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In principle, the environmental impacts of direct use are in the same categories as with power generation. However, but the degree to which utilization affects the environment is proportional to its scale. As the various phases of direct utilization are on a much smaller scale and the heat/fluid production from the subsurface are considerably less than in power generation, the environmental effects of direct use are correspondingly smaller. Possible effects are listed i Table 3. Read more…

Land subsidence
The weight oaf the rock column above a geothermal reservoir is supported by the rock matrix on one hand, and by the content of the pore volume on the other. Increasing production of the pore fluid leads to reduction of the pore pressure, which in turn causes the sinking of the earth surface. Geothermal fluid withdrawal is comparable to large-scale pumping for agricultural purposes (irrigation). Smaller subsidence is experienced in solid (e.g. crystalline) rocks with low porosity. Pronounced subsidence has been experienced in the Wairakei field, New Zealand: the maximum vertical displacement of the surface is now over 10 m; with an average increase of about 0.4 m per year; at some places even higher (Figure 8). Read more…

Discharges to surface waters and into the subsurface
The chemical composition of fluids from geothermal reservoirs varies over wide ranges, from near neutral and relatively dilute values (<200 ppm chloride at pH > 9, Hveragerdi/Iceland) up to acidic and highly saline concentrations (150’000 ppm chloride at pH < 5, Salton Sea/USA). In addition, significant amounts of SiO2 as well as further elements like B, As, Li and Hg can be present. Concentrations in liquid effluents vary not only locally but also with the (condensing or notcondensing) power plant type. Discharge of effluents into surface waters like rivers is applied only at a few places (e.g. Wairakei/New Zealand); in many countries there are legal restrictions with discharge limits. Read more…

Land use
The various development activities and installations need land surface, temporarily or steadily. After constriction completions substantial areas become free again, leaving some restrictions e.g. for agricultural use. Compared to other power generation technologies the geothermal option has the advantage that the production takes place at the resource, whereas for other technologies like coal-fired or nuclear power plants the –often extended– mines are located far away. Read more…

Geothermal power generation creates a much lower emission of greenhouse gases than most other technologies. In any comparison it is important to consider the entire production cycle is considered, i.e. all phases before, during and after power plant operation. Geothermal power plants have particularly low CO₂ emissions compared to other technologies; when CO₂ abatement is concerned, they are therefore more attractive options for power generation than coal, oil or gas sources (Figure 1). Read more…