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1 INTRODUCTION Mr. Kevin Wentworth is proposing to improve a modular(manufactured)two bedroom home on the property he owns,referenced on the Title Page. This proposed modular home is considered a Second Unit Dwelling by San Joaquin County since there is an existing Single Family Residence structure on the property. Currently,the Second Unit Dwelling designation is undergoing various revised definitions pursuant to County Ordinances. The San Joaquin County Environmental Health Department(EHD)required a Soil Suitability Study and Nitrate Loading Study for this project and all projects where exceedance of nitrate loading standards may occur. These Studies were completed by AdvancedGeo (Project No. j 20-6095), dated September 10, 2020 and submitted to EHD on September 18,2020 (SR0082620). The findings from the Soil Suitability and Nitrate Loading Studies indicate: 1.) The soil underlying the property possesses an exceedingly rapid percolation rate of 0.56 min/inch that requires a civil engineering design for the onsite wastewater treatment system(OWTS), and 2.) The calculated nitrate loading from this project exceeds the standards and must also be mitigated by a civil engineer designed system. The rapid perc rate test result stipulates a soil depth separation distance of 20 ft between the floor of the disposal system and the highest anticipated depth to groundwater. From 2011 through 2018,the depth to the water table under the property has fluctuated between 20 and 30 feet below grade,thus encroaching upon this separation distance. The Nitrate Loading Study calculations found the resultant nitrate-nitrogen effluent concentration to be 19.88 ppm nitrate-nitrogen(NO3-N), which is 9.88 ppm (-2x) over the Maximum Contaminant Level (MCL)of 10 ppm NO3-N. This report addresses both issues of the rapid permeability of the soil and excess nitrate loading, and provides EHD with engineered design resolutions,primarily by taking advantage of the high porosity of the native sandy soils and the importation of a sandy loam(silt) soil to impede permeability and promote denitrification. MATERIALS AND METHODS The first procedure to address the rapid percolation of the native soils was to replicate the percolation test results of 0.56 minutes per inch(mpi) obtained by AdvancedGeo. My perc test procedures consisted of soil testing conducted after the extreme presaturation measure of filling the entire 40 inch deep test boring depth with water five times, -24 hrs prior to testing. Since it is a critical standard to conduct percolation testing under saturated soil conditions,this presaturation procedure, in addition to conducting the perc test over a four-hour period(in lieu of a one hour time period)was performed to induce maximum soil saturation. Six inches of water readily infiltrated and percolated within each 30-minute interval over the four test period. To not observe percolation rates decrease over a four-hour test period, is highly unusual and very rare,particularly in this case where the native soils were significantly presaturated. Page -1- Chesney Consulting