time the screen is cleaned using surging methods, and whenever regular
Preparing the Disinfectant. The best method of disinfection
involves preparing a stock chlorine solution that, when mixed with 100 gallons (400
liters [L]) of water in the well, provides a dosage of 100 milligrams per liter (mg/L). The
stock chlorine solutions described below have a volume of 2 quarts (2 L), the amount
required for each 100 gallons (400 L) of water in the well. Use calcium hypochlorite
(65 percent available chlorine) or sodium hypochlorite (liquid household bleach
containing 5.25 percent available chlorine) to make the solution. Prepare the solutions
in clean crockery, glass, or rubber-lined containers. Metal containers will be corroded
by the strong chlorine solution.
Calcium Hypochlorite. Add 2 ounces (66 grams [g]) of
granular high-test calcium hypochlorite to a small quantity of water and stir to a
smooth watery paste free of lumps. Add this mixture to enough water to make
2 quarts (2 L). Stir the solution for 10 to 15 minutes before allowing the inert
ingredients to settle. Use the clear liquid with the chlorine and discard the inert
ingredients. Use 2 quarts (2 L) for every 100 gallons (400 L) of well water.
Sodium Hypochlorite. Dilute 1 quart (1 L) of common liquid
household bleach with 1 quart (1 L) of water. Use 2 quarts (2 L) for every 100 gallons
(400 L) of well water.
Disinfecting Drilled, Driven, and Bored Wells. Calculate the
quantity of water in the well based on the depth of water and the contents of the well in
gallons per foot or liters per meter (Lpm) (Table 1). Introduce 2 quarts (2 L) of stock
solution for each 100 gallons (400 L) of water in the well. Pour the stock solution
directly into the well through a clean hose that is alternately raised and lowered in the
well water. Operate the pump until a distinct odor of chlorine can be detected in the
water discharged. Allow the well to stand for 24 hours, then pump water to waste until
the chlorine residual drops to an acceptable level. Surging during chlorine treatment is
helpful (see par. 22.214.171.124[g]). Obtain samples for bacteriological analysis and determine
potability before putting well into service.