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1.11: Distribution System Water Quality

  • Page ID
    6982
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    Learning Objectives

    • Describe sampling procedures
    • Describe water quality parameters
    • Explain the causes behind water degradation in the distribution system
    • Explain cross-connection
    • Explain corrosion
    • Describe data reporting
    • Outline problem resolution

    Sampling

    All of the drinking water regulations apply to all public water systems. It makes no difference whether the water system is publicly or privately owned. A public water system (PWS) is defined as any system that has the following characteristics:

    • Has at least 15 service connections
    • Regularly serves an average of at least 25 individuals daily at least 60 days out of the year

    Any water system that provides services for fewer connections or persons than these rules outline are not covered by the SDWA. Certain other individuals and residences also are excluded, such as those whose water is supplied by an irrigation, mining, or industrial water system. However, regardless of size, all operators must strive to provide consumers with a potable drinking water.

    Drinking water regulations also take into account the type of population served by the system and classify water systems as community or non-community systems. Therefore, in order to understand what requirements apply to any specific system, it is first necessary to determine whether the system is considered a community system or a non-community system.

    A community water system is defined as a public water system that has the following characteristics:

    • Has at least 15 service connections used by all-year residents
    • Regularly serves at least 25 all-year residents

    Any public water system that is not a community water system is classified as a non-community water system. Restaurants, campgrounds, and hotels could be considered non-community systems for purposes of drinking water regulations.

    In addition to distinguishing between community and non-community water systems, EPA identifies some small systems as non-transient non-community systems if they regularly serve at least 25 of the same persons over 6 months per year. This classification applies to water systems for facilities such as schools or factories where the consumers served are nearly the same every day but do not actually live at the facility. In general, non-transient non-community systems must meet the same requirements as community systems.

    A transient non-community water system is a system that does not regularly serve drinking water to at least 25 of the same persons over 6 months per year. This classification is used by EPA only in regulating nitrate levels and total coliform. Examples of a transient non-community system might be campgrounds or service stations if those facilities do not meet the definition of a community, non-community, or non-transient non-community system.

    EPA has revised the Total Coliform Rule so that public water systems in the US take steps to ensure the integrity of the drinking water distribution system and monitoring for the presence of microbial contamination. Public water systems and the state and local agencies that oversee them must comply with the RTCR beginning April 1, 2016. The final RTCR requires the following:

    • Public water systems are to notify the public if a test exceeds the MCL for E. coli in drinking water
    • Public water systems that are at risk and therefore vulnerable to microbial contamination are required to identify and fix the problems, including the potential sources and the pathways of contamination
    • Criteria will be used for public water systems that are well operated to qualify for and stay on reduced monitoring, which could reduce water system burden
    • Provide incentives for better system operation, in particular, small systems
    • Require additional monitoring requirements for seasonal systems such as campgrounds and state and national parks

    The RTCR establishes an MCLG and an MCL for E. coli and eliminates the MCLG and MCL for total coliforms, replacing them with treatment techniques for coliforms that require assessment and corrective action. EPA has established an MCLG of zero for E. coli, which is a more specific indicator of fecal contamination and those pathogens that are potentially more harmful than total coliform. EPA has removed the 1989 MCLG and MCL for total coliforms, although the acute total coliform MCL violation under the 1989 TCR has been maintained as the MCL for E. coli under the RTCR.

    Under the new treatment technique, total coliforms serve as the indicator of a potential pathway of contamination into the system’s distribution system. Public water supplies that exceed a specified frequency of total coliform occurrence must conduct an assessment to determine if any sanitary deficiencies exist; if found, they must be corrected. A public water system that experiences an E. coli MCL violation must conduct an assessment and correct any sanitary defects that are identified.

    Monthly notification requirements based only on the presence of total coliforms will no longer be required. Instead, the RTCR will require public notification when an E. coli MCL violation occurs, indicating a potential health threat or when a water system fails to assess and take corrective action.

