Photo by Bill Youngblood

It’s considered one of the legacies of the Cold War, a reminder of the arms race that ended with the collapse of the Soviet Union in the early 1990s. As the use of solid rocket motors decreased and the defense budget was reduced, new detection technology became available that showed the presence of a new contaminant—one that would trigger a different type of race to clean up our water supplies.

It was perchlorate—a simple, salt-like chemical made up of chlorine and oxygen. Although found in nature, perchlorate is also manufactured and used as the primary oxidizer in rocket fuel. Airbags, fireworks and some fertilizers also contain a form of the substance, which is produced when sodium perchlorate reacts with ammonium chloride.

Perchlorate was first detected by Metropolitan Water District in the Lower Colorado River in 1997. Today, monitoring shows perchlorate to be a widespread contaminant in California, primarily found in well water in Los Angeles, San Bernardino and Riverside counties. The U.S. Environmental Protection Agency reports the detection in 35 U.S. states of low levels of perchlorate in both drinking water and groundwater.

Because perchlorate at high levels can interfere with thyroid function, it is a health concern, although there is currently no federal drinking water standard for perchlorate. As of press time, Congress was considering measures that would set a deadline for EPA to establish such a standard. In October 2007, the state of California Department of Public Health adopted a drinking water standard of 6 parts per billion after extensive public review (see sidebar for more details). California joined Massachusetts as the only two states in the nation to regulate perchlorate.

The detection of perchlorate levels in Lake Mead triggered the Nevada Division of Environmental Protection to join with the Southern Nevada Water Authority (SNWA), the U.S. Environmental Protection Agency and others to make both short and long-term plans for cleanup once the contamination source was found.

It didn’t take long.

“With new methods to analyze for perchlorate, we were able to chase down the source pretty quickly,” explained Mic Stewart, manager of Metropolitan’s Water Quality section. “We methodically sampled water up the Colorado River and were able to trace the contamination to Lake Mead and the Las Vegas Wash.”

Lake Mead is the primary drinking water source for 1.8 million residents of Las Vegas Valley and the Colorado River is a source of drinking water for nearly 18 million Southern California residents and 4 million residents of Arizona.

Nevada’s state environmental division and SNWA conducted additional sampling in the Las Vegas Wash to identify where perchlorate-impacted groundwater was entering the wash. The area identified with the highest perchlorate concentrations were downhill from the Kerr McGee (name changed to Tronox in November 2005) chemical plant in Henderson, Nev.

A plume of contaminated groundwater flowed north about three miles from Tronox to the Las Vegas Wash. (See area of perchlorate influence.) The plant produced perchlorate from 1945 until 1998 under a series of different owners and operators including the U.S. government, Western Electrochemical Company, American Potash & Chemical Company, and Kerr-McGee. From 1945 through the mid 1970s large amounts of wastewater containing perchlorate were released and allowed to drain into unlined ponds. Other releases occurred within the perchlorate production process area.

Groundwater contaminated with perchlorate was also found at the former site of a facility (now developed commercially) a few miles west of the Tronox site. Here, perchlorate chemicals were produced by the American Pacific Corporation (AMPAC) from 1958 until 1988, before AMPAC moved its perchlorate manufacturing operation to southern Utah. Because this contamination was of a lower concentration and didn’t appear to extend to the Las Vegas Wash, the remediation effort first focused on the Tronox property.

The Nevada Division of Environmental Protection assumed management of the remediation process in 1998.

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