I have a new customer who had st aug sod put down last summer and the installers left a few low spots around a french drain that are collecting lots of water when it rains. The area does drain slowly but stays wet and the sod is not doing well there. Its raining hard here today and the customer just called and wants me to put down some river sand in the low spots. Will this do any good as a long term fix for the low spots or will the sod stay too wet and die or the long run? My idea is to build the area up with top soil and lay new sod on top. But will the existing grass run and grow into the sand filled areas if the customer won't go to the expense of top soil and new sod for the area?