    Sampling Plan

    The Total Coliform Rule requires each water supply system to develop and follow a written sampling plan. Each plan must specifically identify sampling points throughout the distribution system. Sampling plans must be approved by the state regulatory agency and it is necessary to check with the state agency to determine the details of their review process and what documents need to be submitted.

    Data and Reporting

    Monitoring Frequency

    The routine monitoring frequency for community water systems is based on the population served. Routine monitoring frequencies for non-community systems are based on the source of supply and, in some cases, the population served. Whenever a routine sample tests positive for total coliform, two provisions of the Total Coliform Rule take effect: repeat samples (formerly referred to as check samples) must be taken and the original coliform-positive sample must be tested for the presence of fecal coliforms or E. coli to determine whether an actual or potential violation of the coliform MCL exists.

    The reason repeat samples are required is to investigate whether the original coliform-positive sample was caused by a contamination problem that exists throughout the distribution system or if it is a localized problem that exists only at that one sampling point. With this information, appropriate corrective action can be taken to eliminate the problem as quickly as possible.

    The Total Coliform Rule specifies how many repeat samples must be taken, when, and from what locations. It also directs the water utility to collect a specific number of samples the following month, based on the number of routine samples ordinarily collected.

    Non-community systems serving more than 1,000 people have the same requirements as community water systems. Non-community systems serving fewer than 1,000 people are required to collect one routine sample per quarter. When the routine sample tests positive, four repeat samples are required in the same quarter and five samples are required the following quarter.

    Whenever a routine or repeat sample tests positive for total coliform, the water agency must collect a set of three or four repeat samples within 24 hours of receiving the laboratory results. At least one of the repeat samples must be taken from the same tap as the original coliform-positive sample; the remaining repeat samples in the set must be collected at nearby taps (within five service connections of the original sampling point), upstream and downstream of the original.

    Repeat samples must be taken until no coliforms are detected or until the MCL is exceeded and the state is notified.

    Determining Compliance

    The MCLG for total coliforms (including fecal coliforms and E. coli) is zero. The MCL, based on the presence-absence concept, is as follows:

    • For water systems analyzing at least 40 samples per month, no more than 5.0 percent of the samples (including routine and repeat samples) may be positive for total coliforms
    • For water systems analyzing fewer than 40 samples per month, no more than one sample per month may be positive for total coliforms

    The Total Coliform Rule makes another significant change in the way compliance is calculated. All valid coliform-positive samples, routine and repeat samples, must be counted when calculating compliance with the monthly MCL. Under previous regulations, check or repeat samples were not included in the monthly MCL calculation. On a case-by-case basis, the state may declare a sample invalid for one of several reasons, including interference by heterotrophic bacteria during laboratory analysis, as previously discussed.

    Total-coliform-positive samples may be invalidated by the state under any of the following conditions:

    • The analytical laboratory acknowledges that improper sample analysis caused the positive result
    • The state determines that the contamination is a local plumbing problem
    • The state has substantial grounds to believe that the positive result was unrelated to the quality of drinking water in the distribution system

    Reporting and Notification Requirements

    Reporting frequencies for coliform test results increase in step with the urgency of the problem. A water agency must report the results of monthly coliform testing to the state regulatory agency within the first 10 days of the following month.

    Any time a water agency fails to collect a sample as required, the state must be notified within 10 days after the system learns of the violation. An invalid sample result is considered a failure to monitor and must be reported.

    If the MCL is exceeded, the state must be notified no later than the end of the next business day and the public within 14 days. This requirement could occur when the water agency exceeds its monthly coliform-positive limit or when test results show the presence of fecal coliforms or E. coli in any sample.

    The most critical situation exists when either of two situations occurs:

    • A routine sample tests positive for total coliforms and for fecal coliforms or E. coli, and any repeat sample tests positive for total coliforms
    • A routine sample tests positive for total coliforms and negative for fecal coliforms or E. coli, and any repeat sample tests positive for fecal coliforms or E. coli

    These situations are considered an acute risk to health. This occurrence is a Tier 1 violation, which requires that the state and the public be notified within 24 hours.

