The total deposits held by BSB Bancorp, the parent of Belmont Savings Bank, surpassed $1 billion for the first time last quarter, tripling what the bank held when CEO Robert Mahoney took the helm five years ago. Belmont Savings (Nasdaq: BLMT) finished the first quarter of 2015 with $1.04 billion in deposits and $1.47 billion in assets, increases of 6 and 3 percent from the end of 2014, respectively, it said in a statement released Friday.