Environmental Engineering-I

- ByProf S S Jahagirdar

How much is Acceptable?

If Water loss is

1. 5 to 7 % then it is acceptable

2. 10 to 20 % then it is unsatisfactory :-action is advisable

3. Beyond 20% :- remedial measure must be immediately taken

Causes of leakage in mainsCorrosion

Cracks

Faulty joints

Fixtures in consumers premises – faulty washers, valves and taps, not closing the taps knowingly or unknowingly

Usually, wastages from reservoirs cannot be accounted for metering

Types of leakages

Leakage can lead to:

—consumer inconvenience , by reducing pressure at taps, appliances and showers, etc.;

—damage to infrastructure , by creating voids which can lead to collapse of highways and buildings;

—increased loading on sewers due to infiltration, leading to the need to over-design sewer capacity;

—excessive costs, not only from compensation payments and from repairs to damaged structures, but also production costs (if leakage is 50% of production, energy and treatment costs have been doubled);

—introduction of air into the distribution network if the water supply is intermittent, causing damage to meters, and leading to over-measurement of the true consumption and errors in water bills;

—health risks, in low pressure systems or where the supply is intermittent, by allowing infiltration of sewage and other pollutants into the pipe network.

Pressure

Soil movement

Pipe condition

Poor quality materials and workmanship

Soil characteristics

Traffic loading

Leakage control method

The water losses can be termed into two categories.

1. Physical losses (Technical or real losses)

2. Non-physical losses (Non-technical losses/Commercial or apparent losses).

Physical Losses

This is mainly due to leakage of water in the net work and comprises of physical losses from pipes, joints & fittings, reservoirs & overflows of reservoirs & sumps.

Non Physical Losses- Theft of water through illegal, already

disconnected connections,

- under-billing either deliberately or through defective meters,

- water wasted by consumer through open or leaky taps,

- errors in estimating flat rate consumption,

- public stand posts and hydrants

Water Audit

The objective of water audit is to assess the following.

i) Water produced,

ii) Water used,

iii) Losses both physical and non-physical,

iv) To identify and priorities areas which need immediate attention for control.

Fixing bulk meters

Leakage detection methods1. By visual inspection

2. By using sounding rods or

3. electronic leak detectors or

4. using radioactive isotopes etc

5. By plotting Hydraulic Gradient Lines

1.Visual inspectionWalking over the main looking for signs of presence of stagnant water over ground.

Stagnant water presence depends upon soil characteristics.

Many times difficult to find out exact location of leak,

2. Sounding rodThe sound made by water leaking from a

pipe is the basis for the majority of leak locating techniques.

Under traditional sounding air inspector uses the simplest instrument for leak detection a listening rod or the sounding rod.

This is prepared from a 12 mm light steel rod of 1.2 to 1.5 m long. At the top of the rod a brass bowl of 25 mm is fixed.

To locate the exact leaky point the rod is moved on the ground surface along the center line of the alignment of the buried pipeline, by keeping the ear on the top of the rod.

The vibration due to the leak is picked by the sounding rod and converted into sound and is heard by human ear.

The sound emitted by a leak is a ‘low drumming noise’ or ‘continuous buzzing sound’ and tends to be continuous without any change of audibility or quality.

It stops abruptly when and if, the water can be turned off. Thus locating the possible leak is identified.

Sounding should be done at night when the background noise is low. It is absolutely necessary that the persons be trained properly in using this technique.

3. The theory of Water Leak Detection using acoustics: using ground microphone

When a pressurized water pipe develops a leak the water flows out into the surrounding ground at high speed, which causes the pipe and soil to vibrate at the exit point.

This sound, or vibration, is transmitted by the pipe, (structure borne) and surrounding material (ground borne) where it can be heard with the highly sensitive microphones.

Electronic leak detector consists of a ground microphone, amplifier and headphone.

The electronic leak detector is sensitive and can pinpoint the position of the leaks.

Modern electronic leak detection devices permit discrete filtering of many background sounds that compete with the sound of leak itself.

Ground Microphone

4. Beta Radiation in Leak DetectionLeaks in underground pipelines can be

detected by the injection of a radioactive isotope.

This is achieved by adding a small amount of a radioisotope which is a source of beta radiation to the fluid.

The area above ground where a high intensity of beta radiation is detected will pin point the leak source in the pipeline. This saves time as the correct area is dug up.

Use of radioactive isotopes

Sodium 24

It is important to use a radioisotope with a half life of a few hours or days.

This is so it remains long enough for the leak to be detected but not too long that it may pose a safety or health risk. Sodium 24 is an example of a radioisotope used in leak detection. It has a half life of about 15 hours and emits beta radiation along with gamma radiation.

5. By plotting hydraulic gradient linesIn this method , the pressures at

various points of suspected pipe line are measured.

Hydraulic gradient line is plotted.

The appearance of any change in slope of hydraulic gradient line indicates the location of leak in the pipe line

MaintainaceMaintainace should include

1. Periodical inspection of source, intake, treatment plant units, storage reservoirs, pipes, valves, meters, connections etc.

2. Flushing (Cleaning) of pipes by

- Water

- Air

- Swabbing

3. Replacing the damaged pipes before life span

4. Speedy and quality repairs of joints, valves and pipes

5.Regular Water quality monitoring.

6. Proper leak detection and management system

7. Keeping check on unauthorised connections

8. Carrying out water audit

9. Pressure management in the system

Advantages of Pressurized water supply

i. Sufficient head will be available even during peak demands.

ii. In case of fire break out water will be available in sufficient quantity and pressure.

iii.Less possibility of wastewater entry and contamination as flow is full and under pressure.

iv. No possibility of accumulation of solids within the pipe network

v. Infiltration is not possible easily.

vi. saving pumping cost at user ends.

Variation in water quality in distribution system

Improper design and operation may result in water of diminished quality in terms of increased water age, reduced disinfectant residual, increased growth of disinfectant by-products and bacterial levels, and may impact the level of compliance with current and impending water-quality regulations

Theory questionsQ1. Enlist various leak detection methods

and explain any two in detail

Q2. Write short note on

1. Sounding rod for leak detection

2. Advantages of Pressurized water distribution systems

3. Maintenance of water distribution system