CONCENTRATIONS AND DYNAMICS OF CARBON DIOXIDE, RADIOACTIVITY AND RADON IN TWO CAVES OF ITALIAN CLASSICAL KARST (MUNICIPALITIES OF SAGRADO AND SAVOGNA D’ISONZO) KONCENTRACIJA IN DINAMIKA OGLJIKOVEGA DIOKSIDA, RADIOAKTIVNOSTI IN RADONA V DVEH JAMAH ITALIJANSKEGA KLASIČNEGA KRASA (OBČINI ZAGRADEC (SAGRADO) IN SOVODNJE OB SOČI (SAVOGNA D’ISONZO) Graziano CANCIAN1*, Damiano CANCIAN1 & Stefano REJC1 Abstract UDC 543.272.62+546.296:551.442(450) Graziano Cancian, Damiano Cancian & Stefano Rejc: Con- centrations and dynamics of carbon dioxide, radioactivity and radon in two caves of Italian Classical Karst (Municipali- ties of Sagrado and Savogna d’Isonzo) A 13-month monitoring was carried out in two caves that open up in the north-western sector of the Classical Karst (Gorizia Karst): Antro Casali Neri and Grotta Due Piani. In both, ß + γ radioac- tivity, radon and CO2 have a seasonal pattern, with maximums in summer and minimums in winter, even if their trends are some- what different, due to the different morphological and thermal conditions. The increases begin when the outside temperature becomes higher than that of the caves and vice versa, decrease is recorded when outside temperature is below the cave temperature. The more modest daily variations of radon, on the other hand, are evident when its concentration is low. Sometimes they are related to meteorological variations or day/night rhythms, but, in other cases, they have no clearly identifiable causes. In Casali Neri cave the maximum radon activity was 50161 Bq/m3, while the CO2 concentration went off the instrument's scale (> 9999 ppm) only in the first days of August 2021. The highest radioactivity value was also recorded in this cave with 0.85 μSv/h (average of 8 min- utes of recording), with peaks up to 1.05 μSv/h. In Due Piani cave, on the other hand, the radon activity was lower, with a maximum of 22138 Bq/m3, however, the CO2 values went off the scale from July to the first days of October 2021. In both cases, in the warm months, radon and CO2 appear to come mainly from the fractured rock of epikarstic zone. Further accumulations can then form in points with poor ventilation. Furthermore, research has shown that high concentrations of these two gases are not only typical of large or deep caves, but also of modest and easily accessible caves. Key words: Casali Neri cave, Due Piani cave, Italian Classical Karst, carbon dioxide, radioactivity, radon. Izvleček UDK 543.272.62+546.296:551.442(450) Graziano Cancian, Damiano Cancian & Stefano Rejc: Kon- centracija in dinamika ogljikovega dioksida, radioaktivnosti in radona v dveh jamah italijanskega klasičnega krasa (občini Zagradec (Sagrado) in Sovodnje ob Soči (Savogna d’Isonzo) Izvedeno je bilo 13-mesečno spremljanje v dveh jamah, ki se odpirata v severozahodnem delu klasičnega krasa (Goriški Kras), in sicer Casali Neri in Due Piani. V obeh so radioak- tivnost žarkov ß + γ, radon in CO2 sezonsko značilni, z najvišjimi vrednostmi poleti in najnižjimi vrednostmi pozimi, čeprav so njihovi trendi nekoliko drugačni zaradi različnih morfoloških in toplotnih razmer. Vrednosti se povečajo, kadar je zunanja temperatura višja od temperature v jamah, v obratnem primeru se vrednost znižajo. Ob tem so, kadar je njegova koncentracija nizka, opazna manjša dnevna nihanja vrednosti radona. Včasih so povezana z meteorološkimi spremembami ali izmenjavo dneva in noči, v drugih primerih pa nimajo jasno prepoznavnih vzrokov. V jami Casali Neri je bila največja aktivnost radona 50161 Bq/m3, koncentracija CO2 pa je z instrumentalne lestvice (> 9999 ppm) izginila šele v prvih dneh avgusta 2021. V tej jami je bila zaznana tudi največja vrednost radioaktivnosti, in sicer 0,85 μSv/h (povprečno 8 minut snemanja), najvišja vrednost je segala celo do 1,05 μSv/h. V jami Due Piani pa je bila aktivnost radona nižja, pri čemer je bila največja vrednost 