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25th Avenue North Stormwater Pump Station Overview
Purpose
The 25th Avenue North Stormwater Pump Station conveys stormwater collected within the 25th Avenue North Basin to the Mississippi River through the flood protection levee.  
Theory of Operation
The Stormwater Pump Station was designed to eliminate sanitary sewer overflow events, and to provide stormwater pumping capacity for the 25th Avenue North Basin including future sewer separation projects within the basin. The stormwater pump station is sized to pump 100 MGD (69,000 gpm), a rate equivalent to the five year design storm for the basin.
Equipment
The 25th Avenue North Stormwater Pump Station includes the following equipment:
  • Stormwater influent (propeller) pumps
  • Stormwater influent pump reduced voltage solid state (RVSS) starters
  • Wet well level monitoring
  • Submersible sump pump
  • Water control gates
  • Outfall level monitoring 
  • Manual bar screen     
  • Gas detector
  • Radio transceiver
  • Emergency engine generator
Description

Stormwater within the basin is collected and conveyed from the City side of the levee to the river side of the levee through a 60 inch steel outfall pipe tunneled through the levee. During normal river elevations water bypasses pumping entering the structure in an 84 inch storm sewer and flows via gravity through the bypass channel as well as an open water control gate (STWG-2) to the Mississippi River. Under high river elevations STWG-2 ("outfall" water control gate) is closed and STWG-1 (“diversion” water control gate) is opened forcing stormwater through the manual bar screen located in the influent channel and down into the wet well. From the wet well water is elevated via four propeller pumps (one redundant) above critical river elevations from 575.00 feet to a water elevation of 600.50 feet (approximately 0.3 feet above levee elevation), creating a head differential and enabling water to flow to the river. Pumps are powered by RVSS starters and operate at a constant speed. The TDH for the pumps consists of static head and discharge headloss. Flow through pump discharge piping results in approximately one foot of headloss for a flow of 33.33 MGD (23,000 gpm) per pump. More information on the hydraulics of the stormwater pump station is presented in the 25th Avenue North Draft Concept Design Memorandum.

The pump station utilizes an Allen Bradley PLC to control the four stormwater pumps. The pump station communicates with the Clinton WWTP through radio transceivers, extending the existing Plant SCADA. There is a transmitter mounted upon the Stormwater Pump Station, a repeater on a cell tower immediately adjacent the Chancy Fire Station, and a receiver at the Beaver Channel Pump Station.

Alliant Energy provides electrical service to the three pump stations located at the 25th Avenue North Location. The pad mounted metering cabinet for all three facilities is located on the west side of the Stormwater Pump Station. Additionally, the location contains two natural gas powered emergency engine generators. Two automatic transfer switches (one for each generator) are housed in the Stormwater Pump Station Electrical Room.

As a remote, unmanned facility, the 25th Avenue North Pump Station is equipped with the following devices to provide alarm notification through SCADA back to the Clinton WWTP:

  1. The wet well high-high and low-low switches are a part of the wet well level indicator and transmitter. The switches send an alarm signal when wet well levels rise above or below a set point. High and low alarms are set at a wet well level of 20 ft (elevation 580.0 ft) and 8.0 ft (elevation 569.0 ft) respectively.
  2. The outfall level element is a submersible type level transmitter that provides outfall shaft elevations which are adjusted to display river level conditions (according to the Fulton gage). The device is set to provide a pre-flood condition warning.  This warning alerts the operator when the "outfall" water control gate (STWG-2) should be closed, and the "diversion" water control gate (STWG-1) should be opened to enable automatic stormwater pumping. High outfall level is currently set at a river stage of 8.7 ft (5 ft AFF).
  3. The wet well sump pump level element is a Multitrode sensing element with a high level alarm that alerts the operator of a sump pump failure (when pump station is otherwise out of service).
  4. Combustible gas detector provides a signal to the PLC based on percent LEL in the Pump Room. Alarms are set at 10% for high LEL and 20% for high-high LEL.
  5. Room temperature transmitter located in the Electrical Room reads the room temperature and sends the data through SCADA to the operator. Alarms are set at 45oFand 90oF.
  6. Intrusion alarms are installed on all doors and hatches of the pump station. These are normally open proximity switches held closed by the door or hatch they are monitoring. Opening the door or hatch activates the alarm.
  7. The waterline temperature switch initiates an alarm in the event of a heat trace failure on the incoming water service line in the Feeder Electrical Vault.
  8. The UPS system for the PLC is equipped with an alarm that will signal the operator of a problem with the UPS or loss of power to the UPS.
  9. The surge protection devices in power panel 10-PP01 and switchboards 10-MSB01 and 10-SB02 are equipped with an alarm, signaling an electrical fault to the operator.

