Without some type of disinfectant in drinking water, disease-causing organisms may exist and cause widespread health issues for a community. Disinfection of drinking water was one of the greatest achievements in public health of the 20th century, eliminating most cases of water-borne disease in the United States and developed countries throughout the world.
How does disinfection of water occur in public water systems?
Disinfection of water in public water systems occurs in two stages. Primary disinfection occurs at the water treatment plant, where trained and certified operators use well developed operating practices to assure disease-causing organisms are removed from the water or killed. The most common primary disinfectant is free chlorine, but some water plants today are effectively using emerging technologies, particularly where water supply sources are more polluted, such as ozone, ultraviolet light or either of these combined with hydrogen peroxide.
Secondary disinfection is introduced at the end of the water treatment plant process, after the disease-causing organisms have already been removed or inactivated by primary disinfection, in order to retain a trace of residual disinfection in the clean water as it moves through underground distribution system pipelines to homes and businesses. This keeps the water disinfected until it reaches the tap. Some primary disinfectants, such as ozone and ultraviolet light, would be poor secondary disinfectants because their effectiveness dissipates rapidly (within seconds to minutes) and drinking water may be in pipelines for several days. The most common secondary disinfectants are free chlorine and chloramines. Their job is to prevent the regrowth of harmful organisms in water that has already been disinfected.
How is the water disinfected by the Rivanna Water and Sewer Authority?
Water at all water treatment plants operated by the Rivanna Water and Sewer Authority (RWSA) is disinfected using free chlorine for both primary and secondary stages. RWSA consistently complies with federal and state public health regulations with respect to disinfection in all phases of water treatment, including disinfection.
Disinfection byproducts are the chemical compounds that are formed when a disinfectant reacts with naturally occurring organic matter in water. Natural organic matter includes the end products of the decay of leaves, sticks, and other organic material found in the environment, which comes in contact with water through rivers and streams, reservoirs, or storm water runoff. A significant amount of the organic matter is removed in conventional water treatment plant processes such as those operated by RWSA, but traces of the dissolved natural organic matter are not removed by conventional water plants. All disinfectants react with organic matter, some to a greater degree than others.
Are disinfection byproducts harmful?
Research by the US Environmental Protection Agency (EPA) has shown that some disinfection byproducts, in sufficient concentrations and over long-term exposure, are potential human carcinogens, therefore, limiting the concentration in drinking water to safe levels is important.
Are disinfection byproducts regulated in water?
EPA regulates those byproducts that it determines has the greatest potential to adversely affect human health. EPA presently regulates total trihalomethanes (TTHMs), five haloacetic acids (HAA5), bromate, and chlorite because its research has shown that absent proper water treatment operations these have the greatest potential to reach concentrations of concern to public health. The regulations are designed so that human exposure from drinking water is as low as possible, and is consistently well below thresholds of public health concern even when data are averaged over the period of a year.
Both TTHMs and HAA5 are formed from free chlorine. Bromate is generally a byproduct of ozone disinfection and chlorite is a byproduct of chlorine dioxide oxidation/disinfection. Because RWSA is not using ozone or chlorine dioxide, EPA would not expect appreciable levels of bromate or chlorite to be in water produced by RWSA and therefore does not require RWSA to monitor for these parameters. RWSA is required to test for TTHMs and HAA5.
For more information on regulated disinfection byproducts, click here to go to this information on EPA's website.
What have been the EPA regulations for TTHMs and HAA5?
Water treated by RWSA is presently required to be monitored quarterly at the recently defined Stage 2 sites, but the calculation of running annual averages is computed in accordance with the Stage 1 rule. The initial rule developed in 1979 regulated only TTHMs at an average of 100 parts per billion. Stage 1 amended the rule to require quarterly sampling at various points in the water distribution system, with the composite average of all samples looking back one year at or below 80 parts per billion for TTHMs and 60 parts per billion for HAA5. Water samples from our local public water systems, averaged as prescribed by the Stage 1 rules, have consistently met the Stage 1 average limits since the regulation was initially adopted.
