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This projected nitrate-nitrogen contribution of 6.3 lbs. NO3-N/ac/yr can be considered medium potential impact. This is primarily due to the fact that the Mission will meet only on Sundays. The following calculations quantify the anticipated impact: The top aquifer has a small assimilative capacity for additional nitrate-nitrogen impact. At present, the nitrate concentration in the upper two feet of the top aquifer is 38 ppm. The drinking water standard is 45 ppm thus allowing an additional concentration of 7 ppm NO3. To correlate an anticipated impact of 6.3 lbs. NO3 N/ac/yr with the existing 38 ppm nitrate (NO3), the 6.3 lbs. NO3- N must be converted to nitrate exclusively, since the nitrate concentration in the water was reported as nitrate and not nitrate-nitrogen: 6.3 lbs. x 4.4 (conversion factor) = 28 lbs. of nitrogen as nitrate. If the first two feet of the top aquifer or phreatic zone (the zone sampled) are considered over 2.7 acres=235,224 cubic feet of saturated zone,which has an approximate porosity of 40%. Therefore: 235,224 x .40=94,090 cu ft of water x 7.48 = 703,790 gallons x 8.33 lbs./gallon= 5,862,571 lbs. of assumed 38 ppm nitrate laden water. The calculated impact of 28 lbs. of nitrate = 28 lbs. _ 5.8 million lbs. = 4.8 ppm of nitrate. Therefore, the project as a whole (2.7 acres) is projected to contribute nitrogen in the form of nitrate which should not exceed the drinking water standard in the top aquifer: 7 ppm-4.8 ppm=2.2 ppm NO3 assimilative capacity after project development. The primary concern regarding nitrate impact is the aquifer from which the on-site well receives water. This aquifer has been impacted from upgradient sources of nitrate at the areas of recharge. In many cases, the design of the well may alleviate nitrate impact from drawing water from several aquifers, thus mixing and diluting water from impacted aquifers with other aquifer water. We are recommending that a reverse osmosis water treatment system be placed on the drinking water supply for the new Mission, instead of constructing a new well designed to draw water from more than one aquifer. Another significant issue which must be addressed with nitrate loading is the proper operation of the proposed system, so there are no failures. A failure by effluent surfacing could be caused by severe clogging mat formation, large and frequent precipitation events (climatic stress) and groundwater mounding. Although any or all three of these scenarios could cause failure, high groundwater is probably the greatest concern. As the effluent percolates through the native soil, treatment occurs, then the effluent must enter the shallow groundwater where a potentially detrimental event occurs. This is known as "mounding." Since the zone of saturation is composed of a fine grained, silty material, the hydraulic conductivity of the saturated zone is low. Consequently, this zone cannot manage the 8 Vadey Ag?Zssearch