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6.20.460 Design calculations.
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The developer shall perform a study and make the determination to assure that the lift station installation is sized to serve the overall sewage flows generated within the potential service area. The flow study shall include the developer’s plat boundary area as well as adjacent and future service areas. The service areas shall be the areas within that which could be served by the installation of the lift station(s).

The station’s design flow capacity shall be based on an average daily per capita flow with related peaking factors and inflow/infiltration allowances.

Documentation of present and future service area flow rates for lift station size and capacity determination shall be provided to the district.

The effects of the minimum flow conditions shall be estimated to be sure that retention of the sewage in the wet well will not create a nuisance and that pumping equipment will not operate too infrequently. The wet well shall be sized to limit pump cycles to a maximum of four cycles per hour per pump, with two pumps alternating at pump design capacity.

Lift station capacity shall meet the maximum rate of flow expected. At least two pumping units shall be provided at each lift station installation. The pump shall have sufficient capacity and capability to efficiently handle the peak design flow with one pump out of service and to ensure a minimum velocity of three feet per second in the force main.

The force main shall be sized for a minimum velocity of three feet per second and a maximum of eight feet per second. The minimum diameter of the force main shall be six inches.

The capacity of the receiving sewer shall exceed the flow expected.

Three copies of the design report shall be submitted to the district for review. As a minimum, the report shall include:

(1) Project description.

(2) Projected flows.

(3) Connection point with downstream capacity.

(4) Wet well sizing.

(5) Run time calculation and cycle time.

(6) Pump station head calculation.

(7) Pump selection.

(8) Force main size, length and material.

(9) Electrical load study.

(10) Generator sizing.

(11) Odor potential calculations.

(12) Wet well buoyancy calculations.

(13) Force main surge calculations.

The design report shall be approved by the district prior to starting the design of the lift station. [Res. 735 § 1, 2017.]

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