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Soil Suitability/Nitrate Loading Study Irerracon Vacant Commercial Property■ Stockton, California December 7, 2018 ■ Terracon Project No. NA187056 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 Terracon reviewed the USDA Soil Survey of San Joaquin County(1992)for information regarding soil properties. Based on information obtained from the USDA sources, site soils consist of Jacktone clay and Stockton clay soils. Refer to Sections 1.1 and 2.12 for further discussion of the soils. Selected physical and chemical properties are listed in the following table. Table 7. Physical and Chemical Properties* Soil Name/ Depth USDA Unified Soil Clay Permeability Soil Salinity Septic tank reaction (m Map (in) Texture Classification (% cm) ) (in/hour) absorption Symbol (pH) cm) fields 0-29 clay CL 40-55 0.06-0.2 7.4-8.4 <2 29-37 clay silty CL 40-55 0.06-0.2 7.4-8.4 <2 Stockton clay Severe; clay/ clay loam, 0.06-0.2 percolates 250 37-42 silty clay CL 27-40 7.4-8.4 <2 slowly loam 42-60 cemented ---- --- --- --- --- Responsive■ Resourceful ■ Reliable 15