PDFWAC 296-45-195
Trenching and excavation.
(1) During excavation or trenching, in order to prevent exposure of employees to the hazards created by damage to dangerous underground facilities, efforts must be made to determine the location of such facilities and work conducted in a manner designed to avoid damage.
(2) Trenching and excavation operations must comply with the provisions of Part N, chapter 296-155 WAC.