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Soil attenuation mechanisms including volatilization, and adsorption of ammonia- <br /> nitrogen and denitrification of nitrate-nitrogen in the clayey soils present on the property, <br /> may remove at least 25 to 50 percent of the nitrogen originally present in the septic tank <br /> influent. Denitrification may remove up to 75 percent of the nitrate present in liquids <br /> under ideal conditions. Conservatively, if we assume that denitrification removes <br /> _ 25 percent of the nitrogen (48 pounds N/year), approximately 144 pounds of N/year <br /> would be loaded onto soils from the 5-acre property. <br /> In general, agricultural activities in the area use nitrogen fertilizers at the rate of <br /> 50 to 300 pounds of N/Acre-year. Given the efficiency of N fertilizer, uptake by crops, <br /> which varies from approximately 25 to 75 percent, nitrate leaching from agricultural <br /> fertilization ranges from approximately 50 to 100 pounds N/Acre-year. If we assume that <br /> the proposed Phase 2 expansion contributes 144 pounds of N under the worst-case <br /> conditions, the loading rate from the Phase 2 expansion would be equivalent to 28.8 <br /> pounds N/Acre-year. We would expect much lower rates of actual nitrogen loading from <br /> the septic system because the nitrogen loading estimates are conservative (higher than <br /> we expect). We have assumed a very low value (25%) for denitrification and other soil <br /> nitrogen attenuation factors. <br /> 7.0 SUMMARY AND CONCLUSIONS <br /> This section presents a summary and conclusions on the suitability of the property <br /> for septic system expansion. Information on the regional and local land use, depth to <br /> groundwater, groundwater quality, flow direction, soil profile description, percolation <br /> tests, density of septic systems in the vicinity, existing septic system design, the <br /> proposed Phase 1 and 2 loading estimates of liquids and nitrogen were used to assess the <br /> soil suitability and nitrogen loading study for the proposed expansion of the septic system <br /> on the property. Our summary of these results are presented below: <br /> • The Proposed Phase 1 expansion of the property will result in liquid loading <br /> at the rate of approximately 2,025 gallons/week, and nitrogen loading of <br /> 1 .14 lbs/week (60 lbs N/year); <br /> • The proposed Phase 2 expansion will result in a liquid loading rate of <br /> approximately 6,525 gallons/week, with approximately 3.7 lbs N/week <br /> (192 lbs N/year); <br /> SAC 125.12 12 <br /> �, DAMES &MOORE <br />