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<br />OG?511- <br /> <br />Operation studies indicate that the increase in Well ton-Mohawk <br />bypass related to the Yuma delivery will vary depending upon the <br />salinity conditions in the river. To be provided desalted water <br />of up to about 50 Mgaljd (38,000 acre-feet per year), the City <br />would need to release a like amount of Colorado River water plus <br />up to 10 percent of the quantity delivered. For example, for <br />38,000 acre-feet of desalted water the city would release up to <br />41,800 acre-feet of Colorado River water. <br /> <br />To provide Desalting Plant capacity greater than 50 Mgaljd the <br />amount of additional release required would increase gradually up <br />to a maximum of about 14 percent of the amount delivered. <br /> <br />Years When Reverse osmosis Plant Is Not Being Used. <br />During years of excess flows, the Desalting Plant would not <br />normally be operating. The operating costs for using a portion <br />of the Reverse Osmosis System to provide desalted water to the <br />City would be excessive. While the pretreatment facilities of <br />the Desalting Plant are comparable to a normal municipal water <br />treatment plant, the water quality of the pretreated Wellton- <br />Mohawk return flow (2700 pjm) is unacceptable. <br /> <br />Colorado River water normally has a salinity level of between 700 <br />pjm and 880 pjm and is currently used as the City's supply <br />source. To reduce the operating costs, and provide acceptable <br />quality water an intake could be constructed that would allow <br />Colorado River water to be diverted into the pretreatment <br />facilities of the Desalting Plant. Following pretreatment, the ~ <br />treated water would be of potable quality and could be provided <br />directly to the City at a cost comparable to current city <br />treatment costs. <br /> <br />Years When Reverse Osmosis Plant is partially Being Used. <br />During years of partial operation, desalted Wellton-Mohawk return <br />flow or pretreated Colorado River water or a mix of both sources <br />could be provided to the City. with minor modifications the <br />three SCR's and the gravity filters will have some flexibility in <br />isolating the two water sources. One or two of the SCR's could <br />be providing treated Colorado River water for the city while the <br />remaining SCR's could be providing Wellton-Mohawk return flow for <br />desalting and discharge to the river. <br /> <br />DESIGNS AND ESTIMATES SUMMARY <br /> <br />INTAKE SOURCE OPTIONS <br />To develop the most cost effective proposal three options for <br />diverting Colorado River into the Desalting Plant were evaluated <br />and compared. As described in the Feasibility Design Appendix, <br />these intake sources include: <br /> <br />13 <br />