Karsten described it perfectly. Everything else regarding costs and depreciation is wrong. He offers you compensation. He should quantify it for you, and based on this and your own expectations, you decide.
The plot we are currently building on also has such a right of way. Gas and sewage for the neighboring house. Both ran diagonally across the property; we had to bear the costs for relocating them to the new route. That it would have somehow reduced the purchase price, I absolutely cannot confirm! :D