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Ground water in fractured bedrock at the Holton Circle Superfund site in Londonderry, New Hampshire, contains volatile organic compounds and chloride concentrations as high as 23,500 mg/L. Geophysical logs obtained from eight bedrock observation wells that range in depth from 65 to 382 feet were used to identify depths of possible water-bearing fractures. Logs included natural gamma, spontaneous potential, single-point resistance, caliper, temperature, and fluid resistivity. All but the natural-gamma log had anomalies that indicate possible fractures. Anomalies at the same depths on several logs from a single well support identification of likely fractures. Charts presented in the report show depths of anomalies that may indicate fractures. INTRODUCTION Volatile organic compounds and high concentrations of dissolved constituents, principally sodium (Na) and chloride (CD, are present in ground water at the Holton Circle Superfund site in Londonderry, N.H. (fig. 1). Water in the bedrock moves primarily through fractures in the foliated schist. During October and November 1990, eight wells were drilled into bedrock by the U.S. Environmental Protection Agency (USEPA) to characterize the hydrology of the site. In cooperation with the USEPA, the U.S. Geological Survey (USGS) logged these eight wells by means of six borehole geophysical methods to identify the locations of possible fractures and fracture zones. Borehole logs were run on each of the eight wells between November 16,1990, and January 23, 1991. The purpose of this report is to describe the logging methods used, present the logs obtained, and identify depths of possible fractures in each well logged. The author thanks James M. Di Lorenzo, Waste Management Division, U.S. Environmental Protection Agency, Boston, Mass., who provided background information and logistical assistance during the logging survey. BOREHOLE LOGS A borehole logger with single-conductor logging cable was used for this survey. Continuous

Locations of fracture intervals inferred from borehole logs of eight wells at the Holton Circle Superfund site, Londonderry, New Hampshire