Toronto Water is responsible for the operation and maintenance of the 35 km long Mid-Toronto Interceptor (MTI) sewer system. This sewer ranges in size from 1500 mm to 3050 mm diameter and includes some 65 large diversion, control, and vortex chambers. Toronto Water retained Andrews.engineer(A.E) to undertake a detailed inspection and assessment of each of the chambers and to develop a long-term maintenance program. Inspections involved over 250 confined space entries into various rooms within the chambers, some of which were multi-leveled and up to 35 m deep. As part of the work, large diameter pressure fittings and dome covers were inspected and serviced to determine long-term maintenance requirements.
The MTI is designed to operate under sustained surcharge conditions. Pressure fitting domes were installed at the base of access chambers in order to prevent sewage from surcharging into the chambers. The dome covers vary in size from 1200 mm to 1500 mm diameter and are secured with Victaulic-style couplings with 225 mm long, 90 mm diameter bolts. A.E removed one of the 1500 mm domes at the base of a 25 m deep chamber using hydraulic and pneumatic equipment and a hoisting gantry. Staff from A.E also removed a stainless steel plug which was intended to prevent grease buildup on the underside of the dome. Internal measurements and conditions within the dome were documented and the dome re-installed.
Real-time monitoring protocols were implemented to ensure worker safety in the chamber as the dome was serviced. Removing and servicing the domes enabled A.E staff to develop parts lists, spare parts requirements, and equipment needs. These lists enabled development of a long-term inspection and servicing program for the system.