Conceptual multiphase modelling of an LNAPL contaminated site

Transkript

1 2 nd European Conference on Natural Attenuation Dechema, Frankfurt 19 th May 25 Conceptual multiphase modelling of an LNAPL contaminated site Benedict Miles* 1, Anita Peter 1, Ed Sudicky 2, Roudrajit Maji 2, Georg Teutsch 3 1 Tuebingen Groundwater Research Institute (TGF) 2 Department of Earth Sciences, University of Waterloo, Canada 3 Environmental Research Center (UFZ) Leipzig-Halle, Germany * ben.miles@uni-tuebingen.de

2 Motivation LNAPL Vertical movement of NAPL Volatilisation and diffusion NAPL retained at residual saturation in pores Unsaturated zone NAPL migration at groundwater surface Capillary fringe Emission: Dissolution and diffusion across capillary fringe Dissolved contaminant plume Advective transport Degradation & Sorption

3 COMPFLOW code for multiphase flow and transport (Forsyth et al., 1998) Gas phase (immobile) Non-Aqueous phase flow Kinetic dissolution of NAPL Advective/dispersive transport in aqueous phase Aqueous phase flow

4 Site: Niedergörsdorf TLII TLII 5m Approx. area of NAPL contamination

5 Kerosene reduced to single component NAPL Alkanes (C8-C13) Alkanes (>C13) Cycloalkanes BTEX Cycloalkenes Naphtha compounds Undefined Mole fraction weighted averaging Representative NAPL properties

6 Development of model domain based on TLII TL 2-3 N TL 2-28 TL 2-2 TL 2-19 TB 1 1 TB 1 TB 9 SB 2-3 SB 2-4 V 2-2 TL 2-5 TL 2-18 TB 6 TL 2-1/ 1 OP TL 2-1/ 2 UP SB 2-2 TL 2-7 TL 2-17 TL 2-11 TB 1 2 TL 2-31 SB 2-13 TB 5 V 2-6 TL 2-12 TB 3 TL 2-6 SB 2-5 TB 4 TB 2/99 TL 2-8 TL 2-24 TL 2-3/ 1 OP TL 2-3/ 2 MP TL 2-3/ 3 UP TL 2-15 TL 2-23 Downstream Approximate TL 2-26 Control plane groundwater flow Tankfarm area TL 2-25 direction1 TL 2-29 TL 2-21 TB 1/99 SB 2-1 TL 2-1 V 2-1 Z TB 8 TB 7 SB 2-6 TL 2-4 TL 2-14 TL 2-9 SB 2-14 TL 2-16 z [m] Z TL 2-13 TL 2-2 Z TL 2-22 TL 2-27 Wells without NAPL phase Wells with NAPL phase Approximate model area Features TL Meters y [m] Fixed head conditions for up- and downstream boundaries x [m] Groundwater flow direction, Gradient, i =.5

7 Scenarios Base scenario Heterogeneous realisations Phase extraction Groundwater fluctuation 3 m³ NAPL introduced over 1 years Constant recharge 12 mm/yr Geostatistical realisations for permeability and porosity 5 years NAPL extraction following injection Groundwater fluctuation after NAPL distribution reaches steady state 4 year simulation time

8 Basic scenario Phase body, isosurface for So =.1 &.4 Aqueous phase flux across downstream control plane and area of lower surface of phase body (So =.1)

9 Scenarios Base scenario Heterogeneous realisations Phase extraction Groundwater fluctuation 3 m³ NAPL introduced over 1 years Constant recharge 12 mm/yr Geostatistical realisations for permeability and porosity 5 years NAPL extraction following injection Groundwater fluctuation after NAPL distribution reaches steady state 4 year simulation time

10 Heterogeneous realisations 1 Geostatistically similar realisations of porosity and permeability distributions; Mean Std. Deviation, σ ln Correlation lengths in x, y, z Porosity m, 1m, 1m Permeability [m²] 5.6e m, 1m, 1m Surface area of phase body (So =.1) ZONE 1 Mass flux across downstream control plane ZONE 1 Lower surface of NAPL body [m 2 ] Realisations Mean +/- Std. deviation Time [days] Mass flux across control plane [mol/day] Realisations Mean +/- Std. deviation Time [days]

