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[51 CONCLUSIONS The shallow percolation rate for the subject parcel suggests there would be effluent percolation at the leachline depths of approximately 42 inches below grade. However, based upon the number of repairs and additions to septic systems in the project locale, leachlines in this area have a limited lifespan. Percolative capacity does exist at deeper depths because it is well known that this area possesses significant gravel strata. The final sewage disposal area for any proposed structure should be dependant upon the number of bedrooms. We are recommending a 10,000 to 12,000 square feet leachfield area to provide treatment of the septic effluent. Seepage pits must be installed for any future residential or commercial structure. The number of seepage pits will also depend on the number of bedrooms or offices the structure will have. If there will be several people inhabiting the structure, particularly children, a septic system should be oversized (increase the number of seepage pits) to accommodate additional wastewater flows. A 50% standby replacement area (100% for commercial) must also be incorporated into the design of the septic system. All related septic system structures and the domestic well must comply with published "distance" requirements from property borders, roads, easements, irrigation fields, etc. It must be recognized that all septic systems have lifespans. If the leachfield area should fail, the seepage pits will manage the effluent percolation. Seepage pits can also fail, although over a longer time period. As referenced earlier, a failure would primarily result from the advanced formation of a "biomat" or "clogging mat" on the wetted soiUeffluent 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 subsurface soils consist of a tight, silty material, anaerobic conditions will probably prevail, which may hasten leachfield and seepage pit failure. If additional development should take place in the future on Parcel 1, we are recommending a deep perc test of 25 feet in the proposed location of the seepage pits. 3