face downhill from the disposal site. If a layer of rock, clay, or other impermeable or slowly permeable soil exists below the surface, a deep trench can be used to get below that layer and into a more permeable stratum. Seepage pits serve the same functions as deep trenches, and they can be installed in smaller areas. However, because they are gener- ally deeper than deep trenches, a considerable depth of soil is required to install them. ONSITE WASTEWATER DISPOSAL Sand mounds serve to elevate standard absorption trenches (or beds) above the soil surface in order to provide sufficient soil below to cleanse the sewage effluent before it reaches a limiting zone, such as the ground water table, bedrock or coarse sand or gravel. Where there is a shallow layer of relatively permeable soil over a relatively impermeable layer, the sand mound can distribute a reasonably clean effluent to that top permeable layer of soil. This is a practical alternative to the deep trench or seepage pit, where the imperme- able layer is quite thick. Sand filters produce a very high quality of effluent, and are used most often where federal discharge standards must be met as sew- age effluent is discharged into a watercourse. This option is not a practical disposal method for the individual homeowner because of the nature of the federal permitting process. Nevertheless, state or local regulatory agencies may be willing to reduce the clearance requirements from the bottom of disposal fields to bedrock or ground water, based on the superior effluent quality. Further, where coarse sand or gravel is present, sand filters are an alternative which can provide adequate cleansing before discharge into this too coarse soil. Land application is a method of wastewater reuse, as well as dis- posal. Land application can be accomplished by spraying treated effluent onto the land surface with sprinklers, irrigating at the land surface, or distributing effluent beneath the land surface in shallow covered trenches. Since this alternative provides either s