Open Access is an initiative that aims to make scientific research freely available to all. To date our community has made over 100 million downloads. It’s based on principles of collaboration, unobstructed discovery, and, most importantly, scientific progression. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. How? By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers.
We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the world’s most-cited researchers. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too.
To purchase hard copies of this book, please contact the representative in India:
CBS Publishers & Distributors Pvt. Ltd.
www.cbspd.com
|
customercare@cbspd.com
The sulfurous groundwater of Longroiva Medical Spa, having a use that comes from a long time ago, was the subject of several studies and research. In the last 50 years, its quality has been tested at the physical-chemical and microbiological levels in the different abstractions, namely, in the Classic Spring and the Well TD1, currently deactivated, and with greater detail in the current abstraction, Well AC1A. It was based on detailed studies, namely, systematic physical-chemical and microbiological analyses, that the sulfurous water from Well AC1A was legalized as natural mineral water; this situation made possible major investments in the place, such as the construction of the new Longroiva Medical Spa, among others. In this chapter, the stability of water quality over time is analyzed, based on studies resulting from the application of classical and multivariate statistical methods as well as the results of studies on the microbiome of these waters. The main conclusions are presented regarding the vulnerability of the aquifer and the exploration plan.
Trás-os-Montes e Alto Douro University, Vila Real, Portugal
*Address all correspondence to: pedroferreirajc@gmail.com
1. Introduction
The sulfurous waters of Longroiva, associated with very extensive fractures of the Vilariça Fault family, have a very old tradition. Their first allusion appears in a document of the Order of Christ, dated 1570 [1]; later, they were referenced in Aquilégio Medicinal by Fonseca Henriques, the first inventory of medicinal waters in Portugal, published in 1726 [2] and later mentioned and studied by several authors, such as Almeida and Almeida [3], with the elaboration of the Hydrological Inventory of Portugal. The studies carried out by Ferreira-Gomes [4, 5] finally allowed their classification as a hydromineral and also a geothermal resource, with high potential for wealth creation, in the domains of classical thermalism, leisure, and well-being; in tourism; and with regard to geothermal use, as they are naturally hot water (47°C). The concession of that resource was attributed to the Municipality of Meda with the Exploration Contract signed on October 29, 2004, between the Municipality of Meda and the Portuguese State, having been published in the Portuguese Decree of January 26, 2005 [6].
Since 1970, these waters have been tested at physical-chemical and microbiological levels; however, it is since their legalization (2004) that they have come to comply with very demanding quality-control criteria. This control is carried out at several levels: (i) water is sampled on a weekly basis to carry out microbiological analyses (viable microorganisms at 37°C, viable microorganisms at 22°C, total coliforms, fecal coliforms, escherichia coli, fecal enterococci, pseudomonas aeruginosa, and spores of anaerobic sulfite-reducing bacteria); (ii) two to three annual harvests for physical-chemical analyses of the main chemical elements, namely, the global parameters, anions, and cations that represent the type of water in the aquifer being explored; (iii) complete physical-chemical analyses are carried out every 5 years for special control of trace chemical elements (metals, organic, and radiological), namely, those that may occur due to anthropogenic contamination.
Systematic analytical control of these waters makes it possible to assess their quality over time, detect possible contamination, and contribute to greater knowledge of the geohydraulic model of the aquifer system. In this sense, classical and multivariate statistical methods were applied to the results of the physical-chemical analyses collected during the licensing period for sulfurous water from the AC1A well (19 consecutive months) and to the samples obtained for quality control, over the last 20 years. Subsequently, a comparative analysis was executed with the results obtained in analyses carried out on water from other abstractions that served the Medical spa in Longroiva, prior to the AC1A well. At the microbiological level, the results of all the classic microbiology analyses carried out on the waters of Longroiva were analyzed, and the results of the study on the natural microbiology of these waters were analyzed.
The methodology of this work is organized into 3 phases, namely:
1st phase - bibliographical research of published works with results of physical–chemical and microbiological analyses of the Longroiva waters, sampled in various abstractions that served the medical spa of Longroiva. We also used data on the microbiome of the waters of Longroiva, obtained in the Hidrogenoma project carried out by the Directorate-General for Energy and Geology [7].
2nd phase – analysis of results of physical-chemical and microbiological tests on water from well AC1A between 2014 and 2020.
3rd phase - treatment of data from physical-chemical and microbiological analyses of the Longroiva waters, in order to demonstrate the stability of these waters.
The analytical methods used in carrying out the analyses are generally in line with those presented in Directive 80/778/EEC [8].
3. Geographical, geomorphological, and geological framework
In the extreme west of Europe, located in the northeastern part of mainland Portugal, is located Vila de Longroiva, where the sulfurous waters that are the subject of study in this work occur; it is part of the Municipality of Meda, in the District of Guarda (Figure 1).
Figure 1.
Location of Longroiva Medical Spa [9, 10].
With regard to the geomorphological framework, in terms of relief, the region fits into a transition zone between the Central Plateaus, where flattened surfaces dominate, associated with slopes with steep slopes, and the plateau area of the surface of the Iberian Meseta [11]. This separation is materialized by the tectonic accident of the Vilariça fault (Bragança – Manteigas) [11], which compartmentalizes this area into two large blocks; this fault is characterized by being a left strike-slip deformation structure, with about 5.5 km of horizontal displacement that triggered a parallel fracturing in a range of 0.5 to 1 km wide, which, with the unevenness of the extreme blocks and the subsiding of the central block, originated the graben of Longroiva [12]. Locally and with interest for the current work, it is worth mentioning that at the geomorphological level, a mountain range with an average altitude of 750 m (granitic plateau, about 35 km long and 4 km wide) develops from Trancoso, in the NNE-SSW direction along the major axis, throughout the study area (Figure 2). In the eastern part, there is a vast plain, which reaches an altitude of 350 m. The drainage network that starts along the central mountain range (ridge line) is of the dendritic type and develops toward the Northeast, feeding the Massueime and Centieira streams toward the Côa river, and toward the Northwest, feeding the Teja stream, both tributaries on the left bank of the Douro River.
Figure 2.
Geomorphological framework: (a) Hypsometry of the region; (b) Hydrographic basin [13, 14].
The area under study is part of the Ancient Massif, which corresponds to the western sector of the morphostructural unit of the Iberian Peninsula, called Hercynian basement [15], more specifically in the Central Iberian Zone, dominated by formations from Precambrian to Cambrian, Ordovician, and Permo- Carbonic, covered by more recent formations of the Tertiary and Quaternary [12].
