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, � D-36 Part 3: Gravelless Options for Trench Systems The Gravelless Trench has been used in Texas since 1971. It is an extremely viable option for onsite sewage treatment in Minnesota, and testing and data show that it is as reliable as a trench filled with gravel. As a result, it has been adopted as a standard system for use in Minnesota. (See Figure D-33.) The idea of using something other than rock to hold the trenches apart is not new. Chapter 7080 currently recognizes two acceptable options. The first is gravelless pipe, which is corrugated pipe surrounded by a synthetic fabric. The second is a chamber made out of a nondegradable material, typically plastic, used to hold the soil apart. Natural soil has been used to construct gravelless systems, and they � should be backfilled with natural soil. Do not backfill with drainfield rock. If an excavation is only 2 feet wide and has been filled with gravel with the pipe on the inside, the biomat will not develop at the pipe-gravel interface, but will instead develop at the rock-soil interface. Instead of having a 3-foot-wide trench, the size has been effectively cut down to a 2-foot-wide trench, causing a potential problem. Tree roots do not affect gravelless systems. The solidity of the joints and the other parts of the system allow placement of this system close to trees. The system may, however, cause potential damage to nearby tree roots, but the tree roots will not affect the system. Advantages of a Gravelless System O It can be relatively shallow. O It is easy to install. O It is lightweight and can be carried into remote, difficult-to-reach sites. It is also easy to handle and deliver. O Little cleanup is required after installation. O It can be installed on a steep slope because of the minimal amount of equipment necessary for installation.