The regulation of disinfected byproducts by EPA has evolved slowly because EPA recognizes disinfection and disinfection byproducts as putting the treatment plant operator between "a rock and a hard place". EPA believes adequate disinfection of water is critical to human health, to prevent water borne disease, and has been careful not to regulate byproducts ahead of practicable technological advances that assure that adequate disinfection is not sacrificed to meet byproduct regulations.
How significant is 80 parts per billion?
Relative to measures and statistics that people are accustomed to comprehending on a day-to-day basis, 80 parts per billion is an extremely small amount. It is the equivalent of 8 cents in $10 million, or 1 inch in 197 miles.
How are the EPA regulations now changing?
EPA’s latest changes to disinfection byproduct regulations, called Stage 2, retains as limits the average of 80 parts per billion for TTHMs and 60 parts per billion for HAA5, but changes the method by which the average is computed in a way that is stricter and makes compliance more difficult. First, the new rule provides stricter procedures on how the sampling locations in the water distribution system are collected, assuring that a representative number of sites will be measured where it can be expected the byproducts will be highest (TTHMs in particular will increase with longer time to react with the disinfectant, so that distribution locations furthest from the water treatment plant will likely have the highest numbers). Second, Stage 2 requires that the average be computed and compared to the regulatory limit at each sampling location over four quarters of the year, instead of an average of all locations across the entire water system. Third, Stage 2 requires a formula to calculate an average for each site based on the two previous quarters plus the current quarter added twice, and requires an “operational evaluation” of corrective steps if any location exceeds the 80 parts per billion for TTHMs or 60 parts per billion for HAA5 at any location in any quarter.
To use an analogy to further explain how the new rule is stricter, let’s say the parents of a high school teenager set a high expectation that to receive an automobile at the end of a school year, the student had to achieve an overall 93 average of the grades in all courses for all report card periods taken over an entire school year. If the student then averaged over the year a grade of 98 in literature, 96 in history, 95 in physical education, 95 in foreign language, 91 in science, and 89 in math, that student would meet the parent’s expectation because the overall average of all courses taken would be 94. However, if the parents were to change the expectation to require the same 93 average, but required this average to be achieved for each and every course measured separately, the student would fall short of receiving the automobile because the science and math average scores were both below 93.
In a similar way, EPA’s Stage 2 rules and stricter than Stage 1, requiring many water utilities including RWSA across the country to make changes to how water is treated or disinfected.
When are the new Stage 2 regulations effective?
EPA sets different effective dates for different sized water systems, and they also allow utilities who require the construction of capital improvements in order to comply to seek an extension up to but not exceeding two years, with the exact period of extension determined on a case-by-case basis. In Virginia the Virginia Department of Health (VDH) has primacy to enforce EPA’s rules and VDH would determine if a time extension is granted. Without a time extension, RWSA would be required to begin measuring compliance using Stage 2 rules in November 2012 for the Urban Water System and November 2014 for Crozet and Scottsville Water Systems. RWSA received a two-year extension for the Urban Water System based on the installation of capital improvements in the form of Granular Activated Carbon for assured compliance.
Granular activated carbon (GAC) is an advanced water treatment technique that can be added to conventional treatment processes to adsorb many forms of natural organic matter (NOM). It is particularly effective in removing carbon-based NOM (also referred to as Total Organic Carbon or TOC) that can lead to the formation of TTHMs and HAAs. Because of its effectiveness in removing many types of organic matter, it is used in applications beyond drinking water, to include the clean-up of groundwater contaminated by organic chemicals, as well as other industrial uses. GAC can be derived from high quality bituminous coal, coconut shells, or anthracite coal. It is activated by thermal processes that remove most of the volatile non-carbon constituents in the raw material, yielding a structure with a very high surface area to give it significant adsorption capacity. It is installed within a water treatment plant as a filter media through which the treated water penetrates, allowing significant contact between the water and the surface of the GAC. A significant advantage of GAC is that because it is an adsorption process, it does not add chemicals to the water. As GAC adsorbs organic material, its adsorption capacity diminishes and becomes less effective over time, until it is necessary to “regenerate” the GAC in a special furnace where adsorbed materials are released by heat or oxidation processes, restoring most of the virgin carbon’s adsorption capacity.
