The neighbor's rainwater infiltration is running onto our property

Our neighbor (a large housing construction company) is currently digging the hole for the rainwater infiltration directly behind the wall. The roof area is about 500 sqm. We believe that the location chosen there is completely wrong and are afraid that not all the water can be absorbed and will flow onto our property. The defects we have seen so far: - Infiltration only possible on 2 sides (at 2 sides boundary wall) - Size far too small - There are holes in the concrete wall, which can only be patched up temporarily - The filled soil does not absorb water as well as natural soil, which increases the risk of overflow. Unfortunately, the people (foreign construction crew) are not open to discussion. They do not care about anything and have already damaged our property multiple times. Who can be contacted here for an inspection and what do you think about the implementation? A friendly civil engineer told us that no distances to the boundary need to be observed when it comes to infiltration.

Who can be contacted here for a review and what do you think about the implementation?

Contact the building authority. They must have approved the drainage planning.

A infiltration system is calculated based on the permeability coefficient (soil type) and the connected area, as well as the rainfall amount for your region. Only infiltration through the base area (i.e., not through the sides) is considered. The volume of the system thus serves as storage capacity for extreme rainfall events. Normally, if the parameters are tight, an emergency overflow to the sewer is provided.

- Umfang viel zu klein

How large does it have to be in your experience?
Distances only need to be maintained to buildings with basements (and to the groundwater).
I do not initially see your mentioned concerns that way.

Regards