Seasonal Water Table Fluctuations Research Articles

Seismic behavior of pile foundations in unsaturated soils

Earthquakes have caused significant damage to civil engineering structures worldwide due to inadequate lateral load capacity and excessive deformation of pile foundations supporting these structures. The seismic performance of pile foundations interacting with unsaturated soils could be affected by changes in matric suction due to the moisture content variation induced by seasonal weather changes or water table fluctuations. Hence, the main objective of this study is to investigate the effects of unsaturated soil conditions on the seismic response of a pile-soil system in silty clay soils. This study utilized a stand-alone finite element computer code called DYPAC (Dynamic Piles Analysis Code) developed using the Beams on Nonlinear Winkler Foundation (BNWF) approach. Free field soil displacements and p-y curve parameters, inputs needed for DYPAC analyses, were updated based on the soil suction variations. This study found that soil suction can significantly influence the seismic performance of piles interacting with unsaturated silty clay soils, especially as the soil becomes drier in the transition zone. The best seismic performance of the pile, which is the minimum lateral pile displacement, happened in the transition zone between fully saturated and nearly dry conditions.

Impacts of groundwater level fluctuation on soil microbial community, alkane degradation efficiency and alkane-degrading gene diversity in the critical zone: Evidence from an accelerated water table fluctuation simulation.

Petroleum hydrocarbons are hazardous to ecosystems and human health, commonly containing n-alkanes and polycyclic aromatic hydrocarbons. Previous researches have studied alkane degraders and degrading genes under aerobic or anaerobic conditions, but seldom discussed them in the intermittent saturation zone which is a connective area between the vadose zone and the groundwater aquifer with periodic alteration of oxygen and moisture. The present study investigated the difference in alkane degradation efficiency, bacterial community, and alkane degrading gene diversity in aerobic, anaerobic, and aerobic-anaerobic fluctuated treatments. All biotic treatments achieved over 90% of n-alkane removal after 120days of incubation. The removal efficiencies of n-alkanes with a carbon chain length from 16 to 25 were much higher in anaerobic scenarios than those in aerobic scenarios, explained by different dominant microbes between aerobic and anaerobic conditions. The highest removal efficiency was found in fluctuation treatments, indicating an accelerated n-alkane biodegradation under aerobic-anaerobic alternation. In addition, the copy numbers of the 16S rRNA gene and two alkB genes (alkB-P and alkB-R) declined dramatically when switched from aerobic to anaerobic scenarios and oppositely from anaerobic to aerobic conditions. This suggested that water level fluctuation could notably change the presence of aerobic alkane degrading genes. Our results suggested that alkane degradation efficiency, soil microbial community, and alkane-degrading genes were all driven by water level fluctuation in the intermittent saturation zone, helping better understand the effects of seasonal water table fluctuation on the biodegradation of petroleum hydrocarbons in the subsurface environment.

Variation of bacterial community and alkane monooxygenase gene abundance in diesel n-alkane contaminated subsurface environment under seasonal water table fluctuation

n-Alkanes, the main component of diesel fuel, are common light non-aqueous phase liquids (LNAPLs) that threaten ecological security. The subsurface from vadose zone, through fluctuating zone, to saturated zone, is a critical multi-interface earth layer which significantly affects the biodegradation processes of n-alkanes. A pilot-scale diesel contaminated aquifer column experiment has been undertaken to investigate the variations of bacterial community and alkane monooxygenase (alkB) gene abundance in these zones due to water-table fluctuations. The n-alkanes formed a layer immediately above the water table, and when this was raised, they were carried upwards through the fluctuating zone into the vadose zone. Water content and n-alkanes component C10-C12 are main factors influencing bacterial community variation in the vadose zone, while C10-C12 is a key driving factor shaping bacterial community in the fluctuating zone. The most abundant bacterial phyla at all three zones were Proteobacteria, Firmicutes and Actinobacteria, but moisture-niche selection determined their relative abundance. The intermittent wetting cycle resulted in higher abundance of Proteobacteria, and lower abundance of Actinobacteria in the vadose and fluctuating zones in comparison to the control column with a static water-table. The abundances of the alkB gene variants were relatively uniform in different zones, probably because the bacterial populations harboring alkB gene are habituated to biogenic n-alkanes rather than responding to diesel fuel contamination. The variation in the bacterial populations with height due to moisture-niche selection had very little effect on the alkB gene abundance, possibly because numerous species in both phyla (Proteobacteria and Actinobacteria) carry an alkB gene variant. Nevertheless, the drop in the water table caused a short-term spike in alkB gene abundance in the saturated zone, which is most likely associated with transport of solutes or colloids from the fluctuating zone to bacteria species in the saturated zone, so a fluctuating water table could potentially increase n-alkane biodegradation function.

