Analysis and evaluation of groundwater protection alternatives during waste extraction operations (acid tars) in a lagoon in Arganda del Rey (Madrid)

Abstract

The Community of Madrid is carrying out the integral restoration of an old gravel pit contaminated with hazardous waste, mostly petroleum sulphonates (acid tars), from the treatment of used industrial oil. Part of these discharges, from the 1970s and 1980s, were deposited in a lagoon generated by the exploitation of aggregates below the piezometric level of the aquifer, forming a raft with 50,000 m3 of hazardous waste. The different locations, nature and conditions of the waste require different solutions for its extraction and treatment, so the restoration project consists of several phases. The deposited waste produces an effect of confinement in the aquifer, since the bottom level of the waste is lower than the piezometric level. With these conditions, it is critical to establish a procedure for the protection of the groundwater when executing the next phase, consisting of the extraction of waste located below the piezometric level. This article describes the process that has been carried out to select the best alternative from a hydrogeological point of view, considering all the available data obtained in the previous phases of the project. Once all the possible alternatives had been considered and characterized in a reasoned way, we chose the construction of a perimeter barrier around the raft embedded in a clay layer of 2 m thick located in the base of the raft as the best option.