I have stopped by a few times to look at the site. I was looking at the fill toward the end of last week. From what I saw it looked like the red clay/sand mix that we often see used on roads around here.
From what I saw of the old road bed a few days before they started placing the fill, it looked like a variety of colors which, to me would suggest a variety of soil types; orangy red of clay, light areas of sand, ect. Of course the old road bed was placed long before there was concern for coastal dune lakes, or preservation of sugar white sand beaches. Of course, back then it was probably about convenience and economy more so than preservation of the lake, thus the undersized culvert pipes.
From what I saw of the old road bed a few days before they started placing the fill, it looked like a variety of colors which, to me would suggest a variety of soil types; orangy red of clay, light areas of sand, ect. Of course the old road bed was placed long before there was concern for coastal dune lakes, or preservation of sugar white sand beaches. Of course, back then it was probably about convenience and economy more so than preservation of the lake, thus the undersized culvert pipes.