We have one line on the leach field that has water pooling on the top of the ground. We used a rod and pushed a hole through the ground to the gravel and had a sucking sound when the rod was removed. Then there was black smelly water coming out of the hole. The other 2 branches of the leach field were not having any issues. Someone told me there was a problem with the bacteria, and suggested we have some type of mixer put into the septic tank. The tank was pumped out about 2 years ago. Any suggestions?

This is not a DIY project,consult a septic contractor. Tanks should be pumped every 5-10 years but depending on how many are in the home, tank size and what is being flushed it may need to be pumped more often. Bacteria eat the solids while in the tank, mostly clear water flow out to the field to be absorbed abd evaporated. It could be a failed field. The contractor can do a perc test to see.