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I KLEINFELDER upper acquifer. In discussions with the Environmental Health Division (EHD), we understand that similar observations have been made by San Joaquin County. Nevertheless, in order to be consistent with requirements for the adjacent subdivisions in the area, and because of the calculated nitrate loading value, we understand that some enhanced features of the leach field design will be required by San Joaquin County. Although the final system design for this project was provided by Valley Ag Research and is presented below, we recommend that all seepage pits extend at least 20 feet in depth, because of the variability of the more permeable sand lenses on which our percolation tests were generally performed. SYSTEM DESIGN The system design prepared by Don Chesney of Valley Ag Research is presented on Plate 1 attached and is described below. As stated, all details of the system must comply with the San Joaquin County Environmental Health Division Sewage Standards (11/96). We suggest that new home owners sign Plate 1 acknowledging receipt and acceptance of the construction and maintenance procedures. As you are aware our analysis indicates a nitrate loading above the maximum level of 10 mg/L. According to Mr. Chesney, nitrate-nitrogen impact mitigation will be primarily accomplished by using two septic tanks through the following processes: It has been well documented that gaseous nitrogen emanates from septic tanks. The gaseous formation is apparently attributable to denitrification which is the biological reduction of nitrate (NO3) and nitrate (NO2) to volatile gases. The biochemical processes that occur in septic tanks are highly complex, but can be described simplistically: A microbe digesting a waste organic molecule with an attached nitrogen atom may have the freed nitrogen as a surplus atom. To digest the N atom, the microbe can combine it with dissolved molecular oxygen 02 and release it in solution as a molecule of nitrite or possibly nitrate. This occurs under aerobic conditions and is referred to as nitrification. If a microbe needs oxygen within an anaerobic environment, it can take the oxygen from nitrite or nitrate molecules. Not requiring surplus nitrogen atoms, the microbe can combine pairs of surplus nitrogen atoms to form nitrogen gas (N2). This is called denitrification. Therefore, by using two septic tanks in series, the first tank should contain some oxygen from sink faucet aeration and the flushing action of toilets. This should promote nitrification. As the oxygen is consumed in the first tank, effluent flowing into the second tank should be predominately anaerobic, if this tank is sealed. Under these conditions, denitrification should be promoted in the second tank. The following data was obtained from J.H.T. Winneberger, Sotic-Tank Systems — A Consultant's Toolkit 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 one part argon. When each of these gases come to equilibrium in water under one atmosphere of pressure, they exist in a ration 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) is liberated. 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 these values exceed the expected nitrogen:argon ration of 37 and suggest nitrogen gas liberation. This data supports the theory that denitrification occurs within septic tanks and by using two tanks in series, theoretically encourages the denitrification process. Other details of the Double System Design are shown on Plate 1. Please note that the number and length of leach lines shown is for a single leach field and must be doubled per county standards. In addition all set back and dimensional requirements shown on Plate 1 and described in Sewage Standards must be followed by the civil engineer or architect on the project. 20-2921-02/2011 R1169 Page 4 of 5 Copyright 2001 Kleinfelder,Loc. September 25,2001