In accordance with the Interim Consent Agreement between the Nevada Environmental Response Trust (NERT) and Nevada Division of Environmental Protection (NDEP) (effective February 14, 2011), NERT initiated a comprehensive environmental study, called a Remedial Investigation (RI), in 2014. Investigation activities have taken place within the NERT RI Study Area, which includes the NERT Site and areas to the north, east and northeast of the NERT Site. The primary objective of the RI is to characterize the nature and extent of environmental impacts within the NERT RI Study Area and support the Risk Assessments and Feasibility Study (FS).
The NERT RI Study Area has been divided into three areas, termed “operable units” or “OUs”, as shown in the figure below. Each of the three OUs has its own cleanup goal approved by NDEP, called a Remedial Action Objective (RAO), which are described below, with the overall goal of mitigating the migration of contaminated groundwater to the Las Vegas Wash.
Remedial Action Objectives (RAOs):
· OU-1: Plume Containment and Source Control
· OU-2: Mid-Plume Containment and Mass Removal
· OU-3: Mitigate Discharge into the Las Vegas Wash
Å plume is the area of groundwater that has been affected by the presence of contaminants. In this case, the plume mentioned in the RAOs is the contamination specifically related to former Kerr-McGee/Tronox operations on the NERT Site.
In order to meet these cleanup goals, the contamination in all three OUs first needs to be defined through an investigation, the RI, and then engineering evaluations of cleanup options need to be completed through the FS. Final remedy can only be determined after all investigations and engineering evaluations are completed.
The figure above shows the three operable units (OUs) comprising the NERT RI Study Area.
The RI has been conducted in three phases (now referred to as the Phase 1 RI, Phase 2 RI, and Phase 3 RI), each of which built upon the previous phase or expanded the investigation area and are further described below. Please note that the Phase 1, Phase 2, and Phase 3 RI areas do not match the OU-1, OU-2, and OU-3 designations (for example, the Phase 2 RI took place within all three OUs).
The Trust has been installing groundwater monitoring wells and soil gas probes, and collecting samples of soil, soil gas, groundwater, and surface water as part of the RI since 2014. Through this nine-year program, more than 64,000 analyses were performed on approximately 11,500 samples. These analyses have produced over 480,000 analytical results, ensuring NERT has a comprehensive understanding of the nature and extent of environmental impacts within the Study Area. A report detailing the findings of the investigations within OU-1 and OU-2 was submitted to NDEP in July 2021. The Trust received NDEP comments on the RI report for OU-1 and OU-2 on February 9, 2022, which the Trust responded to on June 9, 2022. NDEP provided additional comments on August 31, 2022. The Trust provided a response to comments and a revised report (Revision 1) to NDEP on August 15, 2023. NDEP provided comments to the revised report on December 21, 2023 and January 11, 2024. The Trust responded to the two NDEP comments and submitted the RI Report for OU-1 and OU-2, Revision 2 on February 13, 2024 (NDEP approved on February 26, 2024). The main findings of the RI Report for OU-1 and OU-2 include the following:
· The location and vertical extent of soil and groundwater contamination from historic operations at the NERT Site have been identified in both OU-1 and OU-2.
· The investigation has determined the direction and rate of groundwater flow within OU-1 and OU-2.
· Releases to groundwater originating from the NERT Site in OU-1 are completely captured by the existing treatment system and do not reach the Las Vegas Wash. However, groundwater contamination already present in the eastern portions of OU-2 and OU-3 due to historical contaminant migration via ditches and the historical pond system continue to flow towards the Las Vegas Wash and will be addressed in the future as part of the final remedy.
· Contaminants migrating into OU-1 and OU-2 from other sites for which NERT is not responsible have also been defined.
NERT’s planned investigation of contamination in OU-3 is complete. Preparation of the RI Report for OU-3 is currently underway with an anticipated submittal in 2024.