    Water Quality

    Water quality is used to describe the chemical, physical, and biological characteristics of a water source or a water supply. Water quality depends on the context of usage that is the suitability of the water for a particular use. A domestic water supply is considered to be of high quality when it is free of disease-causing organisms (pathogenic), toxic chemicals, attractive in taste and appearance, of such chemical composition that it may be distributed without corrosive or scale-forming effects on the water distribution system, and will satisfy the requirements of domestic and industrial customers.

    The quality of water that is received by the distribution systems depends on the quality of the water sources that are sued and the type of treatment that is provided. Initially, water quality depends on the prevention of contamination and pollution of the source water. If water quality control is not established at the source, then any problems during the treatment process can result in the delivery of questionable water quality to the distribution system. The primary responsibility of the treatment plant is to produce safe and esthetically pleasing water. And the treatment plant must deliver to the distribution system water that is minimally corrosive to the distribution system.

    The importance of providing water of acceptable quality is paramount. Delivering a poor quality water can result in a range of consequences from the water not being acceptable to the consumer because of its appearance or taste to illnesses caused by contamination. Utilities and operators are responsible for the quality of the water that is served to customers. The quality of treated water put into the water distribution system from water treatment plants is high. The most pervasive water quality problem that affects most American communities results from the deterioration of water quality within water distribution systems.

    The water industry supplies one product. Potable water as in any industry, must be of good quality to ensure the acceptability of the product. Water quality standards have been prepared and set by law. Water quality standards have changed considerably over the years. Increased knowledge of the substances found in water supplies and their effects has led to substantial revisions in the types and the concentrations of substances allowable in water supplies.

    Distribution Systems

    Conditions exist in the distribution system that could result in degradation of water quality in the distribution system. The system operator must be aware of them and take corrective or protective measures where possible.

    Causes of Quality Degradation

    Cross-connections

    A cross-connection is an unprotected connection between a part of a water system used or intended to be used to supply water for drinking purposes and any source or system containing water or a substance that is not or cannot be approved as safe drinking water. It is a connection between a regulated and approved drinking source and an unregulated drinking water source.

    Contamination from the back-flow of unacceptable substances through cross-connection to distribution systems has consistently caused more waterborne disease outbreaks in the United States than any other reported factor. Back-flow can occur through a cross-connection by back-siphonage or back-pressure.

    Cross-connection in a distribution system
    Figure \(\PageIndex{1}\): Cross-connection in distribution system – Image by Machovka is licensed under CC0 1.0 (modified by COC OER)

    Back-siphonage is a form of back-flow caused by a negative or below atmospheric pressure within the water supply piping. Back-siphonage can develop from such causes as main breaks, an inadequate source of supply capacity, undersized mains, unusual water demands, planned shutdowns for maintenance or repair, or the use of on-line booster pumps. Back-flow caused by back-pressure can occur when the user’s water system is at a higher pressure than the public water system.

    Cross-connections in the distribution system are potentially very hazardous, and they can be a source of taste and odor complaints. Cross-connections commonly occur in these instances:

    • A sprinkler system using non-potable water is connected to a potable water supply
    • A potable water source is used as a seal supply is connected to a pump delivering unapproved or non-potable water
    • A hose connected to a house is left in a swimming pool. When water is drawn from indoor taps, the hose sucks the pool water into the potable water supply because of the pressure differences.
    • A hose connected to the house is used to apply chemical fertilizers or pesticides. Without a vacuum breaker or other back-flow-prevention device at the house connection, the chemicals will enter the potable water supply.

    Corrosion

    Corrosion is the gradual deterioration or destruction of a substance or material by chemical action proceeding inward from the surface. Corrosion is frequently induced by electrochemical reaction. Corrosion is of significant health and economic, as well as aesthetic, significance. Elevated levels of toxic or suspected toxic substances such as lead, cadmium, copper, zinc, asbestos, and certain organic compounds have been found in water being served from distribution systems as the result of corrosive action of water on distribution system materials. Increased incidences of cardiovascular disease have been associated with consumption of soft corrosive water.