Regolith characterization and landscape evolution for geochemical exploration of the covered Yamarna Terrane, Western Australia

The easternmost Archaean Yamarna Terrane is the least explored terrane under transported cover in the Yilgarn Craton of Western Australia. Our aims are to understand the evolution of the paleolandscape, determine the weathering history and depositional processes, and the provenance, mineralogy and geochemistry of the Permian to Quaternary transported cover. This is a necessary step for selecting the appropriate sample media to vector towards buried mineral deposits in this terrane. The Permian cover was deposited in broad, structurally controlled valleys that were carved into and partly to completely truncate the previously weathered Archaean rocks. UPb dating of zircon grains indicates that the main provenance of the Permian cover on the Yamarna Terrane is the Albany-Fraser Orogen, with limited contribution from the Yilgarn Craton, Musgrave Province and Antarctica. The Permian cover of the paleovalleys wedges out laterally towards pre-existing, weathered basement paleohighs, capped by lateritic residuum. The Permian cover is deeply weathered, and consists of upper ferruginous (mottled, brecciated, pisolitic and nodular) and lower kaolinitic, poorly lithified sandstones and mudstones with a basal gravel at the bottom. Above the basal unconformity between the Permian and weathered Archaean, the Rb/Zr ratio decreases sharply and the Permian cover shows negative Eu anomalies (Eu/Eu*) compared to positive Eu/Eu* in the underlying weathered and fresh mafic Archaean rocks, suggesting distal felsic source rocks for the Permian cover. In places, where Au increases, the base of the Permian cover still shows positive Eu/Eu* anomalies, suggesting physical dispersion from proximal mineralized mafic rocks.The Post-Permian weathering and erosion processes produced an extensive layer of Au-bearing detrital ferruginous clasts derived from lateritic residuum and ferruginous pisoliths and nodules from the Permian cover. These ferruginous grains occur as loose or cemented by Fe oxides forming ferricrete. Ferricrete is not necessarily related to the underlying weathered dolerite compared to the lateritic residuum. This is shown, in some places, by a sharp decrease in the Ti/Zr ratio, high HFSE, negative Eu/Eu*, high LREE/HREE compared to the underlying weathered dolerite suggest an unconformity and physical dispersion from weathered felsic source rocks. The Au-enrichment in the ferricrete derived from the felsic rocks occurred after deposition as a result of hydromorphic dispersion by groundwater. The weathered Permian cover and Archaean rock are covered by aeolian sand within which Au is concentrated in authigenic pisoliths. These pisoliths were formed by periodical water saturation during seasonal water table fluctuation. The unconformities and the ferruginous regolith materials are relevant to Au exploration through cover in the Yamarna Terrane and are highly recommended for regional-scale systematic sampling.

