19-Final Draft Schedule B-8 - Automatic Operation Sequence.pdf

Automatic Operation Sequence for Wet Weather Events

FINAL

March 2022

Report prepared by:

Patrick Obenauf, P.E.

Cari Roper, P.E.

Kathryn Schmitt

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1.0 INTRODUCTION

This document describes the automatic operation sequence of the Inline Storage System (ISS) and Northwest Side Remote Storage (NWSRS) facilities during wet weather events. The automatic operation sequence is the baseline for storage operations in the conveyance system. It is also the default operation if no human intervention occurs. The ISS has a capacity of 432 million gallons (MG) and serves to provide relief to both the combined and separate sewer areas served by the Milwaukee Metropolitan Sewerage District (MMSD). The NWSRS has the capacity of 88 MG and serves to provide relief for the northwest side of the MMSD sewer service area; as well as to capture wastewater that may otherwise flow into the ISS. Operation of the MMSD conveyance, storage, and water reclamation facilities are optimized to meet the following goals and responsibilities:

• Protect public health and the environment

• Protect water quality in the region

• Meet limits of the Wisconsin Pollutant Discharge Elimination System (WPDES) permit

• Protect against sanitary sewer overflows

• Minimize the impact to municipal and direct connections

2.0 ISS CONTROL STRATEGY DESCRIPTION

The control strategy for the ISS is founded on six main priorities that consider the goals and responsibilities of the MMSD listed above. Furthermore, the priorities were determined and ranked by the impact they would have on the goals and responsibilities of the MMSD. The six priorities from highest priority to lowest priority are:

1. Overfilling the ISS

2. Inundating the water reclamation facilities (WRFs) (Jones Island and South

Shore WRF)

3. Impacts to municipal connections

4. Sanitary sewer overflows

5. Combined sewer overflows

6. Blending

During wet weather, the priorities will be sacrificed in the reverse order (from 6 up to 1), when it becomes clear that the lowest priority available cannot be met without sacrificing a higher priority.

Priority 6 (blending) would be sacrificed first if it is believed that pumping additional flow from the ISS can prevent a combined sewer overflow. Blending begins when flow is

2 | P a g e pumped from the ISS, where it receives the equivalent of primary treatment, to the disinfection facility at the Jones Island WRF. The decision to implement blending is made when the net inflow rate to the ISS multiplied by the expected length of the event indicates that a combined sewer overflow will occur. The net inflow rate to the ISS is the difference between the total inflow into the ISS and the rate of pumping. The net inflow rate can be extremely variable during events. Estimating the future net inflow rate relies on weighing the current net inflow rate (at the time of consideration to implement blending) in the context of the predicted rainfall duration and intensity. The expected length of the event also relies on weighing weather forecast information with weather radar. In the right circumstances, blending has the potential to avoid a combined sewer overflow. However, even if a combined sewer overflow is not avoided, blending will reduce the volume of the combined sewer overflow. Note that blending is an entirely manual decision and operation. It is not programmed into the control strategy and is outside of the scope of this document.

Priority 5 (combined sewer overflows) is sacrificed if it is believed that the remaining available volume in the ISS must be used to capture excess flows from the separate sewer service area. This is predicted by the volume reserved for separate sewer inflow (VRSSI). The VRSSI is calculated by a series of equations that use wastewater depth in the Metropolitan Interceptor System (MIS) and precipitation in real time to forecast the volume of inflow to the ISS from the separate sewer service area for the next 48 hours.

The SCADA system continuously calculates the value of the VRSSI. The value is herein referred to as the calculated VRSSI. The calculated VRSSI is considered, along with changes to flows in the MIS, into the ISS from the separate sewer area, and at the WRFs; as well as weather radar and the current precipitation forecast to determine an actual VRSSI to input into the control system, which is the same as making the determination for when to sacrifice priority 5 (combined sewer overflows) to protect the higher priorities (priorities 4, 3, 2, and 1). Further description of the calculated VRSSI is available in the Implemented RTC Strategy Report, July 2010.

