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preference of landﬁlling as the only environmentally feasible and safe alternative (Höglund et al., 2007; Jani and Hogland, 2014). However, recent studies have shown the potential to extract these elements from such glass waste with high efﬁciency, both as a decontamination measure and as future secondary raw materials (Jani and Hogland, 2017, 2018). Since valorisation processes of waste to secondary raw materials have speciﬁc quality demands and limits for non-glass materials (Beerkens et al., 2010), obtaining a ‘clean’ glass waste is important. This is a big challenge because during the on-going remedial excavations of some of the sites in the region, glass gets mixed with other waste fractions, further presenting sorting challenges (Mutafela et al., 2018). It is hereby hypothesized that in some dump sections there exist regions of ‘clean’ glass (with little or no other material fractions mixed). It is further hypothesized that it could be possible to identify these glass ‘hotspots’ prior to excavations, which could be carefully exca- vated to avoid mixing of this glass with the other materials, thus obtain a more homogeneous glass fraction for metal extraction processes. Geophysical methods could contribute to such an investigation, as they are known for their usefulness in locating subsurface fea- tures like buried wastes, whose volumes can later be estimated (Bernstone et al., 2000). They have been used in landﬁll investiga- tion procedures (such as drilling of boreholes for groundwater monitoring) as a pre-investigation technique aimed at providing valuable information about waste locations, which helps in drilling grid designs and thus aid to rationalize drilling costs (Zarroca et al., 2015; Dumont et al., 2017). Electrical Resistivity Tomography (ERT) in particular can investigate shallow subsurface electrical structures in various environments. Thus based on resistivity dif- ferences among dumped materials, glass hotspots can potentially be identiﬁed and quantiﬁed faster, cheaper and without well- drilling or trench-digging, using such a non-destructive method (Hsu, et al., 2010). Previously, the method has been successfully conducted in various landﬁll and waste dump studies (Bernstone et al., 2000; Pomposiello et al., 2012; Çınar et al., 2015; Abdulrahman et al., 2016; Dumont et al., 2017), although no such study in a glass waste dump is documented. The success of the method in old glass dumps would potentially result in well- coordinated excavation activities and obtaining of more homoge- neous glass waste for metal extraction and other recycling processes. This study, therefore, aimed to investigate the potential for ERT to map glass hotspots for future metal recovery. The investigation was coupled with digging of veriﬁcation test pits (TPs) to identify materials registering different resistivities. The study also aimed at characterising physico-chemical properties of the excavated hotspot materials, since waste management and resource recovery cannot be planned and implemented well in the absence of accu- rate and reliable waste composition data (Edjabou et al., 2015). 2. Materials and methods 2.1. Study sites The study was conducted at Alsterfors glass factory dumpsite and Madesjö glass waste dump, both located in south-eastern Swe- den as shown in Fig. 1. 2.1.1. Madesjö glass waste dump This dump is located in Nybro Municipality in a moraine region with granite bedrock and a shallow soil depth estimated at 3–5 m (SGU, 2019). Open dumping at the site started with municipal solid waste (MSW) in 1960 until 1969 when mostly crushed glass with some demolition waste from Orrefors glass factory began to be Fig. 1.Alsterfors and Madesjö glass dumps in south-eastern Sweden (Map data 2020 Google). 214 R.N. Mutafela et al./Waste Management 106 (2020) 213–225