The oldest formations are the rocks of the Schist-Greywacke Complex, pre-Ordovician [16] (Figure 3); detached from those rocks are the alignments of quartzite crests from the Lower Ordovician, residual reliefs of syncline folds with direction E-W to ENE-WSW [19]; in turn, the granitoids instructed the Schist-Greywacke Complex in the Lamego-Penedono-Escalhão antiform axis, during the third phase of the Hercynian deformation (D3) [12]. The geological cartography of the region represents the sin-D3 granites, from the leucogranites and two-mica granites series as well as the series of biotitic granites and granodiorites, with an approximate age of 320–310 Ma, and the late-post-D3 granites, from series of biotitic-moscovitic granites as well as the series of biotitic granites and associated basic rocks, with around 310–290 Ma, the main groups of the Batholith Granitic of Beiras [20]. Throughout the late and post-Hercynic period, a filonian procession was installed that intruded that entire set (Schist-Greywacke Complex and granitoids) through distensive fractures, consisting of granite/riolitic porphyry dykes, microgabbros, alkaline basalts, masses pegmatitic or aplite-pegmatitic, and quartz veins [12]. Covering the oldest formations, there are the Cenozoic cover formations, which in the study area have greater importance, the Vilariça arkoses.
Figure 3.
Geological framework of the study area, adapted from [17, 18].
The geohydraulic model of the Longroiva water aquifer system was initially advanced by Ferreira Gomes [4], during the works for the licensing of the water under study as a resource to be used in the Medical Spa of Longroiva, and later by Coelho Ferreira [21], the result of several studies developed within the scope of the PhD thesis, as shown in Figure 4.
Figure 4.
Block diagram of the conceptual geohydraulic model of the sulfurous groundwater (natural mineral water) that supplies Longroiva Medical Spa [21].
In general, water of meteoric origin infiltrates the granite massif, since it is very altered and fractured, at altitudes between 770 and 809 m, along the granite plateau that extends from Trancoso to Meda. In the first phase, in the less extensive and more superficial circuits, the water will percolate in depth toward the thalwegs, emerging in some springs resulting from geological traps and forming small punctual aquifers dependent on the alteration and fracturing of the rock mass, of the free or phreatic type, which generally do not exceed 100 meters in depth. During these paths, water in a global way, due to the topography of the land, circulates inside the granite massif from west to east, until it reaches the faults in the NNE-SSW direction, the first barrier that conditions the circulation of water due to the difficulty that it has in crossing it. Thus, as a circulation corridor, the waters percolate along this fault from south to north; however, along the way, the intersections with the ENE-WSW to E-W family of faults allow the water to pass to other fracture corridors with NNE-SSW direction, east of the previous one.
In its downward underground path, it reaches the reservoir at a depth of 2000 m, reaching temperatures of around 115.4°C. After going through an extensive and deep underground circuit, where chemical alterations occur, resulting from water-rock-gas interaction processes and eventually even with a microbiological contribution, which give them unique and special characteristics, these waters emerge together with the contact of the granitoids with the metasedimentary formations (schists), which act as a barrier to their percolation. The emergence is further enhanced by hydraulic loads developed in the aquifer system and by the temperature reached in depth. Regarding discharges from the deep aquifer system, the schist/granite contact is clearly a barrier to the percolation of these waters in depth, and it is understood that, probably, the combination between the main families of faults, with global directions NNE-SSW and NW-SE, promote openings that allow their ascension.
The granitic massif next to the Longroiva Medical Spa constitutes two distinct aquifer systems: (i) the superficial granitic aquifer systems: of the free type, with common water, in the most superficial zone, around 100 m, characterized by not being very productive, and their recharging area in close proximity; (ii) deep granitic aquifer systems: of the confined type, with sulfurous water, and with a recharge area in a very distant zone. In previous studies [22], the hydraulic parameters for the sulfurous water-aquifer system were presented according to the following: hydraulic conductivity, k = 0.4 m/day; transmissivity, T = 5.6 m2/day; and storage coefficient, S = 2.4×10−3.
The abstraction is constituted by the AC1A well, which is a vertical well, 211.7 meters deep, and it should be noted that it is piped with stainless steel from the surface to 104.3 m deep and cement in its annular space. From that depth down, the well is not lined, and the water is captured between 104.3 and 211.7 m deep. The maximum flow rate for operation is 6.2 L/s, which is the value obtained in flowing artesian, with the resulting level at the mouth of the well, 0.6 m above the height of the natural terrain. The maximum piezometric level was recorded at 12 m above the natural ground level, when the hole is not delivering any flow, that is, with the faucet closed. It should be noted that as the piezometric operating level is lower (0.6 m) above the topographic surface, the potential for infiltration of contaminated fluids into the massif is consequently reduced.
5. Vulnerability and risk of aquifer system contamination
The vulnerability of groundwater to pollution can be defined, according to Van Duijvenbooden and Van Waegeningh [23], as “the sensitivity of groundwater quality to an imposed contaminant load, which is determined by the intrinsic characteristics of the aquifer”.
In the natural discharge zone, that is, in the area surrounding the Longroiva Medical Spa, Ferreira Gomes [24] established the vulnerability of the various geological units, based on the DRASTIC method [25] and some adaptations adjusted to the confined aquifer systems taking into account the abstraction site [24], resulting in the vulnerability map presented in Figure 5. From the same, it can be observed in particular that the lands in the AC1A well area present high to very high vulnerability, orienting that it will be necessary to be very careful with anthropic actions that may exist in that area as they could lead to contamination of the aquifer system.
Figure 5.
Perimeter protection of groundwater extraction of Longroiva Medical Spa and vulnerability of the surrounding land (from [26]).
Figure 5 also shows the Protection Perimeter for the waters of Longroiva, published in the Portuguese Decree [27], with the Extended Zone established to safeguard recharge areas [24]; the Intermediate Zone, generically corresponding to the areas close of the sulfurous water-aquifer system with considerable vulnerability; and the Immediate Zone, corresponding to the area with the greatest potential for natural discharge and where the AC1A well is located, being in particular an area to minimize the potential for water contamination in the abstraction itself.
In the area under study, two types of sources of pollution were considered [24]: risks associated with urban areas and risks associated with rural areas.
The risks associated with the urban area are linked to urban management, domestic activities, animal husbandry, and small industries, among others. Next to the Longroiva Medical Spa and in the surrounding areas, the following situations stand out: (i) punctual pits and in particular the general WWTP of the village, about 150 m downstream of Well AC1A; (ii) potential leaks from the sewer systems; (iii) family chicken coops that exist in the village; (iv) small industrial activity (mechanical workshop) that, despite being around 650 m from the Medical Spa, is located close to the Concelha riverside, with the land having high vulnerability; (v) the Longroiva cemetery, which should be treated with some care; (vi) the rural hotel of Longroiva that was built in the immediate area of the protection perimeter, taking advantage of the old thermal spa building; although with the works, there were positive actions of decontamination of the land next to the Classical Spring, and the anthropic pressure next to the Well AC1A increased, due to actions inherent to the hotel’s activities.
The risks associated with rural areas are essentially due to intensive agricultural cultivation and use of fertilizers and pesticides. The use of these chemicals should be considered in places close to the Medical Spa and completely eliminated in the immediate and intermediate protection zones.