Priority 5 (combined sewer overflows) and priority 6 (blending) are sometimes sacrificed together, or in the reverse order, depending on how a precipitation event unfolds, as well as the resulting inflow rates to the ISS and at the WRFs. Priority 5 (combined sewer overflows) takes a stepwise approach as described in Section 3 to limit the volume of combined wastewater that overflows and to maximize the use of the storage volume available in the ISS for both combined and sanitary wastewater.

The Lake Michigan South (LMS) ISS dropshaft receives inflows from the combined sewer system. This dropshaft is treated like a combined sewer dropshaft (Priority 5) during the months of November through April but is treated like a sanitary sewer dropshaft (Priority 4) during the months of May through October. The reason for the https://mmsd365.sharepoint.com/sites/Planning-RS/PlanningReports/Forms/By%20Report%20Type.aspx?id=%2Fsites%2FPlanning%2DRS%2FPlanningReports%2FImplemented%20RTC%20Strategy%20%2D%20Final%20Report%2Epdf&parent=%2Fsites%2FPlanning%2DRS%2FPlanningReports

3 | P a g e different treatment is to help protect the South Shore Park beach during the typical months when the public is active along this beach.

If the predicted net inflow rate to the ISS (after closing of the combined sewer inflow gates) multiplied by the remaining storm duration indicates that the ISS will be filled without taking additional steps to reduce inflows, priority 4 (sanitary sewer overflows) is sacrificed, which means that the separate sewer gates to the ISS are closed, effectively closing the ISS to additional flows. Priority 4 (sanitary sewer overflows) also takes a stepwise approach as described in Section 3 to limit the volume of sanitary wastewater overflows, which maximizes the capture of wastewater and minimizes the effect of ISS gate closures on the conveyance system. Wastewater levels in the MIS can increase when the ISS gates are closed to the separate sewer service area, which can affect municipal connections. Therefore, priority 3 (impacts to municipal connections) may be sacrificed when the ISS is closed to all inflows (this is dependent on the flow rates at the time of closure).

Generally, priority 2 (flooding the water reclamation facilities) should never be sacrificed.

However, extreme circumstances involving power outages, loss of control, non-functioning equipment, and widespread flooding that prevents crews from accessing sites may result in the occurrence of flooding at the WRFs and possible overfilling of the ISS. Priority 2 (flooding the water reclamation facilities) would only be intentionally sacrificed if there was a loss of control of the ISS systems and allowing additional flows to the WRFs could prevent the ISS from overfilling.

Currently, the District is not allowed to sacrifice priority 1 (overfilling the ISS) per the Wisconsin Pollutant Discharge Elimination System (WPDES) permit.

3.0 AUTOMATIC SEQUENCE FOR ISS OPERATION

The operation sequence for the ISS includes two modes: filling and dewatering. The operation of the ISS includes active control of sluice gates at several structures, as described in Sections 3.1 and 3.2.

3.1 AUTOMATIC SEQUENCE FOR FILLING THE ISS

Operations of the ISS during wet weather events when the ISS is filling should follow the sequence below:

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1. Wet weather occurs, ISS begins to fill.

a. Flow is diverted into the ISS by gravity when the elevation of the wastewater in the MIS is high enough to spill over a weir and/or into an adjacent pipe. This is true of most dropshafts, except for the control structures listed in b.

b. Gates to the ISS actively divert flow into the ISS by throttling open based on wastewater elevations in the MIS at the following dropshafts (structures):

Dropshaft (Structure ID) Location CT02 (DC0402) N 59th St (ext’d) & W Trenton Pl NS01 (DC0405-1B) N 51st St & W Hampton Ave NS03 (DC0507) N Lydell Ave & W Fairmount Ave KK01 (DC0103) S 6th St & W Oklahoma Ave

2. ISS predicted to reach the actual VRSSI, Jones Island WRF approaching

330 MGD influent flow rate

a. Sacrifice Priority 6 (blending) to reduce the chance of CSO occurrence and reduce the volume of CSO

b. Start blending at JIWRF

c. This step is not automated and requires human intervention.

