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Title: Testing the suitability of geologic frameworks for extrapolating hydraulic properties across regional scales

The suitability of geologic frameworks for extrapolating hydraulic conductivity (K) to length scales commensurate with hydraulic data is difficult to assess. A novel method is presented for evaluating assumed relations between K and geologic interpretations for regional-scale groundwater modeling. The approach relies on simultaneous interpretation of multiple aquifer tests using alternative geologic frameworks of variable complexity, where each framework is incorporated as prior information that assumes homogeneous K within each model unit. This approach is tested at Pahute Mesa within the Nevada National Security Site (USA), where observed drawdowns from eight aquifer tests in complex, highly faulted volcanic rocks provide the necessary hydraulic constraints. The investigated volume encompasses 40 mi3 (167 km3) where drawdowns traversed major fault structures and were detected more than 2 mi (3.2 km) from pumping wells. Complexity of the five frameworks assessed ranges from an undifferentiated mass of rock with a single unit to 14 distinct geologic units. Results show that only four geologic units can be justified as hydraulically unique for this location. The approach qualitatively evaluates the consistency of hydraulic property estimates within extents of investigation and effects of geologic frameworks on extrapolation. Distributions of transmissivity are similar within the investigated extents irrespective ofmore » the geologic framework. In contrast, the extrapolation of hydraulic properties beyond the volume investigated with interfering aquifer tests is strongly affected by the complexity of a given framework. As a result, testing at Pahute Mesa illustrates how this method can be employed to determine the appropriate level of geologic complexity for large-scale groundwater modeling.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1]
  1. U.S. Geological Survey, Arden, NC (United States)
Publication Date:
OSTI Identifier:
1238791
Grant/Contract Number:
NA0001654
Type:
Accepted Manuscript
Journal Name:
Hydrogeology Journal
Additional Journal Information:
Journal Volume: 24; Journal Issue: 1; Related Information: http://pubs.er.usgs.gov/publication/70168659; Journal ID: ISSN 1435-0157
Research Org:
U.S. Geological Survey, Arden, NC (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES groundwater flow; heterogeneity; hydraulic properties; hydraulic tomography; USA