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r7 2. SUBSURFACE SOILS UNDER EXISTING LEACHFIELD A profile of the soil chemistry under the existing DeAngelis leachfield was completed to illustrate and assess the nitrogen impact from the 36 year old septic system. This was accomplished by quantifying the concentration of different nitrogen species from the surface down to 12 feet in depth. _ A four-inch diameter hand auger was used to drill the boring and retrieve the samples. Samples were taken from 0-24 inches (composited), 5 ft, 8 ft and 12 ft. Drilling began by locating the leachfield area, as denoted in the attached photographs. The leachline trenches were probed in an # attempt to locate the drain rock. Although this proved to be difficult because of the hard, tight clay surface soils, the boring location was determined to be near a leachline trench since some drain rock was encountered during the drilling process. In addition to the analytical chemistry completed on the four samples, Particle Size Analysis was also done on the samples as denoted on the Soil Analysis Report. These soils have been classified by the laboratory as a sandy clay loam and a sandy loam, which correlates with the United States Department of Agriculture - Natural Resources Conservation Service (USDA-NRCS) classification of a Stomar clay loam (4252). The Unified Soil Classification System (USCS) identifies the majority of this soil as a clayey silt and silty clay(CL-ML/CL). .This finer-grained soil material (clay and silt sized particles)promote biological treatment of the effluent. Biological treatment includes the destruction of bacteria and viruses, and denitrification as described above. Chemistry on these four leachfield soil samples were the same as listed above for the cherry orchard soils. Since septic effluent is composed predominately of ammonium (NH4) ions, the pH, along with the Cation Exchange Capacity, have significant influence on ammonium. In all of the samples, there was no ammonia-nitrogen, or NH4 ions. Two explanations for this include the pH of the soil, which is somewhat alkaline below 24 inches and may inhibit ammonium stability. Secondly, the CEC measures the ability of the soil to theoretically trap, hold and convert ammonium molecules. The soil profile has a comparatively medium CEC of approximately 15,which should increase the retention of ammonium molecules for microbial uptake and suppression of nitrification. The significance of cation exchange becomes important when the chemistry of septic effluent is E analyzed. Nitrogen in septic tank effluent consists of approximately 75%N in the ammonium ion (NH4') form and 25%N in the organic form. If the ammonium ion is bound and eventually utilized, nitrification cannot occur. The organic fraction of the soil, as determined by TKN, reveals that the soils are normal, and based on my observations, are concentrations typically found in soils. The results of the soil nitrate-nitrogen concentrations show a decrease with increasing depth, as was observed in the cherry orchard. At the 0-24 inch depth, the NO3-N concentration was 12 ppm, but decreased to 6 ppm at the 5 ft, 8 ft and 12 ft depths. It appears that 6 ppm nitrate-nitrogen is an equilibrium concentration. If it were possible to collect sufficient vadose zone water, the same decrease in nitrate-nitrogen concentrations with increasing depth would probably also be observed. The following Table illustrates the nitrogen fraction concentrations as found under the leachfield. Pa e -4- Chesney Consulting