of Karst Areas

During the 1990s, three European projects addressed the particular problems of protecting and managing groundwater in karstic districts. Groundwater is the main source of drinking water in Europe, and karstic terrains are widespread especially in the Mediterranean countries. These studies took place within the framework of the COST programme which co-ordinates national research at a European level and have a current membership of 28 countries. The paper describes the three karst projects, two of which are ongoing. The three projects are entitled: Hydrogeological aspects of ground-water protection in karstic areas; Vulnerability and risk mapping for the protection of carbonate (karst) aquifers; Ground-water management of coastal karstic aquifers.

The great heterogeneity of karstic environments is determined at the one hand by the external framework of the system given by its geological and tectonical structure, and by its internal structure such as the hierarchical organization of the flow paths on the other hand. Flow and transport processes show great physical differences as a result of the strong hydraulic discontinuities. Starting with a heterogenous recharge mode which varies from diffuse input over the whole outcrop to a predominantly point recharge in a small number of swallow holes, fast and slow flow components are characteristic for karst. Preferential flowpaths, interconnected conduits, have high velocities and short residence times; filtration, sorption etc. are reduced, only dilution might be the main form of attenuation. The almost unaltered rock matrix reacts as a storage area, where fine fractures and matrix pores form the pathways and thus residence time is much longer. The possibility of water-rock interactions can lead to a distinct purification of this slow component. In order to establish a sustainable management in respect to quality and quantity of the often prolific groundwater resources in karstic environments, the knowledge and quantification of the hydrodynamic processes of the karst system is essential. The knowledge of the quantity available, of the residence times as well as profound information about the catchment areas of the springs and the quality of the water are basic requirements.

The paper will present a more generalized scheme for a sustainable karst groundwater management and the necessary protection measures, based on two elaborated case studies (Antalya travertine aquifer, Turkey: Trnovski gozd karst plateau, Slovenia). Both studies including geological, hydraulic, hydrogeological and tracer hydrological investigations, are performed together with other specialized researchers in the framework of interdisciplinary working groups within 1993 and 1996.

The Croatian urban water supply is based mainly on the use of local aquifers which, because of increasing development are becoming ever more vulnerable to pollution. It relates particularly to the alluvial aquifers of two large rivers in northern Croatia, the Sava and Drava. At the same time, the karst aquifers in the areas of large towns have shown low deterioration trends, too. Only time will tell how soon even these karst aquifers pass the prescribed limit of potable water quality, in spite of high protection measures in these areas.

Under such conditions, the Croatian scientists have introduced the idea of "strategic resources" of potable groundwater in the Dinaric mountainous karst areas of Croatia that, if accepted and realized, will assure the future public potable water supply. In this way, mountainous karst aquifers have to be specially protected. It's important to point out that the Dinaric Mountains are very rich in precipitation (up to 4000mm/year) and of considerable retention capacity which sustain basic outflow, even during long summer dry seasons.

In this paper, two cases of valuable karst aquifers in the Dinarides (strategic resources) are presented along with the necessary protection measures (e.g., at the construction of new highways, the management of wastewater from the settlements in the study areas etc.).

The western limestone lowlands of Ireland are an example of a karst area where surface water and groundwater are closely interlinked. Rivers, lakes and turloughs (seasonal lakes) provide line and point recharge to the aquifers, and equally groundwater discharge provides major inputs to surface waters. The naturally fragmented surface drainage network has been artificially integrated in many areas by drainage and channelisation schemes. Surface and groundwater quality are interdependent: surface water contaminants enter the aquifer via sinking streams, while rapid transfer through the aquifer by conduit flow means that groundwater contaminants may in turn be discharged into surface waters. Water resource management in the region, including the delineation of groundwater source protection zones, flood control and nutrient management of surface waters, must take these close linkages into account.

Five karst springs drain a singular limestone massif in Eastern Serbia. Groundwater emerges at different drainage levels (difference between levels is 22 m). The quality of groundwater in this karst region is a direct consequence of the geological and other conditions prevailing in the drainage area. The spring water is bacteriologically unfit for use and turbid at increased discharges. The groundwater flow responds to the increased surface water flows and abundant rainfalls after 24 to 60 hours. Bacterial contaminants infiltrated into the aquifer by river waters, which in the upstream area, flow through some villages. Because the least-affected springs are those at the lowest altitudes, a project of capturing water from deeper parts of the karst aquifer by drilled wells is presently being carried out. It is expected to provide less contaminated water at higher yields to meet water demand, especially during the period of streamflow recession.

The Lincolnshire limestone is a regionally important aquifer in the UK that is in hydraulic continuity with local rivers draining intensely-farmed arable land. In order to assess the impact of riverine chemistry on groundwater quality, concentrations of nutrients (CPN) were monitored in both river water and ground water during a two-year period. Winter peaks in riverine nitrate (NO₃) concentration (up to 170mg l^-1) result from fertiliser applications, combined with heavy rainfall; winter river-flow recharges the aquifer and increases NO₃ concentrations in groundwater. Plumes of NO₃- rich water are drawn into the aquifer by abstraction of large volumes of water by public supply boreholes, so modifying the regional pattern of NO₃ concentrations in groundwater. Riverine concentrations of dissolved organic carbon (DOC) peak in summer (2.6-13 mg 1^-1) and reflect low-flow conditions coupled with point-inputs of effluent from small sewage treatment plants; concentrations are lower in winter (1.7-6.6 mg l^-1) when effluent is diluted by high winter flows. In the unconfined area of the aquifer, concentrations of DOC in groundwater are 0.5-1.0 mg 1^-1 and show little regional variability except for an increase to 2.0 mg 1^-1 in the confined zone where saline connate water occurs. Recharging DOC reacts rapidly with dissolved oxygen (DO) and NO₃ upon entry to the aquifer, but is present in concentrations insufficient to reduce much of the NO₃ contamination. Nitrate reduction must be driven by other mechanisms, such as chemo-autotrophic bacterial metabolism or inorganic reduction. An increase in NO₃ concentration in the aquifer with time suggests that the aquifer is not coping with the current loading of NO₃, so the confined zone of the aquifer is under threat from NO₃ pollution.

