Remediating Contaminated Groundwater with an Aerated, Direct-Push, Oxidant Delivery System

James Reece,Steve Comfort,Clifford E Harris,Yusong Li,Ann Kambhu,Mark Christenson

doi:10.3390/w12123383

Abstract

One of the biggest challenges to treating contaminated aquifers with chemical oxidants is achieving uniform coverage of the target zone. In an effort to maximize coverage, we report the design and installation of a novel aerated, slow-release oxidant delivery system that can be installed by direct-push equipment. By continuously bubbling air beneath a slow-release oxidant in situ, an airlift pump is created that causes water and oxidant to be dispersed from the top of the outer screen and drawn in at the bottom. This continuous circulation pattern around each drive point greatly facilitates the spreading of the oxidant as it slowly dissolves from the wax matrix (i.e., oxidant candle). Given that the aeration rate controls the outward flow of oxidant from the outer screen in all directions, the radius of influence around each drive point is largely a function of the outward velocity of the oxidant exiting the screen and the advection rate opposing the upgradient and lateral spreading. Temporal sampling from three field sites treated with the aerated oxidant system are presented and results show that contaminant concentrations typically decreased 50–99% within 6–9 months after installation. Supporting flow tank experiments that demonstrate oxidant flow patterns and treatment efficacy are also presented.

Highlights

A critical review of two decades of contaminated groundwater sites treated by in situ chemical oxidation (ISCO) has uncovered many examples where liquid oxidant injections have failed to achieve desired cleanup goals [1,2]
In the context of our modular oxidant delivery system, the air bubbles placed in the screen gap created a buoyancy force that lifted and caused water and oxidant to dispel from the upper portions of the screen (Figure 2A)
While the use of extraction wells to create gradients around oxidant cylinders has been proposed as one means of increasing oxidant coverage [13,14], Evans et al [52,53] reported density-driven flow was still observed from persulfate-wax cylinders under an induced hydraulic gradient in the field

Summary

Introduction

A critical review of two decades of contaminated groundwater sites treated by in situ chemical oxidation (ISCO) has uncovered many examples where liquid oxidant injections have failed to achieve desired cleanup goals [1,2]. Unlike the positive results obtained when chemical oxidants are used in well-mixed reactors, such as during the treatment of municipal wastewaters, direct-push delivery techniques of liquid oxidants into groundwater can fail to deliver uniform coverage. The reason for this is the uncontrolled, unmixed and stratified nature of subsurface environments. A review of 40 ISCO sites showed that nearly 50% of the ISCO treatments injected liquid oxidant volumes equivalent to 10% of the contaminant plume [2,3,4].

Methods

Results

Conclusion