Drinking Water Distribution Systems Assessing and Reducing Risks (2006) / Chapter Skim
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7 Integrating Approaches to Reducing Risk from Distribution Systems
7 Integrating Approaches to Reducing Risk from Distribution Systems
Pages 269-315
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From page 269... ...
In addition to industry standards, AWWA "Manuals of Water Supply Practices," such as M6 Water Audits and Leak Detection, are commonly used by drinking water utilities to enhance their operations and service to the public. In 1999 a technical workgroup was organized to develop a Drinking Water Distribution System Assessment Workbook, which began the process that culminated in the G200 Standard.
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From page 270... ...
. These include Section 4.1.1: Compliance with regulations, 4.1.3: Disinfectant residual maintenance, 4.2.1 System pressure monitoring and requirements, 4.2.2 Backflow prevention, and 4.3.1 Storage facilities.
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From page 271... ...
4.2.8 Metering 4.2.8.1 Metering requirements Determine daily peak flows and maximum day peak flows. 4.1.8.2 Metering devices Meters shall meet AWWA require ments or other applicable standard.
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From page 272... ...
4.3 Facility Operation and Maintenance 4.3.1 Treated water storage facilities 4.3.1.1 Storage capacity Establish minimum operating levels in storage facilities. 4.3.1.2 Operating procedures Write Standard Operating Proce dures for turning over facilities and minimizing water age.
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From page 273... ...
As discussed in Chapter 2, the use of the standards such as ANSI/NSF 60, ANSI/NSF 61, and AWWA G200 and Manuals of Practice have advantages over programs such as Hazard Analysis and Critical Control Points (HACCP) in that they are more easily adapted to the dynamic nature of drinking water distribution systems.
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From page 274... ...
Under the SDWA, monitoring or treatment techniques are required for all contaminants regulated under the Act, both at the entry point to a water distribution system and, in some cases, at various locations within the system. Rules and regulations that explicitly require monitoring in the distribution system include the Total Coliform Rule (TCR)
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From page 275... ...
. In addition to being a linkage of processes, the distribution system is also a reactor, in that treated drinking water begins to change physically (e.g., iron and manganese particles settle out)
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From page 276... ...
X Disinfectant residual X (water age) X Main breaks X Water loss X Color X (corrosion)
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From page 277... ...
Turbidity in distribution systems, which can be can be caused by suspended sediments, oxidized iron or manganese, or other corrosion products, is another critical parameter for which on-line, real-time methods are available. Various models exist but in the finished water distribution system, turbidity probes need to be sensitive at low ranges (i.e., < 1 NTU)
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From page 278... ...
Continuous Monitoring of Total Chlorine Residual Continuous Monitoring of Total Chlorine Residual 0.5 0.45 0.4 0.35 0.3 0.25 ppm 0.2 0.15 0.1 0.05 0 08/25/04 08/27/04 08/29/04 08/31/04 09/02/04 09/04/04 09/07/04 09/09/04 09/11/04 09/13/04 00:00 04:47 09:35 14:23 19:11 23:59 04:47 09:35 14:23 19:11 Date/Time FIGURE 7-1 Data from a continuous, on-line chlorine analyzer, showing how a total chlorine residual can vary through a day and the need to relate this to system operations. SOURCE: Data from Philadelphia Water Department, Bureau of Laboratory Services.
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From page 279... ...
is uncertain. Another National Research Council committee is in the process of examining research needs in the area of drinking water homeland security, and further discussion of this issue may be found in its report.
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From page 280... ...
and can be used for approximating the total dissolved solids content. Ion selective electrodes for Cl-, NO3 NH4 and others analytes are avail -, + able but are not entirely ion-specific and can lead to problems of ionic interference.
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From page 281... ...
These data were then used to show the improvements made by the chosen controls. One drawback to customer complaints is that they are end-user in origin and so cannot distinguish between contamination originating within the customer's premise, the service line and local water main, a regional storage facility, or all the way back to the treatment plant and the source water (Burlingame, 1999b)
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From page 282... ...
. © 2006 by American Water.
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From page 283... ...
