Interaction Between City Subsurface Infrastructure and Groundwater

Abstract

The interaction between the underground infrastructure and groundwater generates hydrogeological problems in Bucharest city (1.9 million people/228 km² surface). One is the barrier effect produced by an extensively channelized river, increasing consequently the groundwater hydraulic heads in the surrounding areas. A second one is due to the strong hydraulic interaction between sewerage and the groundwater. As result, the seepage into the sewer network increases the influent flowrate received by the waste water treatment plant. Restoration of the sewer conduits triggers consequently the groundwater hydraulic heads increase. Answers to these problems have been foreseen by developing the Bucharest city hydrogeological model with the support of several institutions, companies, and experts. As a first step the 3D geological model, for the first 50 m below ground level, has been developed. The spatial intersection between the urban infrastructure elements (subway, parking lots, etc.) and the geological model, provided the geometrical parameters needed to quantify their groundwater flow barrier effect. It also enabled to identify the location of the sewer conduits and their potential hydraulic connection with the aquifer strata. The hydrogeological model englobes the following datasets: hydraulic heads, surface water, groundwater recharge from precipitation and from the water supply system losses, drainage systems and seepage into tunnels. The resulted hydrological water balance identified that about 0.92 m³/s wastewater surplus originates from seepage. It has been determined that more than 20% (96.7 km) of the sewer network is completely or partially immersed into groundwater. Scenarios to neutralize the groundwater sink impact have been simulated.