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v r <br /> can occur under saturated effluent flow. Saturated flow fills all pores of the soil, which is easily <br /> achieved in a clay type soil. Unsaturated flow enhances the ability of the soil to retain microbes <br /> which may have passed through the "biomat" or "clogging mat" or through as yet, unclogged soil <br /> interfaces. These microbial retention properties of the clay fraction become more important with <br /> the formation of the biomat. The biomat is of prime consideration concerning leachline and <br /> seepage pit failure since it decreases the soil permeability to the point inefficacy. It forms on the <br /> wetted soil interface and is composed of facultative bacteria, both anaerobic and aerobic in <br /> nature. These bacteria create a slime of polyuronides and polysaccharides which may be black in <br /> color from the precipitation of ferrous sulfide. If the wetted soil interface is well aerated <br /> (aerobic), several types of soil microbes such as nematodes and protozoa may consume the <br /> bacteria, as well as the biomat slime. However, the high clay content soil at the leachfield depth <br /> of 42 inches andh <br /> t e seepage pit depth of 25 feet, may favor an anaerobic environment due to the <br /> micropores of the clay soil, thus leading to biomat formation. If a biomat forms in the seepage <br /> pits, the mat moves upward along the sides, year after year. This forces the effluent to "pond" at <br /> a higher level each year to percolate through an unclogged strata. It may be a possibility that as <br /> the effluent rises, it will eventually reach the 14 to 16 foot fine sand strata where sufficient <br /> percolation and aeration will produce acceptable effluent management. The advantage with <br /> seepage pits is that hydrostatic pressure forces effluent through the biomat, as the buildup <br /> increases. The effluent in a pit will fluctuate up and down at least 1.8 to 4 times the extent as <br /> found in a leachline. This fluctuation may allow the soil-effluent interface to become <br /> theoretically aerated and remain aerobic and permeable. <br /> The other important consideration with regard to the soil is contamination from nitrate. Certain <br /> types of clay soil may be conducive for the attenuation of nitrate formation, through the process <br /> of denitrification. The nitrogen cycle and the eventual formation of nitrates are incredibly <br /> complex_ mechanisms within the soil environment. <br /> 3 <br /> Vafty A9 Ppearch <br />