Chapter 5: Conveyance Assessment 2020 Baseline Conditions

Transcription

1 Chapter 5: Conveyance Assessment 2020 Baseline Conditions 5.1 Introduction The performance of the conveyance system for 2020 Baseline conditions is assessed in this chapter using the hydraulic models. The configuration of the hydraulic models represents the conveyance system including future projects that the Milwaukee Metropolitan Sewerage District (MMSD) has committed to build. The committed projects that were included in the model for this analysis are listed in Table 5-1. Chapter 8 has a more complete list of the committed projects; the list in Table 5-1 contains the projects in the model as of the time of the analysis. The main committed projects are: Harbor Siphon capacity improvements IS (Intercepting Structure) improvements Northwest Side Relief Sewer North 27 th Street ISS Extension West Wisconsin Avenue Relief Sewer Hydraulic simulations used flows generated by the Flow Forecasting System (FFS) model and were based on the estimated 2020 Baseline population and land use conditions. The 2020 Baseline flows are based on the calibrated 2000 flows with additions to the base sanitary flow and the infiltration and inflow (I/I) to account for additional population and increases in commercial and industrial land use areas. The model assumes that I/I from the current system remains constant. This assumption implies that municipalities and MMSD maintain their existing systems so that the I/I does not increase above current levels. The conveyance system assessment consists of the following topics: Conveyance system reaches with hydraulic restrictions Combined sewer overflow (CSO) and separate sewer overflow (SSO) frequencies, volumes, and locations This chapter presents the analytical results of simulations that were run to asses the performance of the committed system with the 2020 Baseline population and land use conditions. Subsequent to this analysis, the modeling system was further refined to evaluate alternatives for the Recommended Plan. At the time of this analysis, the simulation period of record was from January 1940 to December 2002; this was a 63-year period of record. The Mini-MOUSE model was used to simulate the volumes and frequencies of SSOs and CSOs during a 63-year period of record. Subsequent refinements to the modeling system used an extended 64.5-year period of record (from January 1940 through June 2004). Therefore, the simulation results in this chapter and the previous chapter are not based on the most recent refinements to the modeling system. Chapter 9 contains the results from the refined models which were used to develop of the Recommended Plan. 5-1

2 Committed Project Name Jones Island Harbor Siphons and Headworks Northwest Side Relief Sewer North 27 th Street ISS Extension West Wisconsin Avenue Relief Sewer Comment 27 MG New MIS segment East and West Warnimont Avenue 2010 Facilities Plan Project (updated design, December 2005) Honey Creek and South 81 st Street North 31 st and Hampton Avenue South 27 th Street South 35 th Street South 41 st Street Veterans Administration Hospital Barclay / 4 th / Chase (Basin A Relief) Canal Street (Basin D Relief) Central MIS Sewer Lining Projects IS Structure Improvements Scott Street MIS Water Street (Basin A Replacement) Auer Avenue Siphon Replacement and IS207A Bruce Street MIS Replacement Bruce Street / Muskego Avenue MIS Replacement Clybourn Street MIS Rehabilitation Clybourn Street West MIS Relocation Estabrook Park and Auer Avenue Aqueduct Replacement 1 st Street Siphon Green Bay Road Overflow Improvement Project Hopkins Street Near Surface Collector Menomonee Special, MIS Replacement and Realignment Miller Area Rehabilitation Miller Area, State Street and North 37 th Street MIS Northeast Side Flow Control Gates North 30 th Street Relief Sewer North 32 nd and Hampton Avenue Pump Station, BS0502A Nicholson Avenue Diversion Structure, DC0607 NS-6 Outfall Sewer Relay Oak Creek South Interceptor, New MIS Oak Creek SW Interceptor, New MIS Providence Avenue Replacement Range Line Road Relief Sewer South Howell Avenue Pump Station 2010 Facilities Plan Project 2010 Facilities Plan Project 2010 Facilities Plan Project 2010 Facilities Plan Project 2010 Facilities Plan Project 2010 Facilities Plan Project Central MIS Project Central MIS Project Central MIS Project Central MIS Project Central MIS Project Central MIS Project Connection from Hampton Ave MIS to Villard Avenue MIS removal of two SSO sites Disconnection of storm flow and reroute of flow to new NSC Sewer lining project MIS replacement/realignment DC0509 and gate at NS-3 Sewer replacement and new IS73 and IS74A structures Increase size of sewer for better conveyance of flow New pump station and diversion TABLE 5-1 COMMITTED PROJECTS 2020 CONVEYANCE REPORT 5/2/07 CR_05.T cdr

