Disinfection Byproducts
Disinfection, sometimes referred to loosely as chlorination, is a necessary part of the water treatment process. It kills pathogens, and it produces chemical byproducts. Disinfection is typically done by adding small amounts of a chlorine-based disinfectant to water. It destroys water-borne microbes, bacteria, and viruses – organisms that can cause serious illnesses or death. Typhoid and cholera, which have killed hundreds of thousands of people in global epidemics, have been controlled in the United States through the addition of disinfectant to drinking water.
Keeping bacteria out of our water is a constant struggle. There is a possibility that microorganisms might get into treated water after it leaves the treatment plant. This is why public health regulations require that tiny but detectable amounts of disinfectant must remain in the water all the way to the tap. Disinfectant ensures that the water coming from your tap is free of pathogens. Even a filter left too long in a home purification system can develop bacteria, as can a favorite water mug not cleaned on a regular basis.
| Useful Links |
|---|
The Environmental Protection Agency regulates the quality of drinking water on a federal level. Its regulations cover acceptable, safe levels of microorganisms, disinfectant, and disinfection byproducts. In December 2005, after a lengthy review process which included water providers and environmental groups, the EPA added two new rules to the Safe Drinking Water Act: one modifies the old rules for measuring the byproducts of disinfecting potable water (DBP2) and the other regulates protection against disease-causing microorganisms (LT2).
The LT2 regulation deals primarily with Cryptosporidium. Denver Water has been monitoring for "Crypto" for decades, and testing has never detected any in treated water (and very little if any in the raw water). The situation regarding disinfection byproducts (DBPs) is not so simple, though.
A Bit of Background
The term "disinfection byproducts" covers a host of compounds that may be formed after water is treated. Depending on the substances present in the water, a wide range of byproducts may be created. But the only reliable approach to protecting against bacteria in drinking water is to add a disinfectant, which must travel with the water, in minute amounts, all the way to your tap. And any disinfectant creates disinfection byproducts. There is little evidence that these chemicals are dangerous at the level they occur in treated water, but research on the potential effects of specific compounds raised concerns with the EPA.
Like many problems, there is no easy answer. As the EPA report says, "Decreasing disinfection byproduct risk could increase risks from disease-causing microorganisms." The paradox is as old as the use of fire to keep warm: It keeps you from freezing, but it also produces ash and carbon monoxide.
| "Disinfection of drinking water has benefited public health enormously by lowering the rates of infectious diseases (for example, typhoid, hepatitis and cholera) spread through untreated water." – EPA Report |
Denver Water has pioneered techniques for making drinking water safe since before the company was purchased by the City of Denver in 1918. In 1906, the old Marston Treatment Plant introduced chlorination as a public health measure that played a major role in halting a cholera outbreak. In 1918, we switched from chlorine to chloramine, a disinfectant that produces fewer byproducts than chlorine. In the last decade, major changes were made to the newer Marston Plant and to the Moffat Plant to control the treatment process better and thus reduce the formation of byproducts. Similar changes at Foothills are being planned, with construction scheduled for 2007.
Because our water is collected high upstream, above major agricultural or municipal developments, organic materials are much less of a problem than they are for treatment facilities farther away from the origin point of the water. Organic content is a naturally occurring part of fresh ("raw") water, and it must be controlled. Our process ensures that the water is safe to drink. Testing to verify the quality of that raw water and the effectiveness of the treatment are important parts of the water quality process. Because the concentration of organic material is low, the amount of disinfection byproducts created is also low.
How Dangerous Are Disinfection Byproducts?
Some medical research suggests that specific DBPs (total trihalomethanes and haloacetic acids, referred to as TTHMs and HAA5) may cause a variety of medical conditions, including some forms of cancer and miscarriage. Thirty years of research have not provided definitive results, only sparse and inconsistent findings. But even the possibility of very minor effects is a concern to water systems and the public, which is why the EPA has established maximum contaminant levels (MCLs) for the suspect DBPs.
