While completing a project of removing an old cast iron drain pipe and converting it to pvc, I've noticed something. I've been dealing with the "problem hole" ( dug out area of the crawlspace with a retaining wall around it; heating/air system and water heater sit in it and are at risk for flood if pumps fail or power is lost) for a while now and trying to figure out a solution. It only takes on water when it rains a lot. 2-3 days of moderate to heavy rain can bring in tens of gallons per minute. During a local flash flood warning (pretty rare for our area and we live on a street with a hill), I have seen both pumps kick on and stay on for a considerable amount of time. Water did not go above the said makeshift sump hole that exists there, but it also wasn't really going down very fast, either. Those pumps throw out about 100+ gallons per minute with both pumps running. They were keeping it in check and it didn't creep out of the hole, but waterflow was coming in so far as areas all around the wall that they both stayed on for a while. That's not a normal event and may only happen during big rain systems. On the back side of the wall to the left of the water heater, there's the base cinderblock that is turned sideways to let water out of the wall. There are many of these around the wall in various places. That particular one gets most of the water flow out of it for some reason. Tonight when I was fixing a pipe, I saw this on the other side of the wall: The three other sides of the wall do not have this big opening there between the wall and the dirt. I presume that when they were digging this hole to put up the wall, they either dug too far/long and decided to leave some space or...most of the dirt visible on the floor inside of the hole has been washed down from this particular side. Both could be feasible. In the photo above, the foundation wall of the house is behind me about 3 feet or so. The next photo is from the area at the bottom right of the above photo: That little gulley there apparently gets the water flow. I see this "hole" in the dirt under where I took the above photo from: At first I thought, "Are those clam shells?!?" when I saw the white things at the bottom. I'm not quite sure what those are. The dark pieces literally look like a bunch of walnuts or pecans or something with holes in them. I've never seen any squirrels in the basement. The "white" pieces look like a cross between half egg shells and sometimes it looks like some kind of plastic bottle lids at other angles. I stuck the camera down as far as I could down in front of the hole and saw this: Since water flows from that side the most and this hole literally looks like some kind of solid and regular hole that the water flows in through during heavy rains, it brings a lot of questions to mind: If that dirt in fact washed in from behind the wall and into the hole inside of the retaining wall, how is it that there is a single base hole at the bottom of it and not a long "gash" hole from top to bottom as it eroded away? Even if the dirt was dug out that way, what would cause a single hole like this? I didn't expect to see such a thing. I figured that water just comes in from dirt surrounding the wall and that was that. I guess the water "could" carve such a path through the dirt and some of it may have been more hard packed than the other parts, so a hole formed. I don't understand why that didn't happen above or on either side since it is the same type of dirt. I'm pretty much wondering if this random hole is where most of the water flow is coming from. Something related to a cracked foundation somewhere underground? A old bad drain outside funneling water under the house? None of the other 3 sides of the wall have this. I have even entertained the idea of an intermittent stream running underneath the house. Old 1927-1930 topo maps actually show that one was near or under this house and ran from some random place up the street all the way down to the end of the street. However, on later topo maps, that intermittent stream is no longer there. What the heck could this be? I'll be checking it when we get a lot of rain again and see if water flows out of there. If it does...how do I determine what it is and what is causing it?