By June 1856 Bazalgette completed his definitive plans, which provided for small, local sewers about in diameter to feed into a series of larger sewers until they drained into main outflow pipes high. A Northern and Southern Outfall Sewer were planned to manage the waste for each side of the river. London was mapped into high-, middle- and low-level areas, with a main sewer servicing each; a series of pumping stations was planned to remove the waste towards the east of the city. Bazalgette's plan was based on that of Foster, but was larger in scale, and allowed for more of a rise in population than Foster's – from 3 to 4.5 million. Bazalgette submitted his plans to Sir Benjamin Hall, the First Commissioner of Works. Hall had reservations about the outfalls—the discharge points of waste outlets into other bodies of water—from the sewers, which he said were still within the bounds of the capital, and were therefore unacceptable. During the ongoing discussions, Bazalgette refined and modified his plans, in line with Hall's demands. In December 1856 Hall submitted the plans to a group of three consultant engineers, Captain Douglas Strutt Galton of the Royal Engineers, James Simpson, an engineer with two water companies, and Thomas Blackwood, the chief engineer on the Kennet and Avon Canal. The trio reported back to Hall in July 1857 with proposed changes to the positions of the outfall, which he passed on to the MBW in October. The new proposed discharge points were to be open sewers, running beyond the positions proposed by the board; the cost of their plans was to be over £5.4 million, considerably more than the maximum estimate of Bazalgette's plan, which was £2.4 million. In February 1858 a general election saw the fall of Lord Palmerston's Whig government, which was replaced by Lord Derby's second Conservative ministry; Lord John Manners replaced Hall, and Benjamin Disraeli was appointed Leader of the House of Commons and Chancellor of the Exchequer.