I got a call from one of my customers yesterday that a porton of his lawn was sinking in. About an 18 foot by 15 foot area.The section in question in now about 2 to 2 1/2 feet sunk (possibly a little more) below the rest of the lawn.This was not something that happend overnight but has been slowy sinking for about three years now possibly longer. The customer has asked me to fill it in and i assume reseed(in the spring). My question is should i wait till the warmer weather to fill in this hole?It is about 20F degrees today and the ground is pretty well frozen.I figured if i did it now, when the ground thaws it may sink a little more and i will have to bring in more topsoil. I dont think there is any danger of it sinking too much more over the winter.Also it is not near any waterways and he doesnt have a septic tank.The area is on a slight slope im thinking the cause just may be some poor grading.