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Colusa Subbasin Groundwater Sustainability Plan and SGMA Technical Support Services

Colusa Groundwater Sustainability Agency and Glenn Groundwater Sustainability Agency

At nearly three-quarters of a million acres, the Colusa Subbasin is the largest groundwater basin in the Sacramento Valley and the eighth largest in California. Building on our years of experience with groundwater in the Sacramento Valley, West Yost has become a valued member of a multi-consultant team responsible for development of the Groundwater Sustainability Plan (GSP) for the Colusa Subbasin. We are involved in all aspects of GSP development, including engaging with stakeholders and the public, and have the primary responsibility for producing the GSP for the Colusa Groundwater Sustainability Agency (GSA) and Glenn GSA.

Our team developed the Hydrogeologic Conceptual Model (HCM), defined historical groundwater conditions, established the proposed monitoring network, evaluated and recommended the integrated hydrologic model, and assessed existing data and data gaps as part of GSP development. In addition to preparing GSP content, the West Yost team is currently planning additional hydrogeologic investigations to fill identified data gaps and providing ongoing support to the GSAs during development of sustainable management criteria, consideration of management areas, and identification of projects and management actions that will protect the valuable resources of the Colusa Subbasin.

Team Spotlight

Ken Loy, PG, CEG, CHG


Anna Reimer, PG

Associate Geologist I

Peter Dellavalle, PG

Geologist II