Cal. Code Regs. tit. 8, § 7176 – (20-10). Protection Against Water.

(a) No mine working shall be allowed to approach within 16 feet of any part of a winze, stope, or other opening in which there is a known or suspected dangerous accumulation of water.
(b) Notice shall be given to the Division in writing before starting to advance a mine working toward another mine working that is suspected of being filled with water.
(c) A bore hole shall be drilled at least 18 feet ahead of the face when in the vicinity of mine workings suspected of containing a dangerous accumulation of water.
When the exact location of such working is not known, additional bore holes at least 18 feet deep shall be drilled in other directions.
(d) In every mine where there is danger of a sudden inburst of water, additional raises, drifts, bulkheads, or other workings shall be constructed as are necessary in the opinion of the Division to insure the escape of workmen.
(e) No underground mine working shall be allowed to approach within 50 feet of any stream, pond, or other body of water on the surface.