INTEGRATING APPROACHES TO REDUCING RISK FROM DISTRIBUTION SYSTEMS 283 al Technology, Inc Wallace & Tiernon Emerson Hach ProMinent In-Situ Model 1055 TOC Model A 15/B-2-1 Depolox 3 WDM Panel or plus Comp II Process D1C &D2C Troll 9000 Analyzer Pipe SondeTM Analyzer Free or total Multi Free chlorine or chlor- chlorine (or parameter, Multi- Used with Multi- Multi amines chlorine diox- customizable, parameter, WDM parameter, parameter, ide or ozone) on-line on-line on-line on-line 3,000 3,500 15,885 12,000 18,000 7,000 11,200 02, 020 or 0200 020 010 04 (DPD)
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From page 284... ...
. On-line monitoring has the benefit of providing -- in real time-early warning of intentional or accidental contamination, and when fully develop and deployed it could help water utilities take the appropriate actions to safeguard public health.
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From page 285... ...
EPA's Threat Ensemble Vulnerability Assessment (TEVA) program is developing an add-on tool in EPANET to allow water utilities to select the optimal number of sensors and identify strategic locations for installation of on-line sensors to maximize public health protection (http://www.epa.gov/NHSRC/news /news111505b.htm)
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From page 286... ...
. These computer simulations support the use of on-line sensors in providing an early indication of drinking water contamination events.
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From page 287... ...
For example, the Arizona Department of Environmental Quality has partnered with the Tucson Water Department, the University of Arizona, and several Pima County agencies, businesses, and organizations to provide citizens with on-line information about drinking water quality. The effort was made possible by an Environmental Monitoring for Public Access and Community Tracking (EMPACT)
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From page 288... ...
: · Increase the amount of water quality testing by continuous on-line sampling · Improve the access to water quality data in the potable distribution system · Provide information for customers by identifying specific constituencies and methods to individualize data by location · Create a context for understanding water resources data, thus removing misperceptions · Serve as a source of reliable, authoritative information on fast-breaking water quality issues The automatic monitoring stations are currently running and continuously updating water quality data on a map-based website; this program is a model for other utilities. How to Interpret Data and Respond to Monitoring Data Given a stream of data from a monitoring program, a critical task is to determine whether the results indicate an "event" or "problem" and if so, how utilities should respond.
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From page 289... ...
There are limited options for responses at the disposal of utilities, including boil-water, do-notconsume, or do-not-use notices, that can be applied for particular sections of a system or system-wide. The response to a detection event from a monitoring network carries risks associated with both false positives and false negatives.
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From page 290... ...
DISTRIBUTION SYSTEM MODELING Water distribution network (mathematical) models have become increasingly accepted within the water industry as a viable mechanism for simulating the behavior of water distribution systems.
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From page 291... ...
In the early 1980s investigators began introducing the concept of water quality modeling (Clark and Males, 1986; Grayman, et al., 1988; Clark and Coyle, 1990) , and now most water distribution system models routinely incorporate sophisticated water quality
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From page 292... ...
. This section discusses the basic principles underlying routine hydraulic and water quality modeling in drinking water distribution systems and presents new developments.
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From page 293... ...
. Rigorous optimization approaches have been developed and applied to a full range of problems associated with water distribution systems (Boulos et al., 2006)
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From page 294... ...
For example, the EPA public domain EPANET model (Rossman et al., 1994; Rossman, 2000) greatly facilitated the easy application of existing water quality models to municipal drinking water distribution systems.
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From page 295... ...
(2004b) , which has developed algorithms for optimizing the location of water quality sensors in drinking water distribution systems.
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From page 296... ...
BOX 7-1 Calibrating and Validating Network Models A water distribution network model must be properly calibrated before it can be used to support planning, design, operation, or water quality improvement decisions. Calibration establishes the accuracy and credibility of the network model so that its predictions can be interpreted with confidence.
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From page 297... ...
The use of tracer studies greatly enhances the ability of network models to accurately estimate water age and travel times in the system. TABLE 7-7 Draft Calibration Criteria for Modeling Intended Level of Type of Number of Accuracy of Number of Accuracy of Use Detail Simula- Pressure Pressure tion Readings Readings Flow Readings Flow Readings Planning Low Steady or 10% of ±5 psi for 1% of Pipes ± 10% EPS Nodes 100% Read ings Design Moderate Steady or 5% 2% of ±2 psi for 90% 3% of Pipes ± 5% to High EPS Nodes Readings Operations Low to Steady or 10% 2% ±2 psi for 90% 2% of Pipes ± 5% High EPS of Nodes Readings SOURCE: Adapted from AWWA ECAC, (1999)
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From page 298... ...
