scholarly journals Free LNAPL Volume Estimation by Pancake Model and Vertical Equilibrium Model: Comparison of Results, Limitations, and Critical Points

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Eleonora Frollini ◽  
Marco Petitta
Keyword(s):  
Water Table ◽  
Critical Points ◽  
Equilibrium Model ◽  
Model Comparison ◽  
Effective Porosity ◽  
Volume Estimation ◽  
Nonaqueous Phase Liquids ◽  
Contaminated Site ◽  
Vertical Equilibrium ◽  
Thiessen Polygons

Light nonaqueous phase liquids (LNAPLs), due to their low solubility, dissolve slowly, acting as a long-term source of water contamination, and consequently they represent an important environmental issue. In the subsoil, more than 99% of spilled LNAPL remains as adsorbed and free phase; therefore, the volume estimation of free phase, obtained in this case through two different conceptual models (Pancake Model and Vertical Equilibrium Model), is considered a fundamental step for a correct site remediation. According to the first model, the LNAPL floating on the water table and its saturation is up to 100%; instead, according to the second one, the LNAPL can penetrate below the water table and the coexistence of LNAPL, water, and air in the pore fraction, leads to a lower LNAPL saturation, variable with the depth. Actually, in subsoil LNAPL and water saturations vary with depth due to the influence of capillarity, leading to the inaccuracy of Pancake Model assumption. Despite the evident limitation of Pancake Model, both models were applied, coupled with area calculations with Thiessen polygons and grid at regular mesh, to roughly estimate the free LNAPL volume existing in a contaminated site. The volume estimation carried out, considering the LNAPL type and its features, the soil type, and relative effective porosity, provides estimates of volumes having differences up to thousands of cubic meters. The results analysis shows that this estimation has several critical points such as area definition and the lack of site-specific data (e.g., porosity). Indeed, the sensitivity analysis for porosity shows that a reduction of this parameter provides a 20% reduction of estimated volume.

scholarly journals Methodological approach for the estimation of recoverable LNAPL volumes in aquifer and for the analysis of residual phase behaviour in laboratory

2017 ◽  
Author(s):  
Eleonora Frollini
Keyword(s):  
Porous Media ◽  
Equilibrium Model ◽  
Traditional Approach ◽  
Methodological Approach ◽  
Hazard Index ◽  
Volume Estimation ◽  
Phase Behaviour ◽  
Contaminated Site ◽  
Vertical Equilibrium ◽  
Residual Phase

Free and residual phases are the most abundant phases of LNAPL (light non aqueous phase liquid) in the subsoil; therefore the free phase volume estimation and the understanding of residual phase behaviour are fundamental for an effective remediation. The volume estimation of free phase present in a contaminated site was carried out through the application of the Pancake Model and the Vertical Equilibrium Model. This estimation shows a remarkable difference between the two models and between the different delimitation area methods employed. In particular, the estimated volumes are lower for the Vertical Equilibrium Model and the higher difference is observed for a 200x200 mesh. The results underline also some critical points as the amount of the effective porosity; indeed the sensitivity analysis shows that a reduction of this parameter produce a variation of the estimated volume until to 20%. The behaviour of residual phase was analysed through lab-scale column tests carried out using three different porous media and toluene as contaminant. The higher residual saturation and lower dissolution in finer materials reveal the influence of porous media on toluene behaviour. The lower dissolution is confirmed also by the modelling realized using a traditional approach and an approach based on experimental results. The risk analysis, carried out applying a traditional approach and a new experimental approach, shows that the last one allow to have a more reliable hazard index which contemplates the site specific conditions.

Volume Estimation of Light Nonaqueous Phase Liquids in Porous Media

Ground Water ◽  
1990 ◽  
Vol 28 (1) ◽  
pp. 48-56 ◽  
Author(s):  
A. M. Farr ◽  
R. J. Houghtalen ◽  
D. B. McWhorter
Keyword(s):  
Porous Media ◽  
Volume Estimation ◽  
Nonaqueous Phase Liquids ◽  
Light Nonaqueous Phase Liquids

scholarly journals Groundwater budget forecasting, using hybrid wavelet-ANN-GP modelling: a case study of Azarshahr Plain, East Azerbaijan, Iran

2016 ◽  
Vol 48 (2) ◽  
pp. 455-467 ◽  
Author(s):  
Alireza Docheshmeh Gorgij ◽  
Ozgur Kisi ◽  
Asghar Asghari Moghaddam
Keyword(s):  
Water Table ◽  
Mean Squared Error ◽  
Evaluation Criteria ◽  
Absolute Error ◽  
Management Plans ◽  
Thiessen Polygons ◽  
Development Plans ◽  
Groundwater Budget ◽  
East Azerbaijan

Meticulous prediction of hydrological processes, especially water budget, has an individual importance in environmental management plans. On the other hand, conservation of groundwater, a fundamental resource in arid and semi-arid areas, needs to be considered as a great priority in development plans. Prediction of a groundwater budget utilizing artificial intelligence was the scope of this study. For this aim, the Azarshahr Plain aquifer, East Azerbaijan, Iran, was selected because of its great dependence on groundwater and the necessity of cognizance of its budget in future programs. The long-term fluctuations of the water table in 13 piezometers were simulated by a wavelet-based artificial neural network (WANN) hybrid model, and their statistical gaps were covered. Then, the modelled water table was predicted for the next 12 months using genetic programming. The results of simulation and prediction were assessed by performance evaluation criteria such as R2, root mean squared error, mean absolute error and Nash–Sutcliffe efficiency. Thiessen polygons were then utilized, plotting the predicted unit hydrograph of the study area. The predicted water table from September 2012 to August 2013 revealed about 0.12 m depletion. Regarding the area of the Azarshahr Plain aquifer and its average storage coefficient, the aquifer budget will be reduced by about 0.3557 million cubic metres during this period.

