Any thoughts on the distance down in a sump pump should be in a 24 inch sump pit??
Have two drain pipes that empty into the pit and pump goes off all the time in thaw or rain. Wonder the depth either -from the top or below the drain that is optimal. Can't come up with a way to stop the flow into the pit area-where is the water coming from is unknown--and any thoughts as to what is a good sump pump? Any experience with the water pumps that work off a city water line as a backup?? Thanks.

Turn the pump off and see where the natural water level is at. It may only be five or six inches higher then where the pump is already at. If that is the case either raise the pump or adjust it so it does not come on as often.
It is common for sitting water to be in a pump pit.
If you have a plastic pit, be sure that there are holes in the bottom of it to allow any water that may be coming in elsewhere to naturaly drain out if the water table is lower then the bottom of the pit. We had a client that did not do this as water kept coming into the pit turning on the pump. Once we drilled a few 1/2" holes and placed the pump onto a cement slab on the bottom. The water drained out quite quickly. Been dry for the most part ever sense.
When the pump pit is dry, run a hose on the outside of the house in various locations. You may find out where the leak is coming in from and then be able to fix it properly from the outside. Could be a real simple fix.