Page 234 - Materials Chemistry, Second Edition

6

Groundwater Remediation

6.1 Introduction
When an aquifer is impacted, groundwater extraction is often needed.
Groundwater extraction mainly serves two purposes: (1) to minimize
the plume migration or spreading, and (2) to reduce the concentrations
of compounds of concern (COCs) in the impacted aquifer. The extracted
water often needs to be treated before being put back into the aquifer
or released to surface water. Pump-and-treat is a general term used in
groundwater remediation that extracts impacted groundwater and treats
it aboveground.
Groundwater extraction is typically accomplished through one or more
pumping or extraction wells. Extraction of groundwater stresses the aqui-
fer and creates a cone of depression or a capture zone. Deciding spacing
among the extraction wells and choosing appropriate locations for the wells
are important components in design. Extraction wells should be strategi-
cally located to accomplish rapid mass removal from areas of the ground-
water plume where COCs are heavily concentrated. On the other hand,
they should be located to allow full capture of the plume to prevent further
migration/spreading. In addition, if containment of the plume is the main
objective for the groundwater extraction, the pumping rate could be estab-
lished at a minimal rate, just sufficient to prevent the plume migration, since
the extracted groundwater often incurs treatment costs. On the other hand,
if the groundwater cleanup is required, the extraction rate may need to be
enhanced to shorten the remediation time. For both cases, major questions
to be answered for design of a groundwater remediation program are simi-
lar, which include

1. What is the optimum number of extraction wells?
2. Where would be the optimal locations of the extraction wells?
3. What would be the sizes (diameters) of the wells?
4. What would be the well depth and the interval and size of the
perforations?

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