Groundwater Sustainability Plan – Ukiah Valley Groundwater Basin

LACO partnered with Mendocino County Water Agency to obtain a grant and complete an Initial Groundwater Sustainability Plan (GSP) for the Ukiah Valley groundwater basin. When the Sustainable Groundwater Management Act (SGMA) was passed in 2014, The Ukiah Valley groundwater basin was identified as “medium priority;” requiring local agencies to band together to create a Groundwater Sustainability Agency (GSA) and develop a Groundwater Sustainability Plan (GSP). The Initial GSP created an opportunity for the Ukiah Valley GSA to get a head-start on GSP development. 

To best understand and address Ukiah Valley needs, LACO attended and participated in GSA meetings during and after GSA formation. LACO collaborated with the GSA, local government agencies, agricultural industry leaders, non-profit organizations, and the State to obtain data, gain an understanding of local socioeconomic concerns, and get direction on how to utilize grant funding to best benefit the Ukiah Valley population. 

To fulfill the obligations of the grant, LACO prepared several studies addressing the Basin Setting sub-article of the SGMA regulations. The primary deliverables included a Data Gap Analysis, a Hydrogeologic Conceptual Model, and a Preliminary Water Budget Study. LACO compiled and analyzed all available data pertaining to groundwater resources including 2,500 well logs, 500 groundwater elevation measurements, previous studies, and geologic maps. The gathered information was used to create a Geographic information system (GIS) geodatabase of relevant data, and to develop a new three-dimensional representation of the groundwater basin; complete with information pertaining to hydrogeologic properties, water quality, and beneficial uses. For the first time, a numerical groundwater flow model was developed for the Ukiah Valley groundwater basin using GIS and MODFLOW. The groundwater flow model was used to develop a preliminary understanding of the water budget, identify areas that are or are not sensitive to data gaps, and develop new insight into potential sources of bedrock recharge. 

The Initial GSP was a big step in the SGMA process, but substantial amounts of work are yet to be completed. LACO has been thrilled to be a part of the process thus far and is excited to have the opportunity to work with the GSA moving forward. 

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