11 TGF Maximum and minimum examples for heterogeneous realisations Y Y X X x [m ] [m] y 1 2 x [m ] 3 4 z [m] 1 2 z [m] porosity Flux 2.5 Area Z T = 1.8e+4 days 3.E+4 2 Z Aqueous phase flux across downstream control plane and area of lower surface of phase body (So =.1) Lower surface of phase body [m ] Phase body, isosurfaces for So =.1 &.4, T = Tmax 1 5 [m] y Aqueous phase flux [mol/day] Porosity distribution 2.5E E E+4 Homogeneous 1. 1.E E E+ Y X X x [m ] [m] y x [m ] [m] y z [m] 1 Flux 2.5 Area 3.E+4 2 Y z [m] porosity Z T = 1.8e+4 days Aqueous phase flux [mol/day] Z Lower surface of phase body [m ] Time [days] 2.5E E+4 Homogeneous 1.5E E E Time [days] 15.E+

12 Emission to aqueous phase closely linked to surface area of NAPL in contact with groundwater Relationship between downstream mass flux and phase body surface area (So =.1) at T = T max Downstream flux at control plane [moles/day] R 2 = Homogeneous case.e+ 5.E+3 1.E+4 1.5E+4 2.E+4 2.5E+4 3.E+4 3.5E+4 Area of lower surface of phase body [m²]

13 Scenarios Base scenario Heterogeneous realisations Phase extraction Groundwater fluctuation 3 m³ NAPL introduced over 1 years Constant recharge 12 mm/yr Geostatistical realisations for permeability and porosity 5 years NAPL extraction following injection Groundwater fluctuation after NAPL distribution reaches steady state 4 year simulation time

14 Migration of phase results in NAPL pancake responsible for much of the total source emission In the example: - Volume of NAPL in the pancake is only about 1% of the total NAPL reaching the capillary fringe - Accounts for more than 5% of total emission Aqueous phase flux [mol/day] Flux Area Time [days] Lower surface of phase body [m 2 ]

15 Phase extraction Extraction wells run for 5 years following NAPL injection 1 : 3 wells in pancake 2 : 3 wells in main body 3 : 6 wells in main body Extraction well Time [days] Pumping water and NAPL together disturbs groundwater table, leads to increased NAPL migration Aqueous phase flux [mol/day] Map 7 Map 8 1. Flux 1. Area 2. Flux 2. Area 3. Flux 3. Area Lower surface of phase body [m 2 ]

16 Scenarios Base scenario Heterogeneous realisations Phase extraction Groundwater fluctuation 3 m³ NAPL introduced over 1 years Constant recharge 12 mm/yr Geostatistical realisations for permeability and porosity 5 years NAPL extraction following injection Groundwater fluctuation after NAPL distribution reaches steady state 4 year simulation time

17 Groundwater fluctuation Groundwater table falls then rises.5m Phase body, isosurface for So =.1 &.4 Aqueous phase flux across downstream control plane and area of lower surface of phase body (So =.1)

18 Conclusions Extent of NAPL spreading highly variable depending on local conditions Groundwater fluctuations re-mobilise and increase spreading of NAPL Emission from the source zone is mainly a function of surface area of NAPL in contact with groundwater Possible to estimate emission for a site such as TLII simply from the area of the NAPL phase?

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20 Emission to aqueous phase closely linked to surface area of NAPL in contact with groundwater Relationship between emission to aqueous phase and phase body surface area at T = T max Downstream flux at control plane [moles/day] 3.5 R 2 =.9594 R 2 =.884 R 2 = R 2 =.97 R 2 = E+ 5.E+3 1.E+4 1.5E+4 2.E+4 2.5E+4 3.E+4 3.5E+4 So =.1 So =.5 So =.1 So =.15 So =.2 Area of lower surface of phase body [m²]