COUNTY OF SAN MATEO

Inter-Departmental Correspondence

Department of Public Works

DATE:

September 24, 2008

BOARD MEETING DATE:

October 7, 2008

SPECIAL NOTICE/HEARING:

None

VOTE REQUIRED:

Majority

TO:

Honorable Board of Supervisors

FROM:

James C. Porter, Director of Public Works

SUBJECT:

Repair Work to Colma Creek Flood Control District Channel Wall Upstream of Spruce Avenue in South San Francisco (F-149 [9H])

RECOMMENDATION:

Acting as the governing board of the San Mateo County Flood Control District (District), adopt a resolution authorizing the County Manager to enter into agreement(s) with EagleLIFT Inc., in amounts not to exceed a total of two hundred thousand dollars ($200,000), without advertising for bids, to have channel protection work performed on force account basis.

VISION ALIGNMENT:

Commitment: Ensure basic health and safety for all.

Goal 7: Maintain and enhance the public safety of all residents and visitors.

Adoption of this resolution contributes to this commitment and goal by working to effectively preserve the integrity of a flood control facility and adjacent infrastructure for the benefit of the public.

BACKGROUND:

Previous Board Action

Adopted Resolution No. 069270 on February 12, 2008, finding that an emergency existed and emergency work was necessary to repair the Colma Creek Flood Control Channel Walls upstream of Spruce Avenue in the City of South San Francisco and authorizing the County Manager to enter into contracts up to $500,000 to address the emergency without a competitive solicitation for bids.

DISCUSSION:

The emergency work authorized by your Board was performed during March and April of 2008 to minimize additional channel wall movement. Steel braces were installed across the top of the channel walls for approximately 270 linear feet to restrain the walls from further movement, which had created substantial pavement cracking along the north side of the channel and soil subsidence along the south side of the channel. The wall movement threatened the floodwater carrying capacity of the channel; was impacting the roadway owned by the City; and could have impacted a large diameter sanitary sewer pipe owned by the City.

Subsequent to the emergency repair work the District has been monitoring the walls for movement and has found that further wall movement has not occurred. The District retained consultants to perform void detection testing behind the walls and study the potential causes of the walls’ previous movement. This work has concluded that voids behind the walls do exist and they appear to be caused by soil movement from behind the walls through the joints between the reinforced concrete sheet piles and channel transition joints during storm events and tidal fluctuations.

The District has evaluated methods for minimizing the movement of soil while a permanent solution is identified, designed, and permitted. The District has field reviewed the site and received a proposal for purchase and application of a proprietary product utilizing a patented method for void filling and densification of soil. The product is an expanding material, which can be injected into the soil behind the walls at various depths to fill the existing voids in the soil and joints between the sheet piles and channel transition joints to prevent further soil movement and subsidence.

EagleLIFT Inc. has submitted a proposal, which includes injection of approximately 20,000 pounds of the expanding material for 100 linear feet, to depths of 25 feet, at the cost of $170,000. The work can be completed in October 2008, prior to the onset of the winter rains. Public Contract Code Section 21381 allows the Board, acting on behalf of the San Mateo Flood Control District, to purchase materials and to have channel protection work done by force account without advertising for bids. By enabling the County Manager to enter into contract(s) to purchase the necessary materials and have the work performed by EagleLIFT on a force account (a time and materials basis), the work may proceed in an expedited manner to preserve the integrity of existing flood control facility, adjacent roadway, and large diameter sewer before the winter rains begin.

The resolution has been approved as to form by County Counsel.

FISCAL IMPACT:

The total estimated cost for construction is $200,000, which includes an eighteen percent (18%) contingency (approximately $30,000) because the quantity of the expanding material is based on best available soil data and the number and extent of the voids may have increased since the investigation of the voids. The contingency may also be used to pay for additional work resulting from unforeseen conditions not anticipated by the District. This work will be financed by District funds. There is no impact to the General Fund.