American water systems are all designed to be one-way streets. Water from treatment plants enters the pipes, is then transferred by water mains to individual properties or fire hydrants, where it leaves the system, never to return.
The entire plumbing code is engineered to make sure that water sent to an irrigation system never gets back into the potable water system, but the code can be defeated. One of the most common problems—and one which contractors doing irrigation should be aware of—is backflow.
This past December, the city of Corpus Christi, Texas, received a dirty water complaint from Ergon Asphalt and Emulsions, so the city flushed the water main that served the property. When they received a second complaint from Ergon a week later, the main was flushed again. It wasn’t until employees at a nearby company called the public works department to report a ‘white sudsy liquid’ coming from their taps, that the city realized it had a bigger problem.
Ergon did not have a backflow-prevention device installed on its water line, so when the water pressure on the property rose higher than the pressure in the water main, a chemical entered the water supply. Normally, in a case of backflow, a city will issue a boil order, requiring property owners to sterilize their water by boiling it before drinking. However, the chemical in question, Indulin AA-86, could not be boiled out, so the city instituted a ban on water use that would last for the next four days.
That ‘white sudsy liquid’ was a mixture of water, hydrochloric acid, and Indulin AA-86. Indulin AA-86 is a corrosive emulsifying agent that Ergon uses to create asphalt. In concentrated amounts, it can burn the eyes, skin and respiratory tract. Twenty-four gallons of the liquid had gotten into the water main, in a classic, chilling case of backflow. Once the emergency had passed, the city took steps to safeguard against another accident.
This is not a Texas problem, but a national problem, because backflow conditions crop up more often than you might think. To help prevent these incidents from occurring, more cities and municipalities are mandating that backflow prevention devices be installed. Not only are they required on large commercial properties, but in the residential market as well.
The need for backflow devices
Pressure in the mains can drop from a break in the water main, or when a fire breaks out and multiple hydrants are accessed at once. Water pressure on a property can be raised higher than the city’s water pressure by pumps, or by an irrigation system installed on a strong enough gradient.
These examples, like all backflows, fall into one of two categories: backpressure or backsiphonage. Backpressure is when something pushes the water pressure on a property higher than the water pressure in the mains, forcing water which may have been used back into the system. Backsiphonage is when the water pressure in the mains drops lower than a property’s water pressure, which sucks non-potable water out of a property back into the mains.
That’s important to remember, because some backflow-prevention devices are only designed to stop one type of backflow. For rendering irrigation systems safe, the gold standard is the reduced pressure assembly, or RPZ. “This device consists of two check valves and a relief,” said James Rutherford, who owns Kimjon Backflow Testing Service in Corpus Christi, Texas. “If something goes wrong with either check valve, water is supposed to dump out of the relief valve. So if you see it dripping, you automatically know that you have a problem.”
Because RPZs protect against both types of backflow, and there’s a visual indicator if the device fails, they are considered suitable for high-hazard applications, like irrigation systems that use non-potable well water. However, all landscape irrigation systems are considered highhazard to some extent, due to the fertilizers and pesticides used.
Many municipalities do not go so far as requiring RPZs on all irrigation systems. Instead, they require pressure vacuum breakers (PVBs) or atmospheric vacuum breakers (AVBs), which are only effective against backsiphonage. Both of those systems have reliefs, and the primary issue with both models is where they can be installed.
They must be installed at a greater elevation than the highest head of any irrigation system, so that water upslope from the device isn’t causing backpressure. According to the Foundation for Cross Connection Control and Hydraulic Research (FCCCHR) at the University of Southern California in Los Angeles, the guideline is six inches higher for AVBs and 12 inches for PVBs. The FCCCHR is a trusted organization in backflow circles, as they do backflow-prevention device testing and verification for most, if not all, manufacturers.
Paul Schwartz is the chief engineer at the FCCCHR, and he mentioned that installers should also consider whether the backflow device can stand up to constant pressure. “One of the more common errors we see on irrigation systems is where AVBs are installed upstream of the shutoff valve,” he said. “The Uniform Plumbing Code says that AVBs are not to be installed in conditions of continuous use, which means they have to be installed after the valve.”
Another common error he sees is using a double-check valve assembly (DCVA) in place of a vacuum breaker. “That shows up a lot in cold-weather climates, where they want to put in a backflow preventer below-grade, so it won’t be subject to freezing,” he said. Like all the other components of an irrigation system, backflow devices can be damaged by freezing water, and must be winterized in cold weather climates.
DCVAs can stop both backsiphonage and backpressure, but they aren’t rated for conditions where there’s a high degree of hazard. Also, they don’t have a relief valve the way that vacuum breakers and RPZs do, so it isn’t immediately obvious if something is wrong. Despite that, there are regions of the country where a DCVA is all that’s specified.
Backflow prevention is a regional business
That’s because there is no formal regulation at a national level which mandates that ‘all properties must have backflow-prevention devices.’ Instead, water providers that suffer a backflow-related failure will run afoul of the Safe Drinking Water Act and face penalties.
The states have their own rules, and then the counties and municipalities get their chance to add their own tweaks. To discourage backflow and encourage good practices, the EPA publishes a Cross-Connection Control Manual, which states can use in the creation of their own backflow prevention guidelines. But local and state governments will often differ in their approaches.
The end result is that whether or not an irrigation system is considered a danger to the potable supply, and what backflow-prevention device is required, varies from city to city. Sorting out that hodgepodge can be a real headache, but for Thomas Tracy, owner of Dimension2 Associates in Huntington Station, New York, it’s business as usual.
Tracy is a licensed backflow inspector, a master plumber, and a past president of the Irrigation Association of New York. There are upwards of 50 water districts in his area. He has to contact them on a property-by-property basis each year, to make sure that their rules haven’t changed.
“It works that way because the New York Department of Health sets forth the regulations, but they give them over to the water districts to implement,” he said. “The water companies implement their program based on the degree of hazard, and irrigation systems, in some water districts, are considered to be hazardous.”
The term ‘degree of hazard’ is a core concept in backflow, so let’s dive into it. According to the American Backflow Prevention Association, three things are required for a backflow incident. There has to be a cross-connection between two systems (i.e., a pipe); there have to be hydraulic forces (backpressure or backsiphonage); and there must be a hazard (non-potable water).
Water that contains materials that are aesthetically disturbing, but not dangerous to human health, like food dye, is an example of a low hazard, also known in backflow circles as a pollutant. Water that contains material that poses a risk to human health, like motor oil, is an example of high hazard, also known as a contaminant.
For our purposes, consider that anything which can leach into stormwater can also enter an irrigation system, through puddling around a low head, for instance. Applications of pesticides and fertiliz ers can all leak in, as can animal waste from a family pet or from local wildlife. Add in chemigation and fertigation systems, and it’s clear that irrigation systems have the potential to pose health hazards to potable supplies, in the event of a backflow incident.
Where a contractor can help
Unfortunately, sometimes a policy is so centered around protecting the public supply from contamination that it doesn’t take into account the safety of individual property owners. “Some water districts only require a DCVA for containment directly after the water meter, and don’t bother checking to see if there’s anything on the irrigation system,” said Tracy.
A DCVA will protect the public if erty without a separate device for there’s a backflow device on a propthe irrigation system. But the property owner could end up drinking toxins. What’s worse, he’ll be getting water contaminated by bacteria or a more concentrated dose, because there won’t be as much water to dilute it. This is just one example of how landscape contractors who install irrigation systems can better safeguard their clients by educating themselves on the subject of backflow.
Other times, property owners don’t need to be protected from a lax set of codes, but from themselves. “The customer can get sticker shock when they hear the price of a backflow-prevention device, and they’ll ask if you can save them a little money,” said Rutherford. “But the cheap models break after a couple of years, in my experience. For a little bit more, you can get them a device that can go three, four or even five years without needing any replacement parts.”
So, if all that’s going through the system is water, why do these devices break down? Well, the short answer is that not all municipal water is created equal. Poor quality or hard water can leave deposits that build up in the pipes over time, and the chemicals used to purify water can eat away at rubber gaskets.
If your client is willing to invest in a high-quality backflow preventer, it may behoove you to give some thought to securing the device as well. Every year we read about thieves, looking for scrap metal, who will cut backflow devices off the pipes and sell them. Not only is their behavior callous, dangerous and destructive, it’s incredibly wasteful, because the scrap price of these devices are a small fraction of their cost.
To address this problem, some companies sell cages that can be set in concrete to protect large, expensive backflow units. For smaller applications, there are fake rocks which can be used to camouflage the devices, for the ‘out of sight, out of mind’ approach.
If, after reading this article, you just can’t get backflow out of your head then, by all means, go and learn more. Just make sure that before you go out and start making recommendations to your clients about backflow, you check your local laws. Some areas limit backflow-device testing, or installation, to master plumbers, and your region may have other unique restrictions.
Take the case of Lee Swanner, owner of the Corpus Christi company Swanner Landscape & Irrigation. In order to install irrigation systems and backflow prevention devices, Swanner got licensed through an irrigation school in Dallas, and said the test was no joke.
“I’ve got a finance degree from Louisiana Tech, and that irrigation exam was one of the hardest tests I’ve ever taken,” he said. “It’s an openbook test, but if you haven’t learned the material, having a book won’t help you. A lot of people there were taking it for the second or third time.”
But, even with a state irrigator’s license, Swanner isn’t qualified to test backflow preventers. For that task, he turns to Rutherford. Rutherford is quite familiar with the local rules and regulations, and he claims that weaker testing rules contributed to the city’s problems in the past few years.
“In 2012, Corpus Christi changed residential testing from annually to once every three years, and stopped sending out letters warning property owners to get their devices tested or face penalties,” he said. “Things got kind of lax, but then this incident came along, which opened everybody’s eyes. Now the city is trying to get out and test some 1,500 delinquent customers. They’ve reinstituted the letters, and are enforcing an old rule on the books, which states that commercial properties in the industrial district must have backflow preventers installed at the water meter.”
If you’re already installing backflow preventers for your clients, going the extra mile and becoming a backflow-device tester may be a good thing. Swanner estimates that, on average, it takes more time to drive to a client’s property than to test the device once there. The real savings, though, comes not from increased efficiency or cost reduction, it comes when you save a client from a potential disaster.