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! 1 With regard to the nitrate-nitrogen loading to the underlying groundwater, it is important to recognize that when adding one concentration of a solute (e.g., NO3-N in effluent recharge water) to another concentration of a solute (e.g., NO3-N in groundwater), where both solutes are in ppm, the result is not cumulative or the sum of the two solutes. Parts per million is a mass-to-mass ratio. For example, taking into consideration, the `worst-case"resultant average concentration of nitrate-nitrogen in the recharge water at 9.9 ppm NO3-N as described above: This equals 9.9 milligrams of nitrate in 10' milligrams of water(one liter). If this 9.9 ppm concentration is added to the same volume of groundwater (1 x 106 milligrams) with the concentration determined from the DeAngelis domestic well, which was 9.4 ppm NO N (42 ppm NO3), then the resultant concentration is now 9.9 milligrams + 9.4 milligrams = 19.3 milligrams dams in 2 x 106 milli ams (2 liters, or parts per 2 million) of water. Therefore, to convert back to ppm, the numeratoLand denominator must be divided by 2 with the result of 9.65 milligrams per 1 x 106 milligrams, or 9.65 p m which is slightly under the Maximum Contaminant Level of 10 ppm NO3-N. From the Hantzsche-Finnemore Equation and using the premise of assessing the project as a whole,Aa -' " which is the most accurate analysis as described on Page 10, we find a decrease in nitrate-nitrogen loading to the water table under the entire project area, from a second unit dwelling to be: 3.8 ppm (Nitrate-nitrogen loading from the project as a whole)+ 9,4 ppm (Existing nitrate-nitrogen concentration in the groundwater)= 13.2-2 — L 2 6.6 ppm NO3-N, which is theoretically: 9.4 ppm minus 6.6 ppm=2.8 ppm NO -N lowe than the current groundwater nitrate-nitrogen concentration. However, and just as significant as the above equations, are the soil chemistry profiles of the existing cherry orchard, and of the existing leachfield revealing that the nitrate-nitrogen loading from the existing leachfield is theoretically equivalent to the loading observed from the existing cherry orchard. Thereforesotic e uent,from a second unit dwelling would theoretically contribute the same concentration of nitrate-nitrogen to the groundwater as the existing cheny orchard. This may be attributed to denitrification. It can be hypothesized that the observed nitrate concentrations within "Vaipico Section" are in equilibrium. Sources contributing nitrate to the underlying groundwater include indigenous soil concentrations from decomposing organic matter, rainfall, upgradient and historical agricultural fertilizer inputs, septic systems (particularly sumps and pits), and lawn/landscape fertilization. Factors decreasing the groundwater nitrate concentration include denitrification, groundwater movemcnt (both vertical and horizontal), well pumping and hydraulics, and clean water recharge which contributes to a dilution effect. Therefore, if each of these sources and attenuating factors could be quantified on a mass balance basis, it may be that nitrate input is now roughly equivalent to output, or attenuation. Given that agricultural irrigation recharge is the largest single contributor to groundwater nitrate concentrations, and since the surrounding land has been farmed for several decades, it would be assumed that the nitrate concentrations in the underlying groundwater should be much higher than observed, if the attenuating factors were not significant. This is what was observed with the soil chemical analyses. The nitrate concentration within the soil environment under the DeAngelis leachline revealed decreasing and then static nitrate-nitrogen concentrations with depth, presumably due to denitrification. The denitrification potential is from the comparatively high clay content of the indigenous soils, the higher soil pH, high soil moisture content and organic fraction content. Page -11- Chesney Consulting