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Soil Suitability/ Nitrate Loading Study Irerracon Pickens Property ■ Tracy, California May 12, 2020 ■ Terracon Project No. NA207032 any of the above information provided to our office change or is inconsistent with what is stated, our office shall be contacted to make any necessary modifications to our calculations. Examination and professional judgement, and experience shall be used when selecting a reasonable flowrate. Table 9. Typical Quantity of Effluent. Average Effluent Average Effluent Long Term Number of Quantity or Residence ID Number of total Quantity for Additional Additional Average bedrooms Bedroom 1 Bedrooms Bedroom Discharge Rate (gpd ) (gpd*) (gpd•) Existing 3 100 2 50 200 Proposed Modular 3 100 2 50 200 Total gpd 400 `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 200 gallons per day. The proposed three-bedroom modular home is anticipated to add approximately 200 gallons per day for a combined average discharge rate of 400 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 40 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 soil borings, the proposed leach field is expected to be located within fine sand to a fine sandy silt with clay from 1.8 feet to 10 feet bgs. Based on depth to groundwater(160 feet) and review of the Well Completion records (Section 1.5.4), 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 Responsive■ Resourceful ■ Reliable 15