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Habitat

The sum of the physical, chemical, and biological environment occupied by individuals of a particular species, population, or community, including the food, cover, and space resources needed for plant and animal livelihood.

Half-life

The time required for one-half of a specified substance to degrade or become inert.

Hazardous Air Pollutant (HAP)

A hazardous air pollutant is a substance that is defined as hazardous by the 1990 amendments of the Clean Air Act. These substances include certain volatile organic chemicals, pesticides, herbicides, and radionuclides that present tangible hazard, based on scientific studies of exposure to humans and other mammals.

Hazardous Waste

A waste that: is easily ignitable under ordinary temperature and pressure; readily supplies oxygen or reactive gas to a fire; is corrosive (highly acidic or caustic); is explosive or generates toxic gas; is acutely toxic to animals if it comes into contact with skin or is inhaled, eaten or drunk; or contains toxic chemicals that can be dissolved in an acidic environment, such as a landfill.

Health Based Value (HBV)

1. (EDA Ground Water) The concentration of a groundwater contaminant, or a mixture of contaminants, that poses little or no risk to health, even if consumed daily over a lifetime. The Minnesota Department of Health develops HBVs in response to requests from other Minnesota agencies that have found a contaminant in groundwater.

Learn more about HBVs on the Minnesota Department of Health Web site.

Health Benchmarks for Air

A level of chemical concentration in ambient air, at or below which a chemical or defined mixture of chemicals is not likely to cause an adverse health effect to the general public when exposure occurs over a prescribed period of time.

Health Risk Limit (HRL)

1. (EDA Ground Water) The concentration of a groundwater contaminant, or a mixture of contaminants, that can be safely consumed daily for a lifetime. It is expressed as a concentration in micrograms per liter (ug/L).

Learn more about HRLs on the Minnesota Department of Health Web site.

Health Risk Values (HRV)

Concentrations of chemicals or defined mixtures of chemicals emitted to air that are unlikely to pose a significant risk of harmful effects when humans are exposed to those concentrations over a specified time.

Heavy Metals

Metals with high molecular weights that are of concern because they are generally toxic to animal life and human health if naturally occurring concentrations are exceeded. Examples include, arsenic, chromium, lead and mercury.

Herbicides

Chemicals used to kill undesirable vegetation.

Herptiles

Reptiles and amphibians.

Historical Data

Data sets from previous studies, which can range from handwritten field notes to published journal articles.

HRS

Hazard Ranking System Score. A mathematical score given to each Superfund site, used to set priorities for cleanup of sites. Also called an HRS score.

Hydrogeologic Study

A study of an area's geology, ground water and ground water movement.

Hydrogeomorphic (HGM) Approach

A functional assessment method that compares a wetlandﾒs condition to similar wetland types (as defined by HGM classification) that are relatively unaltered. HGM functions normally fall into one of three major categories: (1) hydrologic (storage of surface water), (2) biogeochemical (removal of elements and compounds), and (3) habitat ( maintenance of plant and animal communities). Hydrogeomorphic classes include riverine, depressional, slope, mineral soil flats, organic soil flats, estuarine fringe, and lacustrine fringe.

Hydrologic Unit Code (HUC)

The 8-character federal code identifying the Cataloguing Unit, the smallest of the different hydrologic units. The coding is hierarchical with a 2-character region, a 4-character subregion, a 6-character accounting unit and an 8-character cataloguing unit.

Hydrology

The science of dealing with the properties, distribution, and circulation of water both on the surface and under the earth.

Hypereutrophic

A very nutrient-rich lake characterized by frequent and severe nuisance algal blooms and low transparency. See Also Algal Bloom, 

Hypolimnion

The bottom layer of lake water during the summer months. The water in the hypolimnion is denser and much colder than the water in the upper two layers.