Retrospective Evaluation of Cured-in-Place Pipe - (NEPIS)(EPA ...

4.2.6 Measurement of Acidity, Alkalinity, and pH. The pH of the soil embedment and the solid
sediments collected from the pipe invert were measured using a Thermo Orion pH meter (Figure 4-5).
The soil samples were placed in a pan (which was rinsed using distilled water) and distilled water was
added to the samples. The soil sample was then stirred, and the pH probe was inserted into the soil-water
mixture. The process was repeated for the sediments collected from the bottom of the liner on the inside
of the pipe. The pH values of the bedding soil, backfill soil, and the sediments are listed in Table 4-4.
Figure 4-5. Measurement of pH Using a
pH Meter
Table 4-4. Soil pH at Designated Locations and
Sewage pH (Denver 8-in. Site)
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Designation Soil, pH Sample Sediment, pH
1 7.46 1 6.59
2 7.23 2 6.35
3 6.53 3 6.14
4 4.20 - -
5 3.84 - -
6 4.03 - -
The soil samples collected from around the pipe (bedding material) were found to be rather acidic in
comparison to the upper backfill soil. The soil pH ranged from 3.8 to 7.5 with a corrosive soil defined as
having a pH less than 5.5. Therefore, the soil above the crown and in the bedding material adjacent to the
pipe (samples 4, 5, and 6) would be considered corrosive. The sediments inside the pipe were found to be
only slightly acidic with an average pH of 6.4, as expected from a residential wastewater stream. Thus, it
is not likely that the liner was subjected to a rigorous chemical attack during its service life.
4.2.7 Annular Gap. Measurements of the annular gap between the liner and the host pipe were
taken at 45 degree intervals around the circumference of the liner. The removal of the host pipe plus liner
allowed measurements to be taken on both sides of each cut face, resulting in a total of four measurement
locations for each of the 8 o’clock positions around the liner circumference. The measurement results are
provided in Table 4-5.
The maximum annular gap measurement was 3.3 mm, but the average annular gap value was only
approximately 0.9 mm compared to the nominal liner thickness of 6 mm. Annular gap is of interest in
liner performance for several reasons. Structurally, a tight liner with small annular gap will have a better
resistance to external buckling for the same thickness of liner. A tight liner is also more likely to be
locked into place within the host pipe by minor irregularities and joints in the host pipe, limiting the
potential longitudinal movement of the liner due to temperature changes or other forces that may act on
the liner. From an infiltration perspective, a tight liner limits the flow of water in the annular space that
may bypass the liner by entering the lined pipe at lateral reconnections or at the manholes (if these are not
sealed). The measurements taken on this liner indicate that it remains a tightly fitting liner.