I’am installing a subsurface drainage system. What i would like to find out is, How much grade per foot and what’s the best way to set your grade. Do i need just a inch or more gravel on the bottom of the trench to then start my grade.Is there away i can use a string and level. thanks scott
Scott, if you a installing a gravity flow drainage pipe for sewage then the preferred grade of the pipe is 1/4 inch drop (or greater)per foot. The minimum grade in most ISDS Regulations is 1/8 inch per foot. If you are draining septic tank effluent, or clear water, then 1/8 inch per foot is adequate.
The most precise method to use to prepare a specific grade in a trench is to rent a laser level, and then get into the trench with a flat shovel, and a rake. Another approach is to determine the desired grade, and then tape a small block of wood to one end of a 2 foot long level. If you desire a 1/8 inch per foot grade in the trench, tape a 1/4 inch thick block of wood to the end of the level. Grade about 10 feet of the trench by “eye balling” it, and then place a “straight” 2 4 in the bottom of trench. Set the modified level on the thin edge of the 2 4. When the bubble on the level is between the lines, then that 8 feet of trench is correctly graded.
If you are installing distribution pipes in a leach field, then the trench should be level. Good Luck. JWA