In 1975, the State of California mapped natural groundwater recharge areas in Sonoma County. These are permeable areas through which rain penetrates to fill the underground aquifer. Not all land permits recharge. The most important man-made impediment to ground water recharge is asphalt. Asphalt actually is harmful in three ways. It is an impenetrable barrier to groundwater recharge; it dramatically facilitates storm runoff that can destroy river and stream beds, and asphalt collects oils, gasoline and grease.

This map was created by geoligists. It examines the underlying rock formation and identifies the best groundwater rechage areas. Another map, made later by the FDA, examined soil permeability. These are very different but complimentary maps

 

 

Click on the image to see the overall map of Sonoma County with prime groundwater recharges areas marked with hatched lines.

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Here is a detail of the same map showing areas of prime groundwater recharge along Petaluma Hill Road. This is the area where Rohnert Park along with investors and land owners plan to construct 4,500 houses and five million square feet of commercial space.

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