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The characteristics of flow from the landfill near Sežana in the area of Kras were studied by the use of tracer test. In well permeable fissure on the karren surface near the landfill the fluorescent dye uranine was injected in order to study the directions and velocities of its flow through the karst aquifer. Monitoring of tracer concentrations in the period of one year and a half enabled us to make some conclusions about the dynamics of groundwater flow in the directions towards the Timava, Brojnica and Sardoč springs. Detailed observations were organised also at the Klariči pumping station, which is the main source of drinking water for the Kras region. Increased concentrations of tracer were measured only during extremely high waters. Different explanations are possible, but we can not exclude the possibility of a weak, not permanent underground water connection with the landfill. Calculation of the amount of recovered tracer confirmed the main flow direction towards the Timava springs (recovery rate 93%) and a secondary direction with lower flow velocity towards the Brojnica and Sardoč springs. Outflow through the Klariči pumping is estimated to only 0.003% of injected uranine.
Vulnerability maps illustrate the potential threat of contaminants to groundwater and can be considered as important tools for land-use planning and related legislation. For karst areas with characteristic preferential infiltration conditions, vulnerability maps are also excellent tools for source and resource protection. However, the resulting qualitative maps are often inconsistent and even contradictive and thus might lead to inconclusive vulnerability assessments. The results of a validation of vulnerability maps produced using four different methods, DRASTIC, GLA, PI and EPIK, are reported for a karst area in southwest Germany. By means of measured hydraulic and transport parameters of the geological sequence, numerical simulations were used based on a conceptual model for the area under study. The mean transit time through the unsaturated zone (resource protection) was used as the validation parameter. The study demonstrates that the highest level of accuracy is achieved with the GLA- and PI methods. Both DRASTIC and EPIK are not able to incorporate highly variable distributions and thickness of cover sediments and their protective properties in the respective mapping procedure. Thus, vulnerability maps produced with DRASTIC, EPIK, and related methods should be used with care when employed in vulnerability assessments for land use planning and related decision-making.
Les cartes de vulnerabilite illustrent la menace potentielle des contaminants envers les eaux souterraines, et peuvent etre considerees comme des outils importants en matiere d'amenagement foncier et de reglementation associee. Sur les domaines karstiques, caracterises par des conditions d'infiltration preferentielle, ces cartes sont egalement d'excellents outils de protection des sources et des ressources. Cependant, les cartes qualitatives resultantes sont generalement incoherentes voire contradictoires, et peuvent par la-meme mener a des evaluations de vulnerabilite peu concluantes. La presente etude expose les resultats de validation de cartes de vulnerabilite produites selon quatre methodes differentes (DRASTIC, GLA, PI et EPIK), dans le cas d'un domaine karstique du sud-est de l'Allemagne. Par le biais des parametres de transport et hydrauliques mesures sur la sequence geologique, des simulations numeriques basees sur un modele conceptuel du secteur d'etude ont ete utilisees. Les temps de transit moyens a travers la zone non saturee (protection de la ressource) ont ete utilises comme parametres de validation. L'etude demontre que le niveau maximum de precision est obtenu par les methodes GLA et PI. Dans la phase de cartographie, les methodes EPIK et DRASTIC sont incapables d'integrer une forte variabilite dans les distributions et les epaisseurs de sediments de couverture, ainsi que dans leurs potentiels de protection. Aussi, les cartes de vulnerabilite produites par les methodes DRASTIC et EPIK doivent etre utilisees avec precaution dans le cadre des evaluations de vulnerabilite a but decisionnaire pour les amenagements fonciers.
