Improved Approaches to Calculating Dilution and Attenuation Factor in Contaminant Hydrogeology

Dilution and attenuation factor (DAF) has a major influence on soil-to-groundwater screening level calculation for protection of contaminant migration from soil into groundwater at solid waste management units (SWMUs). Risk assessment guidance prepared by U.S. Environmental Protection Agency for site investigation and remediation suggests a default DAF of 20. If the base assumptions included in the default DAF are recognized to be not representative of site conditions at a SWMU, calculation of site-specific DAF is recommended when sufficient data are collected to justify using a different DAF value for development of soil screening levels. Commonly used methods of calculating DAF include analytical and numerical simulations that often require too many parameters to be obtained in practice. This paper proposes a probability method to develop site-specific DAF. The approach uses data that are readily available through field reconnaissance and site-specific investigation. A case study is presented in which the probability method was applied to an actual SWMU, and the calculated DAF is compared with that calculated from a dilution method. The probability-based DAF is 67 at 90% probability percentile, which is comparable to the dilution-based DAF of 76. Based on the calculated site-specific DAFs, SSLs could be developed for the contaminants of potential concern and used for evaluation of migration pathways from a contamination source through soil to groundwater. .

Geophysical Reactions to Remote 2022 Tonga Eruption and to Türkiye Earthquakes in Georgia (Caucasus): Hydrogeology, Geomagnetics and Seismicity

The paper is devoted to analysis of hydrogeological, geomagnetic and seismic response to the two great remote geophysical events, 2022 Tonga volcano eruption and 2020-2023 Türkiye earthquakes in Georgia (Caucasus). The geophysical observation system in Georgia, namely, water level stations in the network of deep wells, atmospheric pressure and the geomagnetic sensors of the Dusheti Geophysical Observatory (DGO) as well as seismic data in Garni Observatory (Armenia) respond to the Tonga event by anomalies in the time series. These data show that there are two types of respond: infrasound disturbances in atmospheric pressure and seismic waves in the Earth generated by the eruption. After Tonga eruption January 15 at 04:21 UTC three groups of N-shaped waveforms were registered in the water level corresponding to the global propagation characteristics of the N-shaped waveform of infrasound signals on the barograms generated by eruption at the distance ~15,700 km: they were identified as the Lamb wave, a surface wave package running in the atmosphere with a velocity around ~314 m/s. The paper also presents the WL reactions to three strong EQs that occur in Türkiye 2020-2023, namely Elazığ, Van and Türkiye-Syria EQs. WL in Georgian well network reacts to these events by anomalies of different intensity, which points to the high sensitivity of hydrosphere to remote (several hundred km) strong EQs. The intensity and character of WL reactions depend strongly on the local hydrogeological properties of rocks, surrounding the well.

Hydrogeology of the Ordos Basin, China

The Ordos Basin is located in the east of NW China that is composed of different aquifer systems. Karst groundwater is stored in the Carmbrian-Ordovician carbonates along the margins of the basin. Fissured-pore water is present in the Cretaceous strata in the central-western basin and pore water is stored in the overlying Quaternary deposits discontinuously. The main origin of groundwater in the basin is direct or indirect infiltration of precipitation. Groundwater flows from recharge areas to adjacent local discharge areas. Besides evaporation and abstraction, groundwater feeds springs and rivers, such as the Yellow River and its tributaries. According to the karst aquifer lithologic structure, the features of karst development and circulation, the karst aquifer is divided into three structural and circulation patterns. Based on the control of Cretaceous sedimentary environment, lithologic structure, lithofacies, and palaeogeographic characteristics, the Cretaceous system is divided into the northern desert simple plateau aquifer system and the southern loess plateau aquifer system. PACKER was used to obtain temperature, hydrogeochemical and isotope data at specific depths. Groundwater circulation is studied using hydrodynamic fields, temperature fields, isotopes, hydrogeochemical data and numerical simulations. According to the result, it is divided into local, intermediate and regional systems. The Ordos Basin contains a wealth of natural resources including coal, petroleum, oil shale and natural gas. There are four national-classenergy bases, e.g. northern Shaanxi energy basin, Inner Mongolia Ordos base, eastern Ningxia energy base, and Longdong base. And it is one of the most important bases for China's energy and heavy chemical industries. Because the basin is located in arid and semi-arid areas, the lack of water and its vulnerable ecological environment are the main limitations to the development of local economy and to the improvement of living standards. In order to assess the water resources and the utilization prospect and to provide the hydrological information for the establishment of the energy bases and economic development, groundwater investigation in the Ordos Basin has been carried out.

