The Deep Aquifers are water-bearing sediments lying beneath a relatively continuous clay-rich aquitard located about 500 to 900 feet below the land surface, extending below the 400-Foot Aquifer or its stratigraphic equivalent. They increasingly provide vital groundwater resources for domestic, industrial, and agricultural uses in the Salinas Valley within Monterey County.

The Deep Aquifers Study was a scientific study to better understand the conditions of the Deep Aquifers, the geographic extent and hydrogeologic characteristics. It was completed in 2024 by Montgomery & Associates for SVBGSA and collaborative funding partners including Monterey County Water Resources Agency (MCWRA), County of Monterey, City of Salinas, Marina Coast Water District, Castroville CSD, Alco Water and agriculture.

Since completion of the Study, several agencies continue to monitor and evaluate conditions in the Deep Aquifers. MCWRA has prepared a Monitoring Plan, and ​MCWDGSA and SVBGSA have increased the number of representative monitoring sites.​ This expanded monitoring network supports improved data collection and informs management actions​.

The Deep Aquifers Memorandum has been prepared jointly by SVBGSA, Marina Coast Water District GSA, MCWRA and the County of Monterey as a supplement to the Deep Aquifers Study. Through local agency collaboration, this memo identifies interim local protective management actions, outlines potential long-term projects, strengthens monitoring coordination, and recommends pathways for operationalizing management actions within existing authorities.

Deep Aquifers Map in the Salinas Valley

Appendices for the Deep Aquifers Study

Appendix A

With additional data, the Deep Aquifers’ lateral extent was finalized, and this appendix summarizes the conceptual definition and the data, methods, and results of the lateral extent delineation.

Appendix B

In March 2023, Ramboll carried out a geophysical airborne electromagnetic (AEM) survey of the Deep Aquifers in the northern Salinas Valley. This report presents the methodology, results, and analysis related to the acquired AEM data and integration of the existing data from the survey area.

Appendix C

Pumping test information to support groundwater modeling and for assessing potential hydraulic connection between the Deep Aquifers and the adjacent aquifer system in Gonzalez and Chualar.

Appendix D

Data table with a summary of Available Aquifer Properties for Deep Aquifers Wells.

Appendix E

Analysis of available water chemistry data for the Deep Aquifers and collected isotope data, including raw data collected and used for the Hydrologic Conceptual Model.

Appendix F

Additional information on the Salinas Valley SWI Model and the SVIHM, and the calibration for each model for development of the Deep Aquifers water budgets.

Appendix G

Additional analysis and data related to Chapter 5. Current and Historical Conditions.

Appendix H

Table with wells recommended to be in the Groundwater Level Monitoring Well Network.