Page 281 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

SITE UTILITY SYSTEMS

SITE UTILITY SYSTEMS 6.3

upper zone is called the unsaturated zone, with pores that contain both air and water. It is
also called the zone of aeration. In the lower one, called the saturated zone, all the pore
spaces are completely filled with water.
The unsaturated zone is divided into different layers. The porous, upper part of the
unsaturated zone is called the soil water belt. This belt, composed mostly of soil, is a
layer that extends down from the ground surface at least to the bottom of major plant
roots, and often, much lower. This layer is where water is held in suspension by capillary
action against the force of gravity. Below the soil water belt is an area called the vadose
zone, which is the lower part of the unsaturated zone. This is the area where water under
hydrostatic pressure that cannot be held in the belt by gravity moves downward into the
saturated zone.
The saturated zone is the region where all the pores are completely filled with water.
The top of the saturated zone is called the water table. Water found in the saturated zone is
called groundwater and is the source of drinking water obtained from wells. Groundwater
is replenished, or recharged, from precipitation that infiltrates down into the saturated zone.
Groundwater is discharged through wells.

AQUIFERS

An aquifer is a water-bearing formation or stratum capable of storing or transmitting water
in sufficient quantities to permit development for a specific purpose. To qualify as an aqui-
fer, the formation must have pores or open spaces large enough for water to move in reason-
able quantities. Where pores are so small that water cannot easily move through them, for
example, in clay, the formation is not considered an aquifer even though it is saturated.

Aquifer Classifications
Aquifers can be classified by the nature of the rock that the water is stored in. Unconsolidated
aquifers consist of a high percentage of permeable granular material. This material is often referred
to as alluvial since it is usually sediment deposited by running water. This type of aquifer produces
the greatest amount of water and is recharged directly from precipitation or streams.
The semiconsolidated aquifer is similar to the unconsolidated type except for weak
bonding materials, usually calcium carbonate and iron oxide, that fill a portion of the pore
spaces. These materials tend to be geologically older than unconsolidated materials and are
usually found at a greater depth.
Consolidated aquifers consist of different types of solid rock that have some porosity,
with the available water depending on the number of fractures present in the layer.
Another possible classification of aquifers is based on the intended use of the water.
These classifications, or similar ones, are determined by local and state agencies. The gen-
eral classifications are

1. Class 1: groundwater of special ecological significance
2. Class 2: groundwater for potable water supply
3. Class 3: groundwater for uses other than potable water

Aquifer Categories

Aquifers are often categorized by the conditions in which water is stored and whether a free
water surface (or water table) exists under atmospheric conditions. Unconfined aquifers
occur in the unconsolidated layer and have water and air filling the pores, and the top of the

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