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n � Therefore,the LTAR for a 36" pit should be: 243 ft'/3 ft dia. x 25 ft deep = 121 gallons/day x-three pits/house= 363 gallons/day of effluent absorbed/house. Calculated flows =68 gals/person x 4 persons/house=272 gals effluent generatedihouse. Analytical chemistry done on a water sample from the on-site well reveals a medium nitrate concentration of 18 ppm. The question arises as to the origin of this nitrate concentration. From the USDA Soil Map aerial photo and the USGS Map, land use upgradient (assuming groundwater flow to be in a northeast direction) to the property was in agricultural production. The USGS Map depicts an orchard directly west of the property before the opening of the gravel quarry pit. Given that agricultural production occurred three or more decades ago, it is possible that the nitrate concentration observed in the well originated from this land use. However, this could not be definitively determined without highly sophisticated testing and modeling. Irrigation water suitability has been discussed on Page 4 of this report and reveals moderate limitations of the underlying groundwater for surface and sprinkler irrigations. In addition, the well water is very hard. Consequently, homeowners may want to install sodium-based water softeners. However, sodium would be highly detrimental to the permeability of the on-site soils, and the lifespan of a septic system with water softened influent would be significantly reduced. The sodium concentration of the well water was determined to be 55 ppm, which can be considered an average concentration. 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. Septic system failure would primarily result from the advanced formation of the biomat 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 biomat bacteria. However, since the surface soils are composed of silty clay, anaerobic conditions may prevail. To decrease biomat formation, two septic tanks should be installed in series, and a filter installed in the second chamber of the second tank for each new house. In addition, no garbage disposals should be installed to prevent high organic loading. A second septic tank creates two beneficial and favorable conditions. First, additional retention of solids occur,preventing organic material from entering and clogging the soil/effluent interface, thus alleviating additional nitrate-nitrogen loading. Secondly,nitrate-nitrogen mitigation with two tanks may be accomplished through the following processes: It has been well-documented that gaseous nitrogen emanates from septic tanks. The gaseous formation is apparently attributable to denitrification which is the biological reduction of nitrate (NOO and nitrite (NO2) to volatile gases. The biochemical processes which occur in septic tanks are highly complex but can be described simplistically: A microbe digesting a waste organic molecule with an attached nitrogen atom may have the freed nitrogen as a surplus atom. To digest the N atom, the microbe can combine it with dissolved molecular oxygen Oz and release it in solution as a molecule of nitrite and possibly nitrate. This occurs under aerobic conditions and is referred to as nitrification. If a microbe needs oxygen within an anaerobic environment, it can take the oxygen from nitrite or nitrate molecules. Not requiring surplus nitrogen atoms, the microbe can combine pairs of surplus nitrogen atoms to form nitrogen gas (N). This is the denitrification process. Therefore, the first septic tank should contain a higher concentration of oxygen from sink faucet aeration and the flushing action of toilets. 11 Chesney Consulting