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(§ 7.0) CONCLUSIONS FThe results for proposed Parcel 1 and Parcel 2 sho�acceptabl percolation for the of existing and any future septic system effluen ow ffluent management wills/ ur at the typical leachline trench depth of 42 inches. As noted from the perc test results or Parcel 1, as the soil becomes saturated in the shallow strata,percolation potential decreases. At the discretion of EHD, any future septic system will be installed with either sumps, seepage pits, or leachlines exclusively. This locale has historically had seepage pits and sumps installed; however, EHD may only allow leachlines due to the nitrate concentration in the underlying groundwater. Although the permeability is greater at the deeper depths versus the shallower depths, as biomat formation "climbs" up the walls of the seepage pits or sumps, it will eventually encounter this slower porosity soil for diminished effluent management. Any future proposal to build on Parcel 1 or Parcel l must have the leachfield installed within 100 feet of the perc test locations as denoted on the Tentative Map. The underlying soils possess increasing moisture content with increasing depth, as determined in the 23 ft test boring. This is due to the rainfall that occurred March/April 2006. High moisture content soils are beneficial for the suppression of nitrification, and the promotion of denitrification of nitrate molecules that may have formed through nitrification in the upper soil environments. EHD requires there be sufficient distance for"treatment' of septic effluent before it encounters the groundwater table. This distance is normally regarded to be five feet. Therefore, sufficient distance exists between the bottom of a maximum depth seepage pit of 25 feet and the current groundwater depth of approximately 60 ft. (§ 6.8) The number of leachlines and seepage pits, and septic tank sizes for any future structure will be dependant upon first, applicable governmental agency approval, and secondly, EHD requirements such as setbacks and number of bedrooms a proposed structure will have. (§ 6.7) No problems are anticipated for any future septic system on the property, other than typical lifespan concerns. It is important to recognize that all septic systems have a lifespan, which is dependant on several factors and is therefore difficult to determine. Lifespans can be measured in terns of months or years. Septic system leachline failure would primarily result from the advanced formation of a "biomat" or"clogging mat' on the wetted soilleffluent interface. This mat is composed mostly of aerobic and anaerobic bacteria and bacterial products consisting of a slime of polyuronides and polysaccharides. If the soilleffluent interface is well aerated, a variety of soil microfauna such as nematodes and protozoa may digest the clogging mat bacteria. However, since the shallow subsurface soils on the property consist of silts and clays, anaerobic conditions may prevail over time which could decrease the expectant life of the existing, and any new leachfields. Lifespan will be dependant upon the efficiency of the leachline trench and/or seepage pit structures to manage effluent flows. If the leachlines are installed high in elevation, there will be a greater opportunity for oxygen intrusion from the atmosphere, thus theoretically assisting in biomat degradation, along with promoting evapotranspiration. I Page -5- Chesney Consulting