Consultant recommends polypropylene corrugated pipe for Town Center Plaza storm system

At the meeting, civil engineering consultant John McGraw (CEC) outlined a proposed change to storm-sewer materials for the Town Center Plaza project, recommending polypropylene corrugated pipe as a durable, lighter-weight alternative to reinforced concrete pipe.

McGraw said polypropylene pipe is not high-density polyethylene (HDPE) used for sanitary sewers; rather, the product has watertight joints, comes in longer sections with fewer joints and performs well under proper class B rock backfill. He noted the product has been vetted in the transportation community and approved by DOT agencies in other jurisdictions.

"We anticipate about a 15% savings in storm sewer infrastructure," McGraw said, attributing most of the savings to reduced labor, trucking and mobilization rather than raw material cost. He added that detailed installation criteria — including a minimum two-foot cover and specific SDR selections for larger diameters — would be required in contract specifications.

Commissioners questioned pipe diameters, SDR and outlet/headwall details; McGraw said the minimum proposed diameter is 18 inches and the system includes precast concrete headwalls at outlets. He also emphasized that the substitution would be limited to side drains associated with two long-drive connections, with other detention and precast structures remaining concrete.

The council and staff agreed to consider the recommendation and incorporate the material specification and backfill requirements into contract documents if authorized.