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a free -draining condition. The pressure manifold atop the filter must be self -draining to prevent freezing. Above ground wooden enclosure installations should consider treatment for carpenter ants and burrowing insects. An approved effluent tee filter should be installed in the septic tank. Above -ground units can have varying heights of the containment structure exposed above grade depending on land topography. The units include an electrical panel with a visual and audible alarm. Configuration of the installed system will depend upon the individual site characteristics and the manufacturer's recommendations. Dosing of the filter can be on demand, as tested, or by timer. If the system is designed for timed dose, a larger pump chamber is required. Theory of Operation Wastewater from a source (in most instances a residence) enters a standard septic tank. The septic tank effluent then flows by gravity to a pump chamber which is variously sized. An effluent filter on the outlet of the septic tank prevents the passage of large solids (>1/16") from entering the pump chamber. Within the septic tank, a portion of the solids are settled out, and the organic nitrogen is converted to the reduced mineral form of ammonium (NH4+). From the pump chamber the effluent is dispersed over the foam media. The foam is proprietary open -cell foam cut into 2" x 2" blocks and placed in random attitude in the containment structure. As the effluent percolates through the foam media, the consumption of the organic matter by microbes occurs. An overall reduction in the Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) occurs and the ammonium is oxidized into first nitrite (NO2) and then nitrate (NO3-2). Some microzones within the foam cubes that have the prerequisite anoxic conditions for denitrification result in the conversion of some of the nitrate to nitrogen gas (N2). At the bottom of the foam -media containment structure the percolate is divided by a dam that diverts approximately 50% of the percolate forward toward the soil absorption system. The reminder of the percolate (again approximately 50 %) is diverted back to the septic tank. Within the septic tank, the prerequisite anoxic conditions results in further denitrification of the wastewater. The process is purportedly enhanced by the substrate provided within the cylindrical basket containing man-made fiber. 2. Costs Installation The manufacturer claims that the Waterloo Biofilter® components including installation as installed at the MASSTC are $7,350 and to these costs should be added other conventional system costs for this installation of approximately $7,000. The cost of installation for any treatment technology is very dependent upon the particular site conditions, so readers should use the above estimates as approximations of average costs. Performance Results — WaterlooBiofilter® Page 3 of 28