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Many caves around the world have very high concentrations of naturally occurring 222Rn that may vary dramatically with seasonal and diurnal patterns. For most caves with a variable seasonal or diurnal pattern, 222Rn concentration is driven by bi-directional convective ventilation, which responds to external temperature contrast with cave temperature. Cavers and cave workers exposed to high 222Rn have an increased risk of contracting lung cancer. The International Commission on Radiological Protection (ICRP) has re-evaluated its estimates of lung cancer risk from inhalation of radon progeny (ICRP 115) and for cave workers the risk may now (ICRP 137) be 4-6 times higher than previously recognized. Cave Guides working underground in caves with annual average 222Rn activity > 1,000 Bq m-3 and default ICRP assumptions (2,000 workplace hours per year, equilibrium factor F = 0.4, dose conversion factor DCF = 14 μSv (kBq h m-3)-1 could now receive a dose of > 20 mSv y-1. Using multiple gas tracers (δ13C-CO2, Rn and N2O), linked weather, source gas flux chambers, and convective air flow measurements a previous study unequivocally identified the external soil above Chifley Cave as the source of cave 222Rn. If the source of 222Rn is external to the cave, a strategy to lower cave 222Rn by passively decreasing summer pattern convective ventilation, which draws 222Rn into caves, is possible without harming the cave environment. A small net annual average temperature difference (warmer cave air) due to geothermal heat flux produces a large net annual volumetric air flow bias (2-5:1) favoring a winter ventilation pattern that flushes Rn from caves with ambient air. Rapid anthropogenic climate change over decades may heat the average annual external temperature relative to the cave temperature that is stabilized by the thermal inertia of the large rock mass. Relative external temperature increases due to climate change (Jenolan Caves, 2008-2018, 0.17°C) reduces the winter pattern air flow bias and increases Rn concentration in caves. [ABSTRACT FROM AUTHOR]

• Time lapse electrical resistivity tomography (TL-ERT) identifies different ERT-zones. • TL-ERT and drip logger network identify lag times of water infiltration and storage. • Isolated, persistent water storages are associated with speleothem occurrence. • TL-ERT is part of state of the art tool kit for cave monitoring. This study provides the example of Golgotha Cave, in the south west of Western Australia, where previous long-term hydrological, geochemical and climate monitoring resulted in a theoretical hydrological model of the karst critical zone. We test this model by presenting the results of a 1.5 year monitoring program above the cave using time-lapse electric resistivity tomography (TL-ERT). Between May 2016 and January 2018 several lines up to 200 m long were monitored using a 100 multi-electrode Lipmann 4point light instrument. Various Wenner and Dipole-Dipole arrays provided information of electric resistivity changes at certain points of the year. Laboratory studies measuring volumetric water content versus electric resistivity of various rocks and soils resulted in three different ERT-hydrogeological zones. Besides the annual infiltration patterns, TL-ERT also identified previously unknown, permanent water storages as well as several areas acting as fast hydrological flow pathways most likely caused by pipe structures in the aeolianite. Specific aspects of the TL-ERT study could be correlated with the long term drip water monitoring and thus confirmed and extended the hydrogeological model of the area. A resulting conceptual model of the flow pathways derived from ERT surveys and cave water monitoring results is presented to visualise water flux from the surface to the ceiling of Golgotha Cave. This includes annual recharge to 40 m depth in less than one hydrological year, preferential flow paths to a persistent store of water, and a time lag between soil moisture saturation and seasonal connection of karst stores that indicates a narrower window for seasonal recharge than indicated by soil moisture data. [ABSTRACT FROM AUTHOR]