**5. Atmospheric emissions**

Currently, there are six flash-type 20-MWe power-plant units at Amiata Volcano, three for each of the two geothermal fields of "Bagnore" and "Piancastagnaio" (cf. **Figures 1** and **2**). In addition, for both fields, there is a secondary use of the residual heat for home and greenhouse heating.

To force evaporation of the geothermal fluid, the three fans of each cooling tower pump about 4–6 (\*10<sup>6</sup> Nm3 /h) of fresh air into the base of the tower (cf. **Figure 2b**) [9, 56], and emit the same amount of air plus a fraction of geothermal fluid (much of which is evaporated into the airflow) from the top of the towers (**Figure 2b**). Because from about one-half to three-quarters (cf. [7, 9]) of the geothermal fluid that enters a power plant is emitted to the atmosphere from the cooling towers, a total in the range of 360–585 t/h of geothermal fluids is lost to the atmosphere. In addition to carbon dioxide (CO2), and even if there are abatement technologies for mercury (Hg) and hydrogen sulphide (H2S) (the AMIS—Abatement of Mercury and Hydrogen Sulphide) and for ammonia (NH3) (with the addition of sulphuric acid) the emissions still have high contents of these pollutants and of additional pollutants such as sulphur dioxide (SO2), methane (CH4), arsenic (As), antimony (Sb), boric acid (H3BO3), selenium (Se), cadmium (Cd), chromium (Cr), manganese (Mg), nickel (Ni), lead (Pb), copper (Cu), and vanadium (V) (**Table 2**).

In particular, CO2 and CH4 emissions are over 6.7 � <sup>10</sup><sup>5</sup> and 1.4 � <sup>10</sup><sup>4</sup> t/a, respectively. These two compounds produce an equivalent greenhouse-gas effect that is calculated to be comparable to the emissions of gas-fired power plants per Mega Watt of electrical energy produced [57]. Orlando et al. [58] suggest that this CO2 is generated by the interaction of the geothermal fluids with magnesian siderite in the phyllites of the geothermal reservoir. In addition, the emissions of H2S that amount to 1.2 � <sup>10</sup><sup>3</sup> t/a, of SO2 that consist of 2.7 t/a, and of boric acid have an acidrain potential that is about twice that of coal-fired power plants per MW of electrical energy produced [57].

In addition, the emissions of NH3 amount to 2.1 � <sup>10</sup><sup>3</sup> t/a (**Table 2**) and constitute a notable contribution to the formation of secondary fine particles (aerosols). In 2017 these emissions were close to half of the total Tuscany ammonia emissions [5, 59]. Relative to mercury, the emissions are indeed relevant even with the abatement technology in place; including mercury and mercury compound, they total 1.17 t/a. While the emissions of arsenic and arsenic compounds sum to about 79 kg/ a. To better emphasise the relevance of these values, the only mercury and arsenic emissions are, respectively, 42.5% and 7.5% of the total emissions of these pollutants from all Italian industries [5]. Note that an amount approximately equal to that of


#### **Table 2.**

*Today's approximate emissions per year of some compounds and metals from the power plants of the two Amiata volcano geothermal fields of "Bagnore" and "Piancastagnaio".*

the Amiata Volcano area is emitted by the geothermal power plants of the Larderello area in central Tuscany. Before the emplacement of the mercury abatement technology, the emissions for mercury were probably an order of magnitude higher. The actual amount of mercury emitted from geothermal power plants as a total in the Amiata Volcano geothermal area is not known. However, a gross estimate can be made based on the available data published yearly by the Agenzia Regionale per la Protezione Ambientale della Toscana (ARPAT) since 2002, and the set of measurements made by ENEL [60]. Based on these measurements the total Mercury emitted by the Amiata Volcano power plants could be in the order of 50–60 t in the past 60 years.

Regarding the composition of the fine particles collected in the Piancastagnaio area Tommasini et al. [9] show that they are enriched relative to the fine particles collected in Firenze and Arezzo (these are among the Italian cities that have the largest concentrations of fine particles in the air) in sodium, vanadium, zinc, phosphorous, sulphur, tantalum, caesium, thallium, thorium, uranium, and arsenic (**Figure 10**). Barazuoli et al. [61] report a set of analyses of the condensates produced by several geothermal wells in the Bagnore and Piancastagnaio geothermal fields. From these data, we calculate that the condensate from the geothermal fluids can have a total solid concentration (*Cs*) in solution that is in the order of 1 g/l.

