German construction contract procedures (VOB) – Part C: General technical specifications in construction contracts (ATV) – Horizontal directional drilling works
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 09/01/2016

German construction contract procedures (VOB) – Part C: General technical specifications in construction contracts (ATV) – Horizontal directional drilling works
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 08/01/2015