Saltwater Intrusion

Saltwater intrusion is the process by which coastal groundwater aquifers become contaminated by sea water, raising their salinity. Groundwater contaminated by saltwater is no longer suitable for agricultural use or for drinking water without treatment. Saltwater intrusion is caused by two primary processes: overdrafts of coastal wells and sea level rise. Currently, Monterey County relies on local groundwater reserves for over 80 percent of its total water use (1). A large agricultural sector and high public demand for water has led to overdraft of local groundwater wells causing saltwater intrusion to occur in several of the major coastal aquifers in the Salinas and Pajaro River groundwater basins (1). The issue of saltwater intrusion is much greater for Monterey County than Santa Cruz County as Santa Cruz is largely dependent on surface water resources rather than groundwater. Furthermore, coastal groundwater basins in the region have been experiencing overdraft for many years. From 1964 to 1997 the Pajaro Valley groundwater basin is thought to have lost over 300,000 acre-feet of freshwater storage, two-thirds of which has been attributed to saltwater intrusion (2). The current rate of saltwater intrusion for the Pajaro Valley basin is estimated at 100 to 250 feet per year (30-73 m/yr), meaning that saltwater is moving inland this distance each year, and contamination can currently be seen seven miles inland in the 180 foot aquifer.  

1. Monterey County General Plan (2006). 

2. Pajaro Valley Water Management District, from http://www.pajarowatershed.org/Content/10050/water_supply.html