02145_-_Sewer_Bypassing_and_Dewatering.pdf

Sewer Manhole Rehabilitation 02145-1 Project No. 07693 City of Hayward Sewer Bypassing And Dewatering November 2025

SECTION 02145

SEWER BYPASSING AND DEWATERING

PART 1 - GENERAL

1.01 Summary

A. Scope: This section specifies the requirements for temporary bypassing of flows in gravity sewers around Contractor's work. The existing sewers are currently and continuously receiving and conveying sewage, and those functions shall not be interrupted except as specified herein. The Contractor shall coordinate the work to avoid any interference with normal operation. Contractor shall immediately correct any undesirable conditions which result from bypassing or other operations.

B. Requirements:

1. Contractor shall provide labor, equipment, materials and supervision to temporarily control flow around the Contractor's work during construction. Contractor shall not interrupt the functions of the existing sewers.

2. Bypass pumping shall be done in a manner that will not damage private or public property, or create a nuisance. The pumped sewage shall be in an enclosed pipe or hose that is adequately protected from pedestrian and vehicle traffic, and shall be redirected into the sanitary sewer system. Discharging of sewage on private property, gutters, streets, sidewalks, or into storm sewers is prohibited. The Contractor shall be liable for all damages or fines (including fines imposed on the City as a result of the Contractor's operations) associated with this work. After the work is completed, flow shall be restored to original conditions and temporary facilities shall be removed.

1.02 Submittals

A. The Contractor shall submit sketches showing methods and equipment the Contractor proposes to utilize in sewer bypassing and flow control. The submittal shall be per the City of Hayward Special Provision 1 Sewer Flow Control and Bypass Pumping and include the following information:

1. Site plans showing the size and layout of pumps, valves, and temporary pipelines. The layout shall also show how facilities will be protected during use.

2. Calculations showing the selected pumps are capable of pumping the anticipated flow. The calculations should include head loss of all pipe, valves, and fittings. Calculations shall be stamped and signed by a civil or mechanical engineer licensed in the State of California.

3. Catalog data for selected pumps including pump performance curves.

4. Catalog data for pump controls and audible alarms.

5. Catalog data for generators.

6. Catalog data and plan of operations for temporary line stoppages.

7. An emergency response plan to be followed in the event of a failure of the bypass pumping system.

1.03 Job Conditions

A. Anticipated Flows: Bypass methods and equipment shall be capable of continuously carrying an amount of flow equal to the capacities of the bypassed sewers flowing full under gravity. If the pipe slope cannot be ascertained, the Contractor may assume that the full pipe velocity is three (3) feet per second.

Sewer Manhole Rehabilitation 02145-2 Project No. 07693

B. Notification: The bypassing and dewatering systems shall not be shut down between shifts, on holidays or weekends, or during work stoppages without written permission from the City’s Representative. The Contractor shall provide 1 week advance notice to the City’s Representative of the location and schedule of flow control.

PART 2 - PRODUCTS

No products are included in this section.

PART 3 - EXECUTION

3.01 Sewer Flow Control

A. General: Sewer bypassing shall be accomplished by pumping the upstream flow around the Contractor's work as needed to completely dewater the Contractor’s operations.

The Contractor shall furnish, install and operate pumps, generators, plugs, pipes, valves, manifold piping, ramps, temporary trenching, steel plating, backfilling, paving, striping, and shall provide all other equipment, labor, and materials necessary to divert the flow of wastewater around the Contractor's work area. The bypass system shall be completely leak-free. Any drips or leaks shall be repaired by the Contractor immediately.

B. Performance Test: Prior to beginning construction, the Contractor shall schedule and coordinate with the City’s Representative a performance test of the bypass system. The performance test shall demonstrate the ability of the duty pumps and generators to handle the lift station flows continuously without flooding, leaking or otherwise failing. The performance test shall be conducted in the presence of the City’s Representative for a minimum period of 24 hours.

C. Monitoring and Reporting: Monitoring of the flow levels and pump operation shall be provided to ensure continued operation of the bypass system. Monitoring shall take place at the site on a 24-hour basis. At least one person shall be dedicated solely to the monitoring of the bypass pumping systems. Audible alarm systems shall be installed for each bypass system. The Contractor employee assigned to the monitoring shall have a vehicle and a cellular phone and any additional equipment in their possession to effectively respond to and correct system malfunctions. The City will not provide assistance to the Contractor in the event of bypass system failure.

The flow level in each sewer shall be maintained 12 inches or less above the crown of the pipe.

The alarm system shall be configured to sound if the flow level exceeds this height. The Contractor shall notify City staff within 5 minutes of the activation of any alarm or within 5 minutes of the activation of any standby pumps. The name and telephone number of City personnel to be notified will be given to the Contractor before work begins.

The Contractor shall be responsible for reporting directly to the California State Water Resources Control Board any wastewater spills or overflows resulting from the Contractor’s activities, and to pay any fines or charges levied due to those spills or overflows.

D. Equipment:

1. Duty Pumps and Generators: For each bypass pumping system, Contractor shall provide a duty pump providing the needed capacity for the system. Contractor shall provide one sound-attenuated generator for each duty pump. During operation of the bypass system, Contractor shall arrange for a fuel delivery service to top off all fuel tanks at least once daily.

Sewer Manhole Rehabilitation 02145-3 Project No. 07693

2. Standby Pumps: Contractor shall provide one standby pump with capacity equal to the duty pump unless otherwise indicated herein. The standby pump must be connected and fully operational.

3. Plugs: Plugs shall be designed so that all or any portion of the sewage can be released without delay. Plugs shall be provided with a tag line.

4. Bypass Piping: The bypass system shall be completely leak free. Any drips or leaks shall be repaired by the Contractor immediately. Where bypass piping crosses walkways or driveways, ramps shall be provided to maintain traffic flow and protect the piping.

E. Bypass Piping Removal: Prior to removal of the bypass system, Contractor shall flush system with clean water and completely drain piping to a sanitary sewer manhole or to the rehabilitated lift station wet well. Contractor shall remove all temporary bypass piping at the conclusion of bypassing operations. All improvements shall be restored to their original condition or better.

F. Contingency: The Contractor shall maintain on site sufficient equipment and materials to ensure continuous and successful operation of the bypass and dewatering systems. Standby pumps shall be fueled and operational at all times. The Contractor shall maintain on site a sufficient number of valves, tees, elbows, connections, tools, sewer plugs, piping and other parts or system hardware to ensure immediate repair or modification of any part of the system as necessary.

Contractor shall have, on an on-call basis, personnel and equipment necessary to handle any cleanup that may be necessary due to a spill. In the event that sewage is spilled as a result of the Contractor's operations, the Contractor shall pay any and all fines imposed on the City.

3.02 Sewer Dewatering

A. Contractor shall dewater all gravity sewers before beginning any work that may breach the pipes and cause leakage of wastewater. After plugging or valving off the pipeline, the Contractor shall either pump the flow from within the sewer or excavate the low portion of the sewer and pump the groundwater from below the sewer pipeline.

3.03 Damages

A. The Contractor shall clean and repair without cost to the City any damage that may result from his negligence, inadequate or improper installation, maintenance and operation of bypassing and flow control system including mechanical or electrical failures.

**END OF SECTION**

Sewer Manhole Rehabilitation 02145-4 Project No. 07693

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