Groundwater resource assessment using different hydrological methods and GIS techniques for Central Part of Bengal Delta

Depiction of terrestrial water flux constituents in respect of geospatial distribution and consecutive disparity are important for water resources assessment. Due to the excessive and indiscriminate withdrawal of groundwater (GW), the water table (WT) in Dhaka area is continuously depleting during the last few decades. The consequences of increasing water scarcity being a grave concern for the policymakers of the country become a serious issue to save Dhaka areas from its possible failure in terms of human survivability and sustainability. These challenges set the urgency and great importance for holistic assessment of GW resources in the present context. GW recharge is estimated using combined Water Balance approach, Groundwater Estimation Committee methodology, and empirical technique. The monsoon and non-monsoon rainfall recharges (RRM and RRNM) are found as 63% and 37% in Dhaka City; and 55% and 45% in Dhaka district areas. The contributions for overall GW recharge in Dhaka City and Dhaka district from rainfall (RRAnl), water bodies (RSW), return flow (RRFD), and unaccounted recharge (RUAc) are 40.2% and 59.1%; 8.6% and 23.26%; 39.1% and 17.64%; and 12.1% and 0% in 1996, respectively. These have been altered as 22.1% and 55.9%; 2.8% and 16.2%; 37.6% and 27.9%; and 37.5% and 0% in 2015, respectively. It is observed that the total GW recharge in Dhaka City and Dhaka district has altered from 590 and 440 mm in 1996 to 730 mm and 422 mm in 2015, respectively. But the water draft due to domestic, private and industrial use in Dhaka City has increased from 726 and 373 mm in 1996 to 1092 and 582 mm in 2015, respectively. The water draft due to irrigation, and private & industrial use in Dhaka district is found as 256 and 110 mm in 1996 to 1369 and 166 mm in 2015, respectively. The seasonal WT fluctuation varies from 1.1 to 2.3 m in falling trend except Dhaka City where no significant variations are observed. The WT in Dhaka City has depleted from 17 m bgl with a rate of 1.5 m/year in 1996 to 63 m bgl in with a rate of 3.2 m/year in 2015. The WT in Dhaka district has been uplifted from 6.4 m bgl with a rate of 0.82 m/year in 1996 and then falling downward at a rate of 0.8 m/year in 2003 and reached to 14.45 m bgl at a rate of 1.52 m/year in 2015. The stage of GW development (SGD) and categorization in Dhaka City fall within 172–208% as ‘vulnerable’ during 1996 which have further aggravated to 229–272% as ‘highly vulnerable’ during 2015. The SGD and categorization in peri-urban area are estimated as 108–112% as ‘overexploited’ during 1996 which has further risen to 150–158% as ‘vulnerable’ during 2015, respectively. But, the condition is better in rural areas where, SGD and categorization are analysed as 61–70% as ‘safe’ in 1996 which has further deteriorated to 108–117% as ‘overexploited’ in 2015.

Modelling groundwater evapotranspiration in a shallow aquifer in a semi-arid environment

The use of diurnal or seasonal water table fluctuation (WTF) to estimate groundwater evapotranspiration (ETG) at different land uses and climate conditions is increasing applied in ecohydrological studies. In this study, we applied the WTF method for a shallow aquifer in an urbanized area in Senegal over the dry season 2000–2013.To analyze the applicability and validity of the WTF method for this site, and to understand the impact of the parameters used in this method, the unsaturated /saturated system was first simulated using the HYDRUS 1D model. The drawdown of the water table ranges from 18.1 to 113.2 cm and 10.4 to 101.9 cm for a bare soil and a perennial grass scenario and is highly related to the annual rainfall of the previous rainy season. The results indicate that the mean daily FAO-PM reference evapotranspiration rates for this area ranged from 2 to 4 mmd−1 and that the estimated actual evapotranspiration (ETa) from the HYDRUS 1D model ranged between 0.22 to 1.11 and 0.23 to 1.27 mmd−1 in bare soil and vegetative condition, respectively. ETa and ETG were well correlated for the vegetated scenario. However, the WTF method slightly overestimates ETa fluxes in the bare soil scenario. The study shows that the decline of ETa with water table depth can be simulated by an exponential function. The overall results indicate that higher ETa values were observed when the water table is shallow, suggesting that ETa is mainly driven by the water table depth at this site.