22138 Bq/m3, vrednosti CO2 pa so z lestvice izginile od julija do prvih dni ok- tobra 2021. V obeh primerih se zdi, da v toplih mesecih radon in CO2 izhajata predvsem iz razpokane kamnine epikraškega območja. Nadaljnja kopičenja so možna na območjih, kjer je slaba prezračenost. Poleg tega so raziskave pokazale, da visoke koncentracije teh dveh plinov niso značilne le za velike ali glo- boke jame, temveč tudi za manjše in lahko dostopne jame. Ključne besede: jama Casali Neri, jama Due Piani, italijanski klasični kras, ogljikov dioksid, radioaktivnost, radon. ACTA CARSOLOGICA 52/1, 93-107, POSTOJNA 2023 1 Centro Ricerche Carsiche “C. Seppenhofer” - via Ascoli, 7 - 34070 Gorizia, Italy, e-mail: grcancian@gmail.com * Corresponding author Prejeto/Received: 11. 4. 2022 DOI: https://doi.org/10.3986/AC.V52I1.10719 GRAZIANO CANCIAN, DAMIANO CANCIAN & STEFANO REJC 1. INTRODUCTION Carbon dioxide, present in the air of caves, has been studied in various parts of the world and it has been found that its concentrations are very variable. For ex- ample, they are relatively low in the Nerja cave in Spain (525 ppm in autumn/winter and 750 ppm in spring/ summer) (Linan et al., 2008) or medium in the Sainte Anne cave in Belgium (highs around 7500 ppm in Au- gust/September) (Ek & Gewelt, 1985). In the Classical Karst, however, Dambrosi (2015), in his degree thesis reports CO2 percentages in the air equal to 3.05% in the Lipišca jama (Slovenia) and 3.33% in the Skilan Cave (Italy). The origin of CO2 in karst caves is still an open question, as long-term monitoring is scarce, when com- pared with the high number of caves and with the dif- ferent geological, geographical and climatic situations. Often the origin of CO2 in limestone caves has been considered biogenic, derived from plants with deep roots (Breecker et al., 2012), or originating from the soil and entering the underground cavities by degassing from dripping water (Baldini et al., 2006). However, there are also reports of CO2 of deep origin (Wood, 1985; Mattey et al., 2016; Bergel et al., 2017). For example, the presence, even abundant, of CO2 in the karst subsoil was confirmed by drilling in an experimental site near the Nerja Cave, where increas- ing concentrations with depth and with average values of 40 000 ppm were detected (Vadillo et al., 2010). The much lower concentrations in cave, on the other hand, derive from the fact that it communicates both natu- rally and artificially with the outside atmosphere. Ultimately, CO2 in caves can have multiple origins. Kukuljan et al. (2021) indicate five possibilities: degas- sing of percolation waters, advection and diffusion from the soil and from the epikarstic zone, decomposition of organic substance introduced into the cave or deep va- dose zone, anthropic or biogenic production, geogenic production. Furthermore, some research has shown that CO2 can act as a "carrier" of radon and carry it to surfaces (Etiope et al., 1995; Chyi et al., 2010; Castelluccio et al., 2012; etc.). The presence of radon in the caves has long been known and many measurements have been made around the world. In Friuli Venezia Giulia it was mainly monitored in houses (Giovani et al., 2018; Fontani et al., 2019) but less in caves and mostly in the Classical Karst. In these environments, however, highly variable concentrations have been reported, from a few hun- dred to a few tens of thousands of Bq/m3. Various in- formation was given by Cucchi et al.,1996; Giovani et al., 2007, 2012, 2013; Del Maschio et al., 2011. Rather high values, up to 10 000 ± 3 Bq/m3 were recorded in the Pearls cave and up to 13 400 ± 2 Bq/m3 in the Skilan cave. (Commissone Grotte E. Boegan, 2009). In Divas- ka Jama (Slovenia), on the other hand, concentrations of 19  300 ± 2500 Bq/m3 have been reported (Merlak, 2020), while in a passage of the Postojna Caves, not open to the public, an