Karst terranes of the southern Ozarks in the south-central United States are subject to a wide range of agricultural land uses, most of which concentrate enteric microbes and pathogens on the land surface. Recent research in Northwest Arkansas indicates that microbial densities in streams and springs vary temporally, sometimes by as much as three to six orders of magnitude. The largest bacterial densities in streams typically occur after the hydrograph peak, whereas the largest densities in springs occur during the rising limb or near the crest of the discharge hydrograph. The upper limit of pathogen densities, which may be greater than 1,000,000 colony forming units per 100 milliliters (cfu/100 mL), occur shortly after intense storms; the lowest values of pathogen densities typically may be less than 1 cfu/100 mL and these characteristically occur at base flow, after long periods of groundwater recession. Lagtime between (1) the start of a specific rainfall event and (2) the occurrence of an exponential increase in microbes in stream water and spring water are not consistent with known flow distances or flow velocities in well-characterized karst basins; lagtime in both cases theoretically should be longer. These observations contribute to a strong argument for a new conceptual model of enteric pathogens in shallow karst aquifers. Available data are consistent with a microbial-transport model in which the pathogens are transported during flood pulses, are deposited and become quiescent during recessional stages, and are resuspended and transported again during subsequent turbulent-flow events. The preliminary results of these tests indicate that the pathogens in these karst groundwater flow systems are indeed viable for time periods exceeding several months, and that densities are a complex function of land use, precipitation, climate, and hydrology of the flow system.

In order to distinguish resuspended sediment-bound pathogens from stormwater pathogens derived from recent, surface fecal contamination, a series of in situ field tests are being conducted at the Savoy Experimental Watershed. Multiple tracers and continuous monitoring are being undertaken at selected sites along a previously defined groundwater flow path. The tracers include (1) conservative solutes and fluorescent dyes, used as indicators of groundwater velocity, (2) Lycopodium spores, and (3) genetic particles identifiable using polymerase chain reaction (PCR) and pulse-field gel electrophoresis (PFGE) methods.

Five layers were used in a GIS-based construction of a groundwater vulnerability map (1:50,000 scale) of the Muránska Planina Plateau (Slovakia), a regional karstic aquifer of 126 km² area. The data used consists of: (1) a karst phenomena map derived by stereoscopic interpretation of photogrammetric image; (2) a karst phenomena map derived by geomorphology mapping; (3) a soil cover thickness areas map derived by field investigation; (4) a hydraulic transmissivity map derived by aquifer modelling; and (5) groundwater flow velocity derived by aquifer modelling.

Various weighting and rating was given to the phenomena present in the area, considering specificity of the karst rock environment. The final map should be used for better land use management in the aquifer area, as it represents a valuable source of drinking water, mostly captured in springs at the plateau edge. The map reveals places of concentrated infiltration (swallow holes) that should be specially treated and protected as the "satellite" protected areas of the first degree. On the other hand, some areas on the northern part of the Muránska Planina Plateau seem to be not so vulnerable. The reason is that the rock environment here is formed mainly by dolomites and this fact is influencing even the transmissivity and flow velocity. Also soil cover influence has a remarkable effect and these areas can be considered relatively safer for acceptable human activities.

The destruction and disposal of explosives, propellants, and pyrotechnics have polluted groundwater aquifers through additions of numerous contaminates including sulfate. Sulfur isotopic compositions of sulfates in groundwater have been studied extensively in gypsum springs, acid mine drainage, and from atmospheric fallout of sulfur from the burning of fossil fuels, however, little is known about the sulfur isotopic composition of sulfates derived from the disposal of explosives, propellants, and pyrotechnics.

The Ammunition Burning Ground (ABG) at the Crane Naval Surface Warfare Center, Crane Division, Indiana has been used since the 1940's for the destruction and disposal of ordnance materials. High concentrations of sulfate have been found in a karst aquifer underlying the ABG. Sulfur isotopic analysis of a background well located upgradient and to the north of the ABG resulted in a d ³⁴S of -8.39‰, while isotopic analysis of a burn sample resulted in a d ³⁴S of +7.17‰. The difference between these values was used in an attempt to show the movement of sulfate derived from burning activities in groundwater of the karst aquifer. Five wells located downgradient and to the south of the burn pads and surface impoundments used for the thermal treatment of munitions showed enrichment of d ³⁴S of sulfate (d ³⁴S=+2.53, +3.05, +4.05, +8.37, and +9.39‰), possibly resulting from the presence of sulfate derived from disposal activities. Two wells located to the north of the treatment facilities has d ³⁴S value (d ³⁴S= -8.29 and -9.2‰) near the background level, indicating only naturally derives sulfates in these wells. One spring, which has been shown by dye tracing to be the discharge point for groundwater from the ABG, was also sample resulting ind ³⁴S value which vary over time (d ³⁴S = -1.46 and +2.63‰). This may reflect mixing of background sulfate and sulfate derived from disposal activities.

