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Title: The Application of Radon for Mapping Open Fracture Networks in a Thin Vadose Zone

The use of naturally occurring tracers to elucidate subsurface flow and transport of water and gasses through fractured vadose zones represents a powerful and inexpensive methodology for understanding geologic systems. Our study was conducted at Sheply’s Hill, a highly fractured granite highland at the old Fort Devens military base. This study evaluates the applicability of using cheap, readily available passive radon detectors to identify conductive structures (e.g., fractures and fracture networks) in fracture-dominated vadose zones. Radon data from this study provides strong evidence that, even within an intensively fractured system, a relatively smaller subset of the fractures is responsible for the majority of the vertical migration of gas and water that recharges contaminated groundwater sites. Our study found that zones of high recharge potential associated with open fracture networks could be identified based on the 222Rn flux within the highly fractured Shepley’s Hill. Based on the results of this study, 222Rn is an environmental tracer capable of efficiently detecting major bedrock fracture sets in the vadose zone responsible for water infiltration into contaminated aquifers. Results from the Shepley’s Hill study show a clear spatial correlation of elevated 222Rn concentrations emanating from fracture zones previously identified by independent geologic studies. Atmore » Shepley’s Hill, the 222Rn concentrations measured from detector locations directly above the major bedrock fractures, located within the Disc Golf Fracture Zone (DGFZ) and the Nona-Shep Fracture Zone (NSFZ), were almost exclusively the highest values measured in the study. Conversely, probes located above areas of less-fractured bedrock, although highly fractured, showed relatively low 222Rn concentrations. Furthermore, these two observations provide strong supporting evidence that not all fractures are equal when it comes to their ability to transmit gas or water into and out of the subsurface.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [5]
  1. Idaho National Lab. (INL), Idaho Falls, ID (United States); The Center for Advanced Energy Studies, Idaho Falls, ID (United States)
  2. USEPA Region 1, Boston, MA (United States)
  3. USEPA Region 10, Seattle, WA (United States)
  4. Univ. of Idaho, Moscow, ID (United States)
  5. Idaho National Lab. (INL), Idaho Falls, ID (United States)
Publication Date:
Report Number(s):
INL/JOU-16-39231
Journal ID: ISSN 1539-1663
Grant/Contract Number:
AC07-05ID14517
Type:
Accepted Manuscript
Journal Name:
Vadose Zone Journal
Additional Journal Information:
Journal Volume: 16; Journal Issue: 7; Journal ID: ISSN 1539-1663
Publisher:
Soil Science Society of America
Research Org:
Idaho National Lab. (INL), Idaho Falls, ID (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CR-39; Fort Devens; fracture networks; radon; vadose zone
OSTI Identifier:
1396011