CLEANING UP A FUEL OIL SPILL
Most of us think of a spill of fuel oil in terms of an overturned tank truck, jackknifed, and blocking the highway. These are spectacular but in fact, the most frequent spill occurs in somebody's basement or backyard. In areas not served by natural gas, the "home heating oil" is virtually the only fuel available and is very competitive with electric space heaters.
Home heating oil, or simply fuel oil, is almost always stored in a steel tank. There are still perhaps one million tanks in Northeast / North America. Unfortunately, when a steel tank gets some sludge in the bottom, an oxygen concentration cell forms which corrodes the steel in a pinhole pattern. Once a pinhole is created and the oil bursts through, often this occurs over a few hours after the last fill, the tank empties in eight hours or so. The householder is then faced with some 600-800 litres of oil spread across the basement floor or in the backyard. This spill scenario also applies to buried tanks as well except they can go undetected for some time.
The fact that the spill is on private property and only involves a relatively small quantity of contaminant means that the spill is of very little interest to the regulators such as the Ministry of Environment and Energy or the Fuel Safety Branch of the Ministry of Consumer and Commercial Affairs. The householder and the insurance company are expected to conduct a clean up in accordance with the Guideline for use at Contaminated Sites in Ontario, June 1996 (MOEE) using the best technology available really in order to minimize or eliminate any loss in value to the property.
To expedite the clean-up, the insurance company will probably retain a consultant and a contractor. The job of the consultant is to provide a plan which in the end, will achieve the goal of the clean-up. For potable groundwater areas the goal is 100 ppm of gasoline / diesel hydrocarbons. For non potable water areas it is 1,000 ppm. Inside the buildings, a basement or crawl space below 1 metre depth, must be cleaned up to less than 1,000 ppm.
These regulations say nothing about staining or dour. Unfortunately, odour will persist down to 50 ppm and some persons with sensitive noses can detect odours below the 50 ppm TPH level. Such odour sensitive people some times have to move out until remediation is completed. Achieving an odour free home is therefore the focus of indoor spill clean-up.
There are four clean-up methods available. If the concrete floor of the basement is thick, i.e. the kind of floor found in houses built after the 1940's, then it is sometimes possible to wash and deodorize the floor using a combination of solutions. To ensure that no odour comes back, it is often a good practice to then seal the floor with a high quality coating.
Thin concrete often encountered in pre WW2 homes often permit the spilled oil to permeate through it into the fill below and in some cases this will flow under the footings and into the foundation drain. Depending on the height of the water table and the porosity of the soil, the clean-up methods become more and more elaborate.
A shallow spill, i.e. one which rests just below the footing can be cleaned out fairly readily by simply shoveling the contamination out. This assumes that we have low permeability soil such as a tightly packed clay or a higher water table. On the other hand, sand offers almost no resistance to the flow of oil and if the water table is low, then the plume of oil contamination can go down 25 - 50 feet or more. Many situations are encountered which lie within this range.
If the contamination can't be dug out readily without undermining the foundation walls and the soil is tight and impermeable, then the flushing option, a sophisticated soil washing procedure, can begin to get rid of the odour and remove enough of the contamination. However, in the case of sand, biologically assisted passive soil ventilation appears to be the best method. This is a system where the fuel oil is bio-remediated sometimes by injecting a nutrient which is high in phosphorus and by laying a grid of pipes which will permit air to circulate into the contamination. Naturally occurring bacteria use these two agents in bio-degrading the hydrocarbons. The only drawback to the passive system is that is has to be monitored for up to two or even three years until the level of hydrocarbons has been reduced below the 100 ppm limit. At that point, the consultant can close the file and the spill can be considered remediated. No report is filed with either ministry but a report could be important to a future buyer as evidence of an environmentally clean site.
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Walters Forensic Engineering | 277 Wellington
Street West, Suite 800 | Toronto, ON M5V 3H2