There are some systems that actually will take a circle and drop it just below the surface of the water and have the oil kind of flow into it, almost like a drain, recover it and pump it out.

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One theory is that the summer sun melts ice on the surface of the glacier which creates pools of water which then flow into moulins -- narrow tubular shafts in the glacier.

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Most of that water stays in the well, but 20% returns to the surface as flow-back in the days and weeks after fracking.

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Rather, as a consequence of injecting water and sand into the shale formation to crack the rocks so gas and oil will flow, massive amounts of waste water comes back to the surface with significant amounts of contaminants as a result of leaching out salt, heavy metals and trace amounts of radioactive materials from the rock formation itself.

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Satellites at Mars have long captured images of channels on the planet's surface that were cut by some kind of flow, assumed to be liquid water.

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Detailed studies of the surface indicate that these were formed by a lake caused by the flow of underground water that periodically made its way to the bottom of the crater.

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