For Our San Martin Neighbors

Trunk Line Through San Martin

Wastewater from the City of Morgan Hill travels in a wastewater trunk line through San Martin to the Wastewater Treatment Plant located in the City of Gilroy, where it is treated and discharged. This plant is owned and operated by the South County Regional Wastewater Authority (SCRWA), under a Joint Powers Agreement with the Cities of Morgan Hill and Gilroy.

The trunk line travels north to south through the San Martin area between Monterey Road and Santa Teresa Boulevard Specifically, the alignment of the trunk line as it goes south out of Morgan Hill is south in Monterey Road, then west in California Avenue, then south in Harding Avenue, then continuing south across private property roughly in the Harding Avenue corridor, then continuing south to the Gilroy city limits.

Sewer Trunk Line Inspection Project

History of Sewer Trunk Line

On July 1, 1967, the City of Morgan Hill and the City of Gilroy entered into a Joint Exercise of Powers Agreement to efficiently dispose of sewage produced in each City for the benefit of both Cities. This agreement was written in response to the City of Morgan Hill receiving notification from the Central Coastal Regional Water Pollution Control Board of the State of California to expand its existing capacity to treat and dispose of its sewage. Rather than expand or construct a new facility, a decision was made to share the expense and operating costs of Gilroy's existing treatment plant and that the City of Morgan Hill would construct a sewer trunk line to convey its sewage to the Gilroy treatment. Since the first Joint Exercise of Powers Agreement was executed, various amendments followed. In June 1992, a revised Joint Exercise of Powers Agreement created the South County Regional Wastewater Authority (SCRWA). SCRWA now oversees the wastewater treatment facility functions, such as improvements, operations, and maintenance. The Cities of Morgan Hill and Gilroy share in the costs to maintain and improve the facility.

In 1993, a Sewer Master Plan was developed for the City of Morgan Hill. In 2002, a revised Sewer Master Plan was developed by Carollo Engineers. The revised Master Plan recommended that a parallel (or relief) sewer trunk to Gilroy be installed to increase capacity and for redundancy and reliability. Starting in 2003, City staff began designing the first segment for the sewer relief trunk line. An Initial Study was prepared for this segment. This new dual trunk line was installed in Monterey Road, between Tennant Avenue and California Avenue in 2006/07. Since then, two more segments have been installed, thus the trunk line currently extends to Highland Avenue in San Martin. The City has worked closely with Santa Clara County officials to coordinate the construction of the new trunk line.

Infiltration and Inflow Projects 

Sewer lateral lines all throughout the City of Morgan Hill are susceptible to breaking and cracking, which allows stormwater to enter the pipes. The City is diligently working to repair these lines throughout the City. So far, the City has repaired over 1,700 feet of public lines throughout the city to prevent these overflows from occurring. Currently, a master video assessment is nearing completion covering  the158 miles of public pipeline. The work in the public lines is continuing and a new contact to repair 7,000 more feet is currently underway.

When it comes to the privately-owned lateral lines, video inspections and any necessary repairs will be required to take place beginning on June 1st 2022. For single household properties, this happens in the event of a resale and for larger developments, like townhomes and business complexes, this will take place more regularly.  

Highland Sewer Upgrade Project

In early 2018, the City completed the Highland Avenue Sewer Upgrade Project, providing additional trunk line capacity to the City's sewer trunk line. This project upsized the previous 21-inch diameter pipe to 30-inch pipe. The project also included the installation of new metering equipment with alarm capabilities to alert operators of high flow conditions.

Continuation of New Sewer Relief Trunk

HydroScience Engineers is under contract to complete the design for the remaining segments to Gilroy. The designs for the relief line are underway and the City of Morgan Hill anticipates the plans will be substantially complete and alignment finalized by December 2021. The relief line south of Highland Avenue will follow a different alignment than the existing trunk line. The new line will be constructed entirely in public right of way in the following will follow an alignment East in Highland Avenue to Monterey Road, then south in Monterey Road to the Gilroy city limits.


Sewer Relief Trunk Alignment

Initial Study 

Initial Study Appendix A

Initial Study Appendix B

Initial Study Appendix C

Initial Study Appendix D

Mitigated Negative Declaration

Permit to Operate Sewer Trunk Line

To provide a consistent, statewide regulatory approach to address Sanitary Sewer Overflows (SSO), the State Water Resources Control Board (State Water Board) adopted Statewide General Waste Discharge Requirements (WDRs) for Sanitary Sewer Systems, Water Quality Order No. 2006-0003 (Sanitary Sewer Systems WDR) on May 2, 2006. The Sanitary Sewer Systems WDR requires public agencies that own or operate sanitary sewer systems to develop and implement sewer system management plans and report all SSOs to the State Water Board's online SSO database. The City of Morgan Hill complied with these regulations by first submitting the required Notice of Intent and fee on July 28, 2006. The City then prepared the prepared the required sanitary sewer management plan which was adopted by City Council on July 22, 2009. The City has operated its sanitary sewer collection system Waste Discharge Identification Number: 3SSO10332 since 2006.

