Using tracer tests and hydrological observations to evaluate effects of tunnel drainage on groundwater and surface waters in the Northern Apennines (Italy)

Abstract

The impact of a railway tunnel on groundwater and surface waters in the Northern Apennines (Italy) was demonstrated and characterised by multi-tracer tests and hydrological observations. The 15-km-long Firenzuola tunnel crosses turbidite marls and sandstones previously not considered as aquifers. During the drilling, water inrushes occurred at fracture zones, and the tunnel still continues to drain the aquifer. The water table dropped below the level of the valleys, and gaining streams transformed into losing streams or ran completely dry, as did many springs, causing severe damage to the aquatic fauna and other elements of the ecosystem. Two multitracer tests, each using uranine and sulforhodamine G, were carried out in two impacted catchments in order to confirm and quantify the stream-aquifer-tunnel interrelations. The results proved connection between losing streams and numerous water inlets in the tunnel, with maximum linear distances of 1.4 km and velocities up to 135 m/d. Several of the demonstrated flowpaths pass under previous groundwater divides (mountain ridges), proving that the tunnel has completely modified the regional flow system. Water balance estimations demonstrate that the observed water losses cannot be explained by climate change but can largely be attributed to the tunnel drainage.

Assessing the timing and magnitude of precipitation-induced seepage into tunnels bored through fractured rock

“…Seepage into underground tunnels, cavities, and drifts gained increasing attention during the past few decades as a result of its potential impacts on the construction process (Chen & Tolon, 2012;Huang et al, 2011;Fernandez & Moon, 2010a;Li et al, 2009;Cesano et al 2000;Kitterod et al, 2000), water resources and environment (Vincenzi et al, 2009;Gleeson et al, 2009;Gargini et al, 2008;Scanlon, et al, 2006;Kim et al, 2005;Seyfried, et al, 2005;Rademacher et al, 2003;Scanlon et al, 2002;Shimojima et al, 1993), and the quality of nuclear waste repositories Bagtzoglou & Cesano, 2007;Trautz & Wang, 2002;Liu & Bodvarsson, 2001;Philip & Knight, 1989). Various processes have been identified that govern the spatial and temporal variability of net infiltration, recharge, and seepage into soil and rock excavations and cavities.…”

“…Of these observations, the underlying theme is that infiltration and subsequent seepage most commonly occur where a fracture network acting as a flow conduit is in connection with an overlying source of water, be it a groundwater reservoir in permeable soil, a horizon of permeable conductive soil, or a location of direct recharge (Shimojima et al, 1993;Olofsson, 1994;Rademacher et al, 2003;Seyfried et al, 2005;Scanlon et al, 2005;Scanlon et al, 2006;Gargini et al, 2008;Vincenzi et al, 2009;Gleeson et al, 2009;Moon & Jeong, 2011). Tunnels bored in the unsaturated zone or through fractured crystalline rock are more commonly left without liners than tunnels that are beneath the water table and so are more susceptible to seepage (Vincenzi et al, 2009).…”

“…Tunnels bored in the unsaturated zone or through fractured crystalline rock are more commonly left without liners than tunnels that are beneath the water table and so are more susceptible to seepage (Vincenzi et al, 2009). The overburden was found to be the source of major leakage in some scenarios and for this reason, successful estimates must treat the fractured rock mass and overburden as an interrelated system (Cesano et al, 2000).…”

“…Examples of seepage into transportation and water resources tunnels via localized flow in fractures are also found in literature from Europe. Vincenzi et al (2009) showed that a 15 km long tunnel for high speed rail bored in fractured turbidite marls and sandstones, once considered aquitards, drained such large volumes of water that streams at the surface ran dry. This significantly affected the hydrologic and ecologic systems as very little groundwater remained at the surface for vegetation, streams, and lakes.…”

“…No slope is applied to the top of the domain as Maxwell (2010) showed all overland flow, in a very similar scenario, contributing to run-on, and therefore none leaves the domain. (Pruess, 1998), and Mediterranean (Vincenzi et al, 2009;Gargini et al, 2008;Rademacher et al, 2003). Denver is a good example of a continental semiarid climate and is used for simulations.…”