Removing base of chimney which was leading to trapped moisture

[TriMattRdg]

On the ground floor the lower section of our chimney breast has been removed and supported by a lintel as shown. When I have removed flooring it has been sitting on concrete hearth appears to have trapped moisture . After a few days it’s drying out but I’m keen to lower the level to get some air flow .
How low can I break this out ? Ideally I want to take out the protruding concrete section and also the section underneath chimney itself to allow air flow and so it doesn’t damage flooring when replaced

 

[blup]

The damp is likely from under the hearth because there won’t be a dpm . It’s a case of digging it out to below the floor and dpc level, but best to remove the whole lot as the joist supporting the floor boards may also be in contact with the damp.

 

[TriMattRdg]

The damp is likely from under the hearth because there won’t be a dpm . It’s a case of digging it out to below the floor and dpc level, but best to remove the whole lot as the joist supporting the floor boards may also be in contact with the damp.

Thanks are the bricks either side supported in anyway by the infill in the middle? Ideally I would like to lower this too (leaving the brickwork obviously)

 

[blup]

Thanks are the bricks either side supported in anyway by the infill in the middle? Ideally I would like to lower this too (leaving the brickwork obviously)

The bricks should rest on the sub floor to the same depth as the wall. They should be toothed into the main wall every few courses