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Remediation of Pesticides in Oso Flaco Creek

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Ariel Image of the Project Area
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Coastal San Luis Resource Conservation District (CSLRCD) has worked with public and private landowners and resource management agencies to protect and remediate agricultural land and aquatic systems in the Oso Flaco watershed since 2000. This watershed is characterised by low gradients, highly erosive sandy soils, year-round intensive agricultural production and some of the highest concentrations of legacy pesticides, particularly DDT, in the state.

In 2018, CSLRCD was awarded the Remediation of Pesticides in Oso Flaco Watershed project, funded by the State Water Resource Control Board (SWRCB). Based on numerous studies, assessments and planning efforts undertaken by CSLRCD and partners over the past 20 years, the project successfully remediated 20,000 cubic yards of sediment from 1.2 miles of Oso Flaco Creek where high concentrations of DDT persist. Excavated sediment was remediated on site, using an adaptive remediation process that resulted in levels of DDT below thresholds protective of aquatic habitats and human health.

In addition to sediment excavation and remediation, the project implements a series of Best Management Practices (BMPs) to prevent continued erosion of topsoil into the waterways. Planned BMPs include installation of log check dams designed to flow flows and drop sediment for in strategic locations, resizing an undersized culvert, considered one of the primary contributors of sediment mobilization in the watershed. 

This project is part of a multi-phased remediation process and brings together a broad range of local partners, including private and public landowners, special interests groups and resource management agencies.

CSLRCD District Engineer completed engineered design plans in late 2022, and the project was implemented in mid 2023. CSLRCD staff continues to work with Farmers in the Oso Flaco watershed on projects that protect water quality and support local agricultural operations.

Dirt path beside lush greenery and a narrow waterway under a clear blue sky.
Creek channel prior to excavation
An excavator arm with a claw holding a log over a grassy area, with people walking nearby in a field.
Installation of Log Check dams

 

 

 

 

 

 

 

 

 

 

 

Partners:
CA Dept. of Parks & Recreation, Oceano Dunes District
CA Dept. of Pesticide Regulation
Teixeira Farms
County of San Luis Obispo

Funders: CA State Water Resources Control Board

RCD Contact: Hallie Richard, hrichard@coastalrcd.org