The two stable wells are large-diameter steel-cased and have been geophysically monitored in detail since 1996.
Ulrich Harms, Jochem Kück 2016, 'Superdeep Tests and Experiments at 9.1 km and 4 km', Journal of large-scale research facilities JLSRFhttps://jlsrf.org/index.php/lsf/article/view/132. Retrieved from DOAJ CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0/legalcode)