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�. The percolation test results indicate the typical leachline depth soils of approximately 40 inches below grade have a porosity that allows rapid percolation. Seepage pits and sumps are not warranted or allowed in this area. If the perc rates for any one of the 11 parcels was less than 1 minute/inch, a heavier loam soil would have had to have been imported into over-excavated leachline trenches to an approximate two-ft thickness. This would be in compliance with the U.S.E.P.A. Design Manual- Onsite Wastewater Treatment and Disposal Systems (Page 213). Ultimately however, the formation of a biomat will reduce effluent infiltration and percolation within the leachline trenches. ` Septic system failure would primarily result from the advanced formation of the 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 a sandier soil material, aerobic conditions should prevail over time which may inhibit leachline failure. The total length of leachline will be dependant upon the number of bedrooms each new home will have. Additionally, the system should be oversized if a number of people, especially children, will inhabit the residences. A 50% replacement area must be incorporated into the design. 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 lack of repairs to septic systems within the area, it is evident that systems in this area have significant longevity. However, it is recommended that a financial "sinking fund" be initially established to assist in paying for a possible repair/replacement. An accountant can assist with establishing this fund. The other percentage of nitrate loading can be from lawns/landscaping/gardens, which is estimated to be 20% and could be significantly higher. It is recommended to advise home purchasers to use "slow-release" nitrogen fertilizers to reduce nitrate loading from lawns, etc. Additionally, garbage grinders or disposals can add higher organic nitrogen loading rates and should not be installed. Contemporary scientific literature suggests that denitrification may be enhanced by placing proposed leachlines higher in elevation toward the soil surface. This would be advantageous since the surface soils consist of approximately 20% of the fine soil fraction(silts and clays). Deciduous and evergreen plants may be planted near the leachfield to uptake ammonium ions and nitrate ions which may form. Caution must be given to prevent serious root infiltration into the leachlines. These two procedures would theoretically provide a triple nitrate mitigation system of denitrification, absorption and evapotranspiration. Without sophisticated groundwater monitoring, the groundwater depth at different times of the year,the groundwater directional flow, and potential off-site nitrate sources impacting the subject L property are unknown. This report did not utilize highly complex groundwater modeling techniques since it has been well documented that the impact is tremendously variable and not all information such as well logs or other geophysical information is available. 12 Vaffey Ag Research