Drinking Water Distribution Systems Assessing and Reducing Risks (2006) / Chapter Skim
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4 Physical Integrity
4 Physical Integrity
Pages 142-191
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From page 142... ...
The physical integrity of the distribution system is always in a state of change, and the aging of the nation's distribution systems and eventual need for replacement are growing concerns. Maintaining such a vast physical infrastructure is a challenge because of the complexity of individual distribution systems, each of which is comprised of a network of mains, fire hydrants, valves, auxiliary pumping or booster disinfection substations, storage reservoirs, standpipes, and service lines along with the plumbing systems in residences, large housing projects, high-rise buildings, hospitals, and public buildings.
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From page 143... ...
Storage facility walls, roof, Air contamination, rain, algae, surface runoff, human activity, Concrete, steel, asphaltic, epoxy, plastics cover, vent hatch animals, birds, and insects Backflow prevention Nonpotable water Brass, plastic devices Liquids Not applicable Oils, greases, lubricants Gaskets and joints Soil, groundwater, sewer exfiltration, surface runoff, human Rubber, leadite, asphaltic, plastic activity, animals, insects, and other life forms 143
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From page 144... ...
FACTORS CAUSING LOSS OF PHYSICAL INTEGRITY Losses in physical integrity are caused by an abrupt or gradual alteration in the structure of the material barrier between the external environment and the drinking water, by the absence of a barrier, or by the improper installation or use of a barrier. These mechanisms are summarized in Table 4-2.
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From page 145... ...
cracks and breaks · Poor drainage for runoff · Use of faulty materials Backflow prevention · Corrosion · Missing device will allow a backflow · Use of faulty materials device event via a cross connection · Improper installation · Inadequate drainage of meter pit · Operational failure 145
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From page 146... ...
One must even consider the installation of flawed materials, which might, for example, be brought about because of a lack of protection of materials during storage and handling. Structural Failure of Distribution System Components Metallic pipe failures are divided generally into two categories: corrosion failures and mechanical failures.
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From page 147... ...
Other components of distribution system also experience structural failure, although they have not historically received the attention afforded to pipes. For storage facilities, structural failure is less of a problem than external contamination due to the absence or failure of an essential component such as a cover or vent.
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From page 148... ...
In some cases holes are formed directly in pipes by corrosion, as is the case with pinholes, but in many other instances corrosion weakens the pipe to the point that it will fail in the presence of forces originating from the soil environment. The type of corrosion and mode of failure causing loss of physical integrity are highly system specific.
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From page 149... ...
(2004) , "approximately 72 percent of the materials reported in use for water mains are iron pipe, approximately two-thirds of the reported corrosion is in corrosive soils, and approximately two-thirds of the corrosion is on the pipe barrel." In addition, metallic or cementitious pipe are often designed on the basis of their hydraulic capabilities first and foremost, and corrosion resistance is often a secondary consideration.
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From page 150... ...
. Human Activities that Lead to Contamination A second major cause of physical integrity loss is human activity surrounding construction, repair, and replacement that can introduce contamination into the distribution system.
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From page 151... ...
Between 1997 and 1999, the Philadelphia water supply measured elevated turbidity (>1 NTU) in about 12 to 14 percent of the samples that were collected from newly installed water mains.
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From page 152... ...
. The installation or rehabilitation of facilities such as storage reservoirs with floating covers must include water quality checks for health and aesthetic considerations and not assume that new materials and their installation will be free of contaminants (Krasner and Means, 1986)
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From page 153... ...
Even with covered storage facilities, contaminants can gain access through improperly sealed access openings and hatches or faulty screening of vents and overflows. Four reported waterborne disease outbreaks have been associated with covered storage tanks, in particular, a Salmonella typhimurium outbreak due to a bird contamination of a covered municipal water storage tank (Clark et al., 1996)
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From page 154... ...
CONSEQUENCES OF A LOSS IN PHYSICAL INTEGRITY A loss of physical integrity implies a breakdown in the barrier that prevents contact between the external, unsanitary environment and the internal, drinking water environment. The water quality effects that can result include the introduction into the distribution system of microbial and chemical contaminants, debris, and particulate matter, sometimes accompanied by changes in water color, turbidity, taste, and odor.
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From page 155... ...
The sections below discuss the typical consequences of the loss of physical integrity in pipes, fittings and appurtenances; storage facilities; and backflow prevention devices. Contamination of Mains, Fittings, and Appurtenances Pipe interior, appurtenances, and related materials can be exposed to microbial and chemical contaminants in the external environment (1)
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From page 156... ...
