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' Soil Suitability/Nitrate Loading Study Irerracon Proposed Global Carrier Inc. ■ Manteca, California August 8, 2018 n Terracon Project No. NA187034 The method utilized for the nitrate loading analysis is based on a simple mass balance formula, discussed in a published article by Hantzsche and Finnemore (1992), which provides a convenient and simplified method to estimate long-term groundwater nitrate impacts on an area- wide basis. Hantzsche and Finnemore found that over a long period of time, water quality in the upper saturated groundwater zone closely approximates the quality of percolating recharge waters. 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 B. The units of nitrate used in the mass balance equation are nitrate-N, of which the maximum drinking water contaminant level (MCL) is 10 mg/L. 2.1 Chemical and Physical Properties of Soil 2.1.1 Chemical and Physical Soil Properties For a discussion of on-site soil properties, refer to Section 1.5. 2.1.2 Mass Transport Soil Properties The percolation test has revealed that soils between 0 and 3.5 feet bgs are permeable and will allow for sufficient infiltration of water. In general, the longer the effluent remains near the surface, the more treatment is enhanced due to natural processes within the soil. The high permeability of the silty sandy soils indicates nutrients such as nitrates may leach through the site soils more rapidly than soils with clay strata. Responsive■ Resourceful ■ Reliable 13