California Code, Public Resources Code - PRC § 3606.1

The 150-foot restriction in Sections 3600 and elsewhere in this chapter shall apply only to wells drilled and producing from the same zone or pool;  provided, however, that the well density shall not exceed one well per acre unless the supervisor shall determine that more than one zone or pool underlies the property and that it is not practical to produce from all of such zones or pools from a single well per acre and that such other zones or pools are being drained by offset wells.  In such cases only, a maximum density of two wells per acre may be approved.  These exceptions to the general spacing rule shall apply also to properties qualifying under Sections 3602 and 3606.