scholarly journals A Pseudo-Vertical Equilibrium Model for Slow Gravity Drainage Dynamics

2017 ◽  
Vol 53 (12) ◽  
pp. 10491-10507 ◽  
Author(s):  
Beatrix Becker ◽  
Bo Guo ◽  
Karl Bandilla ◽  
Michael A. Celia ◽  
Bernd Flemisch ◽  
...  
Keyword(s):  
Equilibrium Model ◽  
Gravity Drainage ◽  
Vertical Equilibrium

scholarly journals Water movement in the firn of Storglaciären, Sweden

1999 ◽  
Vol 45 (150) ◽  
pp. 286-294 ◽  
Author(s):  
Thomas Schneider
Keyword(s):  
Water Level ◽  
Water Table ◽  
Water Movement ◽  
Time Lag ◽  
Effective Porosity ◽  
Diurnal Variations ◽  
Glacier Surface ◽  
Pumping Tests ◽  
Saturated Layer ◽  
The Mean

AbstractThe hydraulic properties of the firn on Storglaciären, Sweden, were investigated in firn cores by water-table measurements and pumping tests. The mean density of the firn was 800 850 kg m3, giving an effective porosity of 0.073. The lower part of the firn layer was saturated with water, producing a maximum saturated layer of 5 m in late July. Hydraulic conductivity of the firn aquifer was determined from pumping tests to be 4.9 × 105 m s1. Percolation velocity, calculated from the time lag of maximal water input at the glacier surface and the water-level peaks, was 0.25 m h1. Percolation velocity increased over the ablation season, indicating a widening of the percolation pathways. A decrease in percolation velocity with percolation depth was found, reflecting decreasing permeability. The firn–water table responded to water input at the glacier surface with a delay of about 3 days. No diurnal variations were found in an area which was not influenced by fast drainage, indicating a diffusion of diurnal variations in meltwater production. One borehole intersected a water-filled cavity. Water level in this cavity showed diurnal variations, which probably were caused by diurnally produced meltwater waves moving fast through englacial conduits.

scholarly journals Water movement in the firn of Storglaciären, Sweden

1999 ◽  
Vol 45 (150) ◽  
pp. 286-294 ◽  
Author(s):  
Thomas Schneider
Keyword(s):  
Water Level ◽  
Water Table ◽  
Water Movement ◽  
Time Lag ◽  
Effective Porosity ◽  
Diurnal Variations ◽  
Glacier Surface ◽  
Pumping Tests ◽  
Saturated Layer ◽  
The Mean

AbstractThe hydraulic properties of the firn on Storglaciären, Sweden, were investigated in firn cores by water-table measurements and pumping tests. The mean density of the firn was 800 850 kg m3, giving an effective porosity of 0.073. The lower part of the firn layer was saturated with water, producing a maximum saturated layer of 5 m in late July. Hydraulic conductivity of the firn aquifer was determined from pumping tests to be 4.9 × 105m s1. Percolation velocity, calculated from the time lag of maximal water input at the glacier surface and the water-level peaks, was 0.25 m h1. Percolation velocity increased over the ablation season, indicating a widening of the percolation pathways. A decrease in percolation velocity with percolation depth was found, reflecting decreasing permeability. The firn–water table responded to water input at the glacier surface with a delay of about 3 days. No diurnal variations were found in an area which was not influenced by fast drainage, indicating a diffusion of diurnal variations in meltwater production. One borehole intersected a water-filled cavity. Water level in this cavity showed diurnal variations, which probably were caused by diurnally produced meltwater waves moving fast through englacial conduits.

scholarly journals Catchment-Scale Integrated Surface Water-Groundwater Hydrologic Modelling Using Conceptual and Physically Based Models: A Model Comparison Study

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 363 ◽  
Author(s):  
Mohammad Bizhanimanzar ◽  
Robert Leconte ◽  
Mathieu Nuth
Keyword(s):  
Surface Water ◽  
Groundwater Recharge ◽  
Water Table ◽  
Model Comparison ◽  
Unsaturated Flow ◽  
Regional Scale ◽  
Catchment Scale ◽  
Time Step ◽  
Mike She ◽  
Physically Based

This paper presents a comparative analysis of the use of an externally linked (MOBIDIC-MODFLOW) and a physically based (MIKE SHE) surface water-groundwater model to capture the integrated hydrologic responses of the Thomas Brook catchment, in Canada. The main objective of the study is to investigate the effect of simplification in representation of the hydrological processes in MOBIDIC-MODFLOW on its simulation accuracy. To this aim, MOBIDIC and MODFLOW were coupled in order to sequentially exchange the groundwater recharge and baseflow discharges within each computation time step. Using identical sets of hydrogeological properties for the two models, the coefficients of the gravity and capillary reservoirs in MOBIDIC were calibrated so as to closely predict the hydrological budget of the catchment simulated with MIKE SHE. The simulated results show that the two models can closely replicate the observed water table responses at two monitoring wells. However, in very shallow water table locations, the instantaneous response of the water table was not precisely captured in MOBIDIC-MODFLOW. Additionally, the simplified conceptualization of the unsaturated flow in MOBIDIC-MODFLOW resulted in overestimated groundwater recharge during spring and underestimation during summer. Moreover, the computational efficiency of MOBIDIC-MODFLOW, as compared to MIKE SHE, along with less required input data, confirms its potential for regional scale groundwater-surface water interaction modelling applications.

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