Distribution System Water Quality Control Demonstration [Project #4286]

Transcription

1 Distribution System Water Quality Control Demonstration [Project #4286] ORDER NUMBER: 4286 DATE AVAILABLE: April 2012 PRINCIPAL INVESTIGATORS: Abigail F. Cantor, Eric Kiefer, Kevin Little, Andrew Jacque, Archie Degnan, Barry Maynard, David Mast, and Judith Cantor OBJECTIVES: This study demonstrates the use of three tools for process control in water systems. One is a simple data management tool for making sense of complicated systems: Shewhart control charts used in industrial quality control. Another tool is a relatively simple means of tracking water quality at consumers taps: standardized monitoring stations that are abstractions of consumers plumbing systems. The third tool is a monitoring strategy that identifies key information linking components of a water system together. The use of these tools is demonstrated in the context of a comprehensive consumercentric process control method for drinking water systems. BACKGROUND: There are multiple opportunities, yet unrealized in many drinking water systems, to improve water quality and to save money in doing so. This is a surprising statement in that modern water systems already include the latest in technology to monitor various physical and chemical aspects of the water system. However, there are three ways to more effectively use the monitoring information for comprehensive process and quality control of a water system: 1. Be comprehensive: Identify specific information that links the water sources, treatment, distribution system, and delivered water quality together. 2. Be consumer-centric: Use product quality that is, delivered water quality as the main focus of process control endeavors, allowing it to drive decision-making, expenditures, and planning for the complete water system. 3. Enhance process control: Be proactive in water quality control and improvement rather than allowing regulatory compliance and customer complaints to motivate such efforts. Three tools can be used to more effectively utilize monitoring information in this way. For a comprehensive view of the water system, this project uses a monitoring strategy to identify key water quality parameters that link components of the water system together (Cantor 2009). To capture water samples representative of household plumbing connected to the water distribution system, this project uses a standardized distribution system monitoring station called a PRS Monitoring Station (Cantor et al. 2000, Cantor 2008, 2009, 2010, 2011). Any similar monitoring stations based on the Water Research

2 Foundation pipe loop apparatus (AwwaRF and DVGW-TZW 1996) can be used. For meaningful data interpretation, this project uses techniques of industrial quality control and process improvement that were developed in the 1930s (Wheeler and Chambers 1992). These tools are used in an iterative process, where current information is obtained in order to improve the system in the future. After the improvement, more information is gathered to fuel further improvement. The iterative method is emphasized in this project as a comprehensive consumer-centric method of process control for drinking water systems. Implementing this operational philosophy will achieve: A proactive approach to water quality with a lower possibility of falling out of compliance with drinking water regulations and a lower frequency of consumer complaints A documented decision-making process that is transparent to consumers, produces consistent water quality, and gives managers and water commissioners confidence in the decisions made. APPROACH: The water system of the North Shore Water Commission (NSWC) serving Glendale, Whitefish Bay, and Fox Point in Wisconsin was used to demonstrate this method. The water system draws water from Lake Michigan and serves about 34,000 people. NSWC had previously used the delivered water quality monitoring technique to watch lead and copper concentrations in the water during a major system change from free chlorine to chloramine disinfection. The disinfection switch was successful, predictable, and controllable using this method. This subsequent demonstration project was carried out to show that ongoing routine monitoring can serve as a means of comprehensive consumercentric process control and process improvement. To carry out the previous and the current project, three essential tools were used. First, water quality data studied in the project followed the monitoring strategy in a CRC Press book, Water Distribution System Monitoring: A Practical Approach for Evaluating Drinking Water Quality (Cantor 2009) and included parameters that: describe the water type define the biostability of the water track water treatment chemical addition track source water and pipeline contaminants and debris track metals released from piping material to the water Next, standardized monitoring stations were strategically placed in the distribution system to routinely characterize water delivered to consumers. Any apparatus based on the Water Research Foundation pipe loops apparatus (AwwaRF and DVGW-TZW 1996) can be used for this purpose. In this project, PRS Monitoring Stations were used. The