Numerous papers have been dedicated to the problem of fresh water use in the case of salt water intrusion into collectors in coastal karst aquifers. In this paper, possibilities of separating the influence of sea within localities with incomplete lateral (partly eroded) barrier are discussed. As in the case a barrier is eroded to a limited depth and at a limited area, effects can be expected by use of grout curtain connected to impermeable sides and footwall. Such intervention, with previous experiments, was performed in the area of hollow Trstenica near Orebic (Croatia). The results are presented in a significant part of the paper. Here, among all, at places of eroded flysch zone (along the total length over 130m), concrete walls are built (between plus/minus 3m peak elevations). Obtained results were used to verify the accuracy of applied concept of solving the problem.

In the Ozark Mountains of northwestern Arkansas, geologic mapping, spring data, and dye tracings identify probable structural controls on both the location of large-discharge springs and an interbasin flow of ground water that introduces agricultural contaminants into the upper Buffalo River. Within the exposed Ordovician to Pennsylvanian sedimentary sequence in the study region, the 120-m-thick cherty limestone of the Mississippian Boone Formation is the main host of karst features and the dominant aquifer, as illustrated by a high concentration of springs at its base. This region was mildly deformed, probably during Pennsylvanian time, by a system of normal and strike-slip faults and associated monoclines that vertically offset the strata from 15 to 120 m. These structures influence the hydrogeology of the Boone Formation both by varying its elevation and by changing its hydraulic properties. Two areas with large springs in the Buffalo River watershed both lie in or adjacent to structural troughs in the Boone Formation, suggesting that these troughs preferentially drain water from adjoining regions. In one area, within the drainage of Cecil Creek, large springs and an extensive karst network (including Arkansas' longest mapped cave) occupy a 5-km-wide, 30-m-deep trough situated between two northwest- trending monoclines. In a second area, the large Dogpatch springs lie at the head of a 30- to 45-m deep, keel-shaped trough that is cored by the northeast-striking, right-lateral Elmwood fault zone. Preliminary dye tracings show that nitrate-enriched waters discharging from Dogpatch springs are derived via interbasin flow from the Crooked Creek watershed to the north. The interbasin flow coincides with the area where the trough crosses the watershed boundary. We think this fault-cored trough gathers recharge from its limbs within the Crooked Creek watershed and allows it to flow southwest across the watershed boundary in a network of solutionally enlarged fractures that envelope the Elmwood fault zone. The exit of ground water at the Dogpatch springs coincides with a corner-shaped upstep of the Boone caused by intersection of the Elmwood fault zone with the east-striking Cutoff Road normal fault. More dye tracings are in progress to test this model.

The Upper Floridan aquifer system (UFAS) is heavily karstified and unconfined in most of north Florida. It is vulnerable to non-point source polluted surface-water influx. A two-year study in conjunction with the USGS-Tallahassee examined the hydraulic and geochemical interaction between the Suwannee River and UFAS was studied. Water samples from fifteen wells and one sinkhole were analyzed quarterly for major ions, nutrients and dissolved organic carbon. Ground water levels were monitored on a biweekly basis at these sites and potentiometric surface map were constructed at various river stages. Chemical tracers (SF6 and fluorescein), environmental isotopes (¹⁵N, ¹⁸O, ³H and ²²²Rn) were used to determine ground water flow velocity and direction and to define the dynamics of surface/subsurface aqueous interactions.

Ground water levels in wells adjacent to the river (<3 km away) varied directly with river stage. During a high river stage in April 1996, the potentiometric gradient reversed and ground water flow was directed away from the river. This indicates that it is hydraulically possible for surface water to enter into the UFAS. During low river stage the ground water recharges the river via seep and springs. Ground water geochemistry however remained quite constant throughout the year. Only two sites, a well located adjacent to the river and a sinkhole, displayed surface water characteristics during high river stage.

The ground water levels in the areas adjacent to the river are affected by changes in river stage. It is still uncertain on the geochemical impact the river may have on the UFAS. Surface water enters the UFAS through the numerous karstic features proximal the Suwannee River.

The Gran Sasso ridge, a large regional karstic aquifer, includes 12 groups of springs, with an average discharge of 23 m³/s. Most of the springs, among which those of Tirino are the most important, are concentrated on the southern side of the ridge. The Tirino River is fed almost exclusively by groundwater, receiving an average of 12 m³/s of base-flow recharge from springs. The main springs are Capodacqua, Presciano and Southern Tirino; several other important springs also drain directly into the riverbed.

Discharge data for the Tirino springs are fragmentary and have been collected on a continuous basis only for short periods. Monthly monitoring of discharges and recording of selected parameters (temperature, pH, electrical conductivity, chemistry, with Ca⁺⁺, Mg⁺⁺, Na⁺, K⁺, Cl^-, SO₄⁼, SiO₂) began in 1996. Biological features of the springs were also investigated, especially at Presciano. Significant data on hydrogeological setting, including amount of water resources and impact of human activities were obtained from this monitoring activity.

