Preventative Solutions for Water Distribution Systems

Preventative Solutions for Water Distribution Systems

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Water Quality Challenges
As a function, water quality is dependent on the quality of the source water, the treatment given to that water, the condition of pipes in the distribution system and the amount of time water stays in those pipes.  From a water distribution system perspective, utilities have control over the physical condition of pipes, and the flow of water in them.  Utilities can replace pipe, rehabilitate pipe, re-direct the flow and increase the pressures.

Unfortunately, in most water systems, between 3 and 10 percent of all valves are incorrectly closed.  This creates undocumented dead ends thus increasing the amount of sediment and the age of water on either side of the undocumented dead ends.  These dead ends are the result of several problems that range from lack of documented control over valve closures to contractors who do their own shutdowns.  The impact on water age, corrosion, biofilm accumulation and related water quality problems are significant in their own right and place a higher demand on disinfectant to maintain residuals at points in the water distribution system which are much further away from the source than they were thought to be.

It is very common for long segments of transmission main to be pressurized through water distribution system mains and as such have very low flow conditions and abnormally high water age.  In these cases, the system's behavior cannot be accurately modeled, the hydraulic grade line is compromised and the problem is frequently undetected until a major client is negatively impacted.

Wachs Water Services Solution - is to develop and implement a comprehensive unidirectional flushing program.  Our approach is to perform a field survey of all assets, resolve mapping system problems, open closed valves and make the field conditions match the mapping and hydraulic modeling systems.  Once this has been completed we repair the assets deemed necessary for executing the unidirectional flushing program, design the unidirectional flushing sequences and execute them in the field.  During the execution phase of the program we take water samples testing before and after.  During the field survey phase we test valves and fire hydrants so that we know the flow conditions and also verify that all of the valves are in the open position.  The end result of this approach is:

  • Business systems match field conditions
  • Physical assets reliability is improved
  • Undocumented dead ends are eliminated
  • Demand for disinfectant is reduced and
  • Water quality is improved!

Water Loss Challenges
In the simplest terms, water loss is what is left from the system input volume after authorized consumption has been subtracted.  This loss is stated either as being real or apparent where real loss is what's left after accounting for unauthorized consumption and metering problems; be they input volume or sales volume problems.  Water loss is actionable when it's quantified and when it's determined to be above the economical level of losses - either apparent or real.  Utilities can repair leaks, they can repair meters and they can match the size and type of meter to the quantity of flow so that they will register accurately. 

As a first step, utilities conduct a top down water audit.  In many cases, this desktop study is driven by estimates that are based on a generally lacking data set.  In particular, estimates of:

  • Authorized but unmetered consumption
  • Unauthorized consumption which cannot be metered and
  • Observed leakage during main breaks

In these instances the utility responds by instituting measures for authorized unmetered consumption, such as flushing, and they attempt to better estimate leakage during main breaks.  This leaves the matter of theft which is conservatively estimated in most top-down water audits.  As a result the estimates for non-surfacing / unreported leakage tend to be less conservative.  They are by definition overstated and as such trigger a response when higher than the economical level of real losses.

There are four responses when economical levels of real loss are exceeded; manage pressure, find leaks, fix them and start the bottom-up water audit to get a better handle on the estimated values and include a more thorough look at metering.  Predictably though, leak detection results are inconsistent with real loss estimates; field measurements indicate that real loss is substantially lower than what has been suggested by the initial top-down desktop water audit.  Under these circumstances, the pendulum has a tendency to swing back toward estimated values.

The problem, in part, is that the technology used to perform leak detection on distribution system mains is highly dependent on several variables that can be observed.  The most observable leaks are: on metal pipe, under high pressure, nearby places to listen, not pooling, on pipe segments with only a single leak and in parts of the water system with low ambient noise levels.  When none of these conditions are present then the leak is undetectable by conventional means.

Wachs Water Services Solution - is to employ proprietary in-pipe leak detection systems that are suited to distribution and transmission mains.   This means that the results do not rely on any of the observable variables.  Rather, leak detection relies entirely on accessibility to the mains; we enter through fire hydrants or taps.  This means that we would establish more certain figure for real loss as a first step and then back into the estimates.  In other words by changing the order and applying new technologies we can establish - very closely - real loss numbers that are based on many thousands of pipe insertions worldwide and avoid the costly mistake of overemphasizing real loss.

Overstating real loss can cause unnecessary, difficult and expensive hydraulic grade line changes which are problematic to manage and can create water age problems increasing the demand for disinfectant and the byproduct precipitants associated with them.  As a next step utilizing actual pressure, flow and leakage data, DMAs can be designed and implemented as a preventative measure against leakage and wearing of pipeline appurtenances.

Asset Reliability Challenges
As a function, reliability is dependent on the residual life and the condition of a given asset expressed as the sum of its functional characteristics.  As a term, asset reliability is a statement of the probability that an asset will perform its intended function during routine and extraordinary circumstances.  As an aggregate, asset reliability tells the utility how exposed they are to the consequences of failure; by way of probability.  While utilities can not control the passage of time, they can control the impact time has on the functional characteristics of assets.  By limiting the probability of failure through improved asset reliability utilities can sensibly expect to reduce the cost and frequency of both preventative and reactionary maintenance.

Preplanned Construction

The Problem - construction shutdowns take too long because they are continuously being backed-up causing contractor delay charges and prolonging the water outages.  Operability is an indicator of reliability.  Over time, valve operability declines; sediment and corrosion build up along gate guides and on the stem itself, valves are covered over by pavement, operating nuts become rounded and the list goes on and on.  Lack of preventative maintenance and lack of coordination leads to widespread asset reliability problems.

Reactionary Construction
The Problem - emergency service requests increase over time and the cost for responding to them also increases over time.  It stands to reason that aging infrastructure combined with modest inflation will precipitate higher costs over the long term.  The costs, however, are not linear.  In areas where the consequences of failure are higher, the costs are dramatically higher.  In areas where valve operability is very low the costs are again, dramatically higher.  The degradation curve of asset reliability, over time, can vary significantly due to an array of environmental circumstances that range from lack of maintenance to the makeup of water, system demands, transient pressures and many others.

Wachs Water Services Solution - is to ascertain the current level of reliability system wide and target reliability where it counts most by reducing the probability of failure where the consequences of failure are highest and where preplanned construction is required.  This involves sampling, geo-statistical analysis, hydraulic modeling and field activities to ultimately catch-up the lacking preventative maintenance strategically and develop a long term plan built around the cost effectiveness of practical risk mitigation.

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Water Distribution Systems Solutions

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Wachs Water Services is the leading provider of water distribution system asset management solutions that significantly improve efficiency and network control. Our specialized approach combines condition assessment and rehabilitation services for valves, hydrants and water mains with the capture and integration of critical water asset GIS information. We provide the expertise, equipment and personnel to locate, assess, operate and document virtually any water asset.