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18 September 2020 AdvancedGeo Project No. 20-6116 An Employee-Owned Company Page 14 of 15 '0 N M 9.7. IMPACT OF NITROGEN LOADING FROM SITE PROJECT TO DOWNGRADIENT WATER SOURCES The recharging of groundwater is the most likely potential feature that could impact future nitrogen loading. Since the subject property is flat, AGI does not anticipate percolating effluent will affect any nearby water sources. Based on the volume of wastewater to be generated and the depth to groundwater (20-30 feet bsg), the potential vertical migration would not likely degrade the local groundwater. A total of 1.41 ppm of additional nitrogen is estimated to be added to the site over the long term through wastewater recharge from the proposed septic system. The nitrogen loading value is below the desired value of 10 ppm. 10.0. TOTAL NITRATE IMPACT FROM PROPOSED PROJECT Based on the method and assumptions described, proposed NO3_N mass of wastewater and the calculations of the NO3_N loading predicted, the existing development will not negatively impact NO3_N loading rates within the aquifer. The soil at the site appear to be adequate for nitrate degradation and proper leaching of wastewater. A total of 1.41 ppm of nitrogen is estimated to be added to the site over the long term through wastewater recharge from the onsite septic system. 11.0. MITIGATION METHODS PROPOSED To mitigate any known or potential future impacts of nitrate to soil and groundwater from the proposed septic system, the following mitigations could be implemented: • Maximize wastewater hold time where practical (retention). • Avoid use of bioattenuation chemicals (bleach etc.). • Properly and regularly maintain the property septic system. • Use EHD criteria for sizing the septic disposal field. If re-location or expansion of leach fields becomes necessary, leach lines should include high organic substrates under and surrounding the lines installed. 12.0. CONCLUSIONS AND RECOMMENDATIONS Based on this Soil Suitability and Nitrate Loading Study, AGI concludes the following: • The percolation rates meet the minimum EHD standards. • The nitrogen loading rate is below the desired value of 10 ppm.