EP 1110-1-27
27 Jan 00
Appendix C
Experience Basis and Maintenance Treatment Example
C-1. Case Histories of Well Maintenance Activities
Case histories are illustrative of possible problems and how they were handled elsewhere. A number of
water supply system case histories are summarized in Smith (1992), Borch, Smith, and Noble (1993), and
Cullimore (1993) among others. These are illustrative of the worldwide distribution of problems of wells,
and, in particular, those associated with Fe, Mn, and S biofouling, and how they have been addressed.
Several other geotechnical and environmental-studies case histories are summarized in Smith (1995) and
Alford and Cullimore (1999) and are the basis for the following.
(1) Problems associated with wells are largely the same all over the world.
(2) Lack of planning and adequate response to deterioration problems of wells results in reduced
performance of wells and water collection and distribution systems.
(3) The economic impacts of this deterioration can be significant, but are only now being
quantified adequately in the water supply setting (e.g., Sutherland, Howsam, and Morris 1994), but hardly
at all in the HTRW remediation field. For water supply wells, Sutherland, Howsam, and Morris (1994)
estimate that 40% of wells worldwide are operating inefficiently. It is estimated that 0 million is
annually spent on well and well pump rehabilitation in North America.
(4) Preventive actions useful in limiting the effects of biofouling (as documented in open
literature) have not been widely applied in the planning of ground water supply and control projects to
date.
(5) Design and operations poorly matched to the aquifer being pumped (e.g., choice of corrodible
materials or excessive pumping) aggravate environmental well deterioration causes.
(6) Adverse well deterioration effects on the reliability of ground water quality samples have been
documented.
(7) Wells operating under vacuum and anaerobically exhibit fewer clogging symptoms.
(8) Injection of biocides has largely been ineffectual in solving the immediate well problems.
They almost always fail to prevent a recurrence of problems, although recurrence of performance decline
may be significantly delayed.
(9) Where attention to microbial fouling potential (or the symptoms of such fouling) results in the
institution of a preventive maintenance program, biofouling-related problems can be controlled (see
additional case histories summarized in this section). However, programs have to be revised in response
to experience with a well field over time.
(10) New well construction may serve to temporarily avoid recurrence of a problem. However,
current experience is demonstrating that clogging, biofouling, and Fe/Mn/S transformations may extend
several meters away from wells with existing problems. The performance problems of the former wells
cannot be considered solved with new construction. The problems are likely to recur with the new wells
unless a maintenance program is implemented.
C-1
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