Background

Groundwater is the primary source of drinking water for residents living in the Santa Margarita Groundwater Basin (SMGB) boundary. Groundwater is also important to stream base flow in the summer months. Rainfall is the only source of recharge to the basin. The groundwater basin is shared by users including the Scotts Valley Water District (SVWD), the San Lorenzo Valley Water District (SLVWD), Mount Hermon Association (MHA), as well as local businesses and residents using private wells. To that end, SVWD, SLVWD, and County of Santa Cruz (County) recognize that sustainable groundwater management is essential and ensure reliable and resilient water systems and desire to continue to work collectively on the implementation of SGMA.

The Basin is made up of the Santa Margarita sandstone, Monterey shale and the Lompico and Butano formations. The basin is now in a state of overdraft due to decades of overpumping — taking water out at a higher rate than it can be recharged to the basin. Groundwater levels are now approximately 200 feet below their natural levels. While these levels are no longer decreasing, recovery is still a long way out. Low groundwater levels mean less water in the streams for fish and wildlife, and less water security for people. The Scotts Valley Water District prepares annual reports that focus on groundwater conditions and system operations in the Scotts Valley area of the Santa Margarita Basin.

Previously DWR Bulletin 118 (DWR 2003) did not identify SMGB as a groundwater basin but rather recognized three smaller basins in the vicinity: Scotts Valley Basin, Felton Area Basin, and Santa Cruz Purisima Formation. These basins did not accurately reflect the groundwater supply resources supporting the North Santa Cruz County communities. SVWD with a support from SLVWD and County prepared a boundary modification request that was submitted to DWR in January 2016 and approved in August 2016.

The three agencies, SVWD, SLVWD, and County, are committed to work with each other and engage other stakeholders in forming a Groundwater Management Agency (GSA) and developing a Groundwater Sustainability Plan (GSP) after the State approves the boundary modification request.

Prior Basin Management Activities

The major water purveyors that rely on the supply from Santa Margarita Groundwater Basin (SMGB) are SVWD, SLVWD, and MHA. SVWD has actively managed groundwater in the area since the early 1980s in an effort to increase water supply reliability and to protect local water supply sources. In 1983, SVWD instituted a Water Resources Management Plan to monitor and manage water resources, in 1994 the agency formally adopted a Groundwater Management Plan (GWMP) in accordance with AB3030, also known as the Groundwater Management Act under Water Code section 10750. The overall purpose of the GWMP is to be a planning tool that helps to guide SVWD in the management of the quantity and quality of the groundwater supply and to comply with the requirements of AB3030. The main goal of the GWMP is to better manage the aquifers providing the community’s drinking water. The Basin Management Objectives as stated in the GWMP are:

  1. Encouragement of public participation through an annual report of groundwater management activities and its presentation at one or more public meetings;
  2. Coordination with other agencies;
  3. Continued monitoring and evaluation of groundwater conditions;
  4. Implementation of groundwater augmentation projects; and
  5. Investigation of groundwater quality and prevention of groundwater contamination.

In 1995, SVWD, SLVWD, MHA, LCWD, City of Scotts Valley and County of Santa Cruz signed a Memorandum of Understanding forming Santa Margarita Groundwater Basin Advisory Committee that has been actively involved in the cooperative groundwater management of the basin since then.

Much of the technical information and interpretations used to inform the basin management have been based on modeling and technical studies in the SMGB. The earliest modeling in the SMGB was done by Johnson (1988) who constructed a groundwater model of a portion of the Quail Hollow area to help evaluate the cause of elevated nitrate concentrations in groundwater produced from SLVWD wells. The Johnson model and an earlier model of Scotts Valley (Jacobvitz, 1987) were incorporated into a regional groundwater flow model by the Association of Monterey Bay Area Governments (AMBAG) in 1992 as part of the draft Santa Margarita Groundwater Basin Management Plan (Watkins-Johnson Environmental, 1993) that was not adopted. Portions of the AMBAG model were later updated by SVWD (Todd Engineers, 1997). These models were all run under steady-state conditions that did not evaluate time-varying conditions.

Johnson (2001 and 2002) later updated the Quail Hollow model through a detailed data assessment and conceptual model interpretation that led to the development of a transient model of the Santa Margarita and Monterey for the Quail Hollow area. Johnson (2003) provided a detailed data assessment and conceptual model interpretation of the Pasatiempo area west of Scotts Valley, but the numerical model was not constructed.

The Santa Margarita Groundwater Modeling Project of 2015 updated the SMGB model developed in 2006 (EITC, 2006) for SVWD with funding from the DWR Local Groundwater Assistance Grant Program. The numerical model was based on a conceptual model of the basin developed with input and oversight from a technical advisory committee representing interested local agencies. The model was also used as part of the Phase 1 Conjunctive Use Project (Kennedy/Jenks, 2011) by Santa Cruz County to evaluate potential groundwater recharge projects in SMGB. SVWD has regularly updated the SMGB model as part of their Groundwater Management Program to evaluate changes in groundwater storage. The most recent update of that previous version of the SMGB model included data through 2012.