EP 1110-1-27
27 Jan 00
changes in biofilm consistency, and analyze collected samples for changes in elemental analysis
and crystalline structure of encrusting compounds. This information is useful in adjusting
treatment programs.
(2) Rather than reducing monitoring, cost and labor savings can be realized by using automated
sampling and data reporting and computerized maintenance management software to minimize human
time investment. Automated systems should be evaluated periodically and verified manually.
5-3. Schedule for Reducing Maintenance After First Year
Maintenance (including monitoring) intervals can be reduced as trends are established. (Exception:
troublesome wells that may be on annual or more-frequent treatment schedules based on first-year
experience.) Typically, on wells performing adequately, the frequency of physicochemical and
biofouling parameter testing can drop to quarterly if little change in conditions is noticeable after one
year. Table 5-3 summarizes a post-first-year PM schedule.
5-4. Schedule for Intensive Maintenance for Critical Wells
a. Long-term intensive maintenance. As site experience develops (1 to 5 years), certain wells will
be identified that will require intensive maintenance to continue useful operation. Intensive maintenance
will include the following (detailed in Appendix C):
Premaintenance testing of performance components.
Removal of pump and inspection of components, repair and refurbish as needed.
Chemical treatment (primary well and satellite wells).
Mechanical development.
Re-installation of well components.
Testing (pre- and post-repair testing and PM testing, which includes parameters listed in
Tables 5-1 and 5-2).
b. Schedule. A typical schedule is 3 to 6 months for injection wells and 6 months to annually for
pumping wells. Where pump removal is determined not to be cost effective, or is especially difficult,
pump testing to determine its status on the above schedule is a second option.
c. Well system modifications for treatment.
(1) In situations where pump removal is expensive and difficult (and this situation cannot be
modified readily), some wells may respond well to in-well recirculating cleaning systems properly
installed and operated. Such systems involve installing a return-flow pipe string to the open zone below
the well pump, connected to the well pump discharge. An electronically actuated valve is controlled by a
timer or other control device that flushes the sump or screen to remove built-up slime, oxides and
sediment. Chemical feeds can be added to effect more aggressive cleaning.
(2) Additional wells should be installed at these locations to permit alternating wells in operation.
Wells should be sufficiently far away from their alternating partners to be outside the likely clogging
zones (if possible), but situated to maintain hydraulic control of the plume at this location.
(3) Satellite wells are recommended for introduction of cleaning solutions. Three to five wells
may be installed at regular intervals around the pumping well at a distance of 2 to 7 m (6.6 to 23 ft). The
distance depends on local hydraulic conductivity and the perceived degree of existing clogging).
5-4
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