6. The water quality of the Longroiva Medical Spa aquifer system
6.1 Physical-chemical stability
According to several authors [4, 22], the water from the Longroiva Medical Spa, having a use that goes back a long time, has been the subject of several analyses and research. Of the studies or reports available at that time, the oldest analysis dates from 1970 [28], in water collected from the Classical Spring (NCL). The following analysis dates from 1988 [22]; in this case, the water sample had already been collected from Well TD1, which, however, had been built in order to improve the conditions for capturing and increasing the flow, with the intention of trying to legalize the Medical Spa. Similar results were obtained in the analyses carried out later over time (1988 to 1997), orienting for the water to always have the same origin and the same physical-chemical standard. In any case, the fact that the analysis in 1970 showed significant arsenic, as well as iron, copper and zinc, elements that are not part of the physical-chemical procession of the AC1A well water should be highlighted. Those elements with a high probability originated from the superficial aquifer system, which in the area was very contaminated. The contamination problem was overcome with the construction of the AC1A well, in which stainless steel tubing was carried out to a depth of 104.3 m and cementation in its annular space and also with the neutralization of all nearby springs and old wells, with cement grout injections [22]. Figure 6 shows the location of the abstractions that served Longroiva Medical Spa and that were referred to earlier.
Figure 6.
Location plan of the abstractions that served the Longroiva Medical Spa [12, 29, 30].
A study on the physical-chemical stability was carried out by analyzing the results obtained during the legalization phase of Well AC1A, in 1999/2000. The physical-chemical analyses were carried out in the laboratory of the former IGM (Geological and Mining Institute). The stability that the water showed then made it possible for it to be classified as natural mineral water, which could be used for medicinal purposes in the Longroiva Medical Spa, if the medico-hydrological study to be carried out was guided in this direction. It should be noted that 19 physical-chemical analyses were carried out, one per month, for 19 consecutive months. The basic statistical elements of the results of the analyzed parameters can be seen in Table 1, where it is verified that the relative standard deviation (RSD) of the total mineralization is only 1.92% and, in general, for the ionic parameters, it rarely exceeds 10%.
Parameters
Units
Nr.
Min
Ave
Max
SD
RSD (%)
pH
—
19
8.71
8.86
8.93
0.05
0.55
Conductivity
μS.cm−1
19
515.00
578.63
728.00
49.31
8.52
Total sulfuration
(em I2 0.01 N) – mL/L
19
31.20
44.83
49.70
3.88
8.66
Alkalinity
mg(CaCO3)/L
19
150.00
154.11
165.00
3.93
2.55
Total hardness
mg(CaCO3)/L
19
6.50
7.05
8.00
0.36
5.10
Total CO2
mmolCO2/L
19
2.50
2.64
2.77
0.08
2.98
Silica - SiO2
mg/L
19
58.30
64.50
71.10
2.92
4.52
Dry residue (at 180°C)
mg/L
19
375.00
395.26
407.00
8.27
2.09
Total mineralization
mg/L
19
441.00
462.16
474.00
8.85
1.92
Anions
HCO3−
mg/L
19
146.00
154.47
162.00
4.71
3.05
Cl−
mg/L
19
44.00
45.97
48.30
1.07
2.33
SO42−
mg/L
19
10.00
11.34
12.70
0.76
6.69
F−
mg/L
19
22.20
23.63
25.80
0.80
3.40
CO32−
mg/L
19
4.80
6.49
7.50
0.63
9.77
NO3−
mg/L
19
<0.12
—
<0.38
—
—
NO2−
mg/L
18
<0.01
—
<0.05
—
—
HS−
mg/L
19
5.10
7.38
8.20
0.65
8.77
H3SiO4−
mg/L
19
9.50
12.97
15.30
1.20
9.27
Cations
Na+
mg/L
19
122.00
126.37
132.00
2.61
2.06
Ca2+
mg/L
19
2.60
2.73
3.00
0.13
4.73
K+
mg/L
19
4.10
4.57
5.30
0.25
5.40
Mg2+
mg/L
19
<0.03
—
<0.10
—
—
Li+
mg/L
19
0.59
0.77
0.88
0.08
9.90
NH4+
mg/L
19
0.42
0.53
0.65
0.06
10.75
Table 1.
Results in statistical terms of the main physical-chemical parameters of the water from AC1A well, during the licensing period 1999–2000 [22].
Note: Nr.- number of samples, min- minimum, ave. - average, max - maximum, SD - standard deviation, RSD - SD relative.
By projecting the average values relative to the analyses that were carried out in the water of the NCL, of Well TD1, as well as in the Well AC1A during the legalization phase in the Piper and Stiff diagram (Figure 7), it is verified that, without a doubt, we are facing the same water, although the analyses were carried out at different times and different laboratories.
Figure 7.
Diagrams of Piper and Stiff, of the waters from the abstractions that served the Longroiva Medical Spa during the period 1970–2000.
After licensing the resource, the waters of Longroiva were subjected to systematic control, generally two to four analyses per year until today. Analyses during this period were always carried out by the Analysis Laboratory of the Instituto Superior Técnico in Lisbon. In order to be able to conclude the physical-chemical stability of these sulfurous waters, a detailed study was carried out by Coelho Ferreira et al. [26], which is now complemented. In Table 2 and in Figures 8–11, the basic statistical results of the same parameters surveyed in that period are presented.
Parameters
Units
Nr.
Min
Ave
Max
SD
RSD (%)
pH
—
56
8.60
8.80
8.96
0.09
0.99
Conductivity
μS.cm−1
56
527.00
541.42
688.00
20.97
3.87
Total sulfuration
(em I2 0.01 N) - mL/L
56
34.00
43.73
53.00
4.46
10.20
Alkalinity
mg(CaCO3)/L
55
138.00
149.93
155.00
3.79
2.53
Total hardness
mg(CaCO3)/L
56
4.70
6.24
8.00
0.71
11.32
Silica - SiO2
mg/L
56
59.00
65.41
73.00
3.24
4.95
Dry residue (at 180°C)
mg/L
56
367.00
383.04
398.00
6.79
1.77
Total mineralization
mg/L
56
437.50
456.08
475.00
7.06
1.55
Anions
HCO3−
mg/L
56
134.00
149.66
160.00
4.65
3.11
Cl−
mg/L
56
41.40
45.79
51.00
1.61
3.53
SO42−
mg/L
55
11.40
13.94
20.00
1.95
13.99
F−
mg/L
56
22.00
23.79
26.00
0.73
3.06
CO32−
mg/L
56
2.40
6.71
9.70
1.25
18.60
NO3−
mg/L
56
<0.03
—
<0.03
—
—
NO2−
mg/L
55
<0.005
—
<0.01
—
—
HS−
mg/L
54
5.70
7.21
9.00
0.72
10.06
H3SiO4−
mg/L
55
6.20
9.94
14.00
1.76
17.68
Cations
Na+
mg/L
56
119.00
125.05
134.00
2.97
2.37
Ca2+
mg/L
56
1.90
2.49
3.10
0.25
10.21
K+
mg/L
56
3.70
4.84
8.70
0.94
19.37
Mg2+
mg/L
56
<0.1
—
<0.1
—
—
Li+
mg/L
56
0.44
0.73
0.80
0.05
6.66
NH4+
mg/L
56
0.23
0.67
1.00
0.10
14.82
Table 2.
