Implications of geometry, age and depositional history of a shallow confining layer in a coastal groundwater basin, Monterey County, California, USA

Abstract

We mapped the geometry of a shallow confining layer within the Salinas Valley aquifer system, northern Monterey County, California, using indicator geostatistics. The confining layer was previously interpreted to be mainly Holocene in age, having been deposited as a single unit during post‐Wisconsin sea‐level rise. We interpret this layer in our field area to be associated with Isotope Stages 5 (84–121 kyr) based on three independent arguments: layer geometry, with three distinct clay units rather than one; 14C analyses of peat samples; and consideration of required rates of coastal uplift. The complex stratigraphy of the confining layer likely resulted from deposition over existing topography, erosion during exposure, and uplift during three intervals of sea level rise and fall. Similarly complex layering may occur in other coastal basins, influencing groundwater resource development, remediation and protection in these settings.

The Importance of Institutional Design for Distributed Local-Level Governance of Groundwater: The Case of California’s Sustainable Groundwater Management Act

“…For example, the spatial boundaries of primary aquifers are often weakly defined [38,39]. Responses to pumping or differences in aquifer conditions can vary profoundly even within a single groundwater basin [40][41][42]. Natural groundwater inflows and outflows are difficult to measure and monitor, and groundwater extraction is difficult to measure or control for hydro-social reasons [43].…”