I am working at a construction site and came accross this issue. a borehole needs to be expanded in length inside a container-office. Working space is as little as 6m x 3m (19ft by 9.5ft). Height of the container is about 2m (6'6"). Heigt can somehow be altered up to 5 meters (16'5"). Borehole diameter is 150mm (6"). Current depth of the borehole is 30 m (98 ft). The depth should be increased to 42m (138 ft). See the attached sketch for details.
The borehole was bored before the containers were placed. It is used to measure water levels with piezometric sensors inside them. Water levels have dropped lower than expected and the borehole needs to be expanded in depth to reach lower groundwater deposits. Containers cannot be moved, and the location cannot be changed since this specific borehole is in a sensitive location, so please do not offer boring a new borehole outside the container.
What method or which equipment can be used to work in a small container space and can reach such depth.