In mid-December 1989, unusually cold weather caused two large water mains and 45 in-ground water meters to fail (Figure 4-1)
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From page 157... ...
This outbreak illustrates how, despite a clean groundwater source, lack of disinfection combined with poorly maintained water and sewer lines, unusually cold weather, and casual line replacement practices led to a large drinking water outbreak with fatalities in a small town in an industrialized country. FIGURE 4-2 Cases of diarrheal disease among city residents.
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From page 158... ...
Although there is the potential for water quality degradation as a result of the permeation of plastic pipe, the health impacts associated with such permeation are not well documented nor are they expected to be significant. In some permeation incidents, the concentrations of certain chemicals have been shown to reach levels in the low parts per million, which are well above their respective maximum contaminant levels (MCLs)
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From page 159... ...
Even when covered, storage facilities can suffer from algal growth on the tops of floating covers that can gain entry into the tank through rips and tears or missing hatches. Algae can also be airborne or carried by birds and gain entry into storage tanks through open hatches and vents.
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From page 160... ...
Contamination Due to the Absence or Operational Failure of Backflow Prevention Devices Backflow events via unprotected domestic, commercial, industrial, and fire connection services can introduce contaminants into the potable water supply, with potentially profound health implications. A recent survey (USC, 2002)
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From page 161... ...
In the end, the outbreak investigation concluded that the cold weather in early November caused a thermal inversion in the water storage tanks that mixed the contaminated upper layers of stored water with the water entering the distribution system. The widespread flushing program on November 10 served to draw more contaminated storage tank water into the distribution system than under normal operation.
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From page 162... ...
Box 4-3 describes a waterborne disease outbreak associated with an unprotected cross connection. DETECTING LOSS OF PHYSICAL INTEGRITY In some cases, a loss in physical integrity might actually be observed, such as a hole or tear in a reservoir cover, a missing vent or hatch on a storage facility, or a flooded meter or valve pit.
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From page 163... ...
Structural failure Investigate customer complaints, pressure (break) monitoring Improper installation Inspection Unsanitary activity Inspection, water quality testing Fitting and Structural failure Inspection, pressure monitoring, investigation of appurtenance customer complaints, leak detection, detection of operational failures Improper installation Inspection Unsanitary activity Inspection Storage facil- Structural failure Inspection, water quality testing ity wall, roof, (crack, hole)
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From page 164... ...
Further investigation of the water system revealed that when maintenance work was done on November 29, the drinking water system had been connected to the economy water system in order to flush and clean it, and that the workers had failed to remove the cross-connection when the economy water system was put on-line again. In addition, the economy water supply lines were under higher pressure than the drinking water lines, which forced the economy water to enter the drinking water distribution system.
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From page 165... ...
Taken together, the results of these two retrospective studies suggest that an outbreak of gastroenteritis, probably due to noroviruses, occurred shortly after the cross connection between the economy water distribution system and the drinking water distribution system was created. It is notable that there appeared to be an increased risk of gastroenteritis in the adjacent control community that reportedly was not affected by the crosscontamination incident.
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From page 166... ...
routine inspections, all of which could be predictive of a loss of physical integrity. This is because a lack of training, certification, inspection, and standards often lead to the improper installation and application of materials (for example, using the wrong backflow prevention device or installing plastic pipe in contaminated soils)
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From page 167... ...
Condition assessment requires information from existing pipe to help predict the lifetime of pipe still in use. To make the exercise more economically feasible, it might be done for selected pipes that represent a cross section of installed pipe materials and installation dates.
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From page 168... ...
The ability to detect and track backflow events will allow more focused monitoring to determine their impact on drinking water quality. Main Break Monitoring Main break monitoring consists of utilities recording responses to water main breaks such as time and date of response, location of break, valves operated to shut down the main, properties affected by the shut down, repaired or replaced portion of main, and shut-down time.
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From page 169... ...
Water quality data can also be useful in identifying problems with physical integrity when integrated with others sets of data, such as customer complaints, water main break occurrences, timing of newly installed water mains, cleaning of storage facilities, or backflow events (see Chapter 7 for more discussion of data integration)
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From page 170... ...
Thus, in isolation water quality data are not sufficient to identify failures in physical integrity. But combined with other data, they may be useful for detecting external contamination events.
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From page 171... ...
