Groundwater heat pump - disadvantages?

It is a groundwater protection area 3, but the lower environmental authority explicitly pointed out the possibility of such a heat pump. However, a brine heat pump is therefore out of the question.

When I read something like this again. With the right material for the grouting and the appropriate brine, that should also be possible in a protection area of class 3. At least that works for us.

After all, it is not 1 or 2, but only 3.

Much like with the gravel. Private individuals are not allowed to install RCL in protection area class 3. But on the street next door, the city does exactly that. And against a donation of 200 euros to the city treasury, private individuals are allowed to do it again.

There are WSG 3a and 3B. In Hessen, you are allowed to operate a brine heat pump in 3B. In 3a, not at all since 2015. With an exceptional permit, however, a brine heat pump without deep drilling (trench collector, baskets, ..) is allowed.

Away from water protection areas, sondes can be prohibited, for example, if two groundwater layers would be connected. Laypeople also don't need to babble about injection material and casing if the authority's stamp does not approve.

Far away from water protection areas, a probe can be forbidden, for example, if two groundwater layers would be connected.
Laypeople don't need to babble about plugging material and casing if the authority's stamp doesn't approve.

Or if there is gypsum in the soil. That causes funny faults when water gets in.

Far from water protection areas, a probe can be prohibited, for example, if two groundwater layers would be connected. Laypeople don't need to babble about injection material and casing if the authority's stamp doesn't approve.

But as you yourself have noticed, this has absolutely nothing to do with the water protection area. And you don't necessarily have to drill directly into both if the conditions allow. Then a water-water heat pump would probably only be allowed up to the first layer.

The same applies to gypsum. There, too, a water-water heat pump would likely be rather impractical.

Thank you very much in advance for your comments!

Water Protection Area/ Authority:
We are in a WSG 3a. The (lower) environmental authority has made it very clear to me in several conversations very explicitly that they will not approve a brine heat pump (which other builders who tried also confirmed to me).
At the same time, however, they explicitly referred to the possibility of a groundwater heat pump (verbally, not in writing). Our planner explained to me that this ban is probably not legally tenable, since there are now refrigerants approved for WSG 3a. But do we really want to take legal action here?

Soils:
We are very close to the Rhine, so the soils are sand and gravel. It is only uncertain whether silty extensions of a nearby mountain range would be found at 20m. And of course the usual mineral content/flow rate, which was appropriate in the neighboring projects.