Soil remediation, we have all come across it at some point!
Soil remediation. Nearly all property owners will be affected by this at some point. This could be a house owner with an asbestos sewage pipe in the front garden or an old leaking oil container next to the house. Or this could be a petrol station or petrochemical company with a leaking (underground) fuel line, or a dry-cleaning company whose degreasing agent tank has been leaking unseen for many years.
In-situ
HMVT is a specialist in in-situ soil and in-situ groundwater remediation: the cleaning up of the soil with minimum impact on the surrounding area. An underground system with an installation above ground are common features of such an approach, but there are many possibilities! These can all be found when it comes to “Soil”: biological, chemical, extraction, thermal, all techniques for tackling contamination in the soil.
Techniques
Roughly speaking, soil remediation can be carried out in 2 ways. There is the in-situ approach of HMVT and there is the other technique known as “ex-situ”. “In-situ” literally means: at the place. Ex-situ therefore means “cleaning the soil elsewhere” and so refers to excavating the soil and then transporting it to a cleaning installation. The excavated soil, however, does not necessarily have to be cleaned if put to other uses such as a noise barrier; and contaminated soil from a residential area can also be removed and put to good use at an industrial site. Here one would not have to worry about playing children or vegetable plots.
In-situ remediation at the site itself is different. An installation is usually set up above ground, which is connected through underground pipes to vertical sources, also known as filters. These filters are actually tubes with very small slits in them. Water and air can pass through the slits but not, for example, sand. In this way, you can for example pump water out the soil or air into it over a long period time.
Approach
A special situation arises if contamination occurs through oil or petrol. These substances float on water (just see what happens when you put a few drops of olive oil in a glass of water). If large amounts of oil end up in the soil, a floating layer of oil will form on the water (groundwater) in the soil: a non-aqueous phase liquid layer (NAPL layer). In that case the remediation professional may decide to pump up precisely that floating layer of oil. But because the groundwater level rises and falls throughout the year (the groundwater level falls when we’ve had less rain and rises after more rain), the layer of oil moves along with it! In that case we place the sources in such a way that “approximately” at the level of the oil we extract at high power using a vacuum pump: multi-phase extraction. We extract therefore in three phases: (dirty) groundwater, pure oil and (dirty) air. We then treat the flow in the purification process above ground.