Increasing the productivity of water in takein water-containing crystalline rocks by increasing their fracture by an explosion

Global warming, which has been observed in the world and Ukraine in particular in recent decades, may lead to a decrease in surface and groundwater. In addition, the high level of groundwater pollution and the policy of water purification is a matter of concern. Thus, the question of finding additional and alternative sources of drinking water today is highly urgent. A significant percentage of prospecting works of the last century was devoted to discovering the groundwater fields in fractured crystalline rocks of the Ukrainian Shield. As a rule, the productivity of wells of these formations did not have high flow rates, so even now, mostly the aquifers in sedimentary deposits have been exploited. The low productivity of most wells in water-bearing fractured rocks is associated with the unknown degree of fracturing of the crystalline massif: it is difficult to determine the pathways of groundwater inflow into the fracture system and, accordingly, it is not easy to justify the exploitable groundwater reserves. In this paper, using the groundwater flow model of the Zhashkiv groundwater deposit, it is considered an increase of the productivity of water intake wells in the water-bearing crystalline rocks due to the increasing degree of their fracturing by an explosion. Thus, in hydrogeology, this technique is known when trying to increase the permeability in the near-borehole space, but as a method of artificial recharge of aquiferous crystalline rocks is used very rarely. The paper also examines typical water intakes conditions in fractured crystalline water-bearing rocks, which can be recommended for increasing their productivity by the blasting method. The results indicate that an artificial increase in fracturing degree can have a significant effect on increasing the productivity of water intakes. The basic methods of using explosives, as an example of an artificial increase in fracturing degree, in solving hydrogeological problems and the mechanisms of fractures’ formation during the action of blasting are considered.

MODELLING OF ARTIFICIAL INCREASE IN PRODUCTIVITY OF WATER INTAKE WELLS IN CRYSTALLINE ROCKS (on the example OF ZHASHKIV GROUNDWATER DEPOSIT, UKRAINE)

Global warming, as well as contamination of surface and ground water are currently the main factors that make the search for alternative sources of drinking water extremely pressing. The majority of aquifers commonly exploited for drinking water supply are contained in sedimentary deposits. Utilization of groundwater in fractured crystalline waterbearing rocks may be an alternative source of drinking water. However, experience in effective use of fractured rocks aquifer for water supply is very poor due to the lack of data on the crystalline rocks fracturing and, accordingly, their water-bearing capacity. Improving the effectiveness of using such geological environments is a very challenging task, yet possible with artificial recharge of crystalline rocks aquifers. Computation modeling is a widespread and proven way to study groundwater behavior in sedimentary deposits, unlike in fractured crystalline rocks. The present study focuses on the groundwater flow model to consider the method of improving the productivity of water intake wells in fractured crystalline rocks aquifer through artificially increase of the rocks’ fracturing. On the groundwater flow model for the Zhashkiv groundwater deposit, several scenarios with increase of the crystalline rocks fracturing were simulated and the effect on changing the well pumping rate was evaluated for one of the wells.

Methodology for Hydrogeochemical Sampling to Characterise Groundwaters in Crystalline Bedrock: Developments Made within the Swedish Radwaste Programme

The search by SKB (Swedish Nuclear Fuel and Waste Management Co.) for a site to locate the deep geological repository for spent nuclear fuel in Sweden has involved geoscientific investigations at several locations since the 1970s. The objectives were to characterise geologically a bedrock volume as well as its hydrogeology and hydrochemistry. To acquire high-quality hydrogeochemical data, a complete system for groundwater sampling and analysis, as well as for interpretation strategies, has been developed through a continuous process of modification and refinement. Since the largest part of the Swedish bedrock is composed of granitoids, the site investigations had to adapt to the special difficulties of fractured crystalline rocks. This paper discusses the problems with groundwater sampling that are specific to fractured crystalline rocks and describes the solutions adopted and methods developed by SKB since the early 2000s during the site investigations. The methodology described in this paper for the characterisation of deep groundwaters in crystalline rocks is not only applicable in the context of radioactive waste disposal but also useful when sampling groundwaters for any purpose in such rocks. Sampling of groundwaters in fractured rocks at depth, often down to approximately 1,000 m, involves special challenges since the natural conditions of the groundwater are easily disturbed, especially by the initial drilling, but also by every subsequent activity performed in the borehole, including the actual groundwater sampling. The sampling strategy presented in this paper shows that planning of the sampling preferably starts already when the drilling procedure is decided. Each following step is described in detail and includes tracing the drilling fluid, selecting the best borehole sections to sample, procedures for the actual sampling, and selection of analytical protocol; all this with the goal of taking representative samples. Although the evaluation of the sampling uncertainties is not a straightforward procedure, an adequate categorisation routine has been established to classify groundwater samples regarding sample quality, representativeness, and suitability for further interpretations and modelling.

Geological Processes to Consider for Modeling the Distribution of Hydrogeological Properties in Fractured Crystalline Rocks on a Site Scale

<p>Reliable predictions of the distribution of permeabilities on site scale are economically relevant in a wide range of geoscientific disciplines. Not only are predictions important for modeling hydrogeological conditions at site scale but also for using the underground safely and sustainably.</p><p>Scale dependent, different geological processes are influencing the distribution of hydrogeological properties. A dataset of about 5000 inflows from individual transmissive fractures draining to about 660 km of drifts and 57 km of boreholes has been compiled into depths of 2000 mbgs of the Variscan age German Ore Mountains (Erzgebirge/Krušné hory). Fracture closure with increasing depth is a main process controlling the distribution of transmissivities. Additionally, orientation, age and mode of fault zones exert a major control on the local distribution of inflows. These factors are locally overprinted by with the presence of contact metamorphic aureoles around Variscan granitic intrusions as seen from transmissivity reversals with depth. However, as seen from a decreasing trend of mean log hydraulic conductivity and permeability, the contact metamorphism exerts minor control on the rock mass hydrology with depth than the decreasing secondary porosity provided by fractures.</p><p>These findings are in accordance with results deduced from a worldwide permeability compilation of about 30000 single in-situ permeability measurements to depths of 2000 mbgs. Geological influences on the distribution have been analyzed on permeability-depth relationships using log-log regressions. Depth is generally the most important geological factor, resulting in a permeability decrease of three to four orders of magnitude in the investigated depth range. Beside depth, most influential factors are the long-term tectono-geological history described by geological province which locally is overprinted by current seismotectonic activity as determined by peak ground acceleration. Although petrography might be of local importance, only a low impact has been observed for the global dataset, besides lithologies allowing for karstification.</p><p>In summary, the multi-variate analysis of the datasets has improved our generic understanding of the distribution of hydrogeological properties and provides a basis to model hydrogeological processes in fractured crystalline rocks.</p>