EP 1110-1-27
27 Jan 00
for the disinfection of wells for potable water service. Well cleaning maintenance and rehabilitation are
not standardized but methods are available (Borch, Smith, and Noble 1993). Concentrations as high as
500 to 2,000 mg/L of chlorine are usually desirable for this. This is NOT RECOMMENDED for HTRW
maintenance treatment applications. Chlorine is a powerful oxidant that reacts with organic compounds,
causing chemical alteration of the compounds to more difficult-to-treat forms or to potentially explosive
situations with eruption of chemicals at the surface. This latter reactivity, particularly in light of the
carcinogenic properties of some chlorinated organic compounds, is the basis for increasing regulatory
scrutiny of the use of chlorine for purposes other than maintaining potability of water.
Table 6-2. Common Well Cleaning Chemicals in Use -- Not Recommended
Acids
Safety Concerns*
Effectiveness
Muriatic acid (HCl)
WARNING: Extremely
Powerful for removing mineral and
hazardous to handle. Volatile
inorganic metal oxide scale. Relatively
liquid: Requires respiratory and ineffective against biofouling and
splash protection.
deleterious to stainless steel (CEGS 13405).
DO NOT mix with chlorine
Steel industry pickling liquor by-product.
reaction in well can lead to
Quality is a problem, with cadmium and
surface eruption of chemicals
other impurities often present in industrial
and Cl gas; use inhibitors for
grades, although NSF 61** certified
metal well screens but note that
solutions are available. NOT
some industrial inhibitors should RECOMMENDED for maintenance
not be used in potentially
treatments.
potable ground water (toxicity),
and gelatin (safe) provides
nutrient and inoculum for
regrowth.
Phosphoric acid
WARNING: Extremely
Effective against metal and mineral
hazardous to handle. A strong
hydroxides. Somewhat effective against
food grade quality acid, readily
biofouling, but no more so than some other
available, 75%, in 208 liter (55
mixtures.
gal) drums and 45.4 56.8 liter
(12-15 gal) containers.
Quite hazardous to handle. Full
Leaves phosphate residue behind for
breathing mask and splash
bacteria. NOT RECOMMENDED for
protection required. Adequate
maintenance treatments.
ventilation a must.
* Refer to Chapter 7 and health and safety references.
** NSF International Standard 61 covers the safety of chemicals for human contact.
(b) Ozone. Ozone (O3) is formed by exposure of oxygen O2 to strong electrical charges. Ozone
has to be generated at the point of application due to its instability, which precludes storage under
pressure or transport, making it largely impractical for rehabilitation. Ozone does not have a recognized
practical application in well maintenance treatment, although it may be used in piping system treatment to
repress biological activity (CEGS 13405 and EM 1110-1-4008).
(c) Hydrogen peroxide. Like ozone, aqueous hydrogen peroxide is a powerful disinfectant and
oxidant. It has been used with some effectiveness in removing well biofouling in both water supply and
environmental wells. There are a variety of sources of "generic" 50% peroxide mixtures available
commercially. It should also be noted that H2O2 is aggressively attacked by bacterial enzymes. It breaks
6-3
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