Is the offer for the dimension for infiltration justified?

Hello!

We are currently in the final stages of our planning. A soil survey has already been conducted. Now our architect still needs the dimensions for an infiltration system (most likely as a shaft). We requested these dimensions from our soil surveyor, and he now wants almost as much money for the dimensioning as for the entire soil survey (more than €800).

Is the price justified? It seems very, very high to me. According to my research, a calculation according to "DWA A 138" is quite simple if you have the necessary numbers and formulas (these are also available, for example, as an Excel template or online tool). This should not take a practiced engineer more than 1 to 2 hours, or are we overlooking something? Unfortunately, the offer here only mentions a flat fee and provides no further details.

Thank you very much!

Whether the offer is okay or not, I can't tell you. I would first swallow hard and then ask myself if it could be done more cheaply.

Have you ever thought about a cistern?

Then you could invest the money that the soil expert charges and also what the shaft costs into the cistern.

You can definitely build this yourself as well. I did that a few years ago. This (4 m³ plastic cistern) cost about 1200-1500 Euros with new piping, drainage channel, etc. Unfortunately, I can't say the exact amount now.

Since I couldn't do underground infiltration (too many roots), an above-ground infiltration was used instead. For this, self-slit pipes were placed on the side, more or less well hidden under plants. Excess water is then pumped into them with a pump and thus distributed in the garden.

In summer, you also have water to soak the garden. Unfortunately, always too little.

That probably depends heavily on the execution, in this case the depth.

Basically, amounts under 1000€ are peanuts in construction. If your report is below that, you were lucky.

PS forget [Zisterne], it's not worth it

Thanks for the answers! We definitely swallowed.

Sure, 1000€ is nothing in construction, but just because everything is on a bigger scale doesn’t mean you have to throw money away unnecessarily.

We will probably use a cistern with built-in infiltration (the tank is basically open on the side at the top). But we need to know how big the infiltration area has to be so that the tank doesn’t overflow during heavy rain.
We are not allowed to discharge the rainwater into the sewer.

Does anyone perhaps know a good geologist who could calculate something like this for us? So that we can also get a counteroffer.

We will probably use a cistern with built-in infiltration (the tank is basically open on the side at the top). Only, we need to know how large the infiltration area has to be so that the tank does not overflow during heavy rain.
We are not allowed to discharge the rainwater into the sewer.

Roof area calculation... that's done by the general contractor or the earthworks contractor, right? It's not complicated, done in 5 minutes and is similar for every standard house... so: the wheel won't be reinvented there.

Does anyone maybe know a good geologist who could calculate something like that for us? So that we can also get an alternative offer.

Isn't the geologist portal gone, where geologists register and can be found by postal code?

Just ask directly at, for example, the company Graf. I bought the stuff from them and they did the calculation of the size of the rigole for free. The data they needed was already included in the soil report and in the drainage plan from the architect.