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Soil Suitability/ Nitrate Loading Study Irerracon <br />Eagle's Nest Motorcycle School t Stockton, California <br />July 27, 2021 Terracon Project No. NA217040 <br />Hantzsche and Finnemore mention that "...the equation ignores dispersion, lateral flow, and <br />mixing with groundwater flow from up -gradient areas. These processes would generally <br />contribute to additional reduction of nitrate -nitrogen concentrations in groundwater to the extent <br />that the nitrate -nitrogen concentration of groundwater flow from up -gradient areas is lower." <br />The Hantzsche and Finnemore approach is "...a conservative (worst case) first approximation of <br />groundwater nitrate -nitrogen concentration resulting from the combined effect of on-site sewage <br />disposal systems and precipitation. This (the equation and approach) is for estimation of long- <br />term effect (i.e., over years) on groundwater quality, and is not intended for prediction of seasonal <br />changes" (Hantzsche and Finnemore, 1992). <br />The method takes into account the development area, soil denitrification factor, rainfall volume, <br />rainfall nitrate concentration, waste effluent quantity, and waste effluent nitrate concentration. The <br />formula, assumptions and calculations used for the analysis are shown in Appendix F. The units <br />of nitrate used in the mass balance equation are nitrate -N, whose maximum drinking water <br />contaminant level (MCL) is 10.0 mg/L. <br />2.1 Chemical and Physical Properties of Soil <br />2.1.1 Chemical and Physical Soil Properties <br />Terracon reviewed the USDA NRCS Web Soil Survey and USDA Soil Survey of San Joaquin <br />County (1992) for information regarding Jacktone-Urban land complex soils (Section 1.5). <br />Selected physical and chemical properties for the soil types are listed in the following table. <br />Table 7. <br />Physical and Chemical Properties* <br />Soil Name <br />Soil <br />Septic tank <br />Depth <br />USDA <br />Unified Soil <br />Clay <br />Permeability <br />Salinity <br />/Map <br />reaction <br />absorption <br />(in) <br />Texture <br />Classification <br />(%) <br />(in/hour) <br />(mmhos/cm) <br />Symbol <br />(pH) <br />fields <br />0-22 <br />Clay <br />CL, CH <br />40-60 <br />0.06-0.2 <br />6.6-8.4 <br /><2 <br />Clay loam, <br />Jacktone- <br />22-34 <br />clay, silty <br />CL, CH <br />35-60 <br />0.06-0.2 <br />7.9-9.0 <br /><2 <br />Urban land <br />clay <br />I <br />Severe; <br />complex <br />34-37 <br />Indurated <br />___ <br />___ <br />___ <br /><2 <br />cemented pan <br />slowly <br />(181) <br />Loam, clay <br />peres <br />37-46 <br />CL -ML, CL <br />20-30 <br />0.2-0.6 <br />7.9-9.0 <br />loam <br />46-60 <br />cemented <br />--- <br />--- <br />--- <br />--- <br />'Selected USUA physical and chemical properties <br />2.1.2 Mass Transport Soil Properties <br />The longer the effluent remains near the surface, the more treatment is enhanced due to natural <br />processes within the soil. The percolation test has revealed that the onsite soils have a moderate <br />percolation rate at deep depths (15 to 18 feet and 25 feet bgs); however, the shallow soils at 3.5 <br />feet bgs failed to demonstrate a satisfactory percolation rate. <br />Responsive ■ Resourceful ■ Reliable 13 <br />