GSI assisted Castaic Lake Water Agency (CLWA) staff with developing technical information to support the submittal of basin boundary modifications for two groundwater basins within its service area. These changes are helping CLWA to more effectively manage water supplies in both basins.


Under the Sustainable Groundwater Management Act (SGMA), water users must form a groundwater sustainability agency to collectively manage their groundwater resources. As part of this process, SGMA allows public water purveyors to apply for basin boundary changes that modify the areas they are managing. The application process requires significant technical information to support the need for modifications.


GSI helped CLWA staff in preparing the technical information necessary to submit a modification request. We:

  • Developed maps and technical data on the geology and groundwater conditions in the Upper Santa Clara River Valley East Sub-Basin and the Pleasant Valley Basin.
  • Reviewed well logs and water level data to characterize groundwater conditions.
  • Assisted with preparing applications and technical deliverables for boundary modifications to the California Department of Water Resources (DWR).
  • Helped identify stakeholders that may be affected by the boundary changes.

DWR ultimately approved CLWA’s boundary modification request in October 2016. The boundary changes will give CLWA greater ability to develop a workable SGMA-compliant groundwater sustainability plan for its basins.