At present, the groundwater from the springs is exploited for several uses, including hydropower, irrigation, fish farming, industrial applications and drinking-water supply. Only a small percentage is used for drinking. Nevertheless, the Tirino valley presents a very interesting environmental situation, whose landscape, vegetation and hydrographic network need to be preserved. Exploitation of water resources, vulnerability of the area, human needs and environmental protection call for a wiser management strategy.

The environmental situation is excellent in the northern sector of the valley, where human activities do not interfere with natural characteristics. In contrast, the southern part of the valley has water resources badly exploited, which has resulted in significant degradation of spring-water quality.

Delineation and remediation of subsurface contamination have become a major focus of environmental science during the past years. Conventional technologies available for subsurface investigations (e.g. monitoring wells) always will be required to confirm and monitor subsurface contamination. However the gas transport and contaminant movement through the unsaturated zone plays a significant role for attenuation processes. Soil-gas surveying therefore is the only technique applicable for the investigation of a wide range of volatile organic compounds (VOC_S) and other contaminants within the unsaturated zone under a variety of geological and hydrological settings. This paper presents the most recent the theory and model development for the transport and fate of gases in the unsaturated zone and ground water as well as results from field and laboratory investigations. The model includes the (1) transport and fate of gases in unsaturated soils, (2) additional the mathematical description of reactive gas transport of gaseous components that hydrolyze in water, and (3) transport of dissolved gases in groundwater. The results of the laboratory and field investigations show that physical, chemical, and microbial processes are determining VOC concentrations in soil gas. For example the aerobic biodegradation of VOCs and organic compounds in the unsaturated and saturated zone of porous aquifers decreases the O₂ content and increases the CO₂ content in the soil air and in the groundwater. The VOC- and CO₂-content in soil air is mainly controlled by a combination of the following processes: (1) biological production, (2) diffusional transport, and (3) equilibration between transported VOC/CO₂ and soil water.

In central Italy, a large percentage of the water supply comes from mountain springs in calcareous areas. For example, roughly 70% of the water supply of Rome comes from springs in the Apennines. This is due to the fact that spring water is of good quality (the recharge zones are located in mountain areas with few inhabitants), it is easily obtained and distribution costs are rather low, since the springs are often found at high elevation. Given that water needs continue to rise, and that the majority of alluvial aquifers are already over-utilized and are often polluted, the use of mountain carbonate aquifers and springs is steadily increasing. This leads to the drying up of many springs or to a decrease in the flow of many streams originating from the springs, with serious environmental consequences.

There are essentially three systems for drawing spring water: drainage tunnels, vertical wells and sub-horizontal drains. The traditional system is that of drainage conduits, which have high initial costs but low maintenance costs. Wells, which are used especially for springs having small dynamic reserves in comparison with their geological reserves, have the advantage of providing practically constant flows: during periods of low natural flows, the wells draw from the geological reserves. However, if the mean amounts being drawn are not carefully regulated, the geological reserves are depleted in a relatively short period of time, and as a result the springs remain dry for long periods. Sub-horizontal drains consist of a chamber with a bottom lower than the elevation of the spring. Sub-horizontal drains sloping down radiate from this chamber towards the spring for a distance of 150 - 200 meters. The drains have valves for controlling the flow of water, which is collected in a reservoir and then distributed. These systems have a rather high initial cost but offer the following advantages: they draw water from below the water table, and thus it is always filtered and clear, even after heavy rains; no electricity is needed to draw the water from the aquifer; the water drawn cannot exceed the mean aquifer recharge; large land areas are not needed for well fields. Regardless of the system used for drawing water, the main problems connected with spring management are the following: a) the vulnerability to pollution: being fed by carbonate formations with permeability from fracturing, these springs are potentially very vulnerable; b) the difficulty of constructing reliable mathematical models: this is due to fact that data from pumping tests and potentiometric data are usually not available: also, because of the fracturing, it is difficult to estimate the real flow velocities and in calculating the protection zones.

New geologic maps at scales of 1:24,000 and 1:100,000 are being produced by the U.S. Geological Survey for a part of the Ozark uplift in southern Missouri that contains abundant karst features including some of the largest springs in the United States.The area is largely within the Mark Twain National Forest and includes the Ozark National Scenic Riverways and a number of State Forests. The mapping is being carried out with special attention to lithologic, structural, and geomorphic aspects that may have significant effects on groundwater movement and the general hydrogeological environment of the Ozark and St. Francois aquifers. The potential for lead-zinc mining in the area is critical to water-quality issues in the public lands. Map data will be used along with laboratory testing of the rocks to produce hydraulic conductivity estimates and other hydrologic information bearing on this issue. The area is underlain by Cambrian and Ordovician dolomite with minor amounts of sandstone, shale, and chert totaling about 2,500 ft in thickness, overlying a Precambrian basement of granite and rhyolite. The flat-lying sedimentary rocks form a karst plateau through which Middle Proterozoic rhyolite knobs locally protrude. Much of the area is underlain by unconsolidated surficial deposits, including a thick residual mantle of weathered Paleozoic bedrock on hill tops and colluvial material on slopes. Conodont biostratigraphy, driller's logs, petrographic study of drill cores, and cave mapping augment detailed mapping.The collection of detailed fracture data at each outcrop includes orientation, frequency (spacing), persistence, aperture width, and the presence of any seepage. Faults, generally concealed, are identified by stratigraphic offset, the presence of slickensides and breccia and coincidence with geophysical anomalies. Fracture analysis has shown two predominant joint trends centering about N.75° E. and N.15° W. Several newly recognized faults apparently have both vertical and horizontal slip components, and generally follow the joint trends. Outcrop seeps and localized karst conduits suggest significant groundwater flow along certain bedding surfaces. Buried basement topography may be responsible for diverting or channelling groundwater flow.

