Gilbert staff favor PVC for most sewer work as outside engineer urges clay pipe

Ken Snow, the town’s public works assistant director, told the Gilbert Town Council on Dec. 16 that the town’s life-cycle analysis generally favors polyvinyl chloride (PVC) pipe for most wastewater collection work because it is lighter, installs in longer lengths (fewer joints) and tends to reduce handling and maintenance costs.

The issue matters because Gilbert’s system includes older vitrified clay pipe (VCP) in parts of town and ductile iron in structural or pressurized locations; council members pressed staff about past failures and why certain materials remain in the standards. Snow said VCP remains allowed with town‑engineer approval and that ductile iron is still required for sites that cross highways or railroads, where a structural material is necessary.

During the presentation Snow listed the town’s three principal materials—VCP, PVC and ductile iron—and described trade-offs. “Our life cycle analysis generally favors PVC as the more economical choice,” Snow said, emphasizing PVC’s smoother interior (which aids flow and cleaning) and longer laying lengths. He noted clay pipe is corrosion resistant but brittle and more labor intensive to repair, and that ductile iron requires interior coatings (Protecto 401) that staff sometimes find inadequate and would prefer be replaced by CIPP lining where warranted.

An outside civil engineer who identified himself only as a presenter urged the council to consider clay’s long service record, saying clay “has been around for thousands of years” and citing examples of century‑plus installations in large U.S. cities. That presenter also raised environmental and health concerns about plastics, including claims about microplastic presence in tap water.

James Ashley of the Home Builders Association of Central Arizona spoke in support of staff’s assessment, stressing builders’ practical concerns: heavier, brittle clay pipe raises handling costs and installation risk, and limited supply and labor can double costs compared with PVC. Ashley cited the Maricopa Association of Governments standard recommending PVC SDR‑35 for gravity sewers.

Council members asked for additional data. Snow said staff could prepare a breakout of installed‑cost differences and reiterated that material choice depends on site conditions—whether the pipe is in a gravity or pressurized application, nearby construction activity and other local factors. He also pointed to a recent example in which a corroded ductile iron force main under Loop 202 was slip‑lined with HDPE to remove exposure of wastewater to the ductile iron.

The presentation did not produce a policy vote; staff said clay remains allowed subject to engineering approval and that the engineering standards are under review. Snow invited council to request a more detailed cost comparison and to direct standards updates as part of the broader modernization effort.

Next steps: staff offered to provide a cost differential breakout and to bring standard‑modernization recommendations to council during the engineering department’s standards update process.