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Soil Suitability/ Nitrate Loading Study Irerracon Souza Property Tracy, CA February 28, 2020 Terracon Project No. NA207011 Table 11 Typical Quantity of Effluent. Average Effluent Average Effluent Long Term Number of Quantity For Residence ID Number of total Quantity for Additional Additional Average bedrooms Bedroom 1 Discharge Rate (gpd,) Bedrooms Bedroom (gpd,) (gpd*) Existing 4 100 3 50 250 Proposed 3 100 2 50 200 Total gpd 450 *gpd-gallons per day Based on a review of the above table, the long term average discharge rate for the existing four- bedroom residence is anticipated to be 250 gallons per day. The proposed three-bedroom residence is anticipated to add approximately 200 gallons per day for a combined average discharge rate of 450 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). 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 residence is 45 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 percent to 15 percent. Based on the results of the shallow soil borings, the proposed leach field is expected to be located within silt with sand and lean clay with sand . Based on depth to groundwater and review of the Well Completion records (Section 1.5.4), a denitrification estimate of 20 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 15