Commonwealth Engineers Inc. was hired as part of a design team to perform the planning and design for the Indianapolis Belmont/Southport Interplant Connection. This project was planned to be the largest sanitary improvement project ever undertaken by the City of Indianapolis. This project is a part of the City’s Long Term Control Plan.

The Project

This project consisted of the installation of approximately 33,000 linear feet of 144-inch diameter pipe. The pipe was to be installed using shallow ground tunneling. The pipe was to divert up to 320 million gallons per day of wet weather flow from existing CSOs and existing interceptors entering the Belmont AWT to the Southport AWT.

The Solution

For this project, Commonwealth Engineers focused on the design of structures necessary to connect and convey flow from nearby interceptors transporting flow throughout much of Marion County. In addition, Commonwealth was contracted to perform a design of a lift station located at the Southport AWT plant to pump collected flow from this Interplant Connection into the primary structure entrance to begin treatment processes.

At the 90% design level, Commonwealth was selected, along with three (3) other firms, to participate in value engineering sessions to reevaluate the design concept. Due to increased risks and escalating costs, the recommendation was to revise the interplant to a 36,000 LF, 18-foot diameter tunnel installed 250 feet deep in the bedrock. This allowed the City to increase storage while reducing risk.

Commonwealth is now a part of the design team for the deep rock tunnel connector and is responsible for all diversion structures and approach channels.