Research papers Cross-hole fracture connectivity assessed using hydraulic responses during liner installations in crystalline bedrock boreholes Elisha Persaud a,b,⇑ , Jana Levison a,b , Peeter Pehme a,b , Kentner Novakowski c , Beth Parker a,b a School of Engineering, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada b G360 Institute for Groundwater Research, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada c Department of Civil Engineering, Queen’s University, 99 University Avenue, Kingston, Ontario K7L 3N6, Canada article info Article history: Received 19 June 2017 Received in revised form 10 October 2017 Accepted 6 November 2017 Available online 06 November 2017 This manuscript was handled by P. Kitanidis, Editor-in-Chief, with the assistance of Jean-Raynald de Dreuzy, Associate Editor Keywords: Crystalline bedrock Borehole liners Cross-hole testing Hydraulic testing Fracture connectivity abstract In order to continually improve the current understanding of flow and transport in crystalline bedrock environments, developing and improving fracture system characterization techniques is an important area of study. The presented research examines the installation of flexible, impermeable FLUTe TM liners as a means for assessing cross-hole fracture connectivity. FLUTe TM liners are used to generate a new style of hydraulic pulse, with pressure response monitored in a nearby network of open boreholes drilled in gneissic rock of the Canadian Shield in eastern Ontario, Canada. Borehole liners were installed in six exist- ing 10–15 cm diameter boreholes located 10–35 m apart and drilled to depths ranging between 25–45 m. Liner installation tests were completed consecutively with the number of observation wells available for each test ranging between one and six. The collected pressure response data have been analyzed to iden- tify significant groundwater flow paths between source and observation boreholes as well as to estimate inter-well transmissivity and storativity using a conventional type-curve analysis. While the applied solution relies on a number of general assumptions, it has been found that reasonable comparison can be made to previously completed pulse interference and pumping tests. Results of this research indicate areas where method refinement is necessary, but, nonetheless, highlight the potential for use in crys- talline bedrock environments. This method may provide value to future site characterization efforts given that it is complementary to, and can be used in conjunction with, other currently employed borehole liner applications, such as the removal of cross-connection at contaminated sites and the assessment of dis- crete fracture distributions when boreholes are sealed, recreating natural hydraulic gradient conditions. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction Crystalline bedrock aquifers occur in many regions of the world and are exposed in vast areas, such as the Precambrian rocks of the Canadian Shield, Baltic Shield, and Brazilian Shield. While wells drilled in crystalline rock may be associated with limited yield in some locations, they are nonetheless important for water supply, especially in many developing countries where surface water is often inadequate (Howard and Karundu, 1992; Chilton and Foster, 1995; Adekunle et al., 2007; Kulabako et al., 2007; Neves and Morales, 2007; Holland and Witthüser, 2011; Foster, 2012; Boisson et al., 2015). Unfortunately, these aquifers can be particu- larly vulnerable to contamination (e.g. Kim et al., 2016; Vitale et al., 2017). Crystalline bedrock aquifers generally contain negligible matrix porosity and as a result, groundwater flow is transmitted nearly exclusively through fractures within a largely impervious rock matrix. Although the effective porosity of these pathways is quite small (in the order of 10 4 –10 5 ), average linear groundwa- ter velocities can be significant, creating the potential for rapid contaminant transport and widespread contaminant migration (Allen and Morrison, 1973; Singhal and Gupta, 1999; Conboy and Goss, 2000; Levison and Novakowski, 2009). These conditions may be enhanced by minimal matrix diffusion, storage and associ- ated solute degradation, as well as rapid recharge of groundwater and associated contaminants in areas with thin overburden, which is common in crystalline bedrock environments (Grisak and Pickens, 1981; Gerhart, 1986; Bodin et al., 2003; Gleeson et al., 2009; Levison and Novakowski, 2012; Levison et al., 2012; Praamsma, 2016). Given this inherent vulnerability, characterization of crystalline bedrock aquifers, to gain an enhanced understanding of groundwa- ter flow and contaminant transport, is a necessary task. However, https://doi.org/10.1016/j.jhydrol.2017.11.008 0022-1694/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: School of Engineering, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada. E-mail address: epersaud@uoguelph.ca (E. Persaud). Journal of Hydrology 556 (2018) 233–246 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol