Coyote Creek-Metals TMDL

Background information

Coyote Creek drains a watershed of 165 square miles, 85.5 square miles of which lie in north Orange County, with the remainder in Los Angeles County. The upper watershed contains some open space, most of which is used for oil production. However, most of the watershed is highly urbanized with a mixture of residential, commercial, and industrial development. Coyote Creek flows along the border between Orange and Los Angeles counties and finally flows into the San Gabriel River just above its tidal prism. For additional information about Coyote Creek and San Gabriel watersheds, see the San Gabriel River-Coyote Creek Watershed page.

Monitoring results from 2000-03 in lower Coyote Creek have shown dissolved metals are a potential concern to wildlife.

Regulatory Description

The Los Angeles Regional Water Quality Control Board (LARWQCB) found that metals loads in the San Gabriel River watershed, including Coyote Creek, may be harmful to aquatic life and also may impair the water supply. The LARWQCB Staff Report did not indicate any dry weather impairments in Coyote Creek. However, analysis of storm samples collected by the Los Angeles County Department of Public Works indicated too many exceedances of the copper, lead, and zinc chronic criteria from the California Toxics Rule.

Consequently, the LARWQCB adopted the San Gabriel River and Impaired Tributaries Metals and Selenium TMDL on July 13, 2006. These include wet weather TMDLs for copper, lead, and zinc in Coyote Creek. No dry weather TMDLs were adopted for the creek.

However, LARWQCB has no jurisdiction over the Orange County portion of the Coyote Creek watershed. TMDL provisions in north Orange County watersheds are enforced by the Orange County Stormwater National Pollutant Discharge Elimination System Permit issued by the Santa Ana Regional Water Quality Control Board (SARWQCB). Although the SARWQCB has not adopted TMDLs for Coyote Creek, it deferred to the LARWQCB and incorporated requirements in the Stormwater Permit to comply with TMDLs established for Coyote Creek by LARWQCB, including development of a source control plan and monitoring program (SCP) for copper, lead, and zinc.


Legislation to phase out copper in brake pads in California (SB 346) is expected to help watershed stormwater copper concentrations comply with TMDL requirements. Scientific studies have shown that brake pad dust is by far the greatest source of copper in urban watersheds.

Data Collection

The County of Orange and watershed cities formed a work group to develop a SCP, which was formally approved by all parties in 2010. Monitoring under the SCP began in July 2010 and is ongoing, including dry weather and storm monitoring elements.

Monitoring results to date have shown that dry weather metals loads have been very low and fully comply with the TMDL. Stormwater lead and zinc concentrations also comply with TMDL limits.