Source-Zone Architecture, Elution and Mass Flux Behavior IMPACT OF SOURCE-ZONE ARCHITECTURE AND FLOW-FIELD HETEROGENEITY ON REDUCTIONS IN MASS FLUX Impact of Flushing Agent Impact of Source-Zone Age Acknowledgements Financial assistance for this project was partly provided by the Strategic Environmental Research and Develop- ment Program (SERDP) (Grant Number ER-1614) . We would like to thank Larry Acedo and Aldo Perazzone in the University Research Instrumentation Center and members of the Contaminant Transport Group at the Univer- sity of Arizona. Materials and Methods Accusands: 20/30 (K = 15 cm/min), 40/50 (K = 4 cm/min), 70/100 (K = 0.1 cm/min) DIFILIPPO, Erica L. 1 , CARROLL, Kenneth C. 1,2 , and BRUSSEAU, Mark L. 1,2 1 University of Arizona, Department of Hydrology and Water Resources, Tucson, AZ 85721 2 University of Arizona, Department of Soil, Water and Environmental Science, Tucson, AZ 85721 Abstract A series of flow-cell experiments was conducted to investigate the impact of source-zone architecture and flow-field heterogeneity on the relationship between source-zone mass removal and reductions in contaminant mass flux. The results showed that minimal reductions in mass flux occurred for systems wherein immiscible liquid was present at residual saturation in regions that are hydraulically accessible. Conversely, significant reductions in mass flux occurred for systems wherein immiscible liquid was present as both residual saturation and in high saturation pools. The systems with significant reductions in mass flux exhibited multi-step behavior. Analysis of immiscible-liquid saturation data measured via imaging confirmed that the initial mass flux reductions for these systems were associated with the removal of the source-zone mass that was hydraulically accessible (within the matrix). Conversely, later reductions in flux were associated with mass removal from the less hydraulically-accessible pools. The age of the source zone (time from initial spill to time of initial characterization) significantly impacted the observed mass-flux-reduction/mass-removal behavior. The results of this study illustrate the impact of both source-zone architecture and flow-field heterogeneity on mass-removal and mass-flux processes. Trichloroethene (TCE) dyed with Sudan IV at a conc. of 100 mg/L Control experiment in stainless steel 2 cm ID, 7 cm long column Materials Cylindrical and Rectangular Flow Cells Methods Homogeneous Experiment Source zone in middle of flow cell by manually mixing and packing TCE contaminated sand. Mixed Source Experiment Homogeneous pack of 40/50 sand with 1 cm thick capillary barrier TCE (~12 ml) injected through middle injection port at 1 ml/min Heterogeneous Experiment Matrix of 40/50 sand with lenticular zones of 20/30 and 70/100 TCE (~15 ml) injected through left (66 %) and middle (33 %) injection ports at 1 ml/min Source zone characterized using Light Reflection Visualization (LRV) Method Control Mixed Source Homogeneous Heterogeneous 0.1 1 10 100 1000 10000 Concentration [ppm] 0 20 40 60 80 100 120 140 160 180 200 0 50 100 150 200 300 350 250 Pore Volumes (Control Only) [-] Pore Volumes [-] Figure 3. (a) Source-zone architecture through time for the Mixed Source experiment. (b) Source-zone architecture through time for the Heterogeneous experiment. The black-outlined zones were composed of 20/30 sand and the gray zones were composed of 70/700 sand. (c) Effluent concentration as a function of pore volumes flushed for the four experiments. (d) Mass flux reduction versus mass removal behavior for the experiments. (c) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 S n [-] 0 5 10 15 20 0 5 10 15 20 25 30 35 40 t elapsed = 0 hr PV = 0 GTP = 1.69 MR = 0 % Height [cm] S n [-] 0.4 0.45 0.25 0.3 0.35 0.2 0 0.05 0.1 0.15 t elapsed = 77.78 hr PV = 17.70 GTP = 12.3 MR = 59.0 % 5 10 15 20 0 5 10 15 20 25 30 35 40 Height [cm] S n [-] 0.4 0.45 0.25 0.3 0.35 0.2 0 0.05 0.1 0.15 t elapsed = 17.67 hr PV = 4.00 GTP = 3.0 MR = 17.8 % 5 10 15 20 0 5 10 15 20 25 30 35 40 Height [cm] 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 S n [-] 0 t elapsed = 381.50 hr PV = 81.83 GTP = inf MR = 89.4 % 5 10 15 20 0 5 10 15 20 25 30 35 40 Height [cm] Length [cm] 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 S n [-] 0 t elapsed = 131.22 hr PV = 29.28 GTP = 11.0 MR = 68.8 % 5 10 15 20 0 5 10 15 20 25 30 35 40 Height [cm] 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 S n [-] 0 t elapsed = 285.89 hr PV = 62.05 GTP = 709.6 MR = 81.1 % 5 10 15 20 0 5 10 15 20 25 30 35 40 Height [cm] Mixed Source Experiment (a) MS1 MS2 MS3 MS4 MS5 MS6 MS4 MS2 MS3 MS5 MS6 H2 H3 H4 H5 H6 Height [cm] 5 10 15 20 0 5 10 15 20 25 30 35 40 t elapsed = 0 hr PV = 0 GTP = 1.23 MR = 0 % S n [-] 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 t elapsed = 215.73 hr PV = 50.62 GTP = 0.81 MR = 56.7 % Height [cm] 5 10 15 20 0 5 10 15 20 25 30 