GUIDELINES FOR EX-SITU TREATMENT OF SOIL
The main thing to consider is that you must get the solution of microbes and nutrient in contact with the contaminant. If you have a shallow penetration of a contaminant such as a petroleum product, say 3-4 inches, you will get a quicker clean-up if you can disturb the soil, that is aerate and mix. This can be achieved with a shovel, disked which will penetrate 6-8 inches (this is a farming device, pulled by a tractor), a root rake, or anything else you can think of. With anything less than 3-4 inches, saturating the surface will usually suffice.
For deeper penetrations, the same principal applies though heavier duty equipment is advised. A back hoe which can “toss” the soil to aerate and mix it; a bulldozer with ripper blades for large sites is excellent; even a portable conveyor belt where the soil is loaded at the lower end and “flung” out of the upper end will accomplish the mixing and aeration. As the soil is moving up the conveyor belt, a spray inoculation will achieve good coverage.
You must maintain a moisture level range of between 15% and 20% as a minimum. Remember, oil on soil acts as waterproof so make sure you penetrate that waterproof barrier. See above for mixing suggestions. A 20% moisture level in soil occurs when you can make a mud ball with your hands. Higher than 20% is fine; remember these microbes can treat contaminated water where the moisture level is 100%! If the moisture level drops, all is not lost as the microbes form “spores”, that is go inert until they get more water to activate them.
Mix, aerate, and hydrate.