EMB145 FLT CREW REPORTS SMOKE AND FUMES ON DEPARTURE AND AFTER TURNING OFF PACK #1 RETURN VISUALLY FOR UNEVENTFUL LANDING.

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THERE WAS A MECHANICAL MALFUNCTION WITH OUR ENVIRONMENTAL SYS; WHICH WE ASSUMED WAS COMING FROM PACK #1. WE WERE DEPARTING FROM ZZZ AND SHORTLY AFTER TKOF ON INITIAL CLBOUT WE EXPERIENCED A STRONG BURNING SMELL. WE LEVELED OFF AT 4000 FT TO TROUBLESHOOT THE PROB AND THEN STARTED EXPERIENCING SMOKE. WITH OUR KNOWLEDGE OF A PREVIOUS WRITE-UP IN THE LOG WE ASSUMED IT WAS COMING FROM ENVIRONMENTAL SYS PACK #1; SO WE TURNED IT OFF AND TURNED AROUND TO LAND BACK IN ZZZ. THE APCH WAS A VERY SHORT AND QUICK VISUAL LNDG BACK TO RWY XXL AND WE WERE IN THE AIR FOR A TOTAL OF 10 MINS. WE DETERMINED THERE WAS A PROB RIGHT AFTER TKOF WHEN WE SMELLED A STRONG BURNING SMELL COMING FROM OUR PACK. AS SOON AS WE LEVELED OFF; WE NOTICED THE SMOKE. AFTER WE DETERMINED THE PROB WE TURNED AROUND AND LANDED. WE LEVELED OFF AT 4000 FT TO TROUBLESHOOT THE PROB. ONCE WE SAW SMOKE WE WERE STILL ON AN EXTENDED UPWIND; SO WE JUST TURNED DOWNWIND AND DID A QUICK VISUAL APCH AND LNDG FOR RWY XXL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: SMOKE AND FUMES WERE IN FACT CAUSED BY AN OIL LEAK IN THE NUMBER ONE PACK WHICH HAD BEEN THE SUBJECT OF TWO PREVIOUS LOG BOOK ENTRIES. ONCE THE PACK WAS SECURED THE FUMES DISPERSED RATHER QUICKLY AND A NORMAL LANDING ENSUED.