indicators of seawater intrusion - Seasidebasinwatermaster.org

FINAL DRAFTunits. The slow seepage rates allow the fresh water to maintain pressure beneaththe sea floor, pushing the seawater interface away from the coastline.GROUNDWATER PUMPING AND SEAWATER INTRUSIONPumping groundwater in a coastal aquifer reduces the amount of waterdischarging to the ocean. Sufficient pumping can eliminate ocean discharges,either locally or basin‐wide, triggering seawater intrusion. The response of theseawater interface to groundwater pumping is manifested in two related ways:upconing and interface migration. Upconing refers to the ability of a pumpingwell to draw seawater up from below. Upconing only occurs if seawater existsdirectly below a pumping well. Because no seawater intrusion has beenobserved in the Seaside Groundwater Basin, upconing cannot occur, and onlyseawater interface migration will be further addressed in this report.As mentioned earlier, groundwater pumping reduces the amount of fresh wateroutflow to the ocean. This allows the interface to migrate shoreward.Substantial pumping can allow the interface to move onshore, potentiallyimpacting municipal wells, private wells, or agricultural wells. Figure 3 shows atwo‐dimensional cross section of how the fresh water/seawater interface maymigrate in response to pumping.Seawater Intrusion Response PlanNovember 19, 2008 A-4