East Pit East Opencast Coal Site (operated by Celtic Energy) is situated on the northern outcrop of the South Wales coalfield in the upper Amman Valley near the villages of Tairgwaith, Brynamman and Cwmllynfell where the mine produces high quality anthracite coal from the twelve individual coal seams that are lying up to one hundred and fifty metres below the surface.
Geographically the site is an extension to the previous East Pit Extension site which produced essential supplies of anthracite for domestic, industrial and power generation markets (NPRN 405901), and was named after the East Pit Colliery complex that once dominated the area in the early 1900s.
The site has been in operation since 2005 and covers an area of approximately 400 hectares, although the operational area is just 80 hectares, the remainder of the site comprising soil and overburden storage areas, coal stocking, water treatment areas and an office and workshop complex.
Additional source: http://www.coal.com/operations/operations-east-pit-east/

David Leighton, RCAHMW, 16 May 2017