Towards characterizing LNAPL remediation endpoints

Kaveh Sookhak Lari,John L Rayner,Greg B Davis

doi:10.1016/j.jenvman.2018.07.041

Kaveh Sookhak Lari, John L Rayner + Show 1 more

Open Access

https://doi.org/10.1016/j.jenvman.2018.07.041

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Abstract

Remediating sites contaminated with light non-aqueous phase liquids (LNAPLs) is a demanding and often prolonged task. It is vital to determine when it is appropriate to cease engineered remedial efforts based on the long-term effectiveness of remediation technology options. For the first time, the long term effectiveness of a range of LNAPL remediation approaches including skimming and vacuum-enhanced skimming each with and without water table drawdown was simulated through a multi-phase and multi-component approach. LNAPL components of gasoline were simulated to show how component changes affect the LNAPL's multi-phase behaviour and to inform the risk profile of the LNAPL. The four remediation approaches along with five types of soils, two states of the LNAPL specific mass and finite and infinite LNAPL plumes resulted in 80 simulation scenarios. Effective conservative mass removal endpoints for all the simulations were determined. As a key driver of risk, the persistence and mass removal of benzene was investigated across the scenarios. The time to effectively achieve a technology endpoint varied from 2 to 6 years. The recovered LNAPL in the liquid phase varied from 5% to 53% of the initial mass. The recovered LNAPL mass as extracted vapour was also quantified. Additional mass loss through induced biodegradation was not determined. Across numerous field conditions and release incidents, graphical outcomes provide conservative (i.e. more prolonged or greater mass recovery potential) LNAPL remediation endpoints for use in discussing the halting or continuance of engineered remedial efforts.

Highlights

The release of hazardous organic chemicals including light nonaqueous phase liquids (LNAPLs, such as petroleum hydrocarbons) into the vadose zone and groundwater is a significant environmental concern due to its potential adverse effects (Davis et al, 2009)
To enhance removal of light non-aqueous phase liquids (LNAPLs) mass, various forms of recovery methods may be applicable. These include air, water or solvent flushing or single, dual and multi-phase purging of LNAPL, soil gas and water (Khan et al, 2004; Davis et al, 2013) (Johnston and Trefry, 2009)
We conducted 80 representative multi-phase and multi-component scenario simulations to investigate the performance of various LNAPL recovery techniques

Summary

Introduction

The release of hazardous organic chemicals including light nonaqueous phase liquids (LNAPLs, such as petroleum hydrocarbons) into the vadose zone and groundwater is a significant environmental concern due to its potential adverse effects (Davis et al, 2009). LNAPLs form an immiscible liquid plume in the vadose zone and across the capillary fringe (Lenhard et al, 2018). This induces the partitioning of compounds into gaseous and aqueous phase exposure pathways (Lang et al, 2009; Rivett, 2014; Davis et al, 2005). To enhance removal of LNAPL mass, various forms of recovery methods may be applicable. These include air, water or solvent flushing or single, dual and multi-phase purging of LNAPL, soil gas and water (Khan et al, 2004; Davis et al, 2013) (Johnston and Trefry, 2009). As the dynamics of LNAPL in the subsurface is a function of different parameters (including geo-physical properties of the porous media and the distribution and composition of the LNAPL itself), the feasibility and effectiveness of each (or any combination) of the aforementioned techniques for a particular site is a question to be answered prior to any remedial effort

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