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The San Gabriel River originates in the San Gabriel Mountains, draining a 689 square mile land area. The upper watershed consists of extensive areas of undisturbed riparian and woodland habitats, much of which is within the Angeles National Forest and subject to varying levels of recreational use, along with a series of flood control dams managed by Los Angeles County Flood Control District. As it flows southward, however, the river shifts to parallel the 605 freeway and begins to flow not just through natural parks and open spaces, but also through concrete channels along heavy use corridors populated by commercial agricultural growers.

The Council for Watershed Health will work with project partners to identify the contribution of metal loadings from nurseries and other irrigated agricultural lands in the San Gabriel River watershed and implement procedural BMP’s to reduce metal loads and pesticides to achieve compliance with the metals TMDL. Irrigated agriculture lands, including nurseries, are not subject to waste discharge requirements, including Municipal Separate Storm Sewer System (MS4) or other National Pollutant Discharge Elimination System (NPDES) permits.Still, some reductions will be achieved during the project as procedural BMPs are implemented and monitored.

This project has four major tasks:
1. Identify locations for BMPs through a review of existing water quality data.
2. Implement procedural best management practices (BMPs) at key locations.
3. Evaluate BMP effectiveness through water quality monitoring.
4. Recommend next steps to achieve further load reductions and approach TMDL compliance through future work.


In the first task, the Watershed Council will review existing water quality data from the Nursery Growers Association, Los Angeles Irrigated Lands Group, the San Gabriel River Regional Monitoring Program (SGRRMP) and the Los Angeles County MS4 Stormwater Monitoring Program. Using spatial analysis tools, locations for BMPs will be identified based on the connections between runoff from nurseries, irrigated agriculture and open space to the water quality in the receiving waters. More specifically, nurseries adjacent the San Gabriel River and along the 605 Freeway will be targeted for BMP implementation as dry deposition of metals from adjacent freeways represents a potentially large source of trace metals to surface waters.Runoff from nurseries can also contribute high loadings of new and legacy pesticides and the project will use data from growers surveys, the Department of Pesticide Regulation and the Los Angeles County Agricultural Commissioner to evaluate potential loading rates.

The second task will implement the management practices (MPs) that will be applied to reduce the introduction of pollutants into receiving waters. These will include the initial outreach to landowners and nursery operators by UCCE and the Watershed Council to develop a final list of priority locations and enroll nursery operators in the BMP program. UCCE will provide free best management practices training to nursery operators that enroll and participate in the program and UCCE advisors will develop recommendations customized for each nursery that participates.

In the third Task, the Watershed Council will evaluate the success of the implemented BMPs by monitoring and analyzing the water quality of runoff from nurseries during one dry-weather and one wet-weather event.

In Task Four, we will evaluate the success of the project and deliver recommendations for additional steps needed for continued water quality improvement. The recommendations may include implementation of different or additional BMPs or may recommend looking at additional sources. The report will also discuss uncertainties and assumptions in the adopted TMDL as they relate to this project.

The project will address nurseries and irrigated agriculture as non-point sources of metals to the impaired San Gabriel River. The Nursery Growers Association and Los Angeles Irrigated Lands Group have already identified some of these sites for implementation of their Water Quality Management Plan. Nurseries and irrigated agriculture lands are currently under an agricultural waiver and therefore require additional efforts to achieve load reductions. Our strategy is to prioritize the sites and conduct outreach to the owners and managers of the sites most crucial to achieving the greatest benefit for BMP implementation.

The TMDL for metals identifies brake pads, vehicle wear, building materials, pesticides, erosion of paint and aerial deposition as the main sources of metals to the San Gabriel River. While this project addresses the entire San Gabriel River watershed, it will focus on the areas with nurseries. Although these nurseries comprise less than 1% of the watershed area, many nurseries are adjacent to the San Gabriel River and the 605 Freeway and are likely contributors of constituents of concern to the river, particularly because of the known connection between freeway traffic and deposition of particulates in adjacent lands. In addition, nurseries adjacent to the river often contain new and legacy pesticides and fertilizers in sediments that run-off into the San Gabriel River. As a result, the scale of the contribution of metals from nurseries relative to other sources could be significant but is still uncertain and this will be addressed by this project.

Approximately 242 acres of nurseries adjacent to reaches 1 and 2 of the San Gabriel River will be targeted.

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