This is for the engineers: Regarding the "longitudinal" connecting sidewall drain pipe location: There had been discussion of what the original blueprint designs illustrated verses what the actual design was constructed as. This photo reveals that the longitudinal drain is beneath the lower part of the sidewall footing. This allows the herringbone pattern of underslab drains to connect in coupling joints to this "collector pipe". Each "collector pipe" will have a number of underdrains feeding captured water under the slabs (except for the "underflow" design flaw that channels down the spillway creating "washing voids").
Wet spots in the hillside soil infer water escape flows from (1) the upper hillside level (2) from the "underflow" design flaw of "uncaptured" water channelling down underneath the spillway. Water streaks area also observable on the edges of the sidewall footing. This too is from the same "escape" flow(s) mechanism.
Longitudinal side drain reveals actual construction design - conflicts with the design blueprints (blueprint design flawed in that it would force a complex coupling system with a "gravity jump point" + a sediment collection issue (i.e. not fully self-cleaning in the "upward joint/bend)
