Pond dismantling ends in garden fiasco

Dear forum,
we have a problem. Since we considered a pond on the newly purchased property (with house) too risky for our 1.5-year-old child, we decided to have the pond (approx. 32 sqm x mostly up to 1.60 m deep) filled in. The pond liner was removed as best as possible (but not completely), and the hole was then filled with a mix of edging stones, stones from a terrace, and topsoil. The whole process was done with a mini excavator. The soil was transported with a Bobcat. The mini excavator had also caused some damage in the garden, so we were advised to spread new lawn seed soil on the property (with a Bobcat). Actually, we wanted to sow the lawn ourselves. But although the pond has not visibly settled, water always collects there during heavy rainfall. The landscaper just told us that it will sort itself out once the grass grows.

Is that really the case? Does the water only collect there because it is also the lowest point (since everywhere else only simple soil was piled up, making it higher), or was the former pond too heavily compacted by the excavator/Bobcat traffic?
Can we still save something there? We probably can’t get very far with the motor tiller/cultivator because of the stones, right?

Many thanks for your helpful answers
Stephan

Very cavity-rich waste and strong settlement behavior of topsoil...
That will remain a hollow.

then fill the hole with a mix of curbstones, terrace stones and topsoil.

Was it worth saving the cost of the container? Now just refill with a sand-soil mix until the ground is stable and level.

It's normal for it to settle... The soil compresses. You can plan the project for 2-3 years and keep refilling it repeatedly.

It's normal for it to settle... The soil compacts. You can plan the project over 2-3 years and keep refilling it.

In that time, the child could have learned to swim...

However, I see the current problem more in that coarse material was used for filling. If so, you have to compact it afterwards, was that done?
If not, do it now, refill, do it again. Only then is the lawn seeding worthwhile.

Now, dumb question, where is the water supposed to go?

The pond is still a pond because the liner is underneath and accordingly still prevents the water from seeping away. Filling in the pond does not change that. Surely it will get drier now and the problem will ease. Nevertheless, water will collect and stand on the former pond bottom. This will remain the case over the autumn and winter months.

In order for the water to at least seep away, the pond liner must be made permeable. Drill holes or dredge it up and make holes. Otherwise, you will always have a marshy area there.