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Soil Suitability /Nitrate Loading Study Irerracon ALL STAR HEAVY HAUL & TOWING INCORPORATED Tracy, California July 1, 2022 Terracon Project No. NA217024 2.3.4.1 Quantity and Quality of Wastewater from Project The following discussion is for determining the long-term wastewater flow generated from the proposed development for the nitrate loading analysis and should not be used for septic system design purposes. Typically, use estimates for septic system sizing include a peak use factor. As the facility is proposed to be open daily year-round, a long-term average daily flow rate was not calculated. The total maximum daily flow rate for Phase I and proposed Septic System 1 is 16.875 gpd (Section 1.3.7). Additionally, the total maximum daily septic tank usage for the on-site residence was calculated for a total of 150 gpd consisting of 100 gal per day for the initial bedroom plus an additional 50 gallons per day for each additional bedroom. With the combination of the proposed facility and the residence as a total of 167 gpd. The average total nitrogen concentration of domestic wastewater is normally considered to be 20 to 85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998, Table 4-14). It is estimated that commercial use will have higher concentrations of total nitrogen when compared to residential use. For the purposes of the nitrate loading estimate, it is estimated that the average concentration for total nitrogen in wastewater for the project is approximately 85 mg/L-N. 2.3.4.2 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 to 15 percent. Based on the results of the shallow and deep soil borings, the proposed leach field is expected to be located within silty clay; therefore, a denitrification estimate of 35 percent was selected. 2.3.5 Nitrate Loading Scenario A nitrate loading scenario was performed to determine the impact from the proposed project. The scenario utilizes the variables discussed previously which represent the estimated conditions and uses associated with this project. The following table presents a summary of the nitrate loading calculation for the site. A copy of the nitrate loading calculation is included in Appendix F. Responsive ■ Resourceful ■ Reliable 17