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Northeast Groundwater

OUT OF SIGHT, OUT OF MIND:

Ground Water in the Northeast

 

Why Worry About Ground Water

Ground water is water which is found in the spaces between particles of soil and rocks and within cracks in bedrock. Some amount of ground water can be found under most of the land in the northeast. Because of its availability and generally good quality, it is widely used for household and other water supplies.

Ground water is often taken for granted, but it is now evident that ground water is seriously vulnerable to pollution and depletion. In the northeast, pollution poses the greater threat. Recently, contaminants which threaten people's health have been found in many of the region's important ground water reservoirs, and some contaminants may be so expensive to remove that they make the water virtually unusable for years. Because of this threat, it is important to understand the processes which make ground water available for use and to understand how human activities sometimes threaten this resource.

Ground Water in the Water Cycle

Ground water is an integral part of the water cycle. The cycle starts with precipitation falling on the surface of the earth. Runoff from precipitation goes directly into lakes and streams. Some of the water which seeps into the ground is used by plants. Recharge water drains down through the soil to the saturated zone, where it fills all the spaces between particles of soil and rocks.

The top of the saturated zone is the water table and is usually the level at which water stands in a well, unless the local geology is complicated. Water continues to move within the saturated zone under the influence of gravity from areas where the water table is high towards areas where the water table is lower. Where ground water comes to a lake, stream, or ocean, it discharges from the ground and becomes surface water, which then evaporates and becomes precipitation, completing the cycle.

The Occurrence of Ground Water

Water can be found under the ground almost everywhere, and about 97 percent of the world's fresh water is ground water. The quality and amount of ground water which is available varies from place to place. Major reservoirs of ground water are referred to as aquifers.

Aquifers can occur in two types of geologic formations. Consolidated formations are those composed of solid rock with ground water found in the cracks. The amount of ground water in a consolidated formation depends on how many cracks there are and the size of the cracks. Consolidated limestone formations, for example, often contain large caverns with much water in them.

Unconsolidated formations consist of loose particles of material such as sand, gravel and clay; ground water occurs in the pore spaces between the loose particles. Aquifers which occur in sand and gravel formations often contain large amounts of water. The most productive aquifers in the northeast are generally sand and gravel aquifers.

Ground water may come to the surface naturally at a spring or it can be drawn to the surface from a well. A spring occurs where the water table meets the land surface.

Ground Water and Surface Water

Most people are more familiar with surface water than they are with ground water. Surface water bodies such as lakes, streams and oceans can be seen all around us but ground water bodies cannot be seen. There are some important differences between ground water and surface water bodies which are worth noting.

Ground water usually moves much more slowly than surface water. Water in a stream may move several feet per minute, but water in an aquifer may only move several feet per month. This is because ground water must overcome more friction to move through small spaces between rocks and soil underground. There are exceptions to this general rule. For example, in limestone caverns underground streams may move relatively rapidly.

The exchange of water between surface water bodies and aquifers is important. Rivers usually start as small streams and get bigger as they flow downstream. The water they gain that causes them to get bigger is often ground water. It is also possible for streams to lose water to the ground at some points. In these cases, aquifers are replenished by water from the loss in streams. A stream which flows through an aquifer will lose water to the aquifer if the water level in the stream is higher than the water table in the aquifer.

Pollution and Depletion Threaten Ground Water

Ground water becomes polluted when polluting substances become dissolved in water at the land surface and are carried down (leached) to the aquifer with the water. The properties of the chemical itself, the properties of the soil above the aquifer, and the amount of the substance which is available are among the factors which determine whether a particular substance will pollute a particular aquifer.

Sometimes ground-water contamination occurs naturally but serious contamination is usually the result of human activities at the land surface. The plentiful water supply that an aquifer provides often attracts a multitude of people to the land overlying the aquifer who then use the water for drinking and residential uses, industrial processes, and agriculture. Many of these activities involve the use and disposal of chemictype of contaminants involved and the overall amounts of the contaminants released. The severity of a particular contamination occurrence is also related to the ability of the soil and ground-water system to destroy or dilute the contaminants, and the degree to which the contamination will interfere with the existing uses of the water. Contamination is usually more serious in a drinking water supply than in water for other uses.

Except where contaminated water is injected directly into an aquifer, essentially all ground-water pollutants enter with recharge water from the land surface. A few different kinds of recharge contaminants include:

  • synthetic organic chemicals, such as pesticides and petroleum products;
  • certain heavy metals, such as chrominum and lead;
  • nitrate;
  • bacteria and viruses; and
  • road salts.

These are considered harmful if ingested with drinking water, and they may be carried into surface water bodies by ground water.

Each category of human activity on the land has a particular ground-water impact. Some agricultural activities add nitrate and pesticides to ground water. Residential areas with septic systems usually add nitrate, bacteria, viruses, and synthetic organics used in household products and septic tank cleaners. Industrial activities tend to add organic chemicals and metals, though in widely varying amounts. Gasoline storage areas (including service stations) tend to have leaks and spills of petroleum products. Roads contribute petroleum leaked from vehicles, salt used to melt winter ice, and metals in exhaust and from vehicle parts. The most concentrated impact comes from older sanitary landfills, whose leachate may contain many different chemicals at relatively high concentrations.

Ground Water Protection

Protecting our ground water from contamination will require thoughtful management and cooperation on the part of citizens and various levels of government. Land use planning is, in many cases, the best instrument available for protecting aquifers which still contain good quality water. If potential sources of contamination are kept from locating over critical recharge areas, the risk of contamination can be greatly reduced.

Careful use and proper disposal of the chemicals which can cause contamination is also necessary. Industries, farmers and homeowners located over ground water supplies need to practice good housekeeping with respect to the use and disposal of chemicals. Regulations which govern the use and disposal of hazardous wastes need to be enforced. An equally important step is to make people aware of their potential impact on ground water. In many parts of the northeast, action is needed now to protect our valuable ground-water resources.

This document was prepared by the staff of the Water Resources Program, Keith S. Porter, Coordinator. Further information may be obtained from the Center for Environmental Research, 468 Hollister Hall, Cornell University, Ithaca, NY, 14853. (607) 256-7535. * ** *