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161 CONCLUSIONS The percolation rates and the depths at which they were performed illustrate that seepage pits or possibly sumps will have to be used for any future septic systems on the subject parcels. The information obtained from the Environmental Health Department concerning the number of Application permits for seepage pits also indicates a need for this type of septic system. It will be the determination of the Environmental Health department which type of system may be used. However, if sumps are installed, we recommend using an "extend-a-hoe" to excavate down to 20+ feet. Seepage pits may be more cost effective. The number of seepage pits or sumps for the proposed residence will be dependent upon the number- _ of bedrooms the structure will have, or the number of occupants, particularly children. The pits should be at least 33 inches in diameter and installed to a maximum depth of 25 feet. All related development structures such as wells, leachfields, etc. will have to comply with the published "distance" requirements from applicable objects such as property borders, crops or ponds. Each proposed septic system should have a 12,000 square foot leachfield area due to the virtually non-existent percolation that would occur at the 42 inch depth. A 50% standby replacement area must also be incorporated into any design. This proposed 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 where the effluent enters. 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 nitrates (NO;), the soil structure of the subject parcels, along with the depth to groundwater, can be considered favorable for prevention from contamination. The referenced well with high nitrates may be a shallow well with a poor or non-existent grout seal. It is our opinion that the existing septic systems and any future residential septic system will have an inconsequential impact on the groundwater due to the following: 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 Mality &.w Inspection