3 A hydraulic restriction in the metropolitan interceptor sewer (MIS) system is defined as a reach of pipe that does not have sufficient conveyance capacity to prevent overflows or basement backups from occurring. Consequently, a hydraulic restriction causes the hydraulic grade line to rise above critical elevations. In general, the critical elevations are the inverts of connections from local sewer systems owned by the satellite municipalities. 5.2 Modeling Strategies and Operational Parameters The upgraded harbor siphons, the modified IS structures, and the Northwest Side Relief Sewer were modeled explicitly in the 2020 Baseline configuration. The North 27 th Street ISS extension and the West Wisconsin Avenue Relief Sewer were not modeled explicitly with additional pipe segments or storage elements in the model. Instead, the volume of the inline storage system (ISS) was increased by 27 million gallons (MG) (from 405 MG to 432 MG) and the volume reserved for separate sewer inflow (VRSSI) was increased an equal amount (from 150 to 177 MG) to account for the storage increase represented by these projects. Additional operational parameters used in the simulations are listed in Table 5-2. TABLE 5-2 OPERATIONAL PARAMETERS AND SIMULATION CONDITIONS Parameter ISS Volume VRSSI Jones Island Wastewater Treatment Plant Peak Capacity South Shore Wastewater Treatment Plant Peak Capacity ISS Pump Out Limit to Jones Island Wastewater Treatment Plant ISS Pump Out Limit to South Shore Wastewater Treatment Plant Lake Michigan Water Level 1 (MMSD datum) Meteorological Input Source Population and Land Use Conditions Value 432 MG 177 MG 390 MGD (includes up to 60 MGD of blending) 300 MGD 80 MGD 40 MGD -2.0 ft General Mitchell International Airport 2020 Baseline ft = Feet MG = Million Gallons MMSD = Milwaukee Metropolitan Sewerage District Commission VRSSI = Volume Reserved for Separate Sewer Inflow ISS = Inline Storage System MGD = Million Gallons per Day SEWRPC = Southeastern Wisconsin Regional Planning 1) MMSD datum (equal to feet, NGVD 1929) 5-3

4 5.3 Metropolitan Interceptor Sewer /Near Surface Collector Sewer / Inline Storage System Capacity Evaluation The capacity of the conveyance system was evaluated for two extreme events: March 1960 and August The simulation results were used to evaluate the response of the 2020 committed facilities and the 2020 Baseline population and land use to the hydrologic conditions of the extreme events. These simulations are not reconstructions of the historical events of March 1960 and August Rather, these simulations are used to evaluate the performance of the system (with the committed facilities) in response to the hydrologic conditions similar to the March 1960 and the August 1986 events. Because these simulation results are for extreme events, they are useful for identifying parts of the MIS that were evaluated for potential conveyance restriction in subsequent modeling refinements. Chapter 9 presents the conveyance system improvement projects in the recommended plan for the five- and 10-year levels of protection. Therefore, these extreme simulation results are preliminary results that were used to help focus more detailed evaluations of the conveyance system in further model refinements Extreme Event: Large Simulated Sanitary Sewer Overflow Volume March 1960 As described in Chapter 4, the large wastewater volume and long duration of the March 1960 event produced the largest simulated SSO volume during the period of record. Although the total rainfall depth was only 2.6 inches, with peak intensities less than 0.9 inches/hour, a large wastewater volume was generated by this event due to snowmelt over a four-day period in addition to the precipitation. This type of hydrologic event stressed the storage capacities of the system and resulted in large simulated SSO volumes. Figure 5-1 shows the sections of the MIS with simulated hydraulic restrictions during this extreme event for 2020 Baseline conditions Extreme Event: Large Simulated Combined Sewer Overflow Volume August 1986 The August 1986 event was an intense, short duration storm. The total rainfall depth was 6.8 inches with peak intensities of 4.3 inches/hour. The high peak flow rates generated by this event stressed the conveyance capacity of the system and produce the largest simulated CSO discharge. Figure 5-2 shows the sections of the MIS that had hydraulic restrictions during this event under 2020 Baseline simulated model conditions. Several of the hydraulic restrictions in the 2000 model configuration, as shown in Chapter 4, Conveyance Assessment Existing 2000 Conditions, Figures 4-1 and 4-2, were resolved by the committed projects. Other hydraulic restrictions remained in 2020 Baseline conditions because the committed projects were not designed for the extreme conditions represented by the August 1986 event. Other hydraulic restrictions were due to higher flows simulated in the separate sewer service area with 2020 conditions (compared to the Existing 2000 simulations in Chapter 4) Near Surface Collector Sewer Performance The NSCS had adequate conveyance capacity for 2020 Baseline conditions. No hydraulic restrictions were identified in the NSCS for the simulated extreme events. In these simulations, the NSCS successfully conveyed flow to the ISS while the ISS was open to the combined sewer area. 5-4