*The Geothermal Power Plants of Amiata Volcano, Italy: Impacts on Freshwater Aquifers… DOI: http://dx.doi.org/10.5772/intechopen.100558*

#### **Figure 10.**

*Enrichment factor (EF) of heavy metals in the fine particles collected at Piancastagnaio geothermal field (after [9]). The arrow point to the elements that are enriched in the Piancastagnaio area in comparison to the concentrations found at Firenze (traffic station) and Arezzo (urban background station). Note that the EF scale is logarithmic: Small upward increases in the positions of points on the graph correspond to significant enrichments.*

Recalling that the volume of condensate emitted to the atmosphere (*Vc*) is estimated to be in the order of two-third of the about 130 t/h of geothermal fluid used in a 20 MWe geothermal power plant and that the airflow through the cooling towers

(*Af*) is about 5 Mm3 /h, doing the appropriate units conversion and assuming an equivalence between litres and kg for liquid water solutions, we may calculate:

$$\mathbf{C\_{PM}} = \frac{\mathbf{C\_s} \times \mathbf{V\_c}}{A\_\mathrm{f}} = \frac{10^6 (\mu\mathrm{g}/\mathrm{l}) \times 87 \ast 10^3 \,\mathrm{(l/h)}}{5 \times 10^6 \,\mathrm{(m^3/h)}} \approx 17 \ast 10^3 \,\mathrm{(\mu g/m^3)}.\tag{5}$$

That is, the order of magnitude estimates of fine particles concentration (*Cpm*) emitted from the cooling towers of a 20–MWe geothermal power plant should be in the order of 17 \* 10<sup>3</sup> (μg/m3 ), which is a significant amount. This value should be incremented by the fine particles that are present in the non-condensable gas stream [9]. The primary and secondary fine particles resulting from the geothermal power plant emissions seem to be visible in the haze that is left after the evaporation of the H2O cloud (**Figure 11**). During periods that the power plants are out-ofservice emissions to the atmosphere are even more significant and are unaccounted for (**Figure 12**). In fact, during these periods, because the vapour production from the geothermal wells cannot be stopped, the geothermal fluids are emitted directly to the atmosphere without any pollutant abatement technology.

At the moment, there is no available direct measurement of the concentration of fine particles at the exit of the cooling towers of each power plant. Thus, we can only compare the value calculated above with the fine-particle concentrations of 10–30 μg/m<sup>3</sup> (average 15 μg/m<sup>3</sup> ) measured by Tomassini et al. [9] in the Piancastagnaio geothermal field area approximately 1–2 km uphill of the power plants. Given the approximations made and the fact that we are calculating a potential maximum fine-particle concentration in the emissions, to find a dilution factor of about a thousand, from the emission towers to the place where measurements were taken (1–2 km uphill of the power plants), appears to be consistent with atmospheric modelling of the power plant emissions (cf. [6]). In this respect, we observe that the power plants are located all around the village of Piancastagnaio from NE to E to SW and to S at a distance smaller than 2 km. In addition, in the western direction there are the three power plants of the Bagnore geothermal field at just over 10 km distance. Therefore, no matter from what direction blows the wind (apart from NW and N) the fumes from the power plants always reach the village of Piancastagnaio. It is only when there are strong winds from the north and northwest that the concentration of fine particles decreases [9]. We think that during winter thermal inversion events, when the fumes of the power plants can accumulate and linger in the lower atmosphere even for a few days, the concentration of fine particles could increase significantly above the values that have been occasionally measured up to now.

Finally, we have to recall that some of the elements emitted to the atmosphere, in addition to radon, are radioactive. Geothermal energy production has been included already many years ago [62] among the human activities that generate Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM). In this respect, very little is known about the geothermal power plants of Amiata Volcano.