Results in statistical terms of the main physical-chemical parameters of the water from Well AC1A, during the control period (2001–2020).
Note: Nr.- number of samples, min- minimum, ave. - average, max - maximum, SD - standard deviation, RSD - SD relative.
Figure 8.
Evolution over time of the physical-chemical parameters, in terms of the global parameters, of the water from Well AC1A, during the control period (2001–2020).
Figure 9.
Evolution over time of the physical-chemical parameters, in terms of the majority component - anions, of the water from Well AC1A, during the control period (2001–2020) – Sheet 1/2.
Figure 10.
Evolution over time of the physical-chemical parameters, in terms of the majority component - anions, of the water from Well AC1A, during the control period (2001–2020) – Sheet 2/2.
Figure 11.
Evolution over time of the physical-chemical parameters, in terms of the majority component - cations, of the water from Well AC1A, during the control period (2001–2020).
When analyzing the statistical results, it is verified that most of the parameters present excellent stability with RSD inferior to 10%, including the fact that it is a long period of research (20 years), and the main global parameters such as the total mineralization, the dry residue, the pH, the conductivity, and the silica in the non-ionized form present RSD values lower than 5%, a situation that leads to a great physical-chemical stability of the water; still, in the overall parameters, there is the particularity of the total sulfuration showing a slight tendency to increase over time, despite the RSD still being in the order of magnitude of 10%. Regarding the ionic component, most of the parameters show statistically good stability; however, it is worth mentioning that some statistical trends increase or decrease over time, namely, in the cases of SO42−, Hs−, NH4+, CO32−, H3SiO4−, and K+.
In Figure 12, the results obtained during the control phase are graphically presented and compared with the statistical values, minimum, average, and maximum, obtained in the legalization phase. It should be noted at this point that the fact that the results of the legalization phase were obtained in a laboratory different from the one used in the control phase may justify some small differences, resulting from various situations such as the handling of samples, as it should be noted that we are dealing with very small measurements, on the order of milligrams or parts per million.
Figure 12.
Results of control analyses over 20 years and comparison with statistical values obtained in the licensing phase.
Thus, when analyzing Figure 12, it is highlighted that for global parameters, most of the total values fall within the range between the minimum and maximum obtained in the legalization phase; exception is verified in the total hardness. With regard to ions, despite almost all of the parameters falling within the said fringe, there are some that are out of adjustment, namely: (i) in anions where SO42− is essentially above, CO32− oscillates above and below, and H3SiO4− is below; and (ii) in the cations Ca2+, which is below, and K+ and NH4+, which are essentially above.
A careful analysis of them leads to the mention that some of the deviations found may be essentially related to natural oscillations and even to the tuning of analytical techniques. Of note, the case of silicate (H3SiO4−) as the example containing more significant oscillations, it is also verified that the range of values in the legalization period (1999 and 2000) is above that in the control period (2001 to 2020), and consequently, the values obtained in the IGM laboratory are higher than those obtained in the IST laboratory.
In any case, this simple analysis leaves some doubts, and therefore, there is a need to continue the study with other more specific research techniques. Thus, mathematical techniques such as Principal Component Analysis (PCA) were used. To carry out the PCA on the results of the chemical analyses of water from the Well AC1A, two phases were considered: 1st phase corresponding to the legalization period (1999–2000); 2nd phase corresponding to the control period (2001–2020). For the 1st phase, the matrix of 19 samples was considered, corresponding to the 19 consecutive months during the years 1999 and 2000, with 17 variables (physical-chemical parameters). For the 2nd phase, the matrix of 56 samples was considered, corresponding to all existing analyses of Well AC1A, with 17 variables (physical-chemical parameters).
The multivariate statistical analysis was performed using the Andad software, version 7.12 [31]. The results obtained are presented in Table 3, where the eigenvalues (Vp), the explained variance for each axis (Vi), and the accumulated variance (Vc) are observed. The choice of the number of factor axes to retain was based, once again, on considering those with eigenvalues greater than 1.
Study phase
Axis
Variables explained by axis
Vp
Vi (%)
Vc (%)
1st phase: 1999–2000 (Licensing period)
1
+Si, +SiO2, +RS, +MT, +Na+, +HCO3−
4.98
29.28
29.28
2
+NH4+, -Cl−, +SO42−, +F−, -CO32−, -H3SiO4−
2.76
16.25
45.53
3
+ST, +HS−
2.06
12.11
57.64
4
-Li+, +F−
1.74
10.25
67.89
5
-K+, +SO42−
1.54
9.05
76.94
6
+Cl−
1.28
7.55
84.49
2nd phase: 2001–2020 (Control period)
1
-Si, -SiO2, -RS, −MT
2.99
17.60
17.60
2
+ST, +HS−, -F−, -CO3−
2.60
15.31
32.91
3
− + Si, +SiO2, -Na+, -HCO3−
2.01
11.83
44.74
4
+Li+, +H3SiO4−
1.66
9.78
54.52
5
+HCO3−, -Cl−
1.44
8.45
62.98
6
-Ca2+, +SO42−
1.24
7.27
70.25
7
—
1.08
6.37
76.62
Table 3.
Result of the PCA applied to the results of the physical-chemical analysis from Well AC1A waters.
In studies carried out by Coelho Ferreira et al. [26], the same exercise was carried out, with the control phase including analyses only up to 2013, and the PCA results of the two phases were similar. In the present work, the analyses up to 2020 were considered in the control phase, and the addition of this information allowed verifying that the results of the multivariate statistics (PCA) point to the existence of a trend of slight differences in the two phases. When analyzing the results of the PCA (Table 3), namely, the values of the variables of the factorial axes as well as their projection in the first and second factorial plan, it is worth mentioning the following for the licensing phase:
The first factor axis explains about 29.28% of the total variance; this factor is determined by the lithological/environmental and long temporal context where the water/rock interaction will determine the relatively high and complex mineralization of this water. Another aspect explained in this factorial axis is the hydrochemical facies of this water (sodium bicarbonate).
The second factorial axis explains about 16.25% of the total variance; this factor can be explained by the presence of sulfur in the hydromineral system, which determines the presence of N in the form of NH4+, thus not relating this chemical species to anthropogenic phenomena. The NH4+ species is related to F− and SO42− and in opposition to the CO32−, Cl−, and H3SiO4− species.
The third factorial axis explains about 12.11% of the total variance; the ST – HS− association is strongly correlated with this factorial axis; this association shows the presence of sulfur in these waters, in its reduced forms.
In the case of the control phase, which includes physical-chemical analyses of these waters for 20 years, the results obtained and in comparison with the licensing phase were considered as follows:
The first factor axis explains about 17.60% of the total variance; this factor remains, in relation to the licensing phase, as determined by the lithological/environmental and long temporal context where the water/rock interaction will determine the relatively high and complex mineralization of this water.
