Inter-Departmental Correspondence

Department of Public Works



January 7, 2010


January 26, 2010







Honorable Board of Supervisors


James C. Porter, Director of Public Works


Reimbursement of Costs Incurred by the City of South San Francisco to Protect City Facilities Affected by Distressed Walls of the Colma Creek Flood Control District Channel Upstream of Spruce Avenue in South San Francisco (F-149 [9H])



Acting as the governing board of the San Mateo County Flood Control District (District), adopt a resolution authorizing reimbursement of costs incurred by the City of South San Francisco in connection with the installation and rental of steel sheet piles on North Canal Street to protect its roadway and sanitary sewer facilities, in an amount not to exceed a total of one hundred thirty thousand dollars ($130,000).



A 270-foot section of the Colma Creek Flood Control Channel (Channel) upstream of Spruce Avenue in the City of South San Francisco (City) experienced significant wall movement in early January 2008. The wall movement in association with storm events in the following months created substantial pavement cracking along North Canal Street and soil subsidence adjacent to the walls on the south side of the Channel. The City was concerned that the wall and soil movement could threaten their large diameter sanitary sewer pipe in addition to further disturbing their roadway.


Based on the magnitude of the wall movement and associated distresses, the City hired a contractor to install 100 feet of steel sheet piles between the channel wall and their large diameter sanitary sewer pipe to protect the roadway and provide support to the soil surrounding the sanitary sewer pipe in North Canal Street. The sanitary sewer pipe carries approximately 25% of all sewage from the City to its treatment plant.


Your Board adopted Resolution No. 069270 on February 12, 2008, which approved emergency work to install a temporary bracing system to minimize additional channel wall movement. Your Board later adopted Resolution No. 069729 on October 7, 2008, approving a contract to fill the voids in the soil behind the walls.



The emergency work to install the bracing system to minimize additional channel wall movement was performed during March and April of 2008. An expanding material was placed in October 2008, which was injected into the soil behind the walls at various depths in an effort to fill the existing voids in the soil and prevent further soil movement through the channel joints. The actions taken by the District has temporarily stabilized the channel walls. Staff has been monitoring the site regularly and is currently working with consultants to permanently repair the walls.


In addition to the actions taken by the District, the City had temporary steel sheet piles installed to protect their large diameter sanitary sewer pipe and roadway in April 2008. The City had the temporary steel sheet piles on North Canal Street removed in June 2009 after the bracing system was installed and the void filling work was completed by the District.


The Colma Creek Flood Control Zone Citizen’s Advisory Committee (Advisory Committee) members unanimously approved using District funds in an amount not to exceed $130,000 to reimburse the City for the costs they incurred for the temporary steel sheet piles at the Advisory Committee meeting on March 10, 2009. It was anticipated that the sheet piles may have to be rented for up to three years or until the permanent repair was completed.


County Counsel has reviewed and approved the Resolution as to form.


Adoption of the Resolution will contribute to the Shared Vision 2025 outcome of a Collaborative Community by authorizing the collaboration with other municipalities to effectively maintain and protect public infrastructure and reimburse costs incurred by local agencies affected by District facilities.



The City has incurred $59,063.00 in costs for the initial installation of the steel sheet piles and sheet pile rental fees for a period of thirteen (13) months (May 2008 to May 2009). Reimbursement to the City of these costs will be made upon receipt of an invoice and supporting documents from the City and will be financed by District funds. Based on the current conditions, it is not anticipated that reimbursements beyond the costs incurred by the City to date will be made. However, authorizing a reimbursement amount not to exceed $130,000 is consistent with the recommendation of the Advisory Committee and allows for future reimbursements to be made to the City should additional ground movement occur that affects the City’s facilities prior to construction of the permanent repair and during the design and environmental permitting process.


There is no impact to the General Fund.