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ORDER NO.R5-2002-0148 INFORMATION SHEET MUSCO FAMILY OLIVE COMPANY AND THE STUDLEY COMPANY WASTEWATER TREATMENT AND LAND DISPOSAL FACILITY SAN JOAQUIN COUNTY Effluent Limitation C.2 Loading limits for nitrogen are required because excessive loading of nitrogen can result in a build up of nitrogen in the soil column and eventual leaching to groundwater. The Discharger has presented a plan to crop the land application areas to remove all applied nitrogen. Because crop health in land application areas has historically been poor, the crop may not be able to take up all the applied nitrogen. The Discharger states that the nitrogen limits presented in the WDRs are overly restrictive. The WDRs contain a Discharge Specification that restricts the total nitrogen loading rate to the agronomic rate, which is equal to the nitrogen requirements of the crop planted on the disposal field. Staff believes the restrictions are appropriate. This is a standard specification that has routinely been imposed on food processors, dairies, and other agricultural dischargers. The purpose of the specification is to ensure that the crop utilizes nitrogen to the maximum practical extent, thereby preventing groundwater quality degradation by nitrate. Nitrogen in food processing waste is typically present primarily in organic form. According to Irrigation with Reclaimed Municipal Wastewater, Fate of Wastewater Constituents in Soil and Groundwater, (Chapter 12 of Irrigation With Reclaimed Municipal Wastewater, A Guidance Manual, prepared by California State Water Resources Control Board, Report No. 84-1, 1984) organic nitrogen is mineralized to ammonium and then nitrified to form nitrate which is plant available. Mineralization requires aerobic conditions in the soil and sufficient bacteria. Mineralization does not occur at a constant rate because some forms of organic nitrogen mineralize less readily and tend to stay in organic form until the readily mineralized fraction has been fully utilized. Nitrification also requires adequate oxygen and bacteria to produce plant available nitrogen. For optimal plant uptake, the percolation rate must be slow enough to ensure that nitrogen(whether in organic or mineralized form) stays within the root zone to the maximum practical extent. According to Wastewater Management Systems, nitrogen can be stored in the soil, however,with continued application of wastewater, equilibrium is reached and net storage of nitrogen stops. Wastewater Management Systems states that it is most conservative to assume net storage will be zero. The WDRs are consistent with this conservative approach. Any nitrogen that percolates below the root zone can potentially degrade groundwater quality. However,under certain circumstances, nitrate can be denitrified to nitrogen gas,which resides within the soil matrix or is released to the atmosphere. Denitrification rates vary substantially(from 0% to 90% of total nitrogen), depending on several variables, most of which are site-specific. These variables include those related to soil type or texture; mass of nitrogen per application per unit area; volume of water per application per unit area; resting or drying time between applications; and climactic conditions. Therefore, determination of the denitrification rate for a given discharge can only be made based on a fully supported site-specific model. The Discharger has stated that a considerable percentage of nitrogen is lost to the atmosphere through the process of denitrification. Because of the variable denitrification rate that occurs due to wastewater application rates, ambient temperature, and other factors which may not be controllable, staff believes requiring agronomic application rates are justified.