Except by special permission from the city administrator or his designee, no trench shall be excavated more than two hundred fifty feet (250') in advance of pipe laying nor left unfilled more than five hundred feet (500') where pipe has been laid. The length of the trench that may be opened at any one time shall not be greater than the length of pipe and the necessary accessories which are available at the site ready to be put in place. Trenches shall be braced and sheathed according to generally accepted safety standards for construction work. No timber bracing, lagging, sheathing or other lumber shall be left in any trench. (Ord. 751, 12-18-2000)