37 Miss. Code. R. § 1-7501-04001-604
The encasement material shall be steel pipe. If requested and approved by MDOT, HDPE pipe may be substituted for the steel encasement. Should a Utility company request using HDPE Pipe in lieu of steel for a crossing, they must place it six (6) feet below the ditch bottom or three (3) feet lower than the requirement for a steel encasement. The utility company will certify, by a registered professional engineer, that the HDPE pipe encasement meets industry standards for highway crossings. An example certification can be found in SECTION 1200 - 1203.
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