ngs. (Figure 5.10 shows a backhoe bucket with teeth on the side to rough up the sides of a trench.) If you want to add standpipes for access and observation, now is the time to do it. Perforate the pipe with 0.25- to 0.5-in. holes along the length of the pipe where it will be sitting in the gravel. Later, the pipes will be cut off with 6 in. or more rising above the ground CONVENTIONAL WASTE DISPOSAL SYSTEMS surface. These pipes should be capped at the top to reduce odor and insect problems, but don't cement the caps to the pipe. Tie the standpipes to a stake driven into the trench bottom SO that the lower end of the pipe is several inches above the soil. The stake should be sturdy enough that the addition of gravel will not knock over the stake and pipe. If you plan to install geotechnical fabric, do SO before you add gravel. Be sure to drape it along both sides of the trench and leave enough to fold over the top of the gravel fill. It is not necessary to cover the trench bottom with fabric. The next construction step is to add gravel to the trench. And the next problem is to get the gravel surface level. This can be done by driving stakes into the trench bottom every 10 ft or so, SO that the tops of the stakes are as high above the bottom of the trench as the gravel is to be deep. Then simply add gravel to the level of the tops of the stakes. The gravel should be in the range of 0.75-in. to 2.5-in. diameter rocks. The gravel should be washed SO that no fine soil will wash into the trench sides and plug up the soil pores. Most crushed or river run rock is suitable, but there is some rock, such as soft lime- stone, which will dissolve over time and leave a layer of cement around the trench (Figure 5.11). Crushed shell does this too. If you are unsure about the quality of gravel, ask a supplier. Next, dig a narrow trench from the septic tank outlet to the start of the trench excavation. This connecting trench should slope evenly with the upper end trench bottom at the level of the bottom of the septic tank outlet 