@inproceedings{sgem2019s02021,
  title = {ECOLOGICAL STATUS OF OLD OIL BOREHOLES IN CENTRAL NORTHERN BULGARIA},
  author = {Sava Kolev},
  booktitle = {SGEM International Multidisciplinary Scientific GeoConference EXPO Proceedings; 19th SGEM International Multidisciplinary Scientific GeoConference EXPO Proceedings19th, Science and Technologies in Geology, Exploration And Mining},
  year = {2019},
  pages = {161-168},
  publisher = {STEF92 Technology},
  doi = {10.5593/sgem2019/1.2/s02.021}
}