TWR LCL CTLR; WORKING COMBINED POS; WAS DISTR BY MULTIPLE TASKS AND MISJUDGED ANTICIPATED TFC SPACING BTWN ARR AND DEP TFC. TWR GND CTLR INSTRUCTOR SAW DEVELOPING SIT; BUT WAS ALSO DISTR WITH HIS TASK; TRAINING; ADVISING LCL CTLR AS ACFT WAS ON SHORT FINAL. LNDG TFC WAS 3200 FT FROM DEP TFC; 4500 FT REQUIRED. LCL CTLR ADVISED FACILITY MGMNT 4 DAYS AFTER INCIDENT.

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I HAD STARTED MY SHIFT BY WORKING LCL CTL AND BEING SIGNED ON AS CIC DUE TO STAFFING LIMITATIONS AND TRAINING IN PROGRESS. THE UNIVERSITY HAD JUST STARTED FLYING HEAVILY BECAUSE THE WX HAD IMPROVED SLIGHTLY. I WAS RESTR TO RWY 17L ONLY DUE TO PERSONNEL ON RWY 17R. AFTER ABOUT 1/2 HR ON POS WITH TFC INCREASING; THE PERSONNEL EXITED RWY 17R. AT THAT TIME I MOVED ABOUT 1/2 OF THE TFC TO THAT RWY AND SPLIT THE POS TO RELIEVE FREQ CONGESTION AND WORKLOAD. THE VISIBILITY HAD ALSO BECOME A FACTOR WITH ACFT RETURNING TO THE ARPT AND THE D-BRITE OTS. ACFT IN THE PATTERN WERE BECOMING VERY HARD TO SEE. 6 MINS AFTER THE SPLIT I HAD A SEMINOLE THAT REQUESTED A FULL STOP FOLLOWING A PIPER CADET THAT I HAD CLRED FOR STOP AND GO. I CHANGED THE CADET TO TOUCH-AND-GO ONLY DUE TO TFC; WHICH HE ACKNOWLEDGED. I POINTED OUT TFC TO THE SEMINOLE AGAIN WHO WAS HAVING A HARD TIME SEEING IT. THE SEMINOLE RPTED TFC IN SIGHT; SO I CLRED HIM TO LAND. WITH 5 OTHER ACFT ON MY FREQ; I MADE A COUPLE MORE XMISSIONS. THEN I NOTICED THE CADET MOVING SLOWLY ON THE RWY. I TOLD THE CADET TO USE MINIMUM GND TIME. THINKING THAT THIS HAD SOLVED THE PROB; I MADE A COUPLE MORE TFC CALLS TO OTHER ACFT FOR SEQUENCING; DURING WHICH I HEARD A CTLR SAY 'SEND HIM AROUND.' I SAW THE SEMINOLE HAD CROSSED THE APCH END AT THAT TIME AND THE CADET WAS AIRBORNE; BUT ONLY 3200 FT DOWN THE RWY. 4500 FT REQUIRED. SUPPLEMENTAL INFO FROM ACN 392329: I DID NOT ACTUALLY SEE THE 'ERROR' BUT DID SAY SOMETHING TO MY SUPVR ABOUT 'CTLR A' HAVING A BAD DAY. IN HINDSIGHT I SHOULD HAVE TAKEN IT A STEP FURTHER. HOWEVER; I LEFT IT UP TO 'CTLR A'S' INTEGRITY. 4 DAYS PASSED BEFORE IT WAS FINALLY RPTED.