The Bureau of Mines, at the request of local authorities in Rock Springs, Wyoming, investigated and conducted through contracts a multistage program of exploratory drilling and pumped-slurry backfilling of 15 areas of potential subsidence in abandoned mine workings underneath that community. In 1970 a new technique, the pumped-slurry injection process, was tested for the first time in a site adjacent to the city area of severe surface subsidence. Success of this initial testing program, and of a large-scale project in Scranton, Pennsylvania, led to further large-scale projects, funded by Congress, that resulted in the successful backfilling not only of all 15 target areas of potential subsidence in Rock Springs, but also of several areas in other states. The pumped-slurry method was proved to be much superior to the gravity blind flushing method in terms of the amount of solids that could be injected underground through a single borehole. However, there are special conditions that make this technique more or less applicable in different areas or underground configurations, as noted in the report's conclusions.