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CEE111_Midterm_Exam_W10_Solution

CEE111_Midterm_Exam_W10_Solution - SOLUTION CEE 111 Midterm...

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SOLUTION CEE 111 Midterm Exam Winter 2010 February 17, 2010 Closed Book, Closed Notes Instructions: Answer all questions in the space provided. Show all work. Justify your answers . Problem 1. (20 total points) A city is growing in population and the public works department projects the need for an increased water supply. The current water supply is drawn from a reservoir on a local stream and is of good quality, but future sources—ones to be tapped next—have various problems. Water from a nearby aquifer is available in adequate supply, but its hardness level is too high unless it is either blended with a lower hardness source or chemically treated—chemical treatment can reduce the hardness level by 50%, but is also costly. The total pounds of hardness per million gallons is limited to 1,200 (lb/mg) in the final blended supply. Water from a distant stream is of sufficient quality, but a pipeline would have to be built to convey it, and the cost to pump the water to the water treatment plant is quite high. The costs to obtain water in dollars per million gallons ($/mgd), the supply limits in millions of gallons per day (mgd), and the hardness in pounds per million gallons (lb/mg) for each of the three sources—reservoir (source 1), aquifer (source 2), and distant stream (source 3)—are shown in Table 1. Table 1 Source Property Reservoir (Source 1) Aquifer (Source 2) Stream (Source 3) Untreated Treated Supply limit (mgd) 25 120 100 Hardness (lb/mgd) 200 2300 1150 70 Cost ($/mgd) 500 1,000 2,000 2,000
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