Map showing ranges in probable maximum well yield from water-bearing rocks in the San Francisco Bay region, California

This map presents generalized information regarding the probable maximum yields of wells in the rocks of the San Francisco Bay region.  It is intended to serve the needs of planners and other persons seeking general information on potential yields from water wells.  Four ranges in probable yield, based on adequacy of the range in yield for major beneficial uses of water, are given.  The ranges are related to the concept of normal probability; that is, well yields are expressed in terms of the 68- and 95-percent levels of chance.  For example, there is a 68-percent chance that wells in areas designated A will yield from 0.5 to 5 gpm (gallons per minute) and a 95-percent chance that wells in such areas will yield from 0.1 to 10 gpm. assuming operation without excessive drawdown.  Thus, it can be expected that most wells drilled in area A will obtain water supplies marginal to adequate for domestic purposes, that most wells will yield fewer than 10 gpm, and that some wells will be virtually dray.