Groundwater Circulation Wells (GCW) can be an effective in-situ remediation option allowing high mass recovery of contaminants in cases where contamination hotspots are located in saturated soil having low hydraulic conductivity. Traditional treatment options such as Pump&Treat, Air Sparging (AS)/Soil Vapor Extraction (SVE) and Multi Phase Extraction (MPE) typically require long operation times and significant costs for long-term plume management. GCWs induce meaningful changes in the groundwater flow introducing vertical flows both downward and upward, generating a “circulation cell”, which facilitates contaminant desorption from the soil. This study aims to understand the effects of a GCW on an aquifer in terms of both groundwater flow directions and water balance. A groundwater numerical model was built using MODFLOW-2005 to simulate the effect of the hydraulic parameters of the aquifer on the hydraulic circulation pattern of the GCW. The use of particle tracking simulated by MODPATH 7 showed the circulation cells and the impact on groundwater directions induced by different configurations of hydraulic parameters. The water flowing into the cell comes from both the injection well and the surrounding aquifer and the model shows how the hydraulic parameters of the aquifer, in particular the horizontal and vertical hydraulic conductivity, have a paramount influence in determining the shape and dimension of the circulation cell. A water mass balance analysis was carried out. It allowed to predict the groundwater flows exchanges between the GCW system and the surrounding aquifer, and to verify the sensitivity of the water budget to specific aquifer parameters. The results of this study are useful for further understanding the hydraulics of a GCW remediation system in order to support the design and to predict its performance.
Site is a pharmaceutical facility located in Milan Province with main contamination by TPH and BTEXS (about 100–120 mg/L). The results of pilot test were great (100% of degradation in 5–6 month). At the moment the Emergency Measures Project design is currently in progress (about 33 points of oxygen delivery). Contaminants are not transferred from one media to others, but are biodegraded to CO2 and Water, so this technology is in accordance with AECOM global vision on Sustainable Remediation technologies. S̲p̲e̲c̲i̲a̲l̲ d̲i̲f̲f̲u̲s̲e̲r̲ used allows the minimization/elimination of contaminant volatilization due to no bubbles or micro-bubbles (max Ø less than 0.1 mm) and low flow (0.5 – 1 NL/h); on site these diffuser is able to dissolve up to 50 mg/L oxygen. L̲a̲b̲ s̲c̲a̲l̲e̲ b̲a̲t̲c̲h̲ t̲e̲s̲t̲: The test objective is to evaluate, under controlled conditions, the feasibility of bioremediation, by injection of pure oxygen; Batch tests was performed in controlled microcosm with continuous monitoring of pH, Red-Ox and dissolved oxygen, periodic monitoring of chemical parameters on both the matrix: on water and in air line (by activated carbon) and microbiological analysis; batch test show the complete degradation of organics in 20 days. F̲i̲e̲l̲d̲ P̲i̲l̲o̲t̲ T̲e̲s̲t̲ (one injection well, two lateral monitoring wells and one downgradient monitoring well): The test objective is to assess the feasibility of remediation @ field-scale using bio-stimulation with pure oxygen; first period of injection of a mixture of oxygen and tracer nobles gas (Krypton and Neon) in order to highlight the effectiveness of removal of the contamination and to identify the range of influence of the technology. B̲a̲s̲e̲l̲i̲n̲e̲: Total hydrocarbons and toluene, at maximum concentrations equal to 100 – 120 mg/L; main contaminant is Toluene, the chlorinated organic compounds (low concentrations) are also present upstream site; due to reducing condition there was presence of dissolved iron (5 to 32 mg/L) and manganese (4 and 9 mg/L). After 8 month Removal efficiency (due to aerobic degradation) for organics are: 95 to 99.99%; in addition due to recreation of natural oxidizing condition also metals (Fe, Mn and As) re-precipitate. Bacteric count (general and oxidizing specific bacteria) grow from baseline 10+1/+2 UFC/mL to 10+5/+6 UFC/mL due to correct growing substrate and electron acceptor (O2). Results: Lateral ROI is estimated to be at least 4 m (diffusion of approximately 2 m/month), oxygen influence downstream of at least 25 m (diffusion of approximately 8–9 m/month). These results show that pure oxygen diffused into the groundwater in the area has stimulate indigenous biomass and thus promote the biological aerobic removal of pollutants so contamination can be removed with yields close to 100%. N̲o̲t̲e̲: in one area of site at the end of Pilot test we found also Tetrahydrofuran and Dichloromethane, we perform a fast batch test and we note that also these contaminant are quickly degraded (75% and 97%) due to aerobic co-metabolism in presence of toluene as growing substrate.
This paper presents the work carried out at a coastal contaminated site to define the presence and nature of heterogeneities in a complex hydrogeological aquifer system. The aim of the studies was to identify the effects of acquifer heterogeneities affecting plume migration in order to support remediation strategies. The hydrogeology of the area is characterized by the presence of a multilayer aquifer and a close relationship between groundwater and surface water (tidal fluctuations, lake system). Different approaches were utilized to investigate the system, including field and modeling studies. Field investigations included continuous groundwater level monitoring system, the monitoring of multi-level wells and the installation and sampling of new monitoring wells in order to define the vertical distribution of the chlorinated solvents (CAHs) contamination. The complexity of the hydrogeological system required hydraulic tests and tracers tests in order to verify the hydraulic interactions between aquifer layers and their relationship with surface water. The modeling studies have included the implementation of 3 separate numerical models of groundwater flow, aiming to verify the effectiveness of the previous site emergency remedial actions and to support remediation strategies in different project phases. The studies allowed to understand the downward plume migration of the CAHs: vertical hydraulic gradients induced by the surface water system and the complexity of the multilayered aquifer system due to presence of heterogeneities mainly affected the CAHs transport in the first acquifer.
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