What is the current drinking water disinfection method?
The current method of disinfection used is free chlorine for both primary and secondary disinfection. In this process, chlorine is added to drinking water at a controlled level. Chlorination is an effective way to kill many kinds of bacteria and other germs that may be harmful to your health.
How will disinfection be changed in response to EPA's Stage 2 Disinfection Byproduct regulation?
RWSA proposes to retain the current practice of free chlorine as both the primary and secondary disinfectant at all five water treatment plants it is responsible for operating, so the disinfection practice will not change, except that the content of the free chlorine may be slightly less.
Unlike chloramines, which represent a change in secondary disinfectant that some communities have chosen to address Stage 2 requirements, GAC is not a disinfection technique. It is an advanced filtration technique to remove natural organic matter in the water. Disinfection byproducts require both natural organic matter and a disinfectant to be present in the water to react together. Accordingly, disinfection byproducts can be reduced in water by either of two pathways – (1) by reducing the organic matter content; or (2) by changing to a secondary disinfectant that is less reactive with organic matter. Since GAC removes organic matter, it is possible to continue to use free chlorine as a secondary disinfectant for Stage 2 compliance because the water will have less matter for which the free chlorine can react.
What is the Urban Water System?
The Urban Water System includes all of the City of Charlottesville, and also includes those properties within Albemarle County that are approved through land use regulations to receive access to public water supply, except for the separately defined areas of Crozet and Scottsville. Most of Albemarle County that is part of the Urban Water System is within a "ring" that surrounds the City of Charlottesville.
For more information, Albemarle County has a map on its web site showing the areas approved for public water supply. The Urban Water System in Albemarle County includes "Neighborhoods 1-7", the "Community" located along US Highway 29 from the South Fork Rivanna River bridge to near the Greene County line, and the "Community" east of Shadwell known as Village of Rivanna, or Glenmore.
Can improved watershed protection eliminate natural organic matter in the water?
No. Watershed protection can help address the effects of human land development activity on the source of drinking water, which can then reduce certain types of organic matter in water, but it will never remove all types of organic matter. Some sources of natural organic matter in water come from the decay of leaves, twigs, and other natural plant life as well as wildlife, and have been present in water as long as there have been rivers and streams on earth.
Why is RWSA proposing changes to its water treatment practice if its Stage 1 data showed that it is has consistently met the TTHM and HAA5 limits?
Under Stage 2, the limits upon which the average is judged stay the same (80 parts per billion for total trihalomethanes and 60 parts per billion for the sum of five regulated haloacetic acids), but the annual averages must be computed separately at each sample location, and compliance with the limit is required at every single location. In addition, the number and location of sampling points is determined by a new regulatory protocol. It is the requirement that compliance must be determined at each location, instead of on a system-wide average, that makes Stage 2 rules more stringent. RWSA's consultant, highly knowledgeable in this process, has concluded that RWSA must make water treatment process changes to assure consistent compliance under the new Stage 2 rules. Furthermore, RWSA's existing data, if applied against the future Stage 2 rules now, would not consistently show compliance at every single location.
Under an approved two year extension to allow for capital improvement, RWSA continues to be allowed to calculate running averages based on the system as a whole until September 2015. However, RWSA has been required since November 2012 to monitor at the more stringent Stage 2 sites. RWSA continues to comply with the system-wide average, however, had the Stage 2 Locational Running Annual Average already been in place, one location would have violated the rules between November 2012 and September 2013. This confirms the RWSA consultant’s conclusion that capital improvements are required, and also confirms that statements by a few during public meetings suggesting no action was necessary are unfortunately misguided.
