Proposed Pipeline Project at Redwood Shores at a Glance

Silicon Valley Clean Water (SVCW), formerly called South Bayside System Authority, is in the planning stages for replacing its pipeline that brings wastewater from near the San Carlos airport to the treatment facility at 1400 Radio Road in southeastern Redwood Shores.

            SVCW started construction of another section of pipeline replacement in June of 2013 with a 48-inch diameter pipe from Maple Street in Redwood City through Bair Island. A stretch from Bair Island to San Carlos Airport along Skyway Road is scheduled to begin this June.

The current planning focuses on how to replace the pipeline from the area of San Carlos Airport out to the SVCW plant with the least disruption to the Redwood Shores community during construction and the greatest long term value.  SVCW is seeking input from Redwood Shores residents and businesses before any pipeline location decisions are made.

The new 63-inch pipeline is part of SVCW’s overall Capital Improvement Program (CIP), adopted in 2008, to replace and upgrade aging infrastructure  to ensure the reliable operation of the overall sanitary sewer conveyance system in accordance with permit conditions. The new pipelines and pump stations will be designed to reliably convey wastewater to the treatment plant through the year 2040. Whichever location is chosen, construction of the Redwood Shores portion of the new pipeline would begin in mid-to late 2015.

            Many alternative pipeline alignments from San Carlos Airport through Redwood Shores are being considered. The public is being asked for their thoughts on the options, two of which are more feasible, though no alternative has been ruled out. One is an “in-street” alignment mostly along Redwood Shores Parkway.  One is an “in-levee” alignment.  Lagoon and in-slough alignments have been identified but are not considered as feasible, though in response to initial community input, the lagoon option is being further reviewed to determine if some of the impacts can be mitigated. The feasibility of micro-tunneling through soft “young bay mud” is also being revisited.

            “We do have open ears and eyes as we ask the community for its thoughts on the possible alignments,” said SVCW Manager Daniel T. Child.

Existing Pipeline Needs to be Replaced

• The existing pipeline was built during the early 1970s and was not designed to be pressurized as it is today. The pipeline is made out of reinforced concrete pipe that deteriorates over time as it carries wastewater. As the bay mud, prevalent in Redwood Shores, settles over time the joints every 12 feet move and occasionally leak, requiring repairs along streets and in backyards. To capture sewage flows during peak storm events, improvements have been made to sewage collections systems in the cities served by SVCW. Capturing more peak flow is good for the environment and results in higher peak flows reaching SVCW pumps and pipelines.  These higher peak flows in turn require higher pressures in the existing pipe resulting in further risk of leaks in the old concrete pipe joints.

High Density PolyEthylene (HDPE) Pipe

• The new pipe used for any of the alignments will be HDPE pipe. The pipe will have rugged sides at least three inches thick and fusion welded joints that are as strong as the rest of the pipe. The fusion welding process is confirmed by bend back testing:  bending a section of pipe at the weld with the inside of the pipe facing out until the ends touch and inspecting for any cracks or voids.  The pipe is flexible to allow movement underground through soft “young bay mud” without leaking.
• HDPE piping is used regularly for dredging operations where it is laid out on the beach and subject to ocean wave action.  It is used for drains over ocean bluffs where it is attached at the bluff top and subject to ocean wave action at the bottom. Pipe sections when accidentally crushed flat return to their original shape with no cracking or failure.
• The pipe construction will create a continuous and rugged HDPE pipe from the San Carlos Airport to the SVCW treatment plant.
• HDPE is not subject to corrosion or deterioration from wastewater. 
• Most impacts from digging equipment to the pipe outside glance off of it. The risk of cutting into the pipe is extremely low when the pipe is in a location with minimal construction activity and includes surface and underground location marking.

In-street Alignment Option along Redwood Shores Parkway

• This option would likely take up to three years, one year of excavation in the streets to relocate utilities before the main pipeline construction could begin, which would take an additional two years.
• Residents near the street alignment would see, hear and feel the construction activities. Many residents in the Redwood Shores area would be impacted by extended vehicle traffic detours and delays.
• This option would require a major relocation of existing utilities. In some instances this could cause utility service disruption.  Also in this alternative there would be loud sheet pile driving on both sides of a deep trench. Various traffic detours would be necessary throughout construction.
• Initially micro-tunneling under Redwood Shores Parkway was determined to be infeasible due to the inability to steer the tunneling machine in soft “young bay mud,”  which” gets progressively deeper toward the bay end of Redwood Shores. Soil modification techniques along the route are being investigated to allow reconsideration of micro-tunneling.
• The new pipe would need to be located below existing pipes to avoid conflicts – especially at street crossings. This deep pipe trench would be below groundwater levels and require trench dewatering. Care would need to be taken during dewatering to could avoid settlement in adjacent streets and structures.  Special care and time would need to be taken to seal the sides and bottom of trenches or tunneling shafts to minimize damages associated with dewatering.
• If the new pipeline is installed in one side of Redwood Shores Parkway, both directions of traffic could be detoured to the other side. The large equipment needed for the deep trench construction would likely require severe trimming or removal of the trees on both sides of the trench.
• If the new pipeline is located in the median, traffic could be limited to one lane in each direction on each side of the trench. The trees in the median would need to be removed and replanted with possibly some trimming of trees at the outside edge of the parkway.
• Redwood Shores Parkway would be restored with new paving and landscaping.

