AVAILABLE ONLINE ONLY
By James R. Degnan, Stewart F. Clark, Jr., Philip T. Harte, and Thomas J. Mack
Complete text of report is available as a PDF (6,004 KB)
Plate 1 is available in .gif format (110 KB)
At the cell-house site, thin, generally less than 20-foot thick overburden, consisting of till and demolition materials, overlies fractured crystalline bedrock. Bedrock at the site consists of gneiss with thin discontinuous lenses of chlorite schist and discontinuous tabular pegmatite. Two distinct fracture domains, with principal trends to the west and northwest, and to the north, overlap near the site. The cell-house site shows principal trends common to both domains.
Gneiss is the most abundant rock at the site. Steeply dipping fractures within the gneiss terminate on subhorizontal contacts with pegmatite and on moderately dipping contacts with chlorite schist. Steeply northwest-dipping en Èchelon fracture zones, parallel joint zones, and silicified brittle faults show consistent strikes to the northeast. Gently east-dipping to subhorizontal fractures, sub-parallel to gneissosity, strike northeast.
The impermeable cap, barrier wall, and bedrock surface topography affect ground-water flow in the overburden. There is relatively little ground-water flow in the overburden in the capped area and a poor hydraulic connection between the overburden and the underlying bedrock over most of the site. The overburden beneath the cap may receive inflow through or beneath the barrier wall, or by flow through vertical fractures in the underlying bedrock beneath the barrier wall.
The bedrock aquifer near the river is well connected to the river and head difference in the bedrock across the site are large (greater than 13 ft). Horizontal hydraulic conductivities of 0.2 to 20 ft/d were estimated for the bedrock. Individual fractures or fracture zones likely have hydraulic conductivities greater than the bulk rock. Subhorizontal fractures occur at pegmatite contacts or along chlorite schist lenses and may serve as ground-water conduits to the steeply dipping fractures in gneiss. The effective hydraulic conductivity across the site is likely to be in the low range of the estimated values (0.2 ft/d). Ground water discharges to the river from the bedrock aquifer and is greatest during periods of large river stage fluctuations.
Site Description and History
Purpose and Scope
Geologic Mapping and Analysis
Borehole Geophysical Logs
Results of Hydrogeologic Analyses
Analysis of Surface and Ground-Water Levels
Head Surfaces and Hydraulic Connections
Preliminary Hydrogeologic Characterization
Appendix 1 - Core Logs from Boreholes
Plate 1 Geologic map of exposed bedrock at the cell-house site, Berlin, N.H.
For more information concerning the research in this report, contact:
361 Commerce Way
Pembroke, NH 03275
Web site: http://nh.water.usgs.gov
Phone: (603) 226-7807
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Last modified: Thursday, January 10 2013, 06:36:39 PM