A 2.2-mile-long tunnel is being drilled in RI. Where is the debris going?

Katie Landeck, Providence Journal
Updated ·3 min read

It's been described as the largest public works project most Rhode Islanders will never lay eyes on.

Despite the nearly $1.7 billion price tag, many people forget about the Narragansett Bay Commission's decades-long project to create an underground tunnel network to capture polluted stormwater and sewage and clean it up before it runs into the Bay.

It's a big job, and the drilled tunnels are massive, at 30 feet wide.

This raised a question for one What and Why RI reader who has been keeping tabs on the project: Where is all the material they're drilling out going?

What is this tunnel project?

Work proceeds on Phase 3 of the Combined Sewer Overflow tunnel, part of the Narragansett Bay Commission's two-decade effort to stop stormwater from polluting the Bay.
Work proceeds on Phase 3 of the Combined Sewer Overflow tunnel, part of the Narragansett Bay Commission's two-decade effort to stop stormwater from polluting the Bay.

To take one step back before answering the question, a quick primer on the tunnel project.

In the early 1900s, it was common practice for urban areas to build underground sewer systems that carried both sewage and rainwater in the same pipe, which are called combined sewer overflows. This is what happened in Providence, Pawtucket and Central Falls.

Most of the time, this works, and all the water in the pipeline gets treated. But during big rainstorms, the subterranean systems for dealing with all that water can become overloaded, and when that happens the water gets discharged straight into Narragansett Bay untreated. That untreated water – which may have mixed with household waste, chemicals on the roads, sewage, etc. – can carry bacteria that lead to closing beaches and/or shellfish beds, or carry the nutrients that can cause dangerous (and also gross) algae blooms.

More: Giant RI sewer project is cleaning Narragansett Bay. But is it too costly for ratepayers?

In the 1990s, it became clear to the Narragansett Bay Commission that a better system was needed. And so the planning started for what has been catchily named the "combined sewer overflow project." This plan includes drilling new storage tunnels underground to catch that water during heavy rains so the system can hold it until it can be treated.

The first two phases are done, which includes a 26-foot diameter, 3-mile tunnel that begins under Providence's downtown and follows the Providence River to a treatment plant at Fields Point. That tunnel has captured over 15 billion gallons of overflow. Since it opened in 2014, bacteria counts in New England’s largest estuary have been cut in half, new areas have been opened to shellfishing, and there has been talk of reopening swimming at Sabin Point Park in East Providence.

Now, the commission is in phase three of the project, which includes the construction of a 2.2-mile tunnel along the east bank of the Seekonk River in Pawtucket, which will be able to hold the equivalent of 92 Olympic-sized swimming pools of overflow.

Where is the material they're drilling out going?

Tons of gray shale and sandstone rocks, dubbed "tunnel muck" by construction workers, are loaded onto dump trucks during excavation of the 2.2-mile Combined Sewer Overflow tunnel in Pawtucket.
Tons of gray shale and sandstone rocks, dubbed "tunnel muck" by construction workers, are loaded onto dump trucks during excavation of the 2.2-mile Combined Sewer Overflow tunnel in Pawtucket.

Drilling a 2.2-mile-long tunnel generates a lot of construction debris, colloquially called "tunnel muck." An estimated 1.2 million cubic yards of rock will be loaded onto a conveyor belt and then onto dump trucks that need somewhere to dump it by the end of the project.

What to do with tunnel muck has been the source of much consternation, notably causing a fight between the Narragansett Bay Commission and the Rhode Island Airport Corporation when RIAC rejected an idea to use the tunnel rock as part of a larger effort to build a Rhode Island home for a venture-backed electric sea-glider startup from Massachusetts.

Mucking it up: How 'tunnel muck' sparked a fight between RI agencies and why it will cost taxpayers

Instead, Jamie Samons, public affairs manager for the Narragansett Bay Commission, said the fill is being used for other purposes.

"Approximately 50% of the excavated rock was used to cover the legacy landfills at the NBC’s Bucklin Point Wastewater Treatment Facility (dating before the NBC’s ownership of the facility)," Samons said in an email. "Approximately 40% is going to the RI Resource Recovery Corporation for fill and cover, and approximately 10% is being used to regrade NBC-owned property at the main construction site."

What and Why RI is a weekly feature by The Providence Journal to explore our readers' curiosity. If you have a question about Rhode Island, big or small, email it to klandeck@gannett.com. She loves a good question.

This article originally appeared on The Providence Journal: Debris from 2.2 mile tunnel being drilled in RI has multiple uses