... <br />..~.~:>; <br /> <br />~:~f> <br /> <br />~~. <br />CJl <br />~ <br />..;:~ <br /> <br />CHAPTER I <br /> <br />INTRODUCTION <br /> <br />Background <br />The construction of the Grand Valley unit is scheduled to be completed <br /> <br />in stages. Stage I, which is presently under construction, involves the <br /> <br />concrete lining of a 6.8 mile section of the Government Righline Canal and <br /> <br />the placement in pipe of 29.7 miles of -laterals. Advance planning for the <br /> <br />remainder of the Grand Valley Unit beyond Stage I will be completed during <br /> <br />the construction of Stage I. <br /> <br />All alternatives and increments of alternatives evaluated in the <br /> <br />planning process will be compared in te~ of cost effectiveness. For the <br /> <br />Colorado River Water Quality Improvement Program, cost effectiveness is <br /> <br />defined as the total annual equivalent cost of the alternative or increment <br /> <br />of alternative divided by the the ~/L reduction in total dissolved solids <br /> <br />(TOS) concentration at Imperial Dam. To compute the mg/L effect, the salt <br /> <br />load reduction and depletion of each alternative is calculated. These values <br /> <br />are then inserted into standardized Colorado River Basin equations to <br /> <br />determine the effect at Imperial Dam. <br /> <br />To determine the salt load reduction, internal water and salt budget <br /> <br />models are being developed. These models include precipitation, natural <br /> <br />surface inflow, ground water inflow, irrigation diversions, canal seepage, <br /> <br />lateral seepage, administrative waste, on-farm ditch seepage, consumptive <br /> <br />use, tailwater return flow and ground water return flow. For each of these <br /> <br />flow volumes TOS concentrations and salt losding are either known or <br /> <br />calculated. The values of the many variables in these models are determined <br /> <br />both for pre and post project conditions utilizing field data. Many of these <br /> <br />1-2 <br />