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TCD is a proactive effort by the NTMWD and its customer cities to assist in cleaning city water distribution systems. This annual maintenance is performed once per year for a period of 28 days. During the rest of the year, NTMWD uses a mixture of chlorine and ammonia, called chloramine, for continued disinfection in city distribution systems. During chlorine maintenance, pure chlorine is used instead. It is a stronger disinfectant than chloramine, that effectively eliminates potentially harmful microorganisms that may exist inside distribution pipes. By performing TCD in early spring, NTMWD can reduce the growth of potentially harmful microorganisms, which can flourish during summer heat. NTMWD maintains the same concentration of chlorine in drinking water during TCD that it does of chloramines the rest of the year. By its nature, the chlorine presents a stronger taste and odor than chloramines.Cities may supplement chlorine maintenance with aggressive distribution line flushing. During flushing, treated water is released from fire hydrants to allow microorganisms to be pulled out by high-velocity water. The downside of flushing is that it uses a lot of water and works against water conservation goals.
NTMWD and its customer cities call the process chlorine maintenance because they do not increase the chlorine concentration in the chlorine maintenance period. Some utilities may actually increase chlorine concentrations during this period, hence use of the “chlorine burn” terminology.
Residual disinfectant, whether chlorine or chloramine, must remain in the distribution system of all customers to assure the continued ability to destroy microorganisms that could impact human health. Disinfectant concentrations decrease with increased time in the distribution system. This means customers further from the Wylie water treatment plant will experience concentrations lower than customers near the plant. NTMWD must assure every retail water recipient, such as Allen, is able to maintain the required minimum disinfectant concentrations, regardless of their distance from the water plant. The minimum concentration level for chlorine disinfectant is 0.2 parts per million; for chloramines it is 0.5 parts per million. This minimum is a point-in-time minimum, not a rolling annual average (RAA). Dropping below either minimum level means the system is unable to safeguard human health. This is a significant water quality violation and can cause the issuance of a boil water notice. NTMWD’s position is that producing either chloramine or chlorine-only water at the plant in the 3.8 to 4.0 ppm range is necessary to assure adequate residual disinfectant levels throughout the entire regional water distribution system.
The other means to reduce Disinfection By Product (DBP) production in the distribution system is by reducing the organics, termed Total Organic Carbon (TOC), coming out of the water plant. The organics are the contaminants that interact with the disinfectant to create DBPs. In 2020, NTMWD will complete construction of Biologically Active Filters (BAF). These filters contain live beneficial microorganisms that consume TOC and reduce the levels of contaminants available to form DBPs in treated water.
Human epidemiology studies have suggested a weak association exposure to chlorinated surface water and certain cancers, reproductive and developmental effects. Because hundreds of millions of people drink chlorinated water, the EPA takes the health risks associated with DBPs very seriously. Here are some ways NTMWD and Allen comply with standards.
The EPA required compliance with what is termed their Stage 1 Disinfection and Disinfection Byproduct Rule by January 1, 2002. The rule established the highest levels allowed for the disinfectants chlorine, chloramines, and chlorine dioxide represented as the running annual average (RAA) concentrations of these disinfectants. The rule also set maximum levels as RAAs across all sample points for groups of DBPs called Trihalomethanes (THM) and Haloacetic Acids (HAA), as well as some other dangerous contaminants. The Stage 1 rule also set water plant removal requirements for organic materials called Total Organic Carbon (TOC). The lessening of TOCs in the distribution system reduces the amount of materials that interact with residual disinfectants to from DBPs.
The EPA later tightened the Stage 1 Disinfection and Disinfection Byproduct Rule by implementing a Stage 2 Rule that added more THMs and HAAs to the regulated contaminant lists. It also changed the RAA rule to establish contaminant concentration levels that apply at each sample point rather than the RAA across an entire distribution system. Allen and NTMWD implemented DBP Stage 2 rules in 2012. Though still an annual rolling average, many water systems expected meeting concentration limits at each sample point would be challenging.
Due to DBP Stage 2 rule changes, NTMWD fast-tracked a plan to use ozonation to disinfect water processed at its Wylie plant. The original purpose envisioned for ozonation implementation was to minimize adverse tastes and odors caused by annual summer algae blooms at Lake Lavon. However, it was known that ozonation plus the use of biologically active filters would help reduce TOCs and thus reduce DBP formation. The $125 million conversion helped the district and their customer cities meet DBP Stage 2 TOC limits, improved disinfection at the plant, and dropped DBP levels in the City distribution systems.
The water plant is still undergoing the major construction activity associated with implementation of biologically active filters (BAF). By 2020, NTMWD will complete construction of BAF to treat the water at the Wylie plant. These filters allow beneficial microorganisms living on the treated water filters to consume and further reduce TOCs. After ozonation, water will be processed through the BAF before residual disinfectants like chloramine are introduced. Both ozonation and BAF represent state-of-the-art water treatment processes that reduce the TOCs that, when combined with residual disinfectants, form DBPs. NTMWD continues looking for emerging treatment technologies and processes to improve water quality.
