Definitions of Terms & Measurements

Definitions of Terms & Measurements

MCL= Maximum Contaminant Level: the highest concentration projected to be safe (one-in-a-million chance of illness) over a lifetime of consumption, taking costs into account.

MCLG= MCL Goal: The highest recommended level if costs didn’t matter—usually the same as the MCL, except that carcinogens which are presumed to have no safe “threshold” level are automatically given an MCLG of zero.

NTU= Nephelometric Turbidity Unit. A nephelometer measures the scattering of light rather than the absorbing of light.

MRDL= Maximum Residual Disinfectant Level: like an MCL, except disinfectants are not considered to be “contaminants.”

TT= Treatment Technique: used when an MCL cannot be defined. When a specific concentration is listed, as for Copper and Lead, it is an “Action Level:” if exceeded, the waterworks is required to alter the treatment technique to prevent it.

PS= Performance Standard: used for Turbidity instead of an MCL because it is often intentionally increased during treatment, then removed at the end to assure adequate disinfection. Turbidity is the only parameter that is required to be measured daily. Most waterworks monitor it continuously.

Inorganic Chemicals= Minerals, salts, etc. dissolved from rock, soil, ores, etc. Chemical substances that are not made by living things and do not contain the element carbon.

Organic Chemicals= Chemical substances containing the element carbon that are made by living things, and other synthetic materials manufactured by people—plastics, pesticides, solvents, etc.

Volatile Organic Chemicals=Organic chemicals that are such small molecules that they are gases or evaporate readily. Many pesticides, solvents, industrial wastes and disinfection byproducts are VOCs.

Trihalomethanes (THMs) and Haloacetic Acids (HAAs)= small one-carbon (THMs) and two-carbon(HAAs) fragments of naturally-occurring organic matter caused by chlorination of “color” molecules and other organic materials.

mg/L= milligrams per liter. Essentially the same as parts per million (ppm) because there are a million milligrams in a liter of pure water.

ug/L orμg/L= micrograms per liter. Essentially the same as parts per billion (ppb) because there area billion micrograms in a liter of pure water.

pCi/L = pico-Curies of radioactivity per liter. A Curie is the radioactive output of one gram of pureRadium-226, equal to 3.7 X 1010atomic disintegrations per second. The MCL of 5 pCi/L amounts to one “click” on a Geiger counter about every 54 seconds.

mrem= milli-Roentgen-Equivalent-Man per year. The Roentgen is the physical measurement of a dose of ionizing radiation (X-rays, cosmic rays, gamma-rays), and the REM relates the dose to the actual biological damage it does—like a “wind chill index” does for temperature and wind speed. For comparison, it is estimated that the average American receives some 360 mrem of total radiation yearly, most of which comes from radon gas in the environment, with another 20% from medical X-rays. The maximum annual radiation dose permitted for people who work with radioactive materials is 5000 mrem/year, and the maximum dose for pregnant women and fetuses is 500 mrem/9-months.

This Technical Bulletin is courtesy of Pentair Everpure, Inc.