Mission Trails Project

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Looking south, toward Cowles Mountain, from within Mission Trails Regional Park. All blue vent stacks, seen in the distance, have since been removed as part of the Mission Trails Project.

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Construction of new facilities underway

The first phase of the Mission Trails Project was completed in 2010. Construction included a new pipeline tunnel, removal of existing blue vent stacks, and a stabilized river crossing at the San Diego River. 

The second phase of the Mission Trails Project, called the Mission Trails Flow Regulatory Structure II Project, is currently underway and includes the construction of a new 5-million-gallon underground covered reservoir, a flow control facility and pipeline interconnections. To learn more about the second phase of this project, click here.

About This Project

The San Diego County Water Authority maintains critical water pipelines beneath portions of Mission Trails Regional Park in the city of San Diego. The Water Authority is upgrading its untreated water system in the northwest area of Mission Trails to deliver more water to treatment plants that serve the central and south sections of San Diego County.

Major Elements:

  • Construction of a pipeline tunnel and associated pipeline interconnections (complete),
  • Demolition of all existing above-ground vent stacks in the park,
  • Construction of a stabilized river crossing at the San Diego River (complete), and
  • Construction of a new underground flow regulatory structure.

Pipeline and Tunnel
Two existing small pipelines were replaced with one larger pipeline. Nearly one mile long, the new pipeline was constructed in a tunnel and will be able to deliver larger quantities of untreated water, when the new FRS II is complete. A majority of work on the tunnel and new pipeline took place underground in Mission Trails Regional Park, just east of the community of Tierrasanta in the city of San Diego. The pipeline will connect to the new FRS II after it is constructed.


Flow Regulatory Structure II

FRS II Access Structure
Conceptual Photo of Flow Regulatory Structure II Access Building

A new underground flow regulatory structure, or covered reservoir, will be constructed to help regulate the water system’s flow of untreated water. It will be capable of holding up to 5 million gallons of untreated water. The facility will be covered with soil and vegetation, with the exception of access hatches and above-ground vents to allow for air movement in and out of the reservoir. Construction is anticipated to begin in early 2020 and last approximately 18 months.




Improved Crossing of the San Diego River
A river crossing that allows Water Authority, park ranger, fire, police, and emergency vehicles access to Mission Trails Regional Park was improved as part of this project in September 2009. Concrete slabs with footings, as well as a bollard marking water depth, were added to facilitate crossing for small trucks during low and normal water flows. The new, improved crossing will allow rangers and authorized personnel better access to the park. Pictures of the improved river crossing are included in the Multimedia section, below.


Vent Demolition

FRS II Access Structure
Vent Removal - Elliot vents sit on a hillside in MTRP.

When the new flow regulator structure is constructed, the Water Authority will be able to remove the remaining vent stacks in the park and replace them with smaller structures.






School Information

Street Smart School Poster
Street Smart School Poster

During construction of the pipeline and tunnel portion of the project, Tierrasanta area roads experienced an increase in the number of large construction trucks. The truck activity is expected to be similar when construction of the new flow regulatory structure begins in early 2020.


Construction requires large trucks to travel near certain Tierrasanta schools to access the western part of the park. The major roads that will be used include Clairemont Mesa Boulevard, Santo Road, Via Valarta, Antigua Boulevard, and Portobelo Drive. Truck drivers will be required to follow appropriate traffic rules, as well as weight and speed limits.


Safety is the Water Authority’s first priority, and we want to help keep kids safe. During construction, please talk to your child about street safety. “Street Smart” posters providing street safety tips will be provided to schools near the access routes. Please look for these posters at your local Tierrasanta school.


Trail Closures in the Park
When construction of the new flow regulatory structure begins in early 2020, trail safety will continue to be, as it was during the pipeline tunnel project, an important aspect of the project. Also important is maintaining recreational access to trails at the park during construction, whenever possible. To keep trail users safe when construction resumes, certain trails in the western portion of the park will be closed. During construction hours from Monday through Friday, 7 a.m. to 7 p.m., closed trails will be off-limits to recreational access. However, trails will be accessible outside of these construction hours and on Saturdays and Sundays.

Any closed trails will be reopened after construction completion. 

Helpful Links
Mission Trails Regional Park - http://mtrp.org
City of San Diego Water Department - http://www.sandiego.gov/water/
Tierrasanta Community Council - http://www.tierrasantacc.org/
San Diego Mountain Biking Association - http://www.sdmba.com/

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FRS II construction begins Early 2020
FRS II construction ends Early 2022

*All dates are approximate and subject to change.


Completed Milestones

Trails Reopened October 2010
Project construction begins October 2008
Installation of field office trailers December 2008
Clairemont Mesa Blvd. Bridge Repair December 2008 - January 2009
Establish North Portal December 2008 - January 2009
Establish South Portal December 2008 - January 2009
Major Tunneling Activities February 2009 - mid 2010
Completion of project design July 2007
Final EIR and project approved by
Water Authority Board of Directors
August 24, 2006
45-day public review period closed May 10, 2006
Public hearing at the Water Authority April 27, 2006
Release of Draft Environmental Impact Report March 27, 2006

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CIP Example
Trail closure map for pipeline tunnel project.

(View Larger)



River Crossing Before
The river crossing site prior to installation.
River Crossing Construction
A bulldozer prepares the river bottom for the concrete pad.
River Crossing Form Work
Preparing the river crossing site for rebar installation.
Finished River Crossing Pad
The finished concrete pad for river crossing.
River Crossing with Water Flowing
The new river crossing, shown under water.


There are no videos for this project.



There is no additional Multimedia for this project.


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Mission Trails Project Working Group
From May 2005 to March 2006, the Water Authority convened a public working group to gather community input about the project. Working group members included representatives from the Tierrasanta and San Carlos communities, Mission Trails Regional Park, and park user groups. The group met periodically throughout the design, environmental and planning stages, informing the Water Authority of their concerns and providing suggestions for addressing those concerns.


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Click here to view the Environmental Impact Report and other environmental documents for this project.


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For more information, please call the 24-hour toll-free project information line at (877) 682-9283, ext. 7004 or email CIPinfo@sdcwa.org. A representative from the project team will return your inquiry within one business day.


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