TEMS garding the sign-off at this time may reduce the saleability of your house in the future. On the other hand, you could reexpose the drain field for inspection when the need arises and live in fear of being interrogated by a 200-lb sanitarian until then. When you backfill, be sure to mound the soil over the trenches because there will be significant settling (natural compaction). Even after settling, there should be a mound over the trenches SO that rain runoff will not enter the trenches and overload the system. Also, provide channels SO that runoff will not accumulate on the uphill side of these mounds. Finally, plant some shallow-rooted plants- grasses are fine - to hold the soil together and prevent erosion of the mounded soil. Deep-rooted plants have been known to invade and plug up distribution pipes. A map of the location of the septic tank and drain field will prevent a lot of frustration later. Operation and Maintenance Septic tank absorption systems require little maintenance if prop- erly designed and used. The salt water discharge from regenerating water softeners has not been shown to be a detriment to the func- tioning of the septic tank or absorption system, except that there is an increased hydraulic load which, for safety, should be considered in the initial design. In general, proper maintenance and operation of the septic tank (see the section on Septic Tanks in Chapter 4) is adequate to assure proper functioning of the drain field. Growth of roots into the distribution pipe is normally prevented by the gravel above and around the pipe. Roots don't grow into dry air-filled spaces. Where roots appear to be causing a problem, 2 to 3 lb of copper sulfate flushed down the toilet once a year should kill any invading roots, according to the Manual of Septic Tank Practice. It is a wise precaution to check the plumbing fixtures in the house for leaks on a periodic basis. These leaks, particularly leaks in the toilet reservoir, can overload the drain field in a short time. Finally, use common sense 