California Code, Health and Safety Code - HSC § 25299.39.3

The board, a regional board, or local agency shall be permitted reasonable access to property owned or possessed by an owner, operator, or responsible party as necessary to perform corrective action pursuant to Section 25299.36. The access shall be obtained with the consent of the owner or possessor of the property or, if the consent is withheld, with a warrant duly issued pursuant to the procedure described in Title 13 (commencing with Section 1822.50) of Part 3 of the Code of Civil Procedure. However, in the event of an emergency affecting public health or safety, or the environment, the board, a regional board, or local agency may enter the property without consent or the issuance of a warrant.