    The greatest water quality nuisance is the corrosive and precipitation of iron. Red water is the most common consumer complaint. In this instance, it appears that a number of different microorganisms are involved. Bacteria are rarely absent where iron is found in abundance in treated water. The iron bacteria, Crenothrix, are of special concern. These bacteria precipitate iron, which forms the deposits in pipes, reduces carrying capacity, and produces color in water. The dead organisms also impart a disagreeable taste to the water. Improper potassium permanganate feed may also cause red-colored water.

    Corroded pipe
    Figure \(\PageIndex{2}\): Pipe with corrosion- Image by Mr pantswearer is licensed under CC BY-SA 4.0

    Of the materials used for construction of water systems, metals are the most susceptible to corrosion; however asbestos cement pipe is also susceptible. Plastic pipe is the least susceptible to corrosion. To prevent corrosion of cast-iron (ductile-iron) or steel pipes and to aid in the curing of cement-lined pipes, the inner side of these pipes may be lined with asphalt or coal tar materials. The types and durability of coating for corrosion control are of special importance. Some coatings, on the other hand, can impart taste and odors to the water. Because of its importance and complexity, corrosion is attempted to be mitigated and controlled during the water treatment process at the water treatment plant.

    Biofilm

    Some microorganisms enter the water and can interact with distribution system. Water with turbidity as low as 3.8 units has been reported to have coliform bacteria, and these bacteria have been reported to have survived consistently observed 0.1 to 0.5 mg/L free chlorine residual after 30 minutes contact time. Some non-coliform bacteria are more resistant. The survival and regrowth of these organism is affected by such factors as the amount of exposure to residual concentrations of chlorine, the amount of bacterial nutrients in the deposits, and water temperatures. The term after growth has been used to describe the development of coliform organisms in distribution systems even though water delivered to the system meets bacterial standards and where other causes of contamination of the water appear unlikely.

    Pockets of sediment deposited in the distribution system or pipe encrusted with chemical deposits may form a protected habitat for these organisms. Such deposits often consist of silt, coagulants, precipitated chemicals, or products of corrosion. Some deposits have been found to contain bacterial populations of several thousand organisms.

    Slimes are organic substances of a viscous nature formed from microbiological growth. Tastes and odors can be produced by slime growths of organisms that thrive on ammonia, iron, sulfide, and methane. The development of iron bacteria, Crenothrix, also results in slime growths.

    Increasing levels of microbial activity ultimately results in increased consumer complaints as well as accelerated corrosion and reduced flow from grater turbulence along the pipe walls. Taste and odor problems can result from the death and decay of organisms after heavy chlorination.

    Biofilms are the result of interactions s among microorganisms. The organisms form micro-colonies and secrete extracellular material that makes them highly resistant to biocides. A common example of a biofilm is the black stain around the bottom of a shower curtain. Biofilms appear as a patchy mass within a pipe or as a uniform film inside a storage tank. The majority of microbial growth within a water distribution system occurs within the biofilms at the surface of the pipe and not in the water flowing in the pipe.

    Biofilms grow easier on materials that supply nutrients, such as rubber gaskets or certain oils used in pumps. They need carbon, nitrogen, and phosphate in a ratio of 100:10:1. Iron is also an essential growth nutrient of limited supply in the water in a distribution system. Biofilm activity proceeds year-round; however, the growth rate is faster during warmer months. Tubercle crust contains high concentrations of nutrients for bacterial growth. Corrosion area in iron pipe are often sites with the highest microbial activity.

    Microbial control requires a good disinfectant residual. This residual can be accomplished with chlorine as either free chlorine, chloramines, or chlorine dioxide. Chlorine is considered the more powerful disinfectant than chloramines. Chloramines are more persistent in a distribution system and will eventually penetrate farther into the system for a longer period of time. This persistence is the reason chloramines are more effective against troublesome biofilms, than free chlorine. Free chlorine will attack biofilms and exhaust quickly, whereas chloramines will continue to attack the biofilm and slowly break down the defense of the biofilm. In chloraminated distribution systems, switching to free chlorine a few weeks before flushing each year can be an effective method to remove bacteria that become accustomed to chloramines.

