I concur with Levels 9 and 11 having blind sumps, both Markc and myself looked at them in the past.
One thing you may like to look at is a possible sump in Sunday Mine (COPD page 285).
Myself and markc filled in the old oil drum entrance as it and the associated crawl had collapsed in the past and we dug a 'new' 45deg entrance to intersect the rift above the original crawl.
JSB indicated the rift ending in a choke of large boulders, but when we explored it there was no choke, apart from some HUGE boulders in the roof, after that was a 45 deg slope dropping some 2 to 3m to a water filled pool. The water levels, over the period we were trying to find a way into Aaron's entrance (in the natural passages above but not accessible from Sunday Mine), the water levels did vary. We did think that the water *may* have something to do with the sump/stream in Streaks but we guessed we were a way above that.
Of interest was a very noticable rope rub mark in the wall above and right of the 'sump'.
We also explored Aaron's Entrance workings as well, mostly natural with flat out crawls to a choke at the end, where JSB indicated a shaft had been dug in the past, now collapsed - and dug down towards the choke in Sunday Mine, but to no avail.
We did do a smoke test from Sunday Mine - lower to Aaron's - higher. I lit a smoke 'berm' and succesfully gassed Markc within nano-seconds. There was also voice connection.
Sunday Mine is best accessed with a 6m ladder as the slope is a tad awkward to climb unaided, there is (probably) an old rope tied around the tree to the right of the entrance to clip on to. The entrance is higher and east of the Streaks Lower Entrance, hidden from the road.
Just been looking at my notes for this dig, dated from November/December 2011, and we broke into Sunday Mine (Lower) on 10th Jan 2012.
"There is a pearched sump and no evidence of connection to rest of Sunday Mine (Aaaron's Entrance) although there is a noticable draught at the entrance"
On 13th Feb (2012) "...it was noticed that the sump was low and Markc prodded the metal pole in. The numpty let go and it disappeared!..."
21st Feb 2012 "...Sump had dropped by another 8", Markc retrieved pole!"
As a side note the pole was about 5' long, and it disappeared vertically down into the sump.
29th March 2012 "..trip to see if water levels had changed - which they had, another 20+cm lower,... spent time chasing draughts and theorising...!"
That was our last trip into Sunday Mine as all digging efforts had come to nowt and a certain Treak Cliff Cavern lured us with hidden delights.
