To: Board of Directors, Sonoma Valley County Sanitation District
Department or Agency Name(s): Sonoma Valley County Sanitation District
Staff Name and Phone Number: Greg Guensch 707-547-1972
Vote Requirement: 2/3rd
Supervisorial District(s): First
Title:
Title
Chase Street Bridge Sanitary Sewer Siphon
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Recommended Action:
Recommended action
Authorize Sonoma County Water Agency’s General Manager acting on behalf of Sonoma Valley County Sanitation District, to execute the Amendment No. 1 to Utility Agreement No. 0811-02 with City of Sonoma, in substantially the form as the draft presented to this Board. The amendment increases the amount by $60,395 for a new not-to-exceed agreement total of $173,640 to settle the final amount due and fulfill the obligations of the agreement. (First District)
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Executive Summary:
Sonoma Valley County Sanitation District (District) is responsible for maintaining the sanitary sewer system in Sonoma Valley. One of District’s sewer pipes runs under the Chase Street Bridge across Nathanson Creek in the City of Sonoma (City). This pipe became exposed and was vulnerable to damage or breakage during high creek flows. The preferred solution was to replace the in-line pipe with a siphon located below the creek bed. City has replaced the Chase Street Bridge, and the siphon was installed at a significant cost savings to the District during City’s construction. The Agreement for Funding Chase Street Bridge Sanitary Sewer Facility Relocation (Agreement) established the terms associated with District paying City for the cost of installing the new sewer pipe during its replacement of the Chase Street Bridge, and Amendment No. 1 settles the final cost of the work.
Discussion:
HISTORY OF ITEM/BACKGROUND
In 2010, following the break of an exposed sanitary sewer pipe under the City’s Madrone Road Bridge in unincorporated Sonoma County, District conducted a field assessment of the sanitary sewer stream crossings in Sonoma Valley to identify those that were exposed or potentially vulnerable to damage due to debris or erosion during high creek flows. The sanitary sewer pipe under Chase Street, where it crosses Nathanson Creek, was exposed above the bed of the creek and was identified as a high priority site. Although the pipe was encased in a 6-inch-thick concrete casing, the casing was eroded in places, exposing the pipe. This exposure left the pipe vulnerable to further casing erosion and impacts from rocks moving along the creek bed during high flow events and contributed to further undermining of the pipe due to creek bed scour, and captured debris that could put significant loads on the pipe. Breakage of the pipe could release untreated sewage into the creek resulting in potential environmental damage and regulatory actions and fines. Additionally, the exposed pipe casing restricted the flow area under the bridge which contributed to further erosion of the creek and created a potential fish barrier during lower flows.
The District considered options for protecting the pipe and providing for fish passage but was unable to identify a satisfactory retrofit that resolved the above issues. The preferred option was to replace the in-line pipe with a siphon located below the creek bed, thus eliminating danger to the pipe, and allowing unimpaired fish passage. However, without replacing the entire bridge, a siphon would have to be installed using micro-tunneling techniques, which was prohibitively expensive.
The Chase Street Bridge was old and due for replacement. City received Federal Highway Administration funding, administered by Caltrans, to replace the bridge. This funding provided an opportunity for District to remove the potentially problematic sanitary sewer crossing and replace it with a siphon at a fraction of the cost of installing a siphon with the bridge in place using micro-tunneling techniques. In 2016, District partnered with City and contributed funding for the design of a siphon to be incorporated in the new bridge design. The new bridge was completed in March 2024.
District has an encroachment permit for the sanitary sewer pipe that runs under Chase Street, which requires that District be responsible for paying for any necessary relocation. The Agreement established the terms associated with District paying City for the cost of replacing the sanitary sewer pipe with a new siphon system during their construction of the new bridge. Because City worked with Caltrans-administered funding, City was required to adhere to the Caltrans Utility Agreement template when entering into construction related agreements affecting utilities. In that template, there is language requiring District to pay City up to 125% of the original amount of the agreement (25% is contingency) if costs exceed City’s original estimate. To meet this requirement, the Board approved the Utility Agreement No. 0811-02 between District and City (Agreement) and granted amendment authority to increase the amount of the agreement from $113,245 up to a new total of $141,556.
District and City entered into the Agreement, dated March 15, 2018, in the amount of $113,245. The Agreement was approved by the Board on March 13, 2018, and included authorization for the General Manager to amend the Agreement for an additional $28,311 provided amendments do not cumulatively increase the total amount beyond $141,556. The $28,311 was not spent and is not sufficient to cover the final cost of the work. The increase was due primarily to inflation in labor, equipment, materials, fuel and other related costs that has occurred since the original agreement was executed in 2018. Sheet piling, shoring and bracing of trenches, major components such as the sewer manhole, removal and disposal of existing sewer line, and mobilization were items that were higher than assumed in the original construction cost estimate. Therefore, this item requests authorization for $60,395 for a new not-to-exceed agreement total of $173,640 to settle the final amount.
County of Sonoma Strategic Plan Alignment
N/A
Sonoma Water Strategic Plan Alignment
Goal: Planning and Infrastructure.
Strategy: Conduct planning that integrates and balances operational, maintenance, and infrastructure priorities.
Action: Continue to engage in planning efforts to support reliable wastewater and flood management services.
This item improves operational reliability of the wastewater treatment system in Sonoma Valley by reducing the risk of damage or breakage to the sanitary sewer pipe under Chase Street where it crosses Nathanson Creek.
Racial Equity:
Was this item identified as an opportunity to apply the Racial Equity Toolkit?
No
Prior Board Actions:
03/13/2018: Approved agreement between Sonoma Valley County Sanitation District and City of Sonoma for funding of sanitary sewer line and siphon relocation during construction of Chase Street Bridge in the amount of $113,245.
Fiscal Summary
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Expenditures |
FY24-25 Adopted |
FY25-26 Projected |
FY26-27 Projected |
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Budgeted Expenses |
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Additional Appropriation Requested |
$60,395 |
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Total Expenditures |
$60,395 |
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Funding Sources |
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General Fund/WA GF |
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State/Federal |
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Fees/Other |
$60,395 |
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Use of Fund Balance |
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General Fund Contingencies |
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Total Sources |
$60,395 |
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Narrative Explanation of Fiscal Impacts:
Additional appropriations of $60,395 are required from the Sonoma Valley County Sanitation District Construction Fund to process this expense. With Board approval, unused appropriations budgeted in FY 2023/2024 will be rolled forward to FY 2024/2025 in Sonoma Water’s Q1 Consolidated Budget Adjustments.
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Staffing Impacts: |
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Position Title (Payroll Classification) |
Monthly Salary Range (A-I Step) |
Additions (Number) |
Deletions (Number) |
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Narrative Explanation of Staffing Impacts (If Required):
N/A
Attachments:
Attachment 1: First Amendment to Utility Agreement No 0811-02 with City of Sonoma
Related Items “On File” with the Clerk of the Board:
None