Key Takeaways & Executive Findings
- •• • Benzene, chloroform, and vinyl chloride migration distances reached 154.5 m, 130.5 m, and 165.2 m at 2000 days, with diffusion areas of 18117.4, 13928.5, and 25043.2 m², respectively—critical for designing monitoring networks and remediation footprints. • • Peak concentrations declined by 75.6% (benzene: 53.3→13.0 mg/L), 82.1% (chloroform: 112.0→20.0 mg/L), and 81.3% (vinyl chloride: 128.0→24.0 mg/L) over 2000 days, indicating natural attenuation but insufficient for regulatory compliance without intervention. • • Dynamic pump-and-treat with staged well reduction (9–7 to 1 well) and pumping rates of 25–30 m³/d achieved plume area reductions of 85.8%, 78.0%, and 85.9% at 400 days, and concentration reductions of 90.2%, 82.1%, and 93.8%, demonstrating operational efficiency. • • Total pumping volumes for 500-day remediation were 94500 m³ (benzene), 60000 m³ (chloroform), and 72000 m³ (vinyl chloride), with 3% Fenton reagent achieving达标 treatment—quantifying cost and chemical demand for full-scale implementation.
Abstract
Legacy contaminated sites from relocated chemical plants pose severe risks to groundwater and human health. This study investigated a pesticide-contaminated site using the Groundwater Modeling System (GMS) to construct three-dimensional geological, flow, and solute transport models, simulating migration of benzene, chloroform, and vinyl chloride and evaluating pump-and-treat remediation. Results showed initial uniform spread within 100 days, evolving to elliptical diffusion along southeast-northwest flow by 500–2000 days. Maximum migration distances reached 154.5 m (benzene), 130.5 m (chloroform), and 165.2 m (vinyl chloride), with diffusion areas of 18117.4, 13928.5, and 25043.2 m², respectively. Peak concentrations decreased over time: benzene from 53.3 to 13.0 mg/L (75.6% reduction), chloroform from 112.0 to 20.0 mg/L (82.1%), and vinyl chloride from 128.0 to 24.0 mg/L (81.3%). Dynamic pumping simulations reduced plume areas by 85.8%, 78.0%, and 85.9% at 400 days, with peak concentration reductions of 90.2%, 82.1%, and 93.8%. Within 500 days, all concentrations fell below targets, with total pumping volumes of 94500, 60000, and 72000 m³. Fenton reagent (3% dosage) effectively treated extracted groundwater. Numerical simulation optimizes contamination delineation and pumping strategies, offering a cost-efficient pathway for similar sites.
1. Introduction
Industrial relocation policies in China have left numerous pesticide-contaminated sites with persistent groundwater pollution. Conventional remediation approaches often rely on static pump-and-treat designs that fail to adapt to evolving contaminant plumes, leading to excessive pumping volumes, high energy costs, and prolonged cleanup durations. The lack of predictive modeling for site-specific hydrogeological conditions exacerbates inefficiencies, as contaminant migration is governed by complex advection-dispersion-adsorption processes that vary spatially and temporally.
This study addresses these bottlenecks by integrating GMS-based three-dimensional geological, flow, and solute transport models to simulate the migration of benzene, chloroform, and vinyl chloride over 2000 days. The dynamic pumping scheme, which adjusts well numbers and pumping rates in stages, directly tackles the challenge of plume shrinkage and concentration rebound. By quantifying migration distances, concentration decay, and remediation performance, the protocol provides a data-driven framework to optimize well placement, pumping rates, and treatment chemical dosages, thereby reducing costs and improving remediation efficiency for similar contaminated sites.
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WANG Hongquan (2026). Migration Mechanisms and Pump-and-Treat Remediation Simulation for Benzene and Halogenated Hydrocarbons in Groundwater at a Pesticide-Contaminated Site. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202608016
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Frequently Asked Questions
What are the key hydrogeological parameters that most influence the migration distances and plume shapes observed in the simulation?
The migration distances and plume shapes are primarily controlled by groundwater flow velocity (advection), hydrodynamic dispersion, and retardation factors due to sorption. In this study, the southeast-northwest flow direction and hydraulic gradients dictated the elliptical plume orientation. The maximum migration distances at 2000 days (154.5 m for benzene, 130.5 m for chloroform, 165.2 m for vinyl chloride) reflect the combined effects of these parameters. Site-specific calibration of hydraulic conductivity and porosity is essential for accurate predictions.
How does the dynamic pumping scheme achieve higher contaminant mass removal compared to a constant-rate approach?
The dynamic scheme reduces the number of active wells from 9–7 to 1 over time, with pumping rates maintained at 25–30 m³/d. This staged approach prevents over-pumping in low-concentration zones and focuses extraction on remaining hotspots, as indicated by plume area reductions of 85.8–85.9% and concentration reductions of 90.2–93.8% at 400 days. Constant-rate pumping would likely spread the capture zone too thin, leaving residual contamination and requiring higher total volumes.
What are the cost implications of the total pumping volumes (94500, 60000, 72000 m³) and the 3% Fenton reagent dosage for full-scale implementation?
The total pumping volumes directly translate to energy and disposal costs. For example, pumping 94500 m³ over 500 days implies an average of 189 m³/day, which is manageable with standard extraction systems. The 3% Fenton reagent dosage (by weight) is relatively low, reducing chemical costs. However, the exact cost depends on local electricity rates, labor, and waste treatment fees. The study demonstrates that the dynamic scheme minimizes total pumped volume, thereby lowering overall lifecycle costs compared to non-optimized designs.
How scalable is this modeling approach to other contaminated sites with different contaminants or hydrogeological settings?
The GMS-based approach is highly scalable because it separates geological, flow, and transport models. The methodology can be adapted by inputting site-specific parameters such as hydraulic conductivity, porosity, and contaminant degradation rates. The key is to calibrate the model against field data. The study's success in simulating three different contaminants (benzene, chloroform, vinyl chloride) with distinct properties (e.g., sorption, volatility) demonstrates its versatility. However, for sites with fractured bedrock or complex geochemistry, additional model complexity may be required.
What are the limitations of the simulation regarding the assumption of ideal well operation and the absence of natural attenuation processes?
The simulation assumes continuous, ideal well operation, which may overestimate remediation efficiency if pumps fail or maintenance is delayed. Additionally, the model does not explicitly incorporate biodegradation or abiotic reactions, which could either enhance or hinder cleanup. The observed concentration reductions (75.6–82.1%) over 2000 days without pumping suggest natural attenuation, but the model's conservative approach ensures that the designed pumping scheme is robust even under less favorable conditions. Field monitoring is essential to validate and adjust the model.
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