Officials from Orange County and Orange Water and Sewer Authority convened Tuesday to address local residents’ concerns after deciding to move forward with low-intensity underground blasting to continue the Rogers Road Area Sewer Project.
The project is an effort to extend sewer lines to the Roger Road area, a historically Black community in Chapel Hill and Carrboro. Initially announced in June 2017, construction was expected to last 10-12 months. However, only 62 percent of the sewer system has been installed, and only 34 percent of the system is currently in service.
“We had anticipated to be done around this time, but because of the rock issue and some weather issues, this is where we’re at today,” said Christopher Sandt, a staff engineer for Orange County. “We’re hoping to get the heck out of here by March or April next year.”
Sandt said the primary challenge has been the dense igneous rock impeding their construction on Tallyho Trail in Carrboro. Despite efforts to break the rock with ordinary mechanical methods such as hoe-ramming and rock grinding, engineers now have no choice but fracture the rock through blasting.
“We are going to move forward with controlled rock blasting on this project, and we want to reemphasize what we’re doing here is a very standard procedure for removing rock,” Sandt said.
Sandt said the low-intensity blasting is different, and much milder, than fracking or commercial rock blasting.
“When we first brought this to the public, people had an impression this was dynamite with fire and rocks flying everywhere, and that’s not what this is," he said.
Sandt said these will be controlled, low-impact blasts, as engineers inject energy into the ground in order to fracture the rock, and then workers will proceed to use mechanical tools after the blasting is complete.
Residents within the 500-foot radius of the blasts voiced concerns regarding potential flooding issues, whether their well water would be affected and if trees could potentially fall as a result of the blast.
Phil Vilaro, the on-site water protection supervisor, said that while turbidity could occur within the well to temporarily stir up particles, any damage was extremely unlikely due to the intensity being so small and contained.
“At the particle velocities they’re talking about, it’s unlikely you’ll have any more than the most minor vibrations,” he said. “Think about a sprinkler in your yard versus a firehose to compare the small-scale of this velocity.”
Orange County has contracted third-party engineers to conduct 19 pre-surveys of houses within a 500 foot radius of the blast. The purpose of the surveys are to assess existing structural issues underneath homes prior to the blast, in order to assess damage after the small explosions are complete.
Officials say the obstructing rock should be cleared within the next 6 weeks, enabling construction to focus on finishing the sewer line by spring 2019 — permitting fair weather and lower density rocks.
“No one knows what’s under the ground until you excavate it,” Sandt said.
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