GSA staff: USGS has identified two coastal sites for proposed seawater-intrusion monitoring well; scope in development

Jill Weinberger, representing DoDAC, told the Santa Monica Subbasin Groundwater Sustainability Agency that the United States Geological Survey has identified two potential coastal locations — both parking lots near the ocean — as candidates for a proposed seawater-intrusion monitoring well and is developing a draft scope of work in coordination with the city.

Why it matters: the monitoring well would provide earlier detection of seawater intrusion and better, depth-specific groundwater-quality and elevation data for managers of the Santa Monica Subbasin.

Weinberger said the GSA secretary has not been notified of any new groundwater production-well permit applications in the subbasin since the last meeting. “There has been none since the last meeting,” she said, noting the standing focus is on new production wells rather than other types of permits.

On siting, Weinberger described the factors the USGS considers: proximity to the coast, ownership (public preferred), rig access and long-term ability to maintain and sample the well. She said the USGS survey performed in December identified two viable sites near the shoreline and that the agency was comfortable moving ahead to draft a scope of work with city coordination.

When asked about timing, Weinberger said the USGS anticipates some rig availability toward the end of 2026 but cautioned that scheduling can change. “Were still looking at a 2 to 4 year time frame for total project completion,” she said, and added that the draft scope and scheduling remain subject to coordination and rig availability.

Board members pressed for design details after the meeting notes indicated the well could be roughly 1,000 feet deep with six casings. A board member asked, “On the notes, it said 1,000 feet deep roughly, with six different casings. Do we have an idea of what kind of distribution theyre gonna have for those screening depths?” Weinberger answered that detailed screening and target depths are typically determined after drilling and sampling are underway, when subsurface materials can be examined.

The presentation also pointed to a benefit of siting the monitoring well near existing USGS seismic lines so seismic images can be correlated with physical samples from the borehole.

Next steps: staff said the USGS is preparing the draft scope of work and staff will continue coordinating with the city. Specific funding sources, permits and final screen depths were not specified at the meeting; staff indicated those details will be developed as the scope and schedule proceed.