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File #: 2022-0559   
Type: Consent Calendar Item Status: Agenda Ready
File created: 5/3/2022 In control: Sonoma County Water Agency
On agenda: 6/13/2022 Final action:
Title: Water System Caustic Soda and Chlorine Assessment
Department or Agency Name(s): Sonoma County Water Agency
Attachments: 1. Summary Report, 2. Attachment
Date Action ByActionResultAction DetailsMeeting DetailsVideo
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To: Board of Directors, Sonoma County Water Agency

Department or Agency Name(s): Sonoma County Water Agency

Staff Name and Phone Number: Anjenette Hayre / 707-521-1830

Vote Requirement: Majority

Supervisorial District(s): Countywide




Water System Caustic Soda and Chlorine Assessment



Recommended Action:

Recommended action

Authorize Sonoma County Water Agency’s General Manager to execute an agreement with Carollo Engineers, Inc., in a form approved by County Counsel, for water system caustic soda and chlorine assessment services through June 30, 2025, in the not-to-exceed amount of $400,000.



Executive Summary:

Sonoma County Water Agency (Sonoma Water) requires assessment of the existing pH adjustment and chlorine disinfection systems at the Mirabel and Wohler treatment facilities.




Sonoma Water is a wholesale water supplier to nine cities and water districts that serve more than 600,000 residents in portions of Sonoma and Marin counties.


Sonoma Water produces most of the potable water delivered to its customers from six Ranney collector wells located at two sites along the Russian River, referred to as Mirabel and Wohler. Each collector well extracts groundwater from the alluvial aquifer adjacent to and beneath the Russian River.


The naturally filtered water entering the collector wells is extremely clean and requires no additional treatment; however, chlorine is added as a precaution against possible contamination in the distribution system.


Russian River water has a natural pH of about 7.1 - 7.6. To reduce corrosion of lead and copper present in indoor plumbing fixtures, it is desirable to raise the pH of the river water to 8.3 - 8.5. Sonoma Water operates pH Adjustment/Corrosion Control facilities, located at the Wohler pumping plant and at the chlorination facility, where sodium hydroxide (caustic soda) is added to the water supply. This treatment also helps reduce dissolved metal content entering the wastewater treatment plants in areas served by Sonoma Water.


Mirabel facilities provide disinfection in three collector wells and have a central facility that provides disinfection. Mirabel’s pH adjustment facilities are located in the transmission system, providing treatment before water reaches customers.


Sonoma Water requires assessment of existing pH and chlorine systems at Mirabel and Wohler in order to improve system functionality, expandability, reliability, and resiliency. The existing equipment is problematic and does not meet current operational needs.  The water treatment systems will be assessed at various operating parameters to determine current and future needs.



Carollo Engineers, Inc., was selected from a list of qualified consultants developed from a prior competitive selection process. Carollo Engineers, Inc. was selected for the subject work because of their experience and knowledge of water facilities in general and their familiarity with Sonoma Water facilities.


Attached is a memorandum that explains the competitive selection process.


Sonoma Water may seek to amend or enter into subsequent agreement(s) with Board approval if required, relying upon this competitive selection process, after the preliminary or initial work is completed.



Under the proposed agreement, Carollo Engineers, Inc. will perform condition assessment of the pH and chlorine systems at Mirabel and Wohler and recommend alternatives to improve system functionality.


The cost of services will not exceed $400,000; the term end date is June 30, 2025.


The agreement includes two options for Sonoma Water to extend this agreement for a period of one year each by providing written notice to consultant thirty days in advance of the expiration date of the agreement and of the first extension option.


County of Sonoma Strategic Plan Alignment:



Sonoma Water Strategic Plan Alignment:

Water Supply and Transmission System, Goal 2:  Maintain and improve the reliability of the Water Transmission System.


Performing condition assessment of the pH and chlorine systems at Mirabel and Wohler treatment facilities will update and improve the functionality and reliability of these systems, ensuring that Sonoma Water continues to provide safe, clean water to its customers.


Prior Board Actions:



Fiscal Summary


FY 21-22 Adopted

FY22-23 Projected

FY 23-24 Projected

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Additional Appropriation Requested




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Narrative Explanation of Fiscal Impacts:

Budgeted amount of $400,000 is available from FY 2021/2022 appropriations for the Water Transmission O&M Fund. No additional appropriation is required.


Staffing Impacts:




Position Title (Payroll Classification)

Monthly Salary Range (A-I Step)

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Narrative Explanation of Staffing Impacts (If Required):




Selection Memorandum


Related Items “On File” with the Clerk of the Board: