Backflow Prevention: Protecting Potable Water Supplies
|By Mary Elizabeth Williams-Villano|
Some years ago, effluent from a wastewater treatment plant in San Antonio, Texas, backflowed into the potable water system at the plant due to maintenance activities.
On September 18, 1996, a meter reader with the Hillsborough County Water Department in Florida noticed that the water meter at a home in northwest Hillsborough County was registering backwards. A cross-connection had been created between the potable and reclaimed water systems at this location, and reclaimed water was backflowing into the public water system. The County Water Department estimated that about 50,000 gallons of reclaimed water backflowed into the public potable water system.
Reports like these from case histories are compiled by the Florida Department of Environmental Protection. Bernie Clarke, the owner of Backflow Prevention Device Tester, and Clarke Sales in Newhall, California, says that if you were to start reading histories of backflow incidents in the United States, you wouldn’t be able to stop, “or you may never drink water again. I read about a reddish water, what people thought was rust, coming out of drinking fountains that turned out to be pure blood from a hospital; an elementary school that had a poison, ethylene glycol, pumped into their water supply from a nearby factory. All of the kids had to be rushed to the hospital. Every state in the nation has had an incidence beyond belief.”
It’s surprising, but these incidents are not uncommon. Commercial and residential irrigation sites are a frequent source of water contamination.
In response to this, a number of companies have dedicated years of engineering research and development to creating tools to protect our public water supply systems. These tools, backflow prevention assemblies, function as public health protectors. They protect you, your family, friends and neighbors.
Simply put, “backflow prevention is to protect our drinking water,” said Ivy Munion, an irrigation consultant and principal with ISC Group in Livermore, California. So, the good news for irrigation contractors is that contamination can be contained with adequate backflow prevention assemblies, and a better understanding of backflow prevention.
Because backflow prevention protocols that cover everything from installation, to inspection, testing and maintenance, have been in place and enforced for some time on large commercial sites, contractors who do this work are generally aware and prepared to meet applicable backflow prevention standards.
But for some contractors who focus on residential properties, backflow prevention hasn’t been a serious concern. Even though the backflow prevention codes have existed since the Clean Water Act was passed, they are often not enforced.
According to Eric Santos, vice president of ValleyCrest Landscape Maintenance in Pleasanton, California, if backflow prevention is overlooked by these contractors, it’s usually because permit requirements are more lenient, and often even inspectors don’t fully understand the concept, or its importance. But this is likely to change, and that’s a good thing because it means safer water for all of us, and new opportunities for contractors. Knowing the regulations, how to do the installations, and providing the annual testing and service opens an additional revenue stream, and for those who get the appropriate certifications, the stream could look more like a gushing river.
So what is backflow?
Backflow is the reversal of water flow from its intended direction. Whenever a water utility connects a customer to its distribution system, the intention is for the water to flow from the distribution system to the customer, and not the other way around. Water purveyors don’t want it back, because it’s their responsibility to provide potable water. A backflow event occurs when water is unintentionally pulled or pushed back into a public water source. The problem is, the water could contain anything from generally offensive pollutants to extremely toxic contaminants. Such an event is usually caused by either backpressure, or back-siphonage. Backpressure is a condition that manifests itself when the water pressure within a customer’s piping system ex ceeds that of the public water supply system. This might be caused by a difference in elevation, by a pump in a steam boiler system, or simply because the public water system lost pressure.
Back-siphonage occurs when the water pressure within the distribution system falls below that of the piping system it is supplying. This could happen when a fire department truck pumps water out of the distribution system faster than the water treatment plant equipment can replace it.
Or a broken water main could cause water pressure to drop and create a partial vacuum in piping systems, in the vicinity of the break. Even flushing the water pipes to clean them may cause this phenomenon.
When a backflow event includes an irrigation system, it can be particularly toxic. Rick Williamson, specifications manager at Lasco in Florida, explains, “With an automatic irrigation system, there’s always the danger that someone has a hose hookup and is putting down pesticides, or if an irrigation system includes automatic fertigation, and then somewhere in the neighborhood, they turn on a fire hydrant. Then a back-siphon draws the pesticide or fertilizer from the hose hookup into the drinking water supply. These scenarios pose real dangers.”
A backflow event could pull fertilizer, animal waste, and pests from the irrigation system into the public’s potable water system, and then, there goes the neighborhood.
Such risks exist anytime there is a cross-connection, a connection between a potable water system and a non-potable system, such as one used for irrigation. Backflow prevention assemblies secure cross-connection points, and therefore protect our public water systems.
Types of assemblies
The four most common backflow prevention systems are atmospheric vacuum breakers (AVBs), pressure vacuum breakers (PVBs), reduced pressure principle assemblies (RPs) and double check valve assemblies (DCs).
AVBs are designed to prevent backsiphonage. They rely on standard airgap technology to break up the vacuum that pulls polluted water back through a cross-connection into the potable water supply. The standard AVB design prevents a cross-connection when pressure conditions that are likely to cause back-siphonage occur. The AVB allows air to enter the system, preventing back-siphonage. To function effectively, AVBs must be installed at a six-inch elevation relative to downstream piping and outlets at tached to the irrigation system.
PVBs, just like AVBs, are effective at preventing back-siphonage. These are mechanical systems that consist of a spring-loaded check valve and a spring-loaded air inlet valve. When the air inlet valve senses a drop in system pressure, the spring on the air inlet opens to atmosphere and prevents back-siphonage. This action prevents polluted and contaminated water from an application site from being siphoned back into a public well. The springs in a PVB replace the gravitational force used by AVBs. The PVB must be installed 12 inches above any downstream outlets or piping.
RPs consist of two independently acting, spring-loaded check valves with a spring-loaded pressure differential relief valve between them, and below the first check valve. When a cross-connection is protected by an RP, the pressure between the two check vaslves is lower than the supply pressure. So, when the pressure in this RP protection zone begins to approach the supply pressure, the relief valve opens and prevents both backflow and backsiphonage. The installation of the RP must be 12 inches above any high water level, and should not be installed more than 36 inches above grade, to facilitate the repair of the unit.
Last, but not laeast, the DC is a backflow prevention device that also relies on spring-loaded check valves. Elevation is not as important for DC installation, but many contractors report that below-grade installations can be difficult to maintain, test or drain for freeze protection. Just like the RP, the DC is effective against backpressure and back siphonage. But this type of assembly isn't recommended for use on cross-connections between potable water and irrigation systems, because it only protects against pollutants, not contaminants.
These provide a lot of options. But according to Jeffrey Hawkins, product manager for Watts Water Technologies in North Andover, Massachusetts, the situation is more straightforward. “In our opinion, irrigation systems are a high hazard application, and therefore we typically suggest to our customers, and to regulators, the use of PVBs or RPs for these applications.”
Some sites present even more choices. According to Santos, “For smaller commercial and residential projects, in particular, there are alternatives.” He says an anti-siphon valve that protects each valve individually does the same service as a backflow prevention assembly. It prevents the water from flowing back into the main water-feed, and contaminating that source. “This is an option that contractors often don’t realize, but it’s very important and should be considered.” Santos maintains that an antisiphon valve costs about the same as a regular valve, making it a more viable option than a costly backflow prevention assembly, especially for the residential market. These units must be installed a minimum of 6 inches above all downstream piping and outlets.
All of these options create a lot of room for error. So always consult the local codes to determine the correct types of backflow prevention valves that are needed to protect the potable water systems.
A big consideration
In the world of backflow prevention, there are two levels of public risk posed by flow from unprotected crossconnections: high hazard and low hazard. This distinction is used to determine the type of backflow device that’s used. Low hazard generally applies to pollutants that are distasteful or offensive because they create a strange color, odor or taste in the water, but not a health risk.
A high hazard risk is created by contaminants, such as chemicals, pesticides or fecal coliform. This is the stuff that can make people seriously sick, or worse. And these are exactly the types of contaminants present in a backflow event involving an irrigation system.
In some states, residential landscape irrigation is considered low hazard, but this doesn’t make sense. That’s why the current trend is to change many irrigation systems that are considered low hazard, to high hazard. And stronger code enforcement, along with assembly testing, will follow.
A tangled mess
“The problem that contractors are going to run into is knowing what codes are used in what city, county or water district,” explains Paul Wait, irrigation channel manager at Zurn/Wilkins in Paso Robles, California. Cross connection control programs often change from one area to the next. Additionally, what may be enforced in one city might not be in another.
Such variances are very confusing. Since the passage of the Clean Water Act, a number of attempts have been made by organizations, such as the University of Southern California (USC), Foundation for Cross Connection Control and Hydraulic Research, and the American Society of Sanitation Engineers, to standardize the use of backflow prevention assemblies, but currently it’s still up to the local authority that has jurisdiction.
What authority is that? Well, this also varies. The Clean Water Act applies nationally, but its enforcement is left to the states. And each state handles this differently. In Texas, the Texas Commission on Environmental Quality creates and enforces codes statewide, but in most other places, there can be variation throughout the state.
So it’s important to find out, first, who has the authority, and from this body, what the required standards are. The manufacturers of backflow prevention devices are good resources to begin with, as is the Irrigation Association. Wait suggests contacting distributors and wholesalers as resources for education.
Because of growing environmental concerns and persistent drought conditions, the value of clean drinking water and healthy aquifers will continue to increase. It will become, more and more, a national concern. Therefore, “If a contractor wants to make it, to move forward, to continue and grow his business, keeping up with expanding codes—especially when it comes to backflow—is a must,” says Munion.
But don’t forget the good news. This doesn’t just mean more hassles for contractors who haven’t had to strictly adhere to backflow prevention codes.
This is also an opportunity to provide an additional service, and a way to distinguish your business from the competition. Getting ahead of the curve with backflow prevention demonstrates leadership in your field. Educating your clients, and raising awareness, shows the integrity of your profession.
Williamson encourages, “I would say, if there is a concern, it would be, ‘How can I take advantage of these changes?’” So, backflow prevention isn’t just about meeting standards or passing inspection; it’s a life-safety measure, a responsibility, and an opportunity.