GLOSSARY - Bioaugmentation for Groundwater Remediation - page 366

Heterologous ‐ Literally means “derived from a different organism.” Heterologous
expression refers to the transfer of genetic material from one organism to another, so that
the recipient cell manufactures (“expresses”) a protein that it does not normally make.

Heterotrophic ‐ Describes an organism that cannot synthesize its own food and is dependent
on complex organic substances for nutrition (as opposed to autotrophic).

Hydrocarbon ‐ Chemical compound consisting of hydrogen and carbon (although some or all
of the hydrogen may be replaced by other atoms, such as chlorinated hydrocarbons).

Hydraulic conductivity ‐ A measure of the rate at which water moves through a unit area of
the subsurface under a unit hydraulic gradient.

Hydraulic fracturing ‐ Method used to create fractures that extend from a borehole into
rock and clay formations. Fractures are typically maintained by a proppant, a material such as
grains of sand or other material that prevent the fractures from closing. Used to increase or
restore the ability to transmit fluids.

Hydraulic gradient ‐ Change in head (water pressure) per unit distance in a given direction,
typically in the principal flow direction.

Hydraulic residence time ‐ The average time water spends within a specified region of space,
such as a reactor or a treatment zone within the subsurface.

Hydrocarbons ‐ Chemical compounds that consist entirely of carbon and hydrogen.

Hydrogenolysis ‐ Chemical reaction in which a carbon-carbon or carbon-heteroatom single
bond is cleaved (or “lysed”) by hydrogen. The heteroatom may vary, but it often is oxygen (O),
nitrogen (N), or sulfur (S). Usually conducted catalytically using hydrogen gas.

Hydrolysis ‐ The decomposition of organic compounds by interaction with water.

Hydrophobic ‐ “Water-fearing.” Hydrophobic compounds, such as oils and chlorinated
solvents, have low solubilities in water and tend to form a separate nonaqueous phase.

Hydrogenotrophic ‐ Using hydrogen as an electron donor.

In situ ‐ Latin term meaning “in place”; in the natural or original position, e.g., treatment of
groundwater in the subsurface.

In situ bioremediation ‐ The use of microorganisms to degrade contaminants in place with

the goal of obtaining harmless chemicals as end products. Generally, in situ bioremediation is
applied to the degradation of contaminants in saturated soils and groundwater, although
bioremediation in the unsaturated zone can occur.

In situ chemical oxidation (ISCO) ‐ Technology that oxidizes contaminants in place by

adding strong oxidants such as permanganate or peroxide, resulting in detoxification or
immobilization of the contaminants.