Prior to the State's Water Quality Order No. 2006-0003 there was no requirement for the City have its own permit to operate its collection system. Instead, the Cities of Gilroy and Morgan Hill who each own and maintain wastewater collection systems operated them under the pollution control NPDES Permit No. CA0049964. The NPDES permit is issued to the South County Regional Wastewater Agency (SCRWA) Reclamation Plant which is co-owned by the two Cities. Consequently the City of Morgan Hill has always operated its wastewater collection system as required by State and Federal water quality protection laws.

Environmental Sampling

After the recent sewer spills, the City contacted private water well owners in the San Martin area whose wells were either in the path of the spill or adjacent to the path. The City has completed water sampling at 10 wells in the San Martin area. Only 1 came back with fecal contamination. According to the owner the flooding did not reach this well and therefore wastewater from the spill was not likely the cause of contamination. Staff observed that the well was not constructed properly which may have allowed contamination from another source. The City hired a licensed contractor to decontaminate the well which tested clean after re-sampling. One resident also requested the City to collect soil samples from their property near the spill. The soil samples did not show contamination.

Ownership of Wastewater Trunk Line

The wastewater trunk line that travels from Morgan Hill through San Martin to Gilroy is owned jointly by the City of Morgan Hill and the City of Gilroy. The new relief trunk line will be owned entirely by the City of Morgan Hill.

Significant Rain Storm Events

During significant rain events the wastewater trunk line running through San Martin can become overwhelmed due to infiltration of the wastewater system. This can cause the trunk line to overspill in the area on Harding Avenue between Cox and Highland. This can cause sewage to spill on to properties adjacent to this area and further downstream. When the new relief line is completed, this problem will be eliminated.

The City of Morgan Hill Wastewater Team closely monitors the entire City wastewater system, including the trunk line running through San Martin, leading up to and during significant rain storms. Crews are made ready to respond, if necessary, and bypass pumping equipment is ready to deploy and sometimes staged on site in preparation.

In the event of a spill the City of Morgan Hill Wastewater Team works diligently to first contain and sewage released and then to clean any area impacted. Notification is made to the appropriate agencies as required.

If you suspect a wastewater spill please call the City of Morgan Hill Non Emergency Police Dispatch Number at 408-779-2101. Communication plan in the event of a wastewater spill in San Martin (PDF)


The best way to stay informed about information related to the wastewater trunk line which runs through San Martin is to sign-up to receive email updates from the City of Morgan Hill. Email is the fastest way for the City of Morgan Hill to communicate directly with San Martin neighbors at any time of day or night.

Sign up to receive emails from the City of Morgan Hill regarding the status of the wastewater trunk line.

Plans for the Future

The City of Morgan Hill is taking several steps to eliminate the possibility of future wastewater spills. The projects that support this effort include: 

The Highland Avenue Sewer Upgrade Project

This project increased the overall capacity of the City's trunk line, increasing the size of the trunk line at the location of the previous incident. Status - Project Completed

Infiltration and Inflow (I&I) Reduction Projects

The City is planning to to undergo a series of projects that reduce the amount of rainwater infiltrating the City's sewer collection system and over taxing the trunk line. The first of these projects is began in 2018. Status of projects:
2018 I&I Project - Completed
2021 I&I Project - In Progress

Ongoing Maintenance and Point Repairs

City Utility staff have made significant repairs to several pipes and manholes with observed groundwater inflows. This work continues on a routine basis. Status - Ongoing 

Relief Trunk Line

Plans for a future relief trunk line, which will increase the current capacity for the future are in the City of Morgan Hill's current Capital Improvement Plan.
View current Capital Improvement Project
Status - Design Development
Expected Construction Timeframe - 2023

City Wastewater Planning Documents

Sewer Master Plan- Adopted October 2017
Sanitary Sewer Management Plan - Adopted February 2018

March 7, 2017, Meeting with San Martin Neighbors

Agenda (PDF) & Notes (PDF)

March 15, 2017, City of Morgan Hill City Council Meeting, Agenda Item: Recent Sewage Spill in San Martin

Staff report & Video from meeting

Related Information from other Agencies