California Code, Public Resources Code - PRC § 3740

The owner or operator of any well on lands producing or reasonably presumed to contain geothermal resources shall properly case it with watertight and adequate casing, in accordance with methods approved by the supervisor or the district deputy. The owner or operator shall also use every reasonable effort and endeavor to prevent damage to life, health, property, and natural resources, to shut out detrimental substances from strata containing water suitable for irrigation or domestic purposes and from surface water suitable for such purposes, and to prevent the infiltration of detrimental substances into such strata and into such surface water.