Hydrogeology of Eastern Niger Delta: A Review

This paper characterizes the aquifer system of the Niger Delta for sustainable development of the groundwater resource. The heavy-dependence on groundwater in the region and the fears of its unsustainability triggered by the weak regulations, pollution, increasing user population and industrialization coupled with the present limited knowledge of the true geological condition prevailing within the groundwater domain of the Niger Delta are the considerations that compelled this review study. The hydraulic properties of the region’s aquifers are discussed. The Niger Delta is characterized by a complex multilayered aquifer system hosted in the Benin Formation with the main body of fresh water, with increasing occurrence of intercalating clay units towards the coast. Lithological analysis indicates the prevalence of unconsolidated sand and sandy gravels in the aquiferous horizons, presenting them as pervious and prolific aquifers. Reported hydrochemical data gathered from wells drilled suggest that the quality of groundwater in the Niger Delta is considered generally very good and compares favorably with WHO standards for drinking water. However, relatively high iron/manganese and chloride values are localized in time and space. In the coastal areas however, seawater intrusion has been identified as one of the major influences on hydrochemistry of groundwater in the shallow unconfined aquifers. Regional groundwater flow direction is from north to south. Changes in groundwater flow directions which occur at some places generally serve localized discharge areas. The resultant flow path eventually joins and feeds the major regional north-south flow direction. The increasing pressure on groundwater, the need for urgent attention and the absence of strong institutions and regulations have made the management of groundwater resources in the region a difficult task. Therefore, future ground water resources development in the Niger Delta requires adequate observational data, investments in infrastructure and an integrated management approach to ensure optimal basin-wide benefits.

Hydrogeology of Wadi Qudaid Area, Northeast Jeddah, West Central Arabian Shield, Saudi Arabia

The study area is a part of the Arabian Shield rocks of west central part of Saudi Arabia (150 km to the northeast of Jeddah). Geologically, the study area comprises five main geologic units i.e. 1) Layered basic volcanics and related volcaniclastics which are composed mainly from intercalated basalts and andesites and the related volcaniclastic derivatives, 2) Acidic volcanics and related volcaniclastics which are composed from layered and laminated dark and light acidic to intermediate igneous rocks, quartz and chert and marbles, 3) The Tertiary sedimentary succession which of volcaniclastic red beds and the intercalated clays;5) Tertiary volcanics of Harrart, and 4) The Quaternary wadi fill deposits which are composed from friable pebble supported conglomerates, sandstones and clays. Hydrogeologically, the groundwater aquifer of Wadi Qudaid is present mainly in two main horizons i.e. i) unconfined shallow aquifer (13 - 37 m) within the well porous and permeable conglomerates of the Quaternary Wadi deposits, ii) The deep confined aquifer of the bedded tuffaceous sandstones and mudstone of the Tertiary sedimentary succession of Ash Shumaysi Formation. The water samples are analyzed for major elements i.e. Ca, Mg, Na, Cl, SO4, HCO3 and the results show the normal content of these elements. The study related the addition and depletion of many elements during the running trip of the groundwater from the northeast (recharge area) to the southwest (downstream) area.

Pumping-induced Well Hydraulics and Groundwater Budget in a Leaky Aquifer System with Vertical Heterogeneity in Aquitard Hydraulic Properties

In groundwater hydrology,aquitard heterogeneity is often less considered compared to aquifers,despite its significant impact on groundwater hydraulics and groundwater resources evaluation.A semi-analytical solution is derived for pumping-induced well hydraulics and groundwater budget with consideration of vertical heterogeneity in aquitard hydraulic conductivity(K)and specific storage(S_(s)).The proposed new solution is innovative in its partitioning of the aquitard into multiple homogeneous sub-layers to enable consideration of various forms of vertically heterogeneous K or S_(s).Two scenarios of analytical investigations are explored:one is the presence of aquitard interlayers with distinct K or S_(s) values,a common field-scale occurrence;another is an exponentially depth-decaying aquitard S_(s),a regional-scale phenomenon supported by statistical analysis.Analytical investigations reveal that a low-K interlayer can significantly increase aquifer drawdown and enhance aquifer/aquitard depletion;a high-S_(s) interlayer can noticeably reduce aquifer drawdown and increase aquitard depletion.Locations of low-K or high-S_(s) interlayers also significantly impact well hydraulics and groundwater budget.In the context of an exponentially depth-decaying aquitard S_(s),a larger decay exponent can enhance aquifer drawdown.When using current models with a vertically homogeneous aquitard,half the sum of the geometric and harmonic means of exponentially depth-decaying aquitard S_(s) should be used to calculate aquitard depletion and unconfined aquifer leakage.