annual average of 25 020 ± 12 653 Bq/m3 with maximum values that exceeded 40 000 Bq/ m3 (Gregorič et al., 2013). In the north-western area of the Italian Classical Karts, a few years earlier, we had carried out a monitor- ing in the General Ricordi Cave, where very high con- centrations of both CO2 and radon were found (Can- cian & Cancian, 2021). In particular, a radon peak of 66 840 Bq/m3 was detected, the largest so far reported in the Italian Karst. An investigation with the Ludlums 700 gamma spectrometer allowed us, also, to identify these radionuclides: 40K - 226Ra - 214Bi. 2. RESEARCH PLANNING AND INSTRUMENTS The purposes of the new research was to verify whether high values of CO2 and radon are found in other caves, as in the General Ricordi cave, in the same portion of Karst. We also wanted to verify if the various param- eters have the same dynamics, bringing new data and new observations. In this regard, we considered two caves: “Antro Casali Neri” and “Grotta a Est di San Mar- tino del Carso” known as “Grotta Due Piani”. For sim- plicity, they will be referred to as ACN and DP in the following text. In both, a thirteen-month monitoring was carried out, collecting the following data: temperatures, carbon dioxide concentrations, ß + γ radioactivity and radon activity. The research began in March 2021 and ended in March 2022. Since, even in this new research, the measurements had to be carried out for a long time, in underground environments, the instruments had to be simple, eas- ily transportable, not excessively expensive but reliable. A digital thermometer with probe, model Checktemp1 ACTA CARSOLOGICA 52/1 – 202394 CONCENTRATIONS AND DYNAMICS OF CARBON DIOXIDE, RADIOACTIVITY AND RADON IN TWO CAVES OF ITALIAN CLASSICAL KARST (MUNICIPALITIES OF SAGRADO AND SAVOGNA D’ISONZO) (Hanna Instruments) was used for the temperatures, while the CO2 concentrations were measured using the AZ7755 instrument (AZ Instrument Corp.). Ra- dioactivity ß + γ was measured with a Geiger counter model BR9B (Brand Sanhe Ding Yi Technology) which provides both the immediate value, in μSv/h, and the average after seven minutes. Finally, the Radex MR107 (Quarta Rad) instrument was used for radon, which takes measurements at one-hour intervals and stores them. The internal battery lasts for approximately 140 hours. To plan the research, it was necessary to take into account that the ACN is easily accessible to occasional visitors, while the DP is frequented by speleologists. In both caves, therefore, it was not possible to leave the instruments unattended, so the measurements were carried out at each inspection and transcribed on a notebook. One exception, however, was the detection of radon. In this case, in fact, the Radex MR107 starts making the first measurements after 4 hours, but they are reliable only after 8 or 9 hours from switching on. For this reason, every month, the instrument was left in the caves, normally for 5 or 6 consecutive days, in slightly hidden corners, near point 3 in DP (Figures 1 and 3) and near point 4 in ACN (Figures 3 and 4). Full data collection occurred when the Radex MR107 instrument was left in the caves, usually within the first decade of the month. Other measurements of temperature, CO2 and radioactivity ß + γ were also re- peated when we were returned to collect it. In the fol- lowing chapters, their average is considered. Between the end of July and August, when the ra- dioactivity values were high, it was decided to carry out a verification, certified by the Laboratory, using the pas- sive sensors Fidotrack CR39 (Niton) which were left in the two caves for 27 and 28 days respectively. 