At all locations determined by the district, the water and/or sewer main shall be encased with steel casing. Steel casing shall be of sufficient diameter, size, and strength to enclose the carrier pipe and to withstand maximum loading for the application. Sizing and wall thickness of casing is subject to approval by the district. The carrier pipe shall be ductile iron, Class 52, restrained joint pipe unless otherwise approved by the district. Casing spacers, pipe backfill, and end seals shall be installed in accordance with the adopted construction details in Article VI of this chapter unless otherwise approved by the district.