Site Remediation: Mill Creek Oil Removal

Infrastructure Systems

To remove oil dumped in an Edmonton park creek, Infrastructure Systems borrowed practices used by the petroleum and irrigation industries.

Mill Creek that flows into Edmonton’s River Valley Park downtown joins the North Saskatchewan River after a journey through miles of industrial areas to the southeast. Evidently someone — probably in an automotive or industrial workshop — has been dumping oil into the storm sewers that feed into the creek. The city hired Infrastructure Systems to find a way to detect and divert the spilled contaminants.

The engineers took advantage of an existing pipeline at the edge of the park and borrowed from technology used in the irrigation and petroleum industries to skim off and remove the oil in the 3.9 metre diameter vessel. The engineers have not found any other example where on-line oil removal technology has been installed at a similar scale in a large municipal system.

After creek water enters a 1 12 km. stretch of the pipe, it is halted by a special “tilting weir” or “overshot gate” installed at the end. The velocity of the water slows drastically inside this 2-metre deep reservoir (the separator), allowing the contaminants to rise to the surface. The gate has an internal baffle that allows only water from the bottom of the stream to pass “over” the gate. The design prevents separated contaminants from escaping downstream. A belt skimmer then removes the oil (capacity 200 litres per hour), it is decanted and flows by gravity into a holding tank with a capacity of 1,500 litres. An ultrasonic sensor monitors the level of oil in the tank and signals when it needs pumping out.

To make sure the gate does not cause flooding upstream during heavy storms, a sensor and programmable logic controller (PLC) ensure that the gate automatically opens when water reaches a certain level. Infrastructure Systems began to monitor the $820,000 system in July 2000. In the first year over 1,000 litres of hydrocarbons were removed from the creek. The city takes specimens in order to identify the contaminants and use them to track down the sources and prosecute the polluters.

Consulting engineers: Infrastructure Systems

Electrical subconsultant: Magna IV Engineering