Teoharov, M., et al. “Pedogenesis of Technosols from Chukurovo Соаl Basin in Intiman Sredna Gora”. Bulgarian Journal of Soil Science, Agrochemistry and Ecology, vol. 44, no. 3, Sept. 2010, pp. 12-22, https://agriacad.eu/ojs/index.php/bjssae/article/view/4268.