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Title: Model Evaluation Report for Corrective Action Unit 98: Frenchman Flat, Nevada National Security Site, Nye County, Nevada, Revision 1

Abstract

Model evaluation focused solely on the PIN STRIPE and MILK SHAKE underground nuclear tests’ contaminant boundaries (CBs) because they had the largest extent, uncertainty, and potential consequences. The CAMBRIC radionuclide migration experiment also had a relatively large CB, but because it was constrained by transport data (notably Well UE-5n), there was little uncertainty, and radioactive decay reduced concentrations before much migration could occur. Each evaluation target and the associated data-collection activity were assessed in turn to determine whether the new data support, or demonstrate conservatism of, the CB forecasts. The modeling team—in this case, the same team that developed the Frenchman Flat geologic, source term, and groundwater flow and transport models—analyzed the new data and presented the results to a PER committee. Existing site understanding and its representation in numerical groundwater flow and transport models was evaluated in light of the new data and the ability to proceed to the CR stage of long-term monitoring and institutional control.

Authors:
;
Publication Date:
Research Org.:
Navarro-Intera, LLC (N-I), Las Vegas, NV (United States)
Sponsoring Org.:
USDOE Office of Environmental Management (EM), Office of Groundwater and Soil Remediation (EM-32)
OSTI Identifier:
1158867
Report Number(s):
N-I/28091-088
DOE Contract Number:
DEAC5209NA28091
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Frenchman Flat; CAU 98

Citation Formats

Ruskauff, Greg, and Marutzky, Sam. Model Evaluation Report for Corrective Action Unit 98: Frenchman Flat, Nevada National Security Site, Nye County, Nevada, Revision 1. United States: N. p., 2014. Web. doi:10.2172/1158867.
Ruskauff, Greg, & Marutzky, Sam. Model Evaluation Report for Corrective Action Unit 98: Frenchman Flat, Nevada National Security Site, Nye County, Nevada, Revision 1. United States. doi:10.2172/1158867.
Ruskauff, Greg, and Marutzky, Sam. Mon . "Model Evaluation Report for Corrective Action Unit 98: Frenchman Flat, Nevada National Security Site, Nye County, Nevada, Revision 1". United States. doi:10.2172/1158867. https://www.osti.gov/servlets/purl/1158867.
@article{osti_1158867,
title = {Model Evaluation Report for Corrective Action Unit 98: Frenchman Flat, Nevada National Security Site, Nye County, Nevada, Revision 1},
author = {Ruskauff, Greg and Marutzky, Sam},
abstractNote = {Model evaluation focused solely on the PIN STRIPE and MILK SHAKE underground nuclear tests’ contaminant boundaries (CBs) because they had the largest extent, uncertainty, and potential consequences. The CAMBRIC radionuclide migration experiment also had a relatively large CB, but because it was constrained by transport data (notably Well UE-5n), there was little uncertainty, and radioactive decay reduced concentrations before much migration could occur. Each evaluation target and the associated data-collection activity were assessed in turn to determine whether the new data support, or demonstrate conservatism of, the CB forecasts. The modeling team—in this case, the same team that developed the Frenchman Flat geologic, source term, and groundwater flow and transport models—analyzed the new data and presented the results to a PER committee. Existing site understanding and its representation in numerical groundwater flow and transport models was evaluated in light of the new data and the ability to proceed to the CR stage of long-term monitoring and institutional control.},
doi = {10.2172/1158867},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Sep 01 00:00:00 EDT 2014},
month = {Mon Sep 01 00:00:00 EDT 2014}
}

Technical Report:

