Page 312 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Chapter
8

Nanomaterials for

Groundwater Remediation

Gregory V. Lowry Carnegie Mellon University, Pittsburgh, Pennsylvania, USA

Introduction

Contamination of subsurface soil and groundwater by organic and inor-
ganic contaminants is an extensive and vexing environmental problem
that stands to benefit from nanotechnology. The EPA reports that con-
tamination by chlorinated organic pollutants such as trichloroethylene
(TCE), and heavy metals such as lead and hexavalent chromium are pri-
mary concerns at Superfund National Priorities List sites, which are the
most contaminated sites in the United States. Associated health
risks have led to an extensive remediation effort for the past 30 years.
Remediation is costly and poses significant technical challenges. For
example, life-cycle treatment costs are estimated to exceed $2 billion for
approximately 3,000 contaminated Department of Defense sites (Stroo
et al. 2003).
Remediation efforts aimed at removing deep subsurface contamination
(e.g., pump and treat) have had limited success because most pollutants
are not highly mobile in the subsurface. For example, many organic con-
taminants are only weakly water-soluble and tend to remain as a sepa-
rate nonaqueous phase liquid (NAPL) in the subsurface. Many organic
contaminants are denser than water (DNAPL) and migrate downward
in the aquifer. As sketched in Figure 8.1, DNAPL residual ganglia and
pooled DNAPL are trapped in the porous soil. Heavy metals such as
Pb(II) or Cr(VI) also tend to be concentrated in areas near their release
point. The residual saturation acts as a long-term source for contaminant

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