Both a naturally occurring and man-made chemical used as a component of rocket fuel and fertilizer, perchlorate was first detected in the Lower Colorado River in 1997. Currently, there is no federal drinking water standard for perchlorate. Due to possible environmental health concerns that perchlorate interferes with thyroid function, the Nevada Division of Environmental Protection (NDEP) along with the Southern Nevada Water Authority (SNWA), US Environmental Protection Agency (EPA), the City of Henderson, and Kerr-McGee, began to investigate the source of the perchlorate.
When the sources of perchlorate had been identified, remediation plans were enacted to remove perchlorate from groundwater and surface water. Perchlorate entering the Las Vegas Wash has been reduced approximately 95% since 1997. As of January 2017, approximately 5,637 tons of perchlorate have been removed from the environment. NDEP continues to monitor perchlorate levels reported in the Lower Colorado River, which is below the safety limit set by EPA in February 2005. The EPA is currently in the process of developing a national drinking water standard for perchlorate.
The sources of the perchlorate were traced upstream to the Las Vegas Wash, which discharges into Lake Mead. Perchlorate was entering the Las Vegas Wash through contaminated groundwater and surface water stemming from a manufacturing facility owned and operated by Kerr-McGee Chemical LLC (currently Tronox LLC).
Perchlorate-contaminated groundwater was also found to originate from the former Pacific Engineering and Production Company of Nevada (PEPCON) site, owned by American Pacific Corporation (AMPAC). The U.S. Navy, Western Electrochemical Company, and American Potash and Chemical Company have owned and operated on the current Tronox facility. Perchlorate was produced at this facility from 1945 until 1998. Perchlorate was manufactured at the AMPAC facility from 1958 until 1988 when an explosion destroyed the PEPCON plant.
As owner of the property where Tronox is located, the Nevada Environmental Response Trust (NERT) currently operates a remediation system that extracts perchlorate-contaminated groundwater for ex-situ treatment using bioremediation to reduce the perchlorate concentration followed by discharge into the Las Vegas Wash. The discharge water from this remediation system has been consistently less than the Nevada Interim Action Level for perchlorate of 18 micrograms per liter or parts per billion (ppb). Additional remediation efforts, including an ion-exchange system, are currently being implemented.
Endeavour, LLC was formed in 2015 to continue operation of the AMPAC Groundwater Treatment System, an ex-situ remediation system where perchlorate-contaminated groundwater is extracted, treated, and discharged to the Las Vegas Wash. This system reduces the perchlorate concentration in the discharged groundwater from 120,000 micrograms per liter or parts per billion (ppb) to non-detectable concentrations of less than 5 ppb.
Sampling of groundwater and surface water is conducted by SNWA, NERT, Endeavour, and the Southern California Metropolitan Water District (MWD). Surface water is sampled in the Las Vegas Wash, Lake Mead, and points on the Colorado River downstream of Lake Mead.
Concentrations in the Las Vegas Wash have decreased by more than 94% since 1997. Sampling data from the Willow Beach, AZ sampling point on the Colorado River, approximately 11 miles downstream from Hoover Dam, shows a reduction from a high of 9.7 ppb in June 1999 to 0.8 ppb in June 2018.
Sampling data from the Northshore Road sampling point in the Las Vegas Wash downstream from Lake Las Vegas shows a reduction from a high of 1,200 ppb in October 1998 to 59 ppb in December 2017. NDEP continues to work with EPA, SNWA, MWD, City of Henderson, NERT, Endeavour, and BMI to develop opportunities to further refine groundwater capture and treatment technologies.
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