Cleaning Out Water Tank Sediment Improves Water Quality, Boosts Public Safety

Will hotter summers from climate change create a healthy environment for unhealthful organisms in sediment at the bottom of water tanks and towers?
Cleaning Out Water Tank Sediment Improves Water Quality, Boosts Public Safety
Water Tower

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For more than 20 years I have performed video inspections of water tanks and towers, gaining a unique perspective on water storage infrastructure in states from Arizona to Florida. For the most part, I see little concern over the sediment on the floors of most tanks.

In 2013, my company inspected more than 500 water storage facilities, 80 to 90 percent of which needed cleaning. Only 64 chose to have us remove the sediment. I inspect many of these utilities annually, and in many cases my recommendation is always the same: “Your tanks need to be cleaned.”

Sediment slowly builds up in most water tanks, and that may be a growing public health threat. Record high temperatures from climate change create a warmer environment that may leave tanks at greater risk of chlorine depletion from the growth of microorganisms — including pathogens.

The U.S. EPA has no rules requiring potable water storage tanks to be cleaned — just a recommendation to clean “as needed.” Similarly, the American Water Works Association recommends cleaning every three to five years, or “as needed.” That leaves ample room for interpretation, so utility managers are not motivated to include tank cleaning in maintenance budgets. Few states require scheduled cleaning, and many don’t even require regular inspection. But what are the potential consequences of failure to clean?

A case in point

In August 2013, the death of a 4-year-old boy near Violet, La., was linked to the Naegleria fowleri amoeba. The child had been playing on a backyard slide that used water from the St. Bernard Parish water system, later found to be contaminated with the amoeba. At the time, NBC News reported:

“Naegleria fowleri infects people when water containing the amoeba enters the body through the nose. This typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. The Naegleria fowleri amoeba then travels up the nose to the brain, where it destroys the brain tissue.”

After the boy’s death, the Louisiana Department of Health and Hospitals (DHH) asked the U.S. Centers for Disease Control and Prevention (CDC) for help since the department could not find a lab to test for the amoeba. The CDC usually does not test drinking water but did in this case because of two deaths related to the amoeba that occurred in Louisiana in 2011. CDC also tested DeSoto Parish Waterworks District No. 1 because it was near the site of one of the 2011 deaths.

The CDC confirmed the presence of the rare amoeba in five locations in the district’s water system. Now that this amoeba has been found in a public water system, will more stringent regulations be forthcoming?

One reason Naegleria fowleri has not been found in other U.S. water systems is that tests for it (and many other bacteria, protozoa and viruses) are not routinely performed. The amoeba has been found only in the south half of the country, where high temperatures enable it to become active. With climate change, it may not be long before it is seen in the north, as well.

Since utilities cannot test for every known contaminant, much less those not yet found in water tanks, a coliform test is used to determine whether other fecal pathogens are likely to be present. The new Revised Total Coliform Rule (RTCR) requires assessment and corrective action when there are indications of coliform contamination. The RTCR no longer includes a monthly maximum contaminant level violation for multiple total coliform detections. Instead, systems that have indicators of coliform contamination in the distribution system must assess the problem and take corrective action.

Aging tanks and climate change

As the national water infrastructure grows larger, it is also getting older. Some modern-looking welded steel water towers have been standing for more than 50 years, while others built in the 1920s and 1930s give their age away with their steeple roofs and riveted legs and sidewalls.

In response to the Great Depression in 1933, President Franklin Roosevelt enacted the New Deal programs, including the Works Progress Administration, which was involved in the construction of 3,026 water storage facilities and the reconstruction or improvement of another 738. Many of those facilities are still in service today.

While there is nothing wrong with older facilities that are well-maintained, many tanks and towers rarely, if ever, have had their interiors cleaned. My crews often meet water utility workers who have been on the job for five years or more and have never seen a tank cleaned.

Meanwhile, summers are longer and record high temperatures increasingly common. That combination can make soft sediment in tanks into breeding grounds for bacteria, protozoa and viruses and allow them to get a foothold. Ideal conditions occurring more regularly can enable these organisms to bloom out on a record hot day, overtaking chlorine and other disinfectants and spreading through the distribution system.

With more aging water storage facilities holding warmer water, conditions are perfect for triggering growth of more dangerous contaminants than have ever been reported. The Naegleria fowleri amoeba may have been our first warning.

Current testing: Is it enough?

While pathogens increase in strength and number under the safety of a blanket of sediment, testing at the tap may not reveal a problem. The warmest part of the summer, perhaps on a record hot day, is when a standard test may find that chlorine seems to have been suddenly depleted and the entire system is now at risk. In reality, the problem has been festering under the sediment undetected, for months or in some cases years.

In Texas, assessment of sediment on tank floors is required as a part of an annual tank inspection report. Be sure that your inspection includes the interior tank floor. Do not let it go year after year. If you have an accumulation of sediment, don’t think of it as “just a little dirt.” Know that it is a broken barrier that can allow contaminants to compromise your entire water supply and the health of your customers.

One way to avoid that scenario is to take water samples from the tank floors. If you have sediment with significantly less chlorine residual, act immediately by cleaning the tank and removing the sediment. If you find significantly less chlorine residual at or near the tank floor but no sedimentation problem, you should consider a mixing solution.

Housekeeping pays

In many cases, the most important and effective action a water utility can take is basic housekeeping. If you see extensive sediment, or you know the facility has not been cleaned in the past five years, it is likely that the sediment needs to be removed.

Every water tank should be on a schedule to be cleaned at least once every five years, and perhaps more often if you have an RTCR violation. Once you remove the sediment, you will discover that chlorine costs are reduced because the chlorine is no longer at war with the microbes growing on the floor.

You have many choices when it comes to cleaning water storage tanks and towers. These include a well-qualified potable water diving contractor, who can remove all loose sediment with minimal water loss and minimal disruption in service. For tips on doing your own tank or tower inspection, visit www.watertankinspection.com.

About the author

Ron Perrin is the owner of Ron Perrin Water Technologies, a company that inspects and cleans potable water storage tanks and towers. He can be reached at 888/481-1768 or ronlooks@aol.com.



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