5 FIGURE 5-1 HYDRAULIC RESTRICTIONS: LARGEST SIMULATED SSO EVENT, 2020 CONDITIONS 2020 CONVEYANCE REPORT 5/2/07 CR_ cdr

6 FIGURE 5-2 HYDRAULIC RESTRICTIONS: LARGEST SIMULATED CSO EVENT, 2020 CONDITIONS 2020 CONVEYANCE REPORT 5/2/07 CR_ cdr

7 5.4 Sanitary Sewer Overflow and Combined Sewer Overflow Evaluation Extreme Event Simulated Combined Sewer Overflow and Sanitary Sewer Overflow Volumes The model results presented in Table 5-3 show the simulated CSO and SSO volumes for the two extreme events (March 1960 and August 1986) assuming 2020 Baseline population and land use. For the March 1960 event, both the CSO and SSO volumes are consistent among the three models. The simulated CSO volume was approximately 900 to 1,000 MG and the simulated SSO volume was approximately 900 MG, which is the largest simulated SSO in the period of record. TABLE 5-3 SIMULATED COMBINED SEWER OVERFLOW AND SANITARY SEWER OVERFLOW VOLUMES FOR TWO EXTREME EVENTS ASSUMING 2020 BASELINE POPULATION AND LAND USE Simulated CSO Volume (MG) Simulated SSO Volume (MG) Modeling Tool Maximum Simulated SSO event (March 1960 hydrology) Streamline-Model of Urban Sewers (MOUSE) Mini-MOUSE MACRO 1, Maximum Simulated CSO event (August 1986 hydrology 1 ) Streamline-MOUSE 1, Mini-MOUSE 2, MACRO 2,102 0 CSO = Combined Sewer Overflows SSO = Sanitary Sewer Overflows MG = Million Gallons MOUSE = Model of Urban Sewers 1) SSOs during the August 1986 event are associated with MIS capacity restrictions, not tunnel closing. MACRO cannot model SSOs that are not tunnel related. For the August 1986 simulations, the simulated CSO volume (approximately 2,000 MG) is the largest simulated CSO during the period of record. The August 1986 event stressed the conveyance capacity rather than the storage capacity in the model; consequently, the role of hydraulic routing in the simulation is very important. The Streamline-MOUSE model has the modeling capability to simulate the routing of this event properly. Therefore, the Streamline- MOUSE simulated SSO volume is believed to be the most accurate. The simulated SSO volumes computed by the three models are small. The high intensity and short duration rainfall (and relatively dry antecedent conditions) of this event does not cause a large volume of flow in the separate sewer service area. Because the ISS remains open to separate sewer inflows, the SSOs that do occur are due to hydraulic restrictions in the MIS. These conveyance-related SSOs 5-7

8 are sensitive to the brief but high peak flows of the August 1986 event. The SSO volume is 14 MG in Streamline-MOUSE; 20 MG in Mini-MOUSE; and 0 MG in MACRO because the MACRO model can not simulate conveyance related SSOs Combined Sewer Overflow and Sanitary Sewer Overflow Event Frequency Mini-MOUSE and MACRO simulation results were used to estimate the frequency of overflows and average annual overflow volume assuming 2020 Baseline population and land use. The simulations evaluated the 63-year period from 1940 to The simulated CSO and SSO results presented in Table 5-4 show the consistency between the Mini-MOUSE and MACRO results for the long-term total values. The simulated MACRO SSO events must be compared to the tunnel-related SSO events in Mini-MOUSE. TABLE 5-4 LONG-TERM SIMULATION COMBINED SEWER OVERFLOW AND SANITARY SEWER OVERFLOW RESULTS: MINI-MOUSE AND MACRO FOR 2020 BASELINE CONDITIONS 63-year Simulation Period ( ) 2020 Baseline Population and Land Use Conditions Simulated Quantity Mini-MOUSE MACRO CSO Volume (MG) 47,600 58,400 CSO Events SSO Volume (MG) 8,200 7,100 SSO Events 75 n/a Tunnel-related SSO Events CSO = Combined Sewer Overflows SSO = Sanitary Sewer Overflows MG = Million Gallons MOUSE = Model of Urban Sewers The CSO frequency is expressed as the average number of CSO events per year. During the 63- year period, the simulated number of CSO events was 227 in the Mini-MOUSE model and 224 in the MACRO model. Based on the Mini-MOUSE results, the average simulated CSO frequency is predicted to be approximately 3.6 events per year under assumed 2020 Baseline conditions. In the simulated Mini-MOUSE results, there were 75 SSOs (of which only 40 were tunnel related). The SSO frequency is expressed as a recurrence interval. Based on the Mini-MOUSE results, 75 simulated SSO events during the period of record are equivalent to a 0.8-year recurrence interval for SSO events. 5-8

