CHAPTER 3: REVIEW OF EWS NRW AND OPERATIONAL METHODOLOGIES
3.6 CLEANSING THE DATA – ENSURING ITS CORRECT
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Figure 3.26: Category B Plumbing Leak Detection and Repair. (Photo courtesy of Mr Chris Otto, 2010)
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laboratory tests, asset management data and the finance data. Sensitivity analyses can be conducted to test the outcome of the proposed decisions and data variances.
It is an on-going exercise to improve the accuracy of the existing information in the GIS as well as to ensure that any changes or additions are accurately captured. It is acknowledged that the faults data is not only incomplete but also difficult to extract and interpret and therefore significant improvements are scheduled in this area. An asset management plan has been drafted to ensure that the meters in the system and particular care is taken when specifying and procuring water meters. As mentioned, the number of real time measurements being recorded in the system is scheduled to be significantly increased. The laboratory already conducts more than double the required number of tests on the potable water in the system and as the laboratory has ISO 90001 accreditation, this data is deemed to have the highest integrity and reliability. Asset management systems still need to be put in place so that the knowledge of the condition of the system components and the scheduled maintenance thereon can be easily determined. The financial data is accurate but some cost centres should be disaggregated so that for example, better data on the cost of repairs can be extracted and used in other calculations.
Regardless of the level of sophistication and computerization involved, each Utility should collect information concerning system conditions, implement preventive maintenance measures, identify chronically failing mains, and prioritize these mains for repair or replacement. The Utility policy and replacement criteria may change from year to year, but the basic process remains the same (USEPA, 2007).
No reference whatsoever could be found in the material that was covered in the research with regard to the accuracy of the performance data and the need to cleanse this data before using it.
The literature published by academics demonstrates that they tend to examine problems in sterile laboratory type conditions and these conditions do not resemble the reality of live infrastructure.
It is necessary to undertake a number of steps to ensure that any zone performance data is indicative of the zone that it is supposed to represent. A number of obvious errors can take place, which unless procedures are in place to eliminate the obvious will give rise to totally skewed results leading to premature mains replacement. It is possible that these new mains would continue to perform much the same way that their predecessors did unless these fundamentals have been eliminated first. Some examples of this would be:
• Excessive pressures in a system will result in higher loss rates and burst frequencies. Pressures must therefore be minimised to latest design standards prior to any motivation to replace.
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• Pressure reducing valves (PRV’s) in a reticulation system that are not working correctly can also lead to a high number of bursts occurring and the solution is to ensure that all PRV’s are set correctly and adequately maintained in order to prevent these pressure related bursts from occurring.
• Pressure spikes in a system can also result in high burst frequencies. The cause of these pressure spikes must be determined and eliminated and the system allowed to stabilise before the burst frequency is determined. It is noted that these spikes can emanate from either the municipal infrastructure or the spikes can be caused by equipment being operated incorrectly on the consumers premises.
• A breach in the boundary of a predetermined zone can lead to either water leaving a zone without be quantified or water can enter the zone and seem to improve the performance data. Step testing and proving zone isolation is thus a vital step that must be taken to prove that the water loss figures in the zone are indeed credible.
• The bulk meters in a zone must be verified to ensure that they are accurate as they can either under or over-read. A mechanical meter can be damaged due to debris in the pipeline or may simply slow down over time due to wear and tear. An electronic meter can be damaged by stray currents, lightning, wear and tear, cable damage, coil damage, misalignment, internal pipe restrictions, and air to mention a few causes. The initial installation of any meter could be outside the manufacturers’ specification and perform inaccurately from the day it is commissioned. It is therefore a requirement that a continual programme of bulk meter improvement is embarked upon to ensure that these readings are as accurate as possible. A bulk meter at a reservoir can be quickly tested by performing a drop test and the cartridge of a mechanical meter can be changed out at a relatively low cost. Insertion probe magnetic flow meters, insertion turbine meters and strap-on ultrasonic meters can be utilised to check the accuracy of meters in-situ and it would be advisable at the time of installation to plan ahead for these checks to take place.
• One must ensure that active leak detection has been carried out in any zone that has been flagged for replacement. This may have the result that a number of leaks are found and the system performs adequately thereafter and replacement is not required. Alternatively, successive sweeps of leak detection could repeatedly find a high number of leaks resulting in high repair costs and this money could have been used better if channelled towards replacement and not repairs.
• Scour valves could be left open that discharge to either a storm water pipe or a river and this undetected flow could indicate a false level of very high leakage.
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• In the South African context, there is a poor culture of payment in certain environments and illegal connections are rife. It is estimate that there are some 40 000 such illegal connections in the eThekwini operational area and these unmetered flows can lead a practitioner to conclude that there are high levels of leakage, when in fact these losses are due to theft. A Waste Water Treatment Works (WWTW) water balance has been conducted and it can be seen in some circumstances the inflow to the works exceeds the water sold in the WWTW zone.
These results (not highlighted in pink) are shown in Appendix F. It is therefore a requirement that social campaigns are run either prior to or during a mains replacement programme. A change in consumer behavior could potentially eliminate the need to replace the mains. Another outcome is that after the mains have been replaced, all consumer data is accurate and that all the consumers are paying for the water that they consume.
• It is equally important to determine the modes of failures within a zone and also the causes for these failures. The remedial works can thus be tailored to ensure that these problems do not reoccur. It could be, for example, that a high number of faults occur in a zone triggering potential mains replacement, but upon investigation it could be found that these failures are caused by a poor batch of saddles or by consumer tampering. The performance of the zone could be improved for a fraction of the cost if just the saddles are replaced or consumers are persuaded not to interfere with the municipal infrastructure.
• External damage can occur in an area when another activity takes place alongside an existing water main. For example, another service provider could be installing a fibre optic cable and their activities lead to a high incidence of faults or a roads contractors equipment could be working in close proximity to a water main leading to an unusually high number of faults.
• The workmanship of poorly trained plumbers working to repair existing faults could lead to repeat faults occurring in the system giving the false impression that the main is approaching the end of its service life.
• Similarly, the use of poor quality repair material will also lead to the same fault occurring repeatedly and this could lead the practitioner to falsely conclude that there are a high number of faults occurring in a particular area.
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