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August 27, 2020 BGG Job No. G 164.01 development area, soil denitrification factor, rainfall, rainfall nitrate concentration, waste effluent quantity, and waste effluent nitrate concentration from onsite septic systems. Mass Transport Soil Properties Field percolation test results indicate that the surface soils are moderately permeable.The site soils will permit some infiltration of water through the surface soils.The longer the effluent remains near the surface, the more biologic treatment may occur. If permeable soils exist to the depth of the ground water aquifer, it is possible that any remaining surface contaminants may be transported to the saturated zone of the upper aquifer. Nitrate Sources Septic systems and dairies have been identified to be the most significant sources of nitrate impact to groundwater. Orchard fertilization in sandy soils is also a significant source of nitrate contamination in shallow or sandy aquifers in San Joaquin County. Rainfall Contribution An estimate for rainfall quantity and quality was required for this nitrate loading analysis. The H&F method utilizes the"average recharge rate of rainfall"for calculating potential nitrate impacts to the aquifer. Some portion of total rainfall will dissipate by evapotranspiration,the sum of evaporation and plant transpiration, hence reducing the amount of rainfall percolation into the aquifer and percolating effluent, especially in summer months. Rainfall recharge (deep percolation of rain) is a significant factor in the nitrate loading estimate; however,data on rainfall recharge rates is not widely available. For H&F's study conducted in the Chico area,a recharge rate was calculated to be 75 percent of the average rainfall. Since the Chico area is similar geologically to San Joaquin County region, an estimated recharge rainfall was calculated for this study based upon 75 percent of annual rainfall for the project area. Rainfall data for the Lodi area was obtained from the San Joaquin County Flood Control and Water Conservation District Groundwater Report from Fall 2016. The Stockton Fire Station,the closest reported station to the site, reports the average total annual rainfall from 1941 through 2015 to be 15.6 inches. Assuming 75 percent of this rainwater percolates to the aquifer,a value of 11.7 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 IHO nursery operates five days per week.A maximum of 50 employees per day is anticipated. The proposed nursery improvements will include the addition of two new ADA restrooms,to contain two toilets and two lavatories. Additionally,the existing nursery facility is estimated to contain three restrooms, with a total of three toilets, one urinal,and four lavatories. The estimated sewage flow rates for various uses are available from several references. The uses presented below were guided by the San Joaquin County On-Site Wastewater Treatment Systems Standards(2017)and US EPA(1980). A use of 15 gallons per day for each employee is typical for an agricultural worker; this rate was used for the nurdery employees. The estimated flow values discussed here should not be used for the design and sizing of the septic system. The design and BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-I Nsin Orchids Page 6