Los mapas de vulnerabilidad ilustran la amenaza potencial de contaminantes para el agua subterranea y pueden ser considerados herramientas importantes para planeamiento del uso de la tierra y legislacion relacionada. Para areas carsticas con sus caracteristicas condiciones de infiltracion preferencial, los mapas de vulnerabilidad son tambien excelentes herramientas para proteccion de fuentes y recursos. Sin embargo, los mapas cualitativos resultantes son frecuentemente inconsistentes y hasta contradictorios y por lo tanto podrian conducir a evaluaciones de vulnerabilidad no concluyentes. Los resultados de una validacion de mapas de vulnerabilidad producidos usando cuatro metodos diferentes, DRASTIC, GLA, PI y EPIK, son presentados aqui para un area carstica en Alemania suroccidental. Se usaron simulaciones numericas usando parametros hidraulicos y de transporte medidos de la secuencia geologica y basandose en un modelo conceptual del area en estudio. El tiempo promedio de transito a traves de la zona no saturada (proteccion del recurso) fue utilizado como el parametro de validacion. El estudio demuestra que el maximo nivel de precision es alcanzado con los metodos GLA y PI. DRASTIC y EPIK no fueron capaces de incorporar distribuciones altamente variables ni espesor de sedimentos de cubierta y sus propiedades protectivas en el respectivo procedimiento de elaboracion de mapas. Por lo tanto los mapas de vulnerabilidad producidos con DRASTIC, EPIK y metodos relacionados deberian ser usados con cuidado cuando se usen en evaluaciones de vulnerabilidad para planeamiento del uso de tierra
Epikarst zone, due to its peculiar hydrogeologic features and functions, plays a fundamental role in karst morphogenesis and natural protection of groundwater in the conditions of open karst. The presence of epikarst considerably diminishes high vulnerability of groundwaters, generally characteristic for karst systems. Thickness of the epikarst zone is the most important parameter that determines buffering capacity of epikarst with regard to groundwater resources, its ability to retard and neutralize contaminants, hence – the protective role of epikarst with regard to groundwater resources.
The main problem in evaluation of epikarst during groundwater vulnerability assessment is luck of methods for its mapping in area. This paper, based on the analysis of regularities of epikarst morphogenesis, substantiates a possibility to assess variations in thickness of epikarst by distribution of depth of karst dolines.
Maps of doline depth distribution (representing thickness of epikarst) are created for main massifs of the Mountain Crimea, as well as maps of density of dolines and documented caves. Conjugate analysis of these maps from the standpoint of the epikarst concept gives important information about relationship of surface and underground karstification and serves as a basis for accounting for epikarst during groundwater vulnerability assessment in regions of open karst.
The study of the vadose zone has been based on 35 years research of underground water circulation and the transfer of contaminants in karst and on continuous long-term measurements and analyses of precipitation on the surface and of several representative trickles in the vadose zone of Postojna Cave over consecutive hydrological years and it offers an explanation of the dynamics of the percolation of water and simultaneous transfer of contaminants and their impact on the dissolution of carbonate rock in the vadose zone. Emphasis is placed on a multi-parameter approach based on the simultaneous use of a number of different methods, not only tracing natural tracers but also tests with artificial tracers using different methods of injection. The research contributs to the understanding of the role of the vadose zone in the karst aquifer.
Comparative tracer testing may be used to evaluate the vulnerability of groundwater to specific contaminants by comparing reactive tracer response to that of a simultaneously injected non-reactive “conservative” substance. Conversely, knowledge of tracer reaction with specific materials permits information about subsurface heterogeneity to be inferred. A series of tests completed in the vadose zone overlying a limestone aquifer employed a cocktail of particles along with reactive and
non-reactive solute tracers to investigate transport rates between the ground surface and monitoring points approximately 10 m below ground. Short pulse tests revealed both solutes and particulate contaminants could travel at rates of over 10 m/h. Comparison of particle (microorganisms) and non-reactive solute tracer breakthrough revealed that particle tracers experience pore exclusion resulting in higher peak relative concentrations which arrive earlier than those of the solute. Prolonged tracer injection during subsequent experiments confirmed the response observed and illustrated that over 40 % of flow paths between
injection and monitoring points were inaccessible to particles, but could allow solutes to pass through them. Similarly, the difference in response between various reactive tracers demonstrated tracers reached monitoring points via multiple flow paths and suggests geochemical heterogeneity plays an important role in influencing tracer behaviour. The results of this investigation highlight the complexity of water flow through the epikarst and the vulnerability of groundwater in karst aquifers to contamination when soil cover is thin to absent.