In-levee Alignment Option

• This option could be completed in 1 ½ years and cause less disruption to the Redwood Shores community as a whole though it would be more discernible for those living near the levee.
• Residents near the levee alignment would see, hear and feel the construction activities. Many residents in Redwood Shores would be affected by the temporary loss of access to sections of the trail along the levee.
• The shorter overall duration is possible for a variety of reasons.  There are very few utilities located in the levee; preliminary research indicates there are only three stormwater pipes crossing the levee. No vehicle traffic detours would be needed for construction. No dewatering is required.  The pipeline does not need to be placed deep like in a roadway.
• The tight construction corridor with limited construction staging areas does slow the overall construction duration. However, the limited corridor width tends to limit the duration of construction behind a specific length of the levee. Preliminary constructability reviews indicate that the levee construction could be divided into six segments for construction purposes. Each section would be approximately 2,000 feet long with its own construction schedule. The disruption of each 2,000 foot section would have incentives to the contractor for timely completion of construction activities and restoration of the trail.  The estimated duration of construction along each 2,000 foot section is being determined.  
• Endangered species in the area include the clapper rail. No construction activity will be allowed on the bay side of the levee to avoid impacts. Surveys over the last five years by various projects have not indicated the presence of clapper rail in along this section of levee with the possible exception of limited sightings near the SVCW treatment plant.  Some construction period restrictions may be needed near the treatment plant.
• The levee would be restored with new trails and plantings. Any temporary loss of landscaping between the trail and backyards fences would be replaced.  Interlocked vinyl sheets would be placed below grade continuously along the levee to strengthen the levee against storms and better control rodent problems.
• Prior to construction the design of the pipe and vinyl sheet installation would be reviewed by multiple consultants, Redwood City and the Federal Emergency Management Agency (FEMA) to confirm that the levee functions would be improved with the project.  After completion of construction with appropriate inspections, the levee would be recertified by the City and FEMA.

In Slough and In Lagoon Alignment Options

• Both the in-slough and In-levee alignment options minimize disruption on neighborhoods. However, there are other issues. Both would require excavation in the water due to the large size of the pipeline, thus creating water quality issues, especially when entering and leaving the water in shallow areas.
• Endangered species habitat in the slough is a major problem for the slough alignment and renders the in-slough alignment infeasible.
• The lagoon in Redwood Shores is dredged periodically which indicates that it may be possible to address water quality issues associated with pipeline construction in the lagoon. The periodic dredging also poses a risk to the pipeline which would subject to damage from dredging operations.  Any pipeline leaks, though not expected, would be nearly impossible to detect and repair would be very difficult.  Routine inspection would require scuba diver inspections.
• The in-lagoon option is being further investigated.

Environmental Review

• Environmental review will occur after SVCW has heard from Redwood Shores residents and a preferred alignment has been identified. A California Environmental Quality Act (CEQA) environmental document will be prepared to evaluate the potential environmental effects of the preferred alignment and various alignment options.  The environmental document will be used by regulatory agencies in conjunction with the various approvals and permits that will be required for the project.  An initial study will be completed to determine the type of environmental document that is appropriate.  The public will have the opportunity to review and provide comment on the environmental document prepared for the project.

Benefits of New Pipeline

By replacing the existing 40 year old multi-jointed and deteriorating force main, SVCW will improve pipeline reliability, reduce service disruption and reduce maintenance costs associated with pipe leaks. Other project objectives include:

• Ensure the reliable operation of the overall sanitary sewer conveyance system in accordance with regulatory agency permit conditions.
• Reduce the likelihood of spills and discharges of untreated water to the surrounding environment, which has occurred occasionally with the existing reinforced concrete sewer force main.

If you would like to receive project updates by email, please send us an email to siliconvalleycleanwater@svcwnews.com or duanesandul@gmail.com

SVCW’s website is www.svcw.org

(The SVCW is a joint powers authority (JPA) that owns and operates a regional wastewater treatment plant and related wastewater pumping and transmission facilities.  The JPA members include the cities of Belmont, Redwood City, and San Carlos, and the West Bay Sanitary District (which provides sanitary sewer collection services to the cities of Menlo Park, Portola Valley, and portions of Atherton, Woodside, East Palo Alto, and unincorporated areas of San Mateo County).  The individual members of the JPA own and operate the sanitary sewer collection systems within their respective jurisdictions, and SVCW owns and operates the wastewater treatment plant as well as the sanitary sewer force mains and pump stations that convey sewage to the treatment plant).