The Boring Co., Elon Musk’s underground tunneling venture, has proved better at raising money than ridding cities of traffic. Nearly a decade in, its transit showcase remains a slow-moving conga line of Teslas traveling single-file beneath Las Vegas, construction of which earned it some 800 environmental violations and accolades like “traffic jam in a tube” and “worst transit system on earth.” Hardly the futuristic “hyperloop” Musk first promised. Yet local governments continue to give it new shots. The latest is Tennessee, which agreed to twin car tunnels connecting downtown Nashville to its international airport.
A new geological assessment suggests the city could get more than a shortcut. Construction of the 10-mile tunnels began late last year with a goal of opening in 2027, but the detailed study raises concerns that the project could trigger sinkholes, flood the tunnels and spread existing contamination through groundwater. While the city sits on limestone, the problem is it’s also riddled with subterranean caves and voids known as karst geology, created as groundwater gradually dissolves soluble bedrock.
Tunneling through that presents challenges, including “massive water or mud inflow and flooding, sinkholes,” and ground gradually sinking above the tunneling,” according to the study prepared by Chris Groves, a professor of hydrogeology at Western Kentucky University, done on behalf of the Southern Environmental Law Center, a nonpartisan advocacy group. Nashville’s karst conditions could even lead to Boring Co.’s tunneling machines getting stuck underground, the study said.
As Vanderbilt University geologist Molly Miller, who’s cited in the study, put it: “What makes it tricky is that it is sort of like Swiss cheese.”…