§ 70-342. Design standards.

(a)

Reference. The developer shall comply with the applicable regulations established by the state department of environmental protection. Additionally, the criteria provided in chapter 30, Sewage Pumping Stations, of the Ten State Standards-Recommended Standards for Sewage Works, and WEF Manual of Practice No. 9, may generally be utilized as design guidelines, if not in conflict with state, county, city, or other regulatory agency requirements. See typical submersible lift station design drawing in division 9 of this article.

(b)

Design flows. Sewage pumping stations shall be designed for the total ultimate development flow from all contributory areas. The design average daily flow shall be computed at the unit rates set forth under division 5 of this article. The maximum required pumping capability shall be the product of selected peak factors times the accumulative average daily flow (ADF) from the total service area. In general, the following factors shall be applicable for the range of flow contributions indicated (million gallons per day average daily flow: MGD - ADF), unless larger values are required or smaller amounts are justified, with prior approval from the city.

Flow Range	Peak Factor
0.00 to 0.05 MGD-ADF	3.5 to 4.0
0.05 to 0.25 MGD-ADF	3.0
0.25 to 2.00 MGD-ADFF	2.5

 

Note: Special analysis shall be made for flows beyond 2.00 MGD-ADF and peak factors less than 2.5.

(c)

Pump selection.

(1)

For pumping stations with a maximum flow demand of 1,000 gallons per minute (GPM) or less, a minimum of two pump units shall be provided. Where the peak design flow exceeds 1,000 GPM, three or more units shall be included in the facility (with two operating to meet maximum demand and one on standby).

(2)

The selected sewage pump system shall have the minimum capability of pumping the design peak flow at the maximum computed system total dynamic head (TDH) requirements.

(3)

Head-capacity curves shall be prepared for the proposed pumping system in order to determine the various operational conditions. Hydraulic computations shall be in accordance with good engineering practice, with pipe friction loss calculated by the Hazen-Williams Formula, using standard friction factors based on the materials utilized.

(d)

Wet well design.

(1)

The wet well structure shall provide a minimum capacity between operational water levels sufficient to allow a minimum of five minutes between successive starts of the pumps, when the effluent rate is one-half the maximum one-pump capacity. Low water levels shall provide adequate submergence to preclude pump inlet vortexing, air binding or other design considerations. Operational maximum high water levels shall not exceed the invert elevation of the lowest influent pipe, with high water alarm no higher than the 0.8 of such pipe. A minimum size hopper bottom shall be provided, with the wet well floor sloping to such bottom at a slope of not less than one to one. Additionally, where the wet well extends below the groundwater table, the structure shall be designed to eliminate any possibility of flotation.

(2)

Odor control shall be provided as required and specified by the city utility department for remote stations and/or areas of low flow.

(3)

All capital lift stations shall be provided with a cast-in-place HDPE liner.

(e)

Station water system (nonpotable). All sewage pumping stations shall be provided with a station water system, with adequate capacity and pressure, for washdown or other requirements. Such supply shall be completely separated from the potable supply by use of reduced pressure type backflow preventors or other city approved protective systems. Backflow devices shall be tested by a certified tester within five days of installation, with written results provided to the city.

(f)

Emergency power provisions; generators and emergency power connections. It is in the best interests of the public to maintain uninterrupted wastewater flow even during periods of commercial power outages. Therefore, any newly constructed lift station shall be provided with an on-site standby, diesel power generator and automatic transfer switch. Such generator shall be capable of operating the station at peak flows (i.e., with all equipment operating). The generator shall be enclosed within a weatherproof, locking enclosure and shall have a base mounted, dual-walled fuel tank with sufficient capacity to operate the station for three days, based upon anticipated flow rates. The fuel tank shall be equipped with a leak detector and alarm. All generator sizing calculations shall be submitted to the city engineer for review and approval prior to the contractor ordering the generator set.

(g)

Sewage pumps, motors, and standby generators.

(1)

Pumping units. Sewage pumping units shall be capable of handling raw, unscreened sewage and shall be capable of passing a sphere of at least three inches in diameter. Pumps shall be electric motor driven and of a proven design that has been in sewage service under similar conditions for at least five years. Pumps shall provide the required peak design performance requirements and be suitable for operation within the total hydraulic range of operation. See drawing in division 9 of this article. Pumps and controls shall be as manufactured by Hydromatic, FLYGT, or Fairbanks Morse.

(2)

Pump motors. Pump motors should be nonoverloading, excluding service factor, throughout the entire operating range of the pumps. Two or more normally closed heat sensing miniature switches connected in series and embedded within the motor windings shall be provided to shut off power and initiate alarm light for motor over-temperature condition. See drawing in division 9 of this article.

(3)

Pump controls. Each pumping station control system shall include a liquid level controller which shall sense the sewage level in the wet well and provide appropriate signals to the logic circuits to produce the required mode of operation for the pumping facilities. Capability shall be provided for manual start-stop control for all pumping units, as well as the normal automatic control from the liquid level sensing and logic circuits. An automatic alternator with test switch shall change the starting sequence on each pump cycle. A high water level alarm system with flashing light and horn shall be provided. A separate AMP meter for each pump in the wetwell. Each sewage pump shall be provided with an elapsed time meter to indicate individual pump time. Seal failure indicators, thermal shutdown protection, phase monitor, and ground fault interrupt with circuit breaker shall be provided. The submersible station controls shall be housed within an exterior panel, pole-mounted or freestanding enclosure. The panel will be stainless steel of NEMA 3 R, dead front weathertight construction, with hoop and padlock, lightning arrestors and surge protection, exterior alarm light, audible horn and exterior silence button. An allowance of 36 inches separation between wetwell and panel box is required. See drawing in division 9 of this article.

a.

Lift station control/SCADA panel. The lift station control panel shall be a combination lift station and SCADA control system. The combo panel will be a standard design as manufactured by U.S. Filter Control Systems of Vadnais Heights, MN. The panel SCADA information will be added to the WWTP servers to allow communication and control of the lift station. The panel will be shipped fully tested and include complete control panel, logic controller, level transducer, radio, antenna, and antenna cable. Spare parts will include a radio, analog input model, 10ea pilot lit bulbs, 5ea fuses.

Note: If Flygt pumps are submitted the pump distributor shall provide mini cas units or equal to maintain the warranty of the pumps

(4)

Submersible pump facilities. Installation shall include the removable pump units, aluminum access frame and cover, stainless steel pipe pump guide bars, pump discharge connection and other necessary appurtenances. The submersible pumping system and accessories shall be as manufactured by Flygt Corporation, Hydromatic, or Fairbanks Morse. See standard drawing for submersible lift station in division 9 of this article. Also provide a four-inch camlock quick coupling for emergency bypass at pumping stations.

(5)

Factory built facilities. Factory built facilities shall have prior city approval before inclusion in proposed plans.

(6)

On-site standby generator.

(h)

Valves.

(1)

Valve vaults. Valve vaults must be a minimum of six feet by six feet (inside dimension), with no less than 12 inches from the side wall to the valve clearance. The vault must be coated with Inextol epoxy inside and outside with a finish coat of 32 mils. All metal on the inside of the valve vault shall be coated with Inextol epoxy and will also have a finish coat of 32 mils. See drawing in division 9 of this article.

(2)

Valves. All valves used in station valve boxes shall be DeZurik or Clow with 100 percent full flow plug valves. Any valve eight inches or over must be gear operated.

(Pamphlet 9-25-2001, § 7.2; Ord. No. 2017-02 , § 1, 2-7-2017)