Agency for Toxic Substances and Disease Registry (ATSDR):
The principal federal public health agency involved with hazardous waste issues, responsible for preventing or reducing the harmful effects of exposure to hazardous substances on human health and quality of life. ATSDR is part of the U.S. Department of Health and Human Services.
Aquifer:
An underground formation composed of materials such as sand, soil, or gravel that
can store and/or supply groundwater to wells and springs.
BETX:
Benzene, ethylbenzene, toluene, and xylenes
Carcinogen:
Any substance that can cause or contribute to the production of cancer.
Comparison value:
A concentration of a chemical in soil, air or water that, if exceeded, requires further evaluation as a contaminant of potential health concern. The terms comparison value and screening level are often used synonymously.
Contaminant:
Any chemical that exists in the environment or living organisms that is not normally
found there.
Dose:
A dose is the amount of a substance that gets into the body through ingestion, skin
absorption or inhalation. It is calculated per kilogram of body weight per day.
Exposure:
Contact with a chemical by swallowing, by breathing, or by direct contact (such as
through the skin or eyes). Exposure may be short term (acute) or long term (chronic).
Groundwater:
Water found underground that fills pores between materials such as sand, soil, or
gravel. In aquifers, groundwater often occurs in quantities where it can be used for
drinking water, irrigation, and other purposes.
Hazardous substance:
Any material that poses a threat to public health and/or the environment. Typical
hazardous substances are materials that are toxic, corrosive, ignitable, explosive, or
chemically reactive.
Maximum Contaminant Level (MCL):
A drinking water regulation established by the federal Safe Drinking Water Act. It
is the maximum permissible concentration of a contaminant in water that is delivered to the free flowing outlet of the ultimate user of a public water system. MCLs are enforceable standards.
Media:
Soil, water, air, plants, animals, or any other part of the environment that can contain contaminants.
Model Toxics Control Act (MTCA):
The hazardous waste cleanup law for Washington State.
Monitoring wells:
Special wells drilled at locations on or off a hazardous waste site so water can be
sampled at selected depths and studied to determine the movement of groundwater and the amount, distribution, and type of contaminant.
Parts per billion (ppb)/Parts per million (ppm):
Units commonly used to express low concentrations of contaminants. For example, 1 ounce of trichloroethylene (TCE) in 1 million ounces of water is 1 ppm. 1 ounce of TCE in 1 billion ounces of water is 1 ppb. If one drop of TCE is mixed in a competition size swimming pool, the water will contain about 1 ppb of TCE.
Plume:
An area of contaminants in a specific media such as groundwater.
