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 18.7 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 processes include standard archival research coupled with ground-penetrating radar (GPR) surveys to identify potential archaeological features at any given project area.

This research and analysis is followed with Subsurface Utility Engineering (SUE) investigations, which uses excavation performed with vacuum trucks to uncover the identified features. Use of the vacuum truck allows for faster and safer excavation than traditional Phase I archaeology methods. In addition, this technique has the potential to assist in determining National Register of Historic Places eligibility at an earlier phase of excavation. This can help minimize the uncertainty of what is below ground without the need for a traditional Phase II evaluation. These factors all contribute to reducing the chance of accidental discoveries after project construction has begun and helping keep the project on schedule.

Cardno has currently utilized this technique at 11 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. The success of this approach has helped provide Citizens Energy Group with an accurate description of the cultural resources existing below the ground surface, as well as a more confident project recommendation prior to construction.