Drywell (not in use) and Sunken Area in Yard

[Monty]

My house was converted to municipal water years ago (before we moved in). In the back yard were two pipe openings that were remnants of the earlier septic system. We were told they were for the drywell.

When having a tree removed, the stump grinding machine caused a sink hole to occur. It is around eighteen inches deep and about three feet in diameter but it was about twelve feet from the nearest drywell opening. Obvioulsly we will need to fill it in but I'm interested in any thoughts on why this happened and the best way to deal with this.

Thanks,

Monty

[Goedjn]

The two may not be related. The sinkhole could be another drywell, a cess pit, or something else entirely. Carefully (preferably with someone else around to call for help if it turns out to be a 30' diameter limestone cave, or a tunnel for a secret military 10-terravolt transmission line) dig at the edge of the sinkhole until you find out what's there. Then call for a truckload of gravel and fill it up.

[David Efflandt]

Do you know where the septic tank is (probably somewhere between house and drainfield)? Maybe the stump grinder crushed part of that or its lid. In that case the hole may get deeper when in rains and the soil washes into the septic tank.

[Monty]

As it turned out, it was a septic tank. It took quite a bit of dirt/gravel/sand/topsoil to fill it.

Thanks.

Monty