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. .

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.

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

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

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。

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

20150507Gao Dongdong(State Key Laboratory of Geohazard Prevention and Geoenvironment Protection,Chengdu University of Technology,Chengdu 610059,China);Wu Yong Water Cycle and Groundwater Recharge of Small Watershed Rainfall Process in a Mountain Forest System(Hydrogeology and Engineering Geology,ISSN1000-3665,CN11-2202/P,41(1),2014,p.7-14,4illus.,9tables,32refs.)Key words:hydrologic cycle,groundwater recharge,Sichuan