Use of geospatial technology for delineating groundwater potential zones with an emphasis on water-table analysis in Dwarka River basin, Birbhum, India

Dwarka River basin in Birbhum, West Bengal (India), is an agriculture-dominated area where groundwater plays a crucial role. The basin experiences seasonal water stress conditions with a scarcity of surface water. In the presented study, delineation of groundwater potential zones (GWPZs) is carried out using a geospatial multi-influencing factor technique. Geology, geomorphology, soil type, land use/land cover, rainfall, lineament and fault density, drainage density, slope, and elevation of the study area were considered for the delineation of GWPZs in the study area. About 9.3, 71.9 and 18.8% of the study area falls within good, moderate and poor groundwater potential zones, respectively. The potential groundwater yield data corroborate the outcome of the model, with maximum yield in the older floodplain and minimum yield in the hard-rock terrains in the western and south-western regions. Validation of the GWPZs using the yield of 148 wells shows very high accuracy of the model prediction, i.e., 89.1% on superimposition and 85.1 and 81.3% on success and prediction rates, respectively. Measurement of the seasonal water-table fluctuation with a multiplicative model of time series for predicting the short-term trend of the water table, followed by chi-square analysis between the predicted and observed water-table depth, indicates a trend of falling groundwater levels, with a 5% level of significance and a p-value of 0.233. The rainfall pattern for the last 3 years of the study shows a moderately positive correlation (R 2 = 0.308) with the average water-table depth in the study area.

Field‐scale observations of a transient geobattery resulting from natural attenuation of a crude oil spill

AbstractWe present evidence of a geobattery associated with microbial degradation of a mature crude oil spill. Self‐potential measurements were collected using a vertical array of nonpolarizing electrodes, starting at the land surface and passing through the smear zone where seasonal water table fluctuations have resulted in the coating of hydrocarbons on the aquifer solids. These passive electrical potential measurements exhibit a dipolar pattern associated with a current source. The anodic and cathodic reactions of this natural battery occur below and above the smear zone, respectively. The smear zone is characterized by high magnetic susceptibility values associated with the precipitation of semiconductive magnetic iron phase minerals as a by‐product of biodegradation, facilitating electron transfer between the anode and the cathode. This geobattery response appears to have a transient nature, changing on a monthly scale, probably resulting from chemical and physical changes in subsurface conditions such as water table fluctuations.

A method for simultaneous estimation of groundwater evapotranspiration and inflow rates in the discharge area using seasonal water table fluctuations

As an indispensable component of groundwater circulation, groundwater evapotranspiration rate (ETG) estimation using water table fluctuations is a hot research topic in the past decades. However, most existing methods for estimating ETG using either diurnal or seasonal water table fluctuations are based on the assumptions that groundwater recharge equals 0 in the whole period and ETG equals 0 in a specific duration of time. The aim of the current study is to develop a method to estimate ETG when both assumptions do not apply. In the discharge area of a semi-arid catchment in the Ordos Plateau, NW China, it is found out that the water table fluctuations are influenced greatly by recharge, ETG and the vertical inflow rate (qin) in the seasonal scale but are controlled by atmospheric pressure instead of evapotranspiration in the diurnal scale, which implies that the existing methods are not applicable. Therefore, we propose a method to estimate ETG and qin using the seasonal water table fluctuations based on the assumptions that qin is stable throughout the year and ETG has a linear relationship to the reference evapotranspiration (ET0). It is found out that qin is around 1.12mm/d, and the ratio of ETG to ET0 is around 0.4. ETG in April through July with the highest ET0 of the year is found to be around 3mm/d, which is much larger than qin, thus leads to significant decline in water table. ETG in November with the lowest ET0 of the unfrozen period is found to be 1.0mm/d, which is slightly smaller than qin, thus results in a weak increase in water table. The vertical component of regional groundwater inflow is found to exceed precipitation recharge, indicating that regional groundwater inflow plays the major role on maintaining the shallow water table in the discharge area. Groundwater evapotranspiration is also found to exceed precipitation recharge in most time of the unfrozen period, indicating a specified-flux upper boundary with water loss in the discharge area of an arid catchment. The proposed method could be applied to similar study areas and is critical to understand the budget of groundwater.

Field data and numerical simulation of btex concentration trends under water table fluctuations: Example of a jet fuel-contaminated site in Brazil

Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios – water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion.

