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F e-nitrogen loading from the effluent recharge based on the proposed septic system density, e comparable to the subject property being placed in walnut orchard production. ugh the homes to be built on each of the 15 lots will be upscale, it is recommended that garbage disposals, or grinders not be installed in the kitchens to decrease organic loading. Garbage disposals are typically one of the largest sources of organic loading, and subsequent increase the nitrate-nitrogen loading potential dramatically. The homeowners should use "slow release"nitrogen fertilizer onJawns and landscaping to prevent nitrate contamination from these source areas. These areas can contribute concentrations of nitrate to the underlying groundwater equivalent to, or greater than, the on-site septic systems. It appears from groundwater gradient determined from the lines of equal elevation, the Mokelumne River will be the "sink" for nitrate emanating from the project and surrounding land uses reaching the groundwater in the percolating effluent. The River's influence on the shallow aquifers or perched water table conditions is unknown without highly complex testing and monitoring. As referenced, the firm ofMorlanjCivil Enineeringwill be designy ingthe on-site septic systems for the project. Percolation and soil testing conducted by Chesney Consulting indicates acceptable percolation on proposed Parcel 4 at the shallow and medium depths, but the percolation rate at the deep depth is too rapid for acceptability. To prevent excessive percolation and impede effluent nitrification, the soil/effluent interface should b_eacedas hi h in elevation as racticable ithe sandy loam/loam soil encountered above the 8 ft depth. Contemporary scientific literature suggests that denitrification may be obtained by placing proposed leachlines near the soil surface. This would be advantageous since the surface soils are an organic sandy loam which may impede nitrification and promote denitrification given the clay content in the surface soils is 14%. Certain types of.plants may be used in conjunction with this system to uptake ammonium ions, and nitrate ions that may farm. These three procedures would theoretically provide a triple nitrate mitigation system of absorption by the clay soils present, evapotranspiration and denitrification. This report did not utilize highly complex groundwater modeling techniques since it has been documented that these techniques are overly sophisticated and unreliable in many cases. The groundwater table is ample distance below grade for there to be adequate biological treatment of the septic effluent, according to published scientific literature. The minimum distance is generally recognized to be five feet. In addition, there should be no mounding effects from the leachfields. The historical aerial photos suggest the property was in agricultural production in the early 1960's. The nitrate-nitrogen concentration within the soil profile shows a 50% decrease in NO3-N from the soil surface to the 5 ft depth. This may be attributable to denitrification or leaching. The NO3-N concentrations increase again upon entering the sandy and silty clay loam subsoils, which would be indicative of both denitrification,and leaching. Page-16- Chesney Consulting