Understanding polluted sites and soil what is ground, anyway?
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UNDERSTANDING POLLUTED SITES AND SOILS THE ORIGIN OF SOIL AND GROUNDWATER
The ground beneath our feet is the result of a transformation. It was formed from the breakdown of the original rock by weather, vegetation and other living organisms. Rain, frost, wind and heat promote rock erosion. These fine materials have also been enriched by activity from plants and animals, from large to microscopic, leading to the formation of different types of soil. These elements constitute the solid fraction of the soil. But soil also holds a great deal of water: the liquid fraction. In the unsaturated zone, water-free spaces remain amid the moist materials. In the so-called saturated zone, solid elements are completely surrounded by water. Here, water in the saturated zone forms a water table which moves freely in the solid fraction, a fraction also called an aquifer. The level of the saturated zone rises and falls from season to season, alternating between high water and low water depending on the level of water in the aquifer. Soil naturally contains gases: air, a lot of water vapor, trace gases, such as radon and mercury, hydrocarbons and sulfur compounds. This is the gaseous fraction of the soil. When the groundwater level rises, the gas fraction follows suit and rises with it. High temperatures favor the emission of gases from the ground into the atmosphere. Soil has many functions involving interactions between these three fractions. Water, which in vapor form makes up a large part the gaseous fraction, is in constant exchange with the atmosphere. Thus, the soil participates in the water cycle. Through its capacity to store organic matter, it is also part of the carbon cycle and helps regulate the climate. The role soil plays is essential to life. On the surface, soil supports vegetation and provides a habitat for many organisms. The soil provides flora and fauna with the minerals and water necessary for their development. Soil retains water, purifying it via infiltration or evaporation, and releases it when it evaporates or flows from a spring. When rain seeps in, the soil contributes to flood regulation. Soil provides humans with a large number of services called "ecosystem services." Soil is essential to life. It is a resource that is renewed very slowly and must be preserved.
Understanding polluted sites and ground: the cause of pollution
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UNDERSTANDING POLLUTED SITES AND SOILS ORIGINS OF POLLUTION
Pollution comes from a wide variety of human activities. Some industries or artisanal activities can damage the soil, as can mining and wars. Local pollutants include those emitted by old industrial sites still in operation. They accumulated in the soil over decades following infiltration and atmospheric fallout before the arrival of modern equipment for treating liquid and gaseous effluents. Decommissioned sites sometimes become wastelands, where waste and abandoned substances are a threat to the soil. In either case, it is vital to keep a record of where these sites are located and which activities took place there. The main activities of the past have been inventoried. This historical knowledge is essential when pollution is suspected. In modern factories, soil pollution can still occur in the event of accidents or negligence. Equipment maintenance rules and effective waste management are designed to prevent them. Some facilities are listed by the authorities according to their risk to the environment and are the subject of special attention. These are "installations classified for environmental protection." Regulations impose strict procedures with regard to safety upgrades and site rehabilitation where activity has ceased. In the event of pollution, those responsible are required to take the necessary measures. If a company no longer exists or the managers have disappeared, sites can be taken over, under certain conditions, by ADEME and are then designated as "orphan polluted sites." Among the sources of diffuse pollution are incinerators, transport vehicles, certain agricultural practices and individual or community heating systems. Family homes can also be a source of pollution, like in the garden, from weedkillers and pesticides, and in the garage, from vehicle oil changes, solvents and fuel tanks. Raising awareness among residents, gardeners and handymen is important in fighting these emissions. The sale and use of certain products are regulated. For pollution dispersed in small quantities over large areas, there are few solutions for treatment. Preventive measures should be favored. Given the variety of chemical pollution sources, we need to rely on experts in polluted sites and soils familiar with regulations, standards and the procedures for preventing, identifying and monitoring pollution, along with diagnosing and treating it to effectively manage its impact.
Understanding polluted sites and soil: the different types of pollution
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UNDERSTANDING POLLUTED SITES AND SOILS THE DIFFERENT TYPES OF POLLUTION
Soil is considered to be polluted when its quality is degraded by chemical substances or organisms not naturally found there and the degradation is considered a risk to health, property or the environment. Let's look at chemical pollution. Categories are defined by the nature of the substances concerned, their distribution in the environment and their release time. The most frequently encountered substances that pollute soil are hydrocarbons, certain metals and metalloids, and chlorine-containing compounds, broken into subfamilies. Because of their different chemical properties, these substances do not behave the same way in soil. Certain types of pollution can occur in a very short time, such as when a high concentration of pollutants spreads rapidly in a very localized way after an accident, like carbon tetrachloride, a noxious solvent, spilling from an overturned truck. Though often reported and quickly controlled, accidental pollution can have long-term consequences if pollutants seep into the ground and reach the groundwater. Other types of pollution, however, spread over long periods of time, sometimes very slowly but repetitively or continuously. This is called chronic pollution, like when hydrocarbons leak from a hole in a tank. A slight leak may remain undetected, or small amounts of a product can spread around a tank after careless filling. Local pollution affects a relatively concentrated, small area and has a clearly identified source. Diffuse pollution, though, is emitted in very small quantities over a very wide area. The many sources of diffuse pollution are hard to identify and distinguish. Examples of diffuse pollution that degrade soil include atmospheric fallout from road traffic, factory fumes or older heaters, and emissions from farming activities or fires. The behavior of pollution in the soil varies greatly according to the characteristics of the soil, the groundwater and the pollutants. Monitoring, assessment and diagnostics are needed to characterize the pollution, identify associated risks and define how to best manage each situation.
About the web series
We all use the ground, every day, to get around on, to feed ourselves and much more. But the ground on which we live and grow food can be polluted.
What are the most common pollutants in soil? Why is it important to characterise them and understand their behaviour? What solutions are there for countering this pollution?
In conjunction with the French Ministry for Ecological Transition, BRGM has designed a series of animated educational videos to help you understand everything there is to know about polluted sites and ground. Discover the first of them below.
