In a previous discussion I mentioned that placement of the drip tubing is an important consideration, and the fact that drip distribution is being used indicates that there are some site problems to be overcome, such as shallow soils over bedrock, a high water table or slowly permeable soils. Here are some additional site preparation considerations.

As with any installation, the layout of the dripfields should be staked with relevant elevations indicated on the stakes. Elevations between the drip tubing and the pump tank should be checked and confirmed. This will determine whether the effluent in the supply and return lines will drain back to the pump tank. As mentioned many times this is a key to performance in cold climates where supply and return lines can be subject to freezing.

Usual principles of good installation techniques should be followed, such as the KINN and KIDD principles of “Keep It Natural” and “Keep It Dry.” The soil surface should not be scraped off or graded and tubing installed if the soil is too wet and subject to smearing or compaction.

One advantage of drip tubing is that it can be placed on contours around trees so it can be installed in forested areas with minimal disturbance to trees. If trees are removed on the site the stumps can be left without removal. Just like in mound installation these stumps should be left as they are; removing them causes soil damage and compaction on the site and violates the KINN principle.

In areas with shallow bedrock or a high water table, fill may be required to provide the proper separation distance to provide treatment of the effluent. In my opinion, the fill should be clean sand such as that used in mound installation. The same preparation procedures as with mounds should be used. The soil surface should be scarified before placement of the sand fill. Scarification can be done by backhoe bucket teeth or chisel plows. Tracked equipment should be used to place the sand over the area, keeping at least 6 inches of sand under the tracks to prevent compaction of the original soil.

Typical depth of installation of the tubing is 6 to 12 inches, so if the tubing is placed in the fill it should be at least 12 inches in depth. For the research and demonstration system I worked on while at the University of Minnesota we installed the tubing 6 inches into sand fill 12 to 18 inches deep. As I mentioned in the placement discussion, we did experience freezing problems at this depth due to foot traffic across the site in the winter, so there is a 12-inch depth of bury requirement in the Minnesota code to avoid freezing issues in the dripfield.

Whether the tubing is trenched in or through the use of a proprietary dripline tool, it must be done in a manner that the tubing is not stretched. After the tubing is laid, soil around and over the tubing should be compressed to provide good soil-to-tubing contact. Often this means carefully driving over the lines. Again, it is critical if this is done that the soil be dry.

This article is part of a series on drip distribution:

• Is Drip Distribution Right for Your Site?
• Choosing a Filter for a Drip Distribution System
• Sizing a Drip Distribution System
• Tips for Drip System Design
• Site Prepping for Drip Distribution Installation
• Tips for Drip System O&M
• Controlling the Flow: Drip System O&M