The Phase 1, Phase 2, and Phase 3 RIs were conducted in portions of the NERT RI Study Area that were defined before the OUs were established. The NERT RI Study Area collectively consists of four study areas. These are the NERT Site Study Area and the NERT Off-Site Study Area (established in 2012 as the original NERT RI Study Area), the Downgradient Study Area (added in 2015), and the Eastside Study Area (added in 2016 and comprising the Eastside Sub-Area and the Northeast Sub-Area). The following sections summarize the phased RI activities that occurred in each of these four study areas, which are shown in the figure below.
The figure above shows NERT’s three operable units (OUs), as well as the individual study areas and sub-areas that make up the NERT RI Study Area.
Phase 1 RI
The Phase 1 investigation represented NERT’s first data collection efforts as part of the RI and was conducted between October 2014 and May 2015. Phase 1 RI activities included the collection of soil, soil gas, and groundwater samples in the NERT Site Study Area (OU-1) and the NERT Off-Site Study Area (in both OU-2 and OU-3).
The details of the Phase 1 investigation are described within the original Remedial Investigation and Feasibility Study Work Plan dated June 19, 2014. Initial results of the Phase 1 investigation were reported in May 2016 within an RI Data Evaluation Technical Memorandum which also identified data gaps within the NERT Site Study Area (OU-1) and NERT Off-Site Study Area (in both the western portions of OU-2 and OU-3).
Phase 2 RI
In addition to presenting information from the Phase 1 investigation, the RI Data Evaluation Technical Memorandum from May 2016 also described field work to be conducted as part of the Phase 2 investigation to resolve newly identified soil and groundwater data gaps. These data gaps were investigated as part of the Phase 2 RI field investigation between February 2017 and April 2019. As additional data gaps were identified during the Phase 2 investigation process, the original Phase 2 RI scope of work described within the RI Data Evaluation Technical Memorandum was modified through 15 Phase 2 RI modifications. The field investigations associated with the 15 Phase 2 RI modifications were implemented between 2017 and April 2019. The Phase 2 investigation plus the 15 Phase 2 RI modifications included the collection of soil, soil gas, groundwater, and surface water samples within the NERT Site Study Area (in OU-1) and the NERT Off-Site Study Area (in both OU-2 and OU-3), as well as sampling within the Las Vegas Wash (in OU-3).
Unit Buildings 4 and 5 Investigation
Prior to completion of the NERT RI, historical research identified Unit Buildings 4 and 5 within the NERT Site as historical on-site perchlorate production areas. Previous soil and shallow groundwater sampling efforts had also suggested it was a potential perchlorate and hexavalent chromium source area. Accordingly, an investigation of this area was performed as part of the NERT RI in accordance with the Unit 4 and 5 Buildings Investigation Work Plan. The objective of this investigation was to determine the nature of contamination in this area and the vertical extent of impacted soil and groundwater underneath Unit Buildings 4 and 5. Investigation of Unit Buildings 4 and 5 was conducted between October 2015 and December 2017. The results of this investigation confirmed that the area is a source of contamination to groundwater within the NERT Site. A summary of the investigation is provided in the Unit Buildings 4 and 5 Source Area Characterization Report dated January 7, 2020 (NDEP Approved on January 13, 2020) and in the RI Report for OU-1 and OU-2.
Downgradient Study Area Investigation
The Downgradient Study Area, which was designated by NDEP in 2015, is located entirely within OU-3 (shown in pink on the map above). This NDEP-led portion of the investigation began in early 2016 and was completed in 2019. While the investigative activities in this area conducted by NERT will be fully evaluated within the forthcoming RI Report for OU-3, the following reports summarize initial results:
· Surface water sampling at locations within the Las Vegas Wash was performed in 2016. The results of this sampling program are provided in the Surface Water and Seep Grab Sampling Technical Memorandum dated November 2016.