Are there other alternatives besides granular activated carbon filtration for assuring compliance with EPA's Stage 2 regulations?
Yes. RWSA's consultant, Hazen and Sawyer, looked at several alternatives and identified chloramine conversion, magnetic ion exchange, and membrane filtration in addition to granular activated carbon as the most viable alternatives to consistently comply with the Stage 2 rules. As a part of assuring that all viable options were studied, RWSA co-sponsored a research study on magnetic ion exchange to determine its economic feasibility, and that study has since resulted in a publication by the Water Research Foundation of Denver, CO. Of the options, magnetic ion exchange and membrane filtration were more costly than granular activated carbon, leaving only chloramines as more economical. Click here to view a summary table of the estimated costs of the various alternatives studied.
In May 2011 the RWSA Board of Directors initially selected chloramines based significantly upon its cost-effectiveness. In 2012 a local group of citizens initiated a petition and asked that the Board reconsider its decision. After a public hearing on July 25, 2012 when over 60 citizens spoke against chloramines with no citizens speaking in support, the Board of Directors voted to “take chloramines off the table” and implement granular activated carbon. Many of the 60+ citizens who spoke over a three hour period felt strongly that granular activated carbon would provide a higher quality of water that was worth paying a higher cost to achieve. Click here to review the minutes from this meeting.
Are there any downsides to Granular Activated Carbon?
GAC is not a panacea, nor is any other water treatment alternative. GAC has several advantages but one key disadvantage, by comparison to chloramine conversion, which is its higher cost. In order to install GAC equipment through a licensed construction contractor, and also provide for all other infrastructure to transport conventionally treated water to and from the GAC units, provide electrical supply, perform site work preparation, protect the GAC equipment from adverse weather, and provide for incorporating GAC into water plant’s operating control systems, to include engineering design and engineering construction observation and management, has been estimated by Hazen and Sawyer to be $19.5 million in 2013 dollars for all three Urban Water System treatment plants. This estimate is based on providing GAC treatment at the full rated capacity of each treatment plant.
Can granular activated carbon be installed in the existing filters at the three water plants, and could such an approach be less costly than installing separate GAC filters?
RWSA’s design consultant, Hazen and Sawyer, recommends firmly against this approach. The existing filters, called conventional filters, serve as the most significant part of the multi-barrier approach to producing safe drinking water, and the size of these filter beds, as well as the type, size, and depth of the filter media in these beds, are all specifically designed to achieve very important goals of the treatment process. While RWSA appreciates attempts at creative thinking, creative ideas must also be grounded to avoid unintended consequences before they become solutions. It is both very important and widely accepted among water treatment design professionals that when GAC is to be used to reduce natural organic matter for the reduction of disinfection byproducts, it should not compromise other important treatment objectives. For the existing water plants, it should be added as a treatment step after conventional filtration, and not mixed with conventional filtration.
One water treatment plant in another city recently attempted to install granular activated carbon in its existing filters, and the result was that iron and manganese, present in nearly all source waters but removed through conventional filters when the water is properly oxidized, went back into solution and escaped the filters, as granular activated carbon also adsorbs many oxidants. The result was reddish brown colored water in the taps at homes and businesses, which became a public nightmare. Several years ago another City operated a compromised conventional filtration process and an outbreak of disease resulted.
As described above, there have been a few temptations, outside of recommended engineering practice, to “short cut” the use of granular activated carbon to significantly reduce its costs. It has proven very risky, and RWSA values the importance to drinking water to such a great extent that it will not allow any methods not proven by substantial engineering science.
Are there other ideas on how to use Granular Activated Carbon for Stage 2 compliance that would lower the capital and/or operating costs estimated by Hazen and Sawyer?
