Case Studies to Identify Occurrence, Accuracy and Causes of Reverse Flow Using Meter Systems

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1 Executive Summary Case Studies to Identify Occurrence, Accuracy and Causes of Reverse Flow Using Meter Systems Project Number: 4384 Date Available: November 2016 Principal Investigators: Orren D. Schneider, David M. Hughes, and Minhua Xu, American Water; and Steven L. Barfuss, Utah Water Research Laboratory Project Advisory Committee: Paolo Scardina, Virginia Tech; Thomas Kelly, Washington Suburban Sanitary Commission; and Dan Strub, Austin Water Utility Quick Facts Five types of meters were tested for reverse flow accuracy. Nutating disc and electromagnetic meters showed high accuracy, while jet meters (both single and multi-jet) showed far less accuracy. The fluidic oscillating meter was not capable of registering in reverse at all. The project team identified five separate categories of backflows. The category may be indicative of how and where a utility should investigate. The presentation of data using graphic display can assist in prioritizing which backflow events to investigate. waterrf.org

2 Background Water distribution system research, data from pressure monitoring studies, and hydraulic modeling suggest that periods of low pressure (pressure transients) routinely occur in many water systems. Backflow is a condition where water reenters the distribution system from service lines when distribution system pressures become lower than those in the service lines. Backflow is a recognized threat to the integrity of public water systems, and, depending on the nature of the backflow, it may have serious public health consequences. Backflow implies contamination via reverse flow from customer supply lines or intrusion through pipe flaws (pipe/main breaks) from the surrounding environment. The WRF report Determining Vulnerability and Occurrence of Residential Backflow (Schneider et al. 2010) demonstrated, in four distribution systems, that reverse flow sensing meters (from a single company) could be used to detect possible backflow events. Based on these four systems, an average backflow occurrence rate of 1.6% per month was ascertained. Because there are typically many more meters installed in a system than pressure recorders, the project concluded that reverse flow sensing meters appear to be the best currently available method for determining residential backflow occurrence. Objectives The objective of this project was to use reverse flow sensing meters to better understand the frequency of reverse flow and identify the conditions in distribution systems that promote backflow. The project developed guidance for utilities on reducing the occurrence and severity of reverse flow promoting conditions. This guidance is based upon data collected from a variety of utilities from reverse flow sensing meters; in-depth case studies of backflow promoting conditions; and development and application of, and results from, a testing protocol for the accuracy of reverse flow sensing meters. The project included five tasks: Approach Product Review Meter Testing Utility Screening and Reverse Flow Data Collection Case Studies Reverse Flow Investigation and Remediation Tools Results/Conclusions A review of residential water meters, Automatic Meter Reading (AMR), and Advanced Metering Infrastructure (AMI) systems has shown that numerous meter communicating systems exist to detect reverse flows and transmit data from residential meters to utilities. These systems are available in a number of different meter and transmitter products and from different meter/amr/ami manufacturers. The systems can vary in how frequently they check for reverse flow and the threshold of detection. Twelve different meter models, representing five different types of meters, were selected for reverse flow accuracy testing. The test procedure involved running a precise volume of water through the meters in the forward direction, and then removing the meters and testing the accuracy of the meters flowing in reverse. Following this reverse flow accuracy test, more water was sent through the meter in the forward direction. Reverse flow accuracy tests were performed at 0, ¼, ½, ¾, and full-life of the meters rated lives based on the anticipated volume of full life meters. The results of the accuracy testing showed that accuracy varied substantially across the meter types. Nutating disc and electromagnetic meters showed high accuracy in reverse direction, while jet meters (both single and multi-jet) showed far less accuracy. The fluidic oscillating meter was not capable of registering in reverse at all. In addition, there was less 2 Causes of Reverse Flow project # Water Research Foundation. ALL RIGHTS RESERVED.

