I recently had a large juniper shrub removed from my front lawn and am constructing a three terrace planter to cover the spot. How much new soil should be laid down and how much of the soil that the juniper was in should be removed? Can or should this "old soil" be treated if not removed prior to laying new planting soil over it? My plan is to put in 6 to 8 inches of new soil (compost and planting soil mix), but need to make sure the underlying soil is not to acidic. Thanks

You should be OK with 8" of new composted soil. Junipers like acidic soil but they don't make soil more acidic. Your soild should be pretty much the same elsewhere on your property. If you have general conerns about your soil acidity you cab buy fairly inexpensive soil test kits at some larger home centers. If you are near a university extenion service they may be able to test it for you.