3 stations were re-engineered from the Water Research Foundation pipe loop apparatus concept in 1997 but greatly improved in The monitoring stations are described in detail in the CRC Press book mentioned above and are an open source technology. The third tool is the use of Shewhart control charts for interpretation of monitoring data. These charts have been used in industrial quality control and process improvement since the early 20th Century. Shewhart control charts are described in detail in a SPC Press book, Understanding Statistical Process Control (Wheeler and Chambers 1992) with basic formulae and usage demonstrated in this report. In addition, other data were gathered and compared to the monitoring stations water sample data. The data sources included: Water quality data from four residences visited three times during the one-year monitoring period Lead and Copper Rule compliance sampling data from residences throughout water distribution systems since 1992 Chemical and microbiological data from the examination of monitoring stations internal metal plates after a one year exposure to the system water Water treatment plant data collected at the SCADA system, including physical data and online sensor chemical data Regulatory distribution system data Water quality data from the previous monitoring station project at NSWC Water quality data from previous monitoring station and pipe loop projects in other water systems RESULTS/CONCLUSIONS: This study demonstrated the basic structure of a comprehensive consumer-centric process control methodology. Trends in water quality at consumers taps were characterized. The information was compared to trends in the same parameters at the distribution system s entry point. The information was also compared to physical and chemical aspects of the water treatment process and influent source water. In this way, effects on the consumers water quality could be observed as seasonal, unplanned, or intentional changes occurred anywhere in the water system. In carrying out this consumer-centric method, obtaining water samples from the distribution system that are representative of the water quality that the consumer drinks is essential. The monitoring station data were shown to be indistinguishable from residential data for influent water quality. For lead, the monitoring station data were shown to be equivalent to residential water samples taken directly from lead service lines. In lead service lines, the lead-surface-area-to-water-volume ratio is similar to that in a monitoring station. But, this ratio is lower in a first-draw residential sample where plumbing materials other than lead exist. Therefore, the monitoring station lead concentration data are higher than first-draw residential sample data. The same similarity applies to the copper concentrations found in the monitoring stations. However, there are typically more copper components associated with a first-draw residential sample and,

4 therefore, it is expected that monitoring station copper concentration data and first-draw residential sample copper concentration data will be closer in magnitude than the comparative lead data previously mentioned. This was shown to be the case. Another important comparison between residential data and monitoring station data is microbiological activity, which was also found to be similar. Therefore, the monitoring stations appear to be viable tools for capturing information about consumers water quality. In addition to the water quality data taken from the monitoring stations, the internal metal plates of the PRS Monitoring Stations provide profound information on the chemical and microbiological interactions between the water and metal surfaces in the distribution system. At the end of a year of exposure to the system water, the metal plates were removed from the monitoring stations and the surface scales and films that had developed over time were studied chemically and microbiologically. This gives information similar to studying the scales and films on existing water system pipes. The information reveals the chemical compounds and biofilms that are able to form in the water environment and, therefore, defines the environment in the water system. In this way, the major factors and parameters that shape the water quality in a specific water system are identified. In this project, it was found that biofilms had formed on both the lead and copper plates. It was also found that aluminum from the alum added at the water treatment plant had precipitated significantly on the lead plates but not the copper plates. It is suspected that the crumbling or dissolution of aluminum scales with changing water environment conditions may control lead release into the water. A compound of lead and phosphate, which is assumed to slow lead release to water, was also present within the aluminum scales. Copper showed little signs of aluminum or phosphate scales and its release to water is possibly dependent on the oxidation of copper and on microbiological activity. Readily available and meaningful interpretation of water system data is also essential for effective process control. The Shewhart control charts were shown to be as useful for water system and monitoring data as they have proved to be in industrial quality control and process improvement. The charts definition of typical variation of a parameter is useful for many operational functions, such as signaling atypical behavior in the water system, providing a gauge of process improvement, and documenting consistent, high quality water in the distribution system. The comprehensive approach demonstrated in this project also illuminated the fact that a multitude of factors influence water quality. If only one factor is considered, incorrect conclusions might be made about a causal relationship between that factor and the resulting water quality. In this project, an intentional decrease in orthophosphate concentration corresponded with an increase in the lead concentration. However, data gathered on other water quality parameters in the distribution system and on water treatment operations raised doubts that the orthophosphate dosage change significantly affected the lead concentration. Hypotheses were formed concerning seasonal conditions leading to lead release and to the role that alum dosing in the water treatment process might play. If the project were to have continued past its planned end, these hypotheses

