Importance of Infiltration Rates for Fate and Transport of Benzene in High-Tiered Risk-Based Assessment Considering Korean Site-Specific Factors at Contaminated Sites

Widely used conservative approaches for risk-based assessments of the subsurface transport processes have been calculated using simple analytical equations or general default values. Higher-tier risk assessment of contaminated sites requires the numerical models or additional site-specific values for input parameters. Previous studies have focused on the development of sophisticated models fit into risk-based frameworks. Our study mainly aims to explore the applicability of site-specific parameters and to modify the risk-based fate and transport model according to the types of the site-specific parameters. To apply the modified fate and transport equation and the site-specific default infiltration range, this study assessed the source depletion, leachate concentrations, and exposure concentration of benzene, which is a representative organic contaminant. The numerical models consist of two continuous processes, the fate and transport of contaminants from (1) the soil to the groundwater table in the vadose zone and subsequently (2) from the groundwater table to exposure wells in the saturated zone. Spatially varied Korean domestic recharge data were successfully incorporated into site-specific infiltration parameters in the models. The numerical simulation results were expressed as transient time series of concentrations over time. Results presented the narrow range of predicted concentrations at the groundwater table when site-specific infiltration was applied, and the dilution–attenuation factors for the unsaturated zone (DAFunsat) were derived based on the prediction. When a contaminant travels to the longest path length of 10 m with a source depth of 1 m in the vadoze zone, the simulated DAFunsat ranged from 3 to 4. The highest DAFunsat simulation results are close to 1 when contaminants travel to a source depth of 5 m and the shortest path length of 1 m. In the saturated aquifer below the contaminated sites, the variation in exposure concentration with time at monitoring wells is detected differently depending on the depth of the saturated zone.

Geological and geomorphological conditions of Archar-Orsoya lowland as a factor for the formation of groundwater chemical composition and in risk of its contamination

The Archar-Orsoya lowland is situated in the Danube floodplain west of the town of Lom, NW Bulgaria. It is aligned in a west-east direction along the Danube River and to the south it is bounded by a high landslide slope, built of Pliocene clays and sands. Parallel to the shore, sand dunes are formed with lowered sections between them, in which there are conditions for swamping. The lowland is made up of the alluvial sediments of the Danube, represented by a lower gravelly-sandy layer and an upper sandy-clayey layer. In the gravelly-sandy layer unconfined groundwater is accumulated, with shallow water table – from 0.5 to 7 m beneath the surface. Groundwater is recharged by infiltration of precipitation, surface water and groundwater, which laterally flows into the alluvium from adjacent aquifers. At high waters, the Danube River suppresses the formed groundwater flow and temporarily feeds it. Due to the described formation conditions in the lowland, the chemical composition of groundwater is formed under the influence of intense dynamics and has a low TDS (total dissolved solids). The shallow groundwater table and the corresponding thin unsaturated zone are a prerequisite for easy groundwater contamination with components entering from the surface. Therefore, a map of depth to groundwater table is drawn to identify the most vulnerable areas.

Analysis of the hydrogeological conditions in Bulgaria in connection with the radon potential

Natural radon (222Rn) is a radioactive noble gas that occurs in every rock or soil due to the content of radium (226Ra), part of the 238U family, in the lithosphere. Different types of rocks and soils possess different 226Ra content and different permeability. Radon has high mobility and is driven by diffusion and convection with the soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. Therefore, the radon potential of the area could depend on hydrogeology and its particular settings. The study deals with the general characteristics of the groundwater depths in Bulgaria based on the published since 1960’s sources. After analysis of the collected data several distinct regions have been elaborated based on different depth of the groundwater table regarding lithological, tectonic and geomorphological conditions. In addition, zones for screening assessment of groundwater table influence of radon potential have been precised.

