LESS THAN STANDARD SEPARATION WHEN CTLR FAILED TO DETECT A PENDING LOSS OF LATERAL SEPARATION FOR 2 ACR'S AT THE SAME ALT.

Narrative

I WAS WORKING THE R16 POS DURING THE EVENING MSP ARR PERIOD. MLG Y WAS INBND FROM BAE ON THE JUDAS ARR ROUTE AT FL350 AND AN ASSIGNED SPD OF 250 KTS. WDB X WAS OVER-FLYING THE SE CORNER OF THE SECTOR FROM CAD TO MLD AT FL350. WDB X REQUESTED FL390. AT THAT TIME I OBSERVED THE GREAT SPD DIFFERENCE BTWN THE 2 ACFT. FL390 WAS ASSIGNED TO WDB X. I MADE SEVERAL CALLS TO MLG Y TO START HIS DSCNT BUT THERE WAS NO RESPONSE. I WENT BACK TO WDB X AND ISSUED A LEFT TURN TO HDG 240 DEGS FOR THE TFC. DURING THIS PERIOD OF TIME THE D-SIDE HAD CALLED ZAU AND ASKED THEM TO ASSIGN FL330 TO MLG Y AND CHANGE THE ACFT TO MY FREQ. TFC WAS BUSY WITH A LARGE NUMBER OF ACFT INBND. WE WERE METERING TFC INTO MSP AND TIMES HAD GONE FROM AROUND 9 MINS DELAY TO NO DELAY AND BACK TO AS MUCH AS 14 MINS DELAY. THE TFC IN THE MIDDLE WAS NOT ISSUED HOLDING AND WAS FILLING THE GAP BEHIND THE FIRST ACFT HOLDING AT JUDAS. THE THIRD WAVE OF INBNDS STARTED ARRIVING; HOLDING AGAIN BECAME NECESSARY. HOLDING INSTRUCTIONS HAD BEEN ISSUED TO SEVERAL ACFT WHEN THE ARR RATE WAS INCREASED AND I WAS INSTRUCTED NOT TO HOLD. THE CONFUSION FACTOR OF TRYING TO RE-ALIGN ACFT IN TRAIL CONSIDERABLY DIVERTED MY ATTN FROM THE AREA OF MY SECTOR WHERE THE SEP ERROR OCCURRED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATED THAT THE MAIN REASON THIS LOSS OF SEP HAPPENED IS BECAUSE HE WAS BUSY AND THE MLG THAT HAD COME INTO HIS SECTOR FROM ZAU HAD NOT BEEN SENT TO HIS FREQ. HE CLAIMED THAT HE DID NOT SEE THE PENDING INCIDENT BECAUSE THE MLG HAD NOT JOGGED HIS MEMORY BY CALLING HIM. THE WDB WAS HANDED OFF TO HIM FROM AN ADJACENT ZMP SECTOR AND HE HAD WORKED HIM LONG ENOUGH TO KNOW HE WAS NOT A PROBLEM FOR ANY OF HIS ACFT. THE HDOF OF THE MLG FROM ZAU WAS FAR ENOUGH AWAY FROM THE WDB THAT THERE WAS PLENTY OF TIME TO FIX THE PROB. SINCE THE MLG CAME DEEP INTO HIS SECTOR WITHOUT THE FREQ CHANGE; RPTR FAILED TO SEE THE PENDING CONFLICT UNTIL IT WAS TOO LATE TO DO ANYTHING. THE ERROR WAS CLASSIFIED AS A MINOR.