The one in Punjab has fallen from a couple of metres below the surface to, in parts, hundreds of metres down.

旁遮普邦的一处地下水下降了好几米，从地上算，已经是百米以下。

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Communities of microorganisms have been found hunkered down in groundwater as far as 5 km below the surface of the land.

地表之下5公里的地下水中也发现了微生物群落。

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You are only able to see above the surface of their spending, meaning you have no idea what's happening down below.

你只看到他们表面上花钱的情况，不知道人家在你看不到的地方过什么样的日子。

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Phase II, planned for 2011, will identify both aquifers down to 3, 000 meters below the surface, study soil composition and aquifer replenishment, and prioritize areas for agricultural development.

UNESCO: launches initiative to identify groundwater and alleviate water shortages in Iraq | United Nations Educational, Scientific and Cultural Organization

To torment the players further, the USGA shaved down the banks below seven of the greens, so that balls that just barely miss the putting surface, or are chipped just a smidge too hard, can sometimes race 10 to 20 yards away.

WSJ: 2012 U.S. Open: An Olympian Effort Just to Survive

Things get murkier still when oil companies drill deep below the surface of the ocean floor, since even robots can't go down there to see what's going on.

CNN: John D. Sutter