Long-term Holocene groundwater fluctuations in a chalk catchment: evidence from Rock-Eval pyrolysis of riparian peats

he depositional history of peat-dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change. However, in chalkland valleys, seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen, and there is a need for alternative investigative techniques. The method of Rock-Eval pyrolysis can track changes in organic matter source and degradation, potentially relating to historic changes in vegetation cover. This is the first Rock-Eval on cores from a groundwater-dependent riparian chalk valley wetland combined with radiocarbon dating. The dating showed that the cores represented approximately 4000 years of depositional history. Changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species, relating to periods of climate wetness. These climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest Europe. However, the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment. Nonetheless, this study suggests that Rock-Eval pyrolysis is a useful and cost-effective tool that can provide evidence for long-term Holocene groundwater fluctuations

Hydrogeological Modelling of Water-Level Changes in an Area of Archaeological Significance: A Case Study from Flag Fen, Cambridgeshire, UK

Concern exists regarding the long-term viability of the internationally important archaeological remains of the Flag Fen site near Peterborough. This paper describes a hydrogeological numerical groundwater model which has been used to understand the groundwater situation with regard to the archaeology, including drainage impacts, and also to explore future scenarios. Observed and modelled groundwater levels have been interpreted using three zones: the ‘dry’ zone 1 above the seasonal maximum water table; zone 2 of seasonal water table fluctuation; and a deeper zone 3 of permanent saturation. Archaeological wood is best preserved in Zone 3. Much of the Bronze Age wooden structure is located within Zone 2 or above. The hydrological conditions are therefore not ideal for the long-term in situ preservation of the material. Groundwater modelling indicates that the main factor controlling groundwater levels in the area is artificial drainage. The approach would be applicable to other wet-preserved archaeological sites.

Groundwater salinization processes and reversibility of seawater intrusion in coastal carbonate aquifers

Summary Seawater intrusion (SWI) has led to salinization of fresh groundwater reserves in coastal areas worldwide and has forced the closure of water supply wells. There is a paucity of well-documented studies that report on the reversal of SWI after the closure of a well field. This study presents data from the coastal carbonate aquifer in northeast China, where large-scale extraction has ceased since 2001 after salinization of the main well field. The physical flow and concomitant hydrogeochemical processes were investigated by analyzing water level and geochemical data, including major ion chemistry and stable water isotope data. Seasonal water table and salinity fluctuations, as well as changes of δ 2 H–δ 18 O values of groundwater between the wet and dry season, suggest local meteoric recharge with a pronounced seasonal regime. Historical monitoring testifies of the reversibility of SWI in the carbonate aquifer, as evidenced by a decrease of the Cl − concentrations in groundwater following restrictions on groundwater abstraction. This is attributed to the rapid flushing in this system where flow occurs preferentially along karst conduits, fractures and fault zones. The partially positive correlation between δ 18 O values and TDS concentrations of groundwater, as well as high NO 3 − concentrations (>39 mg/L), suggest that irrigation return flow is a significant recharge component. Therefore, the present-day elevated salinities are more likely due to agricultural activities rather than SWI. Nevertheless, seawater mixing with fresh groundwater cannot be ruled out in particular where formerly intruded seawater may still reside in immobile zones of the carbonate aquifer. The massive expansion of fish farming in seawater ponds in the coastal zone poses a new risk of salinization. Cation exchange, carbonate dissolution, and fertilizer application are the dominant processes further modifying the groundwater composition, which is investigated quantitatively using hydrogeochemical models.

