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12.0 Glossary

Hydrogen Sulfide (H2S): A colorless, flammable, poisonous compound having a
characteristic rotten-egg odor. It is used in industrial processes and may be emitted
into the air.

Hydrology: The study of the water cycle.

Hydromodification: Changes to the storm water runoff characteristics of a watershed
caused by changes in land use.

Hydrophobic: Having low solubility in water.

Illuminance: The amount of total light received from a source by a unit of surface area.

Impact: The effect, influence, or imprint of an activity or the environment. Impacts include:
direct or primary effects which are caused by the project and occur at the same time and
place; indirect or secondary effects which are caused by the project and are later in time or
farther removed in distance, but are still reasonably foreseeable. Indirect or secondary
effects may include growth-inducing effects and other effects related to induced changes in
the pattern of land use, population density, or growth rate and related effects on air and
water and other natural systems, including ecosystems.

Impact Fee: A fee, also called a development fee, levied on the developer of a project by a
city, county, or public agency as compensation for otherwise-unmitigated impacts the
project will produce. The California Government Code (Sections 66000 et seq.) specifies that
development fees shall not exceed the estimated reasonable cost of providing the service for
which the fee is charged. To lawfully impose a development fee, the public agency must verify
its method of calculation and document proper restrictions of use of the fund.

Impervious Surface: Ground surface that cannot be penetrated by water. Includes paved
and compacted surfaces, as well as those covered by buildings.

Important Farmlands: Important farmlands include prime farmlands, farmlands of
statewide importance, unique farmlands, and farmlands of local importance as defined and
mapped by the California Department of Conservation (NRCS 2017a).

Imported Water: Water that has originated from one hydrologic region and is transferred
to another hydrologic region.

Impoundment: A body of water, such as a pond, confined by a dam, dike, floodgate, or other
barrier.

Income Categories/Levels: Four categories are used to classify a household according to
the median income for the county. Under State housing statutes, these categories are as
follows: Very Low (0 to 50 percent of county median); Low (50 percent to 80 percent of
county median); Moderate (80 percent to 120 percent of county median); and Upper (over
120 percent of county median). Four levels are included relating to the Orange County HUD
median income: Income I is defined as households earning 0 to 30 percent of the HUD county
median income. Income II is defined as households earning 30 to 50 percent of the HUD

R:\Projects\PAS\CEN\000306\Draft EIR\12.0_Glossary-051017.docx 12-39 Centennial Project
Draft EIR