3. CAVES AND GEOLOGICAL FRAMEWORK The two caves open in the north-western sector of the Italian Classical Karst (Gorizia Karst) and develop within the Aurisina Limestones (upper Cenomanian - Turonian p.p. - lower Senonian) (Figure 2). They are located 450 m from each other. In this area the limestone formation is mainly represented by mudstones-packestones, often fossiliferous whit rudists, well stratified, with more com- mon thicknesses ranging from a few decimetres to 1.5 meters. In ACN, the situation is particularly interesting as it is a “doline-cave” morphological ensemble. It opens, in fact, with two entrances, at the bottom of an asym- metrical doline, about 13 meters deep. It is a well known cave, easy to access and often visited by tourists as it has Figure 1: The instruments in the upper gallery of Due Piani cave. ACTA CARSOLOGICA 52/1 – 2023 95 an interest linked to the First World War. In practice it is a large cavern, with the floor completely cluttered with boulders of various sizes. Calcite speleothems are scarce. At the bottom of the cave there is a wall with a passage of 75x140 cm, which causes a narrowing of the section. The continuation, then, has more modest dimensions. The measurements were made in surface, in the bottom of the doline and in three points of the cave (Figure 3).In DP, instead, a well of 8.5 m leads to a gallery initially characterized by collapsed boulders and speleothems, then, continuing, the clayey deposits increase. Further- more, in the first section, a 6 m well leads to the lower gallery, which has a different morphology. Here, in fact, the speleothems are scarce. Some mineralogical research, carried out in the past, has shown that the filling deposit is clayey/silty, for several meters, with some lenses of GRAZIANO CANCIAN, DAMIANO CANCIAN & STEFANO REJC Figure 2: Geological map of the zone (from “Carta Geologica del Carso Classico” – Cucchi F. & Pi- ano C. 2013). Figure 3: Caves and points where the measurements were carried out. ACTA CARSOLOGICA 52/1 – 202396 guano, phosphate minerals and gypsum (Cancian, 1985; Cancian & Princivalle, 1997). The measurements were made in surface, in two points of the upper gallery and in two of the lower one (Figure 3). 4. RESULTS 4.1 TEMPERATURES In the Doberdò plateau, that is located immediately south of the area in question, the warm season lasts from the first days of June to the first ten days of Sep- tember, with a maximum daily temperature often above 25° C. The hottest month is July. The cold season, on CONCENTRATIONS AND DYNAMICS OF CARBON DIOXIDE, RADIOACTIVITY AND RADON IN TWO CAVES OF ITALIAN CLASSICAL KARST (MUNICIPALITIES OF SAGRADO AND SAVOGNA D’ISONZO) Table 1: Cadastral data of the two caves. Name Antro Casali Neri Grotta a Est di San Martino del Carso Other name Pecina Grotta Due Piani (Two floors cave) Cadaster number 326/450 VG 1166/4253 VG Municipality Savogna d’Isonzo Sagrado Altitude entrance 191 m 162 m Depth 14.4 m (+ ~ 13 m of doline) 27.2 m Development 55 m 113.6 m Figure 4: Control of the instruments in point 4 of the Casali Neri cave. Note the floor cluttered with collapsed boulders. Table 2: Statistical data regarding temperatures, measured outside and inside the two caves. In Casali Neri cave they were generally measured between 10 and 11 a.m. while in the Due Piani between 06 and 07 p.m. The minimum and maximum values refer to the entire monitoring period (March 2021-March 2022). The 12-month average refers to the period March 2021 - February 2022. measuring points Temperatures Casali Neri cave average 12 months (° C) minimum (° C) maximum (° C) 1 surface 16.0 4.4 (Dec. 2021) 34.7 (Aug. 2021) 2 bottom doline 12.6 3.9 (Dec. 2021) 22.1 (Aug. 2021) 3 cavern (top) 9.5 5.4 (Mar. 2022) 11.8 (Sep. 2021) 4 cavern (bottom) 8.9 5.6 (Mar. 2022) 11.1 (Aug. Sep. 2021) 5 bottom cave 9.4 6.9 (Mar. 2022) 10.9 (Oct. 2021) measuring points Temperatures Due Piani cave average 12 months (° C) minimum (° C) maximum (° C) 1 surface 13.7 1.8 (Jan. 2022) 31.8 (Jul. 2021) 2 upper gallery 8.7 7.6 (Feb. 2022) 12.3 (Oct. 2021) 3 upper gallery 12.6 