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30 March 2022 Project No. 22-6800 Page 14 of 15 AdvancedGeo An Employee -Owned Company and the calculations of the NO3_N loading predicted, the proposed development may 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 12.33 ppm of additional nitrogen is estimated to be added to the site over the long term through wastewater recharge from the proposed 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) by installing a larger septic tank (2,000 gallons). • Avoid use of bioattenuation chemicals (bleach etc.). • Properly and regularly maintain the property septic system. • Use EHD criteria for sizing the septic disposal field. • Utilize an advanced treatment system to reduce nitrate loading and the percolation rate. 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 rate meets the minimum EHD standards in the proposed septic system disposal field. • The nitrogen loading rate is above the desired value of 10 ppm. • Installation of a septic tank that is larger than the minimum requirement to offset the elevated nitrate loading rate. • Nitrates were detected below the State of California Maximum Contaminant Level (MCL) in the onsite water well; and DBCP was not detected above the laboratory reporting limit. • All approved septic system use should follow the EHD Onsite Wastewater Treatment System Standards.