Late Pleistocene Alberca de Guadalupe maar volcano (Zacapu basin, Michoacán): Stratigraphy, tectonic setting, and paleo-hydrogeological environment

The Late Pleistocene (~21,000yrBP) Alberca de Guadalupe maar is one of the few phreatomagmatic volcanoes occurring within the scoria-cone dominated Plio-Quaternary Michoacán-Guanajuato Volcanic Field. The scarcity of this type of volcano implies that conditions favoring their formation are rarely met in this region. We identify these factors by implementing current methods of investigation with emphasis on hydrogeological conditions. We present the stratigraphy (including a set of 40Ar/39Ar and 14C dates) of the SE margin of the Zacapu intermontane tectonic basin, where the maar just forms a hole (~1km in diameter, ~150m deep, bearing a ~9m deep lake) in the otherwise planar topography of the underlying early Pleistocene lava flows of the Cerro Pelón scoria cone. The maar is composed of typical phreatomagmatic surge deposits that are poorly sorted and rich in accidental lithics (>60wt.% of the deposit) with few juveniles (basaltic andesite, SiO2=54–58wt.%). The entire structure is cut by an ENE–WSW trending normal fault and is underlain by andesite lavas and silicic ignimbrites (partly inferred from xenoliths encountered in the maar deposits) that are Miocene to Early Pleistocene in age.The crater is at the center of a N–S elongated drainage basin surrounded by topographic highlands that channel water with high hydraulic pressure from most directions towards the location of the maar. This geometric configuration was already in existence at the time of the maar-forming eruption, but the climate was different. Colder and more humid conditions during the Last Glacial Maximum (Cw2-climate type, annual precipitation of >1000mm) favored the saturation of the fractured shallow aquifer system (hydraulic conductivity of 10−8 to 10−7m/s) that supplied sufficient groundwater at a high flow rate directed towards the center of the basin. Upon contact near surface (<200m) with the rising dike of basaltic andesite magma, the continuous supply of both dike-fed basaltic andesite magma and groundwater at an optimal ratio of 0.2 allowed explosive interaction for the entire duration of the eruption (17–57days) creating a >150m deep crater with steep inner walls and an underlying shallow diatreme (<300m). Since then, partial collapse of the walls along listric ring-fractures has reduced crater steepness. The present climate is much drier (Cw1 climate conditions with annual precipitation of 697.5–874.8mm) and it seems unlikely that a maar would form if these conditions persist. Nonetheless, precipitation is still high enough to sustain a ~9-m-deep lake in the crater with insignificant seasonal water table fluctuations. These findings lend further support to the notion that maars can be used as paleoclimate indicators in central Mexico.

Temporal Hyporheic Zone Response to Water Table Fluctuations.

Expansion and contraction of the hyporheic zone due to temporal hydrologic changes between stream and riparian aquifer influence the biogeochemical cycling capacity of streams. Theoretical studies have quantified the control of groundwater discharge on the depth of the hyporheic zone; however, observations of temporal groundwater controls are limited. In this study, we develop the concept of groundwater-dominated differential hyporheic zone expansion to explain the temporal control of groundwater discharge on the hyporheic zone in a third-order stream reach flowing through glacially derived terrain typical of the Great Lakes region. We define groundwater-dominated differential expansion of the hyporheic zone as: differing rates and magnitudes of hyporheic zone expansion in response to seasonal vs. storm-related water table fluctuation. Specific conductance and vertical hydraulic gradient measurements were used to map changes in the hyporheic zone during seasonal water table decline and storm events. Planar and riffle beds were monitored in order to distinguish the cause of increasing hyporheic zone depth. Planar bed seasonal expansion of the hyporheic zone was of a greater magnitude and longer in duration (weeks to months) than storm event expansion (hours to days). In contrast, the hyporheic zone beneath the riffle bed exhibited minimal expansion in response to seasonal groundwater decline compared to storm related expansion. Results indicated that fluctuation in the riparian water table controlled seasonal expansion of the hyporheic zone along the planar bed. This groundwater induced hyporheic zone expansion could increase the potential for biogeochemical cycling and natural attenuation.

