A cleanup action for contaminated
ground water consisting of a well
or series of wells pumping
continuously to remove ground
water from the aquifer.

A wall of bentonite or similar
material injected underground to
retard horizontal flow of ground
water in order to isolate or
control contamination; a slurry
wall.

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

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.

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.

Chemicals used to kill undesirable
vegetation.

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.

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

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.

A furnace that burns under
controlled conditions