12.2 (Apr. 2021) 13.0 (Nov. 2021) 4 lower gallery 11.9 11.0 (Feb. 2021) 12.4 (Oct. 2021) 5 lower gallery 12.6 12.4 (Apr. 2021) 12.8 (Aug. Nov. 2021) ACTA CARSOLOGICA 52/1 – 2023 97 the other hand, runs from the end of November to the first days of March, with maximum daily temperature often below 13° C. In winter, moreover, the minimum night temperatures below zero are frequent. The coldest month is January. The thermal characteristics of the two caves are dif- ferent. In the ACN, the morphological ensemble "doline- cave" forms a sort of trap for cold air, moreover the inter- nal temperatures are affected quite sensitively by exter- nal weather variations. For this reason, in point 4, near which the radon monitoring was carried out, the maxi- mum temperature was 11.1° C in August and September 2021, while the minimum dropped to 5.6° C in March 2022. It should be noted, however, that the first part of this month was characterized by temperatures below the seasonal averages and cold wind. The situation is different in the DP. Here the temper- atures are more constant and slightly higher, especially towards the bottom of the two galleries, where they are between 12.2° C and 13.0° C. It is useful to add that in both caves, the humidity is close to 100% and that, during the monitoring period, with some exceptions, the dripping was scarce and some- times almost absent. Finally, the atmospheric pressure was measured several times on the surface, in the bottom of the ACN cave and in the lower gallery of DP. Inside the caves it was generally higher, with average differences of + 2.80 and + 2.22 hPa. 4.2 CARBON DIOXIDE - CO2 During this research, elevated CO2 concentrations were recorded in both caves. The curves that show the annu- al trend in the diagrams have the typical seasonal "bell trend" (Figure 5 and 6). The first rises occur between late April and May, while the first decreases occur in Octo- ber and can be quite rapid. For example, at point 4 of the ACN, on 4 October 2021 the CO2 concentration was 5819 ppm but, only five days later, it had dropped to 549 ppm. In DP, on the other hand, the highest concentra- tions did not occur in the lower gallery, but in the upper one, where, from July to early October 2021, the values continuously went off the instrument's scale (> 9999 ppm). In ACN, however, the value went off-scale only in the first days of August 2021. Finally, it was interesting to observe that, in the warm months, the CO2 was a bit high (1400 - 1900 ppm) even at the bottom of the doline, therefore outside. GRAZIANO CANCIAN, DAMIANO CANCIAN & STEFANO REJC Table 3: Statistical data regarding CO2 concentrations in the air outside and inside the two caves. The minimum and maximum values refer to the entire monitoring period (March 2021-March 2022). The 12-month average refers to the period March 2021- February 2022. The annual average in point 3 of DP was only estimated as in some cases the value went out of the instrument scale (>9999). measuring points CO2 Casali Neri cave average 12 months (ppm) minimum (ppm) maximum (ppm) 1 surface 430 396 (Dec. 2021) 465 (Aug. Oct. 2021) 2 bottom doline 759 383 (Dec. 2021) 1920 (Aug. 2021) 3 cavern (top) 1983 401 (Dec. 2021) 8290 (Aug. 2021) 4 cavern (bottom) 2750 389 (Dec. 2021) 9990 (Aug. 2021) 5 bottom cave 3032 405 (Mar. 2022) > 9999 (Aug. 2021) measuring points CO2 Due Piani cave average 12 months (ppm) minimum (ppm) maximum (ppm) 1 surface 418 383 (Aug. 2021) 441 (Sep. 2021) 2 upper gallery 2226 414 (Jan. 2022) 7649 (Aug 2021) 3 upper gallery > 8500 442 (Apr. 2021) > 9999 (Jul.Sep. 2021) 4 lower gallery 2191 427 (Apr. 2021) 7567 (Aug. 2021) 5 lower gallery 2150 415 (Apr. 2021) 7509 (Aug. 2021) ACTA CARSOLOGICA 52/1 – 202398 CONCENTRATIONS AND DYNAMICS OF CARBON DIOXIDE, RADIOACTIVITY AND RADON IN TWO CAVES OF ITALIAN CLASSICAL KARST (MUNICIPALITIES OF SAGRADO AND SAVOGNA D’ISONZO) Figure 5: Trend of carbon dioxide concentrations in doline and in Casali Neri cave (March 2021 – March 2022). Figure 6: Trend of carbon dioxide concentrations in Due Piani cave (March 2021- March 2022). 