Disinfection of Pipelines - Disinfection of Pipelines and Storage Facilities Field Guide - page 31

6. Collect samples in sterile bottles treated with sodium
thiosulfate as required by Standard Methods for the
Examination of Water and Wastewater . Do not use hose or
fire hydrants for the collection of samples. A combination
blowoff and sampling tap used for 8 in. (200 mm) mains
and smaller is shown in Figure 3-3. Ensure that there is
no water in the trench up to the connection for sampling.
Use a clean and disinfected sampling pipe that has been
flushed prior to sampling. A corporation cock may be
installed in the main with a copper tube gooseneck
assembly. This assembly can be removed after sampling
and used again.
7. If the HPC test results are greater than 500 colony-
forming units (cfu) per mL, flush and collect a repeat
sample until no coliforms are present and HPC is below
500 cfu/mL.
8. Coliform bacteria must be absent from the samples and
the bacteriological quality of the water equal to or better
than that of the distribution system.
9. If unsatisfactory test results are obtained, flush the main
again and resample. If check samples also fail to produce
acceptable results, rechlorinate the main by the continuous-
feed or slug method until two consecutive sets of acceptable
tests are taken at least 24 hr apart. In some cases, it may
be necessary to pig or pressure wash the pipe prior to
rechlorinating the main. It is advisable to check the qual-
ity of the water entering the new main because high veloc-
ities used for flushing may have disturbed sediment in
the supply piping and resulted in poor quality feed water.
Connection to Distribution System
When all bacteriological tests are satisfactory the new main
may be connected to the distribution system and placed in ser-
vice. If the final connection is one pipe length (18 ft or 5.5 m) or
less, the new pipe, fittings, and valve(s) required for the final con-
nection may be spray-disinfected or swabbed with a 1-5 percent
chlorine solution (Table 3-4) just prior to being installed. If the
final connection is greater than one pipe length (greater than 18 ft