As a result of the 1986 Consent Order, initial remediation of hexavalent chromium in groundwater beneath the Nevada Environmental Response Trust (NERT) Site began in mid-1987 when extraction wells were installed in the north-central portion of the Site. The extracted water was pumped to a chromium treatment facility (referred to as the Groundwater Treatment Plant [GWTP]) where hexavalent chromium was reduced to trivalent chromium that was then precipitated and removed. This on-site extraction well network, called the Interceptor Well Field (IWF), has been expanded several times and hexavalent chromium treatment is on-going. Until the discovery of perchlorate contamination at the NERT Site in the late 1990s, water treated for hexavalent chromium was subsequently reinjected into the ground via recharge trenches located to the immediate north of the on-site extraction wells. Following the discovery of perchlorate contamination, groundwater was no longer reinjected into the ground via the recharge trenches and was retained onsite in a large pond while construction of an additional treatment plant and pipeline to discharge fully treated groundwater to the Las Vegas Wash was completed. The injection trenches were partially removed in September 2010 as part of the soil removal activities.
In response to the discovery of perchlorate in the vicinity of the Las Vegas Wash, and as part of the 1999 Consent Agreement between Kerr-McGee and the Nevada Division of Environmental Protection (NDEP), a seep water collection system was installed adjacent to the Las Vegas Wash in the late 1990s to mitigate the discharge of perchlorate. By November 1999, Kerr-McGee began operating a temporary ion exchange (IX) treatment system to treat perchlorate-impacted groundwater. The temporary IX system near the Las Vegas Wash operated from late 1999 until 2004.
The 1999 Consent Agreement that defined additional response requirements also specified that Kerr-McGee should prepare a work plan outlining a proposed long-term remedy to treat perchlorate contamination in groundwater. After considerable research and process development, a replacement treatment technology was developed. In 2001, Kerr-McGee and NDEP entered into the Administrative Order on Consent that defined the replacement treatment process. The agreement required Kerr-McGee to install additional extraction well systems, called the Athens Road Well Field (AWF) and the Seep Well Field (SWF), and construct an on-site groundwater treatment facility, known as the groundwater extraction and treatment system (GWETS).
An initial on-site IX treatment system operated between 2002 and 2004, adding treatment capacity to the temporary IX system already operating at the Las Vegas Wash. In 2004, the on-site IX treatment system was replaced by the current GWETS, which operates using granular activated carbon and biological fluidized bed reactors (FBRs). A new IX system was added near the Las Vegas Wash in 2017, which treats a portion of the groundwater extracted from the SWF. As a result of this IX system’s installation, the FBRs have had the capacity to treat additional perchlorate from on-site sources and better manage extracted groundwater. Following treatment, extracted water is discharged to the Las Vegas Wash under a National Pollutant Discharge Elimination System (NPDES) permit. Treated effluent discharged from the GWETS typically does not contain detectable concentrations of perchlorate or hexavalent chromium, and NERT has met all numeric discharge limits in its current NPDES permit.
The current GWETS utilizes several groundwater extraction well fields (the IWF, AWF, and SWF, as well as additional on-site extraction wells located several hundred feet south of the IWF). The location of these well fields and other features of the GWETS are shown on the figure below. As shown on the figure, groundwater generally flows to the north towards Las Vegas Wash, which is approximately 3 miles north of the IWF located on the NERT Site. Groundwater is found approximately 30 feet below the ground surface near the IWF and is found within approximately five feet of the ground surface near the Las Vegas Wash. Before the extraction wells were operating, it would have taken approximately 3 to 7 years for shallow groundwater to travel from the IWF to Las Vegas Wash.
The figure above shows the locations of the groundwater extraction well fields, which are part of NERT’s groundwater extraction and treatment system (GWETS).
The IWF, located within the NERT Site, is coupled with an on-site barrier wall that slows the physical movement of groundwater, provides capture of the highest concentrations of perchlorate and hexavalent chromium, and significantly reduces the amount of perchlorate and hexavalent chromium in downgradient groundwater. The AWF, located approximately 8,200 feet north of the IWF, captures moderate concentrations of perchlorate (in comparison to groundwater extracted by the IWF), but operates at higher extraction rates than the IWF, resulting in significant contributions to overall perchlorate mass removal from the environment and mitigation of perchlorate migration further downgradient in groundwater. The SWF, located in close proximity to the Las Vegas Wash, approximately 1.2 miles north of the AWF, operates at the highest extraction rate of the three well fields but extracts groundwater containing significantly lower perchlorate concentrations.
As directed by NDEP, a Treatment System Extension (TSE) was constructed in 2022 through early 2023 to remove perchlorate and chromium from groundwater that migrates from the NERT Site and is captured by TIMET’s GWETS. The TIMET property is located immediately adjacent to the NERT property and is currently used for manufacturing by TIMET. In addition, and similar to the NERT site, the TIMET site has its own environmental issues, and the resolution of those issues is regulated by NDEP. As part of this process, NDEP required TIMET to operate its own GWETS to capture and destroy contamination associated with the TIMET site. Since some of NERT’s contamination impacts groundwater under TIMET’s property, the groundwater that TIMET extracts is first treated by TIMET for its contamination, then it is treated by NERT for its contamination. The treated groundwater is returned to TIMET for discharge into TIMET’s recharge trenches, which are regulated by TIMET’s underground injection control (UIC) permit.
Groundwater monitoring and GWETS performance reports covering performance data for both the hexavalent chromium and perchlorate remediation programs are submitted to NDEP two times per year. Recent groundwater monitoring results indicate significant capture of contaminants and ongoing reduction of the perchlorate and hexavalent chromium plumes. Since 2000, perchlorate concentrations in the Las Vegas Wash have declined by more than 90% due in large part to operation of the GWETS. The most recent groundwater monitoring and GWETS performance report can be viewed here. The groundwater treatment system completely captures all contamination currently migrating from the Site toward the Las Vegas Wash. However, groundwater contamination present to the east and northeast of the NERT Site continues to flow towards the Las Vegas Wash and will be addressed in the future as part of the final remedy.
Last updated: February 2024
