atmosphere. The chlorine- and bromine-containing halocarbons are also involved
in the depletion of the ozone layer.
Hazard A natural, technological, or human-caused source or cause of harm or
difficulty.
Hazardous wastes A hazardous waste is a material that is subject to special
consideration by the US Environmental Protection Agency (USEPA), under
40CFR261. State or local authorities may also designate additional materials as
hazardous waste in their areas. The definition given by 40 CFR 261 defines a
hazardous waste as a solid waste that is not excluded from regulation and meets
one or more of the following criteria: (a) it is a discarded commercial chemical
product, off-specification species, container residue, or spill residue of materials
specifically listed in 40CFR261.33 (P- and U-codes); (b) it is a waste from a
specific source listed in 40CFR261.32 (K-code); (c) it is a waste from a
non-specific source listed in 40CFR261.31 (F-code); and/or (d) it displays any
of the following characteristics of hazardous wastes: ignitability (such as flash
point is below 60
C or 140
F, it is classified by the US Department of
Transportation,DOT, as an oxidizer D001), corrosivity (such as the pH of the
waste material is less than or equal to 2, or greater than or equal to 12.5, or
classified by DOT as D002), reactivity (such as the waste material is unstable,
reacts violently with water, may generate toxic gases when mixed with water, or
classified by DOT as D003), or toxicity (such as it is classified by DOT ad D004D043).
Hazard-specific annex A component of an emergency operations plan that
describes strategies for managing specific hazards.
Headloss It is an indirect measure of loss of energy or pressure of flowing water. It
is measured as the difference in elevation between the upstream water surface and
the downstream water surface.
Headworks The facilities where wastewater enters a wastewater treatment plant.
The headworks may consist of bar screens, comminutors, a wet well, and pumps.
Heat island An urban area characterized by temperatures higher than those of the
surrounding non-urban area. As urban areas develop, buildings, roads, and other
infrastructure replace open land and vegetation. These surfaces absorb more solar
energy, which can create higher temperatures in urban areas.
Heat load Amount of heat exchanged within the tower between water and air,
expressed per unit of time. It can also be expressed as the product of the quantity
of water circulated within the tower per unit time and the cooling range.
Heat waves A prolonged period of excessive heat, often combined with excessive
humidity.
Heavy metal A general term, which applies to the group of metals and metalloids,
and it has an atomic density more prominent than 4000 kg/m
3 .
Herbicide It is a substance that is toxic to plants and is used to destroy unwanted
vegetation.
Heterotrophic Microorganisms that use organic matter (carbon) for energy and
growth and can grow in both aerobic and anoxic environments using both
dissolved and chemically bound oxygen (nitrates)
12 Glossary of Natural Resources and Environmental Pollution Control
455
in the depletion of the ozone layer.
Hazard A natural, technological, or human-caused source or cause of harm or
difficulty.
Hazardous wastes A hazardous waste is a material that is subject to special
consideration by the US Environmental Protection Agency (USEPA), under
40CFR261. State or local authorities may also designate additional materials as
hazardous waste in their areas. The definition given by 40 CFR 261 defines a
hazardous waste as a solid waste that is not excluded from regulation and meets
one or more of the following criteria: (a) it is a discarded commercial chemical
product, off-specification species, container residue, or spill residue of materials
specifically listed in 40CFR261.33 (P- and U-codes); (b) it is a waste from a
specific source listed in 40CFR261.32 (K-code); (c) it is a waste from a
non-specific source listed in 40CFR261.31 (F-code); and/or (d) it displays any
of the following characteristics of hazardous wastes: ignitability (such as flash
point is below 60
C or 140
F, it is classified by the US Department of
Transportation,DOT, as an oxidizer D001), corrosivity (such as the pH of the
waste material is less than or equal to 2, or greater than or equal to 12.5, or
classified by DOT as D002), reactivity (such as the waste material is unstable,
reacts violently with water, may generate toxic gases when mixed with water, or
classified by DOT as D003), or toxicity (such as it is classified by DOT ad D004D043).
Hazard-specific annex A component of an emergency operations plan that
describes strategies for managing specific hazards.
Headloss It is an indirect measure of loss of energy or pressure of flowing water. It
is measured as the difference in elevation between the upstream water surface and
the downstream water surface.
Headworks The facilities where wastewater enters a wastewater treatment plant.
The headworks may consist of bar screens, comminutors, a wet well, and pumps.
Heat island An urban area characterized by temperatures higher than those of the
surrounding non-urban area. As urban areas develop, buildings, roads, and other
infrastructure replace open land and vegetation. These surfaces absorb more solar
energy, which can create higher temperatures in urban areas.
Heat load Amount of heat exchanged within the tower between water and air,
expressed per unit of time. It can also be expressed as the product of the quantity
of water circulated within the tower per unit time and the cooling range.
Heat waves A prolonged period of excessive heat, often combined with excessive
humidity.
Heavy metal A general term, which applies to the group of metals and metalloids,
and it has an atomic density more prominent than 4000 kg/m
3 .
Herbicide It is a substance that is toxic to plants and is used to destroy unwanted
vegetation.
Heterotrophic Microorganisms that use organic matter (carbon) for energy and
growth and can grow in both aerobic and anoxic environments using both
dissolved and chemically bound oxygen (nitrates)
12 Glossary of Natural Resources and Environmental Pollution Control
455