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Open-File Report 2013–1224

Prepared in cooperation with the U.S. Environmental Protection Agency, Region 1 and the New Hampshire Department of Environmental Services

Bedrock Geology and Outcrop Fracture Trends in the Vicinity of the Savage Municipal Well Superfund Site, Milford, New Hampshire

By William C. Burton and Philip T. Harte

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Abstract

The Savage Municipal Well Superfund site consists of an eastward-directed plume of volatile organic compounds, principally tetrachloroethylene (PCE), in alluvium and glacial sand and gravel in the Souhegan River valley, just south of the river and about 4 kilometers west of the town of Milford, New Hampshire. Sampling of monitoring wells at the site has helped delineate the extent of the plume and has determined that some contaminant has migrated into the underlying crystalline bedrock, including bedrock north of the river within 200 meters of a nearby residential development that was constructed in 1999. Borehole geophysical logging has identified a northeast preferential trend for bedrock fractures, which may provide a pathway for the migration of contaminant under and north of the Souhegan River. The current study investigates the bedrock geologic setting for the site, including its position relative to known regional geologic structures, and compiles new strike and dip measurements of joints in exposed bedrock to determine if there are dominant trends in orientation similar to what was found in the boreholes. The site is located on the northwestern limb of a northeast-trending regional anticlinorium that is southeast of the Campbell Hill fault zone. The Campbell Hill fault zone defines the contact between granite and gneiss of the anticlinorium and granite and schist to the northwest and is locally marked by lenses of massive vein quartz, minor faults, and fracture zones that could potentially affect plume migration. The fault zone was apparently not intercepted by any of the boreholes that were drilled to delineate the contaminant plume and therefore passes to the north of the northernmost borehole in the vicinity of the new residential area. Joints measured in surface exposures indicate a strong preferred direction of strike to the north-northeast corroborating the borehole data and previous outcrop and geophysical studies. The north-northeast preferred direction matches the direction of elongation of the cone of depression formed during a pump test of the bedrock wells and could explain a potential pathway for the migration of contaminant north of the river.

First posted September 19, 2013

For additional information contact:
Eastern Geology and Paleoclimate Science Center
U.S. Geological Survey
926A National Center
12201 Sunrise Valley Drive
Reston, VA 20192

Or

William C. Burton
U.S. Geological Survey
926A National Center
12201 Sunrise Valley Drive
Reston, VA 20192

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Suggested citation:

Burton, W.C., and Harte, P.T., 2013, Bedrock geology and outcrop fracture trends in the vicinity of the Savage Municipal Well Superfund site, Milford, New Hampshire: U.S. Geological Survey Open-File Report 2013–1224, 17 p., http://pubs.usgs.gov/of/2013/1224/.



Contents

Abstract

Introduction

Regional Geologic Setting of the Savage Municipal Well Superfund Site

New Bedrock Geologic Mapping

Discussion of Surface and Subsurface Fault and Fracture Trends and Their Hydrologic Significance

Summary and Conclusions

Acknowledgments

References Cited

Glossary of Selected Terms


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