The second factor axis explains about 15.31% of the total variance; in this factor axis, contrary to the licensing phase, the ST – HS− association gains greater preponderance; this association, which shows the presence of sulfur in these waters in its reduced forms, has had an increasing tendency over the years, most likely due to the evolution of the entire system toward stability. In opposition to the previously mentioned association, CO32− and F− are found, with CO32− showing a decreasing trend over the years.
The third factorial axis explains about 11.83% of the total variance; this factorial axis reflects the hydrochemical facies of this water (sodium bicarbonate). The association between Na+ and HCO3− occurs in opposition to the association between SiO2 and Si.
To obtain a better understanding of these aspects, the graphs in Figure 13 are presented, with the results available so far from all abstractions with sulfurous water that have already served the Longroiva Medical Spa. The referred graphs show the analytical results obtained in the Classical Spring in 1970 (n = 1) and in the Well TD1 during the period from 1988 to 1997 (n = 15), and these are compared with the statistical values, minimum, average, and maximum, obtained in the phase of legalization and control of Well AC1A, in the period between 1999 and 2020 (n = 75), which previously proved its physicochemical stability. When analyzing the results, it is verified that most of the global parameters are within the range between the minimum and the maximum mentioned above, with the exception of total sulfuration (ST) and hardness (H). In the case of ions, most of them are also within this range, with the exception of anions being SO42− and HS− and Ca2+ in cations. Once again, the physical-chemical stability of this water over the 50 years during which analyses were carried out is demonstrated. With regard to existing variations in some elements, they may probably be related, as previously mentioned, to natural oscillations and even to the tuning of analytical techniques.
Figure 13.
Comparison of the results over time of the physical-chemical parameters, in terms of the global parameters and major elements (anions and cations), of the sulfurous water from the various abstractions of the Longroiva Medical Spa.
Special control analyses of trace chemical elements (metals, organic, and radiological), namely, those that may occur due to anthropogenic contamination, are carried out less frequently. During the licensing and control phases, only three analyses of this type were carried out, in 2000, 2016, and 2021. The results obtained are shown in Table 4, and from the analysis carried out on them, the following should be mentioned:
the trace elements that form part of the typical procession of these waters, B, Cs, Rb, Sr., and W show an increasing trend over time, with W standing out as the element that most increased its concentration.
In the case of elements that may reveal possible anthropogenic contamination, namely, metals and organic elements, there is no significant increase or trend that points to a situation of potential contamination of the hydromineral resource.
Result of trace elements obtained through the complete physical-chemical analysis of the Well AC1A water.
value lower than detection limit.
Although it was possible to highlight some aspects of the available analytical results, the incipient knowledge about these waters, as well as the reduced number of analyses over such a long time, does not allow reaching consistent conclusions, much less triggering preventive actions that mitigate the possible contamination of the mineral aquifer.
6.2 Microbiological elements
Mineral water, such as the water from Longroiva Medical Spa, in addition to its chemistry as an intrinsic and consequent characteristic of the hydrogeological circuit traversed, may also have a natural microbiome inherent in each water, in addition to having microorganisms that are not common to their normal characteristics and are even pathogenic; the latter are normally associated with anthropic actions and are considered here as research within the classical microbiology of groundwater.
6.2.1 Classical microbiology
Control in terms of classical microbiology in groundwater of the abstractions is directed toward research and quantification of: viable microorganisms – number of colonies at 36 ± 2°C, viable microorganisms - number of colonies at 22± 2°C, total coliforms, fecal coliforms, escherichia coli, fecal enterococci, pseudomonas aeruginosa, and spores of anaerobic sulfite-reducing bacteria.
These microorganisms, researched for either the licensing of new mineral waters or the use of mineral waters, in order to verify if they are in conditions of suitability in terms of public health, are defined in accordance with Law n.° 1220/2000.
Thus, research on classical microorganisms provides guidance on the quality of the terminal phase of the geohydraulic circuit and natural mineral water abstraction, being important for each water point (springs, wells, holes), as far as possible, to have a history of these aspects.
The Longroiva Medical Spa, as already mentioned, goes a long way back in time; however, in the past, there was no microbiological control. Meantime, the rules were changing, and for Longroiva Medical Spa to be licensed, it had to have its resource, which was initially obtained from the Classical Spring, with adequate microbiological results. This did not happen for many years, as the discharge zone of the geohydraulic circuit for the sulfurous water of Longroiva Medical Spa was contaminated; then, it evolved into the Well TD1 with 40 m of depth, and the situation ended up not changing. The results that it was possible to compile by Ferreira Gomes [32] attesting to such situations are presented in Table 5, showing that the water was systematically unsuitable, namely, total coliforms, sometimes fecal coliforms, fecal streptococci, and sulfite-reducing spore-forming anaerobes, plus excess total germs.
Parameters
MRV
MAV
Date (year/month)
69/07 (0)
90/07 (0)
97/07 (1)
97/08 (1)
97/09 (1)
97/10 (1)
97/11 (1)
97/12 (1)
98/01 (1)
98/02 (1)
98/03 (1)
1
5
20
76
10
70
>300
140
42
6
18
8
>300
40
2
20
100
—
90
50
>300
>300
120
30
22
3
>300
20
3
0
0
—
14
>80
>80
>80
>80
3
0
12
0
>80
4
0
0
—
0
0
0
0
0
0
0
12
0
0
5
0
0
—
0
13
50
15
1
0
0
0
0
0
6
0
0
—
0
0
0
0
0
0
0
0
0
0
7
0
0
—
0
>1
>1
>1
1
0
0
0
0
0
Table 5.
Results of bacteriological analyses carried out on Classic Spring and TD1 Well water over the years [32].
MRV - Maximum Recommended Value, MAV - Maximum Admissible Value.
(0)(1) Results of the water collected, respectively, in the Classic Spring and in the Well TD1.
However, relatively recent works have evolved toward Well AC1A, capturing sulfurous water below a depth of 104 m, neutralizing some points of sulfurous water in the vicinity, namely, Well TD1, and the classic microbiological results were adequate in a distinguished way; Table 6 shows the results obtained, from May 1999 to November 2000, during the legalization phase of Longroiva Medical Spa [22].
Date
Research
1
2
3
4
5
6
7
04/05/99
1
1
0
0
0
0
0
09/06/99
2
4
0
0
0
0
0
20/07/99
1
2
0
0
0
0
0
24/08/99
1
1
0
0
0
0
0
07/09/99
2
3
0
0
0
0
0
19/10/99
1
1
0
0
0
0
0
10/11/99
2
1
0
0
0
0
0
07/12/99
1
4
0
0
0
0
0
24/01/00
1
0
0
0
0
0
0
08/02/00
2
1
0
0
0
0
0
14/03/00
1
2
0
0
0
0
0
04/04/00
1
3
0
0
0
0
0
02/05/00
1
1
0
0
0
0
0
19/06/00
1
2
0
0
0
0
0
06/09/00
0
0
0
0
0
0
0
26/09/00
0
0
0
0
0
0
0
10/10/00
0
0
0
0
0
0
0
21/11/00
1
1
0
0
0
0
0
Table 6.
