Groundwater
Monitoring for Pesticides in the Water
The California Department of Pesticide Regulation (DPR) collects and samples groundwater for pesticides to determine if there is contamination from the agricultural use of pesticides. We identify sensitive areas for groundwater contamination and develop mitigation measures if pesticides are moving into the water.
Groundwater Protection
We assess pesticide risks to groundwater both before a pesticide can be registered for use in California and as part of continuous evaluation of pesticides to protect people and the environment from pesticide risks and impacts.
As part of the process to register a pesticide in California, we require data on the environmental fate and chemistry. To reduce the risk of groundwater contamination these data can inform registration or mitigation decisions before a pesticide can be sold or used in California.
Monitoring and Sampling Groundwater
We monitor and sample groundwater for pesticide active ingredients or their degradation products that may contribute to groundwater contamination. We monitor groundwater to determine:
- Whether pesticides with the potential to pollute groundwater are present in groundwater,
- The extent and source of pesticide contamination, and
- The effectiveness of regulatory mitigation measures to reduce risks and impacts.
In addition to the sampling conducted, we collect data from sampling conducted by other state or local agencies. Our scientists evaluate these data to determine overall risks to people and the environment.
Information collected through our sampling and collected from other public agencies are available in the Well Inventory Database and the Annual Well Sampling Report.
Regulatory Actions
If we identify risks to groundwater, we can propose regulations to implement pesticide use restrictions to protect groundwater in vulnerable areas of California. Regulations protect groundwater from contamination resulting from agricultural, outdoor industrial and outdoor institutional use of pesticides. For example, we restrict the use of certain pesticides in areas designated as Groundwater Protection Areas (GWPA), which are areas of land that are vulnerable to the movement of pesticides to groundwater by leaching or runoff or due to excess irrigation or rainfall runoff.
Groundwater Protection Laws and Regulations in California
California has many regulations in place to protect groundwater. Below is an overview of regulations and guidance for pesticide applicators.
Pesticide Contamination Prevention Act
California’s Pesticide Contamination Prevention Act (PCPA) requires us to identify and track potential and actual groundwater contaminants. We determine pesticides that are more likely to leach to groundwater and place these pesticides on our Groundwater Protection List (3CCR 6800) for monitoring.
Our scientists sample the groundwater for the presence of pesticides on the Groundwater Protection List to see if they are present in groundwater and if their presence is a result from legal agricultural uses. If a pesticide is detected and determined to be from a legal agricultural application, California law requires a formal review through the PCPA process to determine if use of the pesticide can continue with conditions for use that protect people and the environment.
Groundwater Database: Well Inventory Database
The PCPA requires us to maintain a statewide database of wells sampled for pesticides by us and other agencies. Public agencies that sample wells for pesticides must submit these results to us promptly. We maintain the data in the Well Inventory Database. To make water quality data more accessible, a version of the database is available online. This database includes information about the well, the study name, the sampling agency, sample date, analysis date, analyzing laboratory, chemical analyzed, concentration reported, reporting limit, legal agricultural use determination (point or non-point source determination) and the year we entered the record into the database. Testing done for other water parameters (i.e., pH, salt, calcium) is not included in the database.
CSV Files by County
View CSV files separated by county for August 1977 to December 31, 2023.
Groundwater Reports: Annual Well Sampling Report
The PCPA requires us to summarize results of groundwater sampling for pesticide residues and actions we take to prevent pesticides from migrating to groundwater. We use these data to evaluate and guide our groundwater protection, monitoring, and research activities.
Pesticide Contamination Prevention Act Status Reports
PCPA requires us to identify and track potential and actual groundwater contaminants. If a pesticide is subject to a PCPA action, DPR conducts a public process as part of next steps.
Each year we report the sales and use information for pesticides on the Groundwater Protection List.
Groundwater Protection Areas
To protect groundwater from contamination resulting from agricultural, outdoor industrial, and outdoor institutional use of pesticides, California regulations (3CCR 6487.1 – 6487.5 and 6457) identify management practices required in Groundwater Protection Areas (GWPAs).
GWPAs are areas of California identified as more vulnerable to groundwater contamination from the agricultural use of pesticides. We implement regulations for certain pesticides in these areas to protect water quality.
GWPAs are one-square mile sections of land vulnerable to the movement of pesticides to groundwater, via runoff or leaching, based either on pesticide detections or on certain soil types and a depth-to-groundwater shallower than 70 feet.
Use our California Pesticide Information Portal (CalPIP) to locate Groundwater Protection Areas.
Approved Alternative Management Practices
Resources and guidelines on alternative management practices within GWPAs.
Chemigation Safety and Backflow Protection Resources
We offer resources for growers, pesticide applicators, pest control advisers, and county agricultural commissioners to protect groundwater from pesticides during mixing and loading operations, and when pesticides are applied through irrigation systems. (Regulation: 3CCR 6610). You can read more about these resources in ENF 01-28.
Wellhead Protection Regulations
To prevent the contamination of groundwater through unprotected wellheads regulations (3CCR 6609) restrict pesticide handling practices within 100 feet of any unprotected wellhead unless certain criteria are met and prohibits the use of specific preemergent herbicides between a berm and the wellhead.
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Still have a Question or Need More Information?
Please contact us with questions or visit the Contact Us page on our website to connect with other programs at DPR.
Email: GWPP@cdpr.ca.gov
Department of Pesticide Regulation
1001 I Street, P.O. Box 4015
Sacramento, CA 95812-4015