Hill Canyon Treatment Plant Stormwater Diversion Project


SCH Number
Lead Agency
City of Thousand Oaks
Document Title
Hill Canyon Treatment Plant Stormwater Diversion Project
Document Type
MND - Mitigated Negative Declaration
Present Land Use
General Plan - Institutional; Zoning - Public, Quasi-Public, and Institutional Lands and Facilities (P-L)
Document Description
The City is proposing improvements to the Hill Canyon Treatment Plant, including storm drain improvements, development of a new debris basin, and development of a new storm water channel to route the offsite storm water flow through and around the treatment plant in a dedicated channel/pipe to an existing discharge location. As part of the self-contained storm drainage system, the Hill Canyon Treatment Plant onsite storm water system includes an existing 30-inch diameter storm drain pipe that connects into a sump pump system and diverts flows to the adjacent sludge-drying beds. The project would demolish the existing sump pump area and structure and re-establish the connection to the existing 30-inch storm drain’s original outfall to transport off-site flows from the adjacent canyon in a dedicated pipeline. The project would include the addition of three storm drain pipes: Pipe A, Pipe B, and Pipe C. Pipe A, located upstream of the flow equalization basins, would divert on-site flows to the existing flow equalization basin’s overflow structure that is routed to the sludge-drying beds. Pipe A would be disconnected from the remaining downgradient 36 inch storm drain pipe. Pipe A would be 36 inches in diameter and have a full flow capacity of 55 cubic feet per second (cfs). Pipe B would receive off-site flows from the proposed channel at the upstream end and tie into the existing 30-inch storm drain at the downstream end just past the Pipe A disconnection point. Pipe B would be 24 inches in diameter and have a full flow capacity of 93 cfs. Pipe C would receive off-site flows from the proposed debris basin at the upstream end and outlet to the proposed channel at the downstream end. Pipe C would be 24 inches in diameter and would have a full flow capacity of 50 cfs. The proposed debris basin would be incorporated at the upstream end of the of the proposed storm drain pipe on the eastern side of the treatment plant to intercept all debris and allow clear water flows from the offsite canyon to continue downstream into the storm drain system pipe, where it is routed to the outfall location. The proposed channel would connect to the proposed debris basin at the upstream end by Pipe C. The proposed channel would convey 50 cfs flows.

Contact Information

Nader Heydari
Agency Name
City of Thousand Oaks
Job Title
Deputy Public Works Director/City Engineer
Contact Types
Lead/Public Agency


Thousand Oaks
Cross Streets
9600 Santa Rosa Road at the confluence of north and south Arroyo Conejo Creek
Total Acres
Parcel #
552-013-001 and 667-012-017
State Highways
Madrona Elementary School
Arroyo Conejo Creek

Notice of Completion

State Review Period Start
State Review Period End
State Reviewing Agencies
California Air Resources Board (ARB), California Department of Fish and Wildlife, South Coast Region 5 (CDFW), California Department of Forestry and Fire Protection (CAL FIRE), California Department of Parks and Recreation, California Department of Water Resources (DWR), California Native American Heritage Commission (NAHC), California Natural Resources Agency, California Regional Water Quality Control Board, Los Angeles Region 4 (RWQCB), Department of Toxic Substances Control, State Water Resources Control Board, Division of Drinking Water, State Water Resources Control Board, Divison of Financial Assistance, California Department of Transportation, District 7 (DOT)
State Reviewing Agency Comments
California Department of Transportation, District 7 (DOT)
Development Types
Other (Stormwater basin)
Local Actions
Site Plan
Project Issues
Aesthetics, Agriculture and Forestry Resources, Air Quality, Biological Resources, Cultural Resources, Cumulative Effects, Drainage/Absorption, Energy, Flood Plain/Flooding, Geology/Soils, Greenhouse Gas Emissions, Hazards & Hazardous Materials, Hydrology/Water Quality, Land Use/Planning, Mandatory Findings of Significance, Mineral Resources, Noise, Population/Housing, Public Services, Recreation, Schools/Universities, Septic System, Sewer Capacity, Solid Waste, Transportation, Tribal Cultural Resources, Utilities/Service Systems, Vegetation, Wetland/Riparian, Wildfire
Local Review Period Start
Local Review Period End


Notice of Completion [NOC] Transmittal form
State Comment Letters [Comments from state reviewing agencies]

Disclaimer: The Governor’s Office of Planning and Research (OPR) accepts no responsibility for the content or accessibility of these documents. To obtain an attachment in a different format, please contact the lead agency at the contact information listed above. You may also contact the OPR via email at state.clearinghouse@opr.ca.gov or via phone at (916) 445-0613. For more information, please visit OPR’s Accessibility Site.

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