Concrete, Municipal, & Farm Structures Concrete box culverts, manholes, farm grates, catch basins, and municipal structures. Tender submissions are welcomed. Municipal Castings Municipal Castings & Frame and Grates are available in a range of OPSD sizes for stormwater management. Concrete Box Culverts Concrete Box Culverts manufactured with stacked top and bottom boxes, designed for increased flow. Concrete Catch Basins Concrete Catch Basins for stormwater collection. Available in 2’x2’x4′. OPSD 705.010, 705.020, 705.030, 705.040. Maintenance Holes Maintenance holes are available from 1200mm, through 3600mm in diameter. OPSD 701 to OPSD 707. Ditch Inlets Precast Concrete Ditch Inlets for stormwater management are available in OPSD 705.030 and 705.040.