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 levels.

A plastic made from the gaseous chemical vinyl chloride.  PVC is used to make pipes, records, raincoats and floor titles.  It produces hydrochloric acid when burned.  Health risks from high concentrations of vinyl chloride  (not the polymer) include liver cancer and lung cancer, as well as cancer of the lymphatic and nervous systems.  Vinyl ch [..]

The direction from which water flows in an aquifer.  In particular, areas that are higher than contaminated areas and, therefore, are not prone to contamination by the movement of polluted groundwater.

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: one for acute (relatively short-term) and one for chronic (longer-term) exposure.

A widely used, highly voatile solvent.  It is readily absorbed by breathing, ingestion or contact with the skin.  Workers who have inhaled acetone have reported respiratory problems.

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 acid have many industrial uses, and can be dangerous to those not familiar to handling them.  Acids are chemical "opposites" to bases, in [..]

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 contaminants are found at concentrations above their action levels, measures must be taken to decrease the contamination.

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 also the product formed when raw sewage is mixed with bacteria-laden sludge, then stirred and aerated to destroy organic matter.

The number of particles or photons ejected from a radioactive substance per unit time.

Hazards associated with short-term exposure to relatively large amounts of toxic substances.