Duggan Sanitary Tunnel Replacement: Mitigating Sewer Odour in Several Edmonton Neighbourhoods

Abstract

Duggan and surrounding neighbourhoods in Edmonton, Alberta have experienced sanitary sewer odour problems due to hydrogen sulphide for a number of years. The main 1,200 mm sanitary trunk (Duggan Tunnel) that services this neighbourhood, and approximately 75,000 residents upstream, was constructed in the 1970s, at a depth of averaging 37 m, in bedrock, to avoid the shallower glacial clay till with intra-till sand layers and rafted bedrock, geotechnical conditions considered less suitable for hand tunnelling at the time. The deep tunnel necessitated several drop manholes along its alignment, and a pump station at the downstream end, connecting to the shallower 1,650 mm outlet tunnel. The drop manholes and pump station have contributed significantly to corrosion and odour problems. Three upstream pump stations that contribute flow to the Duggan Tunnel have also contributed to the corrosion and odour. EPCOR Water Services Inc.’s (EPCOR) Corrosion and Odour Reduction Program aims to reduce the formation of hydrogen sulphide and reduce sewer odour. Under this program, EPCOR proposed to replace the Duggan sanitary tunnel with a 3 km long, shallower tunnel, which would eliminate drop structures, reduce depths of drops, and eliminate the downstream pump station. The downstream 1,650 mm tunnel, which has experienced corrosion at the outlet of the pump station, was also sliplined to extend its service life. This paper will discuss the extensive stakeholder engagement as well as the challenges during the design and construction phases of the Duggan Tunnel Replacement Project, which included major freeway and light rail transit (LRT) crossings, construction in mature residential neighbourhoods and adjacent to several school zones, challenging lateral connections (including hand mining and pipe ramming), and flow bypassing.