The chemical composition of karst groundwater in the Carpatho-Balkanides of Serbia reflects the conditions of their formation.More than three hundred chemical analyses of karst springs were made in the Laboratory of Hydrochemisry of the Faculty of Mining and Geology, in Belgrade. The gravity springs on the higher peaks, are characterized by the rapid filtration, while the ascending springs have more favorable characteristics and a much lower rate of chemical and bacteriological impurity.

The regression and factor analysis were applied for differentiation of many variable influences. The gained factors were marked as limestone and sedimentary factors.

The Savoy Experimental Watershed (SEW) is a University of Arkansas (UofA) property of approximately 1250 hectares (ha) in Northwest Arkansas, within the central United States. The SEW occurs on a mantled (regolith-covered) karst, and is the site of an integrated research effort between the UofA, Arkansas Department of Pollution Control and Ecology (ADPCE), Agricultural Research Service (ARS) of the U.S. Department of Agriculture (USDA), and the U.S. Geological Survey (USGS) to develop a long-term, interdisciplinary field laboratory for the in situ quantitative determination of processes, controls, and hydrologic and nutrient-flux budgets in surfacewater, soilwater, and shallow groundwater environments in response to specific, near-surface anthropogenic (agricultural) activities and land uses. Comprehensive research at SEW encompasses the detailed aspects of flow and solute budgets 1) from precipitation, 2) from near-surface anthropogenic activities, 3) in runoff, 4) from within the soil zone, 5) at the epikarst, 6) from within identifiable components of the shallow karst aquifer, and 7) at spring resurgences. This study is limited to selected elements of budget terms 5), 6), and 7), with the objective of relating areal, stratigraphic, and temporal variations in flow and water quality to identifiable groundwater processes and controls.

Continuous hydrologic monitoring at SEW during storms includes measuring precipitation in .01 inch increments,and measuring interflow, epikarst flow, streamflow, water levels in wells, spring discharge, and appropriate water-quality parameters, all at 15-minute increments with automated probes and samplers. Discrete samples of groundwater from the previously mentioned sources are also collected throughout the storm hydrograph (~1-hour increments) for analyses of water-quality constituents not easily measured by existing sensors. These data provide a wealth of information that allows mass-balance calculations, boundary-flux determinations, and water-quality evolution, all within a well-constrained areal and temporal framework amenable to numerical simulation at a site-specific scale. Temporally random sampling not keyed to specific hydrologic flow conditions is of little value, and does not characterize important transport features of the system. In addition to documenting system variability and helping formulate sampling rationale, preliminary data from continuous monitors and discrete hydrologic event sampling is providing valuable information on budget contributions from these complex springs.

Blanca and Mijas mountains make up the most important hydrogeological unit in the touristic area of the Costa del Sol, it supplies a population of 250,000 persons. This unit has 170 km² in surface and average resources of 50 hm³/year, but the average discharges are superior in nearly 15 hm³/year because of the pumping which is produced in Sierra Mijas.

The aquifer material is a carbonated formation 300m thick, made up of white-dolomitic marbles toward the bottom and blue-calcareous marbles toward the top. The geological structure is very complex and permits differentiating three sectors: western Sierra Blanca with an interference of N-S and E-W folds, eastern Sierra Blanca with a tabular structure and Sierra Mijas with ESE-WNW folds. This folded structure is truncated by fractures NNE-SSW and NNW-SSE.

The geological structure and mineralogical composition of the marbles have conditioned the existence of different piezometric levels-distinct system and different aquifer behaviors. Thus, the western Sierra Blanca systems, are made up of blue-calcareous marbles with a large speleological development, the springs of this sector present hydrogrammes with very marked peaks and variations in the water chemistry and temperature of the waters.So the western Sierra Blanca aquifers are conduit flow systems, they have a scarce natural regulation.

Eastern Sierra Blanca and Sierra Mijas are principally formed by white-dolomitic marbles, little karstified but very fractured, drained by springs which present variations slightly marked in the outflow, in the temperature and in the chemical compositions of their waters. Therefore eastern Sierra Blanca and Sierra Mijas aquifers have a very inertial and a diffuse flow behavior.

In the Blanca-Mijas unit, numerous boreholes have been drilled, some of them by different Spanish Public Organizations which today are included in the Environmental Ministry. These boreholes corroborate the above mentioned interpretation about the hydrogeological behavior of the systems. Thus the boreholes of western Sierra Blanca have specific yields less than l /l /s/m, so normally they are not exploited, and in the eastern Sierra Blanca and Sierra Mijas ones the specific yields are superior reaching even 225 l/s/m, which are very exploited for the urban water supply.

The boreholes have permitted delimitating eight aquifer systems which have been distinguished in the unit and also controlling the piezometric evolution in time, some of these, since 1979. This historic evolution shows, in western Sierra Blanca a natural functioning with the piezometric level, always above the height of the spring, whereas in eastern Sierra Blanca and, above all, in Sierra Mijas the evolution presents a piezometric decrease (reaching 100 m) because of the exploitation but the level being almost recovered with the rainwater.

