The Mill Creek Wetlands Water Quality Treatment Project was the first of its kind to transform an area within a major U.S. flood control facility into a regional natural water quality treatment system. Mill Creek Wetlands, located in Southern California, creates, protects and restores native habitat for both plants and wildlife, improves water quality, and enhances recreational and educational use.

Low-flow discharges and storm water runoff from the 1,500-acre catchment area are discharged into the Cucamonga Creek Storm Channel via local storm drain systems. The storm water runoff is then captured via diversion structures at the point of entry of the Cucamonga Creek into the Prado Basin (Mill Creek). Diverted flows are directed through basins for sedimentation and trash removal and then routed through additional basins for retention and water quality treatment. The affected watershed area includes portions of Ontario, Chino, Rancho Cucamonga, Upland, and San Bernardino and Riverside Counties.

IMEG provided storm drain design, hydraulic modeling, basin flow routing analysis, and HECRAS modeling of the Cucamonga Creek Channel.

This project’s unique regional approach involved multi-jurisdictional planning and coordination. IMEG developed construction documents (Plans & Specifications) as well as provided construction observation for the construction of the Mill Creek Wetlands. This project is providing water quality treatment consistent with the National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges Associated with Construction and Land Disturbance Activities Order No. 2010-0014-DWQ (NPDES No. CAS000002) for storm water runoff emanating from the New Model Colonies Development. The project is also intended to allow for future treatment of storm water for a portion of the Chino Preserve Development Area.