    The link between corrosion and biofilm control is a concern of distribution system operators. Iron corrosion control is more difficult to control than lead and copper corrosion control. When iron pipe corrodes, the accumulation of corrosion products on the pipe surface interferes with the ability of the disinfectant to penetrate the biofilm and inactivate the bacteria. Improved corrosion controls through pH control, adjusting alkalinity, and corrosion inhibitors improve biofilm disinfection. A concern exists among operators that phosphate-based corrosion inhibitors stimulate bacterial growth. Zinc orthophosphate has effectively controlled corrosion for compliance with the Lead and Copper Rule and also has been associated with improved microbial water quality. Because the corrosivity of water changes seasonally, some agencies are increasing the use of corrosion inhibitors during the warmer summer months when biofilm regrowth problems are most common.

    Temperature

    Water temperature has three major impacts on distribution system water quality:

    • Higher temperatures tend to speed the rate of chemical reactions and increase biological growth rates
    • Biological decomposition may be intensified by summer temperatures
    • Chlorine demand may be considerably greater so residuals will not carry as far in the distribution system in the summer

    Flow

    Large variations in flow through a system may adversely affect water quality in three ways:

    • Changes in water velocity and flow reversals can result in sediments being stirred up and carried along until they reach the consumer
    • Low circulation and stagnant water can result in the growth of organisms, formation of sediments, corrosion products, depletion of oxygen, and increased tastes and odors
    • Turbulence can entrain air into the supply causing milky water, which is objectionable to consumers

    Time in System

    The age of water at a particular point in the distribution system can influence water quality. Water delivered to consumers close to the source might be only minutes old, while that water received at remote parts of the system might have been in the system for several days or more depending on storage and demands. The longer water is in the system, the more time is available for chemical and biological changes to take place.

    Age of Facility

    As water mains and reservoirs become older, they require more maintenance. Gradual deterioration in protection against corrosion can lead to water quality problems. Ruptures and leaks in piping become more frequent. In older systems, it is not uncommon to find that the pipes and tanks were of poor construction when installed and have had little or no protective coatings.

    Operation

    Careless or poor operating procedures can also result in water quality degradation. Inadequate cross-connection control, poorly performed water quality monitoring and flushing programs, tolerance of low or negative pressures in the distribution system, insufficient surveillance to determine whether the protective features for storage facilities and mains are adequate, inadequate disinfection after repair or installation of new facilities, and disregard for the hazards of installing facilities such as sewers in close proximity to water lines and reservoirs are examples of operational problems resulting in water quality issues. The lack of trained, qualified, adequately paid operators contribute to water quality problems as well.

    Water Quality Degradation in Water Main

    Water quality deterioration can occur in water mains because of pipe characteristics, materials, construction, and location.

    Large Surface Areas

    Substance can be deposited, biological growths can be attached, and corrosion reactions can take place on the inside surfaces of pipe walls. The large interior surface area provides considerable space for these activities to take place. Reduced flows allow greater chemical and biological activity to take place at the interface where the pipe and water meet. This relatively quiet zone is capable of harboring considerable chemical or biological activity. Therefore, the quality conditions next to the pipe wall are quite different from those conditions in the main stream flow. In smaller mains, the ratio of surface area to volume of water is much greater, making the quality problems in the mains much more likely to be serious if chemical or biological activity occurs.

    Dead-ends

    The lack of circulation in a dead-end creates nearly ideal conditions for degrading water quality. The velocity is very low if not zero, the time of contact of water with the pipe and any deposits, encrustations, or slimes is long, an accumulation of organic matter containing nutrients exists, organisms grow and use the available dissolved oxygen, and oxygen may be depleted, therefore, initiating anaerobic conditions, which produce carbon dioxide, methane, and sulfide odors. Carbon dioxide may increase the corrosion potential. Chlorination may not be effective because of the increased chlorine demand by organics, biological forms, and corrosion products.

