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Salty Waters
Don Mosier | Rimini Road

Solid blue line marks San Dieguito Valley groundwater basin boundary.

The Olivenhain Municipal Water District (OMWD) is investigating withdrawing brackish water from the San Dieguito Valley Groundwater Basin (see map), piping it through a desalination plant, and adding it to their potable water supply. The basin consists of two distinct aquifers separated by an impermeable layer and extends from Lake Hodges to the Pacific Ocean. The basin is fed by water from the San Dieguito River and groundwater runoff from adjacent areas.

The lower aquifer is the most brackish for two reasons. First, wells drilled for agricultural pumping in the 1960s reduced the groundwater levels to below sea level resulting in an inland flow of seawater. Second, rising ocean levels and restoration of the San Dieguito Lagoon have led to further eastward intrusion of seawater, such that both the lower and upper aquifers have increased salinity. The result is that the many wells in the area, whether shallow or deep, provide water that is too brackish for irrigation or agricultural use. The prolonged drought in the past decade prevented freshwater recharging of the aquifers, making the problem even worse.

OMWD has drilled a test well near the eastern end of the Surf Club property and just south of the Morgan Run Golf Club to determine how much water can safely be withdrawn from the lower aquifer and how brackish it is. This pilot project will determine if the plan to build a desalination plant and generate one million gallons of potable water per day is feasible.

One consequence if this project moves forward is that the gradient between rising ocean levels and lower aquifer levels resulting from withdrawal for desalination will result in rapidly increasing salinity levels (particularly during drought periods). The benefit of using well water versus seawater for desalination could diminish under this scenario, particularly for a project with an expected lifetime of 50 years.
Global warming will result in diminishing sources of water for all of California. The OMWD project may be an innovative solution to the problem, or it may have a short-term benefit that turns into a long-term problem.

 

 

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