Lowering of groundwater according to soil report - Your experiences?

Hello everyone,

according to the soil survey, groundwater lowering is necessary during the construction of the basement, which can only be discharged into the sewer system. During the drilling, groundwater was encountered at a depth of 2.5m. The Danube flows by at about 500m in a straight line, so we had already anticipated this. Over the past few months, we have called and emailed numerous companies for water management. Despite follow-ups, we never received any feedback. Either there is no interest in such small projects, or we were told to get in touch again shortly before the start of construction in autumn. Due to the soil survey and the neighbor’s references, we have fairly reliable figures regarding the amount of water to be pumped. We have set aside €30,000 for this trade but have actually been in the dark so far about reliable figures from the company to be commissioned. The neighbor had to do it on his own because he did not order a soil survey and the water only came when they had already started with the floor slab. So it was a chaotic operation and over after 5 days.

My question to the users here with experience in this topic:

What costs did you incur for your water management and how was it carried out? (open, closed, vacuum)
What difficulties did you encounter during implementation?
What would you do differently if you were in the same situation again?

To avoid discussions about "omitting the basement", it should be said that we absolutely depend on the area and could not even approximately represent it at ground level on a 300sqm plot.

When we first excavated the foundation pit for the first house, there was half a meter of water standing. It had to be clarified whether it would drain away or continue to fill. Since a water vein in the clay soil was hit, it continued to fill. We placed a sewage submersible pump in the pit and pumped it into a green rain barrel above. Inside it was a second pump that pumped 30m to the [Gully]. All hoses were 1". After several days, the water vein stopped flowing and our pumps only ran during rainy weather, until the house was finished and backfilled. We had a [weiße Wanne] made, the house still stands in water. Thirty years ago, discharging into the [Gully] was done without permission; now we would probably need a permit for that. Costs: 2 pumps, 50m hose, construction electricity, daily clearing of the water trench around the formwork/floor slab/basement.

After excavating the foundation pit for the first house, there was half a meter of water standing. It had to be clarified whether it would drain away or continue to fill. Since a water vein was struck in the clay soil, it continued to fill. We placed a sewage submersible pump in the pit and pumped it up into a green rain barrel. Inside it was a second pump that pumped 30m to the drain. All hoses were 1". After several days the water vein stopped flowing and our pumps only ran during rainy weather until the house was finished and backfilled. We had a white tank installed; the house is now still in water. 30 years ago we discharged without a permit into the drain; now we would probably need one for that. Costs: 2 pumps, 50m hose, construction power, daily clearing of the water trench around the formwork/floor slab/basement

Have you had problems with water or moisture in the basement despite waterproof concrete? Nowadays, a water rights permit is necessary for this and so forth, but whatever. So you did all of this on your own? According to the soil report, about 20 liters per second flow into our foundation pit. That’s 1,728 cubic meters every 24 hours. At €0.65 per cubic meter wastewater fee, that adds up. In the 3 weeks it takes to pour the floor slab and basement walls, around €23,000 would have been wasted, just to channel fresh water into the wastewater — you have to imagine that…

Our basement is sealed with "Elefantenhaut," even under the floor slab, everything is welded. The general contractor's statement was, this is how we build in Hamburg next to the Elbe. We have never had problems with water in the basement. When pumping occurs, the groundwater level drops like a funnel, the amount of water decreases. Only when the pumps are off does the level rise again. Before I hire a company, I would try it myself, it is cheaper. The 20 liters per second will become much less over time.

With us, the "difficulty" was that the ordered basement walls unfortunately arrived 5 days later than planned. The pumps therefore had to run longer without any real construction progress.

For us, the "difficulty" was that the ordered basement walls unfortunately arrived 5 days later than planned. So the pumps had to run longer without any real construction progress.

How long did you have to operate the dewatering? Can you say anything about the costs? Did you have the whole thing done by a company or did you also carry it out on your own?
Delays in such a phase are probably the most expensive of all, as the fees run practically by the minute and it adds up very quickly.