Living in a mystery for close to a year now. My house is a split level home built in the mid to late 60s. Land is on a slight grade. Front door is ground level and is in middle of the house (when you walk in you can go lower level or upper level). Rear door in lower level is ground level in back of house.
In may of last year we began having drain flies. All drains were cleaned and that was not the problem. I have had plumbers out to check sewer line and all seems fine. Flies congregate around rear door of lower level. I am unsure if flies are coming in from outside (poorly sealed door) only or if there is an entry from inside my house.
Recently I discovered an old 4 in clay drain under my patio slab out my rear door. Pipe seemed abandoned but upon digging into it some water began to come out. I then broke through the patio closer to the house where I knew that drain would be. Very smelly muddy water was inside the drain. This certainly seems to be the home of the flies. Strangely the drain pipe was full of gravel. I have cleared it out as far as my arm can reach into the pipe as it goes under my home. By using my phone I can see the drain is full of gravel further back beyond my reach.
There is no sump pump in my basement.
The water in this drain pipe seems much dirtier than ground water.
What is this drain pipe? Can I safely seal it shut and patch up my patio?
