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
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
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
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
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
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;
- 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
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. * ** *