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  • Note: This document was prepared before the NTS was renamed the Nevada National Security Site (August 23, 2010); thus, all references to the site herein remain NTS. Corrective Action Unit (CAU) 98, Frenchman Flat, at the Nevada Test Site (NTS) was the location of ten underground nuclear tests between 1965 and 1971. As a result, radionuclides were released in the subsurface in the vicinity of the test cavities. Corrective Action Unit 98 and other CAUs at the NTS and offsite locations are being investigated. The Frenchman Flat CAU is one of five Underground Test Area (UGTA) CAUs at the NTSmore » that are being evaluated as potential sources of local or regional impact to groundwater resources. For UGTA sites, including Frenchman Flat, contamination in and around the test cavities will not be remediated because it is technologically infeasible due to the depth of the test cavities (150 to 2,000 feet [ft] below ground surface) and the volume of contaminated groundwater at widely dispersed locations on the NTS. Instead, the compliance strategy for these sites is to model contaminant flow and transport, estimate the maximum spatial extent and volume of contaminated groundwater (over a period of 1,000 years), maintain institutional controls, and restrict access to potentially contaminated groundwater at areas where contaminants could migrate beyond the NTS boundaries.« less
  • This document, the Phase II Frenchman Flat transport report, presents the results of radionuclide transport simulations that incorporate groundwater radionuclide transport model statistical and structural uncertainty, and lead to forecasts of the contaminant boundary (CB) for a set of representative models from an ensemble of possible models. This work, as described in the Federal Facility Agreement and Consent Order (FFACO) Underground Test Area (UGTA) strategy (FFACO, 1996; amended 2010), forms an essential part of the technical basis for subsequent negotiation of the compliance boundary of the Frenchman Flat corrective action unit (CAU) by Nevada Division of Environmental Protection (NDEP) andmore » National Nuclear Security Administration Nevada Site Office (NNSA/NSO). Underground nuclear testing via deep vertical shafts was conducted at the Nevada Test Site (NTS) from 1951 until 1992. The Frenchman Flat area, the subject of this report, was used for seven years, with 10 underground nuclear tests being conducted. The U.S. Department of Energy (DOE), NNSA/NSO initiated the UGTA Project to assess and evaluate the effects of underground nuclear tests on groundwater at the NTS and vicinity through the FFACO (1996, amended 2010). The processes that will be used to complete UGTA corrective actions are described in the “Corrective Action Strategy” in the FFACO Appendix VI, Revision No. 2 (February 20, 2008).« less
  • This CADD/CAP follows the Corrective Action Investigation (CAI) stage, which results in development of a set of contaminant boundary forecasts produced from groundwater flow and contaminant transport modeling of the Frenchman Flat CAU. The Frenchman Flat CAU is located in the southeastern portion of the NNSS and comprises 10 underground nuclear tests. The tests were conducted between 1965 and 1971 and resulted in the release of radionuclides in the subsurface in the vicinity of the test cavities. Two important aspects of the corrective action process are presented within this CADD/CAP. The CADD portion describes the results of the Frenchman Flatmore » CAU data-collection and modeling activities completed during the CAI stage. The corrective action objectives and the actions recommended to meet the objectives are also described. The CAP portion describes the corrective action implementation plan. The CAP begins with the presentation of CAU regulatory boundary objectives and initial use restriction boundaries that are identified and negotiated by NNSA/NSO and the Nevada Division of Environmental Protection (NDEP). The CAP also presents the model evaluation process designed to build confidence that the flow and contaminant transport modeling results can be used for the regulatory decisions required for CAU closure. The first two stages of the strategy have been completed for the Frenchman Flat CAU. A value of information analysis and a CAIP were developed during the CAIP stage. During the CAI stage, a CAIP addendum was developed, and the activities proposed in the CAIP and addendum were completed. These activities included hydrogeologic investigation of the underground testing areas, aquifer testing, isotopic and geochemistry-based investigations, and integrated geophysical investigations. After these investigations, a groundwater flow and contaminant transport model was developed to forecast contaminant boundaries that enclose areas potentially exceeding the Safe Drinking Water Act radiological standards at any time within 1,000 years. An external peer review of the groundwater flow and contaminant transport model was completed, and the model was accepted by NDEP to allow advancement to the CADD/CAP stage. The CADD/CAP stage focuses on model evaluation to ensure that existing models provide adequate guidance for the regulatory decisions regarding monitoring and institutional controls. Data-collection activities are identified and implemented to address key uncertainties in the flow and contaminant transport models. During the CR stage, final use restriction boundaries and CAU regulatory boundaries are negotiated and established; a long-term closure