May 4, 2018 2 min read

A sinkhole that developed in Ken Dyson’s backyard in January was filled in last week, but that won’t be the end of the work that needs to be done on the failing stormwater tunnel that runs under his property at the corner of Fourth Street and Duncan Avenue in Washington.

“This is just the beginning,” he said Wednesday morning.

On April 23, the city conducted an “exploratory dig” where the 6-foot-deep, 4-foot-wide hole sat next to Dyson’s in-ground swimming pool. City engineer Sarah Boyce of Widmer Engineering gave a report to city council Monday, saying the 12-foot-deep dig showed “the void in the yard was due to the nonexistence of a bottom to the tunnel.”

About 115 feet of the 200-foot-long brick tunnel is missing a bottom, Boyce said.

“As the stormwater has continued to erode the bottom area of the tunnel, soil is beginning to pull from underneath the wall sections and cause further failure at the surface,” her report states.

The brick top and walls of the tunnel, which is about 60 inches in diameter, still appeared to be intact, however, according to Boyce.

Boyce provided council with three preliminary options for how to fix the problem. First, they could repair or replace the bottom of the tunnel by pouring in concrete. Second, they could reroute the tunnel by putting in a new one around Dyson’s pool, and abandoning about 135 feet of the existing tunnel. Third, they could use a chemical grouting process to install a lining in the portion of the tunnel that’s failing.

Boyce said she is working to provide council with cost estimates for each of the options, before it makes any decisions.

Dyson said he’s confident the city will do what’s best for the situation, and he’ll still be able to enjoy his pool and backyard this year.

“I don’t envy being in their position,” Dyson said of the council. “They have their hands full. I’m not going to worry about it because it’s in good hands. They’re doing their very best.”