Flushing is the process of using the scouring action of moving water to help rid a water supply of contaminants, and it is an essential part of the disinfection process. Flushing normally takes place several times during the disinfection process.
- Flushing is a normal part of the development of a newly constructed well and the preparation of an existing well before chlorine treatment.
- Flushing a water supply after treatment with chlorine is required to remove the chlorine residual from the well.
Pump LocationInstall the pump as close to the bottom of the well as possible during the flushing stage. For fractured or very porous rock formations, it may be necessary to move the pump up and down the length of the exposed borehole to assure water movement into the entire well bore.
Pumping RateMaximize the pumping rate. The greater the volume and velocity of water being pumped, the more effective the flushing will be.
Duration of FlushingGenerally, the longer the flushing time, the better. A suggested minimum is to pump until at least 20 casing volumes have discharged from the well. For example: A 100-foot deep 5-inch well has a casing volume of 100 gallons. A minimum of 2,000 gallons of water (20 casing volumes times 100 gallons) should be flushed from the well.
Flushing Without More ChlorinationIn some cases, flushing without further chlorination has been effective in correcting contamination problems. Some local health departments have found that allowing water to discharge from a garden hose continuously for a period of at least 24 hours or more has corrected the contamination problem without the need to treat with chlorine. The hose is discharged into a roadside ditch or into the yard away from any on-site sewage disposal system. Open the sill cock valve all the way during the flushing stage.
Do Sampling After FlushingA water sample should be collected from the water supply after the flushing period to determine if the flushing process has corrected the bacterial contamination problem. If coliform bacteria are not present in the water sample analyzed, the flushing may have successfully disinfected the water supply. However, a second water sample is recommended approximately one week later to verify that the bacterial contamination problem has been corrected.
Discharge Water ManagementThe initial discharge of water from a recently chlorinated well may contain elevated levels of chlorine and chlorination byproducts. Do not run the water into a surface water body. Avoid flushing for long periods if discharge water will flow onto neighboring property or roadways, or otherwise create a nuisance condition.