This article, written by the American Ground Water Trust was originally published in THE AMERICAN WELL OWNER, 2000, Number 1

What is Acid Rain?

Most precipitation has a pH level Just below 7 (neutral), making it slightly acidic.  This is natural precipitation acidity resulting from contact of water with carbon dioxide in the air. "Acid Rain" is the term for precipitation with a pH less than 5.6. Our industrial society has significantly increased the amount of acid forming materials in the atmosphere.  In particular, fine sulfur particles from coal-fired power plants, and nitric oxide and nitric dioxide from gasoline engines and power plants are a source for these potentially harmful emissions.  Once in the atmosphere they can oxidize to form sulfuric acid and nitric acid, which becomes incorporated in the atmosphere’s moisture, then eventually returns to Earth’s surface as acid rain or as dry fall-out.


Can Acid Rain Affect Ground Water Quality?

Ground water is replenished almost entirely by rain and snow. Will the ground water become acidic if the precipitation is acidic?  Fortunately, most acid rain is neutralized (buffered) by soil and rocks so ground water is protected from the impact of acid rain.  However, in cases where the soils and rocks are unable to neutralize all of the acidity of the precipitation, the ground water could become more acidic over time.  Where ponds and streams contain decaying vegetation or receive water from wetlands, the water may have a natural acidity related to organic causes.


How Does Buffering Work?

The type of minerals in the rocks and soil help determine how well acidity in precipitation may be neutralized.  Rocks with high amounts of calcium such as limestone and dolomite are very effective in reducing the acidity of water from precipitation that infiltrates underground.  In locations with soils containing calcium, the effects of acid rain may be held in check (buffered) allowing the pH of the ground water to remain near neutral or alkaline (>7 pH) values.  If acid precipitation is not neutralized through rock chemistry, metals such as copper, lead, iron and manganese may dissolve in the ground water.


Is Acidic Water of Concern?

Ground water that is acidic may have corrosive affects on a home’s water system including the pipes and solder in plumbing fixtures.  Reducing acidity (neutralization) can be achieved by water treatment.  The most common method of correcting pH is to run water through a cylinder packed with limestone or marble.  In addition to reducing pH, it may be necessary to use additional conditioning equipment to remove dissolved metals to prevent staining of fixtures or laundry.  The test for pH (water acidity) is easy!  Unfortunately, there is not a one-size-fits-all solution.  What to do about it will probably require the advice of a water treatment professional.


Where was Acid Rain Discovered?

For more information on acid rain, please go to the Hubbard Brook Ecosystem Study (HBES) website at:  The HBES is a long-term ecological research project located at the Hubbard Brook Experimental Forest (HBEF), a 3,160 hectare reserve located in the White Mountain National Forest, near North Woodstock, New Hampshire. The USDA Forest Service established the HBEF in 1955 as a major center for hydrologic research in New England.  It was the site where the term “acid rain” was first used in 1972 to describe the acidification of the earth’s atmosphere from air pollution and the impact of the condition on the environment.


[© American Ground Water Trust.  This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 2000, Number 1]