U can file RTI application with Public Information Officer (PIO) of CIVIL SUPPLIES DEPARTMENT or with PIO of DM office (with request to forward it to correct PIO) for this information. RTI application as per WEST BENGAL RTI RULES - RTI Guide
For detailed information on how to draft & file an RTI application, please see the "All About RTI" links on the homepage & RTI Guide section of the portal.
Below Poverty Line is an economic benchmark and poverty threshold used by the government of India to indicated economic disadvantage and to identify individuals and households in need of government assistance and aid. It is determined using various parameters which vary from state to state and within states. Source: Below Poverty Line (India) - Wikipedia, the free encyclopedia
U can file RTI application for this information. Please see post # 4 (above) for details.