Complex Hydrogeology Research Articles

Landscape controls on phosphorus loading to boreal lakes: implications for the potential impacts of forest harvesting

For 12 low-order lakes in the Western Boreal Forest of Canada, lake position in the groundwater flow system and surface hydrologic connection to wetlands accounted for 57% of the variation in the change in postharvest (1997) relative to preharvest (1996) open-water median total phosphorous concentration ([TP]). Changes in [TP] decreased with calcium and magnesium concentrations, indicating that the largest increases in [TP] are likely to occur in lakes located in areas of groundwater recharge or shallow local discharge. Changes in [TP] increased with the area of wetland connected to the lake, a measure of near-surface hydrologic flushing of TP to the lake. However, the remaining variation (43%) in the TP response of lakes to harvest was not explained by landscape-based criteria. This study illustrates that in landscapes with complex hydrogeology, factors controlling the chemical responses of lakes to disturbance are complex, remain poorly understood, and require further study.

Landscape controls on phosphorus loading to boreal lakes: implications for the potential impacts of forest harvesting

For 12 low-order lakes in the Western Boreal Forest of Canada, lake position in the groundwater flow sys- tem and surface hydrologic connection to wetlands accounted for 57% of the variation in the change in postharvest (1997) relative to preharvest (1996) open-water median total phosphorous concentration ((TP)). Changes in (TP) de- creased with calcium and magnesium concentrations, indicating that the largest increases in (TP) are likely to occur in lakes located in areas of groundwater recharge or shallow local discharge. Changes in (TP) increased with the area of wetland connected to the lake, a measure of near-surface hydrologic flushing of TP to the lake. However, the remain- ing variation (43%) in the TP response of lakes to harvest was not explained by landscape-based criteria. This study illustrates that in landscapes with complex hydrogeology, factors controlling the chemical responses of lakes to distur - bance are complex, remain poorly understood, and require further study.

Groundwater protection zone delineation at a large karst spring in western Ireland

Abstract Pouladower Spring is a large karst spring in County Clare, Ireland which is being considered for use as a public supply. Groundwater protection zones have been delineated as a water quality management strategy for the spring. The Irish national groundwater protection scheme methodology is adapted to take account of the hydrological and hydrogeological complexities of the karst regime. The catchment area for the spring is large (approximately 380 km 2 ) and comprises the zones of contribution for two major outlets of water, the spring and the River Fergus. The actual zone of contribution to the spring varies with different water level conditions and the risk to the source from any point within the catchment, at any given time, is less than that for a conventional groundwater source. The catchment area is highly vulnerable, but dilution and sedimentation occurring in the lakes up gradient of the source, the high throughput, and the contribution from fissures outside the main flow conduits have helped maintain good water quality at the spring. The source is considered to be a combination of both groundwater and surface water as they are intricately inter-linked throughout the catchment. An Inner Protection Area is delineated which does not provide the 100-days travel time to the source required by the national scheme, as this would be impractically large and over-protective. Rather, it delineates the area of highest hydrogeological risk to the source and should allow the local authority sufficient time to act in the event of an accidental spill. A certain degree of microbial contamination is inevitable in a karst regime and treatment is essential, as it would be for a surface water source. The remainder of the catchment is classed as an Outer Protection Area. These protection areas are then combined with the vulnerability in a GIS to give groundwater protection zones which will be used by the planners, in conjunction with groundwater protection responses, to control potentially contaminating activities.

The Lasagna Technology for In Situ Soil Remediation. 2. Large Field Test

A full-scale field test of the Lasagna process was conducted at a Department of Energy trichloroethylene-contaminated clay site in Paducah, Kentucky. The test covered an area 21 ft × 30 ft (6.4 m × 9.2 m) and reached 45 ft (13.7 m) deep. A modified sheet piling method was utilized for installing electrodes and treatment zones in thin layers through stiff clay soil without generating solid waste. Iron filings were used in the treatment zones for in situ TCE degradation. Complications encountered during the test included contamination at significantly higher levels than anticipated and complex hydrogeology in the subsurface. Treatment effectiveness seems to vary with location, but in the contaminated areas bracketed by treatment zones, TCE removal ranged from 95% to over 99%. There are strong indications that some of the TCE was transported and degraded in the DNAPL form, which has significant implications. On the basis of the field results, treatment cost for a typical one-acre site with contamination from 15 to 45 ft deep ranges from about $45 to $80/yd3. Implemented in its full configuration for the first time at a real site, the Lasagna process has demonstrated its robustness and cost-effectiveness in cleaning up TCE-contaminated soil in place.