    Dead End System diagram
    Figure \(\PageIndex{3}\): Dead-end in distribution system – Image by COC OER is licensed under CC BY

    Pipe Material

    Pipes are made of metal, asbestos-cement, or plastic. In metal and asbestos-cement pipe, corrosion can cause the release of substances from the piping materials into the water. With coal tar lined or plastic pipe, however, the physical characteristics of the water are of minor importance. The concern is the possibility of leaching of material from the pipe or the lining by the water. To prevent corrosion, the insides of cement or metal pipes may be lined with asphalt or coal tar coatings. The potential for corrosion then relates to the integrity of the coatings.

    Of special concern are systems that have considerable unlined pipes in the ground; and therefore, are more susceptible to corrosion problems. When pipes of dissimilar metals are connected, increased corrosion near the connection exists. Asbestos-cement pipe will deteriorate if aggressive water conditions exist, releasing increasing amounts of asbestos fibers.

    Pipe Construction and Repair

    An ample opportunity exists for entry of contaminants during the construction of new mains and repair of old mains. To ensure the safety of the delivered water, proper protective, cleaning, and disinfection practices must be followed. When lines are being repaired, keep the hole dewatered to prevent possible contamination of the waterline. After the line has been repaired, thoroughly flush the line downstream from the repair to remove any dirt and mud that could have entered the line. Flushing is important for health reasons and to avoid consumer complaints. After flushing, the line should be disinfected before being returned to service.

    Hazardous Facilities

    When physical conditions or soil conditions prevent minimum separation distances from being met, water mains can be located adjacent to collection system lines, fuel lines, individual septic tanks, and disposal systems or tanks containing dangerous materials. If leakage from such hazardous facilities saturates the soil around the mains, the mains could become contaminated. When they are out of service for any reason and are not under pressure contaminates may seep into the lines through cracked or inadequately sealed joints.

    Appurtenances

    Distribution system water quality can be adversely affected by improperly constructed or poorly located blowoffs or air release and vacuum relief valves. They may be located where they could become flooded and permit the entrance of contaminated water when they are open. A lack of blowoffs would make it difficult or impossible to correct a poor quality condition, or to give temporary relief. Air valves are important to relive entrapped air and to help prevent milky water and surge problems when lines are being filled.

    Water Quality Monitoring

    Water quality monitoring of distribution systems is important to identify when and where water quality changes occur in the system. Routine monitoring consists of collecting samples at remote locations in the system and testing for chlorine residual and coliforms. The minimum number of samples per month is based on the population served. When problems or complaints develop, a more detailed monitoring program is required to identify the cause and source of the problem.

    Operation of Distribution System

    Operators of distribution systems can maintain water quality in distribution systems by developing and implementing an effective distribution system operation and maintenance program. The critical elements of an effective program are:

    • A comprehensive system of surveillance and monitoring
    • Developing and enforcing good water main repair and replacement procedures; especially, for disinfecting mains before placing them in service
    • Instituting a biofilm control program
    • Developing and implementing a unidirectional flushing program
    • Developing a regular schedule and program for inspecting and maintaining storage tanks and making sure an adequate turnover of water in the tank is occurring
    • Developing and maintaining an active corrosion control program
    • Instituting an annual cleaning and lining program
    • Developing a program to eliminate as many of the dead ends as possible in the distribution system
    • Developing a valve exercise program to ensure proper setting and operation of valves
    • Developing and implementing a backflow prevention program
    • Maintaining positive pressure on the system at all times (by rule at least 20 psi)
    • Thoroughly investigating and responding to all consumer complaints

    Review Questions

    1. What is a cross-connection?
    2. How can back-flow occur in a drinking water distribution system?
    3. Define back-siphonage.
    4. Define back-flow.
    5. Name the common situations that can result in a cross-connection in the drinking water distribution system.
    6. Describe corrosion as a process in a drinking water distribution system.
    7. What is the most common consumer complaint received by a drinking water treatment facility?
    8. Describe the problems associated with dead ends in the distribution system.

