There is always the option of having the compaction tested. It really is not very expensive and it will give you the peace of mind you want.
Call a soil testing company close by and tell them what you are doing, and what you want. If you have any questions get back on the forum and we can lead you through it.
look at the cost of 12 sch 40 pipe it will handle a lot more water and the installation will be the same.
