I fail to understand why anyone can't understand that: The subsurface is complex with aquifers, oil, gas, natural fractures, preferential pathways, porous and non-porous strata, etc. You can poke a shallow hole into it and tap into vast, and in some cases, ancient, fresh water supplies You can poke a deeper hole in it and tap into underground formations containing fossil oil and/or gas The deeper hole you poked through the water bearing layers and confining strata, combined with injection of "stuff" under high pressure.. Forces oil, gas, and injected "stuff" to migrate outward and upward through existing or newly created fractures or punched holes to areas where it wasn't before Potentially contaminating water supplies with "stuff" or the petroleum, or gas its pushing around. Or grossly oversimplified: Put two straws in a orange. Pump crap into one and start sucking on the other. Pretty soon you'll taste crap.