Los Osos Valley Groundwater Basin Fringe Areas Characterization

The Sustainable Groundwater Management Act (SGMA) took effect on January 1, 2015, and requires that certain actions be taken in groundwater basins designated as either high or medium priority by the California Department of Water Resources (DWR), including Los Osos Basin. DWR identified the Los Osos Basin as a high priority basin subject to critical conditions of overdraft due to seawater intrusion and nitrate impairment (DWR, 2014, 2016). SGMA does not apply to the Los Osos Basin area that is at issue in Los Osos Community Services District v. Southern California Water Company [Golden State Water Company], et al.1 (Adjudicated Plan Area), for which a Stipulated Judgment was approved in San Luis Obispo Superior Court on October 14, 2015. The boundaries of the Adjudicated Plan Area do not coincide with the Basin boundaries as documented in DWR’s Interim Update to Bulletin 118 (2016). The groundwater basin areas between the Bulletin 118 Basin boundaries (Basin 3‐8) and the Adjudicated Plan Area boundary are referred to as “Fringe Areas” (Figure 1). In order to comply with SGMA, the

County of San Luis Obispo (County) formed the Groundwater Sustainability Agency (GSA) over these Fringe Areas on April 4, 2017. The results of this basin characterization study are intended to produce a basis of knowledge for use in boundary modification requests and potential future use in development of a Groundwater Sustainability Plan (GSP). Decades of technical studies on the basin have focused primarily on aquifers within the Adjudicated Plan Area. This technical memorandum supplements prior work, which together provide a comprehensive hydrogeologic characterization and conceptual model of the Fringe Areas.