Long-term Monitoring Plan for the Central Nevada Test Area

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The groundwater flow and transport model of the Faultless underground nuclear test conducted at the Central Nevada Test Area (CNTA) was accepted by the state regulator and the environmental remediation efforts at the site have progressed to the stages of model validation and long-term monitoring design. This report discusses the long-term monitoring strategy developed for CNTA. Subsurface monitoring is an expensive and time-consuming process, and the design approach should be based on a solid foundation. As such, a thorough literature review of monitoring network design is first presented. Monitoring well networks can be designed for a number of objectives including ... continued below

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Hassan, A. September 2, 2003.

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The groundwater flow and transport model of the Faultless underground nuclear test conducted at the Central Nevada Test Area (CNTA) was accepted by the state regulator and the environmental remediation efforts at the site have progressed to the stages of model validation and long-term monitoring design. This report discusses the long-term monitoring strategy developed for CNTA. Subsurface monitoring is an expensive and time-consuming process, and the design approach should be based on a solid foundation. As such, a thorough literature review of monitoring network design is first presented. Monitoring well networks can be designed for a number of objectives including aquifer characterization, parameter estimation, compliance monitoring, detection monitoring, ambient monitoring, and research monitoring, to name a few. Design methodologies also range from simple hydrogeologic intuition-based tools to sophisticated statistical- and optimization-based tools. When designing the long-term monitoring well network for CNTA, a number of issues are carefully considered. These are the uncertainty associated with the subsurface environment and its implication for monitoring design, the cost associated with monitoring well installation and operation, the design criteria that should be used to select well locations, and the potential conflict between different objectives such as early detection versus impracticality of placing wells in the vicinity of the test cavity. Given these considerations and the literature review of monitoring design studies, a multi-staged approach for development of the long-term monitoring well network for CNTA is proposed. This multi-staged approach will proceed in parallel with the validation efforts for the groundwater flow and transport model of CNTA. Two main stages are identified as necessary for the development of the final long-term monitoring well network for the site. The first stage is to use hydrogeologic expertise combined with model simulations and probability based approaches to select the first set of monitoring wells that will serve two purposes. The first is to place the wells in areas likely to encounter migration pathways thereby enhancing the probability of detecting radionuclide migration in the long run. The second objective is crucial in the short run and is aimed at using this set of wells to collect validation data for the model. The selection criteria should thus balance these two objectives. Based on the results of the validation process that progresses concurrently with the first monitoring stage, either more wells will be needed in this first stage or the second stage will be initiated. The second monitoring design stage will be based on an optimum design methodology that uses a suitable statistical approach, combined with an optimization approach, to augment the initial set of wells and develop the final long-term monitoring network. The first-stage probabilistic analysis conducted using the CNTA model indicates that the likelihood of migration away from the test cavity is very low and the probability of detecting radionuclides in the next 100 years is extremely low. Therefore, it is recommended to place one well in the downstream direction along the model longitudinal centerline (i.e., directly north of the working point), which is the location with the highest probability of encountering the plume. Lack of significant plume spreading, coupled with the extremely low velocities, suggests that this one well is sufficient for the first stage. Data from this well, and from additional wells located with validation as the prime objective, will benefit the model validation process. In the long run, this first monitoring well is going to be crucial for the long-term monitoring of the site (assuming that the flow model is validated), as it will be the most likely place to detect any plume migration away from the cavity.

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  • Report No.: 45201
  • Report No.: DOE/NV/13609-30
  • Grant Number: AC08-00NV13609
  • DOI: 10.2172/850305 | External Link
  • Office of Scientific & Technical Information Report Number: 850305
  • Archival Resource Key: ark:/67531/metadc780931

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  • September 2, 2003

Added to The UNT Digital Library

  • Dec. 3, 2015, 9:30 a.m.

Description Last Updated

  • Dec. 7, 2016, 4:43 p.m.

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Hassan, A. Long-term Monitoring Plan for the Central Nevada Test Area, report, September 2, 2003; United States. (digital.library.unt.edu/ark:/67531/metadc780931/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.