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This report describes a new process that reduces dissolved Total Nitrogen of denitrified effluent water at a wastewater treatment system and the subsequent in situ denitrification in the vadose zone and groundwater below the soil absorption system. This new process adds and mixes a proprietary manmade organic carbon to previously treated effluent having low concentrations of dissolved organic carbon and low concentrations of dissolved Total Nitrogen. The mixed fluid is dosed intermittently to a specially constructed, proprietary stratified sand filter, prior to discharge to the environment. This step removes about 40% of the dissolved TN applied to the proprietary filter. The effluent was discharged into sandy soils in a coastal outwash plain and an estimated removal rate of 50% of the remaining dissolved Total Nitrogen in the upper groundwater under the soil absorption system was found. The apparent carbon source for in situ denitrification is described as microscopic insoluble particles. The calculated in situ removal was estimated using measurements from tests of the groundwater taken from upstream and downstream monitoring wells. The process can be used in any similar waters with low concentrations of dissolved organic carbon and low concentrations of dissolved Total Nitrogen.