3. Remaining Available Storage Volume in the ISS = actual VRSSI

a. Sacrifice initial Priority 5 CSOs to reduce the chance of SSO occurrence and impacts to municipal connections

b. Default VRSSI value is 120 MG and can be changed during an event depending on conditions. Note, at the default VRSSI value the wastewater volume in the ISS is 312 MG.

c. Gates to the ISS close at the following dropshafts (structures):

Dropshaft (Structure ID) Location NS04 (NS4-JC01) N Cambridge Ave & E Providence Ave NS05 (NS5-JC01) E Burleigh St & Milwaukee River NS06 (NS6-JC01) E Park Pl & Milwaukee River NS07 (NS7-JC01) N Commerce St & N Booth St NS08 (NS8-JC01) N Commerce St & E Pleasant St NS09 (NS9-JC01) N Old World 3rd St & W McKinley Ave NS10 (NS10-JC01) N Water St & E St. Paul Ave NS11 (NS11-JC01) N Humboldt Blvd & E Capitol Dr NS12 (NS12-JC01; CS gate) N 31st St & W Capitol Dr CT02 (CT2-JC01) N Hawley Rd & W State St CT3/4 (CT3/4-JC01) N 44th St & W Wells St CT5/6 (CT5/6-JC01) N 25th St & Menomonee River CT07 (CT7-JC01) N 16th St & W Canal St

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CT08 (CT8-JC01) S 3rd St (ext’d) & W Seeboth St KK01 (KK1-JC01) S 6th St & W Cleveland Ave KK02 (KK2-JC01) S 1st St & S Chase Ave KK03 (KK3-JC01) S 4th St & W Becher St KK04 (KK4-JC01) S 1st St & W Lincoln Ave LMN (LMN-JC01) E Bay St & E Ward St

LMS (LMS-JC01)*

S Lincoln Memorial Dr & E Russell Ave

*Operation strategy at LMS only from November through April. Also in Step 3 below. See Combined Sewer Overflow (CSO) Long-Term Control Plan - CSO196 South Shore Park, January 19, 2010.

d. CSOs begin as the result of gate closures.

4. Wastewater Volume in the ISS = 350 MG

a. Sacrifice additional Priority 5 CSOs to reduce the chance of SSO occurrence

b. Volume can be adjusted with the following constraints:

• Must be greater than the maximum ISS volume subtracted by the VRSSI volume

• Must be less than the wastewater volume in Step 3

c. Gates to the ISS close at the following dropshafts (structures):

Dropshaft (Structure ID) Location CT02 (DC0402) N 59th St (ext’d) & W Trenton Pl KK01 (DC0103) S 6th St & W Oklahoma Ave

d. Overflow gates open to relieve the MIS at the following structures:

Dropshaft (Structure ID) Location CT02 (BS0405D1) N 59th St (ext’d) & W State St KK01 (DC0103, overflow gate)

S 6th St & W Oklahoma Ave

e. CSOs continue as a result of overflow gates opening.

5. Wastewater Volume in the ISS = 375 MG

a. Sacrifice remaining Priority 5 CSOs and initial Priority 4 SSO

b. Volume can be adjusted with the following constraints:

• Must be greater than the maximum ISS volume subtracted by the VRSSI volume

• Must be less than the wastewater volume in Step 3

c. Gates to the ISS close at the following dropshafts (structures):

Dropshaft (Structure ID) Location NS01 (DC0405-1B) N 51st St & W Hampton Ave NS02 (DC0504-2B) N 31st St & W Hampton Ave NS03 (DC0503) W River Woods Pkwy (ext’d) & Milwaukee River https://mmsd365.sharepoint.com/sites/Planning-RS/PlanningReports/Final%20CSO%20196%20Transmittal%20Ltr%20to%20DNR%20032013.pdf https://mmsd365.sharepoint.com/sites/Planning-RS/PlanningReports/Final%20CSO%20196%20Transmittal%20Ltr%20to%20DNR%20032013.pdf

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NS11 (DC0502) N Humboldt Blvd & E Capitol Dr

LMS (LMS-JC01)*

S Lincoln Memorial Dr & E Russell Ave

* Operation strategy at LMS from May through October. Also in Step 2 above.

