11.10.250 Back-Fill Material.
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Whenever any excavation for the laying of pipe is made through rock, the pipe shall be laid 6 inches above the rock bottom of the trench and the space under, around and 6 inches above the pipe shall be back-filled with clean river sand, non-corrosive soil or one-quarter inch minus gravel. Broken Pavement, large stones, and debris shall not be used in the back-fill.