cover bottom, sides, and ends. Butyl rubber is better but more expensive. Com- pacted clay or bentonite is acceptable in some areas. 2. Crushed rock or gravel to embed distribution pipes. 3.7 yd3/100 ft of distribution pipe 3. Synthetic filter fabric to cover gravel. Treated building paper is acceptable. Use 18-in. strips. 4. 4-in. diameter perforated distribution pipe 5. Medium sand, 0.06 mm to 2.0 mm, half of which is smaller than 0.1 mm. 10.2 yd3 of ET sand per 100 ft2 of 30- in.-deep bed. 1.2 yd3 of bedding sand per 100 ft2 if bedding required 6. Liner cement and pipe (hose) clamp to seal inlet pipe liner penetration 188 ONSITE WASTEWATER DISPOSAL Construction It is safe to assume that many, if not most, of the ET systems that have failed in the country have failed because of faulty siting and/or faulty installation procedures, SO pay careful attention to this section. First, it's fine to install ET systems in moist clay, and you can smear the clay all you want to. But an ETA bed is extremely difficult to dig without smearing the surface. Install them only in the sum- mer when the soil is bone dry. Then pick up a garden rake and go on a search and destroy mission to eliminate smears that may have slipped by. Make the bed no wider than twice the reach of the backhoe SO that equipment need not drive on the bed surface, and make the bottom level. You don't want permanent saturation at one If the soil where the ET bed is located is rocky, a 2-in. layer of sand is required as a bedding to prevent the liner from being punctured. This bedding should extend about halfway up the sides as well. When digging the trench from the septic tank site to the bed, keep in mind that the inlet pipe to the bed should never enter the bed any lower than about 6 in. below the overflow level of the bed. The reason for this is that as the saturated level in the bed rises, the sewage in the bed should not be allowed to run back into the septic tank. This causes all sorts of problems and could result in sewage exiting the septic tank ins