Expansion of an existing facility Civil Site Grading and Drainage 2

I am working on a project in Kermit and Wink, TX. I was looking for a drainage manual or any drainage design criteria but it seems the entire county does not have any concerns regarding floods in their areas and I cant find any city drainage manual. I've been looking in google maps and can't see any canals nor any inlets that will channel storm water to somewhere and contain it.

I’m working on an expansion of an existing oil and gas facility. This project is a very small portion of their existing facility (Approximately less than a quarter of their existing facility). They are supposed to grade it and construct a detention pond so the water from the North-East in addition to theirs will channel to this pond and therefore contain it rather than building this expansion that will dump water to their future neighbors. The current and existing grade is now flowing towards the adjacent vacant lot. But the client doesn't seem to like building ponds and what's necessary.

My question is, am I violating anything and we can get sued for not planning anything for this water flow in our area? Just want to get your thoughts if I am overthinking this or if should I be worried about future issues once the neighbor in the vacant lot starts to build his property and will file a complaint about this water being dumped on his property. Please note that it's not really a steep slope to the adjacent lot but is minimally graded towards it.