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The following data was obtained from Winneberger(See References) which substantiates the process of denitrification within septic tanks: Argon is an inert gas found in the atmosphere in proportions of 84 parts of nitrogen to 1 part argon. When each of those gases come to equilibrium in water less than one atmosphere,they exist in a ratio of approximately 37 parts of nitrogen to one part argon. Analytical data obtained from septic tank effluent should also correlate with this ratio unless gaseous nitrogen(N2) was liberated or consumed by microbes. Calculations of nitrogen:argon ratios obtained from the analyses of seven different effluents indicate ratios of 100, 60, 43, 50, 60, 54 and 41. All of these values exceeded the expected nitrogen:argon ratio of 37 and indicate nitrogen liberation. This data supports the theory that denitrification occurs within septic tanks. IV. CONCLUSIONS AND RECOMMENDATIONS It is our opinion the subject property is marginally suitable for its intended use with regard to septic effluent management. The percolation rates obtained indicate a marginally permeable soil with permeability decreasing with an increase in soil saturation. Hydraulic head is a significant element to the percolative capability of the soil at seepage pit depth. Ultimately, biomat formation within the leachline trenches and seepage pits will determine percolative capacity. Effluent management, and therefore design should be based on the permeability of the soil eventually reaching a long term application rate (LTAR) of approximately 0.5 to 1.0 gals/ftz/day due to biomat formation. It is imperative that a 100%replacement area be designated in the event a repair is needed or an additional system installed. Additional excavator-dug seepage pits may be installed if there is an increase in the number of people using the system leading to greater wastewater flows than those anticipated in this report. It may be a requirement by the Environmental Health Department to install a flow meter on the wastewater system. The nitrate loading calculations demonstrate groundwater under the leachfield, to a thickness of 10 feet, will not be theoretically impacted above the current Maximum Contaminant Level Drinking Water Standards (MCL/DWS). It is conceivable that Stockton City water and sewer will eventually service this project. The time frame is indeterminable. However,nitrate and septic effluent impact appears to be below levels of concern primarily due to the underlying soil structure. This soil structure is also conducive for microbial and viral destruction. Filters (e.g., Zabel®or OSI® Filters) should be installed in the last chamber of the septic tank. A denitrification potential of 20% is projected within the soil environment due to the referenced soil characteristics of silty clays, clayey silts, and a filter will assist in alleviating a severe biomat formation. Recharge from rainfall will be minimal due to pavement and buildings covering most of the subject property area, along with the semi-impermeable soil structure. The leachfield and seepage pits must be protected against inundation. 8 Valley Ag Research