The deeper you go the more expensive it gets. But generally speaking, keeping top of French drain 6 inches below grade is often adequate.
About Victor Coppola
Victor Coppola has over 20 years in diverse environmental and strategic planning experience in the environmental and land development industries. Look to Victor for eco-friendly consulting and installation services to developers of commercial, industrial and residential projects; private clients; governmental agencies; allied professionals and individuals targeted for enforcement of perceived environmental violations.