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FD. GROUNDWATER INFORMATION eeas S§ 4 17NLS§2.1: Groundwater depths and elevations throughout San Joaquinllustrated-onmaps published by the County Flood Control and Water Conservation District. However, due to the high degree of variability in groundwater elevations in the Tracy area, lines of equal depth and equal elevation are typically not drawn for this area. This is due to the fact that seasonal water table variations occur that are primarily dictated by surrounding surface irrigation. This was observed with the current water table depth determination. Depth measurement occurred at the height of the irrigation season,thus insuring that the highest anticipated depth to groundwater was determined. With regard to groundwater directional flows, it is generally regarded that groundwater flows in a northeasterly direction, toward the San Joaquin River. A water table depth of five feet would preclude the installation of a conventional, or semi- conventional leachfield system since there is a required separation distance of five feet that must / be maintained between the soil-effluent interface and the highest depth to the water table. NL5§ 2.'M9 , SSS§�J, 4.2. Since surrounding properties have been intensely fanned for several decades, the potential for nitrate contamination in the underlying groundwater is significant. Groundwater research in the scientific literature suggests there may be a large denitrification potential within aquifers or saturated zones composed of clay soil. NLS§b, SSS§ 4.3, 4.4anot rsuant to the EHD directive, the domestic water from the we that serves the Church wpled for the typical constitue s-6feoneertt because the is currently monitored for ituents. Calculation of Alkalinity Requirement for Nitrification The estimated nitrate-nitrogen loading found on Page 12 is contingent upon the environmental factors required for nitrification to occur. These conditions include soil pore-space oxygen content, soil temperature, pH, electrical conductivity, organic matter, cation exchange capacity, and alkalinity. Alkalinity is derived from the well water supply, from within the soil environment, and the introduction of human waste constituents. Nitrification consumes approximately 7.1 mg of alkalinity for every mg of ammonia-nitrogen(NH4 N) oxidized. Nitrification of the average Total Nitrogen (TN) concentration of 60.1 mg/L, as determined on Page 11 would require: 60.1 mg/L NH4 N x 7.1 mg CaCO; =426 mg/L alkalinity. The alkalinity in the domestic wastewater supply is presently 301 ppm. This concentration, coupled with the well water alkalinity, groundwater alkalinity and indigenous soil alkalinity may be sufficient to promote nitrification. Mounding Analysis Reference is made to the encountered water table from the soil boring drilled next to the future mound system area and measured at 5 feet below existing grade. This depth to groundwater can be considered very shallow and may induce a phenomenon known as a"mounding effect' in which percolating effluent encounters the water table, or restrictive stratum and cannot disperse laterally fast enough to prevent a mound formation. J,//i Chesney Consulting