Evaluating the characteristics of geological structures in karst groundwater inflow, Nowsud Tunnel

Highly permeable geological structures such as dissolution channels, open fractures, and faults create environmental challenges regard to hydrological and hydrogeological aspects of underground construction, often causing significant groundwater inflow during drilling due to the limitations of empirical and analytical methods. This study aims to identify the geological factors influencing water flow into the tunnel. High-flow zones' geological features have been identified and examined for this purpose. According to the geological complexity of the Nowsud tunnel, presence of different formations with different permeability and karstification have led to a high volume of underground inflow water (up to 4700 L/s) to the tunnel. The Nowsud tunnel faces significant geological and hydrogeological challenges due to its passage through the Ilam formation's LI2 unit, characterized by dissolution channels, faults, and fractures. The highest inflow rate (4700 L/s) occurred in the Hz-9 zone within the Zimkan anticline. The relationship between geological features and groundwater inflow indicates that anticlines are more susceptible to inflow than synclines. Additionally, different types of faults exhibit varying hydraulic effects, with strike-slip faults having the most significant impact on groundwater inflow, thrust faults conducting less water into the tunnel, and inflow through normal faults being negligible compared to the other two types of faults. The novelty of this paper lies in its detailed analysis of geological features influencing groundwater inflow into the Nowsud tunnel, providing empirical data on high-flow zones and differentiating the hydraulic effects of various fault types, which enhances the understanding and prediction of groundwater inflow in underground constructions.

Dynamic simulation insights into friction weakening effect on rapid long-runout landslides:A case study of the Yigong landslide in the Tibetan Plateau,China

This study proposed a novel friction law dependent on velocity,displacement and normal stress for kinematic analysis of runout process of rapid landslides.The well-known Yigong landslide occurring in the Tibetan Plateau of China was employed as the case,and the derived dynamic friction formula was included into the numerical simulation based on Particle Flow Code.Results showed that the friction decreased quickly from 0.64(the peak)to 0.1(the stead value)during the 5s-period after the sliding initiation,which explained the behavior of rapid movement of the landslide.The monitored balls set at different sections of the mass showed similar variation characteritics regarding the velocity,namely evident increase at the initial phase of the movement,followed by a fluctuation phase and then a stopping one.The peak velocity was more than 100 m/s and most particles had low velocities at 300s after the landslide initiation.The spreading distance of the landslide was calculated at the two-dimension(profile)and three-dimension scale,respectively.Compared with the simulation result without considering friction weakening effect,our results indicated a max distance of about 10 km from the initial unstable position,which fit better with the actual situation.

Comparison of Methods for Nitrate Interpolation in Wells in Aguascalientes, Mexico

The accuracy of interpolation models applied to groundwater depends, among other factors, on the interpolation method chosen. Therefore, it is necessary to compare different approaches. For this, different methods of interpolation of nitrate concentrations were contrasted in sixty-seven wells in an aquifer in Aguascalientes, Mexico. Four general interpolation methods were used in ArcGIS 10.5 to make the maps: IDW, Kriging, Natural Neighbor and Spline. In the modeling, only method type was varied. The input parameters (location, temporality, and nitrate concentration) were the same in the four interpolations;despite this, different maximum and minimum values were obtained for each interpolation method: for IDW, 0.2 to 22.0 mg/l, for Kriging, 3.5 to 16.5 mg/l, for Natural Neighbor, 0.3 to 21.7 mg/l and for Spline −30.8 to 37.2 mg/l. Finally, an assessment of the maps obtained was conducted by comparing them with the Official Mexican Standard (OMS), where 24 of the 67 wells were found outside the 10 mg/l that the OMS establishes as maximum permissible limit for human consumption. Taking as a starting point the measured values of nitrates (0.25 to 22.12 mg/l), as well as the spatial distribution of the interpolated values, it was determined that the Krigging method best fitted the data measured in the wells within the studied aquifer.

Pollution source identification methods and remediation technologies of groundwater: A review

Groundwater is an important source of drinking water.Groundwater pollution severely endangers drinking water safety and sustainable social development.In the case of groundwater pollution,the top priority is to identify pollution sources,and accurate information on pollution sources is the premise of efficient remediation.Then,an appropriate pollution remediation scheme should be developed according to information on pollution sources,site conditions,and economic costs.The methods for identifying pollution sources mainly include geophysical exploration,geochemistry,isotopic tracing,and numerical modeling.Among these identification methods,only the numerical modeling can recognize various information on pollution sources,while other methods can only identify a certain aspect of pollution sources.The remediation technologies of groundwater can be divided into in-situ and ex-situ remediation technologies according to the remediation location.The in-situ remediation technologies enjoy low costs and a wide remediation range,but their remediation performance is prone to be affected by environmental conditions and cause secondary pollution.The ex-situ remediation technologies boast high remediation efficiency,high processing capacity,and high treatment concentration but suffer high costs.Different methods for pollution source identification and remediation technologies are applicable to different conditions.To achieve the expected identification and remediation results,it is feasible to combine several methods and technologies according to the actual hydrogeological conditions of contaminated sites and the nature of pollutants.Additionally,detailed knowledge about the hydrogeological conditions and stratigraphic structure of the contaminated site is the basis of all work regardless of the adopted identification methods or remediation technologies.

