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April 6, 2022 BGG No. GI30.09C Rainfall data for the Enriquez Residence site area was reviewed from the California Irrigation Management Information System (CIMIS) Manteca Station #70. The CIMIS Manteca Station, located approximately 3.2-miles northeast of the site,reports the average monthly evapotranspiration (ETo)to be 4.38 inches. The basic nitrate loading calculator developed by Hantzsche indicates that a value of 3.62 inches of average recharge of rainfall should be utilized. H&F estimates the nitrate concentration of rainfall is approximately 1 mg/L-N. Quantity and Quality of Domestic Wastewater The proposed residence will have three bedrooms and two bathrooms,with three estimated residents. Additionally, the residence will contain a total of two toilets, two bathtubs, and three sinks. The estimated sewage flow rates for various uses are available from several references. The uses presented below were guided by the San Joaquin County Onsite Wastewater Treatment Systems Standards(2017)and US EPA(1980). The SJC EHD calculates nitrates loading based on number of bedrooms,with 100 gallons of wastewater per day for the first bedroom and 50 gallons per day for each additional bedroom; hence these rates were used for the proposed residence. The estimated flow values discussed here should not be used for the design and sizing of the septic system. The design and sizing of the septic system should utilize the SJC EHD Onsite Wastewater Treatment Systems Standards which incorporate peak and surge flow factors. The estimates used in the Onsite Wastewater Treatment Systems Standards may be greater than those discussed herein. A typical nitrate as nitrogen (N) concentration for residential use is 35 mg/L (Crites and Tchobanoglous, 1998). This value was used in calculations for the proposed residents. No contributions from crop irrigation or soil amendments are considered for the Hantzsche/Finnemore method. It is reasonably assumed that the irrigation and soil amendments would be applied at close to agronomic rates for a net balance of plant irrigation and nutrients.The following tables present the calculated maximum average daily flow for the site and weighted average concentrations: Table 1 —Average Dail Flow Calculation Use Units Rate Subtotal Average Daily Flow Residents (full-time) 1St Bedroom 100 gal/bedroom 100 gpd 100 gpd Residents (full-time) 2 Bedrooms 50 galibedroom 100 gpd 100 gpd Total 200 gpd Table 2—Weighted Avera a Concentration Calculation Use Average Daily Flow Estimated Waste Weighted Average Water Quality Product Residents 200 gpd 35 mg/L-N 7,000 gpd-mg/L-N full-time Totals 200 gpd 7,000 gpd-mg/L-N Weighted Average Concentration: 1 7,000 d-m /L-N/200 gpd= 35 m /L-N Denitrification Reductions Denitrification is a process that occurs in the septic system drain field whereby certain bacteria oxidize the nitrate(NO3)in the wastewater and release nitrogen gas(N2)to the atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the drain field may undergo a reduction between 10 percent to 25 percent. Soils with higher clay content,moist soil conditions,high pH,and BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-Enriquez Residence,17650 Austin Road Page 7