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FFboundariers t to note that all septic systems have a lifespan. This lifespan is dependant on rs and is therefore difficult to determine. It is evident that septic systems within the It f the subject property and around this area will have a definite lifespan due to the lay soils. Sepfic system leachline failure would primarily result from the advanced a "biomat" or 'clogging mat" on the wetted soil/effluent interface. This mat is composed mostly of aerobic and anaerobic bacteria and bacterial products consisting of a black slime of polyuronides and polysaccharides. If the soil/effluent interface is well aerated, a variety of soil microfauna such as nematodes and protozoa may digest the clogging mat bacteria. Since the shallow subsurface soils consist mostly of clay soil material, anaerobic conditions will prevail over time which may hasten leachfield failure. ------------- Several investigations have been published in the scientific literature that suggests "resting" septic systems that are installed in clay soils. This resting is accomplished by installing a dual, or "minor" system which can be switched periodically between two leachfields. The period of time for switching ranges from six months to one year and must be done faithfully to maximize the lifespan of the system. The on-site filter beds have this "switching" capability. Additionally, installing filter bed or conventional leachlines at shallow depths would be beneficial by taking advantage of evaporation during favorable times of the year and increasing the denitrification potential. A 100% standby replacement area must be incorporated into any future system built on-site. All septic systems and domestic wells must comply with the published "distance" requirements from property borders, roads, irrigation fields, etc. As noted on the Leachline Requirement Map published by the Environmental Health Department, the subject property is in the "High Water Table Areas." The map shows that sumps or seepage pits are not allowed in this area. The nitrate concentrations determined in the underlying water table suggest there apparently has not been serious impact to the water table from the filter bed under examination, or from upgradient agricultural inputs, as would have been expected. This may be attributable to the denitrification potential of the indigenous clay soils. Page -6- Chemq Consulting