Rock samples from Waterway Protection Tunnel reveal Louisville history

Closeup of core sample
August 13, 2018

MSD’s project to build a tunnel 18 stories underground for wastewater and stormwater storage has also unearthed hundreds of millions of years of history.

In January 2018, MSD began construction of its Waterway Protection Tunnel, a 20-foot diameter underground tunnel deep within bedrock that will help prevent hundreds of millions of gallons of wastewater and stormwater from polluting the Ohio River and Beargrass Creek. As part of the preparation for this $200 million project, geologists drilled down 200 feet or more along the path of the tunnel to pull up samples of limestone and shale, and then analyzed the rock as part of planning for the depth of the tunnel. MSD has thousands of linear feet of these rock core samples stored in a southern Indiana warehouse. They act as a library of sorts for contractors to access as the project proceeds. The samples highlight the history of what is now Louisville; each is a unique and contain many fossils.

Upon completion of the tunnel, the core samples likely will be shown in local science museums. Some of the samples may be donated to the Kentucky Geological Survey’s Well Sample and Core Library. Many of the fossils found in the core samples are similar to those seen at the fossil beds at the Falls of the Ohio State Park just across the river in Clarksville.

Facts about the core sampling:

• MSD conducted rock boring at 15 locations along the Waterway Protection Tunnel alignment.

• Ten distinct bedrock units were encountered along the tunnel alignment. The bedrock strata is approximately 350 million years old. Fossilized shell fragments and the remnants of other sea creatures exist within the collected samples.

• Types of rock are often named for the city in which they were discovered or predominantly found. This area includes significant amounts of Louisville, New Albany, Sellersburg and Jeffersonville limestones.

• Analysis of the rock requires specialized equipment and technology. The excavated rock was sent to the Colorado School of Mining for analysis.

• Engineers and geologists use the findings from core sampling to determine the ideal path and depth at which the tunnel should be built as well as to make other determinations about the tunnel’s engineering.

• One key finding during sampling was notable amounts of Waldron Shale – a type of rock native to Indiana which easily fragments. This discovery determined the tunnel would have to be dug 20-feet deeper than originally planned.

Sampling just east of Louisville Slugger Field also found an artesian well – a pocket of deep underground water. This water was three times saltier than seawater, due to the length of time the water was pressurized underground.