U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
  
Hydraulic Characteristics of Fractured Bedrock Underlying the
FSE Well Field at the Mirror Lake Site, Grafton County, New Hampshire
by
Paul A. Hsieh (U.S. Geological Survey, Menlo Park, Calif.) and
Allen M. Shapiro (U.S. Geological Survey, Reston, Va.)
Abstract
At the Mirror Lake site in Grafton County, New Hampshire, 13 wells are
drilled in a 120-m (meter) by 80-m area, known as the FSE well field, the
characterize the hydraulic and transport properties of the underlying fractured
bedrock. Borehole geophysical logs and downhole video camera images show
that each well intersects 20 to 60 fractures within the upper 60 m of bedrock.
However, single-well hydraulic tests show that only one to three fractures
in each well are highly transmissive. Multiple-well hydraulic tests suggest
that the few highly transmissive fractures connect with one another locally
to form fracture clusters. These highly transmissive fracture clusters,
in turn, connected to one another by fractures that are comparatively lower
in transmissivity by several orders of magnitude. In such a fractured-bedrock
setting, the response to a multiple-well hydraulic test is entirely different
from the response in a homogeneous aquifer. These finding s suggest that
it is necessary to identify and characterize explicitly the highly transmissive
fracture clusters in order to analyze multiple-well hydraulic tests at the
FSE well field.
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