TCEQ requires that DBP tests be conducted by the State, not the City, by a state-selected contractor to ensure integrity of the testing. Samples for DBP in Allen are drawn at eight sample sights each quarter, totaling 32 sample sites per year, in accordance with Texas Commission on Environmental Quality (TCEQ) procedures. The contractor submits samples to a state-certified laboratory for analysis. City staff does not touch these samples. In order to view results, City staff must go to the same Texas Drinking Water Watch website available to the general public. Every test result from every sample point for the last two years is available on the site.
To use the website you need to know Allen’s Water System Number (TX0430025), water system name (City of Allen) and county (Collin). After entering this information, click on our water system number. You can view DBP results by clicking on either the LRAA (TTHM HAA5) or the TTHM HAA5 Summary Tabs.
The City’s annual Water Quality Report summarizes TTHM and HAA testing results compared to the EPA/TCEQ standard.
Neither Allen nor NTMWD water transmission and distribution systems have components containing lead. The NTMWD water that comes to Allen does not flow into the water systems of any other cities. So although other cities may have pipes containing lead, it cannot get into either NTMWD or Allen’s water distribution system.
The most common way lead enters drinking water is through brass or chrome-plated brass faucets and fixtures with lead solder. Significant amounts of lead can enter the water through these fixtures, especially through hot water. Although lead-free solder has been required for many years, homes built before 1986 are more likely to have lead pipes, fixtures containing lead or pre-1986 lead containing solder.
Allen participates in the TCEQ lead and copper monitoring program. Through this program, the City asks residents of 30 older homes built before 1986 to draw a “first morning” water sample for laboratory testing. Residents collect the first draw so the lead that is possibly in faucets or solder has had many hours to leach into the water at the tap. These 30 homes are all volunteers approved by the TCEQ for lead and copper program inclusion as “indicative” lead test sites for pre-1986 homes in the City.
After residents submit their samples to the City of Allen, we mail them to the designated state laboratory for testing. Test results are posted on the Texas Drinking Water Watch website and in our Annual Drinking Water Quality Report. To use the DWW website, follow instructions provided above under the DBP discussion. For lead and copper results, see the “PBCU Summary” link.
In-home lead and copper testing is conducted once by the City every three years. Our Annual Water Quality Report and the Texas Drinking Water Watch website reflects the results of the most recent lead and copper testing. The latest report shows our 2016 test results are well under the “action level” set by the EPA and state. Because Allen’s population recently surpassed 100,000, we will add 20 more homes to our next lead and copper sampling schedule, for a total of 50 pre-1986 homes being tested. Based on the water quality and human health issues caused by the drinking water of Flint, Michigan, the EPA will soon revise the lead and copper testing rules. We expect either tighter standards, more testing, or both to be required in the near future.
For information on lead and copper regulation in public water systems, visit the Environmental Protection Agency (EPA) website. You can also learn how the Texas Commission on Environmental Quality (TCEQ) regulates lead and copper by visiting the TCEQ website.
The Safe Drinking Water Act (SDWA) established Federal responsibility in the area of water quality in 1974. At the Federal level, the Environmental Protection Agency (EPA) establishes water quality guidelines that state environmental agencies execute through licensing, regulation and inspection. The Texas Commission on Environmental Quality (TCEQ) administers the state program in Texas. TCEQ provides its public drinking water standards in the Chapter 290 Rules available online.
The EPA regulates drinking water contaminants, deemed as “any physical, chemical, biological or radiological substance or matter in water.” The EPA goes on to say, “Drinking water may reasonably be expected to contain at least small amounts of some contaminants. Some contaminants may be harmful if consumed at certain levels in drinking water. The presence of contaminants does not necessarily indicate that the water poses a health risk.”
There are six classifications of contaminants with a few examples of each:
The EPA currently regulates allowed concentrations of about 90 total contaminants. The EPA determined these are dangerous to human health and set limits on concentrations of those contaminants. In the area of “disinfectant” contaminants, used to assure residual microorganism elimination all the way to the last customer’s tap, the EPA set both minimum and maximum concentration levels. The minimum level to ensure microorganisms are still killed; the maximum to ensure human health is not compromised.
The EPA identifies new, potentially harmful unregulated contaminants for monitoring as part of their Unregulated Contaminant Monitoring Regulations (UCMR). In the program, researchers test public drinking water systems for up to 30 contaminants. These tests establish whether contaminants are present and determine their concentrations. Testing data is put into a national EPA UMCR database. The EPA is now on its fourth UMCR testing cycle.
The contaminant concentration data from the UMCR helps the EPA select broadly present contaminants that may have health effects for inclusion in a Contaminant Candidate List (CCL). The EPA uses a public interest, scientific and medical studies to evaluate CCL contaminants. The EPA is now in its fourth CCL process.
The EPA evaluates the most significant CCL contaminants and emerging contaminants of suspected high risk for broad presence and risk to human health. These go through an EPA regulatory determination process. Contaminants approved during the regulatory determination are placed on the regulated contaminant listing. Precise testing standards for laboratories are specified and maximum exposure limits for public water supplies to meet are established. Exposure limits are set by epidemiological studies and correlations to potential impact on human health as part of the regulatory determination process.
There are many aspects to the UCMR, CCL, and the regulatory determination process that this short summary cannot touch on. The EPA website is a great and user-friendly source for more details.
The CDC and American Water Works Association have developed guidelines on how to address stagnation when reopening buildings to employees and the public.
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