Large volumes of moving water underneath building

[Wesley W.]

Hey folks,

Case Study: a distressed waterfront property that has an unusual ground water situation.  Here's some context.

The property is on a steep grade sloping away from the road.  The property itself is relatively close to the road (perhaps 6 ft from shoulder).  It is a two story structure with one exterior door on the second floor (on R, facing the concrete retaining wall, about 4 ft below grade), and a second exterior door facing the water (L).

The previous owner has torn up the subfloor in the bathroom downstairs, revealing a constant flow of water running towards the lake.  There is a partial slab but also bare earth underneath this room.  The water is definitely moving (you can hear it running), and is about 8-10 inches deep.

The implication was that this water was runoff via the water table from the upslope, which continues to the right across the street.  There is a corrugated 4" outflow pipe at the lake that has a steady stream of water coming out of it.  It seems like a high volume of water, but it is springtime.  I wonder aloud if this might be a leaking water main underneath the road (public water, private septic).

Here are my questions:

(1)  Is there a way to tell if this water is ground water vs. a leaking water main?

(2)  If it is runoff (as the previous owner implied), what kind of professional would I engage to evaluate the situation and come up with a remedy?

Thank you in advance for your collective advice and feedback!