FDA Model Maps Livestock Runoff Risk to Leafy Greens

A new hydrologic screening tool traces how runoff from livestock operations could reach downstream produce farms in California's Salinas Valley.

Updated on Nov. 10, 2026 in Organic Food

Isometric editorial illustration of a sloped grazing hillside draining through a channel toward flat rows of leafy-green crops below. — FDA researchers unveiled a hydrologic screening model that traces how livestock runoff could reach downstream leafy greens farms across 1,239 square kilometers of California's Salinas Valley. AI Illustration. Upload story photo >

Live Poll

Do you trust federal researchers to keep produce safe from farm runoff?

FDA researchers have developed an event-based hydrologic screening model to assess how livestock runoff may expose leafy greens farms downstream. The model was tested on 48 rainfall events recorded during 2018-2021 across a 1,239-square-kilometer area of the Salinas Valley.

Why it matters

Leafy greens are a major California crop, and the model offers a way to identify where runoff pathways link livestock pastures to produce fields. The researchers developed the tool to better characterize potential contamination pathways.

The model linked 58 livestock pastures to 277 downstream farms through 1,818 hydrologic connections, while 86.3 percent of farms showed no modeled upstream pasture contribution under baseline assumptions. One pasture with an estimated 1,170 cattle connected to 56 downstream farms, though only two of 13 physically overlapping farm polygons lay downstream in the modeled network.

The players

U.S. Food and Drug Administration (FDA)

The federal agency responsible for food safety regulation, which developed the screening model as part of produce safety assessment efforts.

The details

The model combines rainfall-derived runoff estimates with mapped surface-water drainage networks and accounts for livestock capacity and the distance runoff travels along drainage pathways. Researchers estimated that upstream influence decreases with distance, with a median modeled flow-path distance of 16.8 kilometers between pastures and downstream farms.

Rainfall events analyzed during 2018-2021 in the Salinas Valley.
The largest analyzed rainfall event occurred January 27-29, 2021, producing 147.3 millimeters of precipitation.

Health Landscape

The model is positioned as a complement to the FDA's existing produce safety assessments, adding a hydrologic screening layer to how the agency evaluates pathways from livestock operations to fresh produce. It could help identify locations that may warrant additional environmental investigation.

For California residents who buy leafy greens, the model highlights that runoff from nearby livestock operations can reach some produce farms through drainage networks. Its findings may guide where additional environmental checks are considered, though the extraction does not describe any immediate change to products on store shelves.

The takeaway

Screening tools that map water pathways can show which farms are plausibly exposed to upstream sources, even when most connections are absent. Readers concerned about produce safety can look for growers and retailers that publish their water and sourcing practices.