In the Marcellus Shale, they say it costs $3 + per barrel (/bbl) to dispose of water — and $7-$10/bbl to haul it away. If a horizontal well uses 4.2 million gallons of water to frack (that would be a slightly bigger than average well, but it makes my math easy ;-)), then that’s 100,000 barrels (42 gallons=1 barrel).