Evaluation of hydrogeological factors and their relationship with seasonal water table fluctuation in Dhanbad district, Jharkhand, India

Due to rapid industrialization and increase in human population, there has been a tremendous pressure on the water resources. In hardrock terrain, the availability of groundwater is confined to fracture and weathered zones. In the present study, the study area is Dhanbad district of which most of the parts lie on hardrock terrain. In this study, an attempt has been made to relate the fluctuation of groundwater level with hydrogeological factors. The various hydrogeological factors that have been considered here which can affect the aquifer recharge are geomorphology, geological structures, geological formations, soil types, and elevation. These hydrogeological factors have been analyzed for 65 monitoring wells and frequency plots between different hydrogeological parameter classes, and water level fluctuation have been used to assess the relative impact of different hydrogeological subclasses on aquifer recharge. Further statistical analysis has been done for all hydrogeological parameters for each subclass based on mean, median, mode, and standard deviation values to further specify the relative effect of each subclass within different hydrogeological parameter. Based on the findings, it has been concluded that there is a definite relationship of surface topography, geology, geomorphology, soil, and elevation with recharge of aquifers based on their specific hydrogeological properties.

Effect of mining on geochemistry of groundwater in Permo-carboniferous Gondwana coalfields: Raniganj Basin, India

Lack of proper reclamation strategy and indiscriminate mining of various economic resources, particularly coal from Permo-carboniferous Gondwana coalfields affects the groundwater quality of the concerned regions. Leaching from mine-tailings along with seasonal fluctuation of water table caused a significant change in groundwater geochemistry of Raniganj coalfield area. Gondwana sequences, developed in intracratonic rift basin, are characterized by numerous longitudinal and cross faults. This results in the formation of many small aquifer systems which may be interconnected laterally as well as vertically providing the conduit for homogenization of aquifers. Although the predominance of major cations (Ca>Na>Mg>K) and anions (HCO3>Cl>SO4>NO3) remain same irrespective of season, the dominance of Na and SO4 have significantly increased in post-monsoon season. The types of groundwater in pre-monsoon and postmonsoon seasons are CaMgCl and CaHCO3 respectively. Leaching of SO4 from surface sources (mine tailings) has increased TDS in post-monsoon. Base exchange (direct and reverse) reactions have taken place between aquifer materials and groundwater.

Curve Number Derivation for Watersheds Draining Two Headwater Streams in Lower Coastal Plain South Carolina, USA

AbstractThe objective of this study was to assess curve number (CN) values derived for two forested headwater catchments in the Lower Coastal Plain (LCP) of South Carolina using a three‐year period of storm event rainfall and runoff data in comparison with results obtained from CN method calculations. Derived CNs from rainfall/runoff pairs ranged from 46 to 90 for the Upper Debidue Creek (UDC) watershed and from 42 to 89 for the Watershed 80 (WS80). However, runoff generation from storm events was strongly related to water table elevation, where seasonally variable evapotranspirative wet and dry moisture conditions persist. Seasonal water table fluctuation is independent of, but can be compounded by, wet conditions that occur as a result of prior storm events, further complicating flow prediction. Runoff predictions for LCP first‐order watersheds do not compare closely to measured flow under the average moisture condition normally associated with the CN method. In this study, however, results show improvement in flow predictions using CNs adjusted for antecedent runoff conditions and based on water table position. These results indicate that adaptations of CN model parameters are required for reliable flow predictions for these LCP catchments with shallow water tables. Low gradient topography and shallow water table characteristics of LCP watersheds allow for unique hydrologic conditions that must be assessed and managed differently than higher gradient watersheds.

Establishing a geochemical heterogeneity model for a contaminated vadose zone — Aquifer system

