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Maintaining Chlorine Residuals has Changed the Water Tank Rules

Posted by Christine Gunsaullus on Wednesday, January 16, 2019

When I started in the water industry almost 25 years ago, we had certain steadfast rules when it came to water tanks:

1. The more storage, the better.
Owners would try to get the most volume, within budget, when building a new tank. If a one million gallon standpipe cost a certain amount, but a one and a half million gallon standpipe was just a little more, why not go bigger?

2. Less piping, lower cost a win/win.
A single inlet/outlet pipe cut flush with the tank bottom was sufficient and the least costly to build, sold!

3. Keep your tank(s) full.
Water operators would run their system with the tanks full, all the time, because you never knew when you’d have a main break or a fire and would need that extra storage.

Those rules have changed.

Throughout the country, states are implementing more stringent water quality regulations. The latest one from the Pennsylvania Department of Environmental Protection (PADEP) goes into effect on April 28, 2019. It requires systems with surface water (SW) or groundwater under the direct influence of surface water (GUDI) to maintain a disinfectant residual of at least 0.2 mg/L throughout the distribution system. Many tank owners are realizing that the ways they have built and run their systems for years are making it difficult to meet these new standards.

Here’s a chart showing how tank owners are managing these changes.

1994	2019
Single Inlet/Outlet Pipe	Encourage mixing with separate inlet/outlet pipes. Install passive mixing systems with check valves, nozzles, and distribution piping inside the tank. Add active mixers.
Bigger is Better	Right size the tank based on the daily usage today. Tear down big old tanks, build new, smaller elevated tanks. Then build interconnects with nearby systems to provide fire flow in an emergency. Install active mixers with chemical injection in problematic tanks, or install a chlorine booster station nearby.
Keep Tanks Full	Cycle tanks more thoroughly, at least 30% daily. Operate tanks at even lower levels if water age and quality is a problem, and still hydraulically feasible. Flush tanks through the overflow when water age is an issue. Install automatic flushers on fire hydrants to keep water age down. Clean out tanks and inspect them every 5 years.

To learn what other tanks owners are doing, check out my presentation on this topic, Then & Now Tank Changes: Maintaining Chlorine Residual to Meet PADEP Regulations, recently shared with the Central PA Region of WWOAP/PA AWWA at their 2018 Fall Conference.

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