Evaluation of Simplified Stream‐Aquifer Depletion Models for Water Rights Administration

AbstractWe assess the predictive accuracy of Glover's (1974) stream‐aquifer analytical solutions, which are commonly used in administering water rights, and evaluate the impact of the assumed idealizations on administrative and management decisions. To achieve these objectives, we evaluate the predictive capabilities of the Glover stream‐aquifer depletion model against the MODFLOW numerical standard, which, unlike the analytical model, can handle increasing hydrogeologic complexity. We rank‐order and quantify the relative importance of the various assumptions on which the analytical model is based, the three most important being: (1) streambed clogging as quantified by streambed‐aquifer hydraulic conductivity contrast; (2) degree of stream partial penetration; and (3) aquifer heterogeneity. These three factors relate directly to the multidimensional nature of the aquifer flow conditions. From these considerations, future efforts to reduce the uncertainty in stream depletion‐related administrative decisions should primarily address these three factors in characterizing the stream‐aquifer process. We also investigate the impact of progressively coarser model grid size on numerically estimating stream leakage and conclude that grid size effects are relatively minor. Therefore, when modeling is required, coarser model grids could be used thus minimizing the input data requirements.

Estuarine barrages and their influence on groundwater

The construction of a number of low crested barrage embankments across esturaries in the UK is under consideration. The structures will modify the hydrological regime to the advantage of certain infrastructural developments but the regime modifications will have repercussions for both surface water and groundwater that will impact upon the environment. Considering groundwater only, the main impact could be the effect of dampness in properties through groundwater head rise in urban areas. Because of the hydrogeological complexity of many of the urban related estuary areas coupled with the small anticipated rise in heads it is concluded that deterministic numerical modelling predictions of the head change cannot be realistically made and that schemes should proceed by staged impoundment, and compatible remediation where necessary.

Engineering concepts for in situ bioremediation

Most organic materials that contaminate soil and the subsurface environment are readily degraded by natural biological processes. Thus, bioremediation can be thought of as a highly successful purification process. However, some organic molecules are naturally refractory to biodegradation, the proper microbial population is not present, or environmental conditions are not suitable to biodegradation so that the compounds become recalcitrant to biodegradation and persist in the environment for years. Where natural processes are slow, the best strategy may still be to wait for the natural degradation to occur because of the current high costs and lack of reliability of engineered solutions. In other cases, the natural recalcitrance may be changed by introduction of degrading populations of microorganisms or by changing the environmental conditions by introduction of chemicals or through mixing and dilution. The potential success of engineering procedures to enhance degradation rates also depends to a large degree upon the complexity of the hydrogeology at a given site. With complex hydrogeology, most remediation approaches are rendered difficult if not impossible. This must be recognized by regulatory authorities and the public. In such cases alternative strategies to site remediation itself should be sought. More attention to such alternatives is needed in order to reduce unproductive expenditure of scarce resources.

Tritium as a tracer for the movement of surface water and groundwater in the Glatt Valley, Switzerland

A pulse of tritiated water (approx. 500 Ci) accidentally discharged by an isotope processing plant in the Glatt River Valley, northern Switzerland, allowed us to observe the migration of a contaminant pulse through a sewage treatment plant, rivers, and various wells of infiltrated groundwater. The accident pointed to various memory effects of the tritium, which acted as a conservative tracer. Tritium concentrations in surface water and groundwater were used to test predictions for the transport of conservative anthropogenic trace contaminants accidentally discharged into the sewer system. Mass balance calculations indicate that about 2-10% of the tritium pulse infiltrated to the groundwater and about 0.5% of the total reached eight major drinking water wells of this densely populated area. In spite of the complex hydrogeology of the lower Glatt River Valley, tritium breakthrough curves could be effectively simulated with modeling approaches developed from an experimental well field.

Mine water control in China's Karst aquifers

The relatively complex hydrogeology of Karst aquifers is often detrimental to mine production. Through experience, China has developed several different methods to control such mine water inflows. Selection of a method should be directed towards controlling the effects of prominent hydrogeological characteristics in different Karst types. For Karst, surface water flows, water cutoff ditches and subsequent diversion trenches are used. For ground water flows in semi-confined aquifers, drainage by deep wells and combinations of special water cutoff drifts and pre-drainage by galleries are used. In addition, in confined aquifers such techniques as combined of methods surface and underground water control, including multiple depressurising wells and water sealing wall operations are used.

