Glossary

Glossary

MAGNETROMETRY:

A geophysical technology used to detect disruptions that metal objects cause in the earth's localized magnetic field.

MASS SPECTROMETRY:

A method of chemical analysis in which the substance to be analyzed is heated and placed in a vacuum. The resulting vapor is exposed to a beam of electrons that causes ionization to occur, either of the molecules or their fragments. The ionized atoms are separated according to their mass and can be identified on that basis.

MAXIMUM CONTAMINANT LEVEL (MCL):

A contaminant level for drinking water, established by the California Department of Health Services, Division of Drinking Water and Environmental Management, or by the U.S. Environmental Protection Agency. These levels are legally enforceable standards based on health risk (primary standards) or non-health concerns such as odor or taste (secondary standards).

MELLO-ROOS SPECIAL TAX:

A special tax that is levied in an area in order to finance a broad range of public capital facilities and services. A local agency can levy this tax by forming a government entity, called a Mello-Roos Community Facilities District.

MERCURY:

A heavy metal that can accumulate in the environment and is found in thermometers, measuring devices, pharmaceutical and agricultural chemicals, chemical manufacturing, and electrical equipment. (See HEAVY METAL.)

METHANE:

An odorless, colorless, flammable natural occurring gas. It can seep up through the ground in areas that have shallow petroleum deposits or improperly abandoned oil wells, such as certain areas of the Los Angeles Basin. It is a greenhouse gas believed to contribute to global warming. 

METHYL ETHYL KETONE (MEK):

MEK is a flammable solvent that has many industrial uses, primarily in the plastic industry as a solvent. MEK is also used in the synthetic rubber industry, in the production of paraffin wax, and in household products such as lacquer and varnishes, paint remover, and glues.

METHYL TERTIARY BUTYL ETHER (MTBE):

A synthetic chemical, is a volatile, flammable, colorless liquid. MTBE has a relatively high vapor pressure and is water soluble to a significant degree. MTBE usually is produced in a refinery by mixing a feedstock of isobutylene with methanol. The isobutylene is derived by steam-cracking during production of olefin and fluid-cracking during production of gasoline. Concern about them arises from its potential contamination of groundwater as a result of releases from underground storage tanks of gasoline that contains oxygenates. 

METHYLENE CHLORIDE:

A colorless liquid that evaporates easily. It has been used as a metal cleaner, paint thinner, in wood stains, spot removers, fabric protectors, shoe polish and aerosol propellants.

MICROGRAM PER GRAM (Mg/g):

A measurable unit of concentration for a solid. A mercury level of 1.0 mg/g means that one microgram (one millionth of a gram) of mercury was detected in one gram of sample. It is roughly equivalent to one part per million (ppm). (See PARTS PER MILLION.)

MICROGRAM PER LITER (Mg/l):

A unit of the concentration of a constituent in water or wastewater. It represents 0.0000001 gram of a constituent in 1 liter of water. It is roughly equivalent to one part per billion (ppb). (See PARTS PER BILLION.)

MIGRATION PATHWAY:

 A potential path or route of contaminants from the source of contamination to contact with human populations or the environment. Migration pathways include air, surface water, groundwater, and land surface. The existence and identification of all potential migration pathways must be considered during assessment and characterization of a waste site.

MILLIGRAM PER CUBIC METER (mg/m3):

A unit of concentration for air contaminants. A mercury vapor level of 1.0 mg/m3 means that one milligram (one thousandth of a gram) of mercury vapor was detected in each cubic meter of sampled air.

MILLIGRAM PER KILOGRAM (mg/kg):

A unit of concentration for a solid. A mercury level of 1.0 mg/kg in fish means that one milligram (one thousandth of a gram) of mercury was found in each kilogram of sampled soil. (A kilogram is 1,000 grams or approximately 2.2 pounds). It is roughly equivalent to one part per million (ppm). (See PARTS PER MILLION.)

MILLIGRAM PER LITER (mg/l):

A unit of the concentration of a constituent in water or wastewater. It represents 0.001 gram of a constituent in 1 liter of water. It is roughly equivalent to one part per million (ppm). (See PARTS PER MILLION.)

MILLION GALLONS PER DAY (MGD):

A measurement of water flow equal to about 0.5 cubic feet per second. 

MONITORED NATURAL ATTENUATION:

The remedial approach that allows natural processes to reduce concentrations of contaminants to acceptable levels. Monitored natural attenuation involves physical, chemical, and biological processes that act to reduce the mass, toxicity, and mobility of subsurface contamination. Physical, chemical, and biological processes involved in monitored natural attenuation include biodegradation, chemical stabilization, dispersion, sorption, and volatilization. 

MONITORING WELL:

A well drilled at a specific location on or off a hazardous waste site at which groundwater can be sampled at selected depths and studied to determine the direction of groundwater flow and the types and quantities of contaminants present in the groundwater.

MONITORING WELL:

A well drilled at a specific location on or off a hazardous waste site at which groundwater can be sampled at selected depths and studied to determine the direction of groundwater flow and the types and quantities of contaminants present in the groundwater.

MOTHBALLED SITES:

Large, idle areas that formerly were used for manufacturing and other industrial uses and are not available for sale or redevelopment.