Results of bacteriological analyses carried out on the water from the Well AC1A for the legalization of Longroiva Medical Spa [22].
Research: 1 – N.° of colonies per mL, at 37°C, 24 hours; 2 – N.° of colonies per mL, at 22°C, 72 hours; 3 – N.° of total coliforms per 250 mL; 4 – N.° of fecal coliforms per 250 mL; 5 - Count of fecal streptococci per 250 mL; 6 - Quantification of spores of anaerobic sulfite-reducing bacteria per 50 mL; 7 - Quantification of pseudomonas aeruginosa per 250 mL.
Following the legalization of medical spas and since they are in operation, it is usual to comply with an annual analytical control plan, determined by the licensing entity, in which the number of microbiological analyses to be carried out monthly is defined. In the case of Longroiva Medical Spa, over about 20 years, it fluctuated between 1 and 5 monthly analyses, a total of 718 (Table 7).
Results of the bacteriological analyses carried out on the water of the Well AC1A throughout the control phase, in a total of 718 analyses (compiled from records in technical reports of the spa’s activities over time, held by the DGEG and the concessionaire (CMM)).
In 2020, due to the COVID-19 pandemic, the Hydromineral Resource Exploitation Plan was suspended as of March 17, in the thermalism aspect, resulting in only 13 microbiological analyses throughout the year.
Research: 1 – Quantification of cultivable microorganisms at 37 °C, 24 hours (CFU/1 mL); 2 – Quantification of cultivable microorganisms at 22 °C, 72 hours (CFU/1 mL); 3 – Research and quantification of total coliforms (CFU/250 mL); 4 – Research and quantification of fecal coliforms (CFU/250 mL); 5 – Research and quantification of Escherichia Coli (CFU/250 mL); 6 – Research and quantification of fecal enterococci (CFU/250 mL); 7 – Research and quantification of Pseudomonas aeruginosa (CFU/250 mL); 8 – Research and quantification of spores of anaerobic sulfite-reducing bacteria (CFU/50 mL).
Law 1220/2000 - Recommended Value (RV); RV = 5 CFU/1 mL for research 1; RV = 20 CFU/1 mL for research 2. Limit Value - maximum admissible value (LV); LV = 0 CFU/1 mL for research 3, 4, 5, 6, 7, and 8.
From the results obtained, it appears that most analyses of the Well AC1A waters are below the MAV in microorganisms cultivable at 37°C and 22°C, and for the remaining microorganisms analyzed, in 20 years, the detection of a CFU of total coliforms occurred only once, in 2015, during the works of the hotel. In this way, the quality of construction of the Well AC1A becomes evident, with the capture of the resource at a depth greater than 104 m and also the relationship between anthropic actions in the surroundings of the well.
6.2.2 Aspects about microbiome
Groundwater has a natural microbial community in its composition, which has been studied over the years; however, knowledge about these aspects is still considered incipient.
The Directorate General for Energy and Geology (DGEG) led the HIDROGENOMA project, during the period 2016 to 2019, which aimed to investigate the natural microbism of 80 Portuguese natural mineral waters, which included the sulfurous water from Longroiva Medical SPA [7]. According to the same authors, this project aimed to correlate scientific knowledge in the areas of geology, hydrogeochemistry, and microbiology and contribute to better management, exploitation, and enhancement of hydromineral resources. The results, among others, will be able to infer about the microbiological ecosystems of the aquifers crossed, giving guidance on the conditions of pressure, temperature, and degree of oxidation-reduction of the environment that will occur in them [7]; thus, it is understood that those elements will contribute to the knowledge of the hydrogeological models of each aquifer system.
The project methodology consisted of collecting four samples at the head of the abstractions, during the years 2017 and 2018, in spring and autumn, in the 80 natural mineral waters that were contemplated in this study [7]. Also, according to Lourenço and Pascoal [7], after each sampling phase, a genomic study of the waters was carried out in the laboratory.
Table 8 presents the results obtained for the various samples, in terms of the taxonomic composition of bacterial communities, based on taxonomic affiliation by class. Using the mean values per class, as shown by DGEG [34], Figure 14 shows the distribution of the various classes identified; there are 7 most-frequent bacterial classes, with two dominant: Gammaproteobacteria (20.09%) and Betaproteobacteria (19.80%). Some classes were also occasionally recorded (Actinobacteria, Flavobacteriia, Nostocophycideae) in the spring samplings, with a relevant percentage of microorganisms not classified at the Class level (17.23%), with a predominance of the same in the samplings of autumn.
Class
%_Reads F1
%_Reads F3
%_Reads F5
%_Reads F7
Average
Standard Deviation
Gammaproteobacteria
56.07
8.46
7.66
8.17
20.09
23.989
Betaproteobacteria
34.99
2.80
31.00
10.41
19.80
15.635
Unclassified
1.90
29.76
8.27
29.00
17.23
14.269
Deltaproteobacteria
0.40
29.31
10.62
5.26
11.40
12.650
Nitrospira
—
7.51
21.33
4.49
11.11
8.979
Alphaproteobacteria
5.21
2.84
—
23.86
10.64
11.513
Clostridia
0.20
9.41
11.22
4.93
6.44
4.929
Deinococci
0.73
2.29
—
3.27
2.10
1.281
Actinobacteria
—
—
3.44
—
—
—
Flavobacteriia
0.20
—
—
—
—
—
Nostocophycideae
—
—
3.59
—
—
—
Table 8.
Comparative summary of the taxonomic composition of bacterial communities, based on taxonomic affiliation by class, for samples of sulfurous water from Well AC1A at Medical Spa Longroiva [33].
Figure 14.
Bacterial communities by class of sulfurous water from Well AC1A at Longroiva Medical Spa (from [34]).
With regard to classification at the level of gender, there is a large variation from sample to sample. However, the genera Desulfomonile, Ectothiorodospira, and Thermodesulfovibrio are present in at least three samples [33].
According to Sá Pereira [33], in terms of species, the most representative are: Desulfomonile tiedjei, Methyloversatilis universalis, Thermodesulfovibrio aggregans, Ectothiorhodospirahalo alkaliphila, Veillonella dispar, Methylobacterium radiotolerans, Methylobacterium mesophilicum, Pseudomonas plecoglossicida, and Chondromyces pediculatus.
The Longroiva Medical Spa has been supplied by several abstractions over the last 50 years, namely, the Classical Spring and the Well TD1, which have since been deactivated, and the Well AC1A that allowed the licensing of this resource as natural mineral water and is currently still in operation.
Well AC1A is vertical, 211.7 m deep, with stainless steel tubing, cement in its annular space from the surface up to 104.3 m, and an exploration flow of 6.2 L/s as artesian (no need for a pump). It has its development in granitic rocks and captures water from a deep confined aquifer system of special and rare characteristics in the region.
