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should have a 12,000 square foot leachfield area due to the virtually non-existent perc rates at the 42 inch depth. A 50% standby replacement area must also be incorporated into the design. This leachfield area will help ensure stability and guard against leachfield failure. A failure would primarily result from the formation of a "biomat" or "clogging mat" on the wetted soil interface where the effluent enters the soil. 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. However, due to the high clay content of the shallow soil horizons, anaerobic conditions will most likely prevail. With respect to the protection of the underlying groundwater from pathogens and primarily nitrates (NOA the soil structure of the subject parcels along with the depth to groundwater can be considered favorable for prevention of contamination. The nitrogen cycle and the eventual formation of nitrates are highly complex within the soil environment. The subject parcel soils are conducive for two beneficial nitrogen cycle processes, namely fixation of ammonium and denitrification. Fixation of ammonium (NH4) can occur with the adsorption of ammonium molecules onto expanding clay particles, which is the predominate shallow soil texture of the subject site. With this adsorption, ammonium becomes "fixed" and is unavailable for biological transformation to nitrate. Denitrification occurs under reduced oxygen supply or anaerobic conditions. This happens when water or effluent fills the soil pores. With a clay soil structure, soil saturation is easily achievable, thus promoting an anaerobic environment. Under these conditions, nitrate-nitrogen serves as an electron acceptor and is reduced to harmless gaseous nitrogen forms. As can be noted, we have opposing and conflicting processes between molecular nitrate denitrification and clogging mat degradation. Denitrification takes place under anaerobic conditions, however, clogging mat degradation is retarded. Therefore, is our opinion that the use of sumps or seepage pits are necessary since anaerobic conditions will probably prevail and promote denitrification and not clogging mat degradation. The number of sumps or pits will be dependent upon the number of bedrooms each structure may have and the number of children that may occupy the residence. In addition, all related development structures such as wells, etc. will have to comply with the published "distance" requirements from the septic systems. E �uulity -ontrol I_P_t1