Lorain Sanitary Sewer Overflow Control Tunnel

Geotechnical Investigation and Tunnel Engineering

The City of Lorain has agreed to a consent decree with the State of Ohio to reduce wet weather sanitary overflows into the Black River. As part of this consent decree, the City has identified several overflows to be captured and their flow redirected to a storage facility during rain events. Once the rain event is over, the storage facility will be dewatered to the existing wastewater treatment plant at a controlled rate.

Project Scope
Initial plans for controlling overflows called for a large (8 million gallon) storage basin to be located near the City Hall, on a reclaimed industrial property. However, a feasibility study performed by Malcolm Pirnie provided an alternate that may have long-term advantages for the City. By constructing a sewage storage tunnel instead of a basin, the community would be able to utilize existing land near the river and lakefront for future development, and may be able to utilize the tunnel for future improvements to the city’s wastewater treatment facilities.

NTH was chosen by Malcolm Pirnie to provide geotechnical and tunnel engineering services for the Phase 1 tunnel.

Project Approach
NTH assisted Malcolm Pirnie and the City of Lorain with initial route planning for the tunnel. Based on NTH’s advice and input from the City, a new alignment was created that better utilized the City’s existing easements and minimized the number of river crossings. Next, NTH recommended a phased geotechnical investigation. Phase A consists of test borings drilled at the proposed shaft locations, and up to 180 feet below ground surface. During Phase A, NTH is providing full-time engineering site inspection, and performing rock coring and testing, insitu Lugeon testing of the rock profile, monitoring for toxic and explosive gases, and installation of monitoring wells to monitor long term groundwater levels. The information obtained in Phase A will be utilized to confirm the feasibility of tunneling along and beneath the Black River, and to determine initial shaft and tunnel support requirements. NTH is currently preparing an initial Geotechnical Data Report, Feasibility Analysis for the proposed tunnel alignment, and recommendations for the next phase of investigations and design.

NTH’s activities in Phase B are anticipated to include:

A geotechnical investigation for the remainder of the tunnel alignment including test borings in the Black River,
Preparation of a final Geotechnical Data Report and Baseline Report (if required)
Design of temporary and permanent structural elements for the tunnel and shafts
Preparation of biddable project specifications relating to the tunneling aspects of the project
And assistance for Malcolm Pirnie and the City during bidding and award.