EP 1110-1-27
27 Jan 00
will be needed to accommodate the procedure, and it is recommended that planning for this option be part
of well system design. Pigging requires:
An upstream entry point for the pig (for example at a well house).
A means of providing water pressure to propel the pig (water pressure from a potable water
system fire hydrant would suffice).
An outlet collection point for wastewater and pig.
(2) Alternatives such as electrostatic dispersion of colloidal fouling components have also been
suggested, and possibly have application.
h. Well array design recommendations. These design recommendations are detailed below.
(1) Have enough wells installed in a pumping or injection array to permit continued operation and
plume control while wells are out of service (being treated or pumps replaced).
(2) Install a ring of treatment wells around pumping or injection wells subject to clogging
(Section 5-4). These can greatly improve treatment success in the near-well formation by providing a way
to force treatment chemicals toward the pumping well screen from the outside and also to provide more
access for agitation of the near-well formation.
(3) On sites with very deep wells, options (1) and (2) may be quite expensive. In these cases,
where both replacement and rehabilitation may be very expensive and difficult, designing and planning
for a rigorous maintenance defense of the existing pumping wells are especially important.
9-2 Chemical Addition
a. Methods of addition. Chemicals may be introduced into wells by gravity (tremie), pumping in
against water column pressure, and high-pressure jetting. A feature of each is that chemical solutions are
directed to the screen region and not simply poured into the well. For maintenance treatments, simple
pouring and pumping (versus jetting or pressurizing) is usually sufficient. Jetting may be used for more
completely developed clogging situations. Note that both redevelopment methods and chemicals used in
maintenance (as well as rehabilitation) treatments can be hazardous to personnel and possibly damaging
to well structures.
b. Professionalism. Any treatment program must be initiated by professional contractors highly
familiar with these treatments. Site personnel can be trained in the safe use and evaluation of the
effectiveness of these methods by the contractor.
9-3 Mechanical Agitation
Chemicals introduced should be mixed through the screen column, either through surging (see Section
9-5) or recirculation pumping. As it is mixed and pumped in, and later during development, the solution
should be checked and adjusted to maintain pH <2. Current research under way at the Canadian Federal
Government's Praire Farm Rehabilitation Administration's geotechnical laboratory suggests that most
chemicals should have a maximum in-well contact time of less than 10 hr where clay swelling is a
possibility.
9-4
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