Sump pump used to be dry, now dark nasty water in it
Our sump pump used to be very dry, the humidifier in the basement would drip a little in and it would evap.(there is gravel in the pti). Now I noticed it has a lot of dark, smelly water were for years it never had any. We are on top of a hill. I turned off the humidifier and it still has water.
If the channels, perimeter drain pipes, weeping tiles, gravel under the foundation etc. had really been a little moist instead of bone dry for months, some mold or fungus could have formed in them. Then the first several gallons of real water from a raised water table would flush some of that crud out into the sump pump pit.
Throw a little bleach into the pit to help reduce bad odors. (an amount about 5% of the volume of water sitting in the pit.)
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.
Exactly what Allen said, if your sump has been dry for so long, anything that was sitting in the piping network would be nasty and flushed out the first time new water comes into the pipe. I would take a hose and dump clean water in the sump to allow the pump to cycle a few times to get the nasty stuff out.