Question

A consulting engineer has been engaged to advise a town how best to proceed with the construction of a 200,000 water supply reservoir. Since only 120,000 of storage will be required for the next 25 years, an alternative to building the full capacity now is to build the reservoir in two stages. Initially, the reservoir could be built with 120,000 of capacity and then, 25 years hence, the additional 80,000 of capacity could be added by increasing the height of the reservoir. Estimated costs are as follows construction cost, and annual maintenance cost, build in 2 stages first stage 120,000 reservoir $14'200,000 $75,000; second stage add 80,000 of capacity $120600,000 and $25,000 additional construction cost build in full capacity now 200,000 reservoir $22'400,000 and $100,000 if the interest is computed at 4%, which construction plan is preferred?

Answer 1

Answer:

Single stage construction

PW of Cost = $22,400,000 + 100,000(P/A, 4%, 25)

PW of Cost = $22,400,000 + 100,000(15.622)

PW of Cost = $22,400,000 + $1,562,200

PW of Cost = $23,962,200

Tow stage construction

PW of cots = $14,200,000 + $75,000(P/A, 4%, 25) + $12,600,000(P/F, 4%, 25)

PW of cost = $14,200,000 + $75,000(15.622) + $12,600,000(0.3751)

PW of cost = $14,200,000 + $1,171,650 + $4,726,260

PW of cost = $20,097,910

Conclusion: We should choose two stage construction as it has lesser Present worth of cost.