As mentioned above, the requirements for environmental monitoring vary as a function of the reservoir context, the project design and the operational phase. Thus, depending on the frequency and severity of the observed/expected impacts, the monitoring system should be adapted. Furthermore, it is important to characterize in advance the initial environmental parameters to correctly evaluate the impact of the geothermal exploitation. In general, the following items should be monitored to minimize environmental impacts.
Due to pumping and reinjection activity, induced seismicity, slow in-depth and surface deformations (creep, subsidence and uplift) may occur, causing damages on buildings and risking human safety. To monitor those physical processes, a multi-parametric geophysical ground motion network may be designed, including seismological and geodetic measurements.
Monitoring geothermal resource features is a necessary preventive process to anticipate changes of reservoir and/or installation conditions. Monitoring may include the continuous measurement of pressure, temperature and flowrate, but also punctual analysis of the resource’s geochemical parameters (e.g. electrical conductivity, pH, Eh, as well as major and trace elements).
Gas, liquid, and solid wastes may be produced during geothermal exploitation and need to be monitored. For gas, continuous or punctual measurements of the plant’s atmosphere and emissions may be required. Liquid waste could be monitored by high-frequency analysis of the basic physico-chemical parameters coupled with occasional analysis of the fluid geochemistry and bacterial activity. For solid wastes, the main concerns include the formation of secondary mineral deposits (silica, carbonates, metals, radioactive material …). The monitoring of those deposits may include geochemical and radioactive characterization, but also in-situ measurements of deposition and corrosion processes by online sensors.
- Underground water monitoring
To avoid groundwater contamination during geothermal exploitation, a network of piezometers equipped with online sensors could continuously monitor peripheral wells to measure the level and the physico-chemical parameters of the water body.
Surface disturbances mainly concern noise and visual impacts. Noise level monitoring during the drilling phase is thus necessary to meet the legal limits. Visual impacts are difficult to monitor but may be mitigated by the installation of visual barriers around the site.