MAIN CABIN DOOR NOT PROPERLY CLOSED UNABLE TO PRESSURIZE. RETURN LAND.

Narrative

DURING TAXI OUT AT DTW FOR FLT TO ROC; LEAD F/A CALLED COCKPIT AND RPTED AIR LEAK AROUND MAIN FWD CABIN DOOR. I PARKED ALONG SIDE RWY 21R AND WENT BACK TO CHK DOOR MYSELF. S/O HAD PRESSURIZED ACFT AND NO LIGHT WAS ON S/O ANNUNCIATOR PANEL; INDICATING DOOR WAS PROPERLY CLOSED. UPON INSPECTION DOOR SEEMED NORMAL AND HANDLE WAS SEATED. NORMAL TKOF WAS MADE (LATER LEAD F/A RPTED THAT NOISE SUBSIDED DURING TKOF ROLL AND DOOR SEEMED NORMAL). IMMEDIATELY AFTER TKOF S/O WAS UNABLE TO PRESSURIZE ACFT IN CLB AND LEAD F/O CALLED RPTING VERY LOUD AIR NOISE AROUND MAIN CABIN DOOR. NOISE WAS VERY NOTICEABLE ON INTERPHONE. DUE TO INABILITY TO PRESSURIZE AND ALSO DUE TO LOUD AIR NOISE IN CABIN; IT WAS DECIDED TO IMMEDIATELY RETURN TO DTW TO HAVE DOOR CHKED. A NORMAL LNDG WAS MADE. ABOUT 10 MINS OF AIR TIME HAD ELAPSED. UPON ARR AT GATE; MECH NOTICED DOOR (FWD MAIN CABIN) WAS PARTIALLY OPEN (STILL NO LIGHT ON S/O PANEL). AFTER WORKING WITH DOOR FOR ABOUT 15 MINS MECH SUCCESSFULLY CLOSED DOOR AND FLT DEPARTED WITH NO FURTHER PROBS. MAIN CABIN DOOR APPARENTLY HAD NOT INITIALLY BEEN PROPERLY CLOSED. ALTHOUGH DOOR IS A PLUG TYPE DOOR AND CANNOT OPEN FULLY IN FLT; THE LACK OF PRESSURIZATION CAUSED US TO RETURN TO BASE. STRONGLY RECOMMEND THAT GND PERSONNEL RESPONSIBLE FOR CLOSING CABIN DOORS BE FULLY TRAINED TO DO SO. MANY GND PERSONNEL LACK SUFFICIENT STRENGTH TO ACCOMPLISH THIS PROPERLY.