Distinctive karst hydrology arises from a combination of high carbonate rock solubility and well developed secondary porosity
(fissures). Soil CO2 is the most important influence on solubility
of carbonate rock (Ford & Williams 2007). Human activity
on the karst surface results in pollution that has an important influence on water quality. Degradation of organic pollution (e.g. waste water, leachates from landfill sites) results in inorganic
acids too. These acids could have an important additional influence on dissolution of carbonate rocks in the vadose zone. In the framework of more than 20 years of research on precipitation
percolation and transfer of contaminants (direct outflow of waste water from a small military facility where about twenty troops were stationed) through the 100-m thick vadose zone of Postojna Cave, contaminated water was observed in drips and trickles in the cave (up to 60 mg Cl-/l, up to 180 mg NO3-/l, up to 2.8 mg PO43-/l, and up to 50 mg SO42-/l). At the same time the sum of calcium and magnesium (Ca+Mg) of trickles was up to two times larger than the Ca+Mg of either the uncontaminated
reference trickle or the input waste water. The amount of dissolved limestone carried by waste water to trickles and drips in the cave was directly proportional to the concentration
of contaminant anions present. This demonstrates that there is an accelerated widening of fissures below source points of wastewater. Water with contaminants can penetrate faster and deeper into the vadose zone along the increasingly permeable
fissures without losing its dissolving power, and thus significant dissolution occurs ever deeper in the vadose zone. This results in ever faster penetration of contaminants through the vadose zone. In the final phase of such development, which takes many decades or longer, relatively rapid transfer of contaminants
through the aquifer all the way to karst springs with minimal self-cleansing effects can be expected.
Karst watersheds with significant losing streams represent a particularly
vulnerable setting for groundwater contamination because of the direct connection to surface water. Because of the existing agricultural land-use and future likelihood of urbanization, two losing-stream karst basins were chosen for intensive monitoring in Boone County, Missouri: Hunters Cave and Devils Icebox. Both caves were formed in Burlington Limestone and have similar recharge areas (33 to 34 km2) and land uses. Year-round monitoring was conducted from April 1999 through March 2002 to characterize the water quality of the main cave streams relative to herbicide, nutrient, and sediment contamination. Water sampling entailed grab samples at regular intervals and runoff-event samples collected using automated sampling equipment. Total nitrogen, phosphorus, and sediment concentrations and loads were consistently higher in the Devils Icebox stream compared to Hunters Cave. Median total N fluxes were 96 g km22 d21 at Devils Icebox and 30 g km22 d21 at Hunters Cave, while median total P fluxes were 8.5 g km22 d21 at Devils Icebox and 3.3 g km22 d21 at Hunters Cave. Herbicides or their metabolites were detected in more than 80% of the samples from both cave streams, and herbicide concentrations and areal loss rates were generally similar between the sites. Overall, the greater loads and mass flux of contaminants in the Devils Icebox recharge area compared to Hunters Cave was a result of both greater stream discharge and the occurrence of more cropped fields (94%) on claypan soils with high runoff potential. These claypan soils are known to be especially problematic with respect to surface transport of contaminants. Prevailing land use has significantly degraded the water quality in both recharge areas, but a watershed plan has been developed for the Bonne Femme watershed, which encompasses these two recharge areas. With the baseline data collected in this study, the impact of changing land uses and the implementation of management practices or new ordinances designed to improve water quality can be documented.
The movement of autogenic recharge through the shallow epikarstic zone in soil-mantled karst aquifers is important in understanding recharge areas and rates, storage, and contaminant transport processes. The groundwater in agricultural karst areas, such as Kentucky’s Pennyroyal Plateau, which is characterized by shallow epikarst and deeper conduits flow, is susceptible to contamination from organic soil amendments and pesticides. To understand the storage and flow of autogenic recharge and its effects on contaminant transport on water flowing to a single epikarst drain in Crump’s Cave on Kentucky’s Mississippian Plateau, we employed several techniques to characterize the nature and hydrogeology of the system. During 2010–2012, water samples and geochemical data were collected every four hours before, during, and between storm events from a waterfall in Crumps Cave to track the transport and residence time of epikarst water and organic soil amendments during variable flow conditions. Geochemical data consisting of pH, specific conductivity, temperature, and discharge were collected continuously at 10-minute intervals, along with rainfall amounts. In addition, stable isotope data from rainfall, soil water, and epikarst water were collected weekly and during storm events to examine storage and recharge behavior of the system. The changes in geochemistry indicate simultaneous storage and transport of meteoric water through epikarst pathways into the cave, with rapid transport of bacteria occurring through the conduits that bypass storage. The isotopic data indicate that recharge is rapidly homogenized in the epikarst, with storage varying throughout the year based on meteorological conditions. Results indicate current best management practices in agricultural karst areas need to be revisited to incorporate areas that do not have surface runoff, but where contaminants are transported by seepage into local aquifers.
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