Environmental Terms and Definitions

Maximum Contaminant Level (MCL)
The highest (maximum) level of a contaminant allowed to go uncorrected by a public water system under federal or state regulations. Depending on the contaminant, allowable levels might be calculated as an average over time, or might be based on individual test results.

Action level
The exposure level (the material's concentration in air) at which OSHA regulations to protect employees take effect (29 CFR 1910.1001-1047); e.g., workplace air analysis employee training, medical monitoring, and record keeping.

HSWA
Hazardous and Solid Waste Amendments (1984); amendments to RCRA establishing a timetable for landfill bans and more stringent UST requirements.

Aquifer
An underground source of water. This water may be contained in a layer of rock, sand or gravel.

Exposure
Contact with a chemical by swallowing, by breathing or by direct contact (such as through the skin or eyes). Exposure may be either short term (acute) or long term (chronic).

Biological monitoring
Analyzing chemicals, hormone levels or other substances in biological materials (blood, urine, breath, etc.) as a measure of chemical exposure, health status, etc. in humans or animals. A blood test for lead is an example of biological monitoring.

Detection limit
The smallest amount of substance that a laboratory test can reliably measure in a sample of air, water, soil or other medium.

AHERA
Asbestos Hazard Emergency Response Act (1986); federal law requiring LEAs to identify asbestos hazards and develop abatement plans.

Analyte
A chemical for which a sample (such as water, air, blood, urine or other substance) is tested. For example, if the analyte is mercury, the laboratory test will determine the amount of mercury in the sample.

Absorption
The process of taking in, as when a sponge takes up water. Chemicals can be absorbed into the bloodstream after breathing or swallowing. Chemicals can also be absorbed through the skin into the bloodstream and then transported to other organs. Not all of the chemical breathed, swallowed, or touched is always absorbed.