Performance Evaluations of Pump-and-Treat Remediations 1

Journal of Hazardous Materials

2017

The purpose of this study is to investigate the effects of well-field hydraulics and permeability heterogeneity on mass-removal efficiency for systems comprising large groundwater contaminant plumes. A three-dimensional (3D) numerical model was used to simulate the impact of different well-field configurations on pump-and-treat mass removal for heterogeneous domains. The relationship between reduction in contaminant mass discharge (CMDR) and mass removal (MR) was used as the metric to examine remediation efficiency. The impacts of well-field configuration on mass removal behavior are attributed to mass-transfer constraints related to regions of low flow associated with the well field, which can be muted by the influence of permeability heterogeneity. These impacts are reflected in the associated CMDR-MR profiles. Systems whose CDMR-MR profiles are below the 1:1 relationship line are associated with more efficient well-field configurations. The impact of domain heterogeneity on mass-removal effectiveness was investigated in terms of both variance and correlation scale of the random permeability distributions and indexed by the CMDR-MR relationship. Data collected from pump-and-treat operations conducted in a section of the Tucson International Airport Area (TIAA) federal Superfund site were used as a case study. The comparison between simulated and measured site data supports the general validity of the numerical model, and results from the case study are consistent with the conclusions of the theoretical study. These results illustrate that the CMDR-MR relationship can be an effective way to quantify the impacts of different factors on mass-removal efficiency.

Section: Introductionmentioning

confidence: 99%

The impact of well-field configuration and permeability heterogeneity on contaminant mass removal and plume persistence

Journal of Hazardous Materials

2017

“…For example, the influence of well-field configuration on the effectiveness of contaminant mass removal has been investigated for pump-and-treat systems (e.g., Satkin and Bedient, 1988; Keely, 1989; Schafer and Kinzelbach, 1992; Cohen et al, 1997; Rivett et al, 2006). In addition, two-well recirculation systems have been investigated for in-situ bioremediation of groundwater (Gandhi et al, 2002; Luo and Kitanidis, 2004; Luo et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Modified Well-Field Configurations for Improved Performance of Contaminant Elution and Tracer Tests

2017

Water Air Soil Pollut

Contaminant elution and tracer (CET) tests are one method for characterizing the impact of mass transfer, transformation, and other attenuation processes on contaminant transport and mass removal for subsurface systems. The purpose of the work reported herein is to explore specific well-field configurations for improving CET tests by reducing the influence of preferential flow and surrounding-plume effects. Three injection-extraction well configurations were tested for different domain conditions using a three-dimensional numerical model. The three configurations were the traditional configuration with a single pair of injection-extraction wells, modified configuration I with one extraction well located between two injection wells, and modified configuration II with two pairs of injection-extraction couplets (one nested within the other). Elution curves for resident contaminant and breakthrough curves from simulated tracer tests were examined for specific landmarks such as the presence and extent of steady-state (relatively high concentrations) and asymptotic (asymptotic decrease to low concentrations) phases, as well as distinct changes in slope. Temporal-moment analysis of the breakthrough curves was conducted to evaluate mass recovery. Effective diffusion coefficients were obtained by fitting selected functions to the elution curves. Based on simulation results for a homogeneous domain, full isolation of the inner extraction well from the surrounding plume was obtained for the modified configuration II, whereas the extraction wells are impacted by the surrounding plume for the other two configurations. Therefore, configuration II was used for additional simulations conducted with layered and heterogeneous domains. Tracer-test simulations for homogeneous and layered domains indicate 100% mass recovery for the inner extraction well. For the heterogeneous domain, decreasing the distance between the inner injection-extraction well couplet and adjusting the pumping-rate distribution between the two extraction wells increased the mass recovery from 69% to 99%.

“…A recent National Research Council report concludes that it is unlikely that remediation of complex sites will be achieved in a time frame of 50–100 years under current methods and standards (NRC (National Research Council), ). Multiple factors, including the presence of source zones containing organic liquids, dispersed reservoirs of dissolved contaminant present in low‐permeability zones, sorbed contaminant, and hydraulic‐related factors, such as nonoptimal remedial well‐field performance, have long been identified as contributing to plume persistence and limited effectiveness of pump and treat (e.g., Berglund & Cvetkovic, ; Brusseau, ; Brusseau et al, ; Brusseau & Guo, ; Brusseau, Hatton, & DiGuiseppi, ; Chapman & Parker, ; Goltz & Oxley, ; Johnson & Pankow, ; Keely, ; Matthieu et al, ; Mutch, Scott, & Wilson, ; Parker, Chapman, & Guilbeault, ; Rabideau & Miller, ; Rasa et al, ; Wilson, Mutch, & Scott, ). One set of factors that have received relatively minimal attention are those related to well‐field hydraulics, such as the number and location of pumping wells and the associated pumping schemes (e.g., Cohen, Mercer, Greenwald, & Beljin, ; Guo & Brusseau, ; Keely, ; Rivett, Chapman, Allen‐King, Feenstra, & Cherry, ; Satkin & Bedient, ; Schafer & Kinzelbach, ).…”

Section: Introductionmentioning

confidence: 99%

The impact of well‐field configuration on contaminant mass removal and plume persistence for homogeneous versus layered systems

2017

Hydrological Processes

A three-dimensional numerical model was used to simulate the impact of different well-field configurations on pump-and-treat mass removal efficiency for large groundwater contaminant plumes residing in homogeneous and layered domains. Four well-field configurations were tested, Longitudinal, Distributed, Downgradient, and natural gradient (with no extraction wells). The reductions in contaminant mass discharge (CMDR) as a function of mass removal (MR) were characterized to assess remediation efficiency. Systems whose CDMR-MR profiles are below the 1:1 relationship curve are associated with more efficient well-field configurations. For simulations conducted with the homogeneous domain, the CMDR-MR curves shift leftward, from convex-downward profiles for natural gradient and Longitudinal to first-order behaviour for Distributed, and further leftward to a sigmoidal profile for the Downgradient well-field configuration. These results reveal the maximum potential impacts of well-field configuration on mass-removal behaviour, which is attributed to mass-transfer constraints associated with regions of low flow. In contrast, for the simulations conducted with the layered domain, the CMDR-MR relationships for the different well-field configurations exhibit convex-upward profiles. The nonideal mass-removal behaviour in this case is influenced by both well-field configuration and back diffusion associated with low-permeability units.