4.3 β + γ RADIOACTIVITY Radioactivity was measured by Geiger counter sensitive to β and γ radiation. Also in this case, the maximum val- ues occurred in the warm months and the minimum in the cold ones. In all probability, these radiations are large- ly due to the decay products of radon, as we had seen in the General Ricordi cave. A gamma spectrometer, in fact, had demonstrated the presence of 40K - 226Ra - 214Bi (Can- cian & Cancian, 2021). The first is ubiquitous, while the last two are part of the decay chain of 238U, within which there is 222Rn isotope: 238U →(α) 234Th →(ß) 234Pa →(ß) 234U →(α) 230Th →(α) 226Ra →(α) 222Rn→(α) 218Po →(α) 214Pb →(ß) 214Bi →(α e ß) 214Po →(α) 210Pb →(ß) 210Bi →(ß) 210Po →(α) 206Pb (stable). The radioactivity was greater in ACN, where the highest values were not observed in the deepest section of the cave, but at the end of the cavern (point 4). Here, on 7 August 2021, the maximum of 0.85 μSv/h (average of 8 minutes of recording) was reached, with peaks up to 1.05 μSv/h. ACTA CARSOLOGICA 52/1 – 2023 99 GRAZIANO CANCIAN, DAMIANO CANCIAN & STEFANO REJC Table 4: Statistical data regarding γ + ß radioactivity outside and inside the two caves. The minimum and maximum values refer to the entire monitoring period (March 2021-March 2022). The 12-month average refers to the period March 2021 - February 2022. measuring points β +γ radioactivity - Casali Neri cave average 12 months (μSv/h) minimum (μSv/h) maximum (μSv/h) 1 surface 0.097 0.08 (Dec. 2021) 0.13 (Aug. 2021) 2 bottom doline 0.101 0.07 (Apr. Dec. 2021) 0.15 (Aug. 2021) 3 cavern (top) 0.164 0.05 (Dec. 2021) 0.37 (Jul. 2021) 4 cavern (bottom) 0.223 0.07 (Nov. Dec. 2021) 0.85 (Aug. 2021) 5 bottom cave 0.151 0.07 (Nov. 2021) 0.30 (Aug. 2021) Figure 8: Trend of ß + γ radioactiv- ity in Due Piani cave (March 2021 – March 2022). Figure 7: Trend of ß + γ radioactivi- ty in doline and in Casali Neri cave (March 2021 – March 2022). ACTA CARSOLOGICA 52/1 – 2023100 4.4 RADON During this research some rather high values were found. The maximum was recorded in September 2021 in ACN: 50 161 Bq/m3. The monitoring was carried out once a month, ex- cept in October 2021, when two were carried out. In that period, in fact, there was an abrupt change in weather conditions, with rapid lowering of temperatures and therefore we wanted to see if this had influenced the con- centrations of radon. Indeed, its concentration dropped from 34 724 to 1748 Bq/m3 in ACN and from 10 804 to 833 Bq/m3 in DP. The annual radon trend, as shown in Figure 9, can- not be exactly overlapped in the two caves. The maxi- CONCENTRATIONS AND DYNAMICS OF CARBON DIOXIDE, RADIOACTIVITY AND RADON IN TWO CAVES OF ITALIAN CLASSICAL KARST (MUNICIPALITIES OF SAGRADO AND SAVOGNA D’ISONZO) measuring points β + γ radioactivity - Due Piani cave average 12 months (μSv/h) minimun (μSv/h) maximum (μSv/h) 1 surface 0.106 0.08 (Dec. 2021) 0.12 (Jun. Sep. 2021) 2 upper gallery 0.087 0.05 (Mar. 2021) 0.14 (Jul. Oct. 2021) 3 upper gallery 0.124 0.07 (Jan. 2022) 0.26 (Aug. 2021) 4 lower gallery 0.138 0.08 (Jan. Feb. 2022) 0.25 (Jul. Aug. 2021) 5 lower gallery 0.140 0.07 (Mar. Dec. 2021) 0.31 (Aug. 2021) Table 5: Activity of radon in the bottom of the great cavern in Casali Neri cave and in the upper gallery of Due Piani cave. days of monitoring Radon - Casali Neri cave average (Bq/m3) minimum (Bq/m3) maximum (Bq/m3) 03 - 07 Apr. 2021 1313 96 4212 10 -15 May. 2021 10 683 7576 13 402 03 – 07 Jun. 2021 10 728 7111 15 179 08 – 13 Jul. 2021 28 043 24 041 33 094 03 – 07 Aug. 2021 30 670 26 612 36 595 06 – 11 Sep. 2021 44 065 39 193 50 161 04 – 09 Oct. 2021 17 – 28 Oct. 2021 34 724 1748 5497 582 49 778 