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Soil Suitability/ Nitrate Loading Study Irerracon Souza Property - Tracy, CA February 28, 2020 Terracon Project No. NA207011 They believe that their method is a good planning tool and provides useful information to planners and local officials but with some real limitations. In their article published in Ground Water, Hantzsche and Finnemore mention that "...the equation ignores dispersion, lateral flow, and mixing with groundwater flow from up-gradient areas. These processes would generally contribute to additional reduction of nitrate-nitrogen concentrations in groundwater to the extent that the nitrate-nitrogen concentration of groundwater flow from up-gradient areas is lower." The Hantzsche and Finnemore approach is "...a conservative (worst case)first approximation of groundwater nitrate-nitrogen concentration resulting from the combined effect of.on-site sewage disposal systems and precipitation. This (the equation and approach) is for estimation of long- term effect(i.e., over years)on groundwater quality, and is not intended for prediction of seasonal changes" (Hantzsche and Finnemore, 1992). The method takes into account the development area, soil denitrification factor, rainfall volume, rainfall nitrate concentration,waste effluent quantity, and waste effluent nitrate concentration. The formula, assumptions and calculations used for the analysis are shown in Appendix F. The units of nitrate used in the mass balance equation are nitrate-N, whose maximum drinking water contaminant level (MCL) is 10.0 mg/L. 2.1 Chemical and Physical Properties of Soil 2.1.1 Chemical and Physical Soil Properties Terracon reviewed the USDA NRCS Web Soil Survey and USDA Soil Survey of San Joaquin County (1992)for information regarding Stomar clay loam soils (Section 1.5). Selected physical and chemical properties for the soil types are listed in the following table. Table 9. Physical and Chemical Properties* Soil Soil Septic tank Name/ Depth USDA Unified Soil Clay Permeability Salinity Map (in) Texture Classification M (in/hour) reaction (mmhos/cm) absorption Symbol (PH) fields 0-17 Clay loam CL 65-85 0.2-0.6 6.6-7.3 <2 Stomar 17-47 Clay CL,CH 70-95 0.06-0.2 6.6-8.4 <2 clay loam,clay Severe: loam/ Clay loam, peres slowly 252 47-60 silty clay CL 60-85 0.2-0.6 7.4-8.4 <2 loam `Selected USDA physical and chemical properties 2.1.2 Mass Transport Soil Properties The longer the effluent remains near the surface, the more treatment is enhanced due to natural processes within the soil. The percolation test has revealed that silt with sand and lean clay with sand have a moderate percolation at shallow depths (<3.0 feet bgs). Responsive■ Resourceful ■ Reliable 12