How Does the Periodic Groundwater Table Fluctuation Impact on Chlorinated Vapor Intrusion?

Periodic groundwater table fluctuations are found frequently in natural aquifers due to sea tides or seasonal recharge. However, their impact on the transport of volatile organic compounds in the vadose zone released from a groundwater contaminant source (i.e., vapor intrusion) has not been well known. A 2D numerical model was developed to explore vapor intrusion processes in the sandy vadose zone, subject to a fluctuating groundwater table with a range of fluctuation amplitudes and periods. A carcinogenic compound, Trichloroethylene (TCE), was chosen as the groundwater contaminant of interest in the current study and assumed to transport into the dwelling through a crack at the corner of the basement. Results showed that the resistant effect caused by high soil moisture contents in the thin capillary fringe is weakened by periodic groundwater table fluctuations, resulting in a higher concentration of gaseous TCE at the building foundation crack, in comparison with that under a static groundwater table. The increase of the gaseous TCE concentration was induced by the enhancement of diffusion and advection due to groundwater table fluctuations. Sensitivity analyses indicated that a higher amplitude and frequency of fluctuations lead to a higher TCE concentration at the crack under the dynamic equilibrium condition. Specifically, compared with the static groundwater table condition, the TCE concentration at the crack increased by one order of magnitude under the condition of groundwater table fluctuations with an amplitude of 0.2 m and a period of one day. The results obtained could provide insights into the importance of the amplitude and frequency of groundwater table fluctuations on vapor intrusion.

Analytical Solution of the Transport Equation for Exponentially Decreasing Initial Concentration in Shallow Water Table Condition in an Irrigated Field

Most of the agricultural activities are limited for the depth of 15 – 20 cm and rest soil remain enact for long periods which inhibits the microbial activities below this depths and create an initial concentration of nutrients exponentially decreasing with depth. An attempt has been made to develop analytical models for time-dependent nitrification/ denitrification and depth-dependent absorption of urea fertilizer in high water table conditions with fertigation. Laplace transformation method was used to solve the unsteady-state advection-dispersion equation. The analytical solutions that can be derived by this method assist understanding of the movement of fertilizer in irrigated fields. The developed models were validated with the experimental results. They were closely predicting the fertilizer movement in one-dimension soil medium. The little deviation of result from observed values may be due to change of dispersion coefficient and velocity with moisture content. Here these parameters were assumed as constant throughout the time under consideration. Models developed for constant degradation rate is predicting very close to observe values which shows that the soil under study has no depth-dependent degradation. The developed models may be helpful for the planning of drain design, nutrient management and assessment of potential hazards to groundwater in agricultural fields by the knowledge of exact transport parameters and boundary conditions universally.

The Effect of Initial Groundwater Table and Rainfall Wetting Towards Slope Stability (Case Study of Landslide in Tangkil Hamlet, Banaran Village, Pulung Subdistrict, Ponorogo Regency)

Landslide is a natural phenomenon that can be controlled by a combination of various factors, such as topography, lithological condition, geological structure, water table, etc. Landslide is stated as a natural disaster if it causes casualties, direct losses and subsequent impacts of the initial destruction, as happened in Banaran Village, Ponorogo Regency. This study is aimed to examine the effects of initial groundwater table conditions and rainfall wetting on Banaran Village landslide. This study was conducted by assuming scenarios of initial groundwater table conditions. Soil parameters were obtained by testing soil samples in the laboratory. Infiltration parameters were acquired through permeability tests using the Philip-Dunne method, while areal rainfall was calculated using the Thiessen polygon method. In addition, slope stability modeling was calculated by using SLOPE/W while rainfall wetting analysis was carried out through SEEP/W. The analysis of Banaran Village landslide through these two numerical models was conducted by considering two conditions: 1) without rainfall and 2) with rainfall and infiltration. The analysis results imply that the landslide occurred in the initial groundwater table condition in scenario 3 with a safety factor of 1.008, and in a similar scenario with a safety factor of 0.973 when taking into account rainfall and infiltration. The results from SEEP/W and SLOPE/W indicate that the initial condition of the groundwater table highly influenced the decrease of the safety factor, while the wetting process did not cause a significant decrease of the safety factor.

The Seepage Control of the Tunnel Excavated in High-Pressure Water Condition Using Multiple Times Grouting Method

Groundwater can cause many hazardous problems when a tunnel is excavating. Seepage force acting on the support structure and the tunnel surface cannot be negligible. Under high groundwater table condition, the seepage situation becomes more complex and it is more difficult to control the leakage of groundwater to flow into a tunnel. In the paper, a multiple times grouting method is proposed, and the mechanical deformation behavior of surrounding rock is analyzed using the FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) software according to the high groundwater table condition of the Hokusatsu tunnel. The results present that multiple times grouting can control leakage and the rock deformation well, compared with one-time grouting condition in rock breaking and high water pressure area. The seepage force decrease around the tunnel and the displacement is controlled effectively. The pore pressure reduces inside the grouting zone using a new kind of grouting material, which is high permeability ultramicro particle cement (average particle size 1.5 μm). In the test fieldwork, the grouting scheme reduces the maximum discharge from 300 t/h to 40 t/h, and there is not obvious deformation and abnormal stress in the tunnel. The multiple times grouting method proposed in this research is verified effectively and can supply a positive experience to on-site construction.

Nitrous Oxide Emission of a Tropical Peat Soil Grown with Pineapple at Saratok, Malaysia

Draining of peatland for agriculture could affect the release of nitrous oxide into the atmosphere. Presently, there is dearth of information on soil nitrous oxide emission from tropical peat soils cultivated with pineapples. Lysimeter and closed chamber methods were used to quantify nitrous oxide emission from root respiration, microbial respiration, and oxidative peat decomposition under controlled water table condition. Treatments evaluated were: peat soil grown with pineapple, uncultivated peat soils, and bare peat soil fumigated with chloroform. Cultivation of Moris pineapple on drained peat soils resulted in the higher release of nitrous oxide emission (15.7 t N2O ha/yr), followed by fumigated peat soil with chloroform (14.3 t N2O ha/yr), and uncultivated peat soil (10.2 t N2O ha/yr). Soil nitrous oxide emission was affected by nitrate fertilization but emission was not affected by soil temperature nor soil moisture.

Hot Rolled Coil Property Heterogeneities due to Coil Cooling: Impact and Prediction

The importance of coil cooling conditions on mechanical properties uniformity of HSLA and AHSS steel grades is discussed. It is namely shown that hot rolled coil under conventional industrial production can be cooled non-uniformly. That is why to predict correctly the final steel microstructure and mechanical properties of hot-rolled products an accurate description of not only run-out table condition but also of coil cooling should be done. Two solutions to provide accurate description of coil cooling were tested. First one is to use 2D finite element (FE) thermal model. When coupled with the ArcelorMittal metallurgical model to predict hot-rolled microstructure and properties (TACSI) it matches well the industrial data within +/-15-20MPa both for the tensile and yield strength. However, this approach is recognized to be heavy and time consuming. A second solution, a new 2D coil cooling simplified model incorporated in TACSI model, proved to be quite efficient, as it leads to performances similar to the more detailed first solution. Moreover, it is able to compute the coupling between the thermal evolution of the hot band and the kinetics of phase transformation during coil coiling and cooling, and will enable a better evaluation of the final mechanical properties especially for the grades for which the phase transformation is not completed before hot band coiling.