4793 05 – 10 Nov. 2021 579 164 2817 04 – 08 Dec. 2021 162 150 187 04 – 08 Jan. 2022 680 91 3063 06 – 12 Feb. 2022 827 347 3446 06 – 12 Mar. 2022 600 211 2429 days of monitoring Radon - Due Piani cave – upper gallery average (Bq/m3) minimum (Bq/m3) maximum (Bq/m3) 04 – 07 Apr. 2021 558 318 1031 28 Apr. – 03 May. 2021 2504 722 3706 05 – 10 Jun. 2021 5986 4145 7373 02 – 08 Jul. 2021 18 873 11 728 22 138 18 – 20 Aug. 2021 14 041 10 372 15 128 12 – 15 Sep. 2021 11 254 10 009 13 161 04 – 08 Oct. 2021 12 – 16 Oct. 2021 10 804 833 7984 478 14 345 2445 05 – 10 Nov. 2021 1567 617 3725 19 – 22 Dec 2021 258 178 299 04 – 09 Jan. 2022 361 207 787 09 – 13 Feb. 2022 389 142 568 08 – 12 Mar. 2022 338 180 552 ACTA CARSOLOGICA 52/1 – 2023 101 mum values, in fact, were reached in July in DP and in September in ACN. The monthly declines were also slow in DP and faster in ACN. Most likely this depends on the different geometry of the two caves and the different ventilation conditions. The argument, however, requires further measurements and observations. Some monitoring was also carried out in the lower gallery of DP, always using the Radex instrument, obtain- ing these results: For further integration of the research, measure- ments were also carried out using the Fidotrack CR39 passive detectors. Since they had to remain in position for 27 days, in ACN, which is also accessible to occasional visitors, the detectors were hidden in two cavities of the cavern, where only one arm could be inserted, the first towards the entrance and the other towards the lower part. Remember that these sensors only give the average value with respect to the time in which they were posi- tioned. For this reason it is not possible to make a direct comparison with the data obtained in the same month with the Radex tool. The values obtained, however, are of the same order of magnitude. The diagrams relating to two significant moments of radon activity are shown below: in the phase of increase (Figure 10) and in reaching the maximum values (Figure 11). GRAZIANO CANCIAN, DAMIANO CANCIAN & STEFANO REJC Figure 9: Average concentrations of radon in the two caves, from April 2021 to March 2022. Table 7: Results of radon activity through the CR39 detectors. Casali Neri cave position of CR39 detectors days of monitoring activity beginning of cavern, east wall from 8 July to 3 August 2021 28 769 Bq/m3 (± 9%) bottom of cavern, east wall from 8 July to 3 August 2021 30 765 Bq/m3 (± 9%) Due Piani cave bottom of upper gallery from 8 July to 4 August 2021 14 915 Bq/m 3 (± 10% bottom of lower gallery from 8 July to 4 August 2021 10 321 Bq/m 3 (± 10%) Table 6: Radon activity in the lower gallery of Due Piani cave. days of monitoring average (Bq/m3) minimum (Bq/m3) maximum (Bq/m3) 28 Apr. – 3 May 2021 2691 1182 4431 10 - 15 Jun. 2021 7088 5771 8670 12 - 17 Sep. 2021 12 479 10 776 13 785 19 - 22 Dec. 2021 726 547 850 ACTA CARSOLOGICA 52/1 – 2023102 CONCENTRATIONS AND DYNAMICS OF CARBON DIOXIDE, RADIOACTIVITY AND RADON IN TWO CAVES OF ITALIAN CLASSICAL KARST (MUNICIPALITIES OF SAGRADO AND SAVOGNA D’ISONZO) Figure 10: Radon monitoring from 3-4 to 7 April 2021 in the two caves. The maximum values occurred at night at the minimums in the af- ternoons. Figure 11: The maximum activity in ACN was recorded in September (50 161 Bq/m3), while in DP it was recorded in July (22 138 Bq/m3). In this case, the highs and lows are clearly not affected by the day/night rhythm. Furthermore, the decrease up to 11 728 Bq/m3 in DP is not re- lated to particular weather events, in fact it occurred on a normal hot summer day, without significant changes in atmospheric pressure. ACTA CARSOLOGICA 52/1 – 2023 103 GRAZIANO CANCIAN, DAMIANO CANCIAN & STEFANO REJC 5. PARAMETERS ANALYSIS 5.1 CORRELATIONS BETWEEN ß + γ RADIOACTIVITY AND RADON ACTIVITY The verification of this correlation is important for prac- tical