Interpretação hidrogeoquímica das águas subterrâneas da ilha de Marajó.

As pesquisas desenvolvidas pelo IDESP na Ilha de Marajó possibilitaram estudos de hidrogeoquímica das águas subterrâneas. As amostras foram coletadas em poços escavados e em poços tubulares. Os resultados das análises físico-químicas evidenciaram significativas variações nas concentrações dos parâmetros de qualidade de água, refletindo a complexidade hidrogeológica da área. As maiores concentrações de sólidos totais dissolvidos ocorrem na parte central e norte da área, sendo pequena na parte sul, sudeste e noroeste. As águas são predominantemente do tipo sódio-cloretada, seguidas pelos tipos mista-cloretada e mista-bicarbonatada. A utilização de diagramas semi-logarítimicos de Schoeller possibilitou o agrupamento das águas subterrâneas com características químicas similares. A evolução da composição das águas subterrâneas evidencia o aumento da concentração dos íons dissolvidos das zonas de fluxo ativo em áreas de recarga para as zonas de fluxo muito lento. Misturas de águas doces com águas salobras conatas ocorrem em proporções variadas. A redução de sulfatos pela matéria orgânica e a troca de bases e adsorção são fenômenos que atuam na concentração dos íons dissolvidos.

The problems of groundwater assessment in the volcanic-sedimentary environment of Central Java

Summary The geology of Central Java can be defined in terms of distance from volcanic centres located along the spine of the island. Coarse ejecta are reworked on the upper volcanic slopes to form a scree, and coarse to medium grade fluviatile sequences slope downwards. At the base, shallow marine sedimentation along a rapidly retreating coast line has created a clay-sand sequence. This variety of depositional facies has produced a lithological inhomogeneity that poses problems of aquifer delineation, and makes the cuttings from direct-flush rotary drilling difficult to interpret. Geophysical logging of the volcanic sediments also presents difficulties as gamma logs lack features because of high background counts so that resistivity logs have to be used to locate well screens. Unconfined conditions exist on the upper and intermediate slopes of the volcanoes while beneath the lower slopes and coastal plains is an upper unconfined aquifer overlying lower, confined aquifers. Despite geological and hydrogeological inhomogeneity, approximate groundwater head distributions can be reasonably determined in the unconfined areas; multilayering makes this difficult in the confined areas. Groundwater development for irrigation is seen as a long-term aim in the unconfined areas of the intermediate slopes of the volcanoes. Further groundwater development, by manipulating the aquifers' specific yield and its high potential recharge currently lost to flood flow, appears to be feasible. Accurate assessment of the potential development is difficult due to the complex hydrogeology and extensive existing groundwater use. Development will therefore be slow and require careful planning.

Nano variations in gravity due to seasonal groundwater movements: Implications for the gravitational detection of tectonic movements

Six nanogravity surveys have been made at two coastal areas of eastern Canada in order to study the gravity changes associated with seasonal groundwater fluctuations. The repeated surveys made with a LaCoste and Romberg model D gravimeter, D6, demonstrate that (1) seasonal changes in gravity differences (∼100 nm/s2, 10 µgal) at Cap Pelé, a region of relatively simple hydrogeology, are in good agreement with well and piezometer measurements, and (2) the corresponding changes (∼120 nm/s2, 12 µgal) at York Point; a region of complex hydrogeology, suggest a different interpretation of seasonal groundwater flow from that inferred from piezometer measurements alone. The results demonstrate that normal variations in groundwater may obscure gravity changes associated with tectonic movements and earthquake precursory effects. When normal variations in groundwater are known or are not significant, the results demonstrate that tectonic gravity changes as small as 20–30 nm/s2 (2–3 µgal) may be detected at the 90% confidence level with the LaCoste and Romberg D meter. Such a gravity change corresponds to a ‘free air’ change in elevation of ∼1 cm.

The Hydrogeology and Utilization of Brines in El Salado, Chile

ABSTRACTThe Rio Salado catchment is located in the southern Atacama Desert. The area is distinctly arid and no ground‐water reserves originating from local recharge exist. To obtain water for a new copper ore processing plant, brines are being utilized. The complex hydrogeology of the brines from their origin in the Andes to their emergence as springs in the vicinity of El Salado is described.The surface and ground‐water discharges indicate that the long‐term supply of brine will be adequate for the processing plant. A design for abstraction incorporating three filter drains with wooden pump‐housings has been adopted to combat corrosion, incrustation and flood damage.