A layer of solid material, such as rock or clay, which does not allow water to pass through.
Glossary » I
IMPERMEABLE LAYER
IRON
The most common element in the earth. In Freshwater, when the concentrations become to high they precipitates on exposure to air, decreasing pond clarity and encouraging iron bacteria, which affects the flavor of both fish and water. Levels greater than 0.3 mg/L can cause staining on buildings and sidewalks when the water is used for irrigation
