Leopold Direct Support Underdrains have been around for awhile. Direct support is defined as having direct support for the sand and anthracite, so no support gravel is needed. Leopold's version of the direct support includes a Type S®, Type SL® or Type XA®. Each of these have different heights to allow for increased freeboard and are designed for wall sleeves, front flumes and center flumes. These blocks can also be configured to handle air scour or surface wash operations.
Most filtration systems that have older types of filter underdrain systems can be retrofitted to these types of new designed underdrains.