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surplus nitrogen atoms, the microbe can combine pairs of surplus nitrogen atoms to form nitrogen gas (NZ). This is referred to as denitrification. Therefore, by using two septic tanks in series, the fust tank should contain a higher concentration of oxygen from sink faucet aeration and the flushing action of toilets and promote nitrification. As the oxygen is consumed in the first tank, effluent flowing into the second tank should be predominately anaerobic. Under these conditions, denitrification should be promoted in the second tank. 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 under one atmosphere, they exists 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(NZ)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 and by using two tanks in series,promote the denitrification process. III. CONCLUSIONS AND RECOMMENDATIONS The primary purposes of this study were to attempt to determine the source(s) of the high concentration of nitrate in the underlying groundwater, quantify nitrate impact from the project as a whole, and design septic systems to mitigate further nitrate impact. It is our opinion this study completes these requirements of the Environmental Health Department. The nitrate loading calculations demonstrate groundwater under the entire project,to a thickness of 10 feet, will be theoretically impacted to 9 ppm which is 1 ppm under the current Maximum Contaminant Level (MCL) drinking water standard of 10 ppm NO3-N (45 ppm as NO3). Influence from the on-site septic systems can be considered "low-to-medium impact" when nitrate-nitrogen loading is considered on an areal basis (14 lbs NO3-N/Ac). From the Delta 'IN test results (See Appendix H), the sources of nitrate impact appears to be highly complex. Test results of groundwater obtained from the basin monitoring well (top aquifer) indicate the nitrate source to be indicative of soil organic nitrogen. However, as referenced earlier, the test cannot reliably distinguish between fertilizer sources and natural soil organic matter. It is known from past history of the subject property that both fertilizers and soil organic matter were used, or could be detected under the property. Fertilizers were most likely used in the past nursery and farming operations. Soil organic matter may have originated from the past farming operations. Therefore,the exact source of nitrate is indeterminable, but probably a combination of the two. Test results from water obtained from the Kenworth well indicate the deeper aquifers may have been impacted from on-site sewage disposal systems. There is an antiquated subdivision directly east of the subject property which originated in the 1940s. Although the housing density is low 8 Nalfey Ag Z(-,search