5 would have been tested by continued strategic monitoring, changes made to operations based on the findings, monitoring continued to confirm results, and so on in an iterative process of system improvement. In summary, routine gathering of the water system information, graphing of the information on Shewhart control charts, discussion of the charts in operational, management, and planning meetings provide in-depth feedback on the operation of the water system. Taking action on behalf of system improvement and stability is the next step. Then, the cycle repeats. This is comprehensive consumer-centric process control. APPLICATIONS/RECOMMENDATIONS: The report suggests a step-by-step approach in adopting this method of comprehensive consumer-centric process control. 1. Use readily available water system data with Shewhart control charts to begin studying data. a. For data on the consumers water quality, use existing regulatory distribution system disinfection data collected around the distribution system for The Total Coliform Rule. b. Use existing SCADA and online sensor data for other water system data. c. For each water quality parameter at each sampling site, enter the dates and data values into a data entry spreadsheet of the Excel add-in that comes with this report. Click the button to create the Shewhart control chart. 2. Evaluate the Shewhart control charts created in Step 1. a. When have any of the parameters exhibited a significant change from typical water system operation as defined by the Shewhart control chart rules of interpretation discussed in this report? b. Do the data exhibit any trends? c. Do parameters have a wide or narrow variation? d. Do average values of the parameters meet water system goals? e. What operational changes might bring parameters to the desired average values and narrow the variability of the parameters? 3. Make operational changes proposed in Step 2 and continue to collect and study the readily available water system data. a. Are the new goals being met? b. Adjust operations accordingly. c. Iterate steps 1, 2, and 3 for process improvement. 4. When comfortable with this method, carry out a more comprehensive monitoring strategy to build a bigger picture of delivered water quality. a. Add the study of metal transfer and biostability to the monitoring strategy by using one or more monitoring apparatuses (derived from the pipe loop concept) strategically placed in the distribution system. b. Join industry-wide water system improvement efforts, such as those promoted by the American Water Works Association, for encouragement and general guidance.

6 5. Keep the monitoring efforts going. A comprehensive consumer-centric process control methodology includes an iterative series of monitoring, evaluation, and decision-making. That is, collect data, create charts, apply the chart rules of interpretation, discuss charts in daily, weekly, and planning meetings, troubleshoot issues, make system changes for improvement, collect data, etc. Benefits to Water Utilities There are many benefits of adopting this method: System operation o Triggering the need to troubleshoot equipment or other system operations o Saving money on treatment chemicals o Minimizing temporary water quality degradation o Evaluating system operations routinely Lead and Copper Rule Issues o Studying lead and copper transfer to water in the context of the whole water system with its multitude of influencing factors o Serving as a surrogate for residential sampling so that lead and copper concentration trends can be known routinely instead of being glimpsed every three years o Aiding in the determination of the mechanism or mechanisms of lead and copper transfer into the water specific to the water system o Establishing key water system water quality parameters that are relevant to the individual water system instead of general parameters listed in a regulation to be applied to all water systems o Monitoring and controlling the key water system water quality parameters, especially those that can be controlled at the water treatment plant to keep them at the desired level with narrow variation; variation of key parameters can cause variation in lead and copper release to water o Monitoring and controlling system transitions, such as changes in corrosion control chemicals, changes in water sources, and changes in disinfection or other water treatment, in order to achieve simultaneous compliance with drinking water regulations o Determining the need for corrosion control chemicals o Comparing and selecting corrosion control chemicals Beyond Lead and Copper Rule Issues o Assessing and controlling biostability of water, aiding in setting an appropriate disinfection concentration, and staying in compliance with the Total Coliform Rule o Assessing cleanliness of the piping system o Developing hypotheses for further research on a system level and on a national level A Comprehensive Consumer-centric Process Control Methodology o Establishing a water quality control methodology o Establishing a water system process improvement methodology

7 MULTIMEDIA: A Microsoft Excel add-in is provided with this report so that the reader can begin to work with Shewhart control charts on data taken over time. The add-in is included with the report on CD-ROM. The add-in calculates Shewhart control chart statistics and creates graphs of time-series data with the associated statistics. RESEARCH PARTNER: North Shore Water Commission