Alternate Filter Material
Alternate filter material for the above systems could include filters of peat which is very permeable and can absorb materials readily, loam, crushed glass, and textiles. The advantages of the alternate media filters are they are moderately inexpensive, have low energy requirements, and do not require very skilled people to produce a high quality effluent. These systems may be used if an existing tile system has failed. They can operate over long periods of time. The disadvantages are that the technologies have not been fully approved, cost and maintenance has not been standardized, the filter medium may not be readily available, and there is a possibility of odors. (See endnote 19.)
A mound system is an above-ground leaching field consisting of a mound of various sizes of aggregate including sand and gravel as well as fill material. The effluent coming from the septic tank either flows down through the mound by gravity or is pumped to the top of the mound and then flows down to drains where the effluent has to still be absorbed in the ground. All of the processing of the effluent must take place in the mound. People object to this type of system because it might not work as described and it makes the property have a funny look. Mounds only work in certain types of conditions. They are especially used if soil permeability is extremely slow or extremely fast, if there is shallow soil cover over cracked or porous bedrock, and if there is a high water table. Construction costs are typically much higher than for the typical septic tank system, the permeable topsoil available is limited and is damaged easily, the mound may affect drainage patterns, and all systems have to have pumps or siphons. (See endnote 18.) A raised bed system is similar to a mound because it is constructed on the top of the soil and a certain amount of treatment of the septic tank effluent happens.