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20 July 2021 AdvancedGeo Project No. 21-6486 AnEmployee-Owned Compony Page 15 of 15 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 (1,600 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. 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. AGI recommends installation of a 1,600- or 2,000-gallon septic tank to offset elevated nitrate levels. • Nitrates were detected above the State of California Maximum Contaminant Level in the domestic water well serving the smaller residence (East Well). Nitrates were detected below the State of California Maximum Contaminant Level in the domestic water well serving the larger residence (West Well). DBCP was not detected abovethe State of California Maximum Contaminant Level in either of the on-site water wells. • All approved septic system use should follow the EHD Onsite Wastewater Treatment System Standards. 13.0. LIMITATIONS Our professional services were performed using that degree of care and skill ordinarily exercised by environmental consultants practicing in this or similar localities. The findings were based on field testing results. Evaluations of the hydrogeologic conditions at the site for the purpose of this investigation were made from a limited number of available data points (i.e., test hole and field data) and subsurface conditions may vary away from these data points. No other warranty, expressed or implied, is made as to the professional interpretations, opinions and recommendations contained in this report.