First, don't panic' Bacterial contamination is very common. Studies have found that over 40 percent of private water supplies are contaminated with coliform bacteria. Spring water supplies are the most frequently contaminated, with over 70 percent containing coliform bacteria.
Improving protection of a well or spring from the inflow of surface water is an important option to consider if the supply is contaminated with bacteria. It is important to remember that the groundwater is not necessarily contaminated in these cases, rather the well is acting to funnel contaminants down into the groundwater.
Although well pits were the common method of construction several years ago, they are no longer considered sanitary construction.
A properly protected well is evidenced by the well casing extending above the surface of the ground and the ground sloping away from the well to prevent water from collecting around the casing.
A properly protected spring is developed underground and the water channeled to a sealed spring box. At no time should the water be exposed to the ground surface.
Keeping the plumbing system clean is an important part of maintaining a sanitary water supply. Anytime work is performed on the plumbing or pump, the entire water system should be disinfected with chlorine. Simply pulling the pump out of the well, setting it on the grass to work on it, and returning it to the well is enough to contaminate the well with bacteria.
The procedure for cleaning and sanitizing a well or spring with chlorine is called shock chlorination. Concentrations of chlorine ranging from 50 to 200 mg/1 are used in the shock chlorination process. This is 100 to 400 times the amount of chlorine found in "city water." The highly chlorinated water is held in the pipes for 12 to 24 hours before it is flushed out and the system is ready to be used again.
Periodic shock chlorination also may be effective in reducing an iron bacteria problem. The amount of chlorine needed to shock chlorinate a water system is determined by the amount of water standing in the well.
Table 3 lists the amount of chlorine laundry bleach or powdered high-test hypochlorite (HTH) that is needed for wells. If in doubt, it is better to use more chlorine than less.