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Soil Suitability / Nitrate Loading Study r ierracon <br /> FLAG CITY TRUCK AND EQUIPMENT PARKING FACILITY I Lodi, California <br /> October 6, 2023 1 Terracon Project No. NA237081 <br /> for septic system design purposes. Typically, use estimates for septic system sizing <br /> include a peak use factor. <br /> As the facility is proposed to be open daily year-round, a long-term average daily flow <br /> rate was not calculated. The total maximum daily flow rate for the proposed Septic <br /> System is 18.75 gpd per person (Section 1.3.7). Additionally, the total maximum daily <br /> septic tank usage was calculated as 375 gal per day for the proposed facility. <br /> The average total nitrogen concentration of domestic wastewater is normally considered <br /> to be 20 to 85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, <br /> 1998, Table 4-14). It is estimated that commercial use will have higher concentrations <br /> of total nitrogen when compared to residential use. For the purposes of the nitrate <br /> loading estimate, it is estimated that the average concentration for total nitrogen in <br /> wastewater for the project is approximately 85 mg/L-N. <br /> 2.3.4.2. Denitrification Estimate <br /> Denitrification is an important process which occurs within the leach field whereby <br /> certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to <br /> the atmosphere. Denitrification is expressed as a percentage, and the normally accepted <br /> range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, <br /> high pH, and organic material denitrify by about 35 percent, and soils with high sand <br /> content and fast percolation rates are estimated to denitrify at a lower rate, about 10 to <br /> 15 percent. <br /> Based on the results of the shallow and deep soil borings, the proposed leach field is <br /> expected to be located within silty sand; therefore, a denitrification estimate of 15 <br /> percent was selected. <br /> 2.3.5. Nitrate Loading Scenario <br /> A nitrate loading scenario was performed to determine the impact from the proposed <br /> project. The scenario utilizes the variables discussed previously which represent the <br /> estimated conditions and uses associated with this project. The following table presents <br /> a summary of the nitrate loading calculation for the site. A copy of the nitrate loading <br /> calculation is included in Appendix F. <br /> Facilities I Environmental I Geotechnical I Materials 17 <br />