TO:Andrew P. Powers, City Manager
FROM:Clifford G. Finley, Public Works Director
DATE:December 3, 2024
SUBJECT: Hill Canyon Treatment Plant Stormwater Diversion Project (CI 5427)
RECOMMENDATION:
1. Authorize staff to advertise for construction bids for Hill Canyon Treatment Plant (HCTP) Stormwater Diversion Project (CI 5427).
2. Find that this action is not a project as defined under the California Environmental Quality Act (CEQA).
LEVINE ACT ITEM: No
FINANCIAL IMPACT:
No Additional Funding Requested. Minimal staff time and costs required to advertise for bids is included in the Adopted FY 2024-25 Wastewater Fund budget. $2,737,125 in carryover budget is included in FY 2024-25 Wastewater Capital Fund for CI 5427. Additional funding for construction costs may be requested at the time of construction contract award depending on bids received.
BACKGROUND:
The City’s HCTP treats wastewater from the entire community of Thousand Oaks.
The HCTP is located in a canyon environment in the northwest corner of the City, located between two creeks in a natural, unimproved environment. On the east side of the facility, there is a canyon wall that drains into the HCTP (Attachment #1). A section of concrete drainage swale behind the block wall directs flow to drain inlets that are 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 the City performs as part of its permit exemption.
HCTP Stormwater Diversion Project (CI 5427)
December 3, 2024
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Recent storms have caused significant runoff from the canyon wall and hillside, resulting in substantial flows that overwhelm the 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 the location of the debris flow can prevent chemical deliveries to the plant. Additionally, the stormwater volume from the canyon wall reduces the detention basin’s available storage capacity, which is needed for managing system flows during heavy rain events. In the past, these 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 were directed to the equalization and emergency retention basins.
On May 12, 2020, City Council approved a Professional Services Agreement with Dudek, Inc., 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. The agreement was amended on several occasions. The first amendment on December 8, 2021, was to extend the project term to December 31, 2022. The second amendment on January 11, 2022, in the amount of $134,101.77 plus $13,409.23 in extra services, added an additional scope of work for technical studies and environmental analysis. The third and fourth amendments 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 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.
This project will create a debris capture area on the eastern boundary of the plant by constructing elevated retaining walls and widening the drainage channel. Piping will be installed to redirect stormwater from the side canyon around the perimeter of the treatment plant. The diverted stormwater from the canyon will be diverted directly to the historical discharge point in the Arroyo Conejo Creek.
DISCUSSION/ANALYSIS:
The work to be performed 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.
HCTP Stormwater Diversion Project (CI 5427)
December 3, 2024
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The tentative schedule for completion of the project is as follows:
Bidding December 2024
Award of Construction Contract January 2025 Start of Construction Spring 2025
Construction Completion Fall 2025 The estimated project costs are as follows:
Design and Engineering (previous) + Support $ 494,397 Design Services During Construction (future) $ 250,000 Construction Phase Estimate (future) $ 1,800,000 Total Estimated Project Cost $ 2,544,397 The overall project cost (including contingencies, design services during construction/testing, project management) is estimated at $2,544,397. Additional budget appropriation at the time of construction award may be requested, depending on the construction bids received.
The project plans and specifications were completed by Dudek, Inc. and reviewed by City staff and are available for review upon request to the Public Works Department by e-mail at [email protected] or by phone at (805) 449-2400.
It is recommended that the project be advertised for bid. Once bids are received, staff will make a recommendation at a future City Council meeting for award of the construction contract.
As part of the project design efforts, the consultant has prepared a Mitigated Negative Declaration (MND) document in accordance with CEQA guidelines. Staff will finalize the MND document with the consultant and recommend its adoption at a future City Council meeting.
Community Outreach: This project will be limited to work at the HCTP and is not expected to impact neighboring residences. The work will be at the south end of the plant and will have limited impact to plant operation. Construction related impacts to hiking trail users will be minimal.
CIP PROJECT PRIORITY (as outlined in FY 2023-24 and 2024-25 CIP Program Budget)
Priority One – Addresses health and safety, legal and regulatory requirements, or a top City Council Priority.
COUNCIL GOAL COMPLIANCE:
HCTP Stormwater Diversion Project (CI 5427)
December 3, 2024
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Meets the following City Council goal:
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
Documents Provided Under Separate Cover:
#1 – Project Plans and Specifications
DPW: 850-20\ev\Council\120324\CI 5427\HCTP Stormwater Diversion Project staff report.docx