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Contact Public Works via web form, email, or call us at (805) 781-5252.

Paso Basin Aerial Groundwater Mapping Pilot Study

Project Status Update

On November 7, 2019, the groundwater mapping survey over the Paso Basin was successfully completed.  Data collected from the survey will be analyzed by Stanford University and project partners. The County will present the results in an upcoming meeting this Summer/Fall 2020.  Stay Tuned! 

Technology Flight Demonstration

The County recently held question and answer session and flight demonstration for the public. To view local news coverage of the event, click here!

Pilot Study Goals

The goal of the pilot study is to acquire survey data to help us make better informed decisions about managing our groundwater resources. Survey data is collected using aerial groundwater mapping technology to characterize and map out the layers and extent of clays, silts, sands, and gravels to a depth of approximately 1000 to 1400 feet below the ground surface. Existing well data will be used to verify the survey results. This pilot study will enhance Sustainable Management Groundwater Act (SGMA) related groundwater modeling and provide a better picture of our groundwater system.

The video above provides an overview of AEM technology and demonstrates how this type of groundwater mapping technology is used. (Video: Stanford University)

Archived News & Announcements

Click on the link above to view archived news and study announcements.

Click here to receive updates on the Paso Basin Pilot Study by subscribing our mailing list!              

Frequently Asked Questions

What are we hoping to learn?

The Paso Basin Pilot Study will use aerial groundwater mapping technology to characterize the subsurface geology and better understand where groundwater occurs and flows, which is necessary for the refinement of the hydrogeologic model of the Paso Basin.

How does it work?

Instruments attached to a low flying helicopter (~100 feet above the ground surface) towing a large hoop will transmit a weak electromagnetic field. This field interacts with the ground, and the response from the ground is measured using a set of receiver coils attached to the hoop. The helicopter flies back and forth along regularly spaced lines and will cover a distance of of approximately 497 miles. The instrument can collect data to a depth of about 1400 feet below ground. Once combined and calibrated with well data and existing knowledge of the subsurface conditions, this dataset can be used to map out the layering of “course” materials (sand and gravel), “fine” materials (silts and clay) and bedrock to show the structure of the basin and groundwater system. This new knowledge will help guide placement of new monitoring wells or identification of recharge locations. 

How is the data obtained?

The map below shows the general area of the flight paths where data will be surveyed, approximately 497 line-miles (800 kilometers) over the Paso Basin. The study will take place in two areas of the Paso Robles Basin, on the east side of the valley, and the area near Highway 46 and Highway 229 by Creston and Whitley Gardens. The helicopter will fly in and out of the Paso Robles Municipal Airport for refueling between production flights.

Health and Safety

Is it Safe?

This project does not pose a risk to health or safety. The very low level of magnetic exposure is about the same as standing one foot from a toaster, as shown on the Figure below [see note 1].

The AEM transmitter generates a magnetic field that is lower than 1/100th of the accepted general public exposure level across all frequencies [see note 2].

The same AEM surveys have been conducted in other location throughout California with no reported ill effects to humans or animals.


[1] Long Island Power Authority:

[2] International Commission on Non-Ionizing Radiation Protection. "Guidelines for limiting exposure to time-varying electric and magnetic fields (1 Hz to 100 kHz)." Health physics 99.6 (2010): 818-836.

Who's involved with this Study?

The State of California signed a landmark agreement to form a partnership with the Kingdom of Denmark to share the latest technology, research, and techniques for water resources management. This Pilot Study presents an opportunity for our community to benefit from this partnership by obtaining a better understanding of our groundwater system.

Project Leads:

  • Stanford University 
  • California Department of Water Resources
  • Kingdom of Denmark

Other Partners:

  • San Luis Obispo County
  • Butte County
  • Indian Wells Valley County

Funding Sources:

  • California Department of Water Resources
  • State Water Resources Control Board
  • Kingdom of Denmark
  • Project Partners
What other projects have been completed using the AEM Method?

In 2017, Stanford University Professor Rosemary Knight spearheaded a project to map underground freshwater resources and forecast the intrusion of saltwater into aquifers beneath the California coastal town of Marina. An overview of this project, which was a collaboration between Stanford, the Marina Coastal Water District, and Aqua Geo Frameworks, can be seen in the video at the top of this page.

Other California locations where AEM studies have been completed:

  • Marina Coast Water District
  • Tulare Irrigation District
  • Kawaeh Sub-basin
  • Santa Cruz Mid-County Groundwater Agency
  • Butte County Indian
  • Wells Valley
Who can I contact for additional information and how can I get involved?

For questions or additional information, please contact:

Cathy Martin, Water Resources Engineer
County San Luis Obispo Department of Public Works

Email: [email protected]
Phone: (805) 781-5275

Mailing address:
County Government Center, Room 206
San Luis Obispo, CA 93408

Click here to receive updates on the Paso Basin Pilot Study by subscribing our mailing list! 

Contact Public Works via web form, email, or call us at (805) 781-5252.