The development of GIS is greatly expanding the applications of water distribution network models. Because of the spatial nature of water distribution systems, many aspects of managing these systems consist of using, analyzing, and displaying geospatial data, which includes the geographic location and characteristics of various water system facilities, including pipes, pumps, storage tanks, reservoirs, and valves.
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From page 299... ...
conditions for the network model as well as real-time measurement data (e.g., pressure and flow measurements) for network model calibration and for identifying water losses during main breaks (e.g., unexplained low pressure reading, excessive pump flow)
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From page 300... ...
Managing and protecting distribution systems from contamination threats and a wide range of emergency situations will require the use of a comprehensive decision support system that integrates modeling applications with the various infrastructure management systems. The term "integration" can refer to a TABLE 7-8 Systems and their Response Roles System Response Role On-line monitoring · Identify event (location and type)
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From page 301... ...
Box 7-2 presents an example of integrating GIS with water quality modeling, master planning, and operational decision-making within the Las Vegas Valley Water District.
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From page 302... ...
For a large network model, the disadvantages include an increase in the run-time of the network model due to the addition of detailed components and relatively slow water quality simulations. To minimize this problem, LVVWD has taken an "all-pipes capable" approach where the distribution system is divided according to existing pressure zones and attached to an operational backbone network (skeletonized)
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From page 303... ...
Technical assistance could also be provided to small systems by larger water utilities in the area. Finally, public education could result in an increased awareness and emphasis on the significance of implementing proactive voluntary efforts.
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From page 304... ...
For example, with respect to water pressure monitoring, a minimum water pressure requirement could be established, not unlike the measurable chlorine residual that is now required. Sanitary Surveys.
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From page 305... ...
The distribution system components of the sanitary survey include: · Distribution system maps and records, field sampling and measurements, system design and maintenance · Finished water storage location, capacity, design, painting, cleaning and maintenance, security · Pumps and pump facilities and controls capacity, condition, pumping station · Water system management and operation administrative records, water quality goals, water system management, staffing, operations and maintenance manuals and procedures, funding · Operator compliance with state requirements such as certification and competency. The Drinking Water Academy developed software for use by state sanitary inspectors in accomplishing all aspects of a sanitary survey with some level of uniformity.
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From page 306... ...
. State Regulatory Approach In lieu of federal regulations, state regulations could require adherence to G200 or the committee's list of preferred activities for reducing risk in distribution systems.
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From page 307... ...
Drinking water utilities in the United States have historically depended on the municipal bond market to finance both the development of public water supplies and their expansion into surrounding
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From page 308... ...
The EPA already provides extensive guidance to help water utilities achieve and maintain compliance, including a capacity development program to assist water systems in achieving SDWA compliance (Stubbart, 2005)
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From page 309... ...
While there is a general agreement in the modeling profession that the extent of development and calibration required for a water distribution network model depends largely upon its intended use, there are no universally accepted standards and there is currently no apparent
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From page 310... ...
Real-time monitoring and modeling of water distribution systems to assist water utilities in making informed operational decisions under routine and emergency conditions requires the integration of network models with SCADA systems, which has yet to be accomplished at most utilities. The SCADA system can be used to update the boundary conditions in the network model such as tank water levels, pump on/off status, isolation valve status, control valve settings, and system demands, and the model can in turn be used to identify the "best" operational strategy for the selected facilities and pass their control logic back to the SCADA system for implementation.
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From page 311... ...
1998. Modeling water quality in drinking water distribution systems.
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From page 312... ...
2003. National Primary Drinking Water Regulations; Announcement of Comple tion of EPA's Review of Existing Drinking Water Standards.
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From page 313... ...
2004. The Threat Ensemble Vulnerability Assess ment Program for Drinking Water Distribution System Security.
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From page 314... ...
1994. Modeling chlorine residuals in drinking water distribution systems.
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From page 315... ...
1998. Development and auto calibration of an input-output model of chlorine transport in drinking water distribu tion systems I.E.E.E.
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