All data, as well as control and alarm signals are transmitted by radio to the Clinton WWTP. Data, control, and alarms can also be viewed locally at the Operator Interface Terminal (OIT) located in the main control panel (10-CP01) on the south wall of the electrical room. Screens at the local OIT and Clinton WWTP are functionally identical.

Stormwater Influent Pumps6
Four stormwater influent pumps are located within the pump room of the 25th Avenue North Stormwater Pump Station and extend into the wet well. The four mixed flow propeller pumps (one redundant) lift stormwater flow up above critical Mississippi River levels and into the discharge channel, where it flows out to the river. All four pumps are operated at a constant speed and controlled by reduced voltage solid state (RVSS) starter. Each pump has a pumping capacity of 33.3 MGD, or 23,000 gpm.

The pumps are only operated during high water conditions.  In the presence of high Mississippi River water elevations, water control gate positioning is manipulated and stormwater flow is permitted to fill the wet well. Pump control is in accordance with liquid level in the wet well as measured by a Multitrode level sensor. Each pump is equipped with a drip-feed oil lubrication system. Oil level in the external pump reservoirs require manual monitoring.
Reduced Voltage Solid State (RVSS) Starters6
  The stormwater influent pumps are equipped with reduced voltage solid state starters which operate the pump motors at a constant speed. The soft start motor starters significantly reduce the in-rush current of the pump motor it is controlling reducing energy consumption and unnecessary stress on the motors.
Wet Well Level Monitoring 6
  The wet well level is monitored by a Multitrode level system. The conductivity level sensor consists of ten conductivity zones along the sensor rod and detects stormwater elevation as the level rises and contacts a probe sensor. A circuit is completed and a signal is sent to the transmitter. The level monitoring system also contains high-high and low-low level switches built in to alert operators of critical conditions in the wet well. A low-low detection in the wet well discontinues stormwater pumping via hardwired interlock. A high-high level in the wet well sends an alarm to the HMIs.
Submersible Sump Pump6
The submersible sump pump located in the SW corner of the Stormwater Pump Station lower level keeps the wet well pumped down when the station is otherwise out of service. A Multitrode sensing element with three sensors sends signals to the pump control panel to operate the sump pump. The lower sensor is the pump stop, the middle is the pump start, and the upper is the high level alarm, indicating a potential sump pump failure.
Stormwater Wet Well Gates6
Two electric actuated, 84 inch stainless steel water control gates are located in the lower level of the Stormwater Pump Station. Travel limit switches indicate gate positioning to the HMIs, but there are no automatic control capabilities. Gates must be manually controlled locally.

Under normal conditions the “outfall” gate located on the north end of the bypass channel is open, permitting stormwater to flow through the channel and out to the river via gravity. The “diversion” gate located on the south end, parallel to the channel is closed, preventing stormwater from entering the wet well. Under high Mississippi River conditions, the “outfall” gate is closed and the “diversion” gate is opened, admitting flow into the wet well to be pumped.

Outfall Level Monitoring6
Level in the Stormwater Pump Station Outfall Channel is adjusted to provide river stage information according to the Fulton gage and is measured by a submersible type level transmitter. Channel level corresponds to Mississippi River water elevation during high river levels. When the outfall level rises above a set point, a pre-flood condition warning issues an alert to the operator, indicating water control gate action is required to enable stormwater pumping.
Manual Bar Screen6
A 21 foot long stainless steel coarse bar screen is located on the upstream end of the Stormwater Pump Station Influent Channel. The purpose of the bar screen is to prevent oversized trash and debris from entering the wet well. The bar screen must be manually cleaned.
Gas Detector6
The gas detector monitors the levels of combustible gases in the Stormwater Pump Station Pump Room. If there is a high concentration of combustible gases detected, an alarm will display at the HMIs, the alarm strobe/horn in the pump room will flash/sound and the ventilation system will come on.
Radio Transceiver6
The three pump stations at the 25th Avenue North location are normally unmanned facilities. Communication with the pump stations is established with radio transceiver equipment. The radio sends pump station operation status information back to the Clinton WWTP and receives control requirements from the remote HMI. In addition, local control of the facility can be accomplished using an Operator Interface Terminal at the main control panel located in the Electrical Room. All the site operation screens will be functionally identical between the HMI and local OIT.
Emergency Engine Generators6
Two natural gas powered emergency engine generators are located between the Stormwater and Sanitary Pump Stations. The two generators serve the location, providing standby power to critical loads in the event of a temporary interruption of the main power supply provided by Alliant Energy. Two automatic transfer switches (one for each generator) are housed in the Stormwater Pump Station Electrical Room and automatically switch operations over to standby power in the event a power outage is detected. A maximum of one stormwater pump and two sanitary pumps will be allowed to run when the pump stations are on emergency power. The control systems are unchanged. It is recommended that the generators are exercised regularly.
 

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Last Updated: 7/5/2018 3:48:20 PM
Version 3.0.1