Legal Definitions - leaching

Leaching describes a process where a liquid, such as rainwater or groundwater, passes through a solid material and dissolves some of its soluble components, carrying them away. In environmental law, this process is often legally significant because it can lead to the "release" of contaminants from a source into the surrounding environment, such as soil, groundwater, or surface water, potentially triggering regulatory action and liability.

Here are some examples to illustrate this concept:

• Agricultural Runoff: Imagine a farm field where fertilizers and pesticides have been applied to the soil. When heavy rain falls, the rainwater can seep into the ground, dissolve some of these chemicals, and then carry them through the soil into nearby streams or groundwater. This movement of dissolved chemicals by the rainwater is an example of leaching, as the water (moving fluid) separates and transports the soluble agricultural chemicals (components) from the soil (material).

• Mining Waste Contamination: Consider a former mining site where large piles of waste rock, known as tailings, remain. These tailings often contain trace amounts of heavy metals and other minerals. When rain falls on these piles, the water can percolate through them, dissolving these metals and minerals. This contaminated water then flows off the site into rivers or seeps into the groundwater, causing environmental pollution. Here, the rainwater (moving fluid) leaches the heavy metals and minerals (soluble components) from the mining tailings (material).