Page 136 - Trenchless Technology Piping Installation and Inspection

102 Cha pte r T h ree

concentrated slug of chlorine is added to the pipe and slowly forced
through the system. The concentration of the slug is monitored and if
the free chlorine residual drops below 50 mg/L, additional amount of
chlorine is added. Several utilities use this method at a concentration
of 300 to 500 mg/L. Disposal and treatment of the heavily chlorinated
water can become a problem with this method (ANSI/AWWA,
2005).

3.9.4 Ozonation
Ozone being an unstable molecule of oxygen, which readily gives
up one atom of oxygen providing a powerful oxidizing agent, is
toxic to most waterborne organisms. Ozonation is an effective
method to inactivate harmful protozoans from forming cysts.
This method also works well against almost all other pathogens.
Ozone gas is prepared by passing oxygen through ultraviolet
light or using a “cold” electrical discharge. To use ozone as a dis-
infectant, it must be created on-site and added to the water by
bubble contact.

3.9.5 U.K. Method
According to “Technical Guidance Notes No. 4—Distributor System
(Renovated Mains),” contained in Principles of Water Supply Hygiene
and Technical Guidance Notes, the lined pipe must be disinfected using a
maximum of 0.013 oz/gal (100 mg/L) of free chlorine. After the dis-
infection, the lined pipe must be flushed for a minimum period of
one hour at a velocity of 1.64 ft/s (0.5 m/s) for available water pipes
before return to service. For lined pipe sections with dead ends, a
flow regime must be established such that the residence time does
not exceed one hour in the first 24 hours of service after recommis-
sioning (Water UK, 2007).

3.10 Pipe Sample Testing
Table 3.3 presents some of the coatings and lining testing methods
based on ASTM standards.

3.11 Quality Control
The liner quality must be acceptable if proper cleaning and application
procedures are followed. Project documentation, for delivery to the
project owner, may include testing results from laboratory (if required);
printouts from the lining rig, postinspection DVD, and so on. Table 3.4
presents a description of common defects found after the application
of the lining and its recommended prevention and remedies.