See Combined Sewer Overflow (CSO) Long-Term Control Plan - CSO196 South Shore Park, January 19, 2010.

d. Overflow gates open (simultaneously with the ISS gate closure) to relieve the MIS at the following structures:

Dropshaft (Structure ID) Location NS02 (BS0502A) N 32nd St & W Hampton Ave NS11 (BS0501D) N Richards St & E Congress St (ext’d)

e. CSOs continue and SSO begins as a result of gate closures

6. Wastewater Volume in the ISS = 405 MG

a. Sacrifice additional Priority 4 (SSOs) to reduce the potential impacts to municipal connections

b. Volume can be adjusted with the following constraints:

• Must be greater than the volume in Step 2

• Must be less than the volume in Step 5

c. Gates to the ISS close at the following dropshafts (structures):

Dropshaft (Structure ID) Location NS12 (NS12-JC01; SS gate) N 31st St & W Capitol Dr

d. Overflow gates relieve the MIS at the structures:

Dropshaft (Structure ID) Location

NS12 (BS0503D) N 35th St & W Roosevelt Dr

e. SSOs continue as a result of gate closures

7. Wastewater Volume in the ISS = 415 MG

a. Sacrifice Priority 3 (impacts to municipal connections) to avoid overfilling the ISS

b. Volume can be adjusted with the following constraints:

• Must be greater than the volume in Step 3

• Must be less than 427 MG

c. Diversion gate DC0409 (N Mill Rd & W Sidney Pl) closes

8. Wastewater Volume in the ISS = 427 MG

a. Sacrifice Priority 3 (impacts to municipal connections) to avoid overfilling the ISS

b. Volume can be adjusted with the following constraints:

• Must be greater than the volume in Step 3

• Must be less than 427 MG https://mmsd365.sharepoint.com/sites/Planning-RS/PlanningReports/Final%20CSO%20196%20Transmittal%20Ltr%20to%20DNR%20032013.pdf https://mmsd365.sharepoint.com/sites/Planning-RS/PlanningReports/Final%20CSO%20196%20Transmittal%20Ltr%20to%20DNR%20032013.pdf

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c. Gates to the ISS close at the following dropshafts (structures):

NS03 (DC0508) N Milwaukee River Pkwy & W Villard Ave (ext’d) NS03 (NS3-JC01) W River Woods Pkwy (ext’d) & Milwaukee River

d. Gates to NS03 at DC0507 (N Lydell Ave & W Fairmount Ave) fully open.

e. SSOs begin as a result of gate closures.

f. Overflow relief occurs at the following overflow sites:

Structure ID Location BS0505 N 27th St & W Villard Ave BS0515 200 E River Woods Pkwy BS0516 4700 N Estabrook Pkwy

Figure 1 is a schematic of the ISS with associated gated control structures.

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Figure 1: ISS Control Schematic

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3.2 ISS CONTROL STRATEGY FOR DEWATERING

When inflow to the ISS has diminished, gates to the ISS can begin to reopen. Gates will reopen in reverse order from which they closed (i.e. Step 5 first, Step 1 last). The following gates will reopen when the wastewater volume in the ISS has dropped to a minimum of 10 MG below the volume to make them close. For example, the gates to the ISS at NS03 (DC0508 and NS3-JC01) will reopen when the volume in the ISS falls below 417 MG. Gates allowing combined sewer inflow are opened one at a time in a prescribed sequence beginning when the volume in the ISS has dropped below 365 MG and the inflow has diminished, such that the ISS pumps are able to, at a minimum, keep up with the additional inflow (as gates are opened).