Arsenic and fluoride co-enrichment of groundwater in the loess areas and associated human health risks:A case study of Dali County in the Guanzhong Basin

This study aims to reveal the occurrence and origin of typical groundwater with high arsenic and fluoride concentrations in the loess area of the Guanzhong Basin—a Neogene faulted basin.Key findings are as follows:(1)Groundwater samples with high arsenic and fluoride concentrations collected from the loess area and the terraces of the Weihe River accounted for 26%and 30%,respectively,of the total samples,with primary hydrochemical type identified as HCO_(3)-Na.The karst and sand areas exhibit relatively high groundwater quality,serving as preferred sources for water supply.It is recommended that local governments fully harness groundwater in these areas;(2)groundwater with high arsenic and fluoride concentrations in the loess area and the alluvial plain of rivers in Dali County is primarily distributed within the Guanzhong Basin,which represents the drainage zone of groundwater;(3)arsenic and fluoride in groundwater originate principally from natural and anthropogenic sources;(4)the human health risk assessments reveal that long-term intake of groundwater with high arsenic and fluoride concentrations pose cancer or non-cancer risks,which are more serious to kids compared to adults.This study provides a theoretical basis for the prevention and treatment of groundwater with high arsenic and fluoride concentrations in loess areas.

Unraveling the hydraulic properties of loess for landslide prediction:A study on variations in loess landslides in Lanzhou,Dingxi,and Tianshui,China

Loess has distinctive characteristics,leading to frequent landslide disasters and posing serious threats to the lives and properties of local re sidents.The involvement of water repre sents a critical factor in inducing loess landslides.This study focuses on three neighboring cities sequentially situated on the Loess Plateau along the direction of aeolian deposition of loess,namely Lanzhou,Dingxi,and Tianshui,which are densely populated and prone to landslide disasters.The variations in hydraulic properties,including water retention capacity and permeability,are investigated through Soil Water Characteristic Curve(SWCC)test and hydraulic conductivity test.The experimental findings revealed that Tianshui loess exhibited the highest water retention capacity,followed by Dingxi loess,while Lanzhou loess demonstrated the lowest water retention capacity.Contrastingly,the results for the saturated permeability coefficient were found to be the opposite:Tianshui loess showed the lowest permeability,whereas Lanzhou loess displayed the highest permeability.These results are supported and analyzed by scanning electron microscopy(SEM)observation.In addition,the water retention capacity is mathematically expressed using the van Genuchten model and extended to predict unsaturated hydraulic properties of loess.The experimental results exhibit a strong accordance with one another and align with the regional distribution patterns of disasters.

HYDROGEOLOGY

20161328Bai Ming(No.2 Hydrological and Engineering Geology Party of Xinjiang Bureau of Geology and Mineral Resources Exploration and Development,Changji 831100,China);Zhang Jing Distribution Characteristic of Groundwater Storage in Santanghu Basin of Ba-

HYDROGEOLOGY

20152705 Chen Peng(Tianjin Center,China Geological Survey,Tianjin 300170,China);Wang Wei Groundwater Age Assessment of Dou River Basin in Tangshan City,Hebei Provence(Geological Survey and Research,ISSN1672-4135,CN12-1353/P,37(4),2014,p.288-293,4illus.,5 tables,5 refs.)

HYDROGEOLOGY & ENGINEERING GEOLOGY

20040749 Chen Chongxi (Institute of Environmental Geoscience, China University of Geosciences, Wuhan, Hubei ) Formation Mechanism of Water Level and Its Determination Method in Conventional Observation Wells for Three-Dimensional GroundwaterFlow (Earth Science-Journal of China U-niversity of Geosciences, ISSN 1000 ?2383, CN42-1233/P, 28(5), 2003, p. 483-491, 6 illus. , 3 tables, 15 refs. , with English abstract) Keywords: water regimes water

HYDROGEOLOGY

20160565Bai Ming(No.2 Hydrological and Engineering Geology Party,Xinjiang Bureau of Geology and Mineral Resources Exploration and Development,Changji 831100,China);Li Xuxu An Analysis of the Control Factors of Groundwater Storage in the Santanghu Basin of Xinjiang(Hydrogeology and Engineering Geology,ISSN1000-3665,CN11-2202/P。