Title
Consider receiving a report on Mechanisms and Pathways of Seawater Intrusion
Report
RECOMMENDATION:
It is recommended that the Monterey County Water Resources Agency Basin Management Advisory Committee:
Receive a report on Mechanisms and Pathways of Seawater Intrusion
SUMMARY:
The Monterey County Water Resources Agency (MCWRA) monitors the movement and extent of seawater intrusion in the Salinas Valley Groundwater Basin. The current understanding of seawater intrusion is shaped by available data on groundwater levels, groundwater quality, geochemistry, hydrogeology, and solute transport.
DISCUSSION:
Regional Seawater Intrusion
In the Salinas Valley Groundwater Basin, seawater intrusion has been documented in the 180-Foot and 400-Foot Aquifers. The geologic formations that comprise these aquifers are in direct hydraulic communication with the Pacific Ocean, a condition that provides a pathway for seawater intrusion (Attachment 1; Kennedy/Jenks, 2004). A secondary contributor to seawater intrusion in the 180-Foot and 400-Foot Aquifers is the persistent reversal of the seawater groundwater gradient (Attachment 1; Kennedy/Jenks, 2004). When combined, these two factors result in regional seawater intrusion wherein seawater infiltrates the 180-Foot and 400-Foot Aquifers through submarine outcrops, then moves inland where groundwater pumping has resulted in groundwater levels that are below sea level in both aquifers.
Inter-Aquifer Seawater Intrusion
A second pathway for seawater intrusion also exists in the 180-Foot, 400-Foot, and Deep Aquifers, termed inter-aquifer seawater intrusion. The results of this type of seawater intrusion were first documented by MCWRA in the 2015 Historical Seawater Intrusion Map for the Pressure 400-Foot Aquifer (Attachment 2), with the appearance of three "islands" of seawater intrusion that were disconnected from the contiguous seawater intrusion front.
Inter-aquifer seawater intrusion occurs when groundwater that is i...
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