Enhanced detection of hydraulically active fractures by temperature profiling in lined heated bedrock boreholes P.E. Pehme a,⇑ , B.L. Parker b,1 , J.A. Cherry c,2 , J.W. Molson d,3 , J.P. Greenhouse e a G360, University of Guelph, Day Hall Room 203, Guelph, Ontario, Canada, N1G 2W1 b G360, Centre for Applied Groundwater Research, University of Guelph, Day Hall Room 200, Guelph, Ontario, Canada, N1G 2W1 c G360, Centre for Applied Groundwater Research, University of Guelph, Day Hall Room 201, Guelph, Ontario, Canada, N1G 2W1 d Quantitative Hydrogeology of Fractured Porous Media, Département de géologie et de génie géologique, Université Laval, Québec (Québec), Canada G1V 0A6 e PO Box 122, Tobermory, Ontario, Canada N0H 2R0 article info Article history: Received 14 July 2012 Received in revised form 31 December 2012 Accepted 31 December 2012 Available online 16 January 2013 This manuscript was handled by Corrado Corradini, Editor-in-Chief, with the assistance of Xunhong Chen, Associate Editor Keywords: Fractured rock Temperature logging Ambient flow Homothermic boundary summary The effectiveness of borehole profiling using a temperature probe for identifying hydraulically active frac- tures in rock has improved due to the combination of two advances: improved temperature sensors, with resolution on the order of 0.001 °C, and temperature profiling within water inflated flexible impermeable liners used to temporarily seal boreholes from hydraulic cross-connection. The open-hole cross-connec- tion effects dissipate after inflation, so that both the groundwater flow regime and the temperature dis- tribution return to the ambient (background) condition. This paper introduces a third advancement: the use of an electrical heating cable that quickly increases the temperature of the entire static water column within the lined hole and thus places the entire borehole and its immediate vicinity into thermal disequi- librium with the broader rock mass. After heating for 4–6 h, profiling is conducted several times over a 24 h period as the temperature returns to background conditions. This procedure, referred to as the Active Line Source (ALS) method, offers two key improvements over prior methods. First, there is no depth limit for detection of fractures with flow. Second, both identification and qualitative comparison of evidence for ambient groundwater flow in fractures is improved throughout the entire test interval. The benefits of the ALS method are demonstrated by comparing results from two boreholes tested to depths of 90 and 120 m in a dolostone aquifer used for municipal water supply and in which most groundwater flow occurs in fractures. Temperature logging in the lined holes shows many fractures in the heterothermic zone both with and without heating, but only the ALS method shows many hydrauli- cally active fractures in the deeper homothermic portion of the hole. The identification of discrete groundwater flow at many depths is supported by additional evidence concerning fracture occurrence, including continuous core visual inspection, acoustic televiewer logs, and tests for hydraulic conductivity using straddle packers as well as rock core VOC data, where available, that show deep penetration and many migration pathways. Confidence in the use of temperature profiles and the conceptual model is provided by numerical simulation and the demonstrated reproducibility of the evolution of the temper- ature signal measured in the lined holes with and without heating. This approach for using temperature profiling in lined holes with heating is a practical advance in fractured rock hydrogeology because the liners are readily available, the equipment needed for heating is low cost and rugged, and the time needed to obtain the profiles is not excessive for most projects. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Most or essentially all groundwater flow in rock formations oc- curs in fractures. To gain insight into how contaminants behave in these environments, and to enable more accurate predictions of their arrival times at receptors, better characterization of ground- water flow in fracture networks is needed (e.g., Berkowitz, 2002; NRC, 1996; Sara, 2003). Many numerical models have been devel- oped for simulating flow and contaminant transport in discrete fracture networks in rock (FRAC3DVS, Therrien and Sudicky, 1996; FEFLOW, DHI-WASY, 2009; HEATFLOW, Molson and Frind, 2012); however, advances in the acquisition of field data for frac- ture parameterization for such models has lagged far behind ad- vances in numerical codes. Data acquisition from boreholes is the primary approach to contaminated bedrock site characterization 0022-1694/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhydrol.2012.12.048 ⇑ Corresponding author. Tel.: +1 519 500 9568; fax: +1 880 9024. E-mail addresses: PPehme@waterloogeophysics.com (P.E. Pehme), bparker@uo- guelph.ca (B.L. Parker), cherryja@rogers.blackberry.net (J.A. Cherry), john.mol- son@ggl.ulaval.ca (J.W. Molson), jpgreenh@amtelecom.net (J.P. Greenhouse). 1 Tel.: +1 519 824 4120x53642. 2 Tel.: +1 647 628 0941. 3 Tel.: +1 418 656 5713; fax: +1 418 656 7339. Journal of Hydrology 484 (2013) 1–15 Contents lists available at SciVerse ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol