Impact of microbial activity on the hydraulic properties of fractured chalk Shai Arnon a,b , Eilon Adar a,b , Zeev Ronen a, * , Alexander Yakirevich a , Ronit Nativ c a Department of Environmental Hydrology & Microbiology, Zuckerberg Institute for Water Research, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer 84990, Israel b Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, Israel c Department of Soil and Water Sciences, The Hebrew University of Jerusalem, Israel Received 10 February 2004; received in revised form 15 November 2004; accepted 26 November 2004 Abstract The impact of microbial activity on fractured chalk transmissivity was investigated on a laboratory scale. Long-term experiments were conducted on six fractured chalk cores (20 cm diameter, 23–44 cm long) containing a single natural fracture embedded in a porous matrix. Biodegradation experiments were conducted under various conditions, including several substrate and oxygen concentrations and flow rates. 2,4,6-Tribromophenol (TBP) was used as a model contaminant (substrate). TBP biodegradation efficiency depended mainly on the amount of oxygen. However, under constant oxygen concentration at the core inlet, elevating the flow rates increased the removal rate of TBP. Transmissivity reduction was clearly related to TBP removal rate, following an initial slow decline and a further sharp decrease with time. The fracture’s transmissivity was reduced by as much as 97% relative to the initial value, with no leveling off of the clogging process. For the most extreme cases, reductions of 262 and 157 Am in the equivalent hydraulic apertures were recorded for fractures with initial apertures of 495 and 207 Am, respectively. The reductions in fracture transmissivity occurred primarily because of clogging by bacterial cells and extracellular polymeric substances (EPS) produced by the bacteria. Most of the biodegradation activity was concentrated near the fracture inlet, where the most suitable biodegradation conditions (nutrients and 0169-7722/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jconhyd.2004.11.004 * Corresponding author. Tel.: +972 8 6596895; fax: +972 8 6596909. E-mail addresses: shuya@bgumail.bgu.ac.il (S. Arnon)8 eilon@bgumail.bgu.ac.il (E. Adar)8 zeevrone@bgumail.bgu.ac.il (Z. Ronen)8 alexy@bgumail.bgu.ac.il (A. Yakirevich)8 nativr@agri.huji.ac.il (R. Nativ). Journal of Contaminant Hydrology 76 (2005) 315 – 336 www.elsevier.com/locate/jconhyd