EP 1110-1-27
27 Jan 00
C-2. Maintenance Treatment for Wells: Basic Procedure
The procedure described below is an invasive maintenance treatment procedure that has proven to be
generally effective in stemming biofouling-related decline of well system performance on HTRW sites.
Note that some well situations will not require Steps 1 and 2, but most do at some point. An approach
similar to this has been approved at a Superfund site location in New Hampshire.
1. Detach and remove the installed well pump and other equipment such as water-level gauge transducers.
Set aside, service, or replace components as needed, and clean in preparation for re-installation. NOTE: It
is better to remove the pump in most situations; however, if the well pump is on the bottom, or if the well
is specially equipped, the pumping system can be used for circulation.
2. Brush casing and screen and bail or pump out to remove settled and surface-attached debris in the well.
Brushes should be properly sized and designed to abrade surface deposits, but not to score or gouge
casing or screen materials. These are often specially shop-fabricated for specific well applications.
3. (Optional): Conduct a downhole TV survey to assess damage or material changes. Conduct the survey
before brushing is started.
4. Mix a solution for treatment in clean (sediment-free) chemical-resistant tanks: In a volume of clean
(potable) water three times that of the calculated volume of the well screen (including the gravel pack
volume often makes for an excessively large treatment volume), add sufficient nonphosphorus anionic
wetting agent to make a 1% solution and mix, add sufficient industrial-grade glacial (87%+) acetic acid
sufficient to make a 12% solution (range 10 to15 %), and amend with sufficient clean, industrial grade
sulfamic acid to adjust the pH to < 2 (mix well to dissolve). Oxalic or citric acids can be used in place of
acetic acid for heavy iron oxide encrustation in waters with less than about 120 to150 mg/L total
hardness. Adjust pH as needed by adding acid. NSF International listed products are available for some of
these applications.
NOTES:
Always add acids to water and not vice-versa. While relatively safe to handle, all the chemicals specified
can cause chemical burns of skin, eyes, and respiratory tissues if mishandled. Anyone handling well
treatment chemicals should have specific training for this purpose, and equipment should be supplied to
minimize the potential for accidental spills or human exposure.
Both acetic acid and sulfamic acid are readily available from conventional chemical supply sources.
While costly in relation to some acid products, acetic acid has the advantage of having some disinfection
properties, is not highly reactive with metals and metal oxides (in contrast to mineral acids), and is the
best detergent acid. Sulfamic acid is inexpensive and a readily transportable and storable solid. Both
acetic and sulfamic acids are Class 55 detergents (nonhazardous), which adds flexibility in transport.
Highly concentrated acetic acid solutions freeze below about 12o C (~ 55o F) and should be kept above
this temperature prior to mixing. Dilute treatment solutions have much lower freezing temperatures far
below most ambient ground water temperatures. Where this may be critical (as in application under very
cold surface conditions into near-freezing ground water), those conducting treatment should calculate the
freezing points of dilute solutions. Hot water can be mixed with acetic acid to avoid freezing, or more
dilute solutions can be used.
Constant rate pumping tests and slug tests (in which an instantaneous charge of water or a solid object is
introduced into a well)
C-2
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