The urban solid waste landfill of Marbella (Andalusia, South of Spain) is located 2 km north of that city and above the marbles of Sierra Blanca, a carbonated aquifer. The hydrogeological situation and the fact that the landfill is unlined, putting in touch directly the wastes with the aquifer materials, produce a degradation of the natural quality of the groundwater, due to the infiltration of the leachates. The natural groundwater flow, towards the S and W in the aquifer, produces the horizontal distribution of the pollutants. In this work the density and the chemistry composition of the landfill leachate and of the groundwater have been studied.

The average density of the leachate (1.012gr/cm³) is due to its high mineralization, with high contents in Cl (4800 mg/l in average). This density is l.2% greater than the non-polluted groundwater (1.0005 gr/cm³) with average contents in Cl of 12.4 mg/l. In the nearest points to the landfill (350 m in distance) and located to the S, a lesser pollution (500mg/l in Cl) have been detected, compared with points as far as 2500 m, where Cl contents of 840 mg/l have been measured. Nevertheless in middle points there are a lesser pollution, and in a piezometer closer to the landfill (550 m in distance) no groundwater contamination evidence have been found, thought they are located in the same sense of the local groundwater flow.

The percentage of leachate in the groundwater, comparing the cloride as conservative ion, has been also calculated. The greater contribution of leachate to the groundwater (17.5%) were found in the farest piezometer (2500 m)between 110m (25m a.s.l.)and 130 m (5m a.s.l.)in depth. The distribution of the pollutants is explained by the density difference (1.2%) and the mineralization, between the leachate and the groundwater, producing a vertical spreading effect of the pollutants and a vertical leachate migration through different groundwater flow lines than those of the non-polluted groundwater. In resume this work is a field example of a previous experimental model in porous media, proposed by Schincariol &Schwartz(1990), but taking into account the non-homogeneous characteristics of the karstic media.

Dawu Well Field which is located in the east of Zibo City, Shandong Province is one of the largest well fields in China and the yield of it is 552,400-535,400 cubic meters per day. It is the most important resources for the urban water supply in Zibo City.

The well field was placed in the Zihe Fault Zone in Zihe Stream Valley. The aquifer is a fractured-karst formation of limestone and dolomite of the Middle Ordovician. Alluvial gravels and pebbles in the streambed directly cover the fracture-karst aquifer and the surface water can infiltrate into the ground and recharge groundwater. Before Taihe Reservoir was built on the upstream reach of Zihe stream in 1972, the groundwater resources of the well field was 650,000 m³/day, of which the leakage from surface water was about 300,000 m³/day. After 1972 the strearn was always dry and the leakage of the stream water disappeared. That caused an over- exploitation of the well field. Authors studied the hydrogeological situation and concluded that the well field was suitable for artificial recharge. The artificial recharge began in 1994 and the groundwater resources has been recovered until 1996.

Heiwang Iron Ore is an open mine located halfway between Taihe Reservoir to Dawu Well Field. The ore is rich in fracture-karst water, and the drainage from 1960 to 1994 was 61.2×10³ m³/day on an average. A stepwise regression equation was obtained in our research. The equation showed that the discharge of Taihe Reservoir water into Zihe Stream is one of the major factors influencing the ore drainage. The above two cases show that the hydrogeological condition makes that the surface water in Zihe Stream is one of the major recharge resources of groundwater.

Karst aquifer is a main source of Xuzhou's water supply. In recent years, the aquifer was extensively exploited in response to the increasing demands of industrial, agricultural and public supply. In addition, industrial wastes seepage, intensive agricultural activities including irrigation with polluted water, use of chemical fertilizer and pesticide, all contributed to environmental geologic problems such as water quality deterioration and karst collapses. Especially, the karst aquifer which occurs under the Kuihe River and the abandoned Yellow River, has been extensively contaminated by industrial waste water. Increases in hardness, total dissolved solids, heavy metal elements and organic matters are threatening the health of urban inhabitants. Based on monitoring data, this study has documented the water-level drawdown, the occurrence of pollution of karst water and the mechanism of karst collapses.

Rivers in Xuzhou City act as sewage drains. During the past two decades pore water and karst water in some areas along the rivers have been polluted with heavy metals and bacteria because the contaminated river water leaks into aquifers. On the basis of monitoring data of water quality, we studied the interaction of river water, pore water, and karst water, and discovered that the thickness of clay and silty-clay in river bed is an important factor for retarding contamination. Where sand directly overlies limestone or thickness of clay bed is less than 3m, the karst water was often polluted; where the thickness of clay is more than 3m, the karst water quality was not impacted.

KARST ENVIRONMENTAL PROBLEMS OF THE SOUTH CENTRAL KENTUCKY KARST

Experience has shown that a number of environmental problems are often associated with urban development upon karst terrains. Bowling Green, Kentucky, the largest city in the U.S. built entirely upon a sinkhole plain, has provided a natural laboratory for the study of these environmental problems, as well as their solutions. Problems directly associated with the surface geomorphology of these areas include sinkhole flooding and sinkhole collapse, which are exacerbated by human changes in drainage and surface characteristics. Groundwater contamination of karst aquifers from urban, industrial, and agricultural landuse activities is also common, as the direct infiltration and rapid flow velocities within these aquifers offer little attenuation of introduced contaminants. Another, very serious problem experienced in Bowling Green in the 1980's was the accumulation of hazardous and explosive gasoline fumes, from leaking underground storage tanks, which accumulated in the large cave system below the city. These fumes rose into homes, schools, and businesses, resulting in evacuations and the declaration of a Health Advisory by the U.S. Centers for Disease Control. Levels of radon gas have also been measured in high concentration within the caves of south central Kentucky, and are probably associated with high levels in many homes in the area.

