Sorcer: Had more time to find the info on Netafim subsurface which might help you. Sorry, not computer savy enough to give you a direct link, but this will take you to their main page on Techline CV and there are several downloadable (pdf & others) that will be most helpful. One in the upper right corner under the "Whats New" column is a 50 page "Subsurface Irrigation Guide" downloadable pdf on just the topic you asked about. Enjoy. Jeff
http://www.netafim-usa-landscape.com/indexal.php