A layer or bed of impermeable or distinctly less permeable material lying below or above one or more aquifers. When the confining layer lies between two aquifers, it keeps water from the upper aquifer [..]

The space in a tank between the top of a tank and the liquid level. If the tank is used to store combustible liquids that easily evaporate, this space can fill with vapors which may reach explosive le [..]

Numbers which describe how toxic a chemical is. The numbers are derived from animal studies of the relationship between dose and non-cancer effects. There are two types of acceptable exposure values: [..]

A class of compounds that can be corrosive when concentrated. Weak acids, such as vinegar and citric acid, are common in foods. Strong acids, such as muriatic (or hydrochloric), sulfuric and nitric ac [..]

A guideline established by environmental protection agencies to identify the concentration of a substance in a particular medium (water, soil, etc.) that may present a health risk when exceeded. If co [..]

A term used to describe sludge that contains microorganisms that break down organic contaminants (e.g., benzene) in liquid waste streams to simpler substances such as water and carbon dioxide. It is a [..]

Molecules of gas, liquid, or dissolved solids that adhere or "stick" to the surfaces they come in contact with. Some chemicals adsorb strongly to soil particles. This differs from absorb: &q [..]

Effects of chemicals or other materials that impair one's health. They can range from relatively mild temporary conditions such as minor eye or throat irritation, shortness of breath or headaches [..]

The level above which an environmental protection agency suggests it is potentially harmful to be exposed to a contaminant, although no action is mandated.

Passing air through a solid or liquid, often part of a process that promotes breakdown or movement of contaminants in soil or water by exposing them to air.