The helicopter you may have seen flying over the Ukiah Valley while carrying what looked like a large hoop in recent days is being used to measure the large aquifer that supplies groundwater to many crucial wells in the region, including those relied upon by the city of Ukiah.
According to the California Department of Water Resources, this month was the first time the Airborne Electromagnetic (AEM) method was used to survey the Ukiah Valley groundwater basin, though it has been used in the Sacramento Valley, Salinas Valley and Indian Wells Valley.
When asked more questions about the survey, including when the results would be available for public review, DWR staff provided these responses:
Q. Has this been done before?
A. The AEM method has been used for decades to map aquifer structures and support groundwater management, both nationally and internationally. Three pilot studies were conducted in California to support the development of the AEM project in the Sacramento Valley in Colusa and Butte county groundwater basins; the Salinas Valley in Paso Robles groundwater basin; and in the Indian Wells Valley groundwater basin. Data collected provided foundational information about the aquifer systems in these areas which has been used to develop or refine the hydrogeological conceptual models for each area.
Q. If not, what specifically will this survey reveal about the basin that previous surveys couldn’t?
A. AEM data have not previously been collected in the Ukiah Valley groundwater basin. AEM surveys are being conducted in California’s high- and medium-priority groundwater basins, where data collection is feasible, to assist local water managers as they implement the Sustainable Groundwater Management Act (SGMA) to manage groundwater for long term sustainability. The AEM method measures the distribution of electromagnetic properties in the subsurface to a depth of approximately 1,000 feet below ground surface. The measured response can be displayed as a three-dimensional diagram and interpreted for the distribution of fine- and coarse-grained materials in the subsurface, which provides information about aquifer structures. Traditional methods for obtaining information about aquifer structure include drilling boreholes to obtain lithology logs, which is time consuming and only provides information at the location of the borehole.
Q. What will the information gleaned from the survey be used for?
A. The AEM data provides information about large-scale aquifer structures that supports local groundwater management and the implementation of the Sustainable Groundwater Management Act (SGMA) and the development of Groundwater Sustainability Plans. The data can be used to improve the understanding of aquifer structures, or layers, in a groundwater basin and show where there are thick layers consisting mostly of gravels and sands or silts and clays. This information supports the development and refinement of groundwater and hydrogeologic conceptual models and can be used to identify potential locations for groundwater recharge projects.
Q. And, probably most important, how and when can residents of the Ukiah Valley expect to learn the results of the survey?
A. All data collected as a part of the statewide AEM surveys will be made publicly available through the California Natural Resources Open Data Portal approximately six to eight months after surveys are complete.