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April 6, 2022 <br /> BGG No. G130.09C <br /> NITRATE LOADING STUDY <br /> Due to concerns of nitrate leaching into groundwater from septic systems,a nitrate loading analysis <br /> was required by the San Joaquin County Environmental Health Department(SJC EHD)for approval <br /> of the proposed Enriquez Residence septic system. The intent of the study is to estimate the <br /> potential concentration of percolating effluent produced by the septic system for an extended period. <br /> Where percolating effluent leaches into the ground, groundwater quality may be impacted to a <br /> degree, should the effluent reach the groundwater table. <br /> The method utilized for the nitrate loading analysis is based on a simple and convenient mass <br /> balance formula, discussed in a published article by Hantzsche and Finnemore (1992), predicting <br /> groundwater Nitrate-Nitrogen impacts. <br /> The H&F equation is a conservative approximation of groundwater nitrate-nitrogen concentration <br /> resulting from the combined effect of on-site sewage disposal systems and rainfall precipitation. The <br /> H&F equation and method are appropriate for estimating longterm effects on groundwater quality;it <br /> is not intended for use in predicting seasonal fluctuations (H&F, 1992). The method considers the <br /> development area, soil denitrification factor, rainfall, rainfall nitrate concentration,waste effluent <br /> quantity, and waste effluent nitrate concentration from onsite septic systems. <br /> Mass Transport Soil Properties <br /> Field percolation test results indicate that the surface soils are moderately permeable.The site soils <br /> will permit some infiltration of water through the surface soils.The longer the effluent remains near <br /> the surface, the more biologic treatment may occur. If permeable soils exist to the depth of the <br /> ground water aquifer, it is possible that any remaining surface contaminants may be transported to <br /> the saturated zone of the upper aquifer. <br /> Nitrate Sources <br /> Septic systems have been identified to be a significant source of nitrate impact to groundwater. <br /> Dairy farming and orchard fertilization in sandy soils is also a significant source of nitrate <br /> contamination in shallow or sandy aquifers in San Joaquin County. <br /> Rainfall Contribution <br /> An estimate for rainfall quantity and quality was required for this nitrate loading analysis. The H&F <br /> method utilizes the"average recharge rate of rainfall"for calculating potential nitrate impacts to the <br /> aquifer. Some portion of total rainfall will dissipate by evapotranspiration,the sum of evaporation <br /> and plant transpiration, hence reducing the amount of rainfall percolation into the aquifer and <br /> percolating effluent, especially in summer months. <br /> Rainfall recharge (deep percolation of rain) is a significant factor in the nitrate loading estimate; <br /> however, data on rainfall recharge rates is not widely available. We reviewed a basic Nitrate <br /> Loading calculator developed by Norman Hantzsche with Questa Consulting for San Joaquin <br /> County, containing average recharge from rainfall for each station in San Joaquin County. The <br /> estimated recharge rainfall for this study was calculated based upon 80 percent of annual rainfall for <br /> the project area. <br /> BAEZ GEOTECHNICAL GROUP Soil Suitability Study and Nitrate Loading Study-Enriquez Residence,17650 Austin Road Page 6 <br />