[This article, written by the American Ground Water Trust was originally published in THE AMERICAN WELL OWNER, 2003, Number 2]


The word perchlorate is heard frequently in the news. While unlikely to be a problem for the vast majority of well owners, the perchlorate story can serve as a reminder about the importance of understanding the origin and flow pathways of well water. Safe ground water from a well is a great asset for a home. Contamination of any kind is not good for the economy or the environment. If we knew back in the 40’s and 50’s what we know now about contamination and health risks, would we have put more control on our manufacturing industries?

What is it?

Perchlorate (ClO4–), is a manufactured chemical used as the main ingredient of rocket fuel, safety flares, matches and fireworks. It is also used in some batteries, and vehicle air bags. Chemically, perchlorate is an anion that originates from the dissolution of ammonium, potassium, magnesium, or sodium salts. It is very mobile in ground water and surface water systems and can persist for many decades. Perchlorate travels with water and unlike some contaminants, doesn't stick to surfaces within the soil or aquifers. Perchlorate contamination of ground water only became widely known in the late 1990’s when new laboratory techniques lowered the detection limit in water from 400 to 4 micrograms/L.

What are the health effects?

The principal health concern is that if perchlorate gets into drinking water it could damage the thyroid gland, which controls growth, development and metabolism. Perchlorate interferes with iodide uptake into the thyroid gland, and because iodide is an essential component of thyroid hormones, it disrupts how the thyroid functions. Impairment of a woman’s thyroid function during pregnancy may impact the baby and result in delayed development and decreased learning capability. Changes in thyroid hormone levels may also result in thyroid gland tumors. Determining the threshold levels of ingested perchlorate needed to inhibit the uptake of iodide, is the subject of ongoing medical research.

Where is it?

Forty-two states have known manufacturers or users of perchlorate. Perchlorate is known to have contaminated drinking water wells in 22 states. The principal problems exist around military bases, or former bases, where rocket fuel was stored or used. In 2000 the California Department of Health Services reported perchlorate in 44 public drinking water systems, 23 of them at levels greater than 18 micrograms/L. The San Martin area of Santa Clara County, California has a 7-mile- long plume of perchlorate-contaminated water that has affected over 200 private wells. This particular contamination is believed to be related to the manufacture of road flares.

A study by the Environmental Working Group revealed high levels of perchlorate in some winter lettuce irrigated by Colorado River water, with some lettuces containing more than 30 micrograms/L of perchlorate. The source of perchlorate was found to be Lake Mead, which was being polluted by flows from an industrial complex near Las Vegas, Nevada, that manufactured perchlorate as a rocket fuel ingredient.

(See for more information)

How is perchlorate removed from water?

Several types of point-of-use or point-of-entry treatment systems for homes, including exchange resins, reverse osmosis and distillation, can reduce perchlorate concentrations in well water. Some ion exchange resins remove all other anions before binding perchlorate, resulting in corrosive water that may need to have some hardness restored. Because perchlorate binds tightly to resins, high salt concentrations may be necessary for resin regeneration. Brine disposal could then be a problem because the perchlorate is concentrated and not destroyed.

For contaminated site clean up, many different technologies are under development, including biological treatment and large-scale ion (anion) exchange systems. Biological processes (bioremediation) may be the most cost efficient, and research continues with bioreactor treatment systems and with below ground in-situ treatment involving trenches filled with bio-barriers of organic material.

What Is Being Done about Perchlorate?

The United States EPA has set a preliminary safety level of 1 microgram/L for perchlorate and is continuing to assess health risks to assist with future rulemaking. Federal drinking water regulations for perchloratecould take several years to develop. The EPA is developing a national database by monitoring perchlorate in utility source water. California is currently working on a state standard of 2 to 6 micrograms/L for water utility supply. Other states are beginning to address the perchlorate issue and are setting their own standards. Assessing the problem, and finding site-by-site solutions, is likely to be an issue for many years to come.

For more information about perchlorate, visit the EPA website: (search for contaminant, then perchlorate).

[© 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, 2003, Number 2]