ᐅ Lowering of Groundwater According to Geotechnical Report – Your Experiences?

Hello everyone,

according to the soil report, groundwater lowering is necessary during the basement construction, and it can only be discharged into the sewer system. During the boreholes, groundwater was encountered at a depth of 2.5m (8 feet). The Danube River flows approximately 500m (1,640 feet) away in a straight line, so we had already anticipated this. Over the past few months, we have contacted numerous companies regarding water management. Despite follow-ups, we have never received a response. Either there is no interest in such small projects, or we were told to get in touch again just before the start of construction in autumn. Based on the soil report and the neighbor’s references, we have fairly reliable estimates of the volume of water to be pumped. We have set aside €30,000 for this scope of work but remain uncertain about reliable estimates from the company to be hired. The neighbor had to handle this independently because they did not commission a soil report, and the water only emerged after they had already begun the foundation slab. So it was a chaotic situation that ended after 5 days.

My question to users here with experience on this topic:

What costs did you incur for your water management, and how was it carried out? (open, closed, vacuum systems)
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 must be said that we absolutely need the space, and on a 300sqm (3,230 sq ft) lot, it would not be possible to build it close to ground level.

When we built our first house, after excavating the foundation pit, there was half a meter of water (1.6 feet) standing in it. We needed to determine whether it would drain away or continue to fill up.
Because a water vein in the clay soil was pierced, it kept filling.
We placed a wastewater submersible pump in the pit and pumped the water into a green rain barrel above. Inside that barrel was a second pump, which pumped 30 meters (98 feet) to the street drain. All hoses were 1 inch in diameter.
After several days, the water vein stopped flowing, and our pumps only ran during rain until the house was finished and backfilled.
We had a waterproof concrete shell (“white tank” method) constructed, but the house still stands in water.
Thirty years ago, we discharged into the street drain without a permit; now, we would likely need one.
Costs included: 2 pumps, 50 meters (164 feet) of hose, construction electricity, and daily clearing of the water trench around the formwork/foundation slab/basement.

Nida35a schrieb:

When we started building our first house, there was half a meter of water standing in the excavation pit after digging. We needed to check whether it would drain away or continue to fill.
Since a water vein was hit in the clay soil, it kept filling up.
We placed a sewage submersible pump in the pit and pumped the water into a green rain barrel on the surface. Inside that barrel was a second pump, which pumped 30m (100 feet) to the drain. All hoses were 1" (1 inch) in diameter.
After several days, the water vein stopped flowing, and our pumps only ran during rainy weather, until the house was finished and the pit filled.
We had a waterproof concrete basement (white tank) constructed, but the house is still sitting in water.
30 years ago, discharging into the drain was done without a permit; nowadays, you’d probably need one for that.
Costs: 2 pumps, 50m (165 feet) of hose, construction electricity, daily clearing of the water around the formwork/floor slab/basement.

Have you experienced any water or moisture problems in the basement despite the waterproof concrete?
Today, a water authority permit is required for this and so on, but that’s beside the point.
So, you managed all of this yourselves?

According to the soil report, about 20 liters (5 gallons) per second flow into our excavation pit—that’s 1,728 cubic meters (1,900 cubic yards) every 24 hours. With a wastewater disposal fee of €0.65 per cubic meter, that adds up quickly. In the three weeks it takes to pour the floor slab and basement walls, roughly €23,000 would be lost just pumping fresh water into the sewage system—that’s quite something to consider…

Our basement is sealed with a waterproof membrane, also beneath the concrete slab, and everything is welded together. The general contractor said this is how buildings are constructed in Hamburg near the Elbe River. We have never had any issues with water in the basement. When the pumps are running, the groundwater level lowers like a funnel, and the amount of water decreases. Only when the pumps are turned off does the level rise again. Before hiring a company, I would try to handle it myself, as it is more cost-effective. The 20 liters per second (approx. 4.4 gallons per second) will decrease significantly over time.

For us, the “challenge” was that the ordered basement walls unfortunately arrived 5 days later than planned. As a result, the pumps had to run longer without any real progress on the construction.

Grobmutant schrieb:

Our "challenge" was that the ordered basement walls unfortunately arrived 5 days later than planned. The pumps had to run longer without any real progress on the construction.

How long did you have to operate the water management? Can you provide any information about the costs? Did you have the entire process handled by a company, or did you manage it yourselves as well? Delays during this phase are probably the most expensive, as fees accrue almost by the minute and add up very quickly.