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[51 CONCLUSIONS 77dep'ths ult for Parcel 1 suggests there will be excellent effluent percolation at deeper e typical shallow leachline depth of 42 inches. This deep test depth of 9 ft can be considererepresentative of percolation that would take place in sump-type septic structures. Although there was percolation within the shallow test boring, which indicates that leachlines in this locale can manage effluent, it was evident that percolative capacity decreases with soil saturation. It is important to note that all septic systems have a lifespan. This lifespan is dependant on several factors and is therefore difficult to determine. From the number of repairs and additions done in the study area, it is evident that septic systems within this area have a limited lifespan. It is recommended that if any structure with a septic system is built on the Designated Remainder, there must be a percolation test done in the area of the proposed leachfield. A shallow perc test at 42 inches should be conducted in the proposed leachfield area, along with a deeper test representative of sumps or seepage pits. With concurrence from the Environmental Health Department, sumps may be preferable to seepage pits since there would only be a 10 ft separation distance between the floor of a 25-ft pit and the static water table. Sumps would allow a greater "treatment" distance. In addition, the leachfield must be hydraulically protected during the rainy season to prevent inundation. A 50% standby replacement area must be incorporated into the design. All related septic system structures and a possible new domestic well must comply with the published "distance" requirements from property borders,roads, irrigation fields, etc. As noted on the attached Leachline Requirement Map,the subject property is just over the border of the silt/sandy clay soil area. The map indicates that sumps or seepage pits are allowed in this area. Septic system leachline failure would primarily result from the advanced formation of 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 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 tight, silty type soil material, anaerobic conditions may prevail over time which may theoretically hasten leachline failure. It is assumed that this accounts for the high number of system failures in this area. Therefore, seepage pits or preferably sumps must be installed. The nitrate concentrations determined in the underlying groundwater suggests there has been very low impact to the deep aquifers and can possibly be considered background nitrate levels. Regardless of the nitrate concentration of any well water in rural areas, it is recommended that bottled water should always be used for drinking and cooking purposes. 4 Va&y Ag Research