How To Recognize Dead-End Danger Zones

Dead-End Danger Zones are the result of uncirculated water in your distribution system. Leaving dead-ends to “rot” can lead to health-threatening situations for your customers and non-compliance with federal standards. These dead-ends exist at the end of water mains at hydrants and underground valves and are caused by stagnant water in your system.

Why do these danger zones exist? And what causes them to reemerge?

Dead-ends occur when stagnant potable water is allowed to exist in pipes combined with how quickly disinfectants in the water break down. Disinfectants can start to dissipate within 200 hours in uncirculated water. Free chlorine dissipates quickly, at a rate of 1.5ppm per week while chloramine dissipates at a rate of .625ppm per week. Water acidity (pH) and local temperatures can adversely affect the rate of disinfectant dissipation.

When naturally occurring organic materials come in contact with chlorine, they can turn toxic. These are called DBPs (disinfectant byproducts). When consumed, DBPs can cause health-related issues such as heart disease, kidney or liver cancer, and even Alzheimer’s disease. DBP’s can form in uncirculated, dead-end water in as little as 4-7 days.

Tools to predict dead-ends

The Dead-End water quality spreadsheet calculator quickly and easily evaluates potential dead ends in your system using an algorithm, so your team knows what mains to target and watch for.

Portable intelligent monitoring systems attach to an existing hydrant to analyze chlorine and disinfectants in your water.

Equipment to prevent dead-ends

Hydrants and their likelihood of becoming dead ends are categorized by risk zones. Critical and high-level risk zones often need constant or regular DBP maintenance, while moderate and safe dead-ends might not require any. Often, it depends on how much usage a specific zone is getting and how often the equipment is maintained.

• For critical-risk zones.
  • These areas require constant maintenance. A permanent intelligent flushing unit installed directly on the main is best for critical areas. These units are programmed to automatically flush and analyze water when needed to get within pre-determined levels.

• For high-risk zones.
  • Like the intelligent units, permanent automatic flushing units differ in that they do not analyze the water coming out. These units are best for zones that do not have unpredictable fluctuations in DBPs but must be flushed regularly.
• For moderate-risk zones.
  • Consider a portable flushing station. These are the most common types of flushing equipment, can be carried from hydrant to hydrant, and are easy to install. Units can be programmed for time and are a municipalities best defense at keeping customer water clean.
• For low-risk zones.
  • These zones rarely need to be flushed, as the continuous water flowage keeps them from becoming stagnant and developing DBPs. Manual blow-offs ensure that your pipes are never under too much pressure and are repairable and maintainable from above ground.