1. Wastewater Volume in the ISS < 417 MG

c. Gates to the ISS open at the following dropshafts (structures):

Dropshaft (Structure ID) Location NS03 (DC0508) N Milwaukee River Pkwy & W Villard Ave (ext’d) NS03 (NS3-JC01) W River Woods Pkwy (ext’d) & Milwaukee River

d. SSO ceases at the following structures:

Structure ID Location BS0505 N 27th St & W Villard Ave BS0515 200 E River Woods Pkwy BS0516 4700 N Estabrook Pkwy

2. Wastewater Volume in the ISS < 405 MG

c. Volume can be adjusted with the following constraints:

• Must be less than the volume in Step 1

• Must be less than 417 MG

d. Diversion gate DC0409 (N Mill Rd & W Sidney Pl) opens

3. Wastewater Volume in the ISS < 395 MG

• Must be less than the volume in Step 2

• Must be less than 405 MG

d. Gates to the ISS open at the following dropshafts (structures):

Dropshaft (Structure ID) Location NS12 (NS12-JC01; MIS gate) N 31st St & W Capitol Dr

e. Gates to overflow relief close for the following dropshafts (structures):

NS12 (BS0503D) N 35th St & W Roosevelt Dr

4. Wastewater Volume in the ISS < 365 MG

• Must be less than the volume in Step 3

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• Must be less than 395 MG

d. Gates to the ISS open at the following dropshafts (structures):

Dropshaft (Structure ID) Location NS01 (DC0405-1B) N 51st St & W Hampton Ave NS02 (DC0504-2B) N 31st St & W Hampton Ave NS03 (DC0503) W River Woods Pkwy (ext’d) & Milwaukee River NS11 (DC0502) N Humboldt Blvd & E Capitol Dr

LMS (LMS-JC01)

(May – October)*

S Lincoln Memorial Dr & E Russell Ave

* Operation strategy at LMS from May through October.

c. Gates to overflow relief close for the following dropshafts (structures):

Dropshaft (Structure ID) Location NS02 (BS0502A) N 32nd St & W Hampton Ave NS11 (BS0501D) N Richards St & E Congress St (ext’d)

5. Wastewater Volume in the ISS < 340 MG

• Must be less than the volume in Step 4

• Must be less than 365 MG

d. Gates to the ISS open at the following dropshafts (structures):

Dropshaft (Structure ID) Location CT02 (DC0402) N 59th St (ext’d) & W Trenton Pl KK01 (DC0103) S 6th St & W Oklahoma Ave

c. Gates to overflow relief close for the following dropshafts (structures):

Dropshaft (Structure ID) Location CT02 (BS0405D1) N 59th St (ext’d) & W State St KK01 (DC0103, overflow gate)

S 6th St & W Oklahoma Ave

6. Remaining Available Storage Volume in the ISS > VRSSI

a. Volume can be adjusted with the following constraints:

• Must be less than the volume in Step 5

• Must be less than 340 MG

b. Gates to the ISS open at the following dropshafts (structures):

Dropshaft (Structure ID) Location NS04 (NS4-JC01) N Cambridge Ave & E Providence Ave NS05 (NS5-JC01) E Burleigh St & Milwaukee River NS06 (NS6-JC01) E Park Pl & Milwaukee River NS07 (NS7-JC01) N Commerce St & N Booth St NS08 (NS8-JC01) N Commerce St & E Pleasant St NS09 (NS9-JC01) N Old World 3rd St & W McKinley Ave

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NS10 (NS10-JC01) N Water St & E St. Paul Ave NS11 (NS11-JC01) N Humboldt Blvd & E Capitol Dr NS12 (NS12-JC01; CS gate) N 31st St & W Capitol Dr CT02 (CT2-JC01) N Hawley Rd & W State St CT3/4 (CT3/4-JC01) N 44th St & W Wells St CT5/6 (CT5/6-JC01) N 25th St & Menomonee River CT07 (CT7-JC01) N 16th St & W Canal St CT08 (CT8-JC01) S 3rd St (ext’d) & W Seeboth St KK01 (KK1-JC01) S 6th St & W Cleveland Ave KK02 (KK2-JC01) S 1st St & S Chase Ave KK03 (KK3-JC01) S 4th St & W Becher St KK04 (KK4-JC01) S 1st St & W Lincoln Ave LMN (LMN-JC01) E Bay St & E Ward St

LMS (LMS-JC01)

(November – April)*

S Lincoln Memorial Dr & E Russell Ave

*Operation strategy at LMS from November through April

NS04 (NS4-JC01) CT3/4 (CT3/4-JC01)

