April
2001
Groundwater
at Risk?
The Satya Interview With
Payal Sampat
|
|
|
Payal Sampat is a Research Associate at the Worldwatch
Institute, a Washington, D.C.-based organization that analyzes global
environmental and resource issues. She has published numerous articles
on issues including fresh water, industrial ecology, information technology
and the environment, and human development. Sampat’s most recent
publication, In Deep Trouble: The Hidden Threat of Groundwater Pollution
(Worldwatch Paper 154), is an in-depth analysis of the state of global
groundwater. Sampat explains to Catherine Clyne the importance
of groundwater and what we can do to solve the problem.
What is groundwater and how does it differ
from other water sources?
Groundwater is freshwater that lies underground in aquifers—geological
formations made of porous materials, such as sand, gravel, or spaces
between subterranean rocks. Although most people think of freshwater
as something that flows in rivers or streams, most of it is far less
visible—some 97 percent of the planet’s liquid freshwater
is stored in underground aquifers.
Roughly, what percentage
of our water supply comes from groundwater?
Groundwater is the primary source of drinking water for roughly
a third of the world’s people. Some of the largest cities in the
developing world—including Jakarta, Dhaka, Lima, and Mexico City—depend
on aquifers for almost all their water. Almost 99 percent of the rural
U.S. population and 80 percent of India’s villages depend on groundwater
for drinking.
Groundwater also irrigates some of the world’s most productive
cropland. Aquifers supply water to more than half of irrigated land
in India, the country with the largest irrigated area globally. The
U.S. uses groundwater for 43 percent of its irrigated cropland.
Are there areas where aquifers
are at risk of being over-depleted?
On almost every continent, many major aquifers are being drained
far more rapidly than they are being replenished by nature. Groundwater
depletion is most severe in parts of India, China, the U.S., North Africa,
and the Middle East, thus shrinking water reserves by an estimated 200
billion cubic meters a year. This is roughly equivalent to the amount
of water used to grow 10 percent of the global grain harvest each year.
You warn that pollution is one of the major
threats to the health of our aquifers. What are the factors that make
groundwater particularly vulnerable to pollution?
Because it is underground and stationary, groundwater stores pollutants
far longer than, say, rivers or air do. It’s true that some aquifers
recycle water back to the environment fairly quickly. But the average
length of time groundwater remains in an aquifer before it recycles
back to the environment is 1,400 years, as opposed to just 16 days for
river water. Some aquifers contain water that fell as rain as much as
30 millennia ago. So instead of being flushed out to the sea, or becoming
diluted with constant additions of freshwater, aquifers continue to
accumulate pollutants, decade after decade.
A second factor that makes groundwater especially vulnerable to pollution
is that persistent substances can last for a very long time underground.
Aquifers usually contain less in the way of minerals, microbes, and
organic matter than soils—thus making it difficult for chemicals
to break down easily. As a result, the herbicide alachlor, for example,
has a half-life of just 20 days in soil, but has one of nearly four
years in groundwater.
What kinds of contaminants are polluting
groundwater?
Among the chemicals now found underground are pesticides and nitrogen
fertilizers from farmland, industrial chemicals and heavy metals from
factories and a toxic brew of chemicals from city sewers and landfills.
The damage is often worst in the very places where people most need
water. For example, in Northern China nitrate concentrates in groundwater
exceeded the health guidelines in more than half of the locations studied.
In the late 1990s, India’s Central Pollution Control Board found
that groundwater was unfit for drinking in all 22 major industrial zones
it surveyed. Petrochemicals from gasoline are turning up in wells in
the U.S. The Environmental Protection Agency (EPA) estimates that about
100,000 gasoline storage tanks are leaking chemicals into groundwater.
What are some solutions that can alleviate
the groundwater crisis?
Because groundwater recharges with geological slowness, once an
aquifer is excessively depleted or contaminated, the damage is essentially
permanent. And efforts to reduce the contamination are extremely costly.
The U.S. will have to spend an estimated one trillion dollars over the
next 30 years trying to clean thousands of sites where groundwater pollution
is most severe.
It is critical that we shift emphasis away from costly end-of-pipe responses
to preventing the damage in the first place. To preserve this valuable
resource for future generations, we need to make systematic changes
in the way we grow our food, manufacture goods, and dispose of waste.
Here are some examples: In China, by planting more diverse varieties
of rice, instead of monocultures, thousands of farmers have completely
eliminated their pesticide use—and at the same time have doubled
their yields. In Germany, water utilities actually pay farmers to switch
to organic operations because they found it was cheaper to do so than
to clean up chemicals from polluted water supplies. And by reusing discarded
materials and used chemicals, some firms in places as diverse as Denmark
and Namibia are finding ways to shrink their waste production—thereby
protecting groundwater from chemicals that leak out of landfills and
septic systems.
What can individuals do to help change things?
Pesticides and fertilizers used in backyards contribute to groundwater
pollution, as do heavy metals that leak out of batteries, and cleaning
chemicals used by households. Individuals can help protect their water
supplies and health by reducing or eliminating the use of these chemicals
from their daily lives. Because hog farms and poultry operations are
also major contributors to the pollution of groundwater, personal choices
such as meat consumption can also make a difference. A meat intensive
diet consumes roughly twice as much water as a vegetarian diet.
You can read Sampat’s report, In Deep Trouble: The Hidden Threat
of Groundwater Pollution, online at www.worldwatch.org
or call (202) 452-1999 for more information.
