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20th Avenue North Pump Station Overview
Purpose
The 20th Avenue North Pump Station pumps wastewater flows downstream from the 20th Avenue North Basin, in route to the new Clinton wastewater treatment facility. Additionally, new CSO pumps provide pumping capacity during peak wet weather events.
Theory of Operation
The Pump Station replaces the aged existing sanitary (combined) pump station. It includes a new sanitary pumping
station with a firm design capacity of 4.8 mgd, provided by three pumps (i.e. 10 times the future base
sanitary flow). Additionally, the pump station includes new combined sewer overflow (CSO) pumps with a total capacity of 5.2 mgd
provided by two pumps. The sanitary and CSO wet wells are separated by a concrete weir. More information on the design of the 20th Avenue North Pump Station is presented in the 20th Avenue North Concept Design Memorandum. 
Equipment
The 20th Avenue North Pump Station includes the following equipment:
  • Sanitary Influent Pumps
  • Sanitary Influent Pumps Variable Frequency Drives (VFDs)
  • CSO Influent Pumps 
  • CSO Sump Pump
  • Wet Well Level Monitoring 
  • CSO Outfall Level Monitoring  
  • CSO Discharge Sampler
  • Sanitary Flow Monitoring
  • Manual Bar Screen   
  • Radio Transceiver   
  • Emergency Engine Generator 
Description
The cast-in-place structure of the 20 th Avenue North Pump Station consists of an influent channel, valve vault and divided wet well (sanitary/CSO wet wells). This is an underground unit that is controlled and powered from the Pump Station PLC and electrical gear located at grade above the wet well.  The 20th Avenue North Pump Station interacts with the pump station at 25th Avenue North. Flows from both basins are combined in a 20 inch PVC force main downstream of an isolation valve contained in a manhole adjacent the 20th Avenue North Pump Station. Wastewater flows are propelled via pumping from the convergence point to a downstream pumping facility at 1st Avenue.   

Downstream of the existing diversion chamber, wastewater enters the influent channel of the 20 th Avenue North Sanitary Pump Station through a short 36 inch gravity sewer line. The influent channel is the modified wet well of the original Sanitary (Combined) Pump Station. Wastewater passes through the coarse manual bar screen of the influent channel and enters the sanitary pump station wet well through a 36 inch ductile iron pipe. Three submersible non-clog centrifugal influent pumps (one standby), powered by VFDs, propel the wastewater up to the sanitary valve vault. Discharge piping for each pump contains an air/vacuum release valve as well as lever swing check and isolation plug valves. The individual pump discharges connect to a combined header and exit the valve vault, entering a 12 inch PVC force main which transitions to 20 inch at existing SSMH located SW of the pump station site. All flow is metered by a magnetic flow meter in a nearby manhole downstream of the valve vault. Bypass capabilities for isolation of the meter are incorporated.  

Additionally, the pump station includes two submersible non-clog centrifugal CSO influent pumps. The CSO pumps provide capacity for peak wet weather flows. A concrete weir separates the sanitary wet well from the CSO wet well. When capacity of the sanitary pumps is insufficient for the flow demand (e.g. during some wet weather events), the sanitary wet well level will rise and overtop the concrete wall which separates the CSO and sanitary wet wells. The CSO pumps propel the wastewater up to the sanitary valve vault. Discharge piping for each pump contains an air/vacuum release valve as well as lever swing check and isolation plug valves. The individual pump discharges connect to a combined header and exit the valve vault, entering the CSO discharge channel. A measuring weir is located at the downstream end of the channel. The PLC calculates the CSO flow as it overtops this weir based on liquid level in the channel, as recorded by the guided wave type radar level element mounted over the channel. From the discharge channel, CSO flow is conveyed by gravity to a manhole structure and continues to a junction box. It is then directed through a 30 inch interceptor sewer to the Car Barn Ditch, continues by gravity to Joyce's Slough, and then on to the Mississippi River.

The pump station utilizes an Allen Bradley PLC to control the three sanitary and two CSO pumps. The pump station communicates with the Clinton WWTP through radio transceivers extending the existing Plant SCADA. There is a transmitter mounted upon a tower located above the new influent channel (original Sanitary (Combined) 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 pump station located at the 20th Avenue North Location. The pad mounted metering cabinet for the facility is located south of the pump station just outside of the security fence line. Additionally, the location contains a natural gas powered emergency engine generator, along with an automatic transfer switch (housed in the Electrical Room).

As a remote, unmanned facility, the 20th Avenue North Sanitary 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 monitoring system. The switches send an alarm signal when wet well levels rise above or below a set point.
  2. The Valve vault level element is a conductivity type level switch alerting operator of a major leak in the valve vault.
  3. Metering manhole level element is a float switch sending an alarm signal indicating a major leak in the metering manhole.
  4. Intrusion alarm is installed on the electrical room door. This is a normally open proximity switches held closed by the door. Opening the door activates the alarm. A bypass key has been installed to prevent entrance by City of Clinton Staff from activating the alarm. 
  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 45oF and 90oF.
  6. 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.
  7. The surge protection devices in power panel 10-PP01 and 10-MPP01 are equipped with an alarm, signaling an electrical fault to the operator.

