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FNCLUSIONS AND RECOMMENDATIONS NLS§ 4.2. The shallow subsurface soils underlying the subject property where the new filter bed disposal area is to be installed, reveals a loamy sand soil structure with rapid permeability and a low-to-medium degree of natural denitrification potential. The importation of organic material onto the floor of the filter bed must be implemented to attenuate nitrate loading. It so happens that the Heatwole's own a woodworking business and have access to significant amounts of sawdust. A sample of this sawdust was submitted for laboratory analysis of the carbon-to-nitrogen (C:N) ratio that was measured at a very high ratio of 140:1. Nitrification will only occur if the C:N ratio is below 20:1. Therefore, two inches of this sawdust materia is to be placed on the floor of the filter bed and then raked into the soil. Raking and incorporation must be done since I have directly observed that just laying organic matter on the soil-effluent surface creates a manufactured biomat material, thus slowing permeability. The sawdust will increase the C:N ratio of the soil at, and within the two-inch depth of the soil- effluent interface, where most nitrification occurs. s o 1{t2� -For N i-tri�j eg41 art!y kyp-Ws ;f �':lri^q�:a L NLS§4.1. The nitrate loading calculations show the resultant effluent from the second unit dwelling will theoretically possess a concentration of approximately 21.8 ppm as nitrate-nitrogen, which is 2.2x over the MCL. Given that the ADF of 840 gpd has two extreme components of two people per bedroom, and that this flow volume will occur every single day of any given year,has created a very large nitrate loading safety factor. This factor is conservatively estimated at 2.5.C7 Without this factor, the ADF from the proposed residence would be at a reasonable 336 gpd,thus lowering the nitrate loading calculations significantly and possibly below the nitrate loading MCL. The application rate was determined from the perc rate to be 0.743 gallons/ft'/day. The total filter bed area is 720 ft2 of floor area. Therefore, the filter bed can manage: 0.743 gallons/ft2/day x 720 ft2 = 535 gpd. The existing on-site domestic well has a nitrate concentration of 4.57 mg/L, which is 5.43 mg/L under the Maximum Contaminant Level (MCL) of 10 mg/L, or 45 ppm nitrate. NLS§ 4.2. All decentralized wastewater management systems (septic systems)will eventually fail. A reasonably long lifespan of the primary and reserve area systems can be expected based on the perc rates obtained and the incorporated design factors. Page -7- Chesney Consulting