This paper was presented at the session titled `1999 TAC environmental achievement award nominations'. Many of Canada's venerable industrial organisations own or operate sites that carry a legacy from past operations. In the transportation industry, the soil and groundwater at old rail yards and workshops may be contaminated by the cumulative effect of hydrocarbon releases spilled over many years. In 1991, a plume of light non-aqueous phase liquid (LNAPL) was discovered to the west of and underneath the CN railway track in the vicinity of CN's former diesel locomotive repair and refuelling facility in Montreal which operated between the 1950s and 1986. In addition, the plume of diesel was delineated up to the downgradient CN property line. The CN rail line is located on top of an old municipal landfill that operated from 1866 through 1966. The depth to groundwater varies between 7 and 8.5 meters below surface and shows seasonal fluctuations of up to one metre. In 1996, CN initiated a program to contain and recover the LNAPL. Previous studies had estimated the volume of the plume was approximately 500,000 L of diesel. The possible origins of the diesel included the fuelling operations, past spills and a broken fuel pipeline. This presentation provides a description of the largest application in Canada of a leading-edge technology for recovery of a LNAPL plume e.g. bioslurping. The challenge was to find a cost-effective system that would permit the future recovery of the LNAPL while immediately preventing further migration off-site thus bringing overall environmental benefits to the site. Also the continued operation of the rail line was not to be impacted. The conventional means of containing and recovering LNAPL spills involve either physical containment (using pile or slurry walls) or hydraulic containment along with a pump-and-treat system. These two approaches had serious limitations at this site. Physical containment was impracticable because of the length and depth of the site and also because of the presence of 325 kV overhead power lines. Hydraulic containment would result in a large volume of water for treatment and would take too long to remove the risk of further off-site migration. The rejection of conventional approaches led to the consideration and use of an innovative LNAPL recovery technology known as "bioslurping". This technology has been identified as a cost-effective solution providing tremendous environmental benefits to the rehabilitation of the site's contamination. (A)
Samenvatting