Expanded Application of the Passive Flux Meter: In-Situ Measurements of 1,4-Dioxane, Sulfate, Cr(VI) and RDX

Alexander Haluska,Patrick Evans,Michael Annable,Jaehyun Cho,Meghan Thiemann

doi:10.3390/w10101335

Alexander Haluska, Patrick Evans + Show 3 more

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https://doi.org/10.3390/w10101335

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Abstract

Passive flux meters (PFMs) have become invaluable tools for site characterization and evaluation of remediation performance at groundwater contaminated sites. To date, PFMs technology has been demonstrated in the field to measure midrange hydrophobic contaminants (e.g., chlorinated ethenes, fuel hydrocarbons, perchlorate) and inorganic ions (e.g., uranium and nitrate). However, flux measurements of low partitioning contaminants (e.g., 1,4-dioxane, hexahydro-1,3,5-trinitro-s-triazine (RDX)) and reactive ions-species (e.g., sulfate (SO42−), Chromium(VI) (Cr(VI)) are still challenging because of their low retardation during transport and quick transformation under highly reducing conditions, respectively. This study is the first application of PFMs for in-situ mass flux measurements of 1,4-dioxane, RDX, Cr(VI) and SO42− reduction rates. Laboratory experiments were performed to model kinetic uptake rates and extraction efficiency for sorbent selections. Silver impregnated granular activated carbon (GAC) was selected for the capture of 1,4-dioxane and RDX, whereas Purolite 300A (Bala Cynwyd, PA, USA) was selected for Cr(VI) and SO42−. PFM field demonstrations measured 1,4-dioxane fluxes ranging from 13.3 to 55.9 mg/m2/day, an RDX flux of 4.9 mg/m2/day, Cr(VI) fluxes ranging from 2.3 to 2.8 mg/m2/day and SO42− consumption rates ranging from 20 to 100 mg/L/day. This data suggests other low-partitioning contaminates and reactive ion-species could be monitored using the PFM.

Highlights

The freely dissolved concentrations of contaminants and metals in sediment pore water are critical measurements for assessing their fate and transport in groundwater systems
RDX was only detected in Passive Flux Meters (PFMs) 4 (Figure 1) with an average mass flux of 4.9 mg/m2 /day, which equates to a contaminant mass fluxes (Cf) of 174 μg/L
Groundwater samples taken just before deployment of PFM 4 were in good agreement since an RDX concentration of 180 μg/L was measured, which is a 3.4% difference from the PFM Cf value

Summary

Introduction

The freely dissolved concentrations of contaminants and metals in sediment pore water are critical measurements for assessing their fate and transport in groundwater systems. Accurate measurement of metals and organic contaminants using traditional groundwater sampling methods (e.g., low flow point sampling) is challenging due to the differences in solubilities and solid phase partitioning behaviors. Concentrations of compounds in groundwater withdrawn from wells are controlled partly by the transfer of mass to flowing water from other phases: (1) Mass absorbed to aquifer solids; and/or (2) mass trapped in immobile pockets. Transfers of masses can result in underestimating extracted groundwater concentrations because this traditional method cannot account for vertical or horizontal spatial variability in the distribution, nor can it account for how concentrations may change over time due to seasonal variability (e.g., increased rainfall, tidal changes, etc.) [1]. Passive sampling approaches have emerged as a promising method since they allow both temporally and spatially averaged concentrations.

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