Page 235 - Materials Chemistry, Second Edition

218 Practical Design Calculations for Groundwater and Soil Remediation

5. What would be the construction materials of the wells?
6. What would be the optimum pumping rate of each well?
7. What would be the optimal treatment method for the extracted
groundwater?
8. What would be the disposal options for the treated groundwater?

An impacted aquifer can also be remediated using in situ technologies.
This chapter starts with design calculations for the capture zone and opti-
mal well spacing. The rest of the chapter focuses on design calculations for
commonly used in situ and ex situ groundwater remediation techniques,
including activated-carbon adsorption, air stripping, ex situ and in situ bio-
remediation, air sparging, biosparging, chemical precipitation, in situ chem-
ical oxidation, and advanced oxidation.

6.2 Groundwater Extraction

This section covers common calculations for determining the zone of influ-
ence of a groundwater extraction system. The results from these calculations
can provide answers to some of the questions mentioned previously.

6.2.1 Cone of Depression

When a groundwater extraction well is pumped, the water level in its vicin-
ity will decline, thereby providing a gradient to drive water toward the well.
The gradient is steeper as the well is approached, and this results in a cone of
depression. In dealing with groundwater extraction, evaluation of the cone
of depression of a pumping well is critical because it represents the limit that
the well can reach.
The equations describing the steady-state flow of an aquifer into a fully
penetrating well have been discussed in Section 3.3. The equations were
used in that section to estimate both the drawdown in the wells and the
hydraulic conductivity of the aquifer. These equations can also be used
to estimate the radius of influence of a groundwater extraction well and/
or the groundwater extraction rate. This subsection will illustrate these
applications.

6.2.1.1 Steady-State Flow in a Confined Aquifer

Equation (6.1) describes steady-state flow from a fully penetrating well in
a confined aquifer (an artesian aquifer). A fully penetrating well means