Basin 4 Collection System Improvements


San Mateo Neighborhoods in I/I Pilot Project AreaProject Title:  Basin 4 Collection System Capital Improvement Projects

Project Type:  Collection System

Project Schedule/Status: The project is currently in the preliminary design stage.

Condition Assessment Activities: November 2017 to March 2018

Approximate Construction Start & End Dates: Dec 2020 to Dec 2022

Project Location:

Basin 4 is located in a portion of southeast San Mateo. The Basin 4 Storm Water Inflow and Infiltration (I/I) Pilot Project area extends east of Eisenhower St. and Van Buren St. to the lagoon (see map).

Project Description: 

The purpose of the Basin 4 Collection System Capital Improvement Projects is to improve the capacity of the sewer system to deal with wet weather and manage peak flows to help prevent sewer overflows and meet regulatory requirements.

This work includes an Inflow/Infiltration (I/I) Pilot Project that is designed to help the City better understand how, how much, and where rain water enters the sewer collection system. The I/I project will help the City determine the types and locations of repairs, and where to focus rehabilitation efforts.

Three project types are planned for the Basin 4 area: 

  1. Storm Water Inflow and Infiltration (I/I) Pilot Projects
  2. Sewer Pipe Improvement Projects
  3. Pump Station Improvement Projects

How Storm Water Enters the Sewer SystemI/I Pilot Projects

As a part of the Clean Water Program’s comprehensive approach to assessing and upgrading its aging wastewater collection and treatment system, we are evaluating how, how much, and where storm water enters the sewer collection system. This storm water entering the sewer system is called Inflow and Infiltration (I/I). During heavy rains, excess amounts of storm water entering the system can overwhelm its capacity, causing sewer overflows. The CWP identified the I/I project as one way to help determine the best methods of reducing I/I and flows to the treatment plant in order to minimize system overflows.

The first step is to assess the condition of the sewer collection system in those areas. Condition assessments look at sewer mains, manholes, sewer laterals, and storm drains to find cross-connections, leaks, breaks and other pipe defects.

Condition assessments are scheduled to begin in late 2017.

Click here to see answers to frequently asked questions about these activities.

Condition Assessment AreaWhat the Condition Assessment Includes

The condition assessment area is broken into two zones (see map). Zone 1 covers the northern portion of the Marina Lagoon neighborhood, east of the Kehoe Ave. and Roberta Dr. intersection. Zone 2 covers from Kehoe Ave. south to the intersection of Roberta Dr. and Eisenhower St., and east of Van Buren St. and Eisenhower St. to the lagoon.

In Zone 1 and Zone 2, video inspections of the sewer mains and laterals will be conducted. In Zone 2, where the sewers are located in easements on private property, above-ground mapping of the laterals will be conducted in addition to video inspections. Smoke testing will occur in both zones. Depending on findings, colored water tracer tests may be used to locate cross connections between the sewer and storm drain systems. These assessment techniques are detailed below.

Video Inspection

Sewer mains in the project area will be cleaned using high-powered water hoses that are placed down the manholes. After cleaning, a remote-controlled, tethered camera on wheels will travel through the sewer mains and laterals to locate and record pipe defects.

The video inspections will provide information about defects in the sewer pipes which may lead to repairs or replacements. 

Sewer Cleaning and Inspection Equipment

The Field Crew Will Digitally Record and Physically Mark the Lateral Path with Flags or Other Non-Destructive Methods. The Field Crew Will Map the Path of the Lateral; Markers Will Be Removed before the Crew Leaves.In addition to the video inspection of sewer mains and laterals, residences in Zone 2 will also have their backyard lateral mapped. To map a lateral, a field worker will follow the lateral camera above ground using a special piece of tracking equipment. The equipment used will store location data, and small flags (or other non-destructive markers) will be used to mark the path of the lateral. A sketch of the lateral path will be recorded. The flags or other markers will be removed when the field team is finished.

As part of the assessment process, some neighborhood storm drains will be video inspected. The primary goal will be to identify any cross connections between the storm drains and sewer system. Eliminating cross-connections will help prevent storm runoff and lagoon water from entering the sewer system. Storm drains to be inspected are shown below in red. For residences with an access manhole or lagoon outfall in their backyard, field crews will provide a door hanger notification 72 to 48 hours prior to entering the backyard.

Storm Drains to be Inspected Shown in Red

Non-toxic Smoke Testing

Smoke testing helps to locate cracks and other openings or connections where rain water might enter the sewer collection system. A non-toxic smoke is blown into parts of the sewer system, and it will follow the path of any leak. As shown in the figure below, potential smoke release locations include roof vents, catch-basins, clean-outs, roof down-spouts and pipe and manhole defects.

How Non-Toxic Smoke Testing Works

The smoke is clean and non-toxic to humans, pets, food, plants, and material items and no smoke will enter your home or business if it is properly plumbed, vented, and the P-traps contain water.

To prepare for the smoke testing activity, residents should fill P-traps in unused sinks and drains by running water for 5 seconds. If smoke does enter your home, open windows for ventilation, and then inform the crew chief doing the testing in your area.

Residents will be notified approximately 72 to 48 hours before smoke tests are conducted. 

All sewer mains in the condition assessment area will be smoke tested and Public Safety authorities (Police and Fire) will be notified of testing locations and dates.

Example Starting Point for Colored Water Tracer TestingNon-toxic Colored Water Tracer Test

Depending on the results of the video and smoke inspections, some sewer mains and storm drains may have additional testing done to help locate the source of any cross connections. This testing will consist of placing colored water down a sewer or storm drain and observing surrounding flow for the presence of colored water.

The colored water is non-toxic and all regulatory requirements and local laws will be followed.

What this Means for the Community

During the evaluation phase, residents should expect minimal disruption. During video, smoke, and colored water testing there may be minor localized traffic slowdowns when work trucks are present.

Residents will be notified with door hangers approximately 72 to 48 hours before work begins in their neighborhood.

Because the sewer mains in Zone 2 are located in backyards, crews may need to access certain easements for parcels that have manholes in them. Residents in Zone 2 will also be asked to sign a Right-of-Entry to authorize the field crew to enter their property to carry out this work. This process will include marking the path of the lateral using flags, cones, or other non-permanent and non-destructive techniques. Once mapping is complete, the markers will be removed. This process is expected to take 1 to 2 hours per yard. Residents will receive a door hanger notification 72 to 48 hours before lateral mapping field activities are scheduled to occur.

Prior to smoke testing, we recommend that residents fill P-traps in unused sinks and drains by running water for 5 seconds. If smoke does enter your home, open windows for ventilation, and then inform the crew chief doing the testing in your area.

Sewer Pipe Improvement Projects

The Clean Water Program is conducting an analysis of potential sewer main improvement projects within the Basin 4 area. With the help of hydraulic modeling, the analysis will determine the locations where improvements are needed the most to reduce the likelihood of sewer overflows. Improvements may include enlarging and/or rerouting existing sewer mains to increase capacity and more effectively transport waste within the sewer system.

Pump Station Improvement Projects

Pump stations lift wastewater from low elevations to high elevations so that it can continue flowing by gravity from homes and businesses throughout the city to the wastewater treatment plant. Increasing the pump station capacity to move wastewater is another way to reduce the risk of sewer system overflows within the community.

Engineering Design Firm: Woodard & Curran

Construction Contractor: TBD

Estimated Project Cost:  The preliminary budget for this project is being developed and will be informed by the findings from the condition assessment tasks.