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January 21, 2021 BGG Job No. G130.09 Rainfall data for the Valdovinos Residence site area was reviewed from many sources, including data from the California Irrigation Management Information System (CIMIS) Staten Island Station #242 and the U.S. Department of Commerce National Oceanic and Atmospheric Administration (NOAA). The CIMIS Staten Island Station, located approximately 16.5 -miles west-northwest of the site, reports the average monthly evapotranspiration (ETo) to be 4.88 inches and the NOAA Stockton station reports the total annual rainfall from 1948 through 2019 to be 13.73 inches. Assuming 75 percent of this rainwater percolates to the aquifer, a value of 10.3 inches of average recharge of rainfall is calculated. H&F estimates that 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 four bathrooms, with four estimated residents. Additionally, the residence will contain a total of four toilets, four showers, and two 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). A use of 50 gallons per day per resident is typical for rooming houses, hence this rate was 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 San Joaquin County Environmental Health Department 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. Additionally, the proposed residence is in a developed residential area so crop contributions are not applicable. The following tables present the calculated maximum average daily flow for the site and weighted average concentrations: Table 1— Average Daily Flow Calculation Use I Units Rate Subtotal Average Daily Flow Residents full-time 4 50 al/resident 200 gpd 200 gpd Table 2 — Weighted Average 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 7,000 gpd-mg/L-N / 200 gpd = 35 mg/L-N Concentration: BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study - Valdovinos Residence Pagel