The land surrounding the Well AC1A is of high to very high vulnerability, and therefore, there is a need to provide various defense mechanisms for the aquifer system; in this sense, the figure of the Protection Perimeter, namely, the Immediate Protection Zone, presents high restrictions on urban occupation and anthropic actions, in addition to the fact that a flow greater than that of natural a artesian does not withdraw from the well AC1A. There are several potential sources of pollution of the mineral aquifer, and in recent years, with the construction of the hotel in the immediate area of the protection perimeter, although with the works, there have been positive actions to decontaminate the land next to the Classical Spring, where the public washrooms used to be, anthropogenic pressure has increased along with well AC1A; this situation is not very serious immediately due to the characteristics of the aquifer, as it is confined, deep, and has a piezometric level higher than the topographic surface, but since it is of the fissured type and includes some connections to the surface materialized by several natural springs, in the medium- and long-term, there may be a risk of contamination. Thus, systematic analytical control is essential to assess the physical-chemical and microbiological stabilities of the hydromineral resource over time.
In the present work, it was possible to statistically compare two different periods: the legalization period, for 19 consecutive months (1999–2000), and the control period, over the last 20 years (2001–2020). Thus, the statistical study of the physical-chemical analyses of the water from the well AC1A during the legalization period shows great stability of most chemical elements, with RSD lower than 10%, with the exception of ammonium (NH4+) (10.75%). Over the last 20 years (control period), there have been some elements with RSD greater than 10%, revealing some instability, as is the case with ST, H, K+, NH4+, SO42−, CO32−, and H3SiO4−. The use of multivariate analysis techniques, namely, PCA, for the two phases (1st phase includes 19 monthly analyses in a row and 2nd phase includes all 58 analyses carried out on the Well AC1A water) allowed us to understand that the characteristics of this water are determined by complex and diverse water/rock interaction phenomena, where sulfur and residence time contribute to the chemical complexity of these waters. The presence of the NH4+ and SO42− species seems to be related to the sulfurous environment of these waters and not to anthropic contamination phenomena, since they are associated with the F- ion, with a possible profound influence. Regarding the comparison between the two phases, it was observed that there was a tendency toward slight differences, which can be explained by the tendency to increase the concentration of reduced sulfur species (ST, HS−) over time and decrease the concentration of CO32−, a consequence of the evolution of the whole system toward stability.
Analytical results of the water from the Well AC1A were also compared with those existing in relation to the water from the other abstractions that served the Longroiva Medical Spa (Classic Spring and Well TD1), and the respective average values were projected in the Piper and Stiff diagram. From the analysis carried out, it appears that we are facing the same water and confirms the chemical stability of these waters over 50 years, although small variations in some elements have been evident, which are understood to be related to natural oscillations and even to tuning of analytical techniques.
In the case of trace elements, it was verified that the elements that are part of the typical group of these waters (B, Cs, Rb, Sr., and W) show an increasing tendency over time, with W being the element that most increased its concentration; the remaining elements do not show significant increases or trends that point to a potential situation of contamination of the mineral aquifer. The small number of analyses carried out, since the hydromineral resource is analytically controlled, does not allow the acquisition of sustained knowledge about the evolution of these elements over time in these waters.
In terms of analytical control relating to classical microbiology, carried out on water from Longroiva over time, three different periods should be considered: (a) the phase of exploring the water at the Classical Spring and at the Well TD1 (40 m deep), between 1969 and 1998; (b) the licensing phase of the resource as natural mineral water, after the construction of the Well AC1A (211 m deep), during the years 1999 and 2000; and (c) the control phase, in that same well (AC1A), over the last 20 years. From the results obtained, it can be verified that in the first phase, during the exploration of the Classical Spring and that of the Well TD1, the water systematically presented itself microbiologically inappropriate (Table 5); in the licensing phase, with the exploitation of water from the Well AC1A, there were no defaults for 19 consecutive months (Table 6); and in the control phase, over a period of 20 years, 718 analyses were carried out, with 14 analyses with values of quantities of microorganisms cultivable at 37°C, in 24 hours, greater than 5 CFU/1 mL; 4 analyses with values of microorganisms cultivable at 22°C, in 72 hours, greater than 20 CFU/1 mL; and only one analysis with total coliforms, in 2015, when the hotel was being renovated (Table 7). From what was mentioned above, it is understood that the potential microbiological contamination of these waters may be associated with the pressure exerted by anthropic actions along the abstractions.
Regarding the hydrogenome project, from the analysis carried out on the results obtained for the mineral waters of Longroiva, it was possible to highlight the following: (i) the waters of Longroiva can be considered chemically identical to the sulfurous, alkaline, sodium bicarbonate, and fluoridated waters, which are part of this study; however, with regard to the identified microorganisms, although it was not possible to recognize a pattern in the four samples taken, it was possible to perceive that there are differences both in typology and in the number of individuals in these waters; (ii) the diversity of microorganisms increases in the samples collected in autumn (F3-F7) compared to those collected in spring (F1 and F5), contributing to this is the increase in the percentage of microorganisms that it was not possible to classify; (iii) as these waters have great physicochemical stability due to the fact that they come from very deep aquifers, captured through wells that are also relatively deep, and are well isolated in the more superficial areas, one would expect, from the outset, more stable microbiological patterns in all samplings, and the changes that occur from sampling to sampling are surprising (Table 8).
Although, for now, there is no evidence of contaminating effects on this natural mineral water, it must remain under close surveillance, and all the mechanisms and good practices necessary for the preservation of the aquifer system and abstraction must be safeguarded, as provided for in the protection perimeter. The elements highlighted in the present work are guidelines for taking special care and not allowing yourself to be abused by disrespecting either what is foreseen in the Exploration Plan or the restrictions imposed by the Protection Perimeter.
The data sets generated during and/or analyzed during the current study are available from the corresponding author on request after the publication of work.