Study of Rainwater Harvesting in University of Petroleum and Energy Studies in Support of the Eco-Campus Initiative

Rainwater harvesting is a technique for collecting rainwater that would otherwise be wasted, mainly in metropolitan settings. There is essentially no infiltration and percolation due to the completely different land use compared to the metropolitan region. As a result, groundwater levels have been steadily depleted. Rainwater harvesting is nearly completely unknown among the general public. There is a lack of community planning that may result in widespread participation and so replenish the groundwater table. The current research looks at several rainwater gathering techniques and how they may be implemented at the chosen location. The research is being conducted on the Dehradun campus of UPES. The focus is mostly on the water collected on the rooftop, which will be filtered and used for cleaning and gardening. Because it is a hilly location, the region receives a lot of rain, which provides excellent opportunities for rainwater gathering. The total runoff from the entire rooftop is calculated using a rational formula and then distributed to various uses. The paper's main goal is to advocate the wise use of this valuable resource while keeping in mind the economics of the method used. Keywords: Rainwater harvesting, rational formula, groundwater.

Assessment of landslide behaviour in colluvium deposit at Doi Chang, Thailand

The paper presents the case study of the recurrent slope movement in colluvium deposits at Doi Chang, Thailand. A thorough site investigation confirmed the slope movement rate corresponding to slow creep during dry season, while in the rainy season, its velocity remarkably increased. Despite frequent repair, the movement rate was sufficient to result in the recurrent damage of infrastructures like roads and buildings, causing economic loss and public concerns. Furthermore, surface mapping revealed that the hill's topography led to the concentration of flowing water in a particular area. This resulted in a high level of groundwater table, especially during the rainy season. The inclinometer installed in that area suggested an average movement rate of 20.5 mm/month in the wet season. In contrast, during the dry season, it was limited within 2 mm/month, indicating that the increase in the rate of slope movement in the colluvium deposit was primarily due to the rising groundwater table. Field and laboratory tests were conducted to determine the properties of the colluvium deposit. Landslide susceptibility assessment was performed using infinite slope model and later integrated with GIS to evaluate the factor of safety (FS) over a large area. The FS decreased below 1 when the groundwater level rose to 0.3 cm below the ground surface, and using GIS, based on infinite slope model, the potential risk zone were delineated.

Creep behavior of cemented sand investigated under cyclic loading

The influence of stress state on the creep behavior of an artificial cemented sand resembling soft rocks was evaluated. The stress state was characterized by a mean stress and a stress ratio. The cyclic stress-induced creep test was adopted in this study, where the cyclic loading involved a constant deviator stress and a cyclic mean stress (or confining pressure) of the same amplitude and period; the test indicated similar trends as the conventional creep test with a shorter time to creep failure at less creep strain. Results showed that when the creep strain is large enough, the greater the creep strain accumulates, the smaller is the post-creep strength. Under the same number of cyclic loads, with the same stress ratio, the creep strain and the steady-state strain rate in the secondary creep stage increase with increasing mean stress; with the same mean stress, the two said parameters also increase with increasing stress ratio. It was also found that the time to reach creep failure decreases with decreasing mean stress and increasing stress ratio. The stress ratio is proposed to account for the tendency of a stress state to cause failure, and the cyclic variation of mean stress, which is equivalent to the effective mean stress with pore water pressure being zero in the tests conducted, reflects the effective stress state of a geomaterial under fluctuations of groundwater table. Under a fixed deviator stress, a soft porous geomaterial subjected to cyclic variation of effective mean stress may yield contraction and could lead to failure if the stress ratio is high. The findings can help explain the mechanism of ground subsidence or slope failure subjected to cyclic fluctuations of groundwater table.

Summer Drought in 2019 on Polish Territory—A Case Study

The summer 2019 drought in Poland, i.e., the warmest year in observation history, was characterized. Meteorological, agricultural, hydrological, and hydrogeological aspects were taken into account. Meteorological drought in the light of regionally differentiated days of low precipitation frequency lasted the longest, i.e., over 3 months in central-western Poland. In the period between June–August 2019, in the belt of South Baltic Lakes and Central Polish Lowlands, the lowest precipitation sums of 30–60% of the norm were recorded. The values of the climatic water balance (CWB) calculated by the Institute of Soil Science and Plant Cultivation (IUNG) method for individual months of June–August for the Polish area were −129, −64, and −53 mm, respectively. The most threatened were fruit bushes, spring cereals, maize for grain and silage, and leguminous plants. In central-western and south-western Poland, the drought accelerated the date of the lowest flows by two months on average from the turn of September and October to the turn of July and August. In the lowland belt, where the drought was the most intensive, the average monthly groundwater level, both of free and tight groundwater table, was lower than the monthly averages for the whole hydrological year.