Perchlorate in the Pacific Southwest
Nevada and Colorado River
In 1997, the EPA first discovered perchlorate contamination in Nevada's water, hundreds of miles downstream from the Las Vegas area. At that time, as much as 1,000 pounds per day of perchlorate was entering Lake Mead and the Colorado River through contaminated groundwater. Lake Mead provides drinking water to residents of Southern Nevada. The contamination originated from two perchlorate-manufacturing facilities that had operated in the area up until the late 1990s. Cleanup activities are ongoing, and have reduced the perchlorate amount from 1,000 pounds per day to about 100. Cleanup activities are also underway at the only other known perchlorate site in Nevada, the former Rocketdyne Nevada Test Facility in Northern Nevada.
State Advisory Level
In August 1997, the Nevada Division of Environmental Protection selected 18 parts per billion (ppb) as the recommended action level for cleanup pending a more current risk assessment.
This thumbnail clicks to a map showing the locations of all perchlorate detections in Region 9 reported to EPA as of September, 2004 .
Kerr McGee Chemical Company, Henderson / Colorado River
The highest levels of perchlorate contamination in EPA's Pacific Southwest region have been found in Henderson at the Kerr McGee Chemical Company (KMCC) in Henderson, Nevada, where prior owners/operators made perchlorate beginning in the early 1950s. Kerr McGee acquired the property in 1967 and continued perchlorate production until 1998. The contamination seeps from ground water into the Las Vegas Wash, Lake Mead and ultimately the Colorado River, affecting the drinking water supply of 15 to 20 million people in communities and tribal nations in Arizona, southern California and southern Nevada.
Since the discovery of the extent of the contamination in 1997 when a more sensitive test method was developed, EPA and the Nevada Division of Environmental Protection have been working with KMCC to ensure that perchlorate releases to Las Vegas Wash and Lake Mead are reduced as effectively and as quickly as possible.
KMCC is extracting ground water at three locations and treating it to remove more than one ton of perchlorate per day before it reaches Las Vegas Wash. The captured ground water and surface water is treated in fluidized bed reactors (biologically-based wastewater treatment systems) to remove more than 99.99% of the perchlorate.
- Annual average concentrations at the Las Vegas drinking water intake in Lake Mead declined almost 60% between 2000 and 2004 (from 13.1 ppb to 5.6 ppb); the 2005 annual average is expected to decline to less than 5 ppb.
- Annual average concentrations in the Metropolitan Water District Colorado River Aqueduct intake at Lake Havasu on the Lower Colorado River also declined about 50% between 2000 and 2004 (from 6.4 ppb to less than 4 ppb); in 2004 nine of the twelve monthly samples were at levels too low to detect (i.e., below 4 ppb.)
Actions taken to address perchlorate contamination
As a result of these control efforts, perchlorate concentrations in Lake Mead and the lower Colorado River have begun to decline and are expected to decline further in 2005 and 2006.