Biological communities in the Historic Section Ecotones of Mammoth Cave have been adversely affected by human use. Cave entrance modifications have altered airflow and zonation of the cave environment where upper to mid-level passages likely housed the largest bat hibernaculum in the world only 200 years ago. Endangered Indiana and Gray Bats were among the millions of winter residents. In River Styx, remnants of a creosote-impregnated wooden catwalk slowly rot in Endangered Kentucky Cave Shrimp habitat. Equally significant historic and prehistoric cultural resources are at risk of loss through fungal decomposition brought on by condensation from these same changes in the physical environment. Prior to installation of plexiglas baffles on the gate, amplified winter temperature fluctuations in the ecotone resulted in a greater frequency/magnitude of rockfalls and winter air dried tour trails paved with cave sediment such that tour groups raised clouds of dust. The dust joined a layer of lint from the clothes of passing millions forming a patina on everything within thirty feet of the path.

The goal of this effort is to realize a long-term, holistic management strategy that truly protects the world-class natural and cultural resources in Mammoth Cave for their inherent value and for appreciation by visitors. Over the past two years, progress has been made toward restoring airflow rates via plexiglas panels on a new bat friendly gate, and reconstructing original winter conditions via paleontological study of historically documented bat hibernacula. Bats require temperatures within narrow limits while hibernating, by identifying old bat bones, we can know the former winter temperature at that spot. Partially restoring habitat for wildlife is possible in this popular place, and the return of wildlife will enhance the visitor experience. The artificial trail being installed mitigates the most severe dust problem areas, contains lint from visitors, reduces the need for sediment mining, and reduces incidence of graffiti. In River Styx, rotting infrastructure is being removed from the cave.

This multi-year project has been heavily supported by NPS staffers John Fry, Bob Ward, and Joe Meiman in particular. Key partners include (alphabetically) the American Cave Conservation Association, Bat Conservation International, Cave Research Foundation, Canon USA, Earthwatch, Illinois State Museum, and the National Speleological Society.

Hirao-dai karst plateau is one of the Late Paleozoic oceanic limestone bodies widely distributed in Japanese islands. The limestone has been extensively metamorphosed to crystalline with a lot of dyke rock by volcanic activity. The plateau is an ellipse shape (6.3 km NE-SW and 2.7 km NW-SE, 370 to 680 m a.s.l.) and the total area is 14 km². Groundwater channels and their catchments do not correspond to the surface topography.

They have complicated distribution because of dykes intruding into limestone and channel captures under the ground. The existence of six drainage systems was confirmed by dye tracing. The boundary among respective drainage systems was determined by checking the dye injected points where the dye was detected at more than one spring. In the central part of the plateau, the catchment boundary is in the center of the plateau and two well-developed drainage systems are present from the center to northwest and to southeast. It is very interesting that the altitude difference of the discharge points of these two systems is over 200 m, and the area of the southeastern part of the catchment is extraordinarily wide when taking the incline of the route into consideration. There may be three reasons: ¹Non-limestone body such as unknown intrusive rocks is present under the ground and functions as a large scale impermeable barrier. ²It is influenced by many lamprophyre dykes with N-S and NNE-SSW strikes. ³New springs were generated at the lower part of the northeastern mountain foot, because the surface erosion progressed more in the southeastern part than in the northwestern part of the plateau. In the case of 1 and 2, it is expected that the catchment area will not be changed drastically in future. However, in the case of 3, the capture of the drainage systems by the Northeast system will be extended toward the southeastern catchment area.

NITROGEN ISOTOPE ANALYSIS FOR IDENTIFICATION OF ANIMAL WASTE CONTRIBUTIONS TO A KARST AQUIFER

Animal waste from grazing livestock is often a significant and undesirable contributing source of carbon to karst aquifers. The karst area of Greenbrier County, West Virginia is intensively grazed by beef cattle and some dairy cattle. Elevated nitrate concentrations and fecal coliform densities in the karst ground water have been directly linked to surface activities. Enrichment or depletion of the ¹⁵N isotope can be used to fingerprint sources of nitrate in ground water. ¹⁵N enrichment of 9% indicate an animal waste source. Enrichments of -3% to 3% indicate a fertilizer source. This study reports the results of a five-year study in which ¹⁵N enrichment was determined on more than 300 water samples from a karst aquifer. ¹⁵N enrichment ranged from less than 0% to more than 200% with a median of 16%. About 20 percent of the samples indicated a fertilizer source. Animal waste was the significant source of nitrate in the aquifer, especially in the winter and in the vicinity of contained cattle operations. Fertilizer sources of nitrite were found to be a major contributor of nitrate during low flow periods in the summer and fall where cattle were not confined. The study results will be useful for developing management strategies and best management practices to reduce agricultural contaminant inputs to the karst aquifer.