3 variation across meter sizes (ranging from ⅝ʺ ¾ʺ to 1½ʺ). In other words, if a specific model of meter was accurate at one size, it was generally accurate at different sizes. For utilities that wish to monitor reverse flows, it is suggested that they conduct their own reviews and meter testing. Data collected from over 60 districts in the American Water system during the period of September 2012 through August 2013 were used to create a large database of meter reads (over 1,000,000 individual meter reads). This database showed over 14,500 separate reports of reverse flows, with monthly occurrence ranging from a low of 535 reports in September 2012 to a high of 1,761 reports in March The occurrences showed a strong seasonal trend, with the highest numbers in late winter/early spring and the lowest in the late summer/early autumn. It is hypothesized that the high number of reverse flow instances is related to water main breaks and the expansion in water from heating in hot water tanks. With the advent of a new meter data management system at American Water, which was instituted during 2015, a more comprehensive analysis that distinguished between major (10 gallons or more) and minor backflows was conducted to cover all activity during This supplemental study demonstrated that the vast majority of backflows are minor in nature. The data from major backflows were organized in spreadsheet form from the meter data management system and covered several months. Data were then used to detect the categories of backflows and prioritize subsequent investigations. These spreadsheets were later augmented by graphic displays of data that aided in rapid identification of possible operational issues from multiple backflows in neighborhoods (meter routes) and individual locations with repeated backflow events over time. Applications/Recommendations Based on these collected data, five separate categories of backflows in individual systems were created: Type 1: Isolated events unique over the course of a year occurring at only one location within a meter route/neighborhood/pressure zone. Type 2: Isolated events happening multiple times in only one location in an area, meter route or pressure zone. Type 3: Multiple events over the course of a year occurring in only one location within a neighborhood/meter route/pressure zone. Type 4: Multiple events happening multiple times in several locations within a neighborhood/meter route/pressure zone. Type 5: Multiple events occurring system-wide across multiple pressure zones. The type of backflow may be indicative of how and where a utility should investigate. For instance, a type 2 backflow (single event, multiple residences) may be related to a water main break, while a type 3 backflow (single house, multiple occurrences) may be related to meter tampering or an unknown customer well pumping into the distribution system. A type 4 or 5 backflow (multiple occurrences, multiple residences, and multiple pressure zones) may be related to pumping issues at a treatment plant. A type 1 backflow (single residence, single occurrence) would be hard to investigate, as no clear trend exists. If other backflow sensing meters exist in the immediate proximity and none record the event, then it may not be possible to identify a root cause or take remedial actions. One significant element missing in the initial analysis was the ability to differentiate high backflow from low backflow across the surveyed area. The meter manufacturer provided two flags: one detecting backflow between 0.1 gallons and 9.9 gallons (minor backflow) and one detecting major backflow (10 gallons and over). A delay in the implementation of a meter data management (MDM) system until 2015 hampered the extent of the results that could be generated by the intelligent meters. The delay also shifted the case study focus in the first phase of the project to a general population of backflows consisting of what turned out to be minor backflows instead of targeting the more significant backflow events. However, the case studies did serve to confirm that minor backflows, sensitive down to 0.1 gallons in 15-minute 2016 Water Research Foundation. ALL RIGHTS RESERVED. project #4384 Causes of Reverse Flow 3

