Associated Health and Safety Concerns
Historically harvesting geothermal
energy has been limited to areas near tectonic
plate boundaries. This requires construction underground and near places where potential
earthquakes may occur. However this danger is still a risk but can be limited
and controlled. The first risks are vibrations at the surface. When engineers
build an engineered geothermal system (EGS), they create something like an
earthquake underground. It happens during fracturing, as the hot rock collapses
on itself and slips. The slipping is on a much smaller scale than when a big
fault slips to cause an earthquake we can easily feel. We rarely feel these
man-made quakes at the surface, but if we do, it's as a light vibration. The
rock movements are monitored and controlled. By planting seismometers around
the rock to be fractured, engineers can watch the cracks spread. Since their
own water pumps control the cracking and slipping, if engineers want it to
stop, they can turn off the water.
With good planning, no large earthquakes will occur. Developers wouldn't put an EGS site near a big fault, where high-pressure pumping could disturb the fault. Developers can check regional geological maps to know where big faults are. And just in case, developers measure seismicity at sites before they start working in an area.
Water use poses an even bigger issue than surface vibrations. EGS sites use water during building and operation. The first water gets invested to prop open the cracked rock and measures 2 million gallons or more. Once the rock is unsealed, it will suck down nearby reservoirs, lowering the water table. The good news is that the water can be reused and it doesn’t have to be drinkable water.
Water pollution is another issue. As water circulates through the hot rock, it may pick up arsenic and other poisonous substances. The contaminants shouldn't leak at the surface or into underground freshwater. To try to ensure they don't, engineers keep the circulating water contained. On the surface, it flows through pipes that dive down into the wells, and when the water flows through the cracked rock, a jacket of uncracked rock serves as insulation.
With good planning, no large earthquakes will occur. Developers wouldn't put an EGS site near a big fault, where high-pressure pumping could disturb the fault. Developers can check regional geological maps to know where big faults are. And just in case, developers measure seismicity at sites before they start working in an area.
Water use poses an even bigger issue than surface vibrations. EGS sites use water during building and operation. The first water gets invested to prop open the cracked rock and measures 2 million gallons or more. Once the rock is unsealed, it will suck down nearby reservoirs, lowering the water table. The good news is that the water can be reused and it doesn’t have to be drinkable water.
Water pollution is another issue. As water circulates through the hot rock, it may pick up arsenic and other poisonous substances. The contaminants shouldn't leak at the surface or into underground freshwater. To try to ensure they don't, engineers keep the circulating water contained. On the surface, it flows through pipes that dive down into the wells, and when the water flows through the cracked rock, a jacket of uncracked rock serves as insulation.