EP 1110-1-27
27 Jan 00
9-4 Chemical Recovery
Chemical solutions containing biofilm, metal oxides, and other solid debris must be removed from the
well column. It is essential to note that neutralization should never be conducted in the well column itself,
because
Clogging material will drop out of suspension or solution.
Explosive effervescence is possible when caustic solutions are introduced into solids-laden
acid solutions.
a. Containment. Containment and treatment such as neutralization are then necessary before
release into the environment. Options include:
(1) Pump into holding tanks. Development slurries are typically best pumped to pretreatment
tanks for settling and acid neutralization. Such tanks should be sufficiently large to hold three to six times
the borehole volume so that development (Section 9-5) does not have to stop. Other options include
neutralization "on the fly" in smaller tanks using a calculated feed rate of neutralizing chemical solution.
(2) Divert to existing lagoons. On occasion, slurries may be diverted to surface containment and
permitted to lose acid or oxidant power. Solids may settle in place.
(3) Divert to treatment plant. Typically on HTRW remediation sites, water treatment is available,
and development slurries must pass through them prior to release. Typically pretreatment is necessary.
The tolerances and requirements of the treatment process should be known and not exceeded.
b. Regulatory aspects. Environmental regulations and standards that apply to such impoundments
apply. Project agreements with regulators and local regulations may need to be checked before
discharging to existing treatment plants or lagoons if they were not originally intended to accept such
waste. Ultimately solids must go to secure disposal per regulatory requirement.
9-5 Well Development
Practically all methods of drilling cause compaction of unconsolidated materials of variable thickness in
an annulus around a drill hole. In addition, fines are driven into the wall of the hole, drilling mud invasion
may occur to a greater or less extent, and a mud cake (if used) may form on the wall of the hole. These
effects are well described in standard well construction references such as ADITC (1997) and Driscoll
(1986).
a. Defining well development and redevelopment. Well development is the final well construction
step that
Removes formation damage caused by the borehole drilling process.
Establishes the optimal hydraulic contact possible between the well and the aquifer formation
supplying fluids to (or accepting fluids from) the well.
Redevelopment is the process of using development methods to remove accumulating clogging material
from around an installed well.
b. Well development and redevelopment effects. The importance of proper initial well
9-5
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