9 5.4.3 Sanitary Sewer Overflow Locations and Volumes The Mini-MOUSE model has 19 SSO locations. Most sites are the same as those in the 2000 model discussed in Chapter 4, Conveyance Assessment Existing 2000 Conditions, except that one site was added and one was eliminated. A new SSO site on the Milwaukee River, BS0515 (where BS is bypass structure ) was added near the Pillsbury Silos site (200 East River Woods Parkway). The Honey Creek Project (proposed in the 2010 Facilities Plan) eliminated SSO site BS0303. Figure 5-3 shows the locations of the SSO sites by Wisconsin Pollutant Discharge Elimination System (WPDES) number. Figure 5-4 shows the simulated SSO volumes at each SSO location in the Mini-MOUSE model. These volumes are the cumulative SSO volumes from all events in the 63-year simulation period. The overflow at DC0103 was the dominant SSO location, followed by DC0402, BS0515, and BS0404 (the overflowing manholes near the Green Tree Pump Station). All of these sites were responsive to tunnel closure (tunnel-related SSOs). The SSO at BS0101 was due to MIS capacity limitations near Howell and Grange (i.e., not tunnel related). The total simulated SSO volume at all sites was 8,200 MG, which is equivalent to a simulated average annual volume of 130 MG per year Combined Sewer Overflow Locations and Volumes The Mini-MOUSE model has 20 CSO groups associated with the tunnel drop shafts. These are the same CSO groups used for the 2000 conditions, shown in Figure 4-5 of Chapter 4, Conveyance Assessment Existing 2000 Conditions. Figure 5-5 shows the simulated CSO volumes for each CSO group in the Mini-MOUSE model. The overflows associated with dropshafts CT-3/4 (where CT is cross town ) and CT-5/6 were the dominant CSO locations, followed by KK-3 and NS-7. The total simulated CSO volume at all sites was 47,600 MG, which is equivalent to an average annual volume of approximately 755 MG per year. This is 26% less CSO volume than the 2000 simulation results. For the 2020 configuration, the harbor siphons improvement project (one of the committed projects), increased the capacity of the siphons resulting in more gravity flow from the combined sewer service area to Jones Island Wastewater Treatment Plant (JIWWTP). As a result, the CSO volume was reduced. A secondary effect of treating more combined area flow at JIWWTP is a minor reduction in the treatment of separate area flow and, therefore, a small increase in the SSO volume. Most of the increase in the SSO volume, however, is due to the greater flow generated by 2020 Baseline projected increase in population and commercial/industrial growth. 5.5 Summary The models for 2020 conditions include the committed projects and the projected 2020 Baseline population and land use conditions. The simulated conveyance system performance shows more SSOs and slightly less frequent CSOs compared to the Existing 2000 conditions. The CSO volume decreased from 1,000 MG per year for 2000 conditions to 755 MG per year for 2020 Baseline conditions. Fewer CSOs is a consequence of the upgraded harbor siphons. The average number of CSOs decreased from 4.1 to 3.6 CSO events per year. 5-9

10 FIGURE 5-3 MINI-MOUSE SSO GROUPS, 2020 CONDITIONS 2020 CONVEYANCE REPORT 5/2/07 CR_ cdr

11 FIGURE 5-4 MINI-MOUSE SIMULATED SSO VOLUME: 63-YEAR PERIOD ( ) 2020 FACILITIES PLAN 5/2/07 CR_ cdr

12 CT-2 CT-3/4 CT-5/6 CT-7 CT-8 KK-1 KK-2 KK-3 KK-4 LM-N LM-S NS-4 NS-5 NS-6 NS-7 NS-8 NS-9 NS-10 NS-11 NS-12 12,000 10,000 8,000 6,000 4,000 2, Population and Land Use Conditions 2020 Facilities Total CSO Volume = 47,600 MG FIGURE 5-5 MINI-MOUSE SIMULATED CSO VOLUME: 63-YEAR PERIOD ( ) 2020 CONVEYANCE REPORT 5/1/07 CR_ cdr Simulated CSO Volume (MG) During 63-Year Record

13 In the separate sewer service area, the population increase produces significantly more base sanitary flow and more I/I. The average annual SSO volume increased from 36 MG per year for Existing 2000 conditions to 130 MG per year for 2020 Baseline conditions. The SSO recurrence interval also changed from 1.4-years to 0.8 years for 2020 Baseline conditions. Table 5-5 shows the simulated frequency of overflows and the simulated average annual volume of CSOs and SSOs per year for 2020 Baseline population and land use conditions. TABLE 5-5 SIMULATED COMBINED SEWER OVERFLOW AND SANITARY SEWER OVERFLOW FREQUENCY AND AVERAGE ANNUAL OVERFLOW VOLUME FOR 2020 BASELINE POPULATION AND LAND USE CONDITIONS CSO SSO Frequency of overflow 3.6 events per year 0.8-year recurrence interval Average Annual Volume (MG/year) CSO = Combined Sewer Overflow MG/year = Million Gallons per Year SSO = Sanitary Sewer Overflow 5-13