All alarm signals are transmitted by radio to the Clinton WWTP. Alarms can also be viewed locally at the Operator Interface Terminal located in the PLC panel (10-CP01) in the Electrical Room.

Sanitary Influent Pumps 6
 
Three sanitary influent pumps are located within the wet well of the 20 th Avenue North Pump Station and convey wastewater flow through a PVC force main to downstream pumping stations. The three submersible, non-clog, centrifugal pumps, (one redundant) have an ultimate design pumping capacity of 4.8 MGD. Each pump includes a quick connect and guide rail system and is centered under an aluminum floor door for installation/removal. The discharge line for each pump contains an isolation plug, swing check, and air/vacuum release valve. All three pumps are controlled by variable frequency drives (VFDs) enabling pump speed to be adjusted with wet well levels.

Pump control is in accordance with liquid level in the wet well as measured by a submersible level sensor. Float-tilt level switches control pump start/stop. The operator can adjust the pump settings, desired wet well level and alarming at the remote HMI, or locally at the OIT in the Pump Station Electrical Room. Oil in each pump's oil chamber lubricates and cools the mechanical seals. Lubricants require periodic replacement.  

Influent Pumps Variable Frequency Drives (VFDs) 6
The three sanitary influent pumps are equipped with variable frequency drives to provide adjustable speed operation of the influent pumps. This allows the pumps to adjust discharge rate based on varying wet well levels.
 CSO Influent Pumps 6
 
Two CSO influent pumps are located within the wet well of the 20 th Avenue North Pump Station and provide capacity for peak wet weather flows. A concrete weir separates the sanitary wet well from the CSO wet well. CSO flow is discharged into a manhole structure and flows by gravity to a junction box. It is then directed through a 30 inch interceptor sewer to the Car Barn Ditch, continues by gravity to Joyce's Slough, and then on to the Mississippi River.

The
two submersible, non-clog, centrifugal pumps have a design pumping capacity of 5.2 MGD. Each pump includes a quick connect and guide rail system and is centered under an aluminum floor door for installation/removal. The discharge line for each pump contains an isolation plug, swing check, and air/vacuum release valve.

Liquid level in the CSO wet well is measured by a submersible level sensor. Float-tilt level switches control pump start/stop.   

 

CSO Sump Pump 6
After the occurrence of a CSO event, the submersible sump pump located in the SE corner of the Pump Station CSO wet well can be used to pump down the wet well when the station is otherwise out of service. The pump can be placed in an AUTO mode at the pump control panel or operated manually. If in AUTO mode, the lower switch is the pump stop, the middle is the pump start, and the upper is the high level alarm, indicating a potential sump pump failure.
Wet Well Level Monitoring 6
  The liquid level in the sanitary and CSO wet wells are measured by a submersible type level sensor. Float-tilt level switches accompany the submersible level sensor and control pump start/stop,  as well as high-high and low-low wet well level alarms.

A low-low detection in the wet well discontinues pumping via hardwired interlock. A high-high level in the wet well sends an alarm which can be viewed locally at the OIT in the Pump Station Electrical room or at the HMI in the Clinton WWTP Control Room.
CSO Outfall Level Monitoring 6
The discharge of CSO flow to the Mississippi River is calculated by the PLC based on liquid level in the CSO discharge channel. Level at the weir in the CSO Effluent Channel is monitored by a guided wave type radar level element. Weir level and totalized CSO flow are displayed at the HMI. 
CSO Discharge Sampler 6
The CSO Discharge Sampler is set to automatically sample CSO discharge to the Mississippi River. Samples are taken every 30 minutes during a CSO event and stored within the refrigerated unit. 
Flow Monitoring 6
Flow from the sanitary pumps in the 12" PVC force main is monitored with a magnetic flow meter. Flow data is sent to the PLC which transmits the information to the HMIs for display of totalized and instantaneous flows.
Manual Bar Screen 6
  An 18 foot long stainless steel coarse bar screen is located on the upstream end of the Pump Station Influent Channel (modified wet well of original Sanitary Pump Station). 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.
Radio Transceiver 6
The pump station at the 20 th Avenue North location is normally unmanned. Communication with the pump station 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 (OIT) 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 Generator 6
A natural gas powered emergency engine generator is located in the SE corner of the site, within the security fence line. The generator serves the location providing standby power to critical loads in the event of a temporary interruption of the main power supply (provided by Alliant Energy). An automatic transfer switch is housed in the Pump Station Electrical Room and automatically switches operations over to standby power in the event a power outage is detected. It is recommended that the generator is exercised regularly .
 

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Last Updated: 7/5/2018 3:43:09 PM
Version 3.0.1