monitoring program is developed and implemented; and the approaches and policies for institutional controls are initiated. The model evaluation process described in this plan consists of an iterative series of five steps designed to build confidence in the site conceptual model and model forecasts. These steps are designed to identify data-collection activities (Step 1), document the data-collection activities in the 0CADD/CAP (Step 2), and perform the activities (Step 3). The new data are then assessed; the model is refined, if necessary; the modeling results are evaluated; and a model evaluation report is prepared (Step 4). The assessments are made by the modeling team and presented to the pre-emptive review committee. The decision is made by the modeling team with the assistance of the pre-emptive review committee and concurrence of NNSA/NSO to continue data and model assessment/refinement, recommend additional data collection, or recommend advancing to the CR stage. A recommendation to advance to the CR stage is based on whether the model is considered to be sufficiently reliable for designing a monitoring system and developing effective institutional controls. The decision to advance to the CR stage or to return to step 1 of the process is then made by NDEP (Step 5).« less
  • The U.S. Department of Energy (DOE), National Nuclear Security Administration Nevada Site Office (NNSA/NSO) initiated the Underground Test Area (UGTA) Subproject to assess and evaluate radiologic groundwater contamination resulting from underground nuclear testing at the NTS. These activities are overseen by the Federal Facility Agreement and Consent Order (FFACO) (1996, as amended March 2010). For Frenchman Flat, the UGTA Subproject addresses media contaminated by the underground nuclear tests, which is limited to geologic formations within the saturated zone or 100 meters (m) or less above the water table. Transport in groundwater is judged to be the primary mechanism of migrationmore » for the subsurface contamination away from the Frenchman Flat underground nuclear tests. The intent of the UGTA Subproject is to assess the risk to the public from the groundwater contamination produced as a result of nuclear testing. The primary method used to assess this risk is the development of models of flow and contaminant transport to forecast the extent of potentially contaminated groundwater for the next 1,000 years, establish restrictions to groundwater usage, and implement a monitoring program to verify protectiveness. For the UGTA Subproject, contaminated groundwater is that which exceeds the radiological standards of the Safe Drinking Water Act (CFR, 2009) the State of Nevada’s groundwater quality standard to protect human health and the environment. Contaminant forecasts are expected to be uncertain, and groundwater monitoring will be used in combination with land-use control to build confidence in model results and reduce risk to the public. Modeling forecasts of contaminant transport will provide the basis for negotiating a compliance boundary for the Frenchman Flat Corrective Action Unit (CAU). This compliance boundary represents a regulatory-based distinction between groundwater contaminated or not contaminated by underground testing. Transport modeling simulations are used to compute radionuclide concentrations in time and space within the CAU for the 1,000-year contaminant boundary. These three-dimensional (3-D) concentration simulations are integrated into probabilistic forecasts of the likelihood of groundwater exceeding or remaining below the radiological standards of the Safe Drinking Water Act (CFR, 2009) defined as the contaminant boundary. Contaminant boundaries are not discrete predictions of the location or concentration of contaminants, but instead are spatial representations of the probability of exceeding Safe Drinking Water Act radiological standards. The forecasts provide planning tools to facilitate regulatory decisions designed to protect the health and safety of the public.« less
  • This document, which makes changes to Phase II Groundwater Flow Model of Corrective Action Unit 98: Frenchman Flat, Nevada Test Site, Nye County, Nevada, S-N/99205--074, Revision 0 (May 2006) was prepared to address review comments on this final document provided by the Nevada Division of Environmental Protection (NDEP) in a letter dated June 20, 2006. The document includes revised pages that address NDEP review comments and comments from other document users. Change bars are included on these pages to identify where the text was revised. In addition to the revised pages, the following clarifications are made: • Section 6.0 Conceptualmore » Model Uncertainty Analyses. Please note that in this section figures showing the observed versus simulated well head (Figures 6-1, 6-5, 6-7, 6-16, 6-28, 6-30, 6-32, 6-34, 6-37, 6-42, 6-47, 6-52, 6-57, 6-62, 6-71, and 6-86) have a vertical break in scale on the y axis. • Section 7.0 Parameter Sensitivity Analysis. In Section 7.2, the parameter perturbation analysis defines two components of the objective function PHI. These two components include the WELL component that represents the head portion of the objective function as measured in wells and the FLUX component that represents the lateral boundary flux portion of the objective function. In the text and figures in Section 7.2, the phrases “well portion of the objective function” and “head portion of the objective function” are used interchangeably in discussions of the WELL component of the objective function.« less