A large set of sediment samples from a 1600 m² experimental plot within a 2.2 km² vadose zone and groundwater uranium (VI) plume was subject to physical, chemical, and mineralogic characterization. The plot is being used for field experimentation on U(VI) recharge and transport processes within a persistent groundwater plume that exists in the groundwater-river interaction zone of the Columbia River at the U.S. DOE Hanford site. The samples were obtained during the installation of 35 tightly spaced (10 m separation) groundwater monitoring wells. The characterization measurements for each sample included total contaminant concentrations (U and Cu primarily), bicarbonate extractable U(VI), sequential ²³⁸U(VI) contaminant desorption Kd, ²³³U(VI) adsorption K(d), grain size distribution, surface area, extractable poorly crystalline Fe(III) oxides, and mineralogy. The characterization objective was to inform a conceptual model of coupled processes controlling the anomalous longevity of the plume, and to quantify the spatial heterogeneity of the contaminant inventory and the primary properties effecting reactive transport. Correlations were drawn between chemical, physical, and reaction properties, and Gaussian simulation was used to compute multiple 3-D realizations of extractable U(VI), the ²³³U(VI) adsorption K(d), and the distribution of the reactive <2 mm fraction. Adsorbed contaminant U(VI) was highest in the vadose zone and the zone of seasonal water table fluctuation lying at its base. Adsorbed U(VI) was measureable, but low, in the groundwater plume region where very high hydraulic conductivities existed. The distribution of adsorbed U(VI) displayed no apparent correlation with sediment physical or chemical properties. Desorption [²³⁸U(IV)] and adsorption [²³³U(VI)] K(d) values showed appreciable differences due to mass transfer controlled surface complexation and the effects of long subsurface residence times. The ²³³U(VI) adsorption K(d), a combined measure of surface complexation strength and site concentration, was relatively uniform throughout the domain, displaying correlation with fines distribution and surface area. The characterization results revealed U(VI) supplied to the groundwater plume through spatially heterogeneous recharge from residual contamination in the zone of seasonal water table fluctuation, and transport of U(VI) controlled by weak, kinetically-controlled surface complexation in the coarse-textured saturated zone. Geostatistical relationships for the adsorbed contaminant U distribution in the characterization domain allow an extrapolation to inventory at the plume scale, a critical unknown for remedial action.

A survey of groundwater levels and hydrogeochemistry in irrigated fields in the Karamay Agricultural Development Area, northwest China: Implications for soil and groundwater salinity resulting from surface water transfer for irrigation

Analysis of the water budget, along with hydrochemistry and stable isotopes in shallow groundwater were carried out in the Karamay Agricultural Development Area (KADA) in order to assess the impact of transfer of irrigation water from the IrtySh River, in particular in relation to the mechanisms of salinization and the nature of the water table regime. In terms of aquifer dynamics, the addition of the irrigation water without any groundwater abstraction has caused a sharp rise in the water table is and the development of serious soil salinity, together with an almost complete attenuation of inter-seasonal water table oscillations. The mean rise in the groundwater table from September 1997 to October 2009 was 6.9 m, representing an accumulated total water storage change of close to 150 million cubic meters. The analysis of aquifer water budget shows that infiltration of irrigation water occupied over 90% of the total recharge of the groundwater in the KADA. Sources of groundwater recharge and mechanisms of salinization in the KADA were also investigated using geochemical and isotopic techniques. The groundwater is characterized by Cl(SO 4 )–Na type, generally becoming more Na and Cl dominated with increasing salinity. The total dissolved solids (TDS) content of the groundwater ranges from 0.5 g/L to over 65 g/L, with greater TDS values in areas of low topographic relief and shallow water tables. Where the sediments are more permeable (e.g. due to the presence of palaeochannels), TDS values are generally lower and the seasonal water table fluctuations greater. The ratios of K/Cl, Ca/Cl, Na/Cl, and Mg/Cl decrease with increasing Cl − concentrations especially in the shallow groundwater from 10 to 15 m depth, indicating hydrogeochemical evolution via minor water-rock interaction (feldspar weathering) and significant evaporation. The stable isotopic compositions show a characteristic evaporation effect in the shallow groundwater and confirm that direct infiltration of precipitation is generally not a volumetrically important source of recharge to the shallow aquifer. Preferential recharge of river water after irrigation events and/or precipitation from rare heavy rain events is likely responsible for the depleted δ 2 H and δ 18 O values in some of the groundwater samples. The negative relationship between deuterium excess and δ 18 O values indicates that even in groundwater with relatively depleted δ 2 H and δ 18 O values, evaporation has occurred to a significant degree. Careful management of water quantity and quality and implementation of salinity management strategies are considered necessary in order to reduce the risk of further salt accumulation and damage to farming and local ecosystems.