Yes, RWSA staff has discussed with its Board of Directors and the local public an idea that has since been named “Hybrid GAC”. Hybrid GAC represents alternative approaches to either capital construction, operation or both, whereby not all of the water that is purified through the existing conventional water treatment plants are provided the added GAC treatment. The minimum requirement for a Hybrid GAC is that it must provide sufficient treatment so that the drinking water consistently complies with the Stage 2 regulations. The maximum end of the spectrum would be that all public drinking water receives GAC treatment. Within the spectrum between these two “bookends” are several options, which depend on the objectives of the community and the approval of regulatory officials. As examples, Hybrid GAC may mean constructing GAC facilities at a lower capacity than the capacity of the existing conventional water plant, which would mean that on days when the community’s water demand requires one or more water plants to be operated close to capacity, some of that treated water would have to by-pass GAC treatment, and the drinking water would be a blend of water whereby only a portion had been in contact with GAC. Another approach would be to shut down GAC except when the organic content in the source water reached a threshold whereby the use of GAC would be necessary for regulatory compliance. A third option might be seasonal operation of GAC in only the warmer months of the year, when the kinetics of disinfection byproduct reactions in water are higher. All Hybrid GAC approaches extend the life of the GAC by using it less often than 100% GAC, resulting in cost savings, but with the tradeoff that the removal of natural organic matter from the drinking water is also less.
With all Hybrid GAC approaches, GAC would be the “tool” to Stage 2 compliance to the extent that the quality of the source water at any given time were such that the existing conventional water treatment plant were not capable of achieving compliance on its own. In all Hybrid GAC cases, free chlorine would continue to be both the primary and secondary disinfectant.
Most of the citizens who spoke at the July 25, 2012 public hearing advocated that they were willing to pay more for the drinking water to have the assurance of the best quality of drinking water that can be provided through GAC. We understand those comments to be an advocacy for 100% GAC. Some of those citizens stated they would also accept Hybrid GAC if that were the only way the “Four Boards” would support GAC instead of chloramines (Note: “Four Boards” represents a joint meeting of the RWSA Board of Directors with the Albemarle County Board of Supervisors, Charlottesville City Council, and the Albemarle County Service Authority Board of Directors). During discussion among the “Four Boards” after the public hearing, there were several comments requesting that lower cost Hybrid options be further explored.
An analysis of Hybrid alternatives was completed in September 2013. Click here to go to the Project Documents page of this website to review the results of this analysis.
A few citizens at the July 25 public hearing spoke of a cost estimate showing the capital costs of GAC were equivalent to chloramine conversion. Was that estimate feasible?
Unfortunately, the answer is clearly no. RWSA is aware of one cost estimate that was submitted on the date of the July 25 public hearing by a company in California that is an outspoken advocate of GAC and against chloramines. RWSA did review the estimate. The estimate significantly omitted critical infrastructure that would be essential for GAC vessels to be connected to and functional at RWSA’s water plants. Among the infrastructure completely omitted from that estimate was a pump station vital to carry the conventionally treated water to the GAC units, without which the GAC could not operate. The company also suggested that contingency included in the estimate (which is standard practice in engineering estimates to allow for potential future unknowns) was hidden profit to RWSA’s consultant, a statement that was entirely false. RWSA also learned the estimate by the company was not prepared by a professional engineer or by anyone who had seen RWSA’s water plants. It is unlikely that any of us would give credibility to someone who claimed to perform open heart surgery at one-third the cost of UVA Hospital or Martha Jefferson Hospital, if we then also learned that the person responsible for the claim had not attended medical school, was not licensed as a medical doctor, and had no surgical experience. We expect no less of our drinking water. Further, no water plant modifications can be legally performed in Virginia without a permit from the Department of Health (VDH), and VDH permit reviewers are professional engineers who would not issue a permit if the proposed design did not conform to the details of professional engineering practice and bear the seal and signature of a licensed professional engineer.