TO:Andrew P. Powers, City Manager
FROM:Clifford G. Finley, Public Works Director
DATE:January 30, 2024
SUBJECT: Hill Canyon Treatment Plant Stormwater Diversion Project (CI 5427)
RECOMMENDATION:
1. Approve Fifth Amendment to Professional Services Agreement No. 12393-2020 with Dudek, Inc. (Dudek) of San Juan Capistrano, CA, for additional design services on the Hill Canyon Treatment Plant (HCTP) Stormwater Diversion Project (CI 5427) in the amount of $30,860, for a revised not-to-exceed amount of $270,439.77.
2. Authorize expenditure in the amount of $30,860 from A/C #624-8250-682-8300 (CI 5427 HCTP Stormwater Diversion Project).
3. Find that this action is not a project as defined under the California Environmental Quality Act (CEQA).
FINANCIAL IMPACT:
No Additional Funding Requested. $950,000 is included in the Adopted FY 2023-24 Wastewater Capital Fund Budget with an additional budget carryover of $1,778,512 for a total available budget of $2,728,512. The total estimated cost of the project is $2,500,000.
BACKGROUND:
The City’s HCTP treats approximately eight million gallons per day generated by the City’s 34,000 wastewater customers from the community of Thousand Oaks and is located at the confluence of the North and South Arroyo Conejo Creeks. The boundaries of the plant are adjacent to natural slopes and habitat. On the east side of the facility is a side canyon that leads into the HCTP facility near the flow equalization basins and drying beds (Attachment #1).
HCTP Stormwater Diversion Project CI 5427
January 30, 2024
8 9
5 There is an existing section of concrete drainage swale near the boundary of the plant that directs stormwater flow to an existing 30-inch storm drain pipeline. The 30-inch pipe captures the 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 stormwater permit exemption.
Storm events generate substantial flows from the hillside and canyon that can overcome the existing drain inlets. These events deposit natural debris (rocks, vegetation, mud) from outside of the HCTP property onto the access roads and lead to substantial cleanup and debris removal. The debris flows jeopardize the operation of the HCTP because the debris enters near the chemical tank storage area. Additionally, the stormwater volume from the side canyon utilizes storage in the retention basin, which is needed for system flows especially during heavy rain events.
In the past, these drain overflows were transported through the existing HCTP drainage system directly to the Arroyo Conejo Creek. However, with the changes in the stormwater permit, the flows are no longer allowed to leave the plant and are therefore directed to the equalization and emergency retention basins. This new project will create a debris capture area and prevent the stormwater from the hillside from overflowing into the treatment plant site. The stormwater from the canyon will be diverted directly to Arroyo Conejo Creek without ever coming on the plant site.
On May 12, 2020, City Council approved a Professional Services Agreement with Dudek to provide a preliminary design report and preparation of construction contract documents for the HCTP Stormwater Diversion Project in the amount of $105,478. 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, added an additional scope of work for technical studies and environmental analysis in the amount of $134,101.77. 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.
DISCUSSION/ANALYSIS:
During the project design phase, staff determined that a modification to the debris basin design piping connections could help reduce the environmental impact of the project as well as reduce the overall permitting requirements. Staff recommends City Council approve the Fifth Amendment to the Agreement with Dudek in the amount of $30,860 to perform the design revisions (Attachment #2).
HCTP Stormwater Diversion Project CI 5427
January 30, 2024
8 9
5 Staff anticipates that the revised design work will extend into the Spring of 2024, at which point the final permits, construction plans, and specifications will be finalized. It is anticipated that the project will be scheduled for the start of construction in Summer 2024. Staff will return at a future City Council meeting to recommend an advertisement of the project to solicit construction bids.
Community Outreach: This project will be limited to work at HCTP and is not expected to impact any neighboring residences. The work will be at the south end of the plant and will have a limited impact on plant operation. Construction-related impacts to hiking trail users will be minimal.
This project meets City Council’s Top Ten Priorities #6, “Public Works + Infrastructure Investments”.
CIP PROJECT PRIORITY (as outlined in FY 2023-24 and FY 2024-25 CIP Program Budget)
Priority One – Addresses Health and Safety, legal and regulatory requirements, or a top City Council Priority.
COUNCIL GOAL COMPLIANCE:
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
Attachment #2 – Fifth Amendment to Agreement with Dudek, Inc.
DPW: 850-20\nh\etm\Council\2024\013024\CI 5427\ HCTP Stormwater Diversion Project staff report.docx