Urban Archaeology Investigation – DigIndy Deep Tunnel Project

Underground utilities assisting the cultural resources team

By pioneering an innovative technique in urban archaeology, Cardno is helping to identify archaeological sites and determine their National Register of Historic Places eligibility prior to construction on the DigIndy Deep Tunnel Project – a near-impossible feat using traditional reconnaissance techniques for deeply buried urban historic sites.

The Cardno team has developed a new approach to address more than 30 urban locations requiring archaeological investigation. The entire project consists of nearly 19 miles of tunnel being mined through bedrock 200-250 feet beneath downtown Indianapolis, in an effort to reduce combined sewer overflow events throughout the City.

Working on behalf of Citizens Energy Group, Cardno is completing archaeological and architectural history investigations, reporting, and agency consultation. The process for archaeological investigation includes standard archival research coupled with ground-penetrating radar (GPR) surveys to identify potential archaeological features at any given project area.

Cardno then completes archaeological excavations using vacuum trucks, which allows for faster and safer excavation versus traditional Phase I archaeological methods. In addition, this technique has assisted in determining National Register of Historic Places eligibility at an earlier phase of excavation. This helps minimize the uncertainty of what is below ground without the need for a traditional Phase II evaluation, which is expensive and time-consuming. These factors all contribute to reducing the chance of accidental discoveries after project construction has begun and have helped keep the project on schedule.

Cardno has currently utilized this technique at more than 15 separate locations on the DigIndy Deep Tunnel Project, successfully identifying deeply buried historic sites and features, which can exist beneath feet of rubble and modern debris. Excavation with the vacuum truck has identified cultural resources and deposits at a range of depths, with the deepest excavations reaching past 11 feet beneath the ground surface, making their detection and identification nearly impossible through traditional Phase I reconnaissance techniques. This approach provided Citizens Energy Group with an accurate understanding of the cultural resources that exist below the ground surface at their projects areas and has allowed the project to move on to the construction phase with enhanced certainty that no deeply buried, significant archaeological deposits will be encountered during construction.