35 40 S n [-] 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Height [cm] 5 10 15 20 0 5 10 15 20 25 30 35 40 t elapsed = 551.95 hr PV = 135.77 GTP = 0.64 MR = 93.1% S n [-] 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Height [cm] 5 10 15 20 0 5 10 15 20 25 30 35 40 t elapsed = 383.75 hr PV = 93.68 GTP = 0.51 MR = 77.4 % S n [-] 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Height [cm] 5 10 15 20 0 5 10 15 20 25 30 35 40 t elapsed = 458.57 hr PV = 113.11 GTP = 0.25 MR = 83.9 % S n [-] 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Length [cm] Height [cm] 5 10 15 20 0 5 10 15 20 25 30 35 40 t elapsed = 671.78 hr PV = 166.95 GTP = 8.12 MR = 99.8 % S n [-] 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Heterogeneous Experiment (b) H1 H2 H3 H4 H5 H6 Fractional Mass Removed [-] Fractional Mass Flux Reduction [-] 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 Control Mixed Source Homogeneous Heterogeneous (d) MS4 MS2 MS3 MS5 MS6 H2 H3 H4 H5 H6 Impact of Source-Zone Architecture Ganglia-to-Pool (GTP) ratio: GTP = V NAPL, ganglia V NAPL, pool Statistical Measures of Immiscible-Liquid Saturation Source-Zone Architecture Through Time Initial Source-Zone Architecture Figure 8. (a) Mean (µ Sn ) and (b) variance (σ 2 Sn ) of immiscible-liquid distribution for the Mixed Source and Heterogeneous experiments as a function of mass removal. Experiment Control Homogeneous Mixed Source Heterogeneous GTP initial inf inf 1.7 1.2 µ Sn, initial 0.18 6.7 x 10 -3 6.6 x 10 -3 5.3 x 10 -3 σ 2 Sn, initial 0 1.9 x 10 -4 1.1 x 10 -3 9.3 x 10 -4 Table 1. Initial source-zone parameters Figure 7. GTP ratio as a function of mass removal for the Mixed Source and Heterogeneous experiments. 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 GTP [-] Fractional Mass Removed [-] 1000 100 10 1 0.1 Mixed Source Heterogeneous Residual-Dominated Pool-Dominated Impact of Flow-Field Heterogeneity Figure 9. (a) The average hydraulic conductivity for the 20/30 zone in the Heterogeneous experiment as a function of the total mass removed. (b) Hydraulic conductivity variance (σ 2 K ) for the Mixed Source and Heterogeneous experiments as a function of the variance in immiscible-liquidsaturation distribution (σ 2 Sn ). New initial conditions established after the most highly-accessible mass was removed Fractional Mass Removed [-] Fractional Mass Flux Reduction [-] 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 Mixed Source-2 (GTP initial = 3.0) Heterogeneous-2 (GTP initial = 0.3) Figure 4. Mass flux reduction versus mass removal behavior for the modified Mixed Source and Heterogeneous experiments. Mixed Source-2: new initial condition after 29 pore volumes of flushing Heterogeneous-2: new initial condition after 106 pore volumes of flushing Similar source-zone architecture and flow-field heterogeneity Fractional Mass Removed [-] Fractional Mass Flux Reduction [-] 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 2% Tween-80 4% Tween-80 Flushing Agent: Tween-80 How is mass flux behavior impacted by flushing agent? Figure 5. Photograph of initial source-zone architecture for both Tween-80 flushing experiments. Figure 6. Mass flux reduction as a function of mass removal for two Tween-80 flushing experiments. Conclusions Impact of Source-Zone Architecture Evaluation of Source-zone Architecture Digitial photograph taken with Nikon D70 with an AF-S Nikkor 18-70 mm lens Pixel intensity converted to pixel optical density using an optical density photographic card (Kodak) TCE saturation was calculated based on a pre-determined TCE saturation versus optical density calibration curve Fractional Mass Removed [-] K [cm/min] 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 16 14 12 10 8 6 4 2 0 K sat, 20/30 = 15.02 cm/min K sat, 40/50 = 4.33 cm/min (a) 0.49 0.50 0.51 0.52 0.53 0.54 0.55 0.56 0.57 0.58 0.59 8.80 8.60 8.40 8.20 8.00 7.80 7.60 σ 2 Sn (x 10 -4 ) σ 2 K, Heterogeneous σ 2 K, Mixed Source Mixed Source Heterogeneous 0 2.0 4.0 6.0 8.0 10 12 Flushing Time (b) Non-singular mass-flux-reduction/mass-removal behavior Impact of Source-Zone Age Significant difference in mass-flux-reduction/mass removal behavior Impact of Flushing Agent Non-sinuglar mass-flux-reduction/mass-removal behavior preserved Figure 2. Schematic diagram of initial source zone configuration for the Homogeneous experiment. (a) Longitudinal view. (b) Cross-sectional view. 4 cm 2 cm 4 cm 7.58 cm 3 cm 7.58 cm 3 cm (a) (b) Figure 1. Photograph of rectangular flow cell. 2% (wt.) Tween-80 Flood 4% (wt.) Tween-80 Flood µ Sn 0.001 0.010 0.100 1.000 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Fractional Mass Removed (a) Mixed Source Heterogeneous σ 2 Sn 0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Fractional Mass Removed (b) Mixed Source Heterogeneous Stainless Steel Frame Teflon Tape Silicon Sealant Effluent Ports Water Injection Ports TCE Injection Ports