Environmental Engineering Reference
In-Depth Information
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Land use
—Land footprints for hydrothermal power plants vary consider-
ably by site because the properties of the geothermal reservoir fluid and
the best options for wastestream discharge (usually reinjection) are highly
site-specific. Typically, the power plant is built at or near the geothermal
reservoir because long transmission lines degrade the pressure and tem-
perature of the geofluid. Although well fields can cover a considerable area,
typically 5 to 10 km
2
or more, the well pads themselves will only cover
about 2% of the area.
•
Land subsidence
—If geothermal fluid production rates are much greater
than recharge rates, the formation may experience consolidation, which will
manifest itself as a lowering of the surface elevation (i.e., surface subsidence).
This was observed early in the history of geothermal power at the Wairakei
field in New Zealand where reinjection was not used. Subsidence rates in one
part of the field were as high as 0.45 m per year (Allis, 1990). Wairakei used
shallow wells in a sedimentary basin. Subsidence in this case is very similar
to mining activities at shallow depths where raw minerals are extracted, leav-
ing a void that can manifest itself as subsidence on the surface.
•
Induced seismicity
—In normal hydrothermal settings, induced seismic-
ity has not been a problem because the injection of waste fluids does not
require very high pressures. However, the situation in the case of many
EGS reservoirs will be different and requires serious attention. Induced
seismicity continues to be under active review and evaluation by research-
ers worldwide.
•
Induced landslides
—There have been instances of landslides at geothermal
fields. The cause of the landslide is often unclear. Many geothermal fields
are in rugged terrain that is prone to natural landslides, and some fields
actually have been developed atop ancient landslides.
•
Water resources
—Geothermal projects, in general, require access to water
during several stages of development and operation.
•
Disturbance of natural hydrothermal manifestations
—Although numer-
ous cases can be cited of the compromising or total destruction of natural
hydrothermal manifestations, such as geysers, hot springs, or mud pots, by
geothermal developments (Jones, 2006; Keam et al., 2005), EGS projects
will generally be located in non-hydrothermal areas and will not have the
opportunity to interfere with such manifestations.
•
Disturbance of wildlife habitat, vegetation, and scenic vistas
—It is undeni-
able that any power generation facility constructed where none previously
existed will alter the view of the landscape.
•
Catastrophic events
—Accidents can occur during various phases of geo-
thermal activity, including well blowouts, ruptured steam pipes, turbine
failures, fires, etc.
•
Thermal pollution
—Although thermal pollution is currently not a specially
regulated quantity, it does represent an environmental impact for all power
plants that rely on a heat source for their motive force.
