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P.O. Box 42560
1111 Washington ST SE
Olympia, WA 98504-2560
Phone: (360) 902-1800

Regional Pesticide and Nutrient Monitoring Program

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Regional Pesticide and Nutrient Monitoring Program

In 2023, the Washington State Legislature funded a WSDA program to monitor pesticides and nutrients in groundwater, focusing on agriculturally dense areas. The program aims to identify potential water quality issues early, ensuring public health and environmental protection.

This program is vital for public health, as over 60% of Washingtonians rely on groundwater for drinking. It fills in gaps in pesticide data and aims to balance agriculture with health concerns, providing key information for sustainable farming and public health protection.

How the program works

The primary goal of the program is to assess the impact of pesticides on groundwater in Washington's agriculturally dense areas. It involves collecting groundwater samples from private residential wells, where homeowners voluntarily participate.

This free, non-regulatory, research-based program focuses on identifying potential water quality issues and providing local communities with valuable data on groundwater quality, including pesticide and nutrient concentrations.

The program also offers public health information to participants and collects data on contamination levels and severity.

The program operates on a rolling basis, sampling 1-2 regions at a time, with ongoing support for future expansion.


The program's objectives include:

  • Collecting data on the total number of wells sampled
  • Identifying wells with detectable pesticides and/or nutrients
  • Measuring pesticide concentrations
  • Comparing detected concentrations to drinking water criteria

Regions are prioritized based on:

  • Groundwater vulnerability
  • Agricultural land density
  • Soil and hydrogeological characteristics
  • Existing monitoring programs

Key resources used to evaluate regions include data from:

  • The Department of Ecology
  • The Department of Health
  • WSDA agricultural land use data
  • NRCS soil and hydrogeological information
  • The program is supported by the National Resource and Agricultural Sciences (NRAS), which aids with implementation and data collection.


Map showing current and proposed study areas

Regions currently under monitoring

The first two regions being monitored are the Pasco Basin in Franklin County and the Walla Walla Basin in Eastern Washington. Expand the boxes below for more information on each monitoring area.

Pasco Basin sampling began in fall 2024, with 75 wells sampled. The second round of sampling will be in fall 2025.
map showing study area

Pesticides:

  • 10 sampling locations had pesticide detections.
  • 5 unique analytes were detected.
  • All pesticide detections were well below 1% of the protective drinking water level.

Detected analytes:

Analyte Category Example Brand Names
2,6-Dichlorobenzamide* Herbicide/Fungicide Barrier, Casoron
Bromacil Herbicide Emerald, Endura, Pristine
Bentazon Herbicide Basagran
Diphenylamine Fungicide Shield,Ecofog
Sulfentrazone Herbicide Spartan, Zeus
*Breakdown product of dichlobenil or fluopicolide
 

Pasco Basin-nitrate

  • Majority of sites had positive nitrate detections.
  • 2/3 of wells exceeded the drinking water standard of 10 mg/L.
  • ​Next Steps: Results will be mailed to participants in January 2025. WSDA is working with local health departments to provide resources for impacted participants.

 

Walla Walla Basin sampling starts in spring 2025, with 40 wells sampled.
The second round will take place in spring 2026.

Looking ahead

The ongoing monitoring of pesticide and nutrient concentrations in groundwater across Washington state is critical for understanding and protecting water quality. With further rounds of data collection and regional expansion, this program aims to improve both agricultural practices and community health through informed, proactive management.