Page 54 - Water and wastewater engineering

THE DESIGN AND CONSTRUCTION PROCESSES 1-25

The capital cost for each of the membrane alternatives is now estimated to be an
additional $500,000. Is the Membrane A alternative still the best choice? Use the
interest rate and design life from Problem 1-1.

1-3. In the design of a water treatment plant, the design engineer has a choice of selecting
a constant speed pump or a adjustable-frequency drive (AFD) pump. The capital and
operating costs for each pump are shown below. Assume an interest rate of 6.00%
and a 10 year life. Which pump should the engineer recommend?

Option Capital cost Annual electric cost

Constant speed pump $10,000 $16,000
AFD pump $20,000 $10,000

1-4. Using a spreadsheet you have written, by trial and error determine the construction
cost of Alternative B in Table 1-5 that will make its total annual cost equal to the
total annual cost of Alternative A. With the significant figures given, the costs may
be assumed to be “equal” when they are within $1,000 of each other. Note: the
interest during construction and inflation prior to construction used in Table 1-5
was 3.00%.

1-10 DISCUSSION QUESTIONS

1-1. The city engineer has called your firm to ask that you review the design of a sewer
that has had periodic flooding. The design was performed by another consulting firm
in the community. What actions should you take before accepting the job?
1-2. The professional organization that you belong to has been offered the opportunity to
meet in the facilities of a local casino free of charge. As the person in charge of
arrangements, what action would you recommend to the executive committee of your
organization?
1-3. A small community of lakefront homes believes that the algae bloom in their lake is
the result of leaking septic tanks and tile fields. They retained an engineering firm
to explore alternatives for building a collection system and wastewater treatment
plant. An exhaustive feasibility study of alternative wastewater treatment systems
to replace the existing septic tank and tile field system has been completed. The en-
gineering firm has recommended a sewer system and a wastewater treatment plant
to be operated by the community. After the report and recommendation to build has
been accepted by the client, the Department of Natural Resources and county health
department provide a report that declares that the existing system does not contribute
to pollution of the lake and the likely source of pollution is upstream agricultural
runoff. Should the engineering firm pursue the development of a wastewater
treatment system? Explain your reasoning.