purposes, because the speleologist or the tourist can have a first indication about the possible presence of high radon values by simply carrying out a quick mea- surement with a pocket Geiger counter. In this regard, it should be noted that cheap instruments do not record α radiations, such as those emitted during the decay from 226Ra to 222Rn, however the radon that accumulates in the caves is usually accompanied by other radionuclides, as highlighted in chapter 4.2 and which also emit ß and γ radiation. In our case, in both caves an “extremely significant” linear correlation was found between ß + γ radioactivity and radon activity (Figure 12). 5.2 CORRELATIONS BETWEEN TEMPERATURE GRADIENTS, CO2 AND β + γ RADIOACTIVITY We then wanted to see if there are correlations between the other parameters, measured in the points where the instruments for radon monitoring had been placed. As for the temperature, the parameter used was ΔT, which is the difference between the external temperature and that of the point considered inside the cave, at the time of the measurements. Figure 12: Correlation between radon activity (Bq/m3) and ß + γ radioactivity (μSv/h) in Casali Neri cave and in Due Piani cave. P value < 0.0001, r = 0.9161 and 0.8858 (Pearson). ACTA CARSOLOGICA 52/1 – 2023104 CONCENTRATIONS AND DYNAMICS OF CARBON DIOXIDE, RADIOACTIVITY AND RADON IN TWO CAVES OF ITALIAN CLASSICAL KARST (MUNICIPALITIES OF SAGRADO AND SAVOGNA D’ISONZO) In both caves the reciprocal linear correlations be- tween ß + γ radioactivity, CO2 and ΔT were found to be “extremely significant” with a “P value” less than or equal to 0.0001. These data, therefore, confirm that the three parameters interact with each other. In particular, the increases in CO2 and β + γ radioactivity are positively correlated to the ΔT parameter. The increases, therefore, occur when the outside temperatures are higher than those of the caves. 6. CONCLUSIONS High concentrations of CO2 and radon were already known in large or deep caves of the Italian Classical Karst, but, in this case, it has been shown that the same phenomena also occur in modest and easily accessible caves. In the ACN, for example, radon reached a peak of 50 161 Bq/m3, while in the DP the CO2 values went off the instrument scale (> 9999 ppm) from July to October 2021. The two gases have the typical seasonal pattern, but it is not exactly the same in the two caves, most likely due to the geomorphologic, thermal and ventilation differ- ences. The main mechanism influencing their dynamics is the thermal gradient ΔT. The greatest increases of both gases occur, in fact, when the external temperatures are higher than those of the caves, throughout the day or at least for a significant part of it. Furthermore, in the warm months, they appear to come mainly from the fractured rock. As for the contribution of CO2 from the outside air, through ventilation and accumulation in the deepest parts of the caves, it is instead a phenomenon that cer- tainly occurs, but does not seem to be the main one. In this regard, it should be noted that, in winter, when cold air enters the ACN easily, pockets of CO2 are formed only in the deepest part, where there is little air exchange, but with values between only 480 and 560 ppm. The contri- bution by degassing of the dripping water also appears scarce, in fact, precisely in the summer months, when the dripping was scarce - or even absent in various sections of the cave - the highest concentrations of CO2 were re- corded. In December, however, when the dripping was present, the CO2 concentration had even lowered com- pared to the previous months. Finally, it is interesting to add that in ACN the high- est values of β + γ radioactivity did not occur exactly on the bottom, but in the terminal section of the large cave (point 4). 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