Where Groundwater Comes From
Groundwater begins with rain and snow melt that seeps or infiltrates into the ground. The amount of water that seeps into the ground varies widely from place to place according to the type of land surface that is present. Water more readily seeps through porous material such as sand or gravel than less porous material such as clay. The remainder of the rain and snow melt runs off the land surface into streams or returns to the atmosphere by evaporation.

The Saturated Zone
Rain and snow melt that seeps into the ground continues downward under the force of gravity until it reaches a depth where water fills all of the openings (pores) in the soil or rock. This is called the saturated zone. The saturated zone typically includes numerous water-filled crevices in the upper layer of bedrock.

The Water Table
The top of the saturated zone is called the water table. The water table rises and falls according to the season of the year and the amount of rain and snow melt that occurs. It is typically higher in early spring and lower in late summer.

The Unsaturated Zone
A zone is usually present between the water table and the land surface where the openings, or pores, in the soil are only partially filled with water. This is the unsaturated zone. Water seeps downward through it to the water table below. Plant roots can capture the moisture passing through this zone, but it cannot provide water for wells.

Recharge
Water seeping into an aquifer is known as recharge. This takes place intermittently during and immediately following periods of rain and snow-melt. Recharge occurs where permeable soil or rock allows water to readily seep into the ground. These areas are known as recharge areas.

Aquifers
A water-bearing soil or rock formation that is capable of yielding usable amounts of water is called an aquifer.

Confined or Artesian Aquifer
Groundwater that becomes trapped under impermeable soil or rock may be under pressure. This is called a confined or artesian aquifer. A well that pierces a confined aquifer is known as an artesian well.

Unconfined or Water Table Aquifer
Aquifers that are not confined under pressure are called unconfined or water table aquifers. The water level in a well is the same as the water table outside the well.

Groundwater Discharge Points
Groundwater enters the ground in recharge areas and leaves the ground at discharge points. Discharge is continuous, as long as sufficient water is present above the discharge point. Discharge points typically occur as seepage into wetlands, lakes and streams.

Groundwater Flow Rates
Groundwater moves very slowly from recharge areas to discharge points. It may take years, decades or even centuries for groundwater to move long distances through some aquifers. However, ground-water may take only a few days or weeks to move for a short distance through loose soil.

Gaining Streams
Streams that receive groundwater discharges are gaining streams. The level of water in the stream is the water table level for the adjacent aquifer. This is also true for lakes and wetlands that receive groundwater discharges.

Wells: Cone of Depression
Pumping from wells lowers the water table near a well. This known as the cone of depression. Groundwater flow is diverted towards the well as it flows into the depression cone.

Wells: Induced Recharge
The cone of depression from a pumping well may extend to a nearby stream or lake. This lowers the adjacent water table below the steam or lake level. As a result, the stream or lake begins to lose water to the adjacent groundwater aquifer in the vicinity of the well. This is known as induced recharge. Streams and wetlands have been completely dried up by induced recharge from well pumping.

Evidence and Prevention of Groundwater Pollution
This sequence of explanations is reproduced from "Groundwater Contamination," a bulletin prepared by Dr. Lyle S. Raymond, Jr., and published by New York State Water Resources Institute, Cornell University. This tutorial will help explain the nature of groundwater pollution, including the indicators of contamination, potential sources of contamination, and methods of preventing groundwater pollution.

	Evidence of Contamination	Methods of Preventing Groundwater Pollution
SEPTIC SYSTEMS	Waste water shows above ground. Detection of excessive bacteria and chemicals in well water tests.	Proper installation. Inspection and cleaning every 2 to 3 years; annually, if garbage disposal used. Do not dispose of household chemicals into the system.
HOUSEHOLD CHEMICALS	Detection of chemicals in well water tests.	Proper use. Proper storage. Proper disposal. Use of less hazardous products.
DEICING SALTS	Salty taste in well water. High chloride level in well water tests.	Proper protection of salt storage. Minimize use of salt. Use alternative deicing materials.
GARDEN FERTILIZERS AND PESTICIDES	Detection of pesticides in well water tests. Ill effects on animals drinking from nearby wells, springs or surface water. Ill effects on plants watered with nearby well water. Ill effects on aquatic life.	Follow label instructions. Reduce use in recharge areas for water wells.
WELLS (Wells are potential pathways for contaminants to enter groundwater)	Detection of high bacteria levels in well water tests. Well water turbidity. Detection of other contaminants in well water tests.	Watertight well cover. Tight well casing. Tight plumbing connections. Identify and seal abandoned wells.
NATURAL SUBSTANCES	Bad taste or odor in well water. Stains on water fixtures. Detection of unacceptable levels of substances in well water tests.	Avoid areas where natural groundwater problems exist, if feasible. Use water treatment devices. Change to public water supply, if feasible.

Last Updated: September 2006