4 intervals, were indeed trending towards the low end of the 0.1 to 10 gallon (in 15-minutes) range. The manufacturer who created this low sensitivity designed this approach to verify that systems with universal backflow prevention were working effectively. However, the vast majority of water systems do not have universal backflow prevention, and the minor backflow detection for such systems has minimal value except in locations that do have backflow prevention. The case study investigations revealed that most backflows monitored are small (less than 0.5 gallons measured in 15- minute intervals). It is surmised that water expansion in the hot water tank during water heating is a major contributor. This appeared to be confirmed by the case studies as researchers studied when and where these minor backflows were detected. This small volume matches up well with expansion calculations. If one assumes that a large hot water heater (80 gallons, twice the typical residential heater) is half-full of 140 F water after heavy use and 40 new gallons of 40 F water enter the tank, then the change in volume due to thermal expansion is: ΔV = V Coefficient of expansion ΔT where the coefficient of expansion for water is / F; V, the volume introduced is 40 gallons; and ΔT, the change in temperature is 100 F. This change in volume equals 0.48 gallons and is equivalent to a displacement of 21 feet in a ¾ʺ diameter pipe or 12 feet of 1ʺ diameter pipe. It is also important to keep in mind that the expansion may take place over a significant amount of time (>15 minutes), and thus the flow volume may not be fully captured by a residential meter. As these linear distances are likely less than the length of interior plumbing from the water heater and the length of a service line connection, this water is most likely just moving back and forth through a single premise connection. Thus, the water that had previously been in the hot water tank is not re-entering the transmission main. Therefore, the risk of any contamination reaching the transmission main by this vector is judged to be low. In the case study utilities, there was one pressure reducing valve (PRV)-fed system with AMI that was able to differentiate between major and minor backflows over the course of the project. A handful of larger reverse flow events captured in this AMI system were related to water main breaks or water system shutdown activities that created losses of system pressure. Several cases showed large volumes of reverse flow that we believe were caused by air flowing through open fixtures at the customer location as pipes were drained. In 2013, American Water started deploying a meter and transmitter from another manufacturer that had reverse flow detecting capability located in the transmitter (the intelligence shifted to the transmitter from the meter). This system raises an alarm with a 10-gallon threshold, but only if the negative volume lasts for six hours. Six hours is more time than needed to perform most utility operations, such as main break repairs. As a result, the devices of this type discovered only a few significant reverse flows, typically caused by meters installed in reverse. Most of these cases appeared to be due to errors in installation rather than customer manipulation/tampering. Significant concern would exist for either case pointing to a need to revise installation and monitoring procedures. This includes utility response to customers manipulating their meters to reduce billed consumption. As the MDM system was installed and meters read, major reverse flows were identified in selected systems. However, the overwhelming number of backflows appear to be minor backflows. This was confirmed in Phase 2. During the investigations into the causes of reported major backflows, it was discovered through datalogging that a large number of these were not actually backflows, but were false positives due to a meter manufacturing error. Hourly datalog results showed what appeared to be an incorrect elevated read followed by a correction that produced a negative value and a major backflow alarm. Working with the manufacturer, the project team was able to determine that 14,000 meters made in 2011 had possible issues, though only a small percentage showed the pattern of repeated major backflow alarms. It was necessary to identify these cases before moving forward with the analysis. 4 Causes of Reverse Flow project # Water Research Foundation. ALL RIGHTS RESERVED.

