The project aims to reduce overflows from the sewer system into creeks and rivers during flooding by connecting into the upstream end of the OSIS Augmentation Relief Sewer (OARS). The proposed tunnel’s upstream end will provide hydraulic relief to three existing sewers that are in close proximity to each other.

Construction of the LOT will involve a 5.2km-long, 3.66m-diameter TBM-bored tunnel lying at a depth of around 15m. It will be lined with precast concrete segments and have three main shafts located strategically along its length.

A 2.29m diameter microtunnel will also be constructed to relieve the OARS, starting at Second Avenue/Perry Street and flowing west into the LOT at Gowdy Field Shaft. Another 915mm relief sewer will also be required to flow into the LOT.

The LOT forms a key component of the City’s Integrated Plan and 2015 Wet Weather Management Plan. Construction is expected to begin in March 2021 and conclude in December 2026.