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Hydraulic characterization of volcanic rocks in Pahute Mesa using an integrated analysis of 16 multiple-well aquifer tests, Nevada National Security Site, 2009–14

Scientific Investigations Report 2016-5151
Prepared in cooperation with the Department of Energy, National Nuclear Security Administration Nevada Site Office, Office of Environmental Management under Interagency Agreement, DE-NA0001654
By: , , , , , , and 
https://doi.org/10.3133/sir20165151

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Abstract

An improved understanding of groundwater flow and radionuclide migration downgradient from underground nuclear-testing areas at Pahute Mesa, Nevada National Security Site, requires accurate subsurface hydraulic characterization. To improve conceptual models of flow and transport in the complex hydrogeologic system beneath Pahute Mesa, the U.S. Geological Survey characterized bulk hydraulic properties of volcanic rocks using an integrated analysis of 16 multiple-well aquifer tests. Single-well aquifer-test analyses provided transmissivity estimates at pumped wells. Transmissivity estimates ranged from less than 1 to about 100,000 square feet per day in Pahute Mesa and the vicinity. Drawdown from multiple-well aquifer testing was estimated and distinguished from natural fluctuations in more than 200 pumping and observation wells using analytical water-level models. Drawdown was detected at distances greater than 3 miles from pumping wells and propagated across hydrostratigraphic units and major structures, indicating that neither faults nor structural blocks noticeably impede or divert groundwater flow in the study area.

Consistent hydraulic properties were estimated by simultaneously interpreting drawdown from the 16 multiple-well aquifer tests with an integrated groundwater-flow model composed of 11 well-site models—1 for each aquifer test site. Hydraulic properties were distributed across volcanic rocks with the Phase II Pahute Mesa-Oasis Valley Hydrostratigraphic Framework Model. Estimated hydraulic-conductivity distributions spanned more than two orders of magnitude in hydrostratigraphic units. Overlapping hydraulic conductivity ranges among units indicated that most Phase II Hydrostratigraphic Framework Model units were not hydraulically distinct. Simulated total transmissivity ranged from 1,600 to 68,000 square feet per day for all pumping wells analyzed. High-transmissivity zones exceeding 10,000 square feet per day exist near caldera margins and extend along the northern and eastern Pahute Mesa study area and near the southwestern edge of the study area. The estimated hydraulic-property distributions and observed hydraulic connections among geologic structures improved the characterization and representation of groundwater flow at Pahute Mesa.

Suggested Citation

Garcia, C.A., Jackson, T.R., Halford, K.J., Sweetkind, D.S., Damar, N.A., Fenelon, J.M., and Reiner, S.R., 2017, Hydraulic characterization of volcanic rocks in Pahute Mesa using an Integrated Analysis of 16 multiple-well aquifer tests, Nevada National Security Site, 2009–14: U.S. Geological Survey Scientific Investigations Report 2016-5151, 62 p., https://doi.org/10.3133/sir20165151.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Well Network and Data Collection
  • Drawdown Observations
  • Integrated Aquifer-Test Analysis
  • Hydraulic Characterization of Volcanic Rocks
  • Summary
  • References Cited
  • Appendixes 1-3
Publication type Report
Publication Subtype USGS Numbered Series
Title Hydraulic characterization of volcanic rocks in Pahute Mesa using an integrated analysis of 16 multiple-well aquifer tests, Nevada National Security Site, 2009–14
Series title Scientific Investigations Report
Series number 2016-5151
DOI 10.3133/sir20165151
Year Published 2017
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Nevada Water Science Center
Description Report: x, 61 p.; Appendixes 1-3; Data Releases; Read Me
Country United States
State Nevada
Other Geospatial Nevada National Security Site
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details