Hydraulic Modeling of Deep Tunnels Provides Cost Savings

Taymour El-Hosseiny, Karen Reinhart, EMH&T

M.P. Cherian, DLZ

Overview

Background and CSO Long Term Control Plan (LTCP)

Review of Backbone Alternative Initial Solution Modified Solution Model Results Compare Costs of Proposed Solutions Conclusion

P CSO

CSO Area

Legend

Existing Sewer Facilities Design Area

Main Trunk Sewers

CSO Locations, Columbus, OH

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Whittier Street Storm Tank Facility

Combined Sewer Area, Columbus, OH

Whittier Street Storm Tanks

Whittier Street Storm Tank Overflow Location

Technologies Used in CSO LTCP

Transport and Treat (in-line storage)

High Rate Treatment (HRT)

Supported by Increase capture (open regulators)

Increase system storage (Raising weirs)

Source control (Inflow redirection)

Source Control (Complete sewer separation in cost effective areas)

Storage tanks

Existing WSST Facility

Constructed in the late 1920s Along With the Olentangy-Scioto Intercepting Sewer (OSIS).

Three 1.3 mg (4,920 m3) Primary Treatment Tanks for Capturing and Treating Smaller Storm Events.

Direct Bypass for Storm Events that Exceeds Tank Flow Rate Capacity.

Baffles for Solids and Floatables Control

Effectiveness of Baffles Is Questionable.

1-Hour Detention at 100 mgd (4.38 m3/s).

Tank Overflows and Emergency Bypass are the Most Significant CSO Discharge in Columbus, OH.

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Overflow Event

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Cumulative Overflow at Whittier Street Storm Tanks for a Typical Year

Estimated Annual CSO from Whittier Street Storm Tanks and OARS for a Typical Year

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CSO

(MG

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OSIS Augmentation Relief Sewer (OARS)

OARS Tunnel

OSIS

OARS Near Surface Key Components

Whittier St. Storm Tanks O/F

Deshler Tunnel

Jackson Pike WWTP

Mechanical Bypass

OARS FDS

HRT (250 MGD)

Henry St Regulator

Chestnut St Regulator

Spring St Regulator

Long St Regulator

Broad St Regulator

Capital St Regulator

State St Regulator

Town St Regulator

Rich St Regulator

Peters Run Regulator

Whittier St Regulator

Moler St Regulator

10 MG storage

10 ft x 16 ft

(304 x 487 cm)

23,000 ft (7,010 m) of 10 x16 ft (304 x 487 cm) near surface

14 Relief structures

1 Access shaft

1 Pump Station

250 MGD (10.95 m3/s) High Rate Treatment

10 MG (37,850 m3) Storage facility

Pump Station (250 MGD)

OARS

OARS Near Surface Approach

Sluice Gate

Input Sewer

Overflow Sewer

OSISInterception Connection

CSO Regulator

O/F

OSIS Performance with Near Surface OARS

Risks for Open Cut Options

Delays with flooding of construction site

Disruption of downtown streets

Congestion caused by construction traffic

Extensive relocation of utilities

Construction difficulties in crossing river and railroad tracks

Issues with contaminated soils in railroad yards

Possible Construction Methods for OARS

Sluice GateOverflow Sewer

OSISInterception Connection

CSO Regulator

O/F

OARS

Input Sewer

Updated OARS Tunnel Approach

River

OARS Tunnel Key Components

Whittier St. Storm Tanks O/F

Deshler Tunnel

Jackson Pike WWTP

Mechanical Bypass

OARS FDS

10 MG storage

HRT (250 MGD)

FM

Henry St Regulator

Chestnut St Regulator

Spring St Regulator

Long St Regulator

Broad St Regulator

Capital St Regulator

State St Regulator

Town St Regulator

Rich St Regulator

Peters Run Regulator

Whittier St Regulator

Moler St Regulator

20-ft (614 cm)

Tunnel

OARS Tunnel Key Components

10 MG storageWhittier St. Storm Tanks O/F

Deshler Tunnel

Jackson Pike WWTP

Mechanical Bypass

OARS FDSFM

Henry St Regulator

Chestnut St Regulator

Spring St Regulator

Long St Regulator

Broad St Regulator

Capital St Regulator

State St Regulator

Town St Regulator

Rich St Regulator

Peters Run Regulator

Whittier St Regulator

Moler St Regulator

20-ft (614 cm)

Tunnel

HRT (250 MGD)

Relief connections

1. Keep DWF in the OSIS and Flow due to low intensity rainfall 2. Divert WWF from three (3) locations3. Use Tunnel size 20-ft diameter (614 cm)4. Eliminate unnecessary relief connections5. Increase Capture at Chestnut and Henry Regulator6. Eliminate High Rate Treatment7. Real time control at Henry St. regulator.8. Throttle SG from Nationwide Storm sewer (108-in)9. Utilize updated dimensions/elevations for the connections at the Relief

Structures from design layout.10. Improve model stability

Model Parameters Examined to Achieve LOS

OSIS Performance with OARS Tunnel

OARS Near Surface

OARS TunnelOSIS

OSISOverflow

OSIS Performance with OARS

Cost Comparison, 2009 Dollars

Item Near Surface Tunnel

Pump Station N/A $40 M

Near Surface Pipe $260 M N/A

Connections $5 M $30 M

Tunnel and shafts N/A $280 M

Storage $76 M N/A

CSO HRT $125 M N/A

Total $466 M $350 M

Conclusions

Deep tunnel for CSO in-line storage is the optimum solution.

Hydraulic analysis using the model allowed to size the tunnel for appropriate balance to maximize treatment, maximize storage and optimal controls.

For the same performance, Modeling analysis saved $125 M

Questions?