System piping includes valves and fittings, ferrules, and hydrants. Storage facilities range in their composition from concrete to steel with linings of cement, asphaltic, and epoxy.
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From page 172... ...
The diversity, complexity, and value of materials used in drinking water infrastructure are important to distribution system management, especially given the increasing emphasis on system reliability and more stringent water quality demands. The following factors should be considered when choosing distribution system materials: · health effects of the material when in contact with drinking water; · hazards and safety in working with the materials; · structural capabilities of the material; · water quality impacts of the material; · cost and availability of the material; · compatibility of the material with other materials in the system and with the conveyed water and surrounding soils;
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From page 173... ...
. Testing of materials to ensure they meet the standards used for procurement should be a broader practice within the water industry, and not limited to only the largest water utilities.
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From page 174... ...
Corrosion Control The historical use of metallic pipes and the many environmental conditions they come in contact with have made both external and internal corrosion an issue for the water industry for some time. Although most utilities use some form of internal corrosion control to minimize color and turbidity problems and to meet the Lead and Copper Rule requirements, not all utilities practice external corrosion control, even though it is important for maintaining the physical integrity of their distribution systems, as acknowledged by 14 of 34 responding states (see Table 2-3)
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From page 175... ...
. Transmission mains are more frequently engineered for external corrosion control than distribution mains because of the greater need to prevent catastrophic failures in the larger diameter water mains.
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From page 176... ...
Storage facilities have many purposes (see Chapter 1) , such that a disciplined storage facility management program is critical to water utilities.
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From page 177... ...
. When thought of with respect to maintaining physical integrity, it refers to developing an inventory of distribution system components and determining when repair should give way to rehabilitation or replacement (EPA, 2004)
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From page 178... ...
Thus, a water utility typically lumps pipes into classes and assigns to them average failure information, and, using statistics about the system, then predicts investment needs to maintain the assets. Beyond maintaining physical integrity, there are many important reasons for utilities to engage in asset management, including (Morrison, 2004)
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From page 179... ...
Clearly, their increased use and regular inspection would do much to reduce public health risks from drinking water distribution systems. Indeed, for utilities operating dual distribution systems, the need for an effective cross-connection control program is paramount.
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From page 180... ...
Given this variability, Chapter 2 recommends that EPA explicitly define what an acceptable cross-connection control program should be. RECOVERING PHYSICAL INTEGRITY It is impossible for a distribution system of any significant size to be managed in such a way as to prevent any loss of physical integrity over time.
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From page 181... ...
Chlorine and other disinfectants have been used to protect pipes and storage facilities against external microbial contamination, prevent TABLE 4-9 Ways to Recover from a Loss in Physical Integrity Component Mechanism of Integrity Loss Recovery by Pipe Permeation Reline or replace and conduct water quality testing Structural failure (leak) Replace or repair or rehab Structural failure (break)
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From page 182... ...
Nonstructural rehabilitation of water mains, which does not focus on recovering the physical integrity of distribution systems, includes chemical dosing for corrosion control, cement mortar lining, epoxy resin lining, and thin-walled PE lining (Hughes and Conroy, 2002; Grigg, 2004; Damodaran et al., 2005)
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From page 183... ...
replacement of infrastructure pipe components (Damodaran et al., 2005) , although they do not incorporate public health risk and water quality deterioration.
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From page 184... ...
Prior to the release for use of a new or replaced water main or facility, a water utility will typically conduct water quality testing. Total coliform bacteria have been the most common indicator that the new material is sanitary and did not become contaminated during storage or installation.
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From page 185... ...
dechlorinating the water (using sulfur dioxide, sulfite, or bisulfite) if the water is discharged to a surface waterbody so as to minimize adverse impacts to aquatic life.
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From page 186... ...
The following primary conclusions and recommendations for maintaining and restoring physical integrity to a distribution system are made. Storage facilities should be inspected on a regular basis.
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From page 187... ...
At present the best defense against corrosion relies on site-specific testing of materials, soils, and water quality followed by the application of best practices, such as cathodic protection. Indeed, a manual of practice for external and internal corrosion control should be developed to aid the water industry in applying what is known.
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From page 188... ...
1985. Internal Corrosion of Water Distribution Systems.
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From page 189... ...
2005. Assessment and Renewal of Water Distribution Systems.
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From page 190... ...
1991. Water Distribution Systems: A Troubleshooting Manual.
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From page 191... ...
2004. External Corrosion and Corrosion Control of Buried Water Mains.
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