Gates Canyon Park Regional Stormwater Project

Project Specifications

Client: Los Angeles County Department of Public Works

Location: Los Angeles County

Services: Environmental Review & Permitting, Biological Resources, Cultural Resources, Compliance & Construction Monitoring

Aspen prepared an Addendum to the 2015 Los Angeles County Flood Control District Enhanced Watershed Management Programs Final Environmental Impact Report (Program EIR). The purpose of the Addendum was to evaluate site-specific environmental effects associated with the Gates Canyon Park Regional Stormwater Project. Gates Canyon Park was identified in the Program EIR as a potential site for structural best management practices to support the Enhanced Watershed Management Program for Malibu Creek Watershed. Consistent with State CEQA Guidelines Sections 15162 and 15164(a), the Addendum summarized site-specific activities that represent minor additions to the Program EIR, and which do not result in new significant effects, create substantially more severe significant effects, or require new mitigation measures beyond those adopted as part of the Program EIR. The proposed project included constructing a centralized underground infiltration system, including the following components:

• Diversion structure redirecting stormwater and other runoff to a new pretreatment system;

• Pretreatment system that removes trash, sediment, and other pollutants (e.g., oil, grease, metals);

• Cistern (3.5-acre-foot) to capture stormwater, which would be used for park irrigation;

• Disinfection system for stored water to reduce bacteria levels and break down pesticides; 

• Infiltration wells (15) and pumps to empty the cistern and allow water to percolate into the subsurface; and 

• Interpretive signs on sustainable development, and water quality and conservation efforts.

In support of the goals and objectives of the 2015 Program EIR, the proposed project would improve water quality in Las Virgenes Creek, Malibu Creek, and North Santa Monica Bay; assist the County in addressing its stormwater permit requirements; achieve water quality objectives for the project drainage area; provide a water supply benefit by reducing the use of recycled water for park irrigation; and provide recreational and aesthetic enhancements that increase public awareness of water quality and water conservation issues. Aspen was initially contracted to prepare an IS/MND and upon further review it was determined that an Addendum would be adequate to meet the requirements of CEQA, which reduced the project schedule and budget. The project was completed within budget and on schedule. Aspen was further awarded work to complete biological pre-construction monitoring, and construction archaeological and paleontological monitoring, which was completed over a three-month period (March 2019-August 2019).