References
1.Ordem de cristo. Registo dos Tombos das Comendas de Castro Marim, Longroiva, Santa Maria, A Grande, Entre Outras, organizado pelo Dr. Pedro Álvares Seco. ANTT, PT/TT/OCCT/E/003/0236_m218; 1570
2.Henriques FF. Aquilégio Medicinal. Lisboa: Lisboa Occidental; 1726. p. 348. Available from: https://purl.pt/22614/1/index.html#/5/html
3.Almeida A, Almeida JD. Inventário Hidrológico de Portugal. Lisboa: Edição Instituto de Hidrologia de Lisboa; 1975. pp. 88-111
4.Ferreira Gomes LM, Daniel J, Pissarra Cavaleiro VM. O recurso hidromineral das Termas de Longroiva como uma nova água mineral em classificação. In: II Seminário de Recursos Geológicos, Ambiente e Ordenamento do Território. Vila Real: UTAD; 2001. pp. CO-85-CO-97
5.Ferreira Gomes LM, Ferreira Guedes J, Gomes da Costa TC, Coelho Ferreira PJ, Neves Trota AP. Geothermal potential of Portuguese granitic rock masses: Lessons learned from deep boreholes. Environmental. Earth Science; 2015;73(6):2963-2979. DOI: 10.1007/s12665-014-3605-y
6.DR. Diário da República, IIIª Série - N.° 18 de 26 de Janeiro de 2005, para atribuição de Área de Concessão, correspondente ao número HM-53 de cadastro de designação “Longroiva”; 2005
7.Lourenço C, Pasqual R. O Estudo Metagenómico das Águas Minerais Naturais Tendo em Vista o Reconhecimento Científico das Vocações Terapêuticas. Direção de Serviços de Recursos Hidrogeológicos e Geotérmicos da DGEG. Boletim de Minas, 53. Lisboa; 2019. pp. 39-53
8.Directive 80/778/EEC. Council Directive of 15 July 1980 relating to the quality of water intended for human consumption. Official Journal of the European Communities; 1980. No L 229:11-29
9.Direção-Geral do Território. Carta Administrativa Oficial de Portugal (CAOP), shapefile, DGT, Lisboa; 2017
10.Global country boundaries (Arcgis by ESRI). Global country boundaries from DIVA-GIS. Shapefile from: iangliangcun@gmail.com_ucsb. Available from: https://www.arcgis.com/home/item.html?id=2ca75003ef9d477fb22db19832c9554f. [Accessed on 05-05-2019]
11.Ferreira B. O relevo de Portugal Grandes Unidades Regionais. Associação Portuguesa de Geomorfólogos. Vol. II. Coimbra: Edição Fundação para a Ciência e a Tecnologia; 2004. pp. 97-110
12.Silva AF, Ribeiro ML. Notícia Explicativa da Folha 15-A. Vila Nova de Foz Côa. Lisboa: S.G. de Portugal; 1991. p. 52
13.DGT. MDT50m-WMS; 2007. Available from: http://id.igeo.pt/sdg/4d0b0a9e2b4c41a886929d97b61ac459
14.APA, IP. Atlas do Ambiente. Shapefile, APA, Lisboa; 2018
15.Ribeiro A, Antunes MT, Ferreira MP, Rocha RB, Soares AF, Zbyszewski G, et al. Introduction à la géologie générale du Portugal. Serviços Geológicos de Portugal. Lisboa; 1979:114
16.Dias R, Ribeiro A, Coke C, Pereira E, Rodrigues J, Castro P, et al. Evolução estrutural dos sectores setentrionais do autóctone da Zona Centro-Ibérica. In: Dias R, Araújo A, Terrinha P, Kullberg JC, editors. Geologia de Portugal. Vol. 1. Escolar Editora, Lisboa; 2013. pp. 73-147
17.SGP. Carta Geológica de Portugal, Escala 1/500000. Lisboa: Serviços Geológicos de Portugal, Lisboa; 1992
18.LNEG. Carta Geológica de Portugal à escala 1:500000. 5ª edição da Carta Geológica de Portugal à escala 1:500000 Serviços Geológicos de Portugal; 1992. Unidade de Geologia, Hidrogeologia e Geologia Costeira. Laboratório Nacional de Energia e Geologia, I.P., Lisboa; 2019. Available from: http://geoportal.lneg.pt/arcgis/services/CGP500k/MapServer/WMServer?request= GetCapabilities&service=WMS
19.Meireles C, Pereira E, Ferreira N, Castro P. O Ordovícico da Serra da Marofa: novos dados litoestratigráficos e estruturais. In: VII Congresso Nacional de Geologia. Sociedade Geológica de Portugal; 2006. pp. 641-644
20.Azevedo MR, Aguado BV. Origem e Instalação de Granitóides Variscos na Zona Centro-Ibérica. In: Dias R, Araújo A, Terrinha P, Kullberg JC, editors. Geologia de Portugal. Vol. 1. Escolar Editora; 2013. pp. 377-402
21.Coelho Ferreira PJ. Modelação de sistemas geohidráulicos profundos associados a fraturas extensas da região da Meda. [Ph.D. thesis], Univ. da Beira Interior. Covilhã; 2022. (in press)
22.Ferreira Gomes LM. Estudo Hidrogeológico para Enquadramento Legal das Termas de Longroiva. CMM: UBI, Relatório inédito interno; 2001. p. 48
23.Van Duijvenbooden W, Van Waegeningh HG. Vulnerability of soil and groundwater to pollutants. In: Proceedings and Information No. 38 of the International Conference held in The Netherlands, in 1987. Delft, The Netherlands: TNO Committee on Hydrological Research; 1987
24.Ferreira Gomes LM. Perímetro de Proteção das Termas de Longroiva. CMM, Relatório inédito interno, UBI, Covilhã; 2002. p. 52
25.Linda A et al. A standardized System for Evaluation Ground-water Pollution Potential using Hydrologic Setting NWWA. OIH, USA: NTIS; 1987
26.Coelho Ferreira PJ, Ferreira Gomes LM, Carvalho PEM, Oliveira AS. Water quality in deep and confined aquifer systems of granite rocks - the case of sulphurous water from Longroiva, Portugal. In: Cavaleiro et al., editors. Twin International Conferences, 2nd Civil Engineering & 5th Concrete Future, Covilhã, Portugal; 2013. pp. 26-28
27.DR. Diário da República, 1ª Série - N.° 232 de 4 de Dezembro de 2006, fixa o perímetro de proteção para a concessão de água mineral natural denominada de “Longroiva”. DRE; 2006
28.Silva, JJRF, Almeida JD. Relatório de Análise. Água das Caldas de Longroiva (nascente sulfúrea); 1970. p. 10
29.AMCB, DGT. Ortofotomapas à escala 1:2000. Localidade de Longroiva. Associação de Municípios da Cova da Beira e Direção-Geral do Território. Licença de utilização n.° 235/21; 2015
30.AMCB, DGT. Cartografia digital dos Concelhos de Meda, Trancoso, Figueira de Castelo Rodrigo e Pinhel, à escala 1:10000. Temas: eixos de vias, vias e construções. Associação de Municípios da Cova da Beira e Direção-Geral do Território. Licença de utilização n.° 235/21; 2014
31.Andad. Software de estatística ANDAD. Centro de Geosistemas do Instituto Superior Técnico. Versão 7.12; 2013
32.Ferreira Gomes, LM. Estudos, Notas e Trabalhos sobre recursos hidrominerais e geotérmicos das Termas de Longroiva. Relatório Interno; UBI, Câmara Municipal de Mêda; 1999
33.Sá Pereira. Hidrogenoma. Estudo do Microbismo Natural das Águas Minerais Naturais. Relatório Técnico de Longroiva (HM-53). Instituto Nacional de Investigação Agrária e Veterinária, I.P e Direção Geral de Energia e Geologia; 2019. p. 7
34.DGEG. Plataforma Hidrogenoma. Direção Geral de Energia e Geologia, Lisboa; 2020. Available from: https://hidrogenoma.javali.pt/. 2020
Written By
Pedro Jorge Coelho Ferreira, Luis Manuel Ferreira-Gomes and Alcino Sousa Oliveira
Submitted: 01 December 2022Reviewed: 03 January 2023Published: 19 June 2023
Open access peer-reviewed chapter
