Inspection in the main outlet
06.10.2025 – Inspecting a structure before the warranty expires is not normally a major challenge in terms of procedure. In the case of the Offenbach Main outlet near the former Clariant parking lot on Mainstraße, the situation is more challenging. Before the sewer, which was put into operation four years ago, could be inspected by the drainage team from Stadtwerke Offenbach's Stadtservice, around 2000 cubic meters of Main water first had to be pumped out of the pipe.
The Main outlet relieves the combined sewer during heavy rainfall: During cloudbursts, the mixed water is heavily diluted with rainwater and fed directly into the Main instead of into the sewage treatment plant in Frankfurt Niederrad. There is always water from the Main in the pipe, which is forced back by the rainwater and mixed water during downpours. As the warranty has now expired, the drainage team has inspected the pipe for damage and documented its condition. This should now be done before the start of the rainy and flooding season.
Inspection before the warranty expires is a routine part of construction projects
"It is important that we keep an eye on our warranty periods and inform the contracted companies of any damage in good time and ask them to rectify it. Otherwise the city will be stuck with the costs," says city treasurer and responsible department head Martin Wilhelm. "The inspection before the warranty expires is routine for construction projects. However, this inspection is something special, as we have an underground project here and the pipe had to be drained first."
Thorsten Hammer, dispatcher in the civil engineering department, was responsible for ensuring that his colleagues only found a small amount of water when they descended into the pipe and were able to walk through it. To do this, he first had to close the flood gate valve at the end of the pipe. This ensures that, in an emergency, the flood water does not flow under the Main dyke via the canal into the residential areas. The Main water was then pumped out of the pipe and back into the riverbed. This took two full days.
Building survived the first four years unscathed
After walking through the approximately 415-metre-long pipe, the engineers from Stadtservice were satisfied with the condition of the pipe down to the last detail. "The Main outlet has been in operation for four years, is depreciated over 50 years and should last 100 years at best," says Melanie Gessner, Head of the Civil Engineering Department at Stadtservice. "It has survived the first four years unscathed."