A.
General. All pipe used for storm drainage shall be either Class 4 reinforced concrete pipe (RCP) or asphalt-coated corrugated metal pipe (ACCMP). Reinforced concrete pipe shall be used except as otherwise permitted by the Commission as specified herein. Where the bedding of the pipe is to be in unstable material or where the gradient of the pipe exceeds 8%, ACCMP shall be used in lieu of RCP.
B.
Minimum cover. The minimum cover over all storm drainage within the right-of-way shall be three feet. Where conflicts with other subsurface facilities require, and with the approval of the Commission, pipe may have as little as 18 inches of cover, but in such cases extra-strength Class 5 RCP shall be used.
C.
Slotted or perforated storm drains. Where water is encountered in the pipe trenches, or where underdrains are required under § 480-68, storm drains shall either be slotted RCP or perforated ACCMP.
D.
Additional underdrains. Where additional underdrains are deemed necessary in locations not requiring other storm drainage, six-inch perforated ACCMP shall be provided.
E.
Materials and methods. Materials and construction methods shall conform to the requirements of the State Standard Specifications for Culverts and Underdrains and Outlets.