On a recent inspection in Wakefield New Hampshire where septic was included, I discovered that the Effluent disposal area (EDA) was completely overgrown. Small trees and scrub brush covered the entire area. This was a 20 year old seasonal home with very use and the owner never took care of the lawn from day one. The problem with an over grown EDA is not only can roots damage the system but it can't breathe as well. Believe or not air will penetrate the soil and help with absorption. I've posted some picture's below and please..... Mow the lawn!!!!! 

Overgrown septic system                                                                             Overgrown EDA