#### **6. Discussion and conclusions**

Geothermal exploitation for the production of electricity at Amiata Volcano uses flash-type power plants with cooling towers that evaporate much of the geothermal fluid to the atmosphere with minor reinjection, that is from about one-quarter to one-half, of the fluid produced [7, 9]. In addition, the flash of the geothermal fluid is mainly occurring at depth forcing a significant depressurization of the geothermal system from the original undisturbed conditions (cf. [21]).

*The Geothermal Power Plants of Amiata Volcano, Italy: Impacts on Freshwater Aquifers… DOI: http://dx.doi.org/10.5772/intechopen.100558*

#### **Figure 11.**

*Emissions from (a) the PC3 (b) the PC4-PC5 geothermal power plant units with the village of Piancastagnaio in the background. Note how after the evaporation of the water vapour in the atmosphere, a cloud of fine particles persists, much like the fumes emitted from major coal- or oil-fired power plants.*

As a consequence, this depressurization propagates upward inducing a corresponding decrease in pressure at the base of the freshwater aquifer contained in the volcanic edifice [26]. Accordingly, the water table has substantially dropped, reaching in the centre of the volcano a decline of about 250 m (compare

#### **Figure 12.**

*(a) The emissions during the out-of-service of the PC3 geothermal power plant occurred on the 10 of may 2005. (b) Cloud of toxic geothermal fluids, emitted from the Bagnore 25 geothermal well, flowing toward home on 21 November 2007; the inhabitants had run away from their houses.*

**Figure 3a** and **b**) and forming in the Southeastern sector of the volcanic edifice a minimum in the water table (**Figure 3b**), as it has been measured by Compagnia Mediterranea Esplorazioni [24], Marocchesi [29], and its time changes monitored by Manzella [30] with oscillations between 700 and 600 m asl. In December 2018, this minimum had an elevation of 746.39 m asl at the ENEL4 piezometer (**Figure 8**). The presence of this minimum demonstrates that the water is drained downward from the volcano into the rocks that contain the geothermal systems (the Anhydrites and the metamorphosed Tuscan Units; **Figure 1b**) via the many faults and the

#### *The Geothermal Power Plants of Amiata Volcano, Italy: Impacts on Freshwater Aquifers… DOI: http://dx.doi.org/10.5772/intechopen.100558*

volcanic conduits that cut the edifice and its basement (cf. [4, 8], and references therein). This impact of geothermal fluid production on freshwater aquifers need to be evaluated in detail when commissioning geothermal power plants. On the other hand, if a balanced production-reinjection volume of geothermal fluids were to become mandatory, for instance by using air-coolers in place of the evaporative towers, the impact on the superficial aquifers would be substantially reduced because the recharge from freshwater aquifers would need to compensate, as a firstorder approximation, only for the reduced volume of the cold water reinjected relative to hot-water produced.

At Amiata Volcano, geothermal fluid production with its associated small amount of reinjection results in several induced earthquakes that are rarely felt by the population. However, a *ML* = 3.9 induced earthquakes occurred on April 1st 2000 [40, 41, 49], which generated significant damages to houses and buildings in general but luckily no deaths. Given the volcanic spreading process, we suggest that an *ML* = 4–5 earthquake could be triggered in the next few decades. Even if these magnitudes are not indeed large, the fact that the buildings of the many medieval villages in the area are old and not constructed to modern seismic standards, there is the likelihood of significant damages and potential deaths. Thus, increasing the amount of reinjected fluid relative to produced geothermal fluid could increase the earthquake risk, because it has been suggested that earthquake magnitude is related to the volume of fluids reinjected [63]. The suggestion of increasing reinjection to reduce the impact on the freshwater aquifer runs counter to reducing induced seismicity. Retrofitting all buildings, although very expensive, could be in the long term a reasonable answer because even larger-magnitude earthquakes unrelated to geothermal energy production, may occur in this area.

