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Soil Suitability / Nitrate Loading Study <br /> 11065 North Alpine Road I Stockton, California r rerracon <br /> June 30, 2026 1 Terracon Project No. NA267068 <br /> The total maximum daily flow rate for the proposed ADU is 420 gpd. However, the <br /> average long-term daily rate is estimated at 200 gpd. Combined with the existing <br /> residence, the average long-term daily rate is estimated at 450 gpd. <br /> Based on the nitrate loading balance, nitrate levels for the proposed development are <br /> anticipated to increase nitrate levels up to 12.7 mg/L-N which is above the MCL of 10 <br /> mg/L-N. The result of the nitrate loading balance (12.7 mg/L-N) indicates that the <br /> proposed development may cause an increase of nitrates in the aquifer above the MCL. <br /> In summary, the parcel appears suitable for the proposed development. The septic <br /> system design should accommodate peak flows and follow the San Joaquin County <br /> OWTS standards where applicable. If the EHD requires mitigation for the project, an <br /> advanced water treatment product may be considered a mitigation option. Additionally, <br /> water treatment options for drinking water should also be considered. <br /> 4. LIMITATIONS <br /> As indicated, our study takes into account the subject property only with the sewage <br /> load applied over the property site area. The study does not take into account <br /> surrounding properties and/or lands. The method utilized for the nitrate loading analysis <br /> is based on a simple mass balance formula, discussed in a published article by <br /> Hantzsche and Finnemore (1992), which provides a convenient and simplified method to <br /> estimate long-term groundwater nitrate impacts on an area-wide basis. A more detailed <br /> analysis was not requested nor intended. <br /> Our professional services were performed, our findings obtained, and our conclusions <br /> proposed in accordance with generally accepted engineering principles and practices. <br /> This warranty is in lieu of all other warranties either expressed or implied. Test findings <br /> and statements of professional opinion do not constitute a guarantee or warranty, <br /> expressed or implied. <br /> S.SELECTED REFERENCES <br /> California Department of Conservation Geologic Map of California, <br /> https://maps.conservation.ca.gov/cgs/gmc/, accessed October 2023 <br /> California Department of Water Resources Sustainable Groundwater Management Act <br /> (SGMA), https://sgma.water.ca.gov/webgis/?appid=SGMADataViewer#gwlevels, <br /> accessed October 2023 <br /> Facilities I Environmental I Geotechnical I Materials 20 <br />