Remediation of the Former Nitchequon Meteorological Station
The Nitchequon project involved the dismantling of petroleum tanks and the treatment of soil contaminated with diesel at a former meteorological station operated by Transport Canada. The site is located 100 nautical miles southeast of the LG4 dam, 1,600 kilometres from Montreal, in the heart of Quebec.
Since 1987, the site has been occupied by families of the Cree Nation of Mistissini who own the rights of use to develop an outfitting facility for adventure expeditions, etc. and a wellness centre. However, the contamination left by the petroleum installations of the meteorological station has impeded these potential economic activities. Transport Canada therefore decided to finance a remediation project, led jointly with the Cree Regional Authority.
The site is accessible only by helicopter or hydroplane, with no access route, landing field, electricity or services. Thus, all rehabilitation equipment, chemicals, as well as all dismantled petroleum installations had to be transported by air. The short summer period at this northern latitude added to the complexity.
Studying the situation
After Golder Associates became involved in 2002, their research showed evidence that the soil was contaminated by petroleum hydrocarbons at an average concentration of 4,300 mg/kg.
The remediation objective was to decrease the residual petroleum hydrocarbon concentrations to 1,350 mg/kg. Golder proposed a tailor-made remediation that involved permanganate oxidation. They also did a critical risk analysis.
Permanganate oxidation treatment
The process is innovative because permanganate is not usually used for hydrocarbon treatment. Hydrogen peroxide is often preferred because of its more rapid kinetics, but its required dosage is far greater, only available at a 50% per weight concentration. Transportation costs would have been twice as much costs as for the potassium permanganate. The peroxide treatment was, therefore, impossible in the case of a remote site such as Nitchequon.
The soils remediation combines in-situ and ex-situ treatment. The ex-situ step consists of soil mixing in reactors. This process allows for the mixing of soils, hydrocarbon desorption and partial chemical oxidation of the contaminated soils. It is estimated that about 50% of hydrocarbons are oxidized in this first stage. This phase required the design of efficient mixers, a perfect oxidant dosage, and, more importantly, the optimization of the reactive agents’ addition sequence of permanganate, acid and water.
The second state of the in-situ process consists of the transfer of soils to cells. It allows the percentage of hydrocarbon reduction to increase in the order of 10-30%. The permanganate has a slow oxidation kinetic at ambient temperatures. With its low speed of reaction — a few months — the process allows for the retention of a residual concentration of permanganate in the soils, which oxidizes the most refractory hydrocarbons in the long term.
The confining cells are made of an HDPE membrane and a covering membrane. The cells are protected by a layer of sand with no granular particles, placed on top of the membrane. At the end of the treatment the membranes are perforated and the clean cells are covered with clean soil.
Approximately 140 cubic metres of soils, that is, 10% of the contaminated soil total volume, was treated in 2005. The first results obtained that year showed the process was working well, allowing for a reduction of 77% of the hydrocarbon concentrations.
Flying in chemicals and equipment
To manage and implement the above approach, Golder worked in synergy with Gaia Contractors, an arm of Golder.
The complexity of the project resides greatly in the logistical aspects of the remote site. All chemical reagents (108,000 kilograms of KMnO4 and 10,000 kilograms of citric acid) and pieces of equipment were transported by truck from Montreal to the Pourvoirie Mirage, then flown to the Nitchequon site. All the large oil tanks and pipeline have been removed, with 25,900 kilograms of metal sent for recycling. Close to 100 hydroplane trips and 25 helicopter trips were required.
The budget of about $2.5 million was rigorously respected and the work was carried out in record time, between July and September 2005.
Besides the many environmental aspects of the project, the economic social and environmental repercussions will benefit the Cree people. Cree labour was directly employed and it will now be possible for the Cree to develop the outfitting operation on the remediated site.
Name of project: Remediation of former meteorological station, Nitchequon, Quebec
Award-winning firm: Golder Associates (Mathieu Barbeau, eng., Brigitte Bedard, jr.eng., Eric Bergeron, eng., Christian Gosselin, eng., Kateri Normandeau, eng., Isabelle Richard, eng., Helene S. Richer, eng., Michael Z’Graggen
Owner: Transport Canada
Client: Cree Regional Authority