NS05 (NS5-JC01) CT5/6 (CT5/6-JC01)

NS06 (NS6-JC01) CT07 (CT7-JC01)

NS07 (NS7-JC01) CT08 (CT8-JC01)

NS08 (NS8-JC01) KK01 (KK1-JC01)

NS09 (NS9-JC01) KK02 (KK2-JC01)

NS10 (NS10-JC01) KK03 (KK3-JC01)

NS11 (NS11-JC01) KK04 (KK4-JC01)

NS12 (NS12-JC01; CS gate) LMN (LMN-JC01) CT02 (CT2-JC01) LMS (LMS-JC01) (November – April)

7. Flow at JIWRF (from ISS pumping and gravity flow) < 330 MGD

a. Blending process stops

b. Valve to the Inline Flow System channel at JIWRF closes and directs all

ISS pumpout to Preliminary Treatment

c. This step requires human intervention and is not programmed into the ISS strategy.

4.0 INLINE PUMP STATION OPERATION

The Inline Pump Station operates independently from the ISS inflow controls. The ISS Pump Station has the capability to pump flow from the ISS to both the Jones Island Water Reclamation Facility (JIWRF) and the South Shore Water Reclamation Facility (SSWRF). The control strategy provides for manual operation of the three ISS pumps.

Automatic control of the ISS pumping station was not implemented.

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Several factors limit pumping from the ISS, including the ability of the two water reclamation facilities to accept flow, capacities of the ISS pumps, conveyance capacity from the pump station to the water reclamation facilities, and the minimum time between pump starts. The objective of the ISS pump-out control strategy is to empty the ISS as quickly as possible. The Inline Storage System O&M Manual, Part 2 – Unit Process Operations Volume 1, Inline Pump Station describes the pump-out strategy and operation of the Inline Pump Station in detail.

There are three inline pumps that discharge flow from the ISS to one of two head tanks located at the JIWRF. One head tank discharges to JIWRF, the other discharges to a force main that sends flow to a diversion chamber at South 6th Street and West Oklahoma Avenue, then discharges by gravity to the SSWRF.

Pump No. 1 discharges to the South Shore Head Tank, while Pump No. 3 discharges to the Jones Island Head Tank. Pump No. 2 can discharge to either head tank; however, discharge from two pumps would exceed the hydraulic capacity of the South Shore force main. Therefore, Pump No. 2 and Pump No. 3 normally discharge to the Jones Island Head Tank. Two interconnections between the head tanks with knife gate valves can be opened to divert flow from the South Shore Head Tank to the Jones Island Head Tank. With the knife gate valves open, all discharge from the ISS is sent to JIWRF.

Wastewater must be pumped up to a much higher level in the South Shore head tank than in the Jones Island head tank. Therefore, the capacity of each pump varies with the head tank it is pumping to as well as with the level of wastewater in the ISS. The maximum capacity of each pump is nominally 70 MGD and this occurs when the speed of the pump is at 100%. Discharge rates to the Jones Island head tank can vary from 30 MGD to 140 MGD; while 60 MGD can be diverted from the South Shore Head Tank to the Jones Island Head Tank. Nominal rates to the South Shore Head Tank can vary from 30 MGD to 60 MGD.

5.0 NWSRS CONTROL STRATEGY DESCRIPTION

The NWSRS is a 7.1-mile-long, 20-foot diameter storage tunnel at depths ranging from 120 to 165 feet below the ground surface elevation. The NWSRS relieves surcharging of a 72-inch special section MIS and a 72-inch diameter MIS serving the northwest side of the MMSD service area and provides up to 88 MG of wastewater storage during severe wet weather events. The stored wastewater empties into the ISS through the drop shaft for CT01. Figure 2 is a schematic of the NWSRS and associated control structures.