To see details on the EPA's research that resulted in the new regulations, go to their SafeWater site.
Meeting the New Regulations
As shown in our annual consumer confidence reports and Treated Water Quality Summary Reports, Denver Water has been in compliance with the standards, based on testing methods then in place, for some years. In 2004, for example, our levels for TTHMs averaged 33 parts per billion, less than half the allowed level. Our highest reading for that year was also below the required average. Results are similar for HAAs.
In the past decade, Denver Water has spent about $75 million on renovations and projects to improve the quality of your tap water. The changes at Marston and Moffat moved the disinfectant contact basins farther from the raw water end of the treatment process. This lowers the concentration of organic matter in the partially treated water, so that less disinfectant is needed and fewer byproducts are formed. This change allows us to better control the disinfection step and minimizes the disinfectant contact time. Denver Water has been able to anticipate changes as they moved through slow federal processes, and our system is in compliance with the mandated levels.
Compliance with the new regulations is a six-year, two-phase process. In the first phase, the water system is surveyed to determine if existing methods are providing water with DBPs below the maximum levels in the new rule. (The MCL is unchanged from Stage I.) In the second, suppliers will be required to modify their systems, if necessary, to meet the regulations. The survey phase covers a two-year period for systems the size of Denver Water, and another four years are allowed for making modifications.
Modifying the Denver Water system to meet the rules is not a huge concern, because we are already in compliance with the allowed levels and the change planned for Foothills will improve our control over the disinfection process even more. The EPA recommends "removing as much organic material as possible prior to disinfection," which is precisely what the modifications do: They remove most of the organic material before the primary disinfection step begins. As mentioned earlier, Denver Water generally has low organic material concentrations because our water is gathered high in the watershed above any major agricultural, industrial, or municipal sources. Naturally occurring organics are found in the water and their concentration may vary depending on environmental circustances. The modifications to Marston and Moffat have already ensured compliance for water from those plants by optimizing the disinfection process.
The Challenge for Denver Water
Strangely enough, the real challenge for Denver Water is posed by the surveying phase. In the past, compliance with the EPA's MCL for disinfection byproducts was calculated using one average based on all the samples taken at checkpoints all across the distribution system. Under DBP2, compliance will be calculated using annual averages for each sampling location and the number of sampling locations will be increased. The water supplier must use different collection points, including some within the service areas of our distributors, and must maintain the average for each sampling location at or below the maximum levels allowed. It is as if, instead of monitoring the average temperature of your home from a centralized thermostat, you had a thermometer in every room, and the thermostat kicked in whenever any room got cool.
It's not so much a matter of which method of calculation is "right," but that changing the method may have unforeseen effects on the result. Our current methods of handling DBPs have kept the system well within the standards. To prepare for DBP2, Denver Water initiated a complex computer modeling project that simulates the pipes and facilities in the service area. The model will help select monitoring sites and predict DBP formation. Still, the unknown at this point is, how will the numbers change when the calculation methods change?
Because of Denver Water's unique relationship with metro Denver, the new regulations create a unique challenge. About half of Denver Water's customers are served by distributors who take treated water from us and deliver it through their own systems of pipes and storage.
Under the new regulations, these "consecutive systems" are also required to verify the quality of that water, and most of them are not set up to do this, because they have relied on Denver Water's integrated system to ensure water quality. This change presents a raft of thorny problems, even for a cooperative relationship.
Because of the scale of the task, Denver Water cannot provide the resources to support this testing service, so they must do their own testing. They must incur added cost to meet the new requirements. Denver Water has offered to assist distributors in satisfying their new responsibilities to the EPA. With a spirit of cooperation, things should go smoothly.
Keeping your water safe is a key part of Denver Water's mission, just as it is the EPA's and that of the Colorado Department of Public Health and Environment. Together, we will see that you do not need to worry about your drinking water.