RAH how big is your project? I would suggest starting small and see what you can learn. You could also soak the wood chips in a 5 gallon bucket of your well water and see if the PH stays the same. In my mind the water is the key. Fens occur where the pristine water first meets the surface. If you have fish or plants in your pond the outflow may be very different then the inflow water chemistry. I would experiment with the well water before it goes into the pond and after.

Many hydroponic systems use materials other than soil to grow plants in. This is also a situation where the water is the key. Maybe you could test growing plants in you water first.

P.S. My swamp has the classic peat layer with marl soil underneath it. The marl soil contains high amounts of calcium carbonate with a high PH. The marl was formed by the algae Chara living in the glacial melt water. Chara which is plant like and stored it in its branches. Layers of dead Chara over the years built this layer. The peat formed much later when the climate warmed up. Many of us have Chara in our ponds today, including my ponds. This would be hard to build, however the plants themselves will grow in the correct water conditions.