Allow the well to stand for 24 hours. Then pump water to
waste until the chlorine residual reaches 0.1 mg/L. Surging during chlorine treatment is
helpful (par. 220.127.116.11[g]).
Perform three or four successive treatments with chlorine.
Alternating acid treatment with chlorine treatment can be very effective. Complete the
acid treatment first, followed by chlorine treatment after most of the acid has been
pumped to waste. A second series of acid and chlorine treatments can be undertaken
after the initial acid and chlorine treatments have been completed.
Phosphate Treatment. The glassy phosphates (sodium
hexametaphosphates) act as dispersing agents on such screen-plugging materials as
amorphous silicia, hydrated ferric oxide, iron carbonate, and calcium carbonate. Follow
these treatment steps:
Dissolve 15 to 30 pounds (7 to 14 kg) of glassy phosphate
in a minimum amount of water and add 1 pound (450 g) of calcium hypochlorite for
each 100 gallons (400 L) of water in the well casing (under static conditions). To
dissolve the phosphate, suspend the chemical in a wire basket or burlap bag. Do not
simply dump the phosphate in the dissolving tank or barrel. Add the solution to the well
through a hose using the procedure described for acid treatment (par. 18.104.22.168[a]).
Allow the solution to remain in the well for 24 to 48 hours
and surge approximately every 2 hours. If surging is not possible, allow the solution to
stand in the well for 1 week.
Caution: Treatment with glassy phosphate for more than 1 week may
cause the well yield to decrease.
After treatment, pump the well to waste for 8 hours and test
the output. Repeat the treatment until the output no longer improves. Analyze the
phosphate content of the well water after final treatment and pumping to make sure it
has been reduced to normal background levels.
Dry Ice Cleaning. Compressed carbon dioxide gas, or "dry ice,"
has been used for well cleaning with mixed results. This treatment works best in deep
wells with high static levels. Follow these steps:
For wells measuring 6 to 10 inches (150 to 250 millimeters
[mm]) in diameter, use 10 to 15 pounds (4.5 to 7 kg) of dry ice for light surging and
25 to 50 pounds (11 to 23 kg) for heavy surging. Drop pieces of broken dry ice of
about 2 inches (5 centimeters [cm]) in diameter into the well casing until enough has