CEDAR RAPIDS — More investigation has been ordered for the 150-year-old beer caves recently rediscovered under Interstate 380.
The Iowa Department of Transportation has signed a contract with the Iowa Geological Survey at the University of Iowa to conduct a geophysical investigation. The investigation will seek to document the size, location and orientation of 11 to 14 subterranean caverns built in the 1800s to refrigerate and age beer from adjacent brewing companies.
“We can look underground and determine where these historic beer caves are located, how big they are, the orientation of them, and if they are filled in,” said Jason Vogelgesang, a geologist for the Iowa Geological Survey, who is leading the study.
Cathy Cutler, a transportation planner for the Iowa DOT’s District 6 office in Cedar Rapids, said the first electrical resistivity survey was conducted this week under the exit ramp near where the caves were found. A sinkhole was discovered during a routine bridge inspection in July near the Seventh and Eighth streets access ramps to Interstate 380, and it turned out to be the caves.
An electrical resistivity survey runs an electric current through a line of stakes positioned in the ground to study what’s beneath the surface, Vogelgesang said.
“If there was a void or a cave it would be very resistive electrically, so we can tell where the void is compared to the surrounding material,” he said.
A second survey uses an electromagnetic terrain conductivity meter that’s about 15 feet long and is walked back and forth across the site to create an overhead view of the earth below.
The bird’s-eye view from the meter and the cross-sectional view from the resistivity survey together provide a full picture of what’s below ground, Vogelgesang said. The different tests take three to five hours to complete. Nine locations will be studied, and the research will be completed throughout next week, he said.
The contract for the study is $14,604, and the report is due by Jan. 16.
The caves had been largely forgotten since the Magnus Brewing Co. was demolished in the 1930s and I-380 was built in the 1970s.
The DOT hired the Office of the State Archaeologist to study the caves in August, and the office released a report in September revising a previous estimate of three or four caves upward to 11 to 14, including caves that once were part of Williams Cedar Rapids Brewery.
The report recommended further study to determine the proper course of action for the caves.
The DOT has said filling the caves may be the most sensible option because they are not safe to enter, although the roads above remain secure. The plan is to await the outcome of the tests before making a final decision.