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

C.5 Göttingen Stadtentwässerung (GS)
GS was interviewed in Göttingen on November 3, 2010. The interview was conducted in German. GS is
the drainage and wastewater service of the City of Göttingen, Germany. The population served is
130,000. The collection system is a separate system with each of the sanitary and stormwater systems
having a mains length of 375 km (233 mi) and a publicly-owned length of laterals of 300 km (186 mi).
The laterals are owned by the city as far as the property boundary.
The city council decided in 1990 to make serious investments in the wastewater system with the aim of
achieving a watertight and maintenance-free system by 2035, including the privately-owned laterals. The
annual budget is € 25 million (U.S. $33 million), all from local taxes, and GS considers that it receives
this to do the job properly and solve the problem, and not to fiddle about with minor maintenance to keep
the system going. This 45-year timeframe is exceptional and was driven by political pressure. A national
newspaper article in 1988 had been critical of the city for the state of its underground infrastructure as a
result of several large collapses, and the council in 1990 had a strong Green Party representation. As a
result of this policy and its implementation, GS is seen as a leader in wastewater system rehabilitation in
Germany.
GS was an early user of CIPP. Its first use was in 1992. Total installation of all rehabilitation methods is
shown in Table C-5.
Table C-5. Use of Rehabilitation Methods in Göttingen Stadtentwässerung, Germany
Method First Use Total Installed (km) Length in past year (km)
CIPP 1992 42 1
Pipe bursting (replace with PE) 2006 24 incl. methods below 7 incl. methods below
PE Sliplining 2006 Incl. in above Incl. in above
PE fold & form 2006 Incl. in above Incl. in above
The total of the CIPP above that is lateral lining is approximately 6 km (3.7 mi). Of the CIPP installed, 7
km (4.4 mi) has already been replaced. In the longer term, all but about 10 km (6.2 mi) is expected to be
replaced. GS trialed short liners, but experience was poor and all were removed. The main problem was
poor resistance to water jetting during routine cleaning operations. GS also tried steel short liners, but
considered them not to be cost-effective. Similarly, GS has trialed top hats for rehabilitation of the
junction between main sewers and laterals, but again had poor experience and has ceased their use.
GS has taken samples of CIPP lining after 5 and 10 years in service, and some after 12 years. Pieces
roughly the size of a sheet of letter paper were removed in sewers 250 to 600 mm (10 to 24 in.) in
diameter. A total of 50 samples were tested by the Institut für Unterirdische Infrastruktur gGmbH
(Institute for Underground Infrastructure [IKT]) for: E modulus; bending stiffness; thickness; and
watertightness. No results were made available, but on the basis of the results, GS considers CIPP to
have an effective service life of 50 years. GS has not confirmed the methodology for reaching this
conclusion, and review of related published reports by IKT does not provide any information that might
indicate how it was calculated.
Current CIPP installation uses UV-cured methods only. GS had a major contractual disagreement with
the leading heat-cured system supplier and switched its specification to UV-cured and has found better
quality and fewer site problems with this technology. In its specification, GS requires type testing of
materials including creep resistance and tensile and bending modulus. Minimum wall thickness is 6 mm
(0.24 in.) irrespective of design requirements.
C-11