Identification of Construction Sludge Generated by Earth Drilling

Earth drilling is a method of making trenches for constructing piles. In this method, bentonite slurry is used to protect the porous wall during the trench excavation. The sludge from this method is defined as industrial waste under Japanese law and must be treated with an appropriate method. Nevertheless, some companies dispose of construction sludge illegally. However, there are no analytical methods for identifying bentonite sludge and it is unknown whether identification is possible. To identify sludge, bentonite must be detected in suspicious soils, but smectite clay, which is the main component of bentonite, is often contained in soil, and it is unknown whether the smectite in soil interferes with detection of bentonite from sludge.To detect bentonite in construction sludge, we analyzed soils spiked with bentonite at various concentrations using X-ray diffraction. We also examined construction sludge from earth drilling with or without HCl treatment. The bentonite peak was observed in all spiked samples, even when the bentonite concentration was 20% and the soil contained smectite. In construction sludge, bentonite peaks were observed without HCl treatment; however, they were smaller than expected. HCl treatment removed the chlorite peak, which was near that of bentonite, allowing for easier identification of bentonite peaks. We demonstrated that the construction sludge could be detected by identifying bentonite. This was a pilot study to identify industrial waste and provided new insights into the forensic analysis of environmental crime samples.