I asked on scuba-uk a few years ago about the rumour of further quarries behind stoney cove. I got this reply

There are two other flooded quarries to the SE, but they are smaller and
shallower.  The one next to the road seems to have sheer sides all round.  The
other is up a bridal way, so you should be able to get your car up to it.  There
is a rough scramble to a "beach" area on the south side.  I was told by Stoney
staff that it is 20m or so max and to watch out for getting tangled in barbed
wire etc.  Never dived it myself.