string: …following the infiltration of
  wastewater to the ground (Clara et al., 2004; Drewes et al., 2003; Gasser et al., 2010; Glassmeyer et al., 2008; Grünheid et al., 2005; Heberer and Adam, 2004; Heberer et al., 1997; Katz et al., 2009; Rabiet et al., 2006; Sacher et al., 2001; Snyder et al., 2004).