The non-condensable gases, in addition to the evaporation of a large fraction of the geothermal fluid in the cooling towers, produce significant emissions to the atmosphere [2, 5, 57]. In the first place, the CO2 and CH4 emissions produce greenhouse effects that are calculated to be comparable to the emissions of gas-fired power plants per electrical energy produced; therefore, we are forced to consider that the Amiata volcano geothermal power plants are not adequate to substantially reduce greenhouse gas emissions per electric energy produced. In addition, the emissions of H2S, SO2 and H3BO4, have an atmospheric acidification potential (acid rain) that is also similar to coal-fired power plants per electrical energy produced. Also, the emissions of NH3, a notable contribution to secondary fine particles formation, in 2017 were close to half the whole emissions in Tuscany of such pollutant. Relative to Mercury, the emissions are relevant even with the abatement technology in place. Before, the emplacement of the Mercury abatement technology (AMIS) in the years two-thousands, the emissions were around an order of magnitude higher. The emissions of Arsenic and Arsenic compounds are also significant. While these emissions are generally monitored only for about a few hours per year, no controls are made for the rest of the time, even when the AMIS is not adequately functioning. In addition, the emissions that occur as fine particles (aerosol) are unaccounted for since there are no limits imposed by law for them. Primary and secondary fine particles related to the geothermal power plants could account for the relatively high level of fine particles (on average about 15 μg/m<sup>3</sup> ) in the air of this, by all means, rural area that practically has no large emissions from other industries. In the Piancastagnaio area fine particles are enriched in Sodium, Phosphorous, Sulphur, Zinc, Tantalum, Caesium, Thallium, Thorium, and Uranium relative to the particles sampled in Florence and Arezzo [9] suggesting a direct contribution from the geothermal power plants.

Although the concentrations of fine particles measured in the air have been sporadically measured below the law limits, the pollutants contained in these

particles tend to be toxic metals, making these aerosols potentially dangerous for the health of the population living in the area. The WHO REVIHAAP [64], states that all the studies conducted to date show that there is no threshold level below which the effects of pollution on health are not evident. Therefore, in the application of the precaution principle, we suggest that the emissions from the geothermal power plants, in combination with an increase in pollutant content in the freshwater and soil, could be a concomitant cause for the excesses in hospitalizations and deaths in the Amiata Volcano geothermal area (cf. [65]).

In conclusion, the use of air-coolers in place of the evaporative cooling towers, like the ones used today, would drastically reduce the potential impact on the health of the population residing in the Amiata Volcano geothermal area. This technical solution has been already indicated in 2010 by the local government of Tuscany [66], but it has not been applied yet. This technology, which is now proposed for most binary-cycle geothermal power plants in Italy, would substantially reduce both the impact on the superficial freshwater aquifers because all the produced fluid would be reinjected reducing the need for recharge from the superficial volcanic aquifer, and on the atmosphere. After all, the emissions would practically be minimal. On the contrary, the much larger volume of reinjected fluid may increase the risk of inducing or triggering earthquakes. We think that future Life-cycle assessments of the geothermal power plants should attempt at including the environmental impacts reported in this paper and the consequent health risk for the residing population. We stress that the new emerging technologies, such as the deep-borehole heat exchangers should receive more attention and incentives; they produce less energy per unit time but on the other hand, the energy production could probably last for much longer than conventional geothermal power plants, with a minimal environmental impact.

### **Acknowledgements**

We acknowledge funding from the citizens of the municipalities of Amiata Volcano. We thank Curtis M. Oldenburg and Angelo Paone for reviewed the paper and Fabio Landi for his suggestions on the health comments.

### **Conflict of interest**

As a technical consultant, Borgia has served the Public Prosecutor of Grosseto, and worked for the Regione Toscana, the Comunità Montana Amiata Val d'Orcia, the municipalities of Piancastagnaio, Arcidosso and Radicofani, Macchia Faggeta, and several citizens to define the pollution and the environmental impact induced by the geothermal power plants.

Micheli has worked for 35 years in the geology and hydrogeology sections of the Regione Toscana and is now retired.

Carlo Balducci lived his whole life at the foot of Amiata Volcano and is now retired and in the process of creating a public comprehensive database of scientific and government documentation on the geothermal power plants of Amiata.

#### **Notes**

This paper is dedicated to the memory of Alice, Emidio, and all Amiata citizens that become ill and died.

*The Geothermal Power Plants of Amiata Volcano, Italy: Impacts on Freshwater Aquifers… DOI: http://dx.doi.org/10.5772/intechopen.100558*
