QUESTION $23$

A new development is planned for a community, but it is in watershed adjacent to the watershed served by the existing wastewater treatment plant. To transport the wastewater to the wastewater treatment plant, a lift station is needed to pump the wastewater over a ridge to an existing interceptor in the existing collection system. The interceptor has sufficient capacity for the estimated $4\mathrm{.}6$ MGD peak flow from the new development.

B$.$ Design the lift station with two pumps. The influent sewer pipe to the lift station has an invert elevation of $1472\mathrm{.}15,$ the top of the lift station has an elevation of $1486\mathrm{.}00,$ the submersible lift station pumps have a minimum submergence of $4$ feet with motors rated for $10$ starts per hour, and the wet well has a diameter of $12$ feet. Set the high$-$water alarm such that backup of the sewer does not occur before an alarm sounds and that it sounds if the pumps cannot keep up with the incoming flow. The design will use float switches for water level sensing$,$ so set $1$ foot minimum between each float level for operation of the pumps. The bottom elevation of the wet well floor then is most nearly:

a$)1458\mathrm{.}49$

b$)1459\mathrm{.}49$

c$)1460\mathrm{.}49$

d$)1461\mathrm{.}49$

d$)1461\mathrm{.}49$

c$)1460\mathrm{.}49$

a$)1458\mathrm{.}49$

b$)1459\mathrm{.}49$