· In mid-2016, groundwater sampling and gauging were conducted in the Downgradient Study Area. The results of this groundwater monitoring work are reported in the Groundwater Sampling Technical Memorandum dated July 2017.
· Between October and November 2016, a geophysical pilot test was conducted to determine the effectiveness of geophysical methods in identifying the top of the geologic formation called the Upper Muddy Creek formation (UMCf) and potential subsurface pathways (i.e., paleochannels) within a portion of the Downgradient Study Area. The results of this study are provided in the Geophysical Pilot Test Technical Memorandum dated October 2017.
· In late 2016 and early 2017, additional surface water sampling was performed in cooperation with the United States Geological Survey (USGS). This sampling effort was designed to identify areas within the Las Vegas Wash where groundwater is discharged to the wash, or where surface water seeps into the ground and mixes with groundwater. The results of this sampling are provided in the Surface Water Investigation Technical Memorandum dated October 2017.
· In early 2018, a supplemental surface water investigation was performed, which included a two-phase temperature survey to identify potential locations where groundwater discharges into the Las Vegas Wash by measuring temperature differences, maintenance of the water level gages installed in 2017, and surface water sampling along various reaches of the Las Vegas Wash within the Downgradient Study Area. The results of this investigation are provided in the Supplemental Surface Water Investigation Technical Memorandum dated April 2019.
· In mid-2018, nine new groundwater wells were installed and sampled along with 17 existing wells within the Downgradient Study Area as part of the Phase I Groundwater Quality Assessment. Transducers were also installed in the nine newly installed wells. The sampling was designed to address specific data gaps identified following previous groundwater sampling efforts in 2016 and assist in the overall goal of identifying subsurface pathways through which perchlorate-impacted groundwater is entering the LVW. The results of this investigation are presented in the Phase I Groundwater Quality Assessment dated February 2019.
· In early 2019, additional field work was conducted to address specific data gaps identified by the Phase I groundwater sampling conducted in mid-2018, the Las Vegas Wash surface water data collected early 2018, and the data gathered as part of the Las Vegas Wash Bioremediation Pilot Study. Phase II of the investigation included the installation of 14 groundwater wells, 11 observation wells, slug testing, tracer testing, dilution testing, the collection of groundwater data from 40 wells, and installation and monitoring of transducers in the 14 new groundwater wells. The results of this investigation are presented in the Phase II Groundwater Quality Assessment dated November 2019.
Phase 3 RI
In July 2016, NDEP directed NERT to expand its RI Study Area to include the Eastside Study Area (the area shown in purple and tan on the map above). The Eastside Sub-Area (shown in purple) is located east of Pabco Road within OU-2 and the Northeast Sub-Area (shown in tan) is located within OU-3. Perchlorate and other contaminants found in groundwater within the Eastside Study Area migrated from the NERT Site and surrounding industrial facilities within the BMI Complex through a series of unlined ditches used for process wastewaters to a series of unlined ponds located near and within the Eastside Study Area. In the Eastside Sub-Area, NERT is only responsible for evaluating the nature and extent of perchlorate and chlorate.
A Work Plan for investigation of the Eastside Study Area as part of the Phase 3 RI was approved by NDEP in late 2017 and the original work plan was implemented between December 2017 and November 2018. Modifications to the original work plan were made under 15 Phase 3 RI modifications to address additional data gaps. Sampling activities for the modifications conducted within OU-1 and OU-2 were completed between June 2018 and January 2020. Implementation of some of the Phase 3 RI modifications solely within OU-3 continued through October 2022 and will be discussed in the forthcoming RI Report for OU-3.
The original Phase 3 RI investigation included the collection of groundwater and soil samples within the Eastside Study Area (comprised of the Eastside Sub-Area [within OU-2] and the Northeast Sub-Area [within OU-3]). The subsequent Phase 3 RI modifications have included the collection of soil, soil gas, groundwater, and surface water samples throughout the entire NERT RI Study Area.
Last updated: February 2024