5 Subsequent case study examination that focused on major backflows identified causes such as serious breaks, utility water shutdowns, and meters set in reverse as major factors. Monitoring supported by datalogging and utility operation awareness appears to be most useful in determining corrective action. Identifying isolated cases is the most difficult issue to address, and examination of meter data over an extended period is the best approach to observe trends and resolve system and customer issues. Case studies in Phase 2 focused on proper procedures for analyzing the database of backflow data and categorizing the five categories of backflow. One case study did identify a faulty backflow preventer, showing the value of the intelligent meter component when placed on larger meters. Some systems today offer flexibility in setting the backflow quantity and timing. The 10-gallon measure is a significant amount of backflow, but the causes appear to be limited to meters set in reverse, water main breaks, and related shutdowns of portions of the distribution system. A setting of one gallon may have merit, as it would represent the potential for a backflow event to cause contamination issues within the customer s plumbing. The 15-minute duration found in the majority of the devices was useful. The more typical datalogging capability of current AMR systems and AMI monitoring is one hour, which appears to be sufficient to capture events of significance. During the project, methods to confirm and investigate reverse flow evolved with improved monitoring and investigative tools. Many AMR systems can log data on an hourly basis to help determine when the reverse flow occurred. This enables a utility to go back in time and see hourly reads from a recent backflow alarm. Solid-state electronic register heads are replacing mechanical registers, and these offer reverse flow detection. One manufacturer developed electronic register heads that can be adapted to any standard meter body and have a cellular AMI to transmit at 5-minute intervals. This makes an excellent temporary tool to investigate repeated backflow alerts. Most AMI systems bring the hourly data into an MDM system that provides instant analysis and automatic alarms or reports. Other tools include pressure monitoring and onsite inspections. All of these tools will serve to improve system awareness and customer service. The presentation of data using graphic display can assist the utility in prioritizing the major backflow events. New Jersey American Water successfully extracted data from the MDM system to display events that impact multiple locations and identify individual locations with repeated reverse flow. The cause for neighborhood reverse flow events could be readily traced using additional overlays of main break repairs and work activity. Spreadsheet data could also be analyzed using timelines of major reverse flows over extended periods. When utilities are selecting meter reading and meter data management systems, the value of reverse flow and continuous flow monitoring capability should be considered. While it appears that many cases of minor backflow may be occurring, knowing where more significant reverse flow events happen can provide improvements for meter and distribution system operations. During the project, American Water identified the following conditions that merited investigation. The impact of distribution system events, including main breaks, flushing, and maintenance. The most monitored types of major backflow events were main breaks and subsequent shutdowns where required. This was especially noticeable in pressure zones with variation in elevation, where severe leaks in a main in an old pipe network in a valley impacted outlying areas at higher elevations. A few events captured air flowing through service lines reversing the meter to replace the water draining from the pipe. Such conditions suggest the potential for a main collapse if air is not introduced. In such cases, two-way air releases may serve to avoid reliance on a customer leaving a faucet open when no water is coming out. For maintenance activities with shutdowns, depressurizing from a hydrant at low elevation may also require an open connection to let water in (and probably expedite dewatering). In the same way, care should be taken with hydrant flushing and its impact on the system. When a backflow is detected, it may be worthwhile to match the event with activities including breaks and flushing Water Research Foundation. ALL RIGHTS RESERVED. project #4384 Causes of Reverse Flow 5

6 A number of water meters were identified and found running backwards, most apparently installed that way. Prompt detection of meters running in reverse will likely alleviate issues with the customer. For some American Water operations, the indication of a negative read was assumed to be a meter turning over (going from to 000wx, not from 0 to 999yz). In some systems the mechanism to estimate the bill is used, but there is no alert that the meter is running backwards. This was corrected during the project. Unfortunately, the potential for customers to reverse their meters on a periodic basis to lower their bills is a possibility, and detection may be more likely with the advent of AMR and AMI. The isolated customer who shows a pattern of repeated major backflows and low consumption can be identified, and steps can be taken as needed to confirm meter manipulation. While the target of the study is termed the residential meter, any customer service outfitted with the reverse flowing sensing meter or transmitter can appear. Monitoring can serve as a check on backflow preventers or to identify a customer who may need one. It is recognized that this is after an event, but the objective will be to prevent future issues. One of the case studies featured an industrial facility with nearly continuous use where frequent, though minor, backflows were observed. As a result, the customer was required to install an approved backflow preventer. Backflow can be an indication of improper pressure regulation in the distribution system. While American Water did not detect such a situation, one area of backflow in a neighborhood did appear to merit pressure monitoring. Related WRF Research Determining Vulnerability and Occurrence of Residential Backflow, project #3022 Advanced Metering Infrastructure: Best Practices for Water Utilities, project #4000 Accuracy of In-Service Water Meters and Low and High Flow Rates, project #4028 AMR/AMI Standardization for Drinking Water Systems, project # Causes of Reverse Flow project # Water Research Foundation. ALL RIGHTS RESERVED.