https://mmsd365.sharepoint.com/sites/District/ISSOMManuals/Forms/AllItems.aspx?id=%2Fsites%2FDistrict%2FISSOMManuals%2FZ%5FOLD%5FISS%5FOM%5FP2V1%5FPumpStation%5FJan11%2Epdf&parent=%2Fsites%2FDistrict%2FISSOMManuals https://mmsd365.sharepoint.com/sites/District/ISSOMManuals/Forms/AllItems.aspx?id=%2Fsites%2FDistrict%2FISSOMManuals%2FZ%5FOLD%5FISS%5FOM%5FP2V1%5FPumpStation%5FJan11%2Epdf&parent=%2Fsites%2FDistrict%2FISSOMManuals

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Figure 2: NWSRS Control Schematic

Excess wet weather flows are diverted by gravity into the NWSRS from two diversion chambers, DC0307 located at Highway 100 and West Hampton Avenue, and DC0308 located at North 91st Street and West Denver Avenue. Flow diverted into the NWSRS from DC0307 and DC0308 is considered passive inflow; as flows divert over a weir with no active control. Excess wet weather flows are also diverted by gravity into the NWSRS from DC0304 located on the 96-inch diameter MIS in the County Grounds near MMSD drop shaft, CT01. The flows diverted into the NWSRS from the 96-inch MIS are actively controlled by the position of three 96-inch high by 96-inch wide sluice gates in DC0304. Active operation of the NWSRS begins when the ISS is filling and at a volume of 150 MG. Active operation stops when the volume remaining in the NWSRS is equal to the reserve volume, which is normally 36 MG.

The NWSRS is drained through four cone valves to the ISS. There are two 12-inch and two 24-inch cone valves that drain flow from the downstream end of the NWSRS into the CT01 drop shaft.

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6.0 AUTOMATIC SEQUENCE FOR NWSRS OPERATION

The operation sequence for the NWSRS during a wet weather event is as follows:

1. NWSRS Filling

a. When the ISS wastewater volume = 150 MG, open gates at DC0304 to begin active operation of the NWSRS. Flow will enter the NWSRS at the downstream end through DC0309. The 150 MG value can be changed by the operator. The operator can also manually open the gates at DC0304 to begin active filling.

b. When water levels in the 72-inch MIS overtop the weirs at DC0307 and DC0308, passive filling of the NWSRS begins. Passive filling continues until water levels fall below the weir crest levels in the 72-inch MIS.

c. When the NWSRS reaches 52 MG, close gates at DC0304. Using 52 MG for active fill reserves 31 MG for passive fill into the NWSRS (assumes 5 MG enters the NWSRS while gates are in the process of closing).

2. Siphon Mode (MIS Surcharge Relief)

a. DC0309 is open to the NWSRS and closed to the ISS for all events to allow siphoning of the NWSRS to occur without human intervention.

b. When NWSRS > 88 MG and the water level at DC0307 or DC0308 is above the weir crest, siphon mode begins automatically.

c. When the NWSRS is in siphon mode, the NWSRS provides only an alternate flow path from the 72-inch special section and 72-inch MIS on the northwest side of the sewer service area to reach the 96-inch MIS near Milwaukee County Grounds, as shown in Figure 3. Without the NWSRS, surcharge in the 72-inch MIS would be much higher, where it would impact municipal connections.

d. Siphoning of the NWSRS is limited by the downstream 96-inch MIS capacity, thus this mode does not provide adequate MIS surcharge relief under all conditions.

3. NWSRS Dewatering

a. When wastewater volume in ISS < 125 MG, the NWSRS is manually drained through the cone valves.

A summary of the critical decision points during active wet weather operation is included in Table 1.

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Figure 3: NWSRS - Simulated Profile of the Hydraulic Grade Line During Siphon Mode

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Table 1 - Summary of NWSRS Critical Volumes / Elevations for Active Operation

Event Trigger Reasoning

Begin active storage in NWSRS

ISS volume

> 150 MG

Combined sewer overflow is likely to occur.

Active fill helps reduce the volume entering the ISS through KK01 and CT02

Stop active storage into NWSRS

NWSRS volume

> 52 MG

Provide 31 MG reserve in NWSRS to minimize the frequency of having to operate in siphon-mode.

Dewater NWSRS ISS Volume

< 125 MG

(manual only)

Continues preparation for future events to NWSRS while allowing at least 25 MG of capacity for combined sewer inflow to the ISS.