Although sinkhole formation is a natural process in karst, human activities that alter the local hydrology may trigger subsidence. Sinkholes are remediated as subsidence hazards or as inefficient drains. Each type of remediation traditionally has been focused narrowly on subsidence or drainage problems. Most methods used to remediate subsidence appear not to address the hydrological processes active at sinkholes. Remediation that ignores the link between water traveling at the soil/bedrock interface and the conduits that underdrain sinkholes may result in renewed subsidence, new subsidence, flooding of other sinkholes, and the contamination of groundwater resources. Two favored methodologies which may exacerbate subsidence and flooding hazards are not excavating to the solutional throat at the sediment-bedrock interface and attempts to seal sinkholes using grout. Another concern is that a fix may disguise an area of instability and groundwater recharge such that, unless the remediation was engineered to eliminate instability and pollution hazards, future land-users may be unaware of potential hazards. A final concern is the disguise of sinkholes during large scale landscaping in areas undergoing residential development. Some estavelles may generate head pressures capable of entraining engineered graded filters.

Carbonate aquifers, and those specifically identified as karst aquifers have been considered by many to be among the most difficult to monitor for contaminants and the most troublesome to remediate once a contaminant has entered them. Some have suggested that no enterprise with the potential for contaminant release to groundwater, such as a landfill, should be permitted in these terranes.

These assessments are inappropriate in some circumstances, and it can be shown that in these cases, karst aquifers may present monitoring and remediation environments that are technically superior to most granular aquifers. Further, the methodologies for appropriate monitoring a remediation are less costly.

Karst aquifers contain conduits which function as a ramifying system of horizontal bedrock wells beneath whatever overburden may exist. Because of their pervasive nature, these conduits more completely sample the groundwater in the bedrock and overburden than any feasible system of vertical wells can accomplish. A single spring monitoring point, the conduit outlet point can effectively sample an aquifer region far greater, more completely, and more conclusively than most well monitoring systems.

The conduit systems that provide superior monitoring capabilities also provide gravity drains that are equally effective for remediation purposes. These naturally occurring ramifying horizontal conduits with their very low resistance to groundwater movement more completely capture contaminants and more effectively drain them than any single point vertical pumping well or system of wells can accomplish.

Several examples of monitoring systems based upon springs are given, and a redemption system utilizing these natural features are presented.

Cuilcagh Mountain is the highest point in the uplands of south-west County Fermanagh and north-west County Cavan. The Dinantian Dartry Limestone Formation, which crops out on the lower northern slopes, has been extensively karstified and there is a complex underground drainage system with over 50 springs. These include a range of flow types, from short residence-time systems dominated by concentrated allogenic recharge from sinking streams, to longer residence time springs fed entirely by diffuse autogenic recharge. Water samples were collected from selected springs under a range of flow conditions over an 18 month period. As expected the waters are dominantly of a calcium-bicarbonate type with concentrations ranging over an order of magnitude and reflecting the dominant mode of recharge and residence times (e.g. [HCO₃^-] = 10 - 200 mg/L). Water temperature is also a useful diagnostic of recharge type and flow regime. Concentrations of other major anions/cations are low [<50mg/L].

Analysis of sulphate sulphur isotopic ratios allows characterization of sources of sulphate into the karst waters and helps to identify mixing processes within the system. General trends show decreasing d ³⁴ S and increasing SO₄/Cl with respect to rainwater values (SO₄/Cl is used to mitigate effects of differential evapotranspiration processes). Increasing SO₄/Cl must be due to addition of SO₄ to the system and the low d ³⁴ S of the additional S suggests that the source is oxidation of sedimentary diagenetic pyrite. Waters with higher SO₄/Cl and lower d ³⁴ S tend to be those with a large diffuse component consistent with increased water-rock interaction.

Possible deep circulation of water is suggested by results from two sites, SP and B3, which are topographically close. Site B3 shows decreased SO₄/Cl and increased Sr/Ca and d ³⁴ S suggesting an evolved deep circulating water influenced by bacterial sulphate reduction. Under low discharge, site SP shows similar d ³⁴ S and SO₄/Cl values to the majority of springs suggesting a mixture of short and medium residence time waters. However, under high discharge, SP shows increased Sr/Ca, SO₄/Cl and d ³⁴ S implying that under these hydrological conditions a significant amount of B3 type water is discharged from SP which is identified as a putative overflow spring.

Compliance monitoring at most sites involving regulated substances has traditionally been accomplished with monitoring wells. In some karst settings the regulatory agencies require that monitoring be conducted at springs that have been shown to be related to the site of interest through tracer techniques. Small springs are very useful monitoring locations because they are small groundwater basins and can be quite specific to the monitored site. If the site of interest is traced to a large spring, the groundwater basin often has many potential sources for contaminants. Dilution of pollutants is another problem of monitoring at springs with large groundwater basins.

Monitoring wells are often desirable because they have the potential to be more site specific and are controlled by the facility. Wells are usually placed along the low in the potentiometric surface and function on the assumption that they will be able to intercept a plume of material that may be released from the site. Plume development is dependent on the existence of granular flow of the water in the aquifer. The assumption of granular flow is usually inappropriate in Paleozoic carbonate rocks. Some monitoring wells placed in this manner may intercept material that has been released from the facility. Many monitoring wells in karst settings do detect contaminants, however, these wells may not give a complete assessment of the contaminant release. A well that has not detected a contaminant may not be positioned in the correct location to be able to intercept this material. Compliance samples that do not contain regulated substances may be no assurance that the facility is not releasing material.

Traditionally placed monitoring wells in a karst setting must be proven using tracers. Unproven monitoring wells provide no assurance of the value of the samples.

Comments and suggestions to Webmaster,
Copyrights by Karst Dynamics Laboratory and Network Center of Guangxi Normal University,
1995-1999. All rights reserved.