The Santa Maria River Valley Groundwater Basin (Santa Maria Basin), DWR Bulletin 118 Basin No. 3-12 , underlies the coastal portion of the northern Santa Barbara and southern San Luis Obispo Counties. The DWR-defined Santa Maria Basin encompasses approximately 184,000 acres (288 square miles), of which approximately 61,220 acres (95.7 square miles) are within San Luis Obispo County. There are five "fringe areas" within the San Luis Obispo portion of the basin that are not subject to the adjudication stipulated in 2005. These fringe areas include the Pismo Creek Valley (approx. 1,220 acres), Arroyo Grande Valley (3,860 acres), Nipomo Valley (6,230 acres), Southern Bluffs (4,030 acres), and Cuyama River Plains (1,560 acres). Annual precipitation for the basin ranges from 13 to 17 inches with an average of 15 inches. Groundwater is found in alluvium, dune sands, and the Orcutt, Paso Robles, Pismo, and Careaga Formations of the basin. Groundwater is unconfined throughout most of the basin except in the coastal portion where it is confined.
In 2015, the State legislature approved an important new groundwater management law known as the Sustainable Groundwater Management Act (SGMA). SGMA requires that high and medium priority basins comply with the new law, with certain exceptions for certain adjudicated basins – DWR designated Santa Maria Basin as a high priority basin. SGMA does not apply to the portion of the Santa Maria basin that is at issue in the litigation (“adjudicated area”) provided that certain requirements are met. The adjudicated areas cover a majority of the basin, and are managed by the Northern Cities Management Area, Nipomo Mesa Management Area, and the Santa Maria Valley Management Area. However, the fringe areas described above must comply with the new groundwater management requirements. The maps below show both the adjudicated areas exempt from SGMA, and the fringe areas that are subject to SGMA.
The Santa Maria Basin Fringe Areas – County of San Luis Obispo Groundwater Sustainability Agency (GSA) is submitting an initial notification to the California Department of Water Resources (DWR) of the GSA’s decision to explore boundary modification(s) for the Santa Maria River Valley Groundwater Basin (Bulletin 118 Basin No. 3-12; “Santa Maria Basin”). A majority of the Santa Maria Basin is subject to the adjudication stipulated in 2005; however, there are multiple “fringe areas” in the Santa Maria Basin located outside of the adjudicated area. All five non-adjudicated “fringe areas” within the County of San Luis Obispo will be considered for the basin boundary modification request.