    Chapter Quiz

    1. A ___________ is defined as any system that has at least 15 service connections and regularly serves an average of at least 25 individuals daily at least 60 days out of the year.
      1. Public water system (PWS)
      2. Community water system (CWS)
      3. Transient water system
      4. Non-transient non-community water system
    2. A system that has at least 15 service connections used by all-year residents and regularly serves at least 25 all-year residents is defined as a ___________.
      1. Public water system (PWS)
      2. Community water system (CWS)
      3. Transient water system
      4. Non-transient non-community water system
    3. EPA identifies some systems as ___________ if they regularly serve at least 25 of the same persons over 6 months per year.
      1. Public water system (PWS)
      2. Community water system (CWS)
      3. Transient water system
      4. Non-transient non-community systems
    4. The routine monitoring frequency for community water systems is based on the ___________.
      1. Past history of coliforms being present in the sampling
      2. Population served
      3. Type of treatment
      4. Raw water source being surface water or groundwater
    5. The MCL for coliforms is based on the presence-absence concept, such that for water systems analyzing at least 40 samples per month, no more than ___________ of the samples (including routine and repeat samples) may be positive for total coliforms.
      1. Zero
      2. One
      3. One percent
      4. Five percent
    6. The MCL for coliforms is based on the presence-absence concept, such that for water systems analyzing fewer than 40 samples per month, no more than ___________ of the samples per month may be positive for total coliforms.
      1. Zero
      2. One
      3. One percent
      4. Five percent
    7. A ___________ is an unprotected connection between a part of a water system used or intended to be used to supply water for drinking purposes and any source or system containing water or a substance that is not or cannot be approved as safe drinking water. It is a connection between a regulated and approved drinking source and an unregulated drinking water source.
      1. Cross-connection
      2. Back-flow connection
      3. Back-siphonage connection
      4. Dead-end
    8. A critical situation exists when a routine sample tests positive for total coliforms and for fecal coliforms or E. coli, and any repeat sample tests positive for total coliforms and when a routine sample tests positive for total coliforms and negative for fecal coliforms or E. coli, and any repeat sample tests positive for fecal coliforms or E. coli. These situations are considered an acute risk to health. This occurrence is a ___________ violation, which requires that the state and the public be notified within 24 hours.
      1. Tier 1
      2. Tier 2
      3. Tier 3
      4. Sampling error
    9. ___________ is a form of back-flow caused by a negative or below atmospheric pressure within the water supply piping. It can develop from such causes as main breaks, an inadequate source of supply capacity, undersized mains, unusual water demands, planned shutdowns for maintenance or repair, or the use of on-line booster pumps.
      1. A cross-connection
      2. A back-flow connection
      3. A back-siphonage connection
      4. A dead-end
    10. ___________ is caused by back pressure can occur when the user’s water system is at a higher pressure than the public water system.
      1. A cross-connection
      2. A back-flow connection
      3. A back-siphonage connection
      4. A dead-end
    11. The lack of circulation in a ___________ creates ideal conditions for degrading water quality. The velocity is very low if not zero, the time of contact of water with the pipe and any deposits, encrustations, or slimes is long, an accumulation of organic matter containing nutrients exists, organisms grow and use the available dissolved oxygen, and oxygen may be depleted; therefore, initiating anaerobic conditions, which produce carbon dioxide, methane, and sulfide odors. Carbon dioxide may increase the corrosion potential. Chlorination may not be effective because of the increased chlorine demand by organics, biological forms, and corrosion products.
      1. Cross-connection
      2. Back-flow connection
      3. Back-siphonage connection
      4. Dead-end

    This page titled 1.11: Distribution System Water Quality is shared under a not declared license and was authored, remixed, and/or curated by John Rowe (ZTC Textbooks) .

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