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Home > Irrigated Lands > Water Quality Monitoring

Water Quality Monitoring


In February 2009, the Regional Board approved the Coalition’s first comprehensive Management Plan, which details the Regional Plan of Action to address multiple exceedances of water quality parameters at a given site within a three-year period. Within the Coalition’s ten subwatersheds, sitespecific management plans for registered pesticides and toxicity receive the highest priority for implementation with legacy pesticides and trace metals a medium priority and salinity (including conductivity and TDS), dissolved oxygen, pathogens, and pH a low priority, since these parameters have the highest number of potential non-agricultural sources and causes.

Yolo County Farm Bureau Education Corporation ILP Monitoring Site:

Willow Slough Bypass at Pole Line Road (WLSPL)

The Willow Slough is a large drainage including approximately 102,000 total acres. Irrigated acreage (excluding rice acreage) is approximately 66,000 acres. Predominant crops in the drainage are grain, pasture, corn, tomatoes, rice and walnuts.

2018 Pyrethroid Monitoring:

Bifenthrin was detected (Jan-June 2018) in water quality samples collected in the Willow Slough Bypass, but its concentrations weren’t sufficient to result in an “exceedance” of the chronic trigger limit.

Whether or not detected pyrethroid concentrations result in an “exceedance” depends on:
1. How many pyrethroids are detected,
2. Their concentrations,
3. The concentration of organic carbon in the water sample.

The July 2018 monitoring results for Event 149 at Willow Slough Bypass showed detectable concentrations of Bifenthrin and Lambda-Cyhalothrin.
These two detected pyrethroids resulted in an “exceedance” of the chronic trigger limit for pyrethroids that is just barely above the 1 chronic additive concentration goal unit.

We are not reporting these detected pyrethroids as exceedances only because the Central Valley Pyrethroids TMDL has not yet been approved by the State’s Office of Administrative Law and the Central Valley Pyrethroids TMDL is not yet in effect.

The Central Valley TMDL is set to be in effect within 2019.

Sampling Event Summary (Oct. 2016 - Sept. 2017)

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