TO:Andrew P. Powers, City Manager
FROM:Nader Heydari, Public Works Director
DATE:September 23, 2025
SUBJECT: Hill Canyon Treatment Plant Stormwater Diversion Project (CI 5427)
RECOMMENDATION:
1. Approve Change Order No. 1 to Contract No. 13940-2025 with Toro Enterprises, Inc., (Oxnard, CA) for the Hill Canyon Treatment Plant (HCTP) Stormwater Diversion Project (CI 5427) in the amount of $307,782.72 for a new revised not-to- exceed amount of $1,557,282.72.
2. Approve Eighth Amendment to Professional Services Agreement Contract No. 12393-2020 with Dudek, Inc., (Encinitas, CA) for additional Construction Phase Support Services on the HCTP Stormwater Diversion Project (CI 5427) in the amount of $35,094 for a revised not-to-exceed amount of $495,313.77.
3. Authorize expense in the amount of $342,876.72 ($307,782.72 Change Order No. 1 and $35,094 for Amendment No. 8) from A/C #624-8250-682-8300 (Wastewater Fund – Capital Improvements, CI 5427).
4. California Environmental Quality Act: A Mitigated Negative Declaration (MND) was approved for this project by City Council on March 25, 2025.
LEVINE ACT ITEM: Yes
FINANCIAL IMPACT:
No Additional Funding Requested. $1,545,670 in available carryover budget is included in FY 2025-26 Wastewater Capital Fund for CI 5427.
BACKGROUND:
The City’s HCTP treats wastewater from the entire community of Thousand Oaks.
The HCTP is located between two creeks in a natural, unimproved canyon environment in the northwest corner of the City. On the east side of the facility, a canyon wall drains into HCTP (Attachment #1). A section of concrete drainage
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swale behind the block wall directs flow to drain inlets regularly maintained by HCTP staff as part of their storm preparedness activities. The drain inlets connect to an existing 30-inch diameter pipeline that captures storm flows and drains them to the sludge drying beds. This process is part of the zero-discharge storm flow capture program that the City performs as part of its permit exemption.
Rainfall and storm flow have caused runoff from the canyon wall and hillside, resulting in substantial flows that frequently overwhelm the existing drain inlets. These flows deposit natural debris (rocks, vegetation, mud) onto the HCTP parking areas and access roads, creating unmanaged drainage issues that require substantial cleanup and debris removal. The debris flows pose a risk to HCTP operations because they can prevent chemical deliveries to the plant by blocking the road. Additionally, the stormwater volume from the canyon reduces the detention basin’s available storage capacity, which is needed for managing system flows during heavy rain events.
Historically, these stormwater flows were transported through the existing HCTP drainage system directly to the Arroyo Conejo Creek. However, as part of the zero- discharge stormwater permit, the flows are now required to be directed to the equalization and emergency retention basins for treatment.
This project is constructing a debris capture area and diversion channel on the eastern boundary of the plant to prevent stormwater from entering the plant site. This includes constructing elevated retaining walls and widening the drainage channel and installing piping to redirect stormwater from the side canyon around the perimeter of the treatment plant. The diverted stormwater from the canyon will be channeled directly to the historical discharge point in the Arroyo Conejo Creek.
The work to be completed under this project includes the installation of a 30-inch diameter reinforced concrete storm drainage pipe, construction of a retaining wall, open channel, and associated outlet structure, modification/abandonment of an existing storm drainage pump station, and modification to an existing 30-inch diameter storm drain pipeline.
On May 12, 2020, City Council approved a Professional Services Agreement with Dudek, Inc. (Dudek), in the amount of $105,478 plus $10,548 in extra services, to provide a preliminary design report and preparation of construction contract documents for the HCTP Stormwater Diversion Project. Dudek is the project engineer of record and is providing design support services during the construction phase of the project. Dudek’s support services include responding to requests for information (RFI), reviewing material submittals, preparing the final project punch list, and preparing the record drawings upon completion. These professional services also include field observation and testing/inspection throughout the construction phase.
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The agreement was amended on several occasions. The first amendment on December 8, 2021, extended the project term to December 31, 2022. The second amendment, executed on January 11, 2022, in the amount of $134,101.77 plus $13,409.23 in extra services, added additional scope of work for technical studies and environmental analysis. The third and fourth amendments, executed on December 14, 2022, and December 12, 2023, extended the contract term to December 31, 2023, and then to December 31, 2024, respectively. The fifth amendment, executed on January 30, 2024, in the amount of $30,860, increased the not-to-exceed amount to $294,397 and added additional design work to mitigate environmental impact and overall permitting requirements of the project.
The sixth amendment, executed on December 16, 2024, extended the project term to June 30, 2026. The seventh amendment, executed on March 25, 2025, in the amount of $189,780, added additional scope of work for environmental/biological services during the preconstruction and construction phase of the project.
On March 25, 2025, City Council also awarded a construction contract for the HCTP Stormwater Diversion Project to Toro Enterprises, Inc., in the amount of $1,249,500 with a contingency of $124,950.
DISCUSSION/ANALYSIS:
Change Order to Construction Contract
Change Order No. 1 includes removal and replacement of an existing retaining wall back-drain, additional reinforced steel for a retaining wall stepped-footing, piping/valving, and access hatch improvements at the existing reinforced concrete wash water tank that will receive onsite storm flows. Change Order No. 1 also includes costs associated with the installation of a temporary bypass pipe around the wash water tank, along with isolation valves. The valve equipment will benefit the existing project and also stay in place for future isolation of the wash water tank. The bypass pipe will be removed and stored at HCTP for potential future use. This will greatly benefit future and ongoing regular operations and maintenance. The improvements were not originally included in the project documents, as they are not specific to the stormwater diversion components, but are directly related to the wash water tank that needs to be taken out of service during the project. Staff recommends approval of Change Order No. 1 in the amount of $307,782.72 (Attachment #2). The construction work is anticipated to be completed by December 2025.
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The construction cost breakdown is as follows:
Engineering and Project Management Support (prev. action) $ 100,000.00 Construction Contract No. 13940-2025 (previous action) $1,249,500.00 Construction Contingency (previous action) $ 124,950.00 Change Order No. 1 with Toro Enterprises, Inc. (this action) $ 307,782.72 Engineering Design Services Contract
No. 12393-2020 (previous action) $ 460,219.77
Design and Engineering Contingency (previously approved) $ 23,957.23 Construction Phase Design Support Extra
Services (previous action) $ 14,950.00
Amendment No. 8 with Dudek (this action) $ 35,094.00 Permitting and Inspection Fees (future action) $ 50,000.00 Total Estimated Cost $2,366,453.72
The construction phase started in Spring 2025 and is expected to be fully completed by early 2026.
Design Support Services During Construction
During construction, a few modifications were made to the design of the connections to the existing wash water tank, requiring additional design time to complete the requested changes (e.g., two new access hatches and a modified pipeline connection for the onsite storm water discharge). Additional efforts have been expended by Dudek to complete the required environmental permitting filing with the State (Notice of Determination and California Department of Fish and Wildlife filings) as required by the MND in order to keep the project moving ahead on schedule. Staff recommends approval of the Eighth Amendment to Contract No. 12393-2020 with Dudek for $35,094 (Attachment #3) for a revised not-to- exceed amount of $495,313.77 to include these additional services.
An MND was approved for this project by the City Council on March 25, 2025.
This project meets City Council’s Top Ten Priorities #9, “Public Works Infrastructure Investments.”
Community Outreach: This project will be limited to work at the HCTP and is not expected to impact any neighboring residences. The work will take place at the east end of the plant and will have a limited impact on plant operations. Construction-related impact on hiking trail users will be minimal.
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CIP PROJECT PRIORITY (as outlined in FY 2025-26 and 2026-27 CIP Program Budget)
Priority One – Addresses health and safety, legal and regulatory requirements, or a top City Council Priority.
LEVINE ACT (California Government Code § 84308):
This item is subject to the Levine Act. City Councilmembers who have received a campaign contribution of more than $500 (aggregated) within the preceding 12 months from a party or their agent/representative, or a financially-interested participant involved in this proceeding may do either of the following: (1) disclose the contribution on the record and recuse themselves from this proceeding; or if applicable (2) return the portion of the contribution that exceeds $500 within 30 days from the time the official knew or should have known about the contribution, and participate in the proceeding.
All parties and their agents/representatives must disclose on the record of this proceeding any aggregated contribution of more than $500 made to any Councilmember within the preceding 12 months. Councilmembers are prohibited from accepting, soliciting, or directing a campaign contribution of more than $500 (aggregated) from a party, their agent/representative, or a financially-interested participant during a proceeding and for 12 months following the date a final decision is made. In addition, a party, their agent/representative, or a financially- interested participant is prohibited from contributing more than $500 (aggregated) to a Councilmember during a proceeding and for 12 months following the date a final decision is made. The Levine Act Form for Dudek is included in Attachment #3.
COUNCIL GOAL COMPLIANCE:
Meets the following City Council goals:
C. Operate City government in a fiscally and managerially responsible and prudent manner to ensure that the City of Thousand Oaks remains one of California's most desirable places to live, work, visit, recreate, and raise a family.
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F. Provide and enhance essential infrastructure to ensure that the goals and policies of the Thousand Oaks General Plan are carried out and the City retains its role and reputation as a leader in protecting the environment and preserving limited natural resources.
PREPARED BY: Paul Weinstein, Associate Analyst
Attachments:
Attachment #1 – Vicinity and Location Maps
Attachment #2 – Change Order No. 1 with Toro Enterprises, Inc.
Attachment #3 – Eighth Amendment to Contract No.12393-2020 with Dudek
DPW: 850-20\ev\Council\092325\CI 5427\HCTP Stormwater Diversion Project staff report.docx