What we have is a gateway to either a private estate or very large dwelling.
I would offer to clean the entire structure, including cap stones, avoiding the lights electrics and what looks to be a camera on the right hand side, These could be bagged, whilst cleaning.
I would then follow the topic advice as far as resolving the effervescing. I would further up-sell a maintenance package so that it could look its best, ongoing
There's an opportunity there that would be stupid to ignore!
Rob