I have reported the sewage incident to NRW, which now has the Environment Agency role in Wales, and they said they would contact Welsh Water about it. I'm waiting for news.
Likewise, it is appropriate for NRW to inform Costain